Patent Publication Number: US-7583283-B2

Title: Exposure apparatus, image forming apparatus and heat adjustment method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based on and claims priority under 35 USC §119 from Japanese Patent Application No. 2007-069356 filed Mar. 16, 2007. 
   BACKGROUND 
   1. Technical Field 
   The present invention relates to an exposure apparatus and the like that writes information with light in an image forming apparatus such as a printer and a copy machine, and a heat adjustment method. 
   2. Related Art 
   In a color image forming apparatus with an electrophotographic type such as a printer and a copy machine, as an exposure apparatus that is used at the time of forming color toner images, there is a known apparatus that is formed by arranging light emitting elements such as LEDs in the main scanning direction. In such an exposure apparatus, since heat is generated at the time of lighting the light emitting elements, a substrate that supports the light emitting elements elongates and retracts due to an influence of the heat. Therefore, different displacement of the light emitting elements is generated for each exposure apparatus. When the color toner images are combined, there is sometimes a case where color drift is generated. 
   SUMMARY 
   According to an aspect of the invention, there is provided an exposure apparatus including: plural light emitting elements that are arranged in a line; a substrate that the plural light emitting elements are arranged thereon; plural temperature measuring units that are arranged along the arrangement direction of the plural light emitting elements and measure temperatures of the substrate on which the plural light emitting elements are arranged; and plural heating units that are arranged along the arrangement direction of the plural light emitting elements and heat the substrate on the basis of the temperatures measured by the temperature measuring units respectively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a view that shows an entire configuration of a printing system to which an image forming apparatus according to the first exemplary embodiment is applied; 
       FIG. 2  is a view that shows a configuration of the first printer and the second printer according to the first exemplary embodiment (hereinafter, simply referred to as a “printer”); 
       FIG. 3  is a sectional configuration view that shows a configuration of the LED printhead (LPH); 
       FIGS. 4A and 4B  are plan views of the LED circuit substrate; 
       FIG. 5  is a view that shows an example of the page resist mark (ROF) and the color resist marks (ROC) formed on the continuous paper; 
       FIG. 6  is a view that explains a function configuring unit that performs the print width correction in the printers according to the first exemplary embodiment; 
       FIG. 7  is a flowchart that shows an example of the procedure at the time of performing the print width correction; 
       FIG. 8  is a graph that compares the temperature distribution of the LED circuit substrate in the LPH according to the first exemplary embodiment and a temperature distribution of the conventional LED circuit substrate where the sheet shape heaters are not arranged; 
       FIG. 9  is a view that shows an entire configuration of the printing system according to the second exemplary embodiment; 
       FIG. 10  is a view that shows a configuration of the K-color printer of the second exemplary embodiment; and 
       FIG. 11  is a view that explains a function configuring unit that performs the print width correction in the K-color printer according to the second exemplary embodiment. 
   

   DETAILED DESCRIPTION 
   First Exemplary Embodiment 
   Hereinafter, with reference to the attached drawings, a detailed description is given to exemplary embodiments of the present invention. 
     FIG. 1  is a view that shows an entire configuration of a printing system  1  to which an image forming apparatus according to the first exemplary embodiment is applied. The printing system  1  shown in  FIG. 1  is configured so as to use a continuous paper P that is continuously formed in a belt shape as an example of a recording medium, and forms an image on the both sides of the continuous paper P. That is, the printing system  1  according to the first exemplary embodiment is provided with, from the upstream side in the transportation direction of the continuous paper P towards the downstream side, a continuous paper supplying apparatus  300 , a first printer  100 A serving as an example of the image forming apparatus that is arranged on the upstream side, a buffer unit  200 , a front-back reverse unit  500 , a second printer  100 B serving as an example of the image forming apparatus that is arranged on the downstream side, and a continuous paper winding apparatus  400 . 
   The printing system  1  according to the first exemplary embodiment is provided with a control computer  600  that controls actions of the apparatuses configuring the printing system  1 . The control computer  600  is connected to the continuous paper supplying apparatus  300 , the first printer  100 A, the second printer  100 B, and the continuous paper winding apparatus  400  through a communication network  700 . 
   In the continuous paper supplying apparatus  300 , a continuous paper roll  310  around which the continuous paper P is wound, is installed so as to supply the continuous paper P to the first printer  100 A. 
   The first printer  100 A prints an image on a front surface of the continuous paper P that is supplied from the continuous paper supplying apparatus  300  on the basis of image data that is sent from the control computer  600 . 
   The buffer unit  200  transports the continuous paper P of which, in the first printer  100 A, a printing processing is performed on the front surface side towards the second printer  100 B, while holding a predetermined amount of the continuous paper P. That is, in the buffer unit  200 , as a transporting roll, an upstream side hanging roll  201 , a tension roll  202  that is installed movably in, for example, the up and down direction (the arrow direction), and transports the continuous paper P while giving a predetermined tensile force to the continuous paper P, and a downstream side hanging roll  203  are arranged. The continuous paper P is successively transported from the upstream side hanging roll  201  to the downstream side hanging roll  203 , through the tension roll  202  ( 201 → 202 → 203 ). As a result, a loop that is to hold a predetermined amount of the continuous paper P within the buffer unit  200  is formed in the continuous paper P. 
   The front-back reverse unit  500  reverses the front and the back surfaces of the continuous paper P and supplies the continuous paper P to the second printer  100 B. That is, in the front-back reverse unit  500 , a front-back reverse roll  501  that is arranged with inclination of 45 degrees in the transportation direction of the continuous paper P is provided. By transporting the continuous paper P while hanging the continuous paper P with the front-back reverse roll  501 , the front and the back surfaces of the continuous paper P is reversed. Therefore, the transportation direction of the continuous paper P that already passes through the front-back reverse unit  500  is changed by 90 degrees. Consequently, the second printer  100 B is arranged in the direction with 90 degrees displacement from the first printer  100 A. 
   The second printer  100 B is configured similarly to the first printer  100 A. On a back surface of the continuous paper P of which, in the first printer  100 A, the printing processing has been performed on the front surface, the image is printed on the basis of the image data that is sent from the control computer  600 . 
   The continuous paper winding apparatus  400  winds the continuous paper P of which, in the second printer  100 B, the printing processing has been performed on the back surface around a winding roll  410 . 
   It should be noted that in the printing system  1  according to the first exemplary embodiment, the first printer  100 A forms the image on the front surface of the continuous paper P, and the second printer  100 B forms the image on the back surface of the continuous paper P, respectively. However, the printing system  1  may be configured such that the first printer  100 A forms the image on the back surface of the continuous paper P and the second printer  100 B forms the image on the front surface of the continuous paper P respectively. 
   The control computer  600  outputs the image data to be printed on the front surface side and the image data to be printed on the back surface side at predetermined timing to the first printer  100 A and the second printer  100 B respectively through the communication network  700 . Moreover, the control computer  600  outputs control signals that control actions of the first printer  100 A and the second printer  100 B respectively. 
   The communication network  700  is configured so as to communicate interactively by using a communication line and a cable, or may be configured by, for example, a network such as LAN (Local Area Network), WAN (Wide Area Network) and the like. 
   In the printing system  1  according to the first exemplary embodiment, under the control of the control computer  600 , the first printer  100 A prints a full color image on the front surface side of the continuous paper P that is supplied from the continuous paper supplying apparatus  300 . The continuous paper P of which, in the first printer  100 A, the full color image is printed on the front surface side is transported to the buffer unit  200 , and while a predetermined amount of the continuous paper P is held in the buffer unit  200 , the continuous paper P is transported to the front-back reverse unit  500 . The front-back reverse unit  500  reverses the front and the back surfaces of the transported continuous paper P and transports the continuous paper P to the second printer  100 B. 
   In the second printer  100 B to which the reversed continuous paper P is transported, the full color image is printed on the back surface side of the continuous paper P, while the page thereof is aligned with the image that is printed on the front surface side in the first printer  100 A. Thereby, the full color images are formed on the both sides of the continuous paper P. The continuous paper P on which the printing processing has been performed in the second printer  100 B is fed to the continuous paper winding apparatus  400  and wound around the winding roll  410 . 
   Next, a description is given to the first printer  100 A and the second printer  100 B according to the first exemplary embodiment. In the first exemplary embodiment, the first printer  100 A and the second printer  100 B have the same configuration each other. 
     FIG. 2  is a view that shows a configuration of the first printer  100 A and the second printer  100 B according to the first exemplary embodiment (hereinafter, simply referred to as a “printer  100 ”). The printer  100  shown in  FIG. 2  is an image forming apparatus with, for example, an electrophotographic type. The printer  100  is provided with, from the upstream side in the transportation direction (arrows in the figure) of the continuous paper P towards the downstream side, a paper transporting unit  20  that transports and drives the continuous paper P, and four image forming units, that is, a K-color image forming unit  30 K that forms a toner image of black (K), a C-color image forming unit  30 C that forms a toner image of cyan (C), a M-color image forming unit  30 M that forms a toner image of magenta (M), and a Y-color image forming unit  30 Y that forms a toner image of yellow (Y) on the continuous paper P. Further, the printer  100  is provided with a fixing unit  40  that fixes the color toner images. 
   In the paper transporting unit  20 , from the upstream side to the downstream side in the transportation direction of the continuous paper P, back tension rolls  24 , an aligning roll  22 , a main drive roll  21  and a paper transportation direction changing roll  25  are arranged. 
   The main drive roll  21  has a function of nipping the continuous paper P with a predetermined pressure, receiving drive from a main motor (not shown in the figure) that is arranged in the paper transporting unit  20 , and feeding the continuous paper P at a predetermined transportation speed. The aligning roll  22  has a function of cooperating with a guiding member  23  which is in a partially cylindrical shape, and constantly keeping a transportation route of the continuous paper P on the upstream side of the main drive roll  21 . The back tension rolls  24  have a function of rotating at a lower speed than that of the main drive roll  21  and giving the tensile force to the continuous paper P on the upstream side of the main drive roll  21 . The paper transportation direction changing roll  25  is a driven roll that is driven by winding and hanging the continuous paper P and has a function of changing the transportation direction of the continuous paper P that is fed from the main drive roll  21  to the direction towards the K-color image forming unit  30 K. 
   Each of the K-color image forming unit  30 K, the C-color image forming unit  30 C, the M-color image forming unit  30 M and the Y-color image forming unit  30 Y (hereinafter, also collectively referred to as an “image forming unit  30 ”) is provided with a photoconductor drum  31  serving as an image carrier, an electrically charging device  32  that electrically charges a surface of the photoconductor drum  31  at a predetermined potential, a LED printhead (LPH)  33  serving as an example of an exposure apparatus that exposes the surface of the photoconductor drum  31  on the basis of the image data, a developing device  34  that develops an electrostatic latent image formed on the surface of the photoconductor drum  31  by each of the color toners, a transfer device  35  that transfers the toner image formed on the surface of the photoconductor drum  31  to the continuous paper P, and a pair of transfer guiding rolls  36  and  37  that are arranged on the upstream side and the downstream side of the transfer device  35  respectively, and press the continuous paper P onto the photoconductor drum  31 . 
   Further, the K-color image forming unit  30 K is provided with a page resist mark reading unit  38 K that reads a page resist mark (described later) for aligning the pages formed on any one of the front surface and the back surface of the continuous paper P or on both the front surface and the back surface, and outputs a timing signal. The K-color image forming unit  30 K, the C-color image forming unit  30 C, the M-color image forming unit  30 M and the Y-color image forming unit are provided with color resist mark reading units  39 K,  39 C,  39 M and  39 Y as an example of an exposure position detecting unit that reads a color resist mark (described later) for aligning the color images formed on the surface of the continuous paper P, and outputs the timing signal and reading position data, respectively. 
   The fixing unit  40  is provided with a flash fixing device  41  that fixes the color toner images formed on the continuous paper P to the continuous paper P by a luminous body such as a flash lump in a non-contact state, tensile force giving roll members  42  that give the tensile force to the continuous paper P on the downstream side of the flash fixing device  41 , an aligning member  43  that corrects the route of the continuous paper P in the width direction on the downstream side of the tensile force giving roll members  42 , and tension rolls  44  that nip the continuous paper P in the vicinity of an exit, rotate at a higher speed than the transporting speed of the continuous paper P, and gives the tensile force to the continuous paper P. 
   Further, the printer  100  is provided with a comprehensive controller  50  serving as an example of a controller that controls an entire action of the printer  100 , a paper transporting controller  60  that controls the paper transporting unit  20 , a K-color image forming controller  70 K serving as an example of a controller that controls an action of the K-color image forming unit  30 K, a C-color image forming controller  70 C serving as an example of a controller that controls an action of the C-color image forming unit  30 C, a M-color image forming controller  70 M serving as an example of a controller that controls an action of the M-color image forming unit  30 M, a Y-color image forming controller  70 Y serving as an example of a controller that controls an action of the Y-color image forming unit  30 Y, and a fixing controller  80  that controls an action of the fixing unit  40 . 
   The paper transporting controller  60 , the K-color image forming controller  70 K, the C-color image forming controller  70 C, the M-color image forming controller  70 M, the Y-color image forming controller  70 Y, and the fixing controller  80  are comprehensively controlled by the comprehensive controller  50 . 
   In the printing system  1  according to the first exemplary embodiment, when the printing system  1  is started, the image data for the front surface side and the image data for the back surface side are inputted from the control computer  600  to each of the comprehensive controller  50  of corresponding one of the printers  100  through the communication network  700 . The comprehensive controller  50  divides the inputted image data into image data respectively corresponding to the K-color, C-color, the M-color and the Y-color, and sends the K-color image data, the C-color image data, the M-color image data and the Y-color image data to the K-color image forming controller  70 K, the C-color image forming controller  70 C, the M-color image forming controller  70 M and the Y-color image forming controller  70 Y, respectively. 
   In synchronization with the inputting of the image data to the comprehensive controller  50 , the comprehensive controller  50  controls the paper transporting unit  20  through the paper transporting controller  60  and further controls the fixing unit  40  through the fixing controller  80  so as to transport the continuous paper P at a predetermined transportation speed while giving a predetermined tensile force to the continuous paper P. 
   Under the control of the comprehensive controller  50 , the K-color image forming controller  70 K, the C-color image forming controller  70 C, the M-color image forming controller  70 M and the Y-color image forming controller  70 Y (hereinafter, collectively referred to as a “color image forming controller 70”) control formation of each of the color toner images in corresponding one of the color image forming units  30 . 
   That is, in the color image forming unit  30 , under the control of the color image forming controller  70 , the photoconductor drum  31  starts rotation, and the surface of the photoconductor drum  31  is electrically charged by the electrically charging device  32  at a predetermined potential (for example, −500 V). Further, by exposure by the LPH  33  that emits light on the basis of the color image data, the electrostatic latent image is formed. The electrostatic latent image on the photoconductor drum  31  is developed by the developing device  34  with the color toner to form the color toner image. The color toner image formed on the surface of the photoconductor drum  31  is transferred to the continuous paper P by the transfer device  35  and the transfer guiding rolls  36  and  37 . 
   The continuous paper P is successively transported from the K-color image forming unit  30 K to the Y-color image forming unit  30 Y through the C-color image forming unit  30 C and the M-color image forming unit  30 M ( 30 K→ 30 C→ 30 M→ 30 Y). Thereby, the color toner images are superimposed with each other, and a full color toner image is formed on the continuous paper P. 
   After that, the continuous paper P on which the full color toner image is formed is transported to the fixing unit  40 , and the toner image is fixed to the continuous paper P by the flash fixing device  41 . Thereby, in the first printer  100 A, the full color image is formed on the front surface side of the continuous paper P. In the same way, in the second printer  100 B, the full color image is formed on the back surface side of the continuous paper P. 
   Subsequently, a description is given to the LED printhead (LPH)  33  that is provided in the first printer  100 A and the second printer  100 B according to the first exemplary embodiment. 
     FIG. 3  is a sectional configuration view that shows a configuration of the LED printhead (LPH)  33 . In  FIG. 3 , the LPH  33  is provided with a base  61  serving as a supporting body, a self-scanning LED array (SLED)  63 , a LED circuit substrate  62  that mounts the SLED  63 , a signal generating circuit  110  driving the SLED  63  and the like, a rod lens array  64  that forms an image with light irradiated from the SLED  63  on the surface of the photoconductor drum  31 , and a holder  65  that shields the SLED  63  from the exterior while supporting the rod lens array  64 , and a plate spring  66  that pressurizes the base  61  in the direction to the rod lens array  64 . 
   The LPH  33  is provided with three sheet shape heaters  108 A,  108 B and  108 C (hereinafter, also referred to as “sheet shape heaters 108” collectively) serving as an example of heating units that are arranged so as to be brought in contact with the LED circuit substrate  62  on the back surface side of the LED circuit substrate  62  (on the base  61  side), an insulating sheet  109  that is composed of a material with high thermal conductivity that electrically insulates between the sheet shape heaters  108  and the base  61 , and three temperature sensors  107 A,  107 B and  107 C (hereinafter, also referred to as “temperature sensors  107 ” collectively) that are arranged on the surface side of the LED circuit substrate  62  (on the rod lens array  64  side) and serve as an example of temperature measuring units that measure the temperatures of the LED circuit substrate  62 . 
   The base  61  is formed by a block or a steel plate including a metal such as aluminum and SUS, and supports the LED circuit substrate  62 . The holder  65  supports the base  61  and the rod lens array  64 , and performs setting so as to maintain a predetermined optical positional relationship between the SLED  63  and the rod lens array  64 . Further, the holder  65  is configured so as to seal the SLED  63 . Thereby, the holder  65  prevents adhesion of dirt onto the SLED  63  from the exterior. Meanwhile, the plate spring  66  pressurizes the LED circuit substrate  62  on which the SLED  63  is installed in the rod lens array  64  direction through the base  61  so as to maintain the optical positional relationship between the SLED  63  and the rod lens array  64 . 
   The LPH  33  that is configured as mentioned above is, by an adjusting screw (not shown in the figure), configured movably in the optical axis direction of the rod lens array  64  and adjusted so that an image forming position (focal point surface) of the rod lens array  64  is located on the surface of the photoconductor drum  31 . 
   Here,  FIGS. 4A and 4B  are plan views of the LED circuit substrate  62 :  FIG. 4A  shows the surface side of the LED circuit substrate  62  (the rod lens array  64  side); and  FIG. 4B  shows the back surface side (the base  61  side). 
   As shown in  FIG. 4A , on the surface side of the LED circuit substrate  62 , the SLED  63  including, for example, fifty-eight SLED chips (CHIP 1  to CHIP 58 ) is arranged in a line with high accuracy so as to be in parallel with the axial direction of the photoconductor drum  31 . In such a case, on an end border of arrangement (LED array) of the light emitting elements (LED) that are arranged in the SLED chips (CHIP 1  to CHIP 58 ), the SLED chips are alternately arranged in a zigzag shape so that each LED array is continuously arranged in a connection portion between the SLED chips. 
   On the surface side of the LED circuit substrate  62 , the signal generating circuit  110  that generates a signal for driving the SLEDs  63 , a three terminal regulator  101  that outputs a predetermined voltage, an EEPROM  102  that stores light quantity correction data and the like for each LED, and a harness  103  that sends and receives a signal between the LED circuit substrate  62  and the color image forming controllers  70  and supplies electric power and the like are provided. 
   Further, on the surface side of the LED circuit substrate  62 , the three temperature sensors  107 A,  107 B and  107 C are arranged along the arrangement direction of the SLED  63  at equal intervals. That is, the temperature sensors  107 A,  107 B and  107 C are arranged in central portions of respective three areas that are formed by dividing an area between one end portion of the arranged SLEDs  63  and the other end portion of the arranged SLEDs  63  into three. 
   The temperature sensors  107 A,  107 B and  107 C measure the temperatures of the LED circuit substrate  62 , respectively. Specifically, the temperature sensor  107 A measures the substrate temperature in an end area that is located on the signal generating circuit  110  side among the areas mentioned above. The temperature sensor  107 B measures the substrate temperature in a central area. The temperature sensor  107 C measures the substrate temperature in an end area on the opposite side of the signal generating circuit  110  side. The temperature sensors  107 A,  107 B and  107 C send their respective measured temperature values to the color image forming controllers  70 . 
   Meanwhile, as shown in  FIG. 4B , on the back surface side of the LED circuit substrate  62 , corresponding to the arrangement position of the SLEDs  63  on the surface side, the three sheet shape heaters  108 A,  108 B and  108 C are arranged in the arrangement direction of the SLEDs  63  at equal intervals so as to be brought in contact with the back surface of the LED circuit substrate  62 . That is, the sheet shape heaters  108 A,  108 B and  108 C are arranged respectively in the three areas that are formed by dividing the area between one end portion of the arranged SLEDs  63  and the other end portion of the arranged SLEDs  63  into three. 
   Therefore, the temperature sensors  107 A,  107 B and  107 C and the sheet shape heaters  108 A,  108 B and  108 C are arranged at positions corresponding to each other on the surface and the back surface respectively. Thereby, the sheet shape heater  108 A heats the LED circuit substrate  62  in one end area on the signal generating circuit  110  side where the temperature sensor  107 A measures the temperature. The sheet shape heater  108 B heats the LED circuit substrate  62  in the central area where the temperature sensor  107 B measures the temperature. The sheet shape heater  108 C heats the LED circuit substrate  62  in the other end area on the opposite side of the signal generating circuit  110  side where the temperature sensor  107 C measures the temperature. 
   Here, each of the sheet shape heaters  108 A,  108 B and  108 C has a structure in which, for example, both surfaces of thin-layer stainless steel serving as a heating element are covered by a polyimide with thickness of approximately 0.2 mm. 
   It should be noted that the LPH  33  according to the first exemplary embodiment has a configuration where the three temperature sensors and the three sheet shape heaters are arranged. However, the number of the temperature sensors  107  and the number of the sheet shape heaters  108  may be properly set as appropriate in accordance with the structure of the LPH  33  as long as they are plural. 
   Next, a description is given to alignment of the image that is formed on each page in the first printer  100 A and the second printer  100 B according to the first exemplary embodiment. The alignment of the image includes alignment of the color toner images that is performed within each of the printers  100  and alignment of the pages that is performed in the first printer  100 A and the second printer  100 B so as to align positions of the pages of the images formed on both sides. Further, the alignment of the color toner images that is performed within each of the printers  100  includes alignment in the sub-scanning direction (the transportation direction of the continuous paper P) and alignment in the main scanning direction (the axis-line direction of the photoconductor drum  31 ). In the alignment in the sub-scanning direction of the first exemplary embodiment, timing for starting the exposure of the image in each of the LPHs  33  is adjusted. The alignment in the main scanning direction is performed by controlling the temperature of the LED circuit substrate  62  of each of the LPHs  33  and adjusting the length of the LED circuit substrate  62 . The alignment of the color toner images is performed on the basis of the color resist mark (ROC), while the alignment of the pages is performed on the basis of the page resist mark (ROF). 
   In the printing system  1  according to the first exemplary embodiment, for example, the K-color image forming unit  30 K that is located on the most upstream side of the first printer  100 A forms the page resist mark (ROF) that is the fiducial of the alignment of the pages of the image formed in the second printer  100 B. Each of the color image forming units  30  of the printers  100  forms the color resist mark (ROC) that is the fiducial of the alignment of the color toner images formed in the image forming units  30 . It should be noted that a preprinted paper on which the page resist mark (ROF) is printed in advance may be used. In such a case, the K-color image forming unit  30 K does not form the page resist mark (ROF). 
     FIG. 5  is a view that shows an example of the page resist mark (ROF) and the color resist marks (ROC) formed on the continuous paper P. The page resist mark (ROF) and the color resist marks (ROC) shown in  FIG. 5  are formed on non-image areas that are located on the both end sides other than an image area where the image is formed on the continuous paper P for each page. It should be noted that  FIG. 5  shows the case where the color resist marks (ROC) are formed on one end side of the non-image areas, however, the color resist marks (ROC) may be formed on both end sides of the non-image areas. In such a case, color resist mark reading units  39 K,  39 C,  39 M and  39 Y are provided at two places on the both ends in the main scanning direction. 
   The alignment of the color toner images for each page that is performed in each of the printers  100  is performed as follows. Firstly, with regard to the alignment in the sub-scanning direction, a color resist mark of K-color (ROC_K 1 ) is formed in the K-color image forming unit  30 K of the first printer  100 A, and a color resist mark of C-color (ROC_C 1 ) is formed in the C-color image forming unit  30 C on the downstream side thereof at a predetermined timing. The color resist mark reading unit  39 C that is arranged on the downstream side of the transfer device  35  of the C-color image forming unit  30 C generates timing signals that show timing when the color resist marks of K-color and the C-color (ROC_K 1 , ROC_C 1 ) pass through respectively, and sends the signals to the C-color image forming controller  70 C. 
   On the basis of time difference between the timing signals, the C-color image forming controller  70 C generates alignment correction data in the sub-scanning direction (sub-scanning position correction data) at the time of forming the image in the C-color image forming unit  30 C. 
   The C-color image forming controller  70 C sets image formation starting timing in the sub-scanning direction on the basis of the generated sub-scanning position correction data and a page timing signal in the K-color image forming unit  30 K described below, at the time of forming the image on a page that is next to the page where the color resist marks (ROC) serving as a basis for generating the sub-scanning position correction data are formed. 
   That is, as shown in  FIG. 5 , since the color resist marks (ROC) are formed within the page, the image formation starting timing in the color image forming units  30  for the page may not be set on the basis of the color resist marks (ROC) on the page. However, since the continuous paper P is continuously transported, the transportation speed is considered to be hardly changed between the page where the color resist marks (ROC) serving as a basis for setting the image formation starting timing are formed and the page that is next to the above page. Therefore, the color image forming controllers  70  set the image formation starting timing on each page on the basis of passage timing of the respective color resist marks (ROC) that are formed on the immediately previous page. 
   The same is true with regard to the page resist marks (ROF) described later. Therefore, at the time of forming the image on the first page, in advance, a blank page where only the page resist marks (ROF) and the color resist marks (ROC) serving as a basis of alignment of the pages and alignment of the color images on the first page is printed. 
   It should be noted that, as well as the above description, in the M-color image forming unit  30 M, on the basis of the sub-scanning position correction data that is generated based on the color resist mark of K-color (ROC_K 1 ) and the color resist mark of M-color (ROC_M 1 ), and the page timing signal in the K-color image forming unit  30 K described below, the image formation starting timing in the sub-scanning direction on the next page is set. In the Y-color image forming unit  30 Y, on the basis of the sub-scanning position correction data that is generated based on the color resist mark of K-color (ROC_K 1 ) and the color resist mark of Y-color (ROC_Y 1 ), and the page timing signal in the K-color image forming unit  30 K described below, the image formation starting timing in the sub-scanning direction on the next page is set. 
   Thereby, the alignment of the color toner images that are formed in the first printer  100 A in the sub-scanning direction is performed with high accuracy. The same is true in the second printer  100 B. 
   Meanwhile, with regard to alignment in the main scanning direction, when the color resist mark of K-color (ROC_K 2 ) is formed in the K-color image forming unit  30 K of the first printer  100 A, the color resist mark reading unit  39 K generates reading position data of the color resist mark of K-color (ROC_K 2 ) and sends the data to the K-color image forming controller  70 K. The K-color image forming controller  70 K compares the reading position data of the color resist mark of K-color (ROC_K 2 ) with standard position data that is set in advance, and generates alignment correction data (main scanning position correction data) with regard to the main scanning direction at the time of forming the image in the K-color image forming controller  70 K. That is, the main scanning position correction data is data that shows a displacement amount from a predetermined standard position in the LED of the LED circuit substrate  62 . On the basis of the main scanning position correction data, the temperatures of the LED circuit substrate  62  in the LPH  33  described later are controlled and length of the LED circuit substrate  62  is adjusted. 
   Similarly, in the C-color image forming unit  30 C, on the basis of the main scanning position correction data that is generated from the color resist mark of C-color (ROC_C 2 ), the temperatures of the LED circuit substrate  62  in the LPH  33  described later are controlled and the length of the LED circuit substrate  62  is adjusted. In the M-color image forming unit  30 M, on the basis of the main scanning position correction data that is generated from the color resist mark of M-color (ROC_M 2 ), the temperatures of the LED circuit substrate  62  in the LPH  33  described later are controlled and the length of the LED circuit substrate  62  is adjusted. Further, in the Y-color image forming unit  30 Y, on the basis of the main scanning position correction data that is generated from the color resist mark of Y-color (ROC_Y 2 ), the temperatures of the LED circuit substrate  62  in the LPH  33  described later are controlled and the length of the LED circuit substrate  62  is adjusted. 
   Thereby, the alignment of the color toner images that are formed in the first printer  100 A in the main scanning direction (hereinafter, referred to as a “print width correction”) is performed. The same is true in the second printer  100 B. 
   The alignment of the pages between the image that is formed in the first printer  100 A and the image that is formed in the second printer  100 B is performed as follows. As mentioned above, the K-color image forming unit  30 K that is located on the most upstream side of the first printer  100 A forms the page resist mark (ROF) for each page of the continuous paper P (refer to  FIG. 5 ). The page resist mark reading unit  38 K that is arranged in the K-color image forming unit  30 K of the second printer  100 B reads the page resist mark (ROF) on each page, and generates the page timing signal that shows the timing when the page resist mark (ROF) passes through the page resist mark reading unit  38 K. The generated page timing signal is sent to the K-color image forming controller  70 K. 
   The K-color image forming controller  70 K of the second printer  100 B sets image forming timing in the K-color image forming unit  30 K on the basis of the acquired page timing signal. Then, on the basis of the set image forming timing, the K-color image forming controller  70 K starts the exposure with the LPH  33 . 
   The K-color image forming controller  70 K sends the page timing signal to the comprehensive controller  50 . The comprehensive controller  50  sends the page timing signal to the image forming controllers  70  of the color image forming units  30  other than the K-color image forming unit  30 K. The image forming controllers  70  of the color image forming units  30  set the image formation starting timing on the basis of the acquired page timing signal and the sub-scanning position correction data mentioned above, and starts exposure by the LPH  33 . 
   As mentioned above, the second printer  100 B according to the first exemplary embodiment is configured so that the image forming timing in each of the color image forming units  30  is set on the basis of the timing when the page resist mark (ROF) that is formed on the continuous paper P passes through the page resist mark reading unit  38 K of the K-color image forming unit  30 K. That is, in the printing system  1  according to the first exemplary embodiment, since the exposure start timing of each of the color image forming units  30  is set on the basis of the position of the page resist mark (ROF) on the continuous paper P, the alignment of the pages with the image that is formed on the front surface in the first printer  100 A and the image that is formed on the back surface in the second printer  100 B is performed. 
   Subsequently, a description is given to the alignment of the color toner images in the main scanning direction (the print width correction) in the printers  100  according to the first exemplary embodiment. 
   As mentioned above, the print width correction is performed by controlling the temperature of the LED circuit substrate  62  of the LPH  33  that is arranged in each of the color image forming units  30  and adjusting the length of the LED circuit substrate  62 . 
   With regard to each SLED  63  that is arranged on the LED circuit substrate  62 , an arrangement position thereof varies at the time of manufacturing. Therefore, among the color image forming units  30 , original displacement in the arrangement position of the LED is generated. 
   Although each of the LEDs that configures the SLED  63  is a light emitting element with a relatively small heat quantity, for example, the number of the LEDs is about 12,000 in the case where the LEDs are arranged in the LPH  33  that has the overall length of 500 mm with a resolution of 600 dpi (dot per inch). Therefore, a large heat quantity to the extent that expands the LED circuit substrate  62  is generated. Thereby, the displacement in the arrangement position of the LEDs on the LED circuit substrate  62  is also generated. 
   In general, a thermal expansion rate of a print substrate that forms the LED circuit substrate  62  is approximately 10 μm/degree C. for 500 mm, for example. Therefore, in the above-mentioned LPH  33  of 500 mm that has the resolution of 600 dpi, the overall length is changed by approximately 300 μm. Thereby, in the case where a LED lighting rate is different according to each of the color image forming units  30  and the like, there is sometimes a case where each of heat expansion amounts of the LED circuit substrates  62  is different and hence color drift that is difficult to be overlooked is generated in the image. Particularly, since the lighting rate in the K-color image forming unit  30 K is often high, the thermal expansion amount of the LED circuit substrate  62  highly tends to be increased. 
   In the case where the LED lighting rate is different according to an image area, a temperature distribution is generated in the longitudinal direction of the LED circuit substrate  62  so that there is sometimes a case where a deformation or a warp is generated in the LED circuit substrate  62 . In such a case, there is sometimes a case where light from the LED is not formed into the image on the photoconductor drum  31 , so that image failure may be generated. 
   Meanwhile, each of the color image forming units  30  is provided with a cooling unit (not shown in the figure) that cools down the LPH  33  such as a fan. However, since the difference of the lighting rates and the like is not to be avoided even with the cooling unit, it is difficult to cool down the LPH  33  so as to make the temperature distribution of the LPH  33  uniform. Particularly, it is difficult to eliminate a tendency in which the temperatures are relatively low in both ends of the LPH  33  where a heat dissipation amount is large, and the temperature is relatively high in a central portion where heat dissipation is not easily generated. As in the printers  100  according to the first exemplary embodiment, in the case where the color image forming units  30  are formed within frame bodies thereof respectively, due to difference of internal temperatures, it is difficult to adjust the temperatures of the LPHs  33  to the same level by the cooling unit. 
   Then, in the printer  100  according to the first exemplary embodiment, the temperatures in the LED circuit substrate  62  of the LPH  33  arranged in each of the color image forming units  30  are controlled and hence the thermal expansion amount of the LED circuit substrate  62  is adjusted. Thereby, each displacement amount of the LED on the LED circuit substrate  62  of the LPH  33  arranged in the color image forming unit  30  is controlled to be substantially the same so as to perform the print width correction. 
   The three temperature sensors  107 A,  107 B and  107 C are provided along the arrangement direction of the SLED  63 , and the three sheet shape heaters  108 A,  108 B and  108 C are provided corresponding to the arrangement position of the temperature sensors. The respective areas where the temperature sensors and the sheet shape heaters are arranged are independently controlled. Thereby, while temperature adjustment of the entire LED circuit substrate  62  is performed, the temperature distribution in the longitudinal direction is adjusted so as to be substantially uniform. 
     FIG. 6  is a view that explains a function configuring unit that performs the print width correction in the printers  100  according to the first exemplary embodiment. As shown in  FIG. 6 , the print width correction is performed under the control of the color image forming controllers  70  and the comprehensive controller  50 . It should be noted that in  FIG. 6 , a description is given taking the K-color image forming unit  30 K as an example. 
   As the function configuring unit that performs the print width correction, the K-color image forming controller  70 K is provided with a first temperature detecting unit  711 , a second temperature detecting unit  712 , a third temperature detecting unit  713 , a main scanning position correction data calculating unit  721 , a heater controller  731 , a first heater drive unit  741 , a second heater drive unit  742 , and a third heater drive unit  743 . The comprehensive controller  50  is provided with a correction amount calculating unit  501  and a memory  502 . 
   Further, as the function unit that performs setting of the light quantity of the LPH  33  in association with the print width correction, the K-color image forming controller  70 K is provided with a light quantity setting unit  751  serving as an example of a light quantity setting device. 
   It should be noted that a CPU (not shown in the figure) of the K-color image forming controller  70 K reads a program that executes functions of the first temperature detecting unit  711 , the second temperature detecting unit  712 , the third temperature detecting unit  713 , the main scanning position correction data calculating unit  721 , the heater controller  731 , the first heater drive unit  741 , the second heater drive unit  742 , the third heater drive unit  743 , and the light quantity setting unit  751  from a main memory (not shown in the figure) into a RAM or the like within the K-color image forming controller  70 K so as to perform various processing. 
   In the K-color image forming controller  70 K, the first temperature detecting unit  711  acquires the measured temperature value from the temperature sensor  107 A on the LED circuit substrate  62 . Thereby, the first temperature detecting unit  711  detects the substrate temperature in the one end area that is located on the signal generating circuit  110  side in the LED circuit substrate  62 , and sends the substrate temperature to the heater controller  731  as temperature data of the one end area that is located on the signal generating circuit  110  side. The second temperature detecting unit  712  acquires the measured temperature value from the temperature sensor  107 B on the LED circuit substrate  62 . Thereby, the second temperature detecting unit  712  detects the substrate temperature in the central area in the arrangement of the SLEDs  63  in the LED circuit substrate  62 , and sends the substrate temperature to the heater controller  731  as temperature data of the central area. The third temperature detecting unit  713  acquires the measured temperature value from the temperature sensor  107 C on the LED circuit substrate  62 . Thereby, the third temperature detecting unit  713  detects the substrate temperature in the other end area on the opposite side of the signal generating circuit  110  side of the SLEDs  63  in the LED circuit substrate  62 , and sends the substrate temperature to the heater controller  731  as temperature data of the other end area on the opposite side. 
   As mentioned above, the main scanning position correction data calculating unit  721  compares the reading position data of the color resist mark of K-color (ROC_K 2 ) that is generated in the color resist mark reading unit  39 K with the standard position data that is set in advance, and generates the main scanning position correction data. The main scanning position correction data is to show the displacement amount from the predetermined standard position of the LED in the K-color image forming unit  30 K. The generated main scanning position correction data is sent to the comprehensive controller  50 . 
   On the basis of the temperature data of the areas that is acquired from the first temperature detecting unit  711 , the second temperature detecting unit  712  and the third temperature detecting unit  713 , and a correction amount that is calculated in the correction amount calculating unit  501  of the comprehensive controller  50  (described later), the heater controller  731  sets a supplying amount of electric power to the respective three sheet shape heaters  108 A,  108 B and  108 C that are arranged on the back surface side of the LED circuit substrate  62 . 
   That is, the heater controller  731  stores a correspondence relationship between the substrate temperature in the LPH  33  and a position changing amount of the LED in, for example, a ROM or the like (not shown in the figure) serving as an example of a memory, as a table. For example, from a size of the LED circuit substrate  62  in the longitudinal direction and the thermal expansion rate of a material that forms the LED circuit substrate  62 , the correspondence relationship between the substrate temperature of the LPH  33  and the position changing amount of the LED is determined. With using the table, target temperature values for respective areas are set from the temperature data of the areas and the correction amount, and the supplying amount of electric power to the respective sheet shape heaters  108 A,  108 B and  108 C that adjusts the temperatures in the areas to the set target temperature values is set. 
   The heater controller  731  sends data on the target temperature values (target set temperature data) that is set in the areas of the LED circuit substrate  62  to the light quantity setting unit  751 . 
   The first heater drive unit  741  supplies the electric power that is set by the heater controller  731  to the sheet shape heater  108 A. The second heater drive unit  742  supplies the electric power that is set by the heater controller  731  to the sheet shape heater  108 B. The third heater drive unit  743  supplies the electric power that is set by the heater controller  731  to the sheet shape heater  108 C. 
   The light quantity setting unit  751  sets light quantity values in the LPH  33  on the basis of the target set temperature data in the areas that is acquired from the heater controller  731 . With regard to setting of the light quantity values, a description is given later. 
   In the comprehensive controller  50 , the memory  502  stores an initial displacement amount of the LED in the main scanning direction for each LPH  33  that is installed in the color image forming unit  30 . The initial displacement amount here is an amount that is preliminarily measured at a predetermined temperature (for example, 20 degrees C.) as, for example, the displacement amount to a designed amount at the time of manufacturing. At the time of manufacturing the printer  100 , the initial displacement amount for each LPH  33  that is installed in the color image forming unit  30  is stored in the memory  502  as, for example, 4-bit data. 
   The correction amount calculating unit  501  extracts the LPH  33  with, for example, the largest initial displacement amount among the LPHs  33  of the color image forming units  30  from the initial displacement amounts of LPHs  33  that are stored in the memory  502 . On the basis of the LPH  33  with the largest initial displacement amount, the correction amount in the LPHs  33  of other image forming units  30  is calculated. That is, on the basis of the main scanning position correction data (the displacement amount) of the LPH  33  serving as the basis, a difference from the main scanning position correction data (the displacement amount) of each of the LPHs  33  of other color image forming units  30  is calculated. The difference is sent to the heater controller  731  of the color image forming controllers  70  as the correction amount. The calculated correction amount here is an amount of adjusting the length of the LED circuit substrate  62  that makes the position changing amount of each of the LPHs  33  of the other image forming units  30  the same as that of the LPH  33  serving as the basis. 
   Subsequently, a description is given to a procedure at the time of performing the print width correction in the printers  100  according to the first exemplary embodiment.  FIG. 7  is a flowchart that shows an example of the procedure at the time of performing the print width correction. The procedure is, as mentioned above, performed under the control of the color image forming controllers  70  and the comprehensive controller  50 . Here, a description is given with using the configuration shown in  FIG. 6 . 
   As shown in  FIG. 7 , firstly, the first temperature detecting unit  711 , the second temperature detecting unit  712  and the third temperature detecting unit  713  acquire the measured temperature values from the temperature sensor  107 A, the temperature sensor  107 B and the temperature sensor  107 C respectively (S 101 ). The temperature data of the areas are generated from the acquired measured temperature values and sent to the heater controller  731  (S 102 ). 
   The main scanning position correction data calculating unit  721  generates the main scanning position correction data on the basis of the reading position data of the color resist mark of K-color (ROC_K 2 ) that is acquired from the color resist mark reading unit  39 K, and sends the main scanning position correction data to the comprehensive controller  50  (S 103 ). 
   The correction amount calculating unit  501  of the comprehensive controller  50  acquires the main scanning position correction data from the color image forming controllers  70  (S 104 ). Initial displacement amount data for each LPH  33  of the color image forming unit  30  is acquired from the memory  502  (S 105 ). On the basis of the LPH  33  with the largest initial displacement amount among the LPHs  33  of the color image forming units  30 , the difference between the main scanning position correction data of the LPH  33  serving as the basis and the main scanning position correction data of each of the LPHs  33  of other color image forming units  30  is calculated (S 106 ). The correction amount calculating unit  501  sends the calculated difference to each heater controller  731  of the color image forming controller  70  as the correction amount in each LPH  33  (S 107 ). 
   On the basis of the temperature data that is acquired from the first temperature detecting unit  711 , the second temperature detecting unit  712  and the third temperature detecting unit  713  and the correction amount data that is acquired from the comprehensive controller  50 , the heater controller  731  sets the supplying amount of electric power to the respective sheet shape heaters  108 A,  108 B and  108 C (S 108 ) That is, on the basis of the acquired temperature data of the areas and the correction amount data that is acquired from the comprehensive controller  50 , the target temperature values for respective areas of the LED circuit substrate  62  are set so that the displacement amount of the LED on the LED circuit substrate  62  substantially matches the displacement amount of the LED on the LED circuit substrate  62  of the LPH  33  serving as the basis, and the temperature distribution of the LED circuit substrate  62  becomes uniform in the longitudinal direction. The supplying amount of electric power to the respective sheet shape heaters  108 A,  108 B and  108 C that adjust the temperatures in the areas to the set target temperature values is set. 
   The heater controller  731  sends the set supplying amount of electric power to the sheet shape heaters  108 A,  108 B and  108 C to the first heater drive unit  741 , the second heater drive unit  742  and the third heater drive unit  743  respectively. The first heater drive unit  741 , the second heater drive unit  742  and the third heater drive unit  743  drive the sheet shape heaters  108 A,  108 B and  108 C respectively with the set supplying amount of electric power (S 109 ). 
   In each LPH  33  according to the first exemplary embodiment, along the arrangement position of the SLEDs  63 , the three sheet shape heaters  108 A,  108 B and  108 C are arranged in the arrangement direction of the SLEDs  63 . In correspondence with the temperature distribution that is generated in the LED circuit substrate  62 , the set temperatures of the three sheet shape heaters  108 A,  108 B and  108 C are adjusted respectively. Thereby, the displacement amount of the LED on the LED circuit substrate  62  is controlled for each of the plural areas that are divided in the longitudinal direction of the LED circuit substrate  62 . 
     FIG. 8  is a graph that compares the temperature distribution of the LED circuit substrate  62  in the LPH  33  according to the first exemplary embodiment and a temperature distribution of the conventional LED circuit substrate where the sheet shape heaters  108 A,  108 B and  108 C are not arranged. As shown in  FIG. 8 , in the LPH  33  according to the first exemplary embodiment, the temperatures of the LED circuit substrate  62  are set substantially uniformly. 
   As mentioned above, in each LPH  33  according to the first exemplary embodiment, by the three sheet shape heaters  108 A,  108 B and  108 C that are arranged in the arrangement direction of the SLEDs  63 , the length of each of the LED circuit substrates  62  in the LPHs  33  of the image forming units  30  is set so that the displacement amount of the LED becomes uniform, and the temperature distribution of the LED circuit substrate  62  in each of the LPH  33  is set substantially uniformly. Thereby, the LEDs of the LPHs  33  are aligned with each other. 
   Next, a description is given to the light quantity setting unit  751  according to the first exemplary embodiment. The light quantity setting unit  751  sets the light quantity values at the time of performing the light quantity control of each of the areas for controlling uniformly the light quantity of the LEDs which are arranged in each of the areas. That is, the light emitting amount of the LED that constitutes the SLED  63  of the LPH  33  is changed depending on the temperature. Then, the light quantity setting unit  751  sets the light quantity corresponding to the temperature change of the LED. Here, the light quantity setting unit  751  stores a relationship between the temperature and the light emitting amount of the LED measured in advance as a table. The light quantity setting unit  751  sets the light quantity values in each of the areas from the target set temperature data in the areas of the LED circuit substrate  62  that is acquired from the heater controller  731  and the relationship between the temperature and the light emitting amount of the LED stored in the table. 
   It should be noted that the light quantity correction control that controls the light quantity of each LED is set on the basis of the light quantity correction data that is stored in the EEPROM  102  of the LED circuit substrate  62 . 
   As mentioned above, in each of the printers  100  according to the first exemplary embodiment, along the arrangement direction of the SLEDs  63 , the three temperature sensors  107 A,  107 B and  107 C and the three sheet shape heaters  108 A,  108 B and  108 C are arranged at positions corresponding to each other on the surface and the back surface respectively, and the temperatures of the LED circuit substrate  62  are controlled for each of the areas. 
   Thereby, the alignment of the LEDs between each of the LPHs  33  is performed. In correspondence with the temperatures that are set for each of the areas of each LPH  33 , the light emitting amount of the LED is adjusted for each of the areas respectively. 
   Second Exemplary Embodiment 
   In the printing system  1  according to the first exemplary embodiment, the description is given to the configuration where the first printer  100 A and the second printer  100 B are arranged so that full-color images are formed on the both sides of the continuous paper P respectively. In a printing system  2  according to the second exemplary embodiment, a description is given to a configuration where four printers are arranged so that color toner images are formed on one side of the continuous paper P. It should be noted that the same reference numerals are used for the same configuration as in the first exemplary embodiment, and a detailed explanation thereof is omitted. 
     FIG. 9  is a view that shows an entire configuration of the printing system  2  according to the second exemplary embodiment. The printing system  2  shown in  FIG. 9  is configured by connecting four printers serving as an example of the image forming apparatus that forms the color image on the one side of the continuous paper P. From the upstream side in the conveying direction of the continuous paper P towards the downstream side, the printing system  2  is provided with a continuous paper supplying apparatus  300 , a K-color printer  150 K serving as an example of the image forming unit that forms a toner image of black (K) on the continuous paper P, a first buffer unit  200 A, a C-color printer  150 C serving as an example of the image forming unit that forms a toner image of cyan (C) on the continuous paper P, a second buffer unit  200 B, a M-color printer  150 M serving as an example of the image forming unit that forms a toner image of magenta (M) on the continuous paper P, a third buffer unit  200 C, a Y-color printer  150 Y serving as an example of the image forming unit that forms a toner image of yellow (Y) on the continuous paper P, and a continuous paper winding apparatus  400 . 
   In the printing system  2  according to the second exemplary embodiment, a control computer  600  that controls operations of the K-color printer  150 K, the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y is connected to the K-color printer  150 K, the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y through a communication network  700 . 
   It should be noted that, hereinafter, the K-color printer  150 K, the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y are also referred to as color printers  150  collectively. 
   Next, a description is given to the K-color printer  150 K of the second exemplary embodiment.  FIG. 10  is a view that shows a configuration of the K-color printer  150 K of the second exemplary embodiment. The K-color printer  150 K shown in  FIG. 10  is an image forming apparatus with, for example, an electrophotography, and is provided with a photoconductor drum  31  serving as an image carrier, an electrically charging device  32  that electrically charges a surface of the photoconductor drum  31  at a predetermined potential, a LED printhead (LPH)  33  that exposes the surface of the photoconductor drum  31  on the basis of the image data, a developing device  34  that develops an electrostatic latent image formed on the surface of the photoconductor drum  31  by K-color toner, a transfer device  35  that transfers the toner image formed on the surface of the photoconductor drum  31  to the continuous paper P, a pair of transfer guiding rolls  36  and  37  that are arranged on the upstream side and the downstream side of the transfer device  35  respectively, and press the continuous paper P onto the photoconductor drum  31 , and a flash fixing device  41  that fixes the toner images formed on the continuous paper P by flashing. 
   Further, the K-color printer is provided with a page resist mark reading unit  38 K that reads a page resist mark formed on any one of the front surface and the back surface of the continuous paper P or on both the front surface and the back surface, and outputs a timing signal, and a color resist mark reading unit  39 K as an example of an exposure position detecting unit that reads a color resist mark for aligning the K-color image formed on the surface of the continuous paper P, and outputs the reading position data. 
   As a paper supplying and transporting system, back tension rolls  24 , a main drive roll  21  that receives drive from a main motor (not shown in the figure), and a transportation belt member  26  are provided. As a paper exit system, tensile force giving roll members  42  that apply tensile force on the continuous paper P, and tension rolls  44  that nip the continuous paper P in the vicinity of an exit and rotate at circumferential speed that is faster than the transportation speed of the continuous paper P so as to apply the tensile force on the continuous paper P are provided. 
   Further, a K-color printing controller  90 K that controls the operation of the entire K-color printer  150 K is provided. 
   It should be noted that the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y are configured similarly to the K-color printer  150 K. 
   The K-color printing controller  90 K serving as an example of a controller that controls the operation of the entire K-color printer  150 K, a C-color printing controller  90 C serving as an example of the controller that controls the operation of the entire C-color printer  150 C, a M-color printing controller  90 M serving as an example of the controller that controls the operation of the entire M-color printer  150 M, and a Y-color printing controller  90 Y serving as an example of the controller that controls the operation of the entire Y-color printer  150 Y have the same functions as the comprehensive controller  50  and the color image forming controllers  70  of the printer  100  according to the first exemplary embodiment, and are connected to the control computer  600  through the communication network  700 . 
   The K-color printer  150 K according to the second exemplary embodiment prints a K-color image on the continuous paper P that is supplied from the continuous paper supplying apparatus  300  under the control of the K-color printing controller  90 K. 
   Specifically, when the printing system  2  according to the second exemplary embodiment is started, K-color image data is inputted from the control computer  600  to the K-color printing controller  90 K of the K-color printer  150 K through the communication network  700 . In synchronization with the input of the K-color image data to the K-color printing controller  90 K, the transportation of the continuous paper P is started at predetermined speed, and the photoconductor drum  31  starts rotating. The surface of the photoconductor drum  31  is electrically charged by the electrically charging device  32  at a predetermined potential (for example, −500 V), and by the LPH  33 , an electrostatic latent image corresponding to the K-color image data is formed. Then, the electrostatic latent image on the photoconductor drum  31  is developed by the developing device  34  with the K-color toner to form the K-color toner image. The color toner image that is formed on the surface of the photoconductor drum  31  is transferred onto the continuous paper P by the transfer device  35  and the transfer guiding rolls  36  and  37 . Thereby, the K-color toner image is formed on the continuous paper P. 
   Then, onto the continuous paper P on which the K-color toner image is formed, the K-color image is fixed by the flash fixing device  41 . 
   The continuous paper P on which the K-color image is printed in the K-color printer  150 K is transported to the first buffer unit  200 A. While a predetermined set amount of the continuous paper P is held in the first buffer unit  200 A, the continuous paper P is transported to the C-color printer  150 C. 
   With the same process, the C-color printer  150 C prints the C-color image onto the continuous paper P that is supplied from the first buffer unit  200 A, while aligning the pages to the K-color image that is printed in the K-color printer  150 K. The continuous paper P on which the C-color image is superimposingly printed on the K-color image in the C-color printer  150 C is transported to the second buffer unit  200 B. While the predetermined set amount of the continuous paper P is held in the second buffer unit  200 B, the continuous paper P is transported to the M-color printer  150 M. 
   With the same process, the M-color printer  150 M prints the M-color image onto the continuous paper P that is supplied from the second buffer unit  200 B, while aligning the pages to the K-color image that is printed in the K-color printer  150 K. The continuous paper P on which the M-color image is superimposingly printed on the K-color image and the C-color image in the M-color printer  150 M is transported to the third buffer unit  200 C. While the predetermined set amount of the continuous paper P is held in the third buffer unit  200 C, the continuous paper P is transported to the Y-color printer  150 Y. 
   With the same process, the Y-color printer  150 Y prints the Y-color image onto the continuous paper P that is supplied from the third buffer unit  200 C, while aligning the pages to the K-color image that is printed in the K-color printer  150 K. The continuous paper P on which the Y-color image is superimposingly printed on the K-color image, the C-color image and the M-color image so as to form a full-color image in the Y-color printer  150 Y is transported to the continuous paper winding apparatus  400  and is wounded by the windig roll  410 . 
   The K-color printer  150 K that is arranged on the most upstream side prints the page resist marks (ROF) serving as a basis of the page position at the time of forming the image in the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y that are arranged on the downstream side (refer to  FIG. 5 ). In the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y, on the basis of the page resist marks (ROF), in order to align the pages to the K-color image that is printed in the K-color printer  150 K, image forming timing of the C-color image, the M-color image and the Y-color image is set respectively. Here, in the printing system  2  according to the second exemplary embodiment, since the respective color toner images are formed on the one side of the continuous paper P, the page alignment represents the alignment with regard to the sub-scanning direction (the moving direction of the continuous paper P). 
   Meanwhile, the alignment with regard to the main scanning direction of the K-color printer  150 K is performed as follows. That is, when the color resist mark of K-color (for example, ROC_K 2  in  FIG. 5 ) is formed in the K-color printer  150 K, the color resist mark reading unit  39 K generates the reading position data of the color resist mark of K-color, and sends the data to the K-color printing controller  90 K. The K-color printing controller  90 K compares the reading position data of the color resist mark of K-color with the standard position data that is set in advance, and generates the alignment correction data (the main scanning position correction data) with regard to the main scanning direction (the axial direction of the photoconductor drum  31 ) at the time of forming the image in the K-color image forming controller  90 K. That is, the main scanning position correction data is the data that shows the displacement amount from the predetermined standard position of the LED of the LED circuit substrate  62 . On the basis of the main scanning position correction data, the temperatures of the LED circuit substrate  62  on the LPH  33  described later are controlled and the length of the LED circuit substrate  62  is adjusted. 
   Thereby, the alignment of the K-color toner image that is formed in the K-color printer  150 K in the main scanning direction (the print width correction) is performed. The same is true in the C-color printer  150 C, the M-color printer  150 M and the Y-color printer  150 Y. 
     FIG. 11  is a view that explains a function configuring unit that performs the print width correction in the K-color printer  150 K according to the second exemplary embodiment. As shown in  FIG. 11 , the print width correction is performed under the control of the K-color printing controller  90 K. 
   As the function configuring unit that performs the print width correction, the K-color printing controller  90 K is provided with the first temperature detecting unit  711 , the second temperature detecting unit  712 , the third temperature detecting unit  713 , the main scanning position correction data calculating unit  721 , the heater controller  731 , the first heater drive unit  741 , the second heater drive unit  742 , the third heater drive unit  743 , and a correction amount calculating unit  761 . The memory (not shown in the figure) that stores the initial displacement amount of the LED in the main scanning direction for each LPH in the first exemplary embodiment is provided in the control computer  600 . 
   Further, as the function unit that performs setting of the light quantity of the LPH  33  with regard to the print width correction, the K-color printing controller  90 K is provided with the light quantity setting unit  751  serving as an example of the light quantity setting unit. 
   In the K-color printer  150 K according to the second exemplary embodiment, the print width correction is performed as follows. 
   Firstly, the first temperature detecting unit  711 , the second temperature detecting unit  712  and the third temperature detecting unit  713  acquire the measured temperature values from the temperature sensor  107 A, the temperature sensor  107 B and the temperature sensor  107 C. The temperature data of the areas is generated from the acquired measured temperature values and sent to the heater controller  731 . 
   The main scanning position correction data calculating unit  721  generates the main scanning position correction data on the basis of the reading position data of the color resist mark of K-color (for example, ROC_K 2  in  FIG. 5 ) that is acquired from the color resist mark reading unit  39 K, and sends the main scanning position correction data to the control computer  600  and the correction amount calculating unit  761 . The main scanning position correction data is sent to the control computer  600  through the communication network  700 . 
   The control computer  600  acquires the main scanning position correction data from the respective color printers  150 . The control computer  600  extracts the LPH  33  with, for example, the largest initial displacement amount among the LPHs  33  of the color printers  150  from the initial displacement amounts of LPHs  33  that are stored in the memory. On the basis of the main scanning position correction data in the extracted LPH  33  with the largest initial displacement amount, a reference value serving as the basis of the alignment in the main scanning direction is set. That is, the displacement amount from the standard position with regard to the LPH  33  with the largest displacement amount serves as the basis. The control computer  600  sends the set reference value to the correction amount calculating unit  761  of the color printer  150 . 
   The correction amount calculating unit  761  calculates a difference between the main scanning position correction data that is acquired from the main scanning position correction data calculating unit  721  and the reference value that is acquired from the control computer  600 . The correction amount calculating unit  761  sends the calculated difference to the heater controller  731  as the correction amount. 
   On the basis of the temperature data that is acquired from the first temperature detecting unit  711 , the second temperature detecting unit  712  and the third temperature detecting unit  713  and the correction amount data that is acquired from the correction amount calculating unit  761 , the heater controller  731  sets the supplying amount of electric power to the three sheet shape heaters  108 A,  108 B and  108 C. That is, the heater controller  731  stores the correspondence relationship between the substrate temperature in the LPH  33  and the position changing amount of the LED in, for example, the ROM or the like (not shown in the figure) serving as an example of the memory, as the table. For example, from the size of the LED circuit substrate  62  in the longitudinal direction and the thermal expansion rate of the material that forms the LED circuit substrate  62 , the correspondence relationship between the substrate temperature of the LPH  33  and the position changing amount of the LED is determined. With using the table, the target temperature values for respective areas are set from the temperature data of the areas and the correction amount, and the supplying amount of electric power to the respective sheet shape heaters  108 A,  108 B and  108 C that adjust the temperatures of the areas to the set target temperature values is set. 
   The heater controller  731  sends the set supplying amount of electric power to the sheet shape heaters  108 A,  108 B and  108 C to the first heater drive unit  741 , the second heater drive unit  742  and the third heater drive unit  743  respectively. The first heater drive unit  741 , the second heater drive unit  742  and the third heater drive unit  743  drive the sheet shape heaters  108 A,  108 B and  108 C respectively with the set supplying amount of electric power. 
   In each LPH  33  according to the second exemplary embodiment, along the arrangement direction of the SLEDs  63 , the three temperature sensors  107 A,  107 B and  107 C and the three sheet shape heaters  108 A,  108 B and  108 C are also arranged at positions corresponding to each other on the surface and the back surface respectively, and the temperatures of the LED circuit substrate  62  are controlled for each of the areas. Thereby, the alignment of the LEDs between each of the LPHs  33  is performed. 
   As well as the first exemplary embodiment, corresponding to the temperatures that are set for each of the areas of each LPH  33 , the light emitting amount of the LED is adjusted for each of the areas. 
   The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.