Patent Publication Number: US-11027538-B2

Title: Register error detection device, register error detection method, and printed matter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Application No. PCT/JP2016/073734, filed on Aug. 12, 2016, the disclosures of which Application are incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a register error detection device and a register error detection method for detecting a register error based on a register mark and to a printed matter on which the register mark is printed. 
     2. Description of the Related Art 
     In the case of printing a multicolored picture on a web by a rotary printing press, printing is generally done by overlapping colors on a color-by-color basis so as to form a single picture. In this case, there is a case where misalignment occurs in the printing at the time of the overlapping of the colors, and it is therefore necessary to have correct alignment so as not to cause misregister. In order to achieve this purpose, an automatic control device called an automatic registering device is used. This automatic registering device generally includes a register error detection device for detecting register errors based on a register mark printed for each color on a web and controls a compensator roller or plate cylinder of a rotary printing press so as to correct misregister. Register marks are also referred to as register marks. 
     For example, the register error detection device includes two line sensors provided at a reference interval therebetween along the transporting direction of the web, and the amount of deviation of the interval of register marks of two colors, that is detected by the line sensors, from a reference interval is referred to as a register error e.g., see Japanese Patent Application Publication No. H08-267727). 
     After printing, the region of a web in which register marks are printed is cut out. Therefore, in order to save loss, register marks are preferably reduced in size. However, it is difficult to reduce the size of register marks without decreasing the accuracy of detecting register errors. 
     SUMMARY 
     In this background, a purpose of the present disclosure is to provide a technology capable of reducing the size of register marks while suppressing a decrease in the accuracy of detecting register errors. 
     A register error detection device according to one embodiment of the present invention includes: an image capturing unit that captures an image of two first register marks of a first color printed on a substrate by a first plate cylinder of a rotary printing press and a second register mark of a second color printed on the substrate by a second plate cylinder of the rotary printing press; and a calculation unit that compares a reference position located between the two first register marks with a comparison position that is based on the second register mark in the image captured by the image capturing unit. 
     Another aspect of one embodiment of the present invention is a register error detection method. This method includes: capturing an image of two first register marks of a first color printed on a substrate by a first plate cylinder of a rotary printing press and a second register mark of a second color printed on the substrate by a second plate cylinder of the rotary printing press; and comparing a reference position located between the two first register marks with a comparison position that is based on the second register mark in the image that has been captured. 
     Still another embodiment of the present invention is a printed matter. This printed matter is a printed matter is a printed matter on which a register mark for controlling over printing misalignment in a rotary printing press is printed, comprising: a substrate; two first register marks of a first color printed on the substrate by a first plate cylinder of the rotary printing press; and a second register mark of a second color printed on the substrate by a second plate cylinder of the rotary printing press. 
     Optional combinations of the aforementioned constituting elements and implementations of the disclosure in the form of methods, apparatuses, systems, recording mediums, and computer programs may also be practiced as additional modes of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a rotary printing press including a register error detection device according to a first embodiment; 
         FIG. 2  is a diagram showing a part of a printed matter on which register marks according to the first embodiment are printed; 
         FIG. 3  is a diagram showing an image of the register marks captured by an image capturing unit of  FIG. 1 ; 
         FIG. 4  is a diagram showing an image of the register marks when the image capturing unit of  FIG. 1  is rotated in the in-plane direction of the web; 
         FIG. 5  is a diagram showing an image of other register marks when the image capturing unit of  FIG. 1  is rotated in the in-plane direction of the web; 
         FIG. 6  is a diagram showing a part of a printed matter on which register marks according to a second embodiment are printed; 
         FIG. 7  is a diagram showing an image of the register marks captured by an image capturing unit according to the second embodiment; and 
         FIG. 8  is a diagram showing another image of the register marks captured by the image capturing unit according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       FIG. 1  is a diagram showing a rotary printing press  1  including a register error detection device  100  according to a first embodiment. The rotary printing press  1  shown in  FIG. 1  is a multicolor gravure rotary printing press capable of printing four colors on a web  30  such as a film, which is a substrate (printing target material). 
     As shown in  FIG. 1 , the rotary printing press  1  includes a first printing unit  12   a , a second printing unit  12   b , a third printing unit  12   c , a fourth printing unit  12   d , an unwinding unit  14 , a winding unit  16 , a plurality of compensator rollers  32 , a plurality of register motors  34 , a monitor  40 , and a register error detection device  100 . 
     The four units: the first printing units  12   a ; the second printing unit  12   b ; the third printing unit  12   c ; and the fourth printing unit  12   d , are arranged in series. The first printing unit  12   a , the second printing unit  12   b , the third printing unit  12   c , and the fourth printing unit  12   d  are collectively referred to as “printing units  12 ” as appropriate. 
     The unwinding unit  14  for supplying the web  30  on which printing is to be done is installed upstream of the first printing unit  12   a . Further, the winding unit  16  for winding the web  30  on which printing is done is installed downstream of the fourth printing unit  12   d . Each printing unit  12  is provided with a plurality of guide rollers  18 , to form a conveying path for the web  30 . 
     To each printing unit  12 , a cylindrical plate cylinder  20  for transferring ink, which serves as a coating agent, is installed on the lower side of the web  30  and a cylindrical impression cylinder  22  for applying pressure to the web  30  is installed on the upper side of the web  30  in such a manner that the cylindrical plate cylinder  20  and the cylindrical impression cylinder  22  are freely rotatable around their respective cylindrical axes, while sandwiching the web  30 . A dryer  24  for drying the printing surface of the web  30  is disposed downstream of each plate cylinder  20 . 
     The register error detection device  100  includes three image capturing units  26  and a control device  28 . The control device  28  has a calculation unit  28   a  and a control unit  28   b . Between the plate cylinder  20  and the dryer  24  in each of the second printing unit  12   b , the third printing unit  12   c , and the fourth printing unit  12   d , the image capturing unit  26  is disposed. The image capturing units  26  are formed using, for example, a charged coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or the like that receives light and converts the light into an electric signal. 
     For example, the image capturing unit  26  of the second printing unit  12   b  captures an image of a first register mark printed by the first printing unit  12   a  located upstream thereof and a second register mark printed by the plate cylinder  20  of the second printing unit  12   b . The first register mark and the second register mark are marks for controlling printing misalignment in the rotary printing press  1 . The image capturing unit  26  is electrically connected to the control device  28 . The calculation unit  28   a  of the control device  28  calculates the register error between the first register mark and the second register mark based on an image captured by the image capturing unit  26 . The calculation unit  28   a  is able to calculate a longitudinal register error that is misregister in the transporting direction of the web  30  and a lateral register error that is misregister in the direction orthogonal to the transporting direction within the plane of the web  30 . 
     In the same way, the image capturing unit  26  of the third printing unit  12   c  and the image capturing unit  26  of the fourth printing unit  12   d  each captures an image of a first register mark printed by a printing unit  12  located upstream thereof and a second register mark printed by the plate cylinder  20  of the own printing unit. For each of the third printing unit  12   c  and the fourth printing unit  12   d , the calculation unit  28   a  also calculates the register error between the first register mark and the second register mark based on an image captured by the image capturing unit  26 . Details regarding the calculation of register errors will be described later. 
     Compensator rollers  32  for adjusting the supply phase of the web  30  are respectively arranged between the first printing unit  12   a  and the second printing unit  12   b , between the second printing unit  12   b  and the third printing unit  12   c , and between the third printing unit  12   c  and the fourth printing unit  12   d . The compensator roller  32  is driven by the register motor  34 . Each register motor  34  is electrically connected to the control device  28  and moves the compensator roller  32  up and down according to an instruction from the control unit  28   b  of the control device  28  so as to eliminate longitudinal register errors. Thereby, it is possible to correct printing misalignment in the longitudinal direction in each printing unit  12 . 
     The respective plate cylinders  20  of the second printing unit  12   b , the third printing unit  12   c , and the fourth printing unit  12   d  move in the lateral direction so as to eliminate lateral direction register errors based on an instruction from the control unit  28   b  of the control device  28 . Thereby, it is possible to correct printing misalignment in the lateral direction in each printing unit  12 . 
     Further, the monitor  40  is connected to the control device  28  and displays an image captured by the image capturing unit  26  and the like. By monitoring the monitor  40 , the user can visually recognize the condition of misregister. 
     The control device  28  includes a computer, and the various functions of the control device  28  are implemented in hardware by a circuit block, memory, or other LSI&#39;s and in software by a program loaded in memory, etc. Thus, a person skilled in the art should appreciate that the various functions of the control device  28  can be accomplished in various forms by hardware only, software only, or the combination of both, and the way of accomplishing these functions is not limited to any particular one. 
       FIG. 2  is a diagram showing a part of a printed matter  300  on which a register mark  200  according to the first embodiment is printed. The printed matter  300  includes a web  30 , two first register marks  202  and  204  of a first color, and a second register mark  210  of a second color different from the first color. The first register marks  202  and  204  and the second register mark  210  are collectively referred to as a register mark  200 . Although not shown in the figure, a pattern of the first color and a pattern of the second color are printed in a region other than the region of the web  30  where the register mark  200  is printed. 
     The two first register marks  202  and  204  are printed on the web  30  by a plate cylinder (first plate cylinder)  20  of the first printing unit  12   a  of the rotary printing press  1 . The second register mark  210  is printed on the web  30  by a plate cylinder (second plate cylinder)  20  of the second printing unit  12   b  of the rotary printing press  1 . 
     Since the two first register marks  202  and  204  are printed by the same plate cylinder  20 , the distance Dis 1  between the respective centroids of the two first register marks  202  and  204  is substantially constant irrespective of misregister. 
     The two first register marks  202  and  204  and the second register mark  210  are each circular in shape. The area of each of the two first register marks  202  and  204  is substantially half the area of the second register mark  210 . 
     The two first register marks  202  and  204  and the second register mark  210  are arranged along the transporting direction dt of the web  30  in the rotary printing press  1 . The second register mark  210  is arranged between the two first register marks  202  and  204 . 
     In the absence of printing misalignment, the first register marks  202  and  204  and the second register mark  210  are arranged such that the centroid of the second register mark  210  coincides with the centroid of the two first register marks  202  and  204 . In the presence of printing misalignment, the centroid of the second register mark  210  does not coincide with the centroid of the two first register marks  202  and  204 . The centroid of the two first register marks  202  and  204  represents the midpoint between the centroid of one first register mark  202  and the centroid of the other first register mark  204 . 
       FIG. 3  is a diagram showing an image of the register mark  200  captured by the image capturing unit  26  of  FIG. 1 . The calculation unit  28   a  of the register error detection device  100  compares a reference position P 1  located between the two first register marks  202  and  204  with a comparison position P 2  based on the second register mark  210  in the image of  FIG. 3  captured by the image capturing unit  26  and calculates a register error based on the number of pixels between the reference position P 1  and the comparison position P 2 . In the present embodiment, the calculation unit  28   a  uses the centroid of the two first register marks  202  and  204  obtained by known image processing as the reference position P 1  and uses the centroid of the second register mark  210  obtained by known image processing as the comparison position P 2 . During the image processing, the second register mark  210  whose area is different from the areas of the first register marks  202  and  204  can be easily specified. 
     The method of calculating the reference position P 1 , which is the centroid of the two first register marks  202  and  204 , is not particularly limited. For example, by known image processing, the calculation unit  28   a  may obtain the centroid of the first register mark  202 , obtain the centroid of the first register mark  204 , and obtain the midpoint of the centroids as the reference position P 1 . Alternatively, the calculation unit  28   a  can directly calculate the reference position P 1  based on the areas of the two first register marks  202  and  204  by known image processing. Since the area of each of the two first register marks  202  and  204  is substantially half the area of the second register mark  210 , the sum of the number of samples (i.e., the number of pixels) of the two first register marks  202  and  204  in the image and the number of samples of the second register mark  210  are substantially equal. Therefore, the number of samples used to directly calculate the centroid using the two first register marks  202  and  204  is approximately equal to the number of samples used in calculating the centroid of the second register mark  210 . Therefore, in such calculation, an error in the calculation of the centroid can be suppressed. 
     Based on the number of pixels between the respective centroids of the two first register marks  202  and  204  in the image and the known distance Dis 1  between the respective centroids of the two first register marks  202  and  204  that have been printed, the calculation unit  28   a  calculates the distance per pixel. For example, when the known distance Dis 1  is 10 mm and the number of pixels is 100 pixels, the distance per pixel is 0.1 mm/pixel. The calculation of the distance per pixel may be performed every time a new image of the first register marks  202  and  204  is captured or may be performed every predetermined period. 
     The calculation unit  28   a  then calculates the product of the distance per pixel that has been calculated and the number of pixels between the reference position P 1  and the comparison position P 2  as a register error. More specifically, the calculation unit  28   a  calculates the register error in a direction d 1  of a straight line passing through the two first register marks  202  and  204  in the image and a direction d 2  orthogonal to this straight line. The direction d 1  is equal to the transporting direction dt. The calculation unit  28   a  calculates the product of the distance per pixel and the number of pixels between the reference position P 1  and the comparison position P 2  in the direction d 1  as a longitudinal register error. The calculation unit  28   a  calculates the product of the distance per pixel and the number of pixels between the reference position P 1  and the comparison position P 2  in the direction d 2  as a lateral direction register error. 
     The control unit  28   b  adjusts the transportation of the web  30  in the transporting direction dt in accordance with the longitudinal register error that has been obtained and adjusts the transportation of the web  30  in the lateral direction in accordance with the lateral register error that has been obtained, so as to correct printing misalignment. The above-mentioned image capturing, calculation of a register error, and correction of printing misalignment are performed every time the second register mark  210  is printed between the two first register marks  202  and  204 , and the printing misalignment is corrected in real time during printing. 
     In the calculation of the registration error, although the number of pixels between the reference position P 1  and the comparison position P 2  in the image changes in accordance with the distance between the image capturing unit  26  and the register mark  200 , since the number of pixels between the centroids of the two first register marks  202  and  204  in the image also changes, the distance per pixel also changes with the same tendency. Therefore, irrespective of the distance between the image capturing unit  26  and the register mark  200 , the register error can be calculated with high accuracy. 
     The user replaces the plate cylinder  20  when printing another kind of printed matter after printing a certain kind of printed matter. However, the new plate cylinder  20  is often different in width and circumferential length from the one before the replacement. In that case, it is necessary to adjust the position of the image capturing unit  26  in accordance with the new plate cylinder  20 . However, in the present embodiment, since a register error can be detected with high accuracy regardless of the distance between the image capturing unit  26  and the register mark  200 , the adjustment of the position of the image capturing unit  26  is easy. That is, there is no need to accurately adjust the distance between the image capturing unit  26  and the register mark  200  to a certain distance. Therefore, printing of another kind of printed matter can be started in a short time. As a result, it is possible to shorten the printing time of a plurality of kinds of printed matters. 
       FIG. 4  is a diagram showing an image of the register mark  200  when the image capturing unit  26  of  FIG. 1  is rotated in the in-plane direction of the web  30 . There is a possibility that the image capturing unit  26  is rotated in the in-plane direction of the web  30  when the user adjusts the position of the image capturing unit  26 . In that case, the image that is captured is also rotated as shown in  FIG. 4 . As described above, the calculation unit  28   a  calculates the register error in the direction d 1 , that is, the transporting direction dt and in the direction d 2 . Therefore, even when the image capturing unit  26  is rotated in the in-plane direction of the web  30 , the longitudinal register error in the transporting direction dt and the lateral register error in the lateral direction orthogonal to the transporting direction dt can be calculated without being affected by the rotation. Therefore, it is not necessary to adjust the rotation angle of the image capturing unit  26  in the in-plane direction of the web  30  accurately to 0 degrees. Also from this, it is easy to adjust the position of the image capturing unit  26 . 
       FIG. 5  is a diagram showing an image of another register mark  200 X when the image capturing unit  26  of  FIG. 1  is rotated in the in-plane direction of the web  30 . The shape of each register mark may be a quadrangle as shown in  FIG. 5 . However, in the case of a quadrangle, the relationship between the direction of a side of the quadrangle and the direction of the arrangement of the pixels of the image changes according to the rotation of the image capturing unit  26  in the in-plane direction of the web  30 , and an error may thus occur at the end portions of each register mark. That is, the number of samples of each register mark in the image may vary between the case where the image capturing unit  26  is rotated in the in-plane direction of the web  30  and the case where the image capturing unit  26  is not rotated in the in-plane direction of the web  30 . Therefore, an error may occur in the coordinates of the centroid. 
     In contrast, in the examples of  FIGS. 2 to 4 , the first register marks  202  and  204  and the second register mark  210  are each circular in shape. Therefore, the number of samples of each of the first register marks  202  and  204  and the second register mark  210  in the image is hard to vary between the case where the image capturing unit  26  is rotated in the in-plane direction of the web  30  and the case where the image capturing unit  26  is not rotated in the in-plane direction of the web  30 . Therefore, an error in the centroid can be suppressed. In other words, the shapes of the first register marks  202  and  204 , etc., are preferably circular. 
     Regarding the two first register marks  202  and  204  printed by the plate cylinder  20  of the second printing unit  12   b  and the second register mark  210  printed by the plate cylinder  20  of the third printing unit  12   c , a register error can also be calculated in the same way as described above using the image captured by the image capturing unit  26  arranged in the third printing unit  12   c . Regarding the two first register marks  202  and  204  printed by the plate cylinder  20  of the third printing unit  12   c  and the second register mark  210  printed by the plate cylinder  20  of the fourth printing unit  12   d , a register error can also be calculated in the same way as described above using the image captured by the image capturing unit  26  arranged in the fourth printing unit  12   d.    
     As described above, according to the present embodiment, by using the image obtained by imaging the two first register marks  202  and  204  of the first color and the second register mark  210  of the second color, the product of the distance per pixel and the number of pixels between the reference position P 1  and the comparison position P 2  of the image is calculated as a register error. Thereby, even when the distance between the image capturing unit  26  and the register mark  200  changes, the register error can be calculated with high accuracy. 
     Further, since the centroid of the two first register marks  202  and  204  is set as the reference position P 1 , the reference position P 1  can be determined with high accuracy. 
     Further, since an image of the register mark  200  is captured by an image capturing unit  26 , the size of the register mark  200  can be reduced by using a high resolution image capturing unit  26 . 
     Therefore, the size of the register mark  200  can be reduced while suppressing a decrease in the accuracy of detecting register errors. 
     Further, since the register mark  200  can be made smaller and the two first register marks  202  and  204  and the second register mark  210  are arranged in a line along the transporting direction dt, the width of a region where the register mark  200  is printed can be reduced. After printing, the region of the web  30  in which the register mark  200  is printed is cut out, thus allowing for the saving of loss. 
     Second Embodiment 
     The second embodiment is different from the first embodiment in that an additional second register mark is further provided. An explanation will be given in the following mainly regarding differences from the first embodiment. 
       FIG. 6  is a diagram showing a part of a printed matter  300 A on which a register mark  200 A according to the second embodiment is printed. As shown in  FIG. 6 , an additional second register mark  212  of a second color is further printed on a web  30 . In the same way as in the second register mark  210 , the additional second register mark  212  is printed on the web  30  by a plate cylinder (second plate cylinder)  20  of the second printing unit  12   b  of the rotary printing press  1 . The additional second register mark  212  is also circular. The respective areas of the two first register marks  202  and  204 , the second register mark  210 , and the additional second register mark  212  are substantially equal. 
     A first line segment L 1  connecting the respective centroids of the two first register marks  202  and  204  is orthogonal to a second line segment L 2  connecting the centroid of the second register mark  210  and the centroid of the additional second register mark  212 . As long as the first line segment L 1  and the second line segment L 2  intersect with each other, the line segments do not need to be orthogonal to each other. 
     In the absence of printing misalignment, the first register marks  202  and  204 , the second register mark  210 , and the additional second register mark  212  are arranged such that the centroid of the second register mark  210  and the additional second register mark  212  coincides with the centroid of the two first register marks  202  and  204 . In the presence of printing misalignment, the centroid of the second register mark  210  and the additional second register mark  212  does not coincide with the centroid of the two first register marks  202  and  204 . The centroid of the second register mark  210  and the additional second register mark  212  represents the midpoint between the centroid of the second register mark  210  and the centroid of the additional second register mark  212 . 
     The image capturing unit  26  further captures an image of the additional second register mark  212  in addition to the two first register marks  202  and  204  and the second register mark  210 . 
       FIG. 7  is a diagram showing an image of the register mark  200 A captured by the image capturing unit  26  according to the second embodiment. The calculation unit  28   a  uses the centroid of the second register mark  210  and the additional second register mark  212  of the image shown in  FIG. 7  as a comparison position P 2 . 
     When an angle θ formed by the first line segment L 1  and the second line segment L 2  is within a predetermined angle range in the image, the calculation unit  28   a  calculates the product of the distance per pixel and the number of pixels between the reference position P 1  and the comparison position P 2  as a register error, as in the same way as in the first embodiment. Then, the calculation unit  28   a  instructs the control unit  28   b  to control printing misalignment in the rotary printing press  1 . The above angle range is, for example, a range from (90−α)° to (90+α)° with a being a constant, and the optimum value can be appropriately determined by an experiment or the like. 
       FIG. 8  is a diagram showing another image of the register mark  200 A captured by the image capturing unit  26  according to the second embodiment. In  FIG. 8 , the first line segment L 1  is inclined with respect to the transporting direction dt. Such a situation may occur, for example, when the web  30  moves in the lateral direction during a period after the printing of the first register mark  202  and before the printing of the first register mark  204 . 
     In the case where the angle θ formed by the first line segment L 1  and the second line segment L 2  in the image is outside the above angle range, the calculation unit  28   a  performs operation that is different from that in the case where the angle θ is within the above predetermined angle range. For example, when the angle θ is outside the above angle range, the calculation unit  28   a  instructs the control unit  28   b  to prohibit control over printing misalignment in the rotary printing press  1 . 
     As described above, according to the present embodiment, since the control over printing misalignment based on the register mark  200 A whose arrangement is different from the normal arrangement is prohibited, it is possible to suppress the control over printing misalignment that may be erroneous. Therefore, the accuracy for the control over printing misalignment can be improved. 
     Described above is an explanation of the present disclosure based on the embodiments. The embodiments are intended to be illustrative only, and it will be obvious to those skilled in the art that various modifications to constituting elements and processes could be developed and that such modifications are also within the scope of the present disclosure. 
     For example, in the above embodiment, an example in which the register error detection device  100  is applied to the rotary printing press  1  for gravure printing has been described; however, this is non-limiting. For example, the register error detection device  100  can be applied to a rotary printing press for offset printing. Further, as long as the rotary printing press  1  is a multicolor rotary printing press, the rotary printing press  1  is not limited to four color printing. 
     In the case where the two first register marks  202  and  204  are printed by the plate cylinder  20  of the first printing unit  12   a  and the second register mark  210  is printed by the plate cylinder  20  of the third printing unit  12   c , a register error can also be calculated in the same way as described above. In the case where the two first register marks  202  and  204  are printed by the plate cylinder  20  of the first printing unit  12   a  and the second register mark  210  is printed by the plate cylinder  20  of the fourth printing unit  12   d , a register error can also be calculated in the same way as described above. In this exemplary variation, in each printing unit  12 , printing misalignment can be corrected based on a register error calculated using, as a reference, first register marks  202  and  204  printed by the plate cylinder  20  of the same first printing unit  12   a . Therefore, the accuracy for correcting printing misalignment can be improved. In this exemplary variation, for example, in the case of four color printing, it is necessary to print three sets of two first register marks  202  and  204  in a line by the plate cylinder  20  of the first printing unit  12   a . Regarding this point, in the above embodiment, since the first register marks  202  and  204  that are small can be used, even a plate cylinder  20  having a relatively short circumferential length can cope with the situation. 
     Further, when the respective areas of the two first register marks  202  and  204  are different from each other in the image captured, the calculation unit  28   a  may correct a register error based on the areas. When the image capturing unit  26  is inclined in the transporting direction dt with respect to the surface of the web  30 , the respective areas of the two first register marks  202  and  204  are different from each other in the image. In this case, since the centroid of the two first register marks  202  and  204  that has been calculated contains an error, the register error is not accurate, either. In this exemplary variation, a more accurate registration error can be obtained in consideration of the influence of the inclination of the image capturing unit  26 .