Patent Publication Number: US-9834021-B2

Title: Printing apparatus and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2016-051284, filed on Mar. 15, 2016. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The presently disclosed subject matter relates to a printing apparatus, and a control method for the printing apparatus, and particularly, to a printing apparatus for detecting a print defect from a recordable medium (print sheet) after printing, and a control method for the printing apparatus. 
     Description of the Related Art 
     It is proposed that in a case where a defect is detected from a recordable medium (print sheet) on which an image and the like are printed by a printing apparatus, a stamp and the like are applied on a printed matter in which the defect is detected. 
     Japanese Patent Application Laid-Open No. 2015-030183 discloses an inkjet printing apparatus provided with a first stamping device and a second stamping device. The first stamping device causes ink to adhere to a tip end edge of a paper sheet on which an image defect is determined to occur based upon a readout result of an inline sensor  58 , and the second stamping device causes ink to adhere to a tip end edge of a paper sheet corresponding to a sorting section, based upon the preset sorting sheet number (paragraphs [0140] to [0142] in Japanese Patent Application Laid-Open No. 2015-030183). 
     Japanese Patent Application Laid-Open No. 2002-059606 discloses an inkjet printing apparatus provided with a backside mark applying device that applies “a backside mark” clearly specifying a mistake printing surface automatically in a case of performing a necessary print on an opposite surface to a paper sheet mistakenly printed (paragraphs [0002] to [0004], [0028] and [0032] in Japanese Patent Application Laid-Open No. 2002-059606). 
     Japanese Patent Application Laid-Open No. 9-240120 discloses a printing system provided with a printing part (a front printing portion and a back printing portion) having an inspection part and a defect print marking part. The inspection part determines whether or not a printing state is appropriate based upon print image data and inspection image data (paragraphs [0015] and [0033] in Japanese Patent Application Laid-Open No. 9-240120). The defect print marking part has a print head for painting-out in which in a case where it is determined in the inspection part that a print result illustrates a defect printed matter, a content already printed in a predetermined region of the printed matter is painted out to be unidentifiable, and the printed matter is recognized as a detective at first glance, preventing the printed matter from being used as an original printed matter any longer (paragraphs [0045] and [0046] in Japanese Patent Application Laid-Open No. 9-240120). 
     SUMMARY OF THE INVENTION 
     In Japanese Patent Application Laid-Open No. 2015-030183, it is only one kind of a stamp that is attached (imprinted) on a print sheet in a case where the defect is detected. Therefore in a case where an operator sorts out the print sheets by inspecting the extent of the defect of the print sheet after imprinting the stamp on the print sheet, the operator can only confirm presence/absence of the detection of the defect by presence/absence of the stamp. In this case, as detection sensibility of the defect is set the higher, the sheet number of the print sheets on which the stamp is imprinted becomes larger. As a result, there is a problem that loads of an inspection work by an operator increase. As the detection sensibility of the defect is set the lower, the sheet number of the print sheets on which the stamp is imprinted becomes smaller. As a result, a slight defect is overlooked and the print sheet having the defect is not detected appropriately, creating a possibility that the defect print sheet flows out into end users. 
     The art described in Japanese Patent Application Laid-Open No. 2002-059606 is configured to attach a backside mark on a mistake printing surface in a case of reuse of a so-called backing sheet, but is not designed to support a sorting work of defect print sheets by an operator. 
     The art described in Japanese Patent Application Laid-Open No. 9-240120 is designed to, in a case of an invoice or the like with an address, paint out an address part or in a case of a security or a cash voucher, paint out a money amount part thereof, resulting in recognition of being unusable, but is not designed to support a sorting work of defect print sheets by an operator. 
     The presently disclosed subject matter is made in view of such a circumference, and an object of the presently disclosed subject matter is to provide a printing apparatus for supporting a sorting work of recordable media (print sheets) in which a print defect is detected, and a control method for the printing apparatus. 
     In order to solve the above problems, a printing apparatus according to a first aspect of the presently disclosed subject matter includes: an image recording part including an inkjet head that ejects inks from a plurality of nozzles to record an image on a surface of a recordable medium, an image defect detecting part that detects an ejection curve amount of a nozzle in the inkjet head and an image defect from the recordable medium on the surface of which the image is recorded, a stamping device that attaches a stamp indicating presence of the image defect on the recordable medium in a case where the image defect is detected, and a stamp control part that differentiates an attachment form of the stamp by the stamping device in accordance with a magnitude of the ejection curve amount of the nozzle. 
     According to the first aspect, in a case where the image defect (streak) due to the nozzle is detected, it is possible to change the kind of the stamp in accordance with the extent of the streak. Thereby since an operator can recognize the extent of the streak from the stamp, the present embodiment can support an inspection work by the operator and realize efficiency of the inspection work. 
     The printing apparatus according to a second aspect of the presently disclosed subject matter may be configured such that in the first aspect, the image defect detecting part performs detection of the image defect for each of colors of inks and differentiates a threshold of the ejection curve amount of the nozzle to be detected as the image defect. 
     According to the second aspect, it is possible to appropriately perform the detection of the image defect by adjusting the threshold in consideration of a difference in visibility of the image defect for each of the colors of the inks. 
     The printing apparatus according to a third aspect of the presently disclosed subject matter may be configured such that in the first or second aspect, the inkjet head ejects at least a black ink, the image defect detecting part performs detection of the image defect for each of the colors of the inks, and performs detection of the image defect by the black ink is performed prior to detection of the image defect by the ink of the color other than black. 
     The printing apparatus according to a fourth aspect of the presently disclosed subject matter may be configured such that in any one of the first aspect to the third aspect, the inkjet head ejects at least a black ink, the image defect detecting part performs detection of the image defect for each of the colors of the inks, and makes a threshold of an ejection curve amount of a nozzle to be used for detection of an image defect in regard to the black ink smaller than a threshold of an ejection curve amount of a nozzle to be used for detection of an image defect in regard to the ink of the color other than black. 
     According to the fourth aspect, t is possible to perform the strict detection of the image defect in regard to the black ink having a relatively high visibility to the streak. It is possible not to perform detection of the curve of the nozzle in regard to the ink having a relatively low visibility to the streak. 
     The printing apparatus according to a fifth aspect of the presently disclosed subject matter may be configured such that in the third or fourth aspect, the inkjet head ejects a yellow ink, and the image defect detecting part makes a threshold of an ejection curve amount of a nozzle to be used for detection of an image defect in regard to the yellow ink larger than a threshold of an ejection curve amount of a nozzle to be used for detection of an image defect in regard to the ink of the color other than yellow. 
     According to the fifth aspect, it is possible to reduce accuracy in detection of the image defect in regard to the yellow ink having a relatively low visibility to the streak. 
     The printing apparatus according to a sixth aspect of the presently disclosed subject matter may be configured such that in any one of the first aspect to the fifth aspect, the stamp control part differentiates at least one of colors, numbers and positions of the stamp attached by the stamping device in accordance with the ejection curve amount of the nozzle. 
     The printing apparatus according to a seventh aspect of the presently disclosed subject matter may be configured such that in the sixth aspect, the stamping device includes a plurality of stamping devices to attach a plurality of kinds of stamps differing in at least one of colors, numbers and positions of the stamp. 
     The printing apparatus according to an eighth aspect of the presently disclosed subject matter may be configured such that in the sixth aspect, the stamping device includes a plurality of stamping devices to attach a plurality of kinds of stamps differing in accordance with the ejection curve amount of the nozzle for each of the colors of the inks of the inkjet head. 
     The printing apparatus according to a ninth aspect of the presently disclosed subject matter may further include an operating part configured to set an attachment condition of the stamp upon reception of operating input of an operator in any one of the first aspect to the eighth aspect. 
     The printing apparatus according to a tenth aspect of the presently disclosed subject matter may be configured to discharge the recordable medium to a different place in accordance with a magnitude of the ejection curve amount of the nozzle in any one of the first aspect to the ninth aspect. 
     A control method for a printing apparatus according to an eleventh aspect of the presently disclosed subject matter includes an image defect detecting step of detecting an ejection curve amount of a nozzle in an inkjet head and an image defect from a recordable medium on a surface of which an image is recorded by an image recording part provided with the inkjet head having a plurality of nozzles, and a stamp step of attaching a stamp indicating presence of the image defect on the recordable medium by a stamping device in a case where the image defect is detected, the stamp step differentiating an attachment form of the stamp by the stamping device in accordance with a magnitude of the ejection curve amount of the nozzle. 
     A non-transitory computer-readable recording medium according to a twelfth aspect of the presently disclosed subject matter includes a control program for a printing apparatus stored thereon, such that when the program is read and executed by a computer, the computer is configured to achieve: an image defect detecting function for detecting an ejection curve amount of a nozzle in an inkjet head and an image defect from a recordable medium on a surface of which an image is recorded by an image recording part provided with the inkjet head having a plurality of nozzles, and a stamp function for attaching a stamp indicating presence of the image defect on the recordable medium by a stamping device in a case where the image defect is detected, the stamp function differentiating an attachment form of the stamp by the stamping device in accordance with a magnitude of the ejection curve amount of the nozzle, wherein the image defect detecting function and the stamp function are realized by a computer. 
     According to the presently disclosed subject matter, in a case where the image defect (streak) due to the nozzle is detected, it is possible to change the kind of the stamp in accordance with the extent of the streak. Thereby since an operator can recognize the extent of the streak from the stamp, it is possible to support the inspection work by the operator and realize the efficiency of the inspection work. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an entire configuration diagram illustrating an embodiment of an inkjet recording device according to the presently disclosed subject matter; 
         FIG. 2  is a perspective view illustrating an arrangement example of a stamping processing part in  FIG. 1 ; 
         FIG. 3  is an entire configuration diagram illustrating configurations of a first, second and third stamping devices; 
         FIG. 4  is a block diagram illustrating a schematic configuration of a control system in the inkjet recording device; 
         FIG. 5  is a perspective view schematically illustrating the first, second and third stamping devices and a print sheet; 
         FIG. 6  is a perspective view illustrating an example where a stamp is imprinted on the print sheet; 
         FIG. 7  is a flow chart illustrating defect nozzle determining processing according to an embodiment of the presently disclosed subject matter; 
         FIG. 8  is a flow chart illustrating monitoring processing of correction completion; 
         FIG. 9  is a flow chart illustrating stamp imprint determining processing; 
         FIG. 10  is a perspective view schematically illustrating a stamping device according to another embodiment of the presently disclosed subject matter and a print sheet; and 
         FIG. 11  is a perspective view illustrating an example where stamps are imprinted on the print sheet. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of a printing apparatus, and a control method for the printing apparatus according to the presently disclosed subject matter will be described with reference to the accompanying drawings. In the present embodiments, an explanation will be made of an example where a condensation treatment liquid is used and a water-based pigment ink is used, but the presently disclosed subject matter may be applied also to a case where the condensation treatment liquid is not used and a case where an oil-based ink is used. 
     &lt;&lt;Apparatus Configuration&gt;&gt; 
       FIG. 1  is an entire configuration diagram illustrating an embodiment of an inkjet recording device according to the presently disclosed subject matter. 
     An inkjet recording device  10  according to the present embodiment records an image on a paper sheet (recordable medium) P of a sheet in an inkjet method using a water-based pigment ink (ink in which coloring pigment is distributed in an aqueous solvent). As illustrated in  FIG. 1 , the inkjet recording device  10  includes a sheet feeding part  12  that feeds paper sheets P, a treatment liquid applying part  14  that applies a predetermined treatment liquid on a surface (image recording surface) of the paper sheet P fed from the sheet feeding part  12 , a treatment liquid drying processing part  16  that performs drying processing of the paper sheet P on which the treatment liquid is applied in the treatment liquid applying part  14 , an image recording part  18  that records an image on a surface of the paper sheet P subjected to the drying processing in the treatment liquid drying processing part  16  by an inkjet method using the water-based pigment ink, an ink drying processing part  20  that performs drying processing of the paper sheet P on which the image is recorded in the image recording part  18 , a stamping processing part  200  that attaches ink to the paper sheet P, and a sheet discharging part  24  on which the paper sheets P discharged after completion of all the processing are stacked. 
     Conveyance of the paper sheets P from the sheet feeding part  12  to the sheet discharging part  24  is carried out by a conveyance part configured of a drum type conveyance device and a chain gripper type conveyance device as explained as follows. 
     &lt;Sheet Feeding Part&gt; 
     The sheet feeding part  12  feeds paper sheets P stacked on a sheet feeding platform  30  to the treatment liquid applying part  14  one by one. The sheet feeding part  12  includes the sheet feeding platform  30 , a sucker device  32 , a pair of sheet feeding rollers  34 , a feeder board  36 , a front guide  38 , and a sheet feeding drum  40 . 
     The paper sheets P are placed on the sheet feeding platform  30  in a bunch state where multiple paper sheets are stacked. The sheet feeding platform  30  is provided to be capable of elevating by a sheet-feeding platform elevating device that is not illustrated. The sheet-feeding platform elevating device is controlled in driving in association with an increase/decrease of the paper sheets P stacked on the sheet feeding platform  30  and causes the sheet-feeding platform  30  to go up and down in such a manner that the paper sheet P positioned in the top of the bunch is always positioned in a constant height. 
     The paper sheet P as a recordable medium is not particularly limited, but can use a general print sheet (paper sheet having cellulose as a major element such as so-called high-quality paper, coated paper and art paper) to be used in general offset printing. In the present example, the coated paper is used. The coated paper is provided with a coated layer by applying a coating material on a surface of a high-quality paper, an alkaline paper or the like that is generally not subjected to surface treatment. Specifically an art paper, a coated paper, a light-weight coated paper, a finely coated paper and the like are preferably used. 
     The sucker device  32  picks up the paper sheets P stacked on the sheet feeding platform  30  from the top thereof one by one to be fed to the pair of the sheet feeding rollers  34 . The sucker device  32  includes a suction fit  32 A provided to be capable of elevating and swinging, and this suction fit  32 A absorbs and holds an upper surface of the paper sheet P and conveys the paper sheet P from the sheet feeding platform  30  to the pair of the sheet feeding rollers  34 . At this time, this suction fit  32 A absorbs and holds an upper surface on a tip end side of the paper sheet P positioned in the top in the bunch, pulls up the paper sheet P and inserts a tip end of the pulled-up paper sheet P in between a pair of rollers  34 A,  34 B configuring the pair of the sheet feeding rollers  34 . 
     The pair of the sheet feeding rollers  34  includes the pair of the up and down rollers  34 A,  34 B pressed and contacted with each other. One of the pair of the up and down rollers  34 A,  34 B works as a driving roller (roller  34 A) and the other works as a driven roller (roller  34 B), and the driving roller (roller  34 A) is driven by a motor for rotation that is not illustrated. The motor is driven in association with sheet feeding of the paper sheet P, and when the paper sheet P is fed from the sucker device  32 , the driving roller (roller  34 A) is rotated in synchronization with the timing. The paper sheet P inserted in between the pair of the up and down rollers  34 A,  34 B is nipped by the rollers  34 A,  34 B to be fed in a rotating direction (mounting direction of a feeder board  36 ) of the rollers  34 A,  34 B. 
     The feeder board  36  is formed corresponding to a sheet width and receives the paper sheet P fed from the pair of the sheet feeding rollers  34 , and guides the paper sheet P to the front guide  38 . The feeder board  36  is mounted with a tip end side thereof being inclined downward, and causes the paper sheet P placed on the conveyance surface to smoothly slide on the conveyance surface to be guided to the front guide  38 . 
     A plurality of tape feeders  36 A for conveying the paper sheet P are mounted on the feeder board  36  by intervals in a width direction. The tape feeder  36 A is formed in an endless shape and is driven by a motor to be rotated that is not illustrated. The paper sheet P placed on the conveyance surface of the feeder board  36  is conveyed on the feeder board  36  by the tape feeder  36 A. 
     Retainers  36 B and a roller  36 C are mounted on the feeder board  36 . 
     The retainer  36 B includes a plurality of retainers arranged tandemly backward and forward along the conveyance surface of the paper sheet P (two retainers in this example). The retainer  36 B includes a plate spring having a width corresponding to the sheet width, and the plate spring is pressed and abuts on the conveyance surface of the feeder board  36 . The paper sheet P conveyed on the feeder board  36  by the tape feeder  36 A passes the retainer  36 B to correct concavity and convexity. The retainers  36 B have, for easy introduction of the paper sheet P in between the feeder board  36  and the retainer  36 B, rear end portions curled at the opposite side to the conveyance surface of the feeder board  36 . 
     The roller  36 C is arranged between before and after the retainers  36 B. The roller  36 C is mounted to be pressed and abut on the conveyance surface of the paper sheet P. The paper sheet P to be conveyed between before and after the retainers  36 B is conveyed while the upper face is pressed by the roller  36 C. 
     The front guide  38  corrects an orientation of the paper sheet P. The front guide  38  is formed in a plate shape, and is arranged perpendicular to a conveyance direction of the paper sheet P. In addition, the front guide  38  is driven by a motor that is not illustrated and is provided to be capable of swinging. The paper sheet P conveyed on the feeder board  36  abuts on the front guide  38  in the tip end to correct the orientation (what is called skew prevention). The front guide  38  swings in association with the sheet feeding of the paper sheet to the sheet feeding drum  40 , and delivers the paper sheet P the orientation of which is corrected to the sheet feeding drum  40 . 
     The sheet feeding drum  40  receives the paper sheet P fed from the feeder board  36  through the front guide  38  to be conveyed to the treatment liquid applying part  14 . The sheet feeding drum  40  is formed in a cylindrical shape, and is driven by a motor to be rotated that is not illustrated. A gripper  40 A is provided on an outer peripheral surface of the sheet feeding drum  40 , and a tip end of the paper sheet P is gripped by the gripper  40 A. The sheet feeding drum  40  rotates by gripping the tip end of the paper sheet P by the gripper  40 A, and thereby conveys the paper sheet P to the treatment liquid applying part  14  while winding the paper sheet P around the peripheral surface. 
     The sheet feeding part  12  is configured as described above. With this configuration, the paper sheets P stacked on the sheet feeding platform  30  are picked up one by one in order from above by the sucker device  32 , and are fed to the pair of the sheet feeding rollers  34 . The paper sheet P fed to the pair of the sheet feeding rollers  34  are fed forward by the pair of the up and down rollers  34 A,  34 B configuring the pair of the sheet feeding rollers  34 , and are placed on the feeder board  36 . The paper sheet P placed on the feeder board  36  is conveyed by the tape feeder  36 A provided on the conveyance surface of the feeder board  36 . The paper sheet P is pressed on the conveyance surface of the feeder board  36  by the retainer  36 B in the conveyance process to correct the concavity and convexity. The paper sheet P conveyed by the feeder board  36  abuts on the front guide  38  in the tip end, and thereby an inclination of the paper sheet P is corrected, and thereafter the paper sheet is delivered to the sheet feeding drum  40 . In addition, the paper sheet P is conveyed to the treatment liquid applying part  14  by the sheet feeding drum  40 . 
     &lt;Treatment Liquid Applying Part&gt; 
     The treatment liquid applying part  14  applies a predetermined treatment liquid on a surface (image recording surface) of the paper sheet P. The treatment liquid applying part  14  includes a treatment liquid applying drum  42  that conveys paper sheets P and a treatment liquid applying unit  44  that applies the predetermined treatment liquid on the printing surface of the paper sheet P conveyed by the treatment liquid applying drum  42 . 
     The treatment liquid applying drum  42  receives the paper sheet P from the sheet feeding drum  40  in the sheet feeding part  12  and conveys the paper sheer P to the treatment liquid drying processing part  16 . The treatment liquid applying drum  42  is formed in a cylindrical shape, and is driven/rotated by a motor that is not illustrated. A gripper  42 A is provided on an outer peripheral surface of the treatment liquid applying drum  42 , and a tip end of the paper sheet P is gripped by the gripper  42 A. The treatment liquid applying drum  42  rotates by gripping the tip end of the paper sheet P by the gripper  42 A, and thereby conveys the paper sheet P to the treatment liquid drying processing part  16  while winding the paper sheet P around the peripheral surface (conveys one paper sheet P with one rotation). The treatment liquid applying drum  42  and the sheet feeding drum  40  are controlled in rotation such that reception of one paper sheet P and delivery of the other paper sheet P are timed to each other. That is, the treatment liquid applying drum  42  and the sheet feeding drum  40  are driven in such a manner as to have the same peripheral speed, and are driven such that positions of the grippers are in agreement with each other. 
     The treatment liquid applying unit  44  roller-applies a treatment liquid on the surface of the paper sheet P conveyed by the treatment liquid applying drum  42 . The treatment liquid applying unit  44  includes an application roller  44 A that applies a treatment liquid on the paper sheet P, a treatment liquid reservoir  44 B in which a treatment liquid is reserved, and a drawing roller  44 C that draws up a treatment liquid reserved in the treatment liquid reservoir  44 B to be supplied to the application roller  44 A. The drawing roller  44 C is mounted to be pressed and abut on the application roller  44 A, and a part of the drawing roller  44 C is immersed in the treatment liquid reserved in the treatment liquid reservoir  44 B. The drawing roller  44 C meters a treatment liquid to be drawn up, and applies the treatment liquid in a constant thickness on the peripheral surface of the application roller  44 A. The application roller  44 A is provided to correspond to a sheet width, and is pressed and abuts on the paper sheet P to apply the treatment liquid applied on the peripheral surface on the paper sheet P. The application roller  44 A is driven by a contact-separation mechanism that is not illustrated and moves between an abutting position of abutting on the peripheral surface of the treatment liquid applying drum  42  and a separation position of being separated from the peripheral surface of the treatment liquid applying drum  42 . The contact-separation mechanism moves the application roller  44 A in response to a passing timing of the paper sheet P, and the treatment liquid is applied on the surface of the paper sheet P conveyed by the treatment liquid applying drum  42 . 
     In the present example, the treatment liquid is designed to be roller-applied, but a method of applying the treatment liquid is not limited thereto. In addition to or instead of the above roller-applying method, the configuration of using the inkjet head for application or using a spray for application may be adopted. 
     The treatment liquid applying part  14  is configured as described above. With this configuration, the paper sheet P delivered from the sheet feeding drum  40  in the sheet feeding part  12  is received by the treatment liquid applying drum  42 . The treatment liquid applying drum  42  rotates by gripping the tip end of the paper sheet P by the gripper  42 A, and thereby winds the paper sheet P around the peripheral surface for conveyance. In this conveyance process, the application roller  44 A is pressed and abuts on the surface of the paper sheet P to apply the treatment liquid on the surface of the paper sheet P. 
     Here, as the treatment liquid applied on the surface of the paper sheet P, a treatment liquid having a function of causing color materials in a water-based pigment ink struck in the form of droplets on the paper sheet P in the image recording part  18  in the subsequent stage to be condensed is applied. This treatment liquid is applied on the surface of the paper sheet P to strike droplets of the water-based pigment ink thereon, and thereby even in a case of using a general print sheet, it is possible to perform a high-grade print without causing impact interference of droplets or the like. 
     &lt;Treatment liquid Drying Processing Part&gt; 
     The treatment liquid drying processing part  16  performs drying processing to the paper sheet P on a surface of which the treatment liquid is applied. The treatment liquid drying processing part  16  includes a treatment liquid drying processing drum  46  that conveys the paper sheet P, a sheet conveying guide  48 , and a treatment liquid drying processing unit  50  that blows heated air on a printing surface of the paper sheet P conveyed by the treatment liquid drying processing drum  46  to dry the paper sheet P. 
     The treatment liquid drying processing drum  46  receives the paper sheet P from the treatment liquid applying drum  42  in the treatment liquid applying part  14 , and conveys the paper sheet P to the image recording part  18 . The treatment liquid drying processing drum  46  is formed in a frame body assembled in a cylindrical shape, and is driven by a motor to be rotated that is not illustrated. A gripper  46 A is provided on an outer peripheral surface of the treatment liquid drying processing drum  46 , and a tip end of the paper sheet P is gripped by the gripper  46 A. The treatment liquid drying processing drum  46  grips the tip end of the paper sheet P by the gripper  46 A and rotates, and thereby conveys the paper sheet P to the image recording part  18 . 
     The treatment liquid drying processing drum  46  in the present example is provided with grippers  42 A arranged in two locations on the outer peripheral surface, and is configured to be capable of conveying two paper sheets P by rotation of one time. The treatment liquid drying processing drum  46  and the treatment liquid applying drum  42  are controlled in rotation such that reception of one paper sheet P and delivery of the other paper sheet P are timed to each other. That is, the treatment liquid drying processing drum  46  and the treatment liquid applying drum  42  are driven in such a manner as to have the same peripheral speed, and are driven such that positions of the grippers  42 A are in agreement with each other. 
     A sheet conveying guide  48  is arranged along the conveyance path of the paper sheet P by the treatment liquid drying processing drum  46 , and guides the conveyance of the paper sheet P. 
     The treatment liquid drying processing units  50  are arranged inside the treatment liquid drying processing drum  46 , and blow air heated to more than an environment temperature (heated air) on a surface of the paper sheet P conveyed by the treatment liquid drying processing drum  46  to perform the drying processing. In this example, the two treatment liquid drying processing units  50  are arranged inside the treatment liquid drying processing drum  46 , and blow the heated air on the surface of the paper sheet P conveyed by the treatment liquid drying processing drum  46 . 
     The treatment liquid drying processing part  16  is configured as described above. With this configuration, the paper sheet P delivered from the treatment liquid applying drum  42  in the treatment liquid applying part  14  is received in the treatment liquid drying processing drum  46 . The treatment liquid drying processing drum  46  grips the tip end of the paper sheet P by the gripper  46 A and rotates, and thereby conveys the paper sheet P. At this time, the treatment liquid drying processing drum  46  conveys the paper sheet P directing the surface (surface on which the treatment liquid is applied) of the paper sheet P to the inside. In the process where the paper sheet P is conveyed by the treatment liquid drying processing drum  46 , the heated air is blown on the surface from the treatment liquid drying processing unit  50  mounted inside the treatment liquid drying processing drum  46  to perform the drying processing. Thereby solvent components in the treatment liquid are removed to form an ink condensation layer on the surface of the paper sheet P. 
     &lt;Image Recording Part&gt; 
     The image recording part  18  strikes droplets of inks (water-based pigment inks) of the respective colors of C (cyan), M (magenta), Y (yellow) and K (black (key plate)) on the printing surface of the paper sheet P to draw a colored image on the printing surface of the paper sheet P. The image recording part  18  includes an image recording drum  52  for conveying the paper sheet P, a sheet pressing roller  54  that presses the paper sheet P conveyed by the image recording drum  52  to cause the paper sheet P to come into close contact with the peripheral surface of the image recording drum  52 , inkjet heads  56 C,  56 M,  56 Y and  56 K that eject ink droplets of the respective colors of C, M, Y, K on the paper sheet P, an inline sensor  58  for reading in an image recorded on the paper sheet p, a mist filter  60  for trapping ink mists, and a drum cooling unit  62 . 
     The image recording drum  52  receives the paper sheet P from the treatment liquid drying processing drum  46  in the treatment liquid drying processing part  16 , and conveys the paper sheet P to the ink drying processing part  20 . The image recording drum  52  is formed in a cylindrical shape, and is driven by a motor to be rotated that is not illustrated. A gripper  52 A is provided on an outer peripheral surface of the image recording drum  52 , and a tip end of the paper sheet P is gripped by the gripper  52 A. The image recording drum  52  grips the tip end of the paper sheet P by the gripper  52 A and rotates, and thereby conveys the paper sheet P to the ink drying processing part  20  while winding the paper sheet P around the peripheral surface. The image recording drum  52  is provided with multiple suction holes (not illustrated) formed in a given pattern on the peripheral surface. The paper sheet P wound around the peripheral surface of the image recording drum  52  is sucked through the suction holes, and thereby is conveyed while being absorbed and held onto the peripheral surface of the image recording drum  52 . As a result, the paper sheet P can be conveyed with high flatness. 
     The suction through the suction holes works only in a constant range, and works between a predetermined suction start position and a predetermined suction end position. The suction start position is set to a mounting position of the sheet pressing roller  54 , and the suction end position is set in the downstream side of the mounting position of the inline sensor  58  (for example, is set to a position of delivering the paper sheet to the ink drying processing part  20 ). That is, at least at mounting positions (image recording positions) of the inkjet heads  56 C,  56 M,  56 Y and  56 K and a mounting position (image reading position) of the inline sensor  58 , the paper sheet P is set such that the paper sheet P is to be absorbed and held on the peripheral surface of the image recording drum  52 . 
     The mechanism for causing the paper sheet P to be absorbed and held on the peripheral surface of the image recording drum  52  is not limited to the absorption method by the above vacuum, but may adopt a method by an electrostatic absorption. 
     The image recording drum  52  in this example is provided with grippers  52 A arranged in two locations on the outer peripheral surface, and is configured to be capable of conveying two paper sheets P by rotation of one time. The image recording drum  52  and the treatment liquid drying processing drum  46  are controlled in rotation such that reception of one paper sheet P and delivery of the other paper sheet P are timed to each other. That is, the image recording drum  52  and the treatment liquid drying processing drum  46  are driven in such a manner as to have the same peripheral speed, and are driven such that positions of the grippers  52 A of each other are in agreement. 
     The sheet pressing roller  54  is arranged in the vicinity of a sheet receiving position of the image recording drum  52  (position of receiving the paper sheet P from the treatment liquid drying processing drum  46 ). The sheet pressing roller  54  is formed of a rubber roller, and is mounted to be pressed and abut on the peripheral surface of the image recording drum  52 . The paper sheet P delivered to the image recording drum  52  from the treatment liquid drying processing drum  46  passes the sheet pressing roller  54  to be nipped and is brought into close contact with the peripheral surface of the image recording drum  52 . 
     Four inkjet heads  56 C,  56 M,  56 Y and  56 K are arranged by constant intervals along the conveyance path of the paper sheet P by the image recording drum  52 . The inkjet heads  56 C,  56 M,  56 Y and  56 K are configured with line heads corresponding to a sheet width, and a nozzle surface thereof is arranged to face the peripheral surface of the image recording drum  52 . The inkjet heads  56 C,  56 M,  56 Y and  56 K each eject droplets of inks toward the image recording drum  52  from a nozzle array formed on the nozzle surface, and thereby an image is recorded on the paper sheet P conveyed by the image recording drum  52 . 
     As described above, a water-based pigment ink is used as the ink ejected from each of the inkjet heads  56 C,  56 M,  56 Y and  56 K. By causing the water-based pigment ink to condensation-react with the treatment liquid applied by the treatment liquid applying part  14 , it is possible to condense coloring pigment in the water-based pigment ink. 
     The inline sensor  58  is mounted downstream of the rear-most inkjet head  56 K to the conveyance direction of the paper sheet P by the image recording drum  52 , and reads out an image recorded by the inkjet heads  56 C,  56 M,  56 Y and  56 K. The inline sensor  58  is configured with, for example, a line scanner, and reads out the image recorded by the inkjet heads  56 C,  56 M,  56 Y and  56 K from the paper sheet P conveyed by the image recording drum  52 . 
     An image defect is detected based upon the imaging pickup result of the inline sensor  58  by an image defect detecting part (not illustrated in  FIG. 1  and illustrated by reference numeral  136  in  FIG. 4 ). “Image defect” herein is assumed to be a defect due to ejection abnormality of each of the inkjet heads  56 C,  56 M,  56 Y and  56 K, for example, a streak due to ejection curve of the ink from the inkjet head. Further, an example of the image defect may include defects due to color deviation and adherence of foreign objects such as ink mists and the like. 
     The image defect may include abnormality on the paper sheet P recognizable from the imaging pickup result of the inline sensor  58 , and is not limited to the above listed. Along with the inline sensor  58  or instead of the inline sensor  58 , a sensor (dirt detecting part) for detecting a dirt of the paper sheet P or the like may be independently prepared. 
     The present example exemplifies the form of using the imaging pickup result of the inline sensor  58  configured with the line scanner as a defect detecting device, but the presently disclosed subject matter is not limited thereto, but the other configurations and methods may be applied to the defect detecting part and the dirt detecting part. 
     For example, in addition to the inline sensor  58 , the form of being provided with an imaging pickup device (high-speed camera) that directly images an ejection state of inks of the inkjet heads  56 C,  56 M,  56 Y and  56 K is made possible. 
     A contact prevention plate  59  is placed close to the inline sensor  58  downstream of the inline sensor  58 . The contact prevention plate  59  prevents the paper sheet P from coining into contact with the inline sensor  58  in a case where the paper sheet P floats due to a defect of the conveyance or the like. 
     A mist filter  60  is arranged between the inkjet head  56 K in the rear-most tail and the inline sensor  58  and sucks air in the circumference of the image recording drum  52  to trap ink mists. In this way, by sucking the air in the circumference of the image recording drum  52  to trap the ink mist, it is possible to prevent the entry of the ink mist into the inline sensor  58 , preventing occurrence of the readout defect or the like. 
     A drum cooling unit  62  blows air (cooling air) adjusted in temperature on the image recording drum  52  to cool the image recording drum  52 . The image cooling unit  62  includes an air conditioner (not illustrated) and a duct  62 A for blowing cooling air supplied from the air conditioner on the peripheral surface of the image recording drum  52 . The duct  62 A blows the cooling air on the image recording drum  52  in a region other than the conveyance region of the paper sheet P to cool the image recording drum  52 . In this example, since the paper sheet P is conveyed along an arc surface of the substantially upper half of the image recording drum  52 , the duct  62 A blows cooling air on the region of the substantially lower half of the image recording drum  52  to cool the image recording drum  52 . Specifically a blowout port of the duct  62 A is formed in an arc shape to cover the substantially lower half of the image recording drum  52  to blow the cooling air on the region of the substantially lower half of the image recording drum  52 . 
     Here, a temperature of cooling the image recording drum  52  is defined by a relationship to temperatures of the inkjet heads  56 C,  56 M,  56 Y and  56 K (particularly a temperature of the nozzle surface), and the image recording drum  52  is cooled to have a temperature lower than the temperature of each of the inkjet heads  56 C,  56 M,  56 Y and  56 K. This can prevent dew condensation from being generated in the inkjet heads  56 C,  56 M,  56 Y and  56 K. That is, by lowering the temperature of the image recording drum  52  to a temperature lower than that of the inkjet heads  56 C,  56 M,  56 Y and  56 K, it is possible to induce the dew condensation on the image recording drum side and prevent the dew condensation (particularly the dew condensation to be generated on the nozzle surface) from being generated in the inkjet heads  56 C,  56 M,  56 Y and  56 K. 
     The image recording part  18  is configured as described above. With this configuration, the paper sheet P delivered from the treatment liquid drying processing drum  46  in the treatment liquid drying processing part  16  is received in the image recording drum  52 . The image recording drum  52  grips the tip end of the paper sheet P by the gripper  52 A and rotates, and thereby conveys the paper sheet P. The paper sheet P delivered in the image recording drum  52  passes through the sheet pressing roller  54  to be brought into close contact with the peripheral surface of the image recording drum  52 . Simultaneously with this, the paper sheet P is sucked through the absorption holes of the image recording drum  52  to be absorbed and held on the outer peripheral surface of the image recording drum  52 . The paper sheet P is conveyed in this state, and passes through the respective inkjet heads  56 C,  56 M,  56 Y and  56 K. At the passing time, droplets of inks of the respective colors of C, M, Y and K from the respective inkjet heads  56 C,  56 M,  56 Y and  56 K are struck in the form of droplets on the surface to draw a colored image on the surface. Since the ink condensation layer is formed on the surface of the paper sheet P, it is possible to record a high-grade image without causing feathering, bleeding and the like. 
     The paper sheet P on which the image is recorded by the inkjet heads  56 C,  56 M,  56 Y and  56 K next passes through the inline sensor  58 . The image recorded on the surface is read out at the passing time of the inline sensor  58 . The readout of the recorded image is performed in regard to all the paper sheets P. At the readout time, since the readout is performed in a state where the paper sheet P is absorbed and held on the image recording drum  52 , it is possible to perform the readout with high accuracy. Further, since the readout is performed immediately after the image recording, for example, abnormality of the ejection defect or the like can be immediately detected, and the measure to the abnormality can be quickly taken. Therefore wasteful recording can be prevented and occurrence of the damaged paper sheet can be controlled to the minimum. 
     Thereafter, the paper sheet P is, after the absorption is released, delivered to the ink drying processing part  20 . 
     &lt;Ink Drying Processing Part&gt; 
     The ink drying processing part  20  performs the drying processing to the image-rerecorded paper sheet P to remove liquid components remaining on the surface of the paper sheet P. The ink drying processing part  20  includes a chain gripper  64  that conveys the image-rerecorded paper sheet P, a back tension applying mechanism  66  that applies the back tension to the paper sheet P conveyed by the chain gripper  64  and an ink drying processing unit  68  that performs the drying processing to the paper sheet P conveyed by the chain gripper  64 . 
     The chain gripper  64  is a sheet conveying mechanism used in common to the ink drying processing part  20 , the stamping processing part  200  and the sheet discharging part  24 , and receives the paper sheet P delivered from the image recording part  18  to be conveyed to the sheet discharging part  24 . 
     The chain gripper  64  includes first sprockets  64 A arranged close to the image recording drum  52 , second sprockets  64 B mounted on the sheet discharging part  24 , endless chains  64 C wound around the first sprockets  64 A and the second sprockets  64 B, a plurality of chain guides (not illustrated) that guide travel of the chain  64 C, and a plurality of gripers  64 D attached on the chains  64 C by constant intervals. The first sprockets  64 A, the second sprockets  64 B, the chains  64 C and the chain guides are respectively configured to be paired and are arranged on both sides of the paper sheet P in the width direction. The plurality of grippers  64 D are provided between the pair of the chains  64 C, and both end parts of a tip end edge (illustrated in P 1  in  FIG. 2 ) of the paper sheet P are gripped by the plurality of grippers  64 D. 
     The first sprockets  64 A are mounted close to the image recording drum  52  such that the paper sheet P delivered from the image recording drum  52  can be received in the plurality of grippers  64 D. The first sprockets  64 A are supported on bearings that are not illustrated to be rotatably provided and connected to a motor that is not illustrated. The chains  64 C wound around the first sprockets  64 A and the second sprockets  64 B travel by driving the motor. 
     The second sprockets  64 B are mounted in the sheet discharging part  24  in such a manner as to be capable of collecting the paper sheet P received from the image recording drum  52  in the sheet discharging part  24 . That is, the mounting position of the second sprocket  64 B is designed to be a terminal end of the conveyance path of the paper sheet P by the chain gripper  64 . The second sprocket  64 B is supported on a bearing that is not illustrated and is rotatably provided. 
     The chains  64   c  are formed in an endless shape, and are wound around the first sprockets  64 A and the second sprockets  64 B. 
     The chain guides are arranged in a predetermined position to guide the chains  64 C to travel in a predetermined path (that is, the paper sheet P is guided to travel and be conveyed in a predetermined path). In the inkjet recording apparatus  10  of the present example, the second sprockets  64 B are in a position higher than the first sprockets  64 A. Therefore a travel path is formed in such a manner that the chain  64 C is inclined in the half way. Specifically the travel path includes a first horizontal conveyance path  70 A, an inclined conveyance path  70 B and a second horizontal conveyance path  70 C. 
     The first horizontal conveyance path  70 A is set to the same height with the first sprocket  64 A, and is set such that the chain  64 C wound around the first sprocket  64 A travels horizontally. 
     The second horizontal conveyance path  70 C is set to the same height with the second sprocket  64 B, and is set such that the chain  64 C wound around the second sprocket  64 B travels horizontally. 
     The inclined conveyance path  70 B is provided between the first horizontal conveyance path  70 A and the second horizontal conveyance path  70 C and is set for connection between the first horizontal conveyance path  70 A and the second horizontal conveyance path  70 C. 
     The chain guides are arranged to form the first horizontal conveyance path  70 A, the inclined conveyance path  70 B and the second horizontal conveyance path  70 C. Specifically the chain guides are arranged at least in a joint point between the first horizontal conveyance path  70 A and the inclined conveyance path  70 B and in a joint point between the inclined conveyance path  70 B and the second horizontal conveyance path  70 C. 
     The paired grippers  64 D arc attached on the chains  64 C by constant intervals. The attaching interval of the gripper  64 D is set to correspond to the receiving interval of the paper sheet P from the image recording drum  52 . That is, the attaching interval of the gripper  64 D is set to correspond to the receiving interval of the paper sheet P from the image recording drum  52  such that the paper sheets P delivered in order from the image recording drum  52  can be received from the image recording drum  52  timed to the delivery. 
     The chain gripper  64  is configured as described above. With this configuration, when a motor (not illustrated) connected to the first sprocket  64 A is driven as described above, the chain  64 C travels. The chain  64 C travels in the same speed as the peripheral speed of the image recording drum  52 . The paper sheet P delivered from the image recording drum  52  is timed to be capable of being received in each of the grippers  64 D. 
     The back tension applying mechanism  66  applies the back tension to the paper sheet P conveyed while tip end thereof is gripped by the chain gripper  64 . The back tension applying mechanism  66  includes guide plates  72 , and a suction mechanism (not illustrated) that sucks air from suction holes (not illustrated) formed on the guide plates  72 . 
     The guide plates  72  are each configured with a hollow box plate having a width corresponding to the sheet width. The guide plates  72  are arranged along the conveyance path (that is, travel path of the chain) of the paper sheet P by the chain gripper  64 . Specifically the guide plates  72  are arranged along the chain  64 C traveling on the first horizontal conveyance path  70 A and the inclined conveyance path  70 B and are arranged at a predetermined distance from the chain  64 C. The paper sheet P conveyed from the chain gripper  64  is conveyed while the backside (surface of the side where an image is not recorded) is making sliding contact with upper surfaces (surfaces opposing the chain  64 C: sliding contact surfaces) of the guide plates  72 . 
     Multiple suction holes (not illustrated) are formed in a predetermined pattern on the sliding contact surface (upper surface) of each guide plate  72 . As described above, the guide plates  72  are each formed with the hollow box plate. The suction mechanism (not illustrated) sucks hollow parts (internal parts) of the guide plates  72 . Thereby air is sucked through the suction holes formed on the sliding contact surface. 
     When the air is sucked through the suction holes of the guide plates  72 , the backside of the paper sheet P conveyed by the chain gripper  64  is sucked to the suction holes. Thereby the back tension is applied to the paper sheet P conveyed by the chain gripper  64 . 
     As described above, since the guide plates  72  are arranged along the chain  64 C traveling on the first horizontal conveyance path  70 A and the inclined conveyance path  70 B, the back tension is applied while the paper sheet P is conveyed on the first horizontal conveyance path  70 A and the inclined conveyance path  70 B. 
     The ink drying processing unit  68  is mounted in an internal part (particularly a section configuring the first horizontal conveyance path  70 A) of the chain gripper  64 , and performs drying processing to the paper sheet P conveyed on the first horizontal conveyance path  70 A. The ink drying processing unit  68  blows heated air on the surface of the paper sheet P conveyed on the first horizontal conveyance path  70 A to perform the drying processing. The ink drying processing unit  68  includes a plurality of units arranged along the first horizontal conveyance path  70 A. The mount number is set according to processing capabilities of the ink drying processing unit  68  and a conveyance speed (=printing speed) of the paper sheet P. That is, the mount number is set such that the paper sheet P can be dried while the paper sheet P received from the image recording part  18  is being conveyed on the first horizontal conveyance path  70 A. Accordingly a length of the first horizontal conveyance path  70 A is also set in consideration of capabilities of the ink drying processing unit  68 . 
     When the drying processing is performed, humidity of the ink drying processing part  20  increases. When the humidity increases, since the drying processing cannot be efficiently performed, it is preferable that a discharging device is mounted together with the ink drying processing unit  68  in the ink drying processing part  20  to forcibly discharge wet air generated by the drying processing. The discharging device, for example, is configured such that a discharging duct is mounted in the ink drying processing part  20  to discharge air in the ink drying processing part  20 . 
     The ink drying processing part  20  is configured as described above. With this configuration, the paper sheet P delivered from the image recording drum  52  in the image recording part  18  is received in the chain gripper  64 . The chain gripper  64  grips the tip end of the paper sheet P by the gripper  64 D, and thereby conveys the paper sheet P along the planar guide plate  72 . The paper sheet P delivered in the chain gripper  64  is first conveyed on the first horizontal conveyance path  70 A. The paper sheet P in the process conveyed on the first horizontal conveyance path  70 A is subjected to drying processing by the ink drying processing unit  68  mounted inside the chain gripper  64 . That is, the heated air is blown on the surface (image recording surface) to perform the drying processing. At this time, the paper sheet P is subjected to the drying processing while the back tension is applied to the paper sheet P by the hack tension applying mechanism  66 . As a result, the drying processing can be performed while suppressing a deformation of the paper sheet P. 
     &lt;Stamping Processing Part&gt; 
     The stamping processing part  200  is provided downstream of the ink drying processing part  20  in the conveyance direction of the paper sheet P and upstream of the sheet discharging part  24  in the same direction to cause inks to adhere to a tip end edge P 1  (refer to  FIG. 2 ) of the paper sheet P in which the image defect is generated or a tip end edge P 1  of the paper sheet P corresponding to the sorting sheet number. Thereby defect paper sheets are specified from the paper sheets P stacked on the sheet discharging part  24  or a sorting section managing the sorting sheet number is specified. 
     In the present embodiment, the stamping processing part  200  is provided downstream of the ink drying processing part  20 , but may be provided downstream of the image recording part  18 , and when the structure of the conveyance part is formed such that the stamping processing part  200  can be arranged, the stamping processing part  200  may be provided downstream of the image recording part  18  (the details will be described later). 
     &lt;Sheet Discharging Part&gt; 
     The sheet discharging part  24  collects the paper sheets P subjected to a series of the image recording processing. The sheet discharging part  24  includes the chain grippers  64  that convey the paper sheet P and a sheet discharging platform  76  that stacks the paper sheets P for collection. 
     As described above, the chain grippers  64  are used in common together with the ink drying processing part  20  and the stamping processing part  200 . The chain grippers  64  release the paper sheets P on the sheet discharging platform  76  and stack the paper sheets P on the sheet discharging platform  76 . 
     The sheet discharging platform  76  stacks the paper sheets P released from the chain grippers  64  for collection. The sheet discharging platform  76  is, for stacking the paper sheets P in order thereon, provided with sheet guides (a front sheet guide, a rear sheet guide, a side sheet guide and the like) (not illustrated). 
     The sheet discharging platform  76  is provided to be capable of going up and down by a sheet-discharging platform elevating device that is not illustrated. The sheet-discharging platform elevating device is controlled in driving in association with an increase/decrease of paper sheets P stacked on the sheet discharging platform  76 , and causes the sheet discharging platform  76  to go up and down such that the paper sheet P positioned on the top is always positioned in a constant height position. 
     &lt;&lt;Detailed Description of Stamping Processing Part&gt;&gt; 
       FIG. 2  is a perspective view illustrating an arrangement example of the stamping processing part  200 , and  FIG. 3  is an entire configuration diagram of first, second and third stamping devices  202 A,  202 B and  202 C configuring the stamping processing part  200 . In  FIG. 2 , for illustrative purposes, reference characters indicating the elements of the first, second and third stamping devices  202 A,  202 B and  202 C are omitted. 
     As illustrated in  FIG. 2 , the stamping processing part  200  includes the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C. The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C are respectively accommodated in casings  206 A,  206 B and  206 C (illustrated in a broken line) upper surfaces of which open obliquely along the inclined conveyance path  70 B of the chain grippers  64 , and the casings  206 A,  206 B and  206 C are arranged in a lower position of the inclined conveyance path  70 B. 
     A length found by adding the respective widths of the casings  206 A,  206 B and  206 C is made to less than an arrangement width of the plurality of chain grippers  64 . Therefore the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C are arranged between the pair of the chains  64 C. The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C are arranged between the grippers in the width direction of the paper sheet P. 
     The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C adopt an arrangement in which stamp positions to the paper sheet P are the same position in the conveyance direction of the paper sheet P. The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C may be arranged to be shifted in the conveyance direction of the paper sheet P. 
     “The same position” herein includes “the substantially same position” of being capable of achieving the same operational effect. 
     Since the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C are arranged in different positions in the width direction of the paper sheet P perpendicular to the conveyance direction of the paper sheet P, ink adherence positions do not overlap in the width direction of the paper sheet P. 
     The term of “perpendicular” in the present specification includes a substantially perpendicular range of angles less than or more than 90° C. 
     The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C cause inks to adhere to the tip end edge P 1  of the paper sheet P in which an image defect is generated based upon the readout result of the inline sensor  58  (refer to  FIG. 1 ), in response to an instruction signal sent out from the stamp control part (not illustrated in  FIG. 2  and  FIG. 3  but illustrated in reference numeral  208  in  FIG. 4 ). 
     Next, the structure of each of the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C will be explained with reference to  FIG. 2  and  FIG. 3 . The first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C may adopt the same configuration. In the following explanation, the first stamping device  202 A will be explained as a representative of the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C. 
     As illustrated in  FIG. 2  and  FIG. 3 , the first stamping device  202 A includes a stamp roller  210  (stamp part) in which ink is immersed and a projectable/retractable mechanism  212  that causes the stamp roller  210  to project/retract from the chain gripper  64 . 
     The stamp roller  210  is rotatably supported in a stamp vessel  214 , which is supported in the projectable/retractable mechanism  212 . 
     The projectable/retractable mechanism  212  includes arms  216  (stamp movement parts) that supports the stamp vessel  214  in the tip end part, support plates  220  (stamp movement parts) that rotatably support the arms  216  through a rotational shaft  218 , and a solenoid actuator  222  (stamp movement parts) that rotates the arms  216  about the rotational shaft  218  to move the stamp vessel  214  between the a waiting position X and a stamp position Y. 
     As illustrated in  FIG. 2  and  FIG. 3 , the stamp vessel  214  positioned in the waiting position X and in the retractable state where the stamp vessel  214  does not project from an opening of each of the casings  206 A,  206 B and  206 C, and the like are illustrated in a two-dot chain line, and the stamp vessel  214  positioned in the stamp position Y and in the projectable state where the stamp vessel  214  projects from the opening of each of the casings  206 A,  206 B and  206 C, and the like are illustrated in a solid line. 
     In regard to a relation of the arms  216  in the first stamping device  202 A, the support plates  220  and the solenoid actuator  222 , a support structure of each other is formed when the arms  216  are rotatably supported to the support plates  220 , the support plates  220  are supported to an outer frame part  224  of the solenoid actuator  222  and the outer frame part  224  is fixed to a bottom surface of the casing  206 A. 
     In a case of forming the arm  216  with a material of a resin or the like not absorbed by a magnetic force other than a metal capable of being absorbed to a magnetic force of a solenoid, a metallic plate for absorption is attached to a base end part of the arm  216 . 
     ON/OFF of the solenoid actuator  222  is controlled in response to an instruction signal to be sent out from the stamp control part (refer to  FIG. 4 ). That is, when the solenoid actuator  222  is ON, an exciting current flows in a coil that is not illustrated in the solenoid actuator  222  to generate a magnetic field by the exciting current, and the base end parts of the arms  216  are pulled to the solenoid actuator  222  by a function of the magnetic field. 
     Then, the arms  216  waiting in an inclined state rise up, the stamp vessel  214  supported by the tip end parts of the arms  216  moves from the waiting position X to the stamp position Y, and the stamp vessel  214  appears from downward to upward of the chain grippers  64  (from the opening of the casing  206 A). 
     Since the first stamping device  202 A includes a latch mechanism that holds a state of the arm  216  risen once, even after the exciting current flowing in the coil of the solenoid actuator  222  is OFF to disperse the magnetic field, the rising state of the arms  216  is held. 
     The stamp vessel  214  is provided with an opening/closing lid  225  that opens/closes in association with the projectable/retractable mechanism  212  to expose a stamp surface of the stamp roller  210  from the stamp vessel  214  or tightly closes the stamp roller  210 . An opening/closing mechanism of the opening/closing lid  225  includes an optical sensor  226  (position detecting part) that detects a base end part position (home position) of the arms  216 , and an opening/closing actuator (not illustrated) that opens/closes the opening/closing lid  225  based upon the detection result of the optical sensor  226 . 
     That is, when the arms  216  move to the stamp position Y and the base end parts of the arms  216  are not detected by the optical sensor  226  (OFF state), the opening/closing actuator drives to open the opening/closing lid  225 . 
     In addition, when the arms  216  move to the waiting position X and the base end parts of the arms  216  are detected by the optical sensor  226  (ON state), the opening/closing actuator drives to close the opening/closing lid  225 . In other words, the opening/closing lid  225  opens/closes in association with projection/retraction of the stamp vessel  214  with rotation of the arms  216 . 
     An example of the opening/closing mechanism of the opening/closing lid  225  may include a system of opening/closing the opening/closing lid  225  by supporting the opening/closing lid  225  to support anus  230  through a rotational pin  228  to the stamp vessel  214  and rotating the rotational pin  228  by a motor. 
     The paper sheet P is conveyed in a direction indicated in a void arrow line, and the tip end edge P 1  of the paper sheet P abuts on the stamp roller  210  (the opening/closing lid of the stamp vessel is in an open state) positioned in the stamp position Y to cause ink to adhere to the tip end edge P 1 . 
     The solenoid actuator  222  is OFF immediately before the paper sheet P abuts on the stamp roller  210  for the arms  216  to fall with momentum of abutment of the paper sheet P on the stamp vessel  214 . Therefore since the stamp vessel  214  retracts in the downward side of the chain grippers  64  (since it is accommodated in the casing  206 A), the conveyance of a normal paper sheet P to be conveyed subsequently is not interrupted. 
     The first stamping device  202  is provided with a stopper mechanism (not illustrated) that stops the arms  216  in the waiting position X. 
     In the present embodiment, the projectable/retractable mechanism of the stamp vessel  214  is configured such that the arms  216  rotate to be risen/fallen, thereby causing the stamp roller  210  to project/retract to the chain grippers  64 , but is not limited to this system if the similar operation is possible. 
     &lt;&lt;Control System&gt;&gt; 
       FIG. 4  is a block diagram illustrating a schematic configuration of a control system of the inkjet recording apparatus  10  according to the present embodiment. 
     As illustrated in  FIG. 4 , the inkjet recording apparatus  10  includes a system controller  100 , a communication part  102 , an image memory  104 , a conveyance control part  110 , a sheet feeding control part  112 , a treatment liquid applying control part  114 , a treatment liquid drying control part  116 , an image recording control part  118 , an ink drying control part  120 , a stamp control part  208  (a first stamp control part and a second stamp control part), a sheet discharging control part  124 , an operating part  130 , a display part  132  and a sheet counter  134 . 
     The system controller  100  works as a control device that integrally controls the respective parts in the inkjet recording apparatus  10  and a calculation device that performs various types of calculation processing. The system controller  100  includes a CPU (central processing unit), a ROM (read only memory) and a RAM (random access memory). The system controller  100  operates according to predetermined control programs and controls the respective parts in the inkjet recording apparatus  10  upon reception of operating inputs through the operating part  130  from an operator. The control program to be executed by the system controller  100  and various types of data necessary for the control are stored in the ROM. 
     The operating part  130  includes an operating device (for example, operating buttons, a key board, a touch panel and the like), and outputs operating information input from the operating device to the system controller  100 . 
     The communication part  102  includes a required communication interface, and performs transmission/reception of data to a host computer connected to the communication interface. 
     The image memory  104  works as a temporary memory device of various types of data including the image data, and performs the reading and writing of the data through the system controller  100 . The image data taken in through the communication part  102  from the host computer is stored in the image memory  104 . 
     The conveyance control part  110  controls the conveyance part  11  of paper sheets P in the inkjet recording apparatus  10 . That is, the conveyance control part  110  controls drives of a tape feeder  36 A, a front guide  38  and the sheet feeding drum  40  in the sheet feeding part  12 , and controls drives of the treatment liquid applying drum  42  in the treatment liquid applying part  14 , the treatment liquid drying processing drum  46  in the treatment liquid drying processing part  16  and the image recording drum  52  in the image recording part  18 . The conveyance control part  110  controls drives of the chain grippers  64  and the back tension applying mechanism  66  used in common in the ink drying processing part  20  and the sheet discharging part  24 . 
     The conveyance control part  110  controls the conveyance part  11  according to an instruction from the system controller  100  such that the paper sheets P are conveyed from the sheet feeding part  12  to the sheet discharging part  24  without any delay. 
     The sheet feeding control part  112  controls the sheet feeding part  12  according to an instruction from the system controller  100 . Specifically drives of the sucker device  32 , the sheet-feeding platform elevating mechanism and the like are controlled such that the paper sheets P stacked on the sheet feeding platform  30  are fed in order one by one without overlapping. 
     The treatment liquid applying control part  114  controls the treatment liquid applying part  14  according to an instruction from the system controller  100 . Specifically the treatment liquid applying control part  114  controls a drive of the treatment liquid applying unit  44  such that the treatment liquid is applied on the paper sheet P conveyed by the treatment liquid applying drum  42 . 
     The treatment liquid drying control part  116  controls the treatment liquid drying processing part  16  according to an instruction from the system controller  100 . Specifically a drive of the treatment liquid drying processing unit  50  is controlled such that the paper sheet P conveyed by the treatment liquid drying processing drum  46  is subjected to drying processing. 
     The image recording control part  118  controls the image recording part  18  according to an instruction from the system controller  100 . Specifically drives of the inkjet heads  56 C,  56 M,  56 Y and  56 K are controlled such that a predetermined image is recorded on the paper sheet P conveyed by the image recording drum  52 . The image recording control part  118  controls an operation of the inline sensor  58  for the recorded image to be read out. 
     The ink drying control part  120  controls the ink drying processing part  20  according to an instruction from the system controller  100 . Specifically a drive of the ink drying processing unit  68  is controlled to cause the heated air to be blown on the paper sheet P conveyed by the chain grippers  64 . 
     The stamp control part  208  controls operations of the stamping processing part  200  (the first, second and third stamping devices  202 A,  202 B and  202 C illustrated in  FIG. 2  and  FIG. 3 ) and a buzzer  201  according to an instruction from the system controller  100 . 
     The sheet discharging control part  124  controls the sheet discharging part  24  according to an instruction from the system controller  100 . Specifically drives of the sheet-discharging platform elevating mechanism and the like are controlled for the paper sheets P to stack on the sheet discharging platform  76 . 
     For example, in a case of sorting the paper sheets P stacked on the sheet discharging part  24  by the sheet number of every 100 sheets, the sorting sheet number is input from the operating part  130 . The input sorting sheet number is stored as a sorting sheet number setting value. The sorting sheet number setting value is read out to the stamp control part  208 , which is applied to the control of the stamping processing part  200 . 
     The setting part  138  illustrated in  FIG. 4  is a block that performs various types of settings such as a setting of the sorting sheet number, and includes a setting value obtaining part that obtains the setting, a setting value storing part that stores the obtained setting value, and a memory control part that controls write-in and readout of the setting value to the setting value storing part. 
     The display part  132  includes a required display device (for example, an LCD (liquid crystal display) panel and the like), and causes required information to be displayed on the display device according to an instruction from the system controller  100 . 
     The sheet counter  134  is a device that counts the sheet number of the paper sheets P fed from the sheet feeding part  12 . The sheet number information of the paper sheets P obtained from the sheet counter  134  is sent out to the stamp control part  208  through the system controller  100 , which is applied to the control of the stamping processing part  200 . 
     The image defect detecting part  136  detects whether or not a defect is generated in the image formed on the paper sheet P. Presence/absence of the image defect is determined based upon the imaging pickup result of the inline sensor  58 . The detection result is sent out to the stamp control part  208  through the system controller  100 , which is applied to the control of the stamping processing part  200 . As explained before, the dirt detecting part that detects the dirt of the paper sheet P may be provided to determine the dirt of the paper sheet P as the image defect. 
     The buzzer  201  is a device that issues a warning for a constant period based upon control of the stamp control part  208  in a case where a stamp execution condition by the first stamping device  202  is established. Instead of the buzzer  201  or together therewith, at least one of lighting-on, blinking and lighting-off of a lamp, and a display by character information to the display part may be applied. 
     &lt;&lt;Description of Image Recording&gt;&gt; 
     Image data recorded on a paper sheet is taken in the inkjet recording apparatus  10  through the communication part  102  from the host computer. The taken image data is stored in the image memory  104 . 
     The system controller  100  executes required signal processing to the image data stored in the image memory  104  to generate dot data. A drive of each of the inkjet heads  56 C,  56 M,  56 Y and  56 K in the image recording part  18  is controlled according to the generated dot data to record an image expressed by the image data on a paper sheet. 
     The dot data is generally generated by executing color conversion processing and halftone processing to the image data. The color conversion processing is processing of converting image data (for example, image data of RGB eight bits) expressed by sRGB (standard RGB) or the like into ink amount data of each color of inks used in the inkjet recording apparatus  10  (in the present example, converted into ink amount data of each color of C, M, Y and K). The halftone processing is processing of converting the ink amount data of each color generated by the color conversion processing into dot data of each color in the processing of error dispersion or the like. 
     The system controller  100  executes the color conversion processing and the halftone processing to the image data to generate dot data of each color. According to the generated dot data of each color, a drive of the corresponding inkjet head is controlled to record an image expressed by the image data on a paper sheet P. 
     In the present embodiment, the opening/closing lid  225  of the stamp vessel  214  opens/closes in association with a projectable/retractable operation of the stamp vessel  214  by the solenoid actuator  222 . Therefore it is possible to prevent the ink on the stamp roller  210  from drying in the waiting period of not performing the stamp. 
     In this case, when inks (stamp inks) used in the first, second and third stamping devices  202 A,  202 B and  202 C are formed of a water-retentive material, the drying of the ink of the stamp roller  210  can be further prevented. 
     The present example illustrates a unit form where the first, second and third stamping devices  202 A,  202 B and  202 C are respectively accommodated in the casings  206 A,  206 B and  206 C, and the device that controls operations of the first, second and third stamping devices  202 A,  202 B and  202 C is commonalized, but devices for controlling operations of the first, second and third stamping devices  202 A,  202 B and  202 C may be separately provided. A part of the devices that control the operations of the first, second and third stamping devices  202 A,  202 B and  202 C may be commonalized. 
     The present example exemplifies the rotational operation of the arms  216  as the projectable/retractable operations of the first, second and third stamping devices  202 A,  202 B and  202 C, but the form of causing the stamp vessel  214  to go up and down is also possible. 
     The present example exemplifies the inkjet recording apparatus  10  in which the coated paper is applied as the paper sheet P, but the presently disclosed subject matter may adopt a sheet-shaped material and a substrate other than the paper, such as a resin sheet (substrate), a metallic sheet (substrate) or a glass substrate as the paper sheet P. 
     An application range of the presently disclosed subject matter is not limited to the image forming apparatus (printing apparatus) for graphic use. The presently disclosed subject matter can be applied widely to, for example, an industrial image forming apparatus such as a pattern forming apparatus that forms a wiring pattern and a mask pattern on a substrate. 
     [Stamp Imprinting Processing] 
       FIG. 5  is a perspective view schematically illustrating the first, second and third stamping devices and a print sheet, and  FIG. 6  is a perspective view illustrating an example where a stamp is imprinted on a paper sheet. An arrow in each of  FIG. 5  and  FIG. 6  indicates the conveyance direction of a paper sheet P. 
     As illustrated in  FIG. 5 , the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C can attach stamps having different colors with each other to different positions. In the present embodiment, the first stamping device  202 A, the second stamping device  202 B and the third stamping device  202 C respectively attach the stamps of colors A, B and C. 
     The image defect detecting part  136  measures an ejection curve amount of a nozzle (error of a dot position) from an image on a paper sheet P of an inspection object (measurement object) output from the inline sensor  58 . The image defect detecting part  136  outputs the measurement result of the ejection curve amount of the nozzle to the system controller  100 . Here, the ejection curve amount of the nozzle (error of the dot position) can be measured, for example, using a dot position measuring method described in Japanese Patent Application Laid-Open No. 2011-079257 (paragraphs [0092] and subsequent thereto). 
     In the present embodiment, not only the ejection curve amount of the nozzle but also a streak due to non-ejection can be detected. For example, the non-ejection can be detected assumed as an equivalent to a case where the ejection curve amount of the nozzle is the largest. 
     The system controller  100  controls the stamp control part  208  according to the data of the measurement result of the ejection curve amount of the nozzle input from the image defect detecting part  136  and causes the stamp control part  208  to imprint a stamp according to the data of the measurement result of the ejection curve amount of the nozzle on a paper sheet P of an inspection object. For example, when the ejection curve amount of the nozzle is indicated at x, in a case where x&gt;17 μm, a stamp of color A is imprinted by the first stamping device  202 A, in a case where 13 μm&lt;x≦17 μm, a stamp of color B is imprinted by the second stamping device  202 B, and in a case where 7 μm≦x≦13 μm, a stamp of color C is imprinted by the third stamping device  202 C. Therefore an operator can visually recognize the ejection curve amount of the nozzle based upon the color of the stamp. 
     The measurement result of the ejection curve amount may differ for each nozzle. 
     For example, when the measurement result of the ejection curve amount of the nozzle in a nozzle i is indicated at x i , x i &gt;17 μm (case where a stamp of color A is to be imprinted), when the measurement result of the ejection curve amount of the nozzle in a nozzle j is indicated at x j , 13 μm&lt;x i ≦17 μm (case where a stamp of color B is to be imprinted), and when the measurement result of the ejection curve amount of the nozzle in a nozzle k is indicated at x k , 7 μm≦x k ≦13 μm (case where a stamp of color C is to be imprinted). 
     In the above case, a stamp (stamp A in the above example) corresponding to a case where the measurement result of the ejection curve amount of the nozzle is the largest (stamp condition  1 ) may be imprinted. In a case of the stamp condition  1 , a stamp corresponding to a case where the measurement result of the ejection curve amount of the nozzle in a paper sheet P of an inspection object is the largest is imprinted. Therefore an operator can confirm the extent of a streak having the highest visibility in the paper sheet P of the inspection object based upon the color of the stamp. As a result, an operator can efficiently inspect only the streak having the relatively high visibility. 
     In the above case, a stamp (stamp C in the above example) corresponding to a case where the measurement result of the ejection curve amount of the nozzle is the smallest (stamp condition  2 ) may be imprinted. In a case of the stamp condition  2 , a stamp corresponding to a case where the measurement result of the ejection curve amount of the nozzle in a paper sheet P of an inspection object is the smallest is imprinted. Therefore an operator can confirm the extent of a streak having the lowest visibility in the paper sheet P of the inspection object based upon the color of the stamp. As a result, an operator can perform an accurate inspection in regard to the streak having the relatively low visibility. 
     In the present embodiment, the stamp condition is changeable by the operating part  130 , and an operator can select, according to the kind of a paper sheet P of an inspection object, the stamp condition  1  in a case where the number of the paper sheets P of the inspection object is large and required accuracy of the inspection is relatively low, and the stamp condition  2  in a case where the number of the paper sheets P of the inspection object is small and required accuracy of the inspection is relatively high. 
     In regard to a threshold for determining whether or not a stamp is imprinted and which color stamp is imprinted, it is preferable to change the threshold for each color as illustrated in Table 1 in terms of visibility for each color. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 SETTING 
                 K 
                 C and M 
                 Y 
               
               
                   
                   
               
             
            
               
                   
                 HIGH 
                  7 μm 
                 10 μm 
                 15 μm 
               
               
                   
                 MIDDLE 
                 13 μm 
                 13 μm 
                 17 μm 
               
               
                   
                 LOW 
                 17 μm 
                 17 μm 
                 19 μm 
               
               
                   
                   
               
            
           
         
       
     
     In general, a streak of a K ink has the highest visibility, and a streak of a Y ink has the lowest visibility. The visibility of the streak of each of a C ink and an M ink is an intermediate level between K and Y. In an example illustrated in Table 1, a threshold used for determination of the K ink is set to the smallest (detection accuracy is the highest) and a threshold used for determination of the Y ink is set to the largest (detection accuracy is the lowest) in terms of a difference in visibility for each color. 
     No detection of the streak of the Y ink may be performed in terms of low visibility of the Y ink. 
     Further, detection of the streak of the K ink having the highest visibility to the streak may be first performed, detection of the streak of the C ink or M ink may be next performed, and detection of the streak of the Y ink having the lowest visibility to the streak may be finally performed. 
     In the example illustrated in Table 1, in a case of the K ink, when the measurement result of the ejection curve amount of the nozzle is indicated at x, in a case where x&gt;17 μm (low), a stamp of color A is imprinted by the first stamping device  202 A, in a case where 13 μm&lt;×≦17 μm (middle), a stamp of color B is imprinted by the second stamping device  202 B, and in a case where 7 μm≦x≦13 μm (high), a stamp of color C is imprinted by the third stamping device  202 C. 
     In a case of the C ink and M ink, when the measurement result of the ejection curve amount of the nozzle is indicated at x, in a case where x&gt;17 μm (low), a stamp of color A is imprinted by the first stamping device  202 A, in a case where 13 μm&lt;x≦17 μm (middle), a stamp of color B is imprinted by the second stamping device  202 B, and in a case where 10 μm≦x≦13 μm (high), a stamp of color C is imprinted by the third stamping device  202 C. 
     In a case of the Y ink, when the measurement result of the ejection curve amount of the nozzle is indicated at x, in a case where x&gt;19 μm (low), a stamp of color A is imprinted by the first stamping device  202 A, in a case where 17 μm&lt;x≦19 μm (middle), a stamp of color B is imprinted by the second stamping device  202 B, and in a case where 15 μm≦x≦17 μm (high), a stamp of color C is imprinted by the third stamping device  202 C. 
     In the example illustrated in Table 1, three thresholds are used for determination of the defect nozzle, and the extent in defect of the defect nozzle (evaluation of the streak) is classified into four stages of “high”, “middle” “low”, and “no stamp” (OFF), but the presently disclosed subject matter is not limited thereto. 
     In the example illustrated in Table 1, for example, in a case where the determination result of the nozzle of the K ink is made as “low”, the determination result of the nozzle of the C ink is made as “high”, and the determination result of the nozzle of the Y ink is made as “high”, all the stamps (the stamps A and C in the above example) corresponding to the determination results may be imprinted (stamp condition  3 ). 
     In the above case, the stamp (stamp A in the above example) corresponding to the lowest result in the ejection curve amount of the nozzle (stamp condition  4 ) may be imprinted. In a case of the stamp condition  4 , since the stamp corresponding to the largest result in the ejection curve amount of the nozzle in the paper sheet P of the inspection object is imprinted, an operator can confirm the extent of the streak having the highest visibility based upon the color of the stamp, in the paper sheet P of the inspection object. As a result, an operator can efficiently inspect only the streak having a relatively high visibility. 
     In the above case, the stamp (stamp C in the above example) corresponding to the highest determination result in the ejection curve amount of the nozzle may be imprinted (stamp condition  5 ). In a case of the stamp condition  5 , since the stamp corresponding to the lowest result in the ejection curve amount of the nozzle in the paper sheet P of the inspection object is imprinted, an operator can confirm the extent of the streak having the lowest visibility based upon the color of the stamp in the paper sheet P of the inspection object. As a result, an operator can perform a strict inspection on the streak having a relatively low visibility. 
     As described above, an operator can select whether to change the threshold of the determination for each color, and the stamp condition in a case of changing the threshold of the determination for each color. 
     Hereinafter, the method for attaching the stamp will be specifically described. In a case where there is present only one nozzle in which the curve is detected (defect nozzle and nozzle for correction object), a stamp corresponding to the ejection curve amount of the nozzle is imprinted. That is, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), the stamp A is imprinted, in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), the stamp B is imprinted, and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp C is imprinted. 
     In the stamp condition  3 , in a case where there are a plurality of nozzles in which the curve is detected, all the stamps corresponding to the ejection curve amounts of the respective defect nozzles are imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (high), the stamps A, B and C are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low) and in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), the stamps A and B are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamps A, B and C are imprinted. 
     In the stamp condition  4 , in a case where there are a plurality of nozzles in which the curve is detected, only the stamp corresponding to the lowest determination level in the detection threshold is imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (high), the stamp A is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low) and in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), the stamp A is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp A is imprinted. 
     In the stamp condition  5 , in a case where there are a plurality of nozzles in which the curve is detected, only the stamp corresponding to the highest determination level in the detection threshold is imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (high), the stamp C is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low) and in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), the stamp B is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp C is imprinted. 
     As described above, the threshold of the determination is differentiated for each color and the stamp condition is changeable for each determination level, and therefore an operator can easily carry out the inspection according to the print content to the paper sheet P. 
       FIG. 7  is a flow chart illustrating a defect nozzle determining processing according to the embodiment of the presently disclosed subject matter. The processing in  FIG. 7  is repeatedly executed to the paper sheets P of the inspection object one by one. 
     First, the image defect detecting part  136  obtains an image of the paper sheet P as the inspection object from the inline sensor  58  to make a determination of a color of an ink to be detected (ink color determining step: step S 10 ). 
     Next, the image defect detecting part  136  uses a dot position measuring method described in Japanese Patent Application Laid-Open No. 2011-079257 (paragraphs [0092] and subsequent thereto) to measure an injection curve amount (an error of a dot position) of a nozzle (measuring step: step S 12 ). 
     Next, in step S 12 , in a case where the curved nozzle is detected (Yes in step S 14 ), the defect nozzle determining processing is executed (image defect detecting step: step S 16 ). In step S 16 , for example, as illustrated in Table 1, three kinds of thresholds of “high”, “middle” and “low” set for the respective colors are used to make a determination of the defect nozzle. In step S 16 , the image defect detecting part  136 , for example, (1) in a case where the curve of a nozzle is detected twice in total in printing of one time, may determine the nozzle as a defect nozzle, or (2) in a case where the curve of a nozzle is successively detected twice, may determine the nozzle as non-ejection correction. The criterion for determination of the defect nozzle is not limited to the above (1) and (2). For example, an operator may increase/decrease the detection number of times of the curve in the above criterion. 
     Next, in a case where there is present the nozzle that is determined as a defect nozzle by the image defect detecting part  136  (Yes in step S 18 ), the system controller  100  makes a correction of the nozzle determined as the defect nozzle (step S 20 ). In step S 20 , for example, it is possible to apply a defect recording element correction step described in Japanese Patent Application Laid-Open No. 2011-161646. 
     The system controller  100  determines whether or not a stamp is imprinted on a paper sheet P and the kind and the number of stamps to be imprinted on a paper sheet P based upon the result of the determination in step S 16  and makes stamp flag F n, i, j  ON. The system controller  100  controls the stamp control part  208  and keeps on the imprinting of the stamp on the paper sheet P until the correction of the defect nozzle is completed. 
     The system controller  100  makes the stamp flag F n, i, j  OFF in a case where the correction in step S 20  is completed. Here, the stamp flag F n, i, j  indicates whether or not correction of a nozzle of i color (i=C, M, Y, K) detected in the n-th paper sheet P ends. “j” is a parameter indicating the kind of a stamp imprinted for each ink color, for example, is set such that in a case of imprinting a stamp A of “low”, j=1, in a case of imprinting a stamp B of “middle”, j=2, and in a case of imprinting a stamp C of “high”, j=3, in a case of imprinting stamps A and B of “low” and “middle”, j=4 . . . . 
       FIG. 8  is a flow chart illustrating monitoring processing of correction completion. As illustrated in  FIG. 8 , it is determined whether or not correction of a nozzle of i color (i=C, M, Y, K) detected in the n-th paper sheet P ends (step S 30 ), and in a case of the correction completion, F n, i, j  is set to OFF (step S 32 ), and on the other hand, in a case of non-correction completion, F n, i, j  is maintained to ON (step S 34 ). 
       FIG. 9  is a flow chart illustrating stamp imprint determining processing. 
     As described above, On and OFF are set to the stamp flag F n, i, j  for each of the paper sheets P and for each of ink colors (i color (i=C, M, Y, K)). In a case where there are present one or more of F n, i, j  set thus to ON (Yes in step S 50 ), that is, in a case where there is present the nozzle where the correction is not completed, a stamp is imprinted on the paper sheet P according to a stamp condition set by an operator (stamp step: step S 52 ). On the other hand, in a case where all the stamp flags are OFF (No in step S 50 ), the imprint of the stamp is not carried out (step S 54 ). 
     According to the present embodiment, in a case where the streak due to the nozzle is detected, the kind of the stamp can be changed according to the extent of the streak. Therefore since an operator can recognize the extent of the streak from the stamp, it is possible to support the inspection work by the operator and realize efficiency of the inspection work. 
     Further, according to the present embodiment, it is possible to change the threshold used for the determination of the defect nozzle (streak) according to the visibility for each of the colors of the inks and set the stamp condition in a case of a plurality of the defect nozzles. Thereby an operator can set the attachment method of the stamp according to use of the print sheet, the required accuracy and the like, and can facilitate the inspection work. 
     [Another Embodiment of Stamp Imprinting Processing] 
     Next, another embodiment of stamp imprinting processing will be explained with reference to  FIG. 10  and  FIG. 11 . Components identical or similar to those in the above embodiment are referred to as identical reference signs to omit the explanation. 
     The inkjet recording apparatus  10  according to the present embodiment includes the stamping devices (stamping devices  202 A k ,  202 B k  and  202 C k  for K, stamping devices  202 A c ,  202 B c , and  202 C c , for C, stamping devices  202 A m ,  202 B m , and  202 C m  for M and stamping devices  202 A y ,  202 B y  and  202 C y  for Y), wherein three stamps can be imprinted for each color (CMYK). The colors of the stamps A, B and C imprinted by the stamping devices for the respective colors differ mutually for each kind, but in regard to each color of CMYK, the colors of the stamps A, B and C of the same kind may be respectively the same. 
       FIG. 10  is a perspective view schematically illustrating stamping devices according to another embodiment of the presently disclosed subject matter and a print sheet, and  FIG. 11  is a perspective view illustrating an example where stamps are imprinted on the paper sheet. Arrows in  FIG. 10  and  FIG. 11  indicate the direction of a paper sheet P. 
     In a case where there is present only one nozzle in which the curve is detected (defect nozzle and nozzle for correction object), a stamp corresponding to the ejection curve amount of the nozzle is imprinted. That is, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), the stamp A for K is imprinted by the stamping device  202 A k  for K. In a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), the stamp B for C is imprinted by the stamping device  202 B c  for C. In a case where the ejection curve amount of the k-th nozzle of Y is 16 μM (high), the stamp C for Y is imprinted by the stamping device  202 C y  for Y. 
     In the stamp condition  3 , in a case where there are a plurality of nozzles in which the curve is detected, all the stamps corresponding to the ejection curve amounts of the respective defect nozzles are imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 pin (high), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (low), the stamps A, B and C for K are respectively imprinted by the stamping devices  202 A k ,  202 B k  and  202 C k  for K. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle), and in a case where the ejection curve amount of the k-th nozzle of C is 11 μM (low), the stamp A for K, the stamp B for C and the stamp C for C are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (low), the stamp A for K, the stamp B for C and the stamp C for Y are imprinted. 
     In the stamp condition  4 , in a case where there are a plurality of nozzles in which the curve is detected, only the stamp corresponding to the lowest determination level in the detection threshold is imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (low), only the stamp A for K is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of C is 15 μm (middle), the stamp A for K and the stamp B for C are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp A for K, the stamp B for C and the stamp C for Y are imprinted. 
     In the stamp condition  5 , in a case where there are a plurality of nozzles in which the curve is detected, only the stamp corresponding to the highest determination level in the detection threshold is imprinted. In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 μm (low), only the stamp C for K is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of C is 15 μm (middle), the stamp B for K and the stamp B for C are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp B for K, the stamp B for C and the stamp C for Y are imprinted. 
     In addition, in a case where there are a plurality of nozzles in which the curve is detected, it is possible to imprint only the stamp corresponding to the lowest determination level in the detection threshold, for each color (stamp condition  6 ). In this case, in a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of K is 10 (low), the stamp A for K is imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (high), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of C is 15 μm (middle), the stamp A for K and the stamp B for C are imprinted. In a case where the ejection curve amount of the i-th nozzle of K is 20 μm (low), in a case where the ejection curve amount of the j-th nozzle of K is 15 μm (middle), in a case where the ejection curve amount of the j-th nozzle of C is 15 μm (middle) and in a case where the ejection curve amount of the k-th nozzle of Y is 16 μm (high), the stamp A for K, the stamp B for C and the stamp C for Y are imprinted. 
     In the present embodiment, the paper sheet P may be discharged to a different place according to a magnitude of the ejection curve amount of the nozzle. For example, the sheet discharging part may include a plurality of sheet discharging parts, and in the sheet discharging part a position where the paper sheet P is discharged may differ in a direction perpendicular to the conveyance direction of the paper sheet P, for example, the paper sheet P may be discharged in order of “high”, “middle”, “low” and “OFF”. 
     The presently disclosed subject matter can be realized as a program (control program in the printing apparatus) that causes the computer to execute the above processing, or as a non-temporary recording medium or program product storing such program. By applying such program to the computer, it is possible to cause the calculation device and the like of the computer to work as the image defect detecting function and the stamping function.