GB2282565A

GB2282565A - Registration in a multi-colour printing press

Info

Publication number: GB2282565A
Application number: GB9419119A
Authority: GB
Inventors: Richard D Lasken
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1993-09-22
Filing date: 1994-09-22
Publication date: 1995-04-12
Anticipated expiration: 2014-09-22
Also published as: GB9419119D0; JPH07214760A; DE4433905A1; GB2282565B

Description

1,.

DEVICE FOR OBTAINING REGISTRATION IN A MULTI-COLOUR PRINTER PRESS BACKGROUND OF THE INVENTION

The present invention relates to devices for obtaining registration in a multi-color printing press.

2282565 In the past, printing presses have been known having a plurality of cylinders for printing inks of different colors on a web of the press, with the cylinders separately placing the inks of different colors sequentially on the paper web. However, it is necessary to maintaining registration of the inks of different colors on the web, otherwise the press will print an image on the press which is blurred.

In the current registration systems, an operator of the press views the printed web, and makes adjustments to the press based on trial and error in an attempt to obtain registration of the cylinders on the press. in this procedure, the paper web is passed through the press, and the operator makes adjustments to the press while the press is running at slow speed, and the operator makes additional adjustments in order to obtain correct registration in the press. This procedure is very time consuming, thus resulting in excessive start-up time and procedure paper waste during the registration procedure.

The current automatic registration systems also can only bring a 4-color image to within close proximity of - registration, such as.007 inches, which is the correct not satisfactory. This procedure produces paper waste as the operator makes the.11final adjustments of the press. In addition, such systems require targets printed on the page which are undesirable or trimmed off creating waste.

SUMMARY OF-THE INVENTION

A principal feature of the present invention is the provision of an improved device to obtain registration in a multi-color printing press.

The device of the present invention comprises, means for forming a first image of an ink L- from a printed sheet having a first color, means for forming a second image of at least one other ink from the printed sheet having a second color, and means for comparing the first and second images.

A feature of the invention is that the press is corrected in response to the comparing means such that the first and second images are registered in the press.

Another feature of the invention is that a web of the printing press is stopped while the images are formed.

7 Still another feature of the invention is that four colors of ink in a four-color printing press may be processed such that the press may be corrected to register the four colors of ink on a printed web or sheet of the press.

Another feature of the invention is that the device also has means for separating the four colors through the use of color filters and different light sources to obtain a digitized composite of each component, and a device for creating an outline drawing from these images and comparing each image with another.

Yet another feature of the invention is that the images are formed by a suitable camera.

A further feature of the invention is that the camera may determine the light intensity at a plurality of positions on the printed sheet.

Another feature of the invention is that the sheet is illuminated by a source of light and a source of infrared rays.

A feature of the invention is-that the camera has suitable filters to determine at least 3 colors of ink on the printed sheet.

Yet another 4eature of the invention is that the infrared rays are utilized to determine the ink of the color black.

i Another feature of the invention is that the camera has a plurality of gray scales at each measured position of the printed sheet in order to determine the intensity oú the images at the plurality of positions.

Yet another feature of the invention is that outlines of the images of different colors of inks are formed.

Still another feature of the invention is that the outline images are compared to determine the difference in the outline images.

Another feature of the invention is that the compared outline images are formed from the inks of different colors at a plurality of laterally and longitudinally displaced positions for one reference image.

Yet another feature of the invention is that the outline images of the different colors of inks are compared at the different positions in order to determine the difference having least value.

5.

Still another feature of the invention is that the relative location of the outline images havinq the leas value represents the best fit of the images.

Another feature of the invention is that the differences of least values for the different compared inks is utilized to correct the press.

Yet another feature of the invention is that the various images of inks having different colors are superimposed at the positions of least value differences in order to obtain registration of the press.

A further feature of the invention is that images of different colors corresponding to inks of different colors are determined by the camera from the printed sheet.

Yet another feature of the invention is that the average light intensity or gray scale is determined for each of the images.

A further feature of the invention is that each of the images corresponding to different colors of inks are compared with the average light intensity associated with the image.

A feature of the invention is that if the intensity 6.

of the image at each position is less than the average intensity, then a minimum intensity is assigned to this position of the image.

Yet another feature of the invention is that if the intensity of the image at each position is greater than the average intensity, then a maximum intensity is assigned to this position of the image.

Still another feature of the invention is that the minimum and maximum intensity values for the various positions determined by the camera are utilized to form the outline images.

Another feature of the invention is that one of the outline images is superimposed on the other outline image.

Yet another feature of the invention is that the difference between the two superimposed images is determined.

Still another feature of the invention is that the difference between the two images is determined at a plurality of laterally and longitudinally displaced positions of the printed sheet.

A further feature of the invention is that the 7.

outline images are compared at the plurality of displaced positions in order to determine the location of minimum value of the difference.

A feature of the invention is that the closest match of the images at the plurality of displaced positions is utilized to correct the press, and superimpose images of different color on the printed web or sheet to obtain registration of the press.

Yet another feature of the invention is that each of the outline images of different colors are checked for a minimum difference at the plurality of position in order to obtain registratio'n of the press for all of the inks of different colors.

Another feature of the invention is that the device automatically registers the cylinders of the press by moving the cylinders horizontally and/or vertically based on the best fit information calculated from the various outline comparisons.

Yet another feature of the invention is that the press is registered in a simplified manner.

Another feature of the invention is that the press is registered in a more quick manner.

8.

Still another feature of the invention is that the device registers the press in a more accurate manner.

Yet another feature of the invention is that the device minimizes down time of the press, and minimize waste of the paper while obtaining correct registration of the press.

Still another feature of the invention is that a skew of a plate in the press may be determined, and the associated cylinder may be corrected to remove the skew of the plate.

Another f eature of the invention is thatt. the device also maintains the correct registratIon when the 1Dress is operating by continuing this process.

A further feature of the invention is that the device obtains registration automatically before running the press, and then holds the registration while running the press, which markedly reduces time and paper waste.

Further features will become more fully apparent in the following description of the embodiments of this invention, and from the appended claims.

9 DESCRIPTION OP TEE DRAWINGS

In the drawings:

Fig. 1 is a diagrammatic view of a dev!c6 to obtain registration in a multi-color printing press of the present invention; Fig. 2 is a diagrammatic view of a printed sheet or web of the press; Fig. 3 is a block diagram of the registration device of the present invention on the press; Fig. 4 is a diagrammatic view of the printed sheet showing a skew angle of an image on the sheet; and Pig. 5 is a diagrammatic view of cylinders for the press of Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Refereeing now to Fig. 1, there is shown a multi-color printing press generally designated 10 having a device generally designated 12 for obtaining registration in the press 10. As shown, the press 10 has a plurality of printing units 14, 16, 18, and 20 for o.

printing inks having a color such as cyan (C), magenta (m), yellow (Y), end black (K), with each of the printing units 14-20 having blanket cylinders 22 and 24 on opposed sides of a web or sheet 26 which passes through the press 10 to a folder 46, with each of the printing units 1420 applying inks of different colors to the web 26. As shown in Fig. 5, a pair of plate cylinders 23 and 25 may be associated with the blanket cylinders 22 and 24 respectively, with the plate cylinders 23 and 25 having outer plates for transferring inks. In an alternative form, the press 10 may have a plurality of print cylinders rather than the plate cylinders in order to directly form images on the print cylinders of the press 10.

As shown in Figs. 2 and 3, a coordinate system along x and y axes may be associated with the sheet 26, with the x axis extending longitudinally along the web 26, and -%he y axis extending laterally across the web 26. The coordinate system may be utilized as a reference while obtaining registration of the press 10.

As shown in Fig. 1, the device 12 has a pair of cameras 28 facing opposed sides 30 and 32 of the printed web or sheet 26, with both of the camera having an associated hood 34. As shown, the device 12 may have a plurality of idler rollers 36 disposed adjacent opposed sides of the viewing field of the camera 28 on opposed ill.

sides of the web 26 in order to stabilize the web 26 in the region of the cameras 28. Each of the came.ras 28 may have an associated light souzce 38, such as a fluorescent light, directed towards the web 26 for generating light rays in the visible region of electromagnetic waves having wavelength in the range of approximately 400- 700nm, and source of infrared rays 40 in the infrared region of electromagnetic waves directed towards the web 26, such that the sources 36 and 40 illuminate the sheet 26, and the light and infrared rays are reflected from the printed sheet 26 to the respective cameras 28. In this manner, the four-color images corresponding to four colors of inks on the printed sheet 26 may be viewed by the cameras 28 in order to obtain registration of the press 10, as will be described below.

In a preferred form, the cameras 28 comprise a CCD (charge coupled device) camera which has a plurality of sensors in the camera 28 for determining the light and infrared intensity at a plurality of positions on the printed sheet 26 corresponding to the pixels in the camera 28. Each of the pixels at the plurality of positions determine a relative light intensity or gray scale which may vary from a value 0 to a value 255 in a CCD camera having a 256 gray scale for each of the pixels of the camera 28 depending upon the intensity of the light or infrared rays. if necessary, the signals corresponding to : 2.

each of the pixels in the camera 28 may be digitized by a suitable A/D converter 42, and then may be supplied to a suitable computer 44 or Central Processing Unit (CPU)having a read only memory (RO14) and a random access memory (RAM), as shown in Fig. 3, where the data corresponding to the gray scales is stored in the memory of the computer 44 for subsequent processing.

The camera 28 preferably has a plurality of filters for the colors cyan, magenta, and yellow. In use, the three such visible colors are viewed and determined for each of the inks of different colors by the camera 28, and the information corresponding to each of the colored inks is supplied to the CPU where it is stored, as previously described. The source of infrared rays 40 may also be utilized to illuminate the printed sheet 26, and the corresponding signals determined by the camera 28 are supplied to the computer 28 for storage in the memory of the computer. The infrared rays are utilized to determine the color black in an image on the printed sheet 26, and is utilized in order to control the press 10 in printing the separate color black, since it is less expensive to print the color black by the printing unit 20, than to mix the other three colors to form an ink with the color black.

In a preferred form, as shown in Fig. 3, the CPU may 1 3.

be utilized to control the press 10 in order to move the printed sheet 26 very slowly beneath the cameras 28. The cameras 28 are utilized to determine when a printed image Is located in the viewing field of the cameras 28, at which time the CPU stops the cylinders of the press 10 in order to provide a clear viewing field of the printed sheet 26 by the cameras 28.

After viewing and storage of the data for the inks of different colors, the information is processed, as discussed below.

First, the CPU determines the average gray scale or intensity for each of the different images stored in the memory of the CPU, resulting in 4 different averages of gray scale corresponding to the four different colors of inks. Next, the average gray scale values of the different images is utilized as a threshold for the different images of different colors. If the gray scale or intensity of an image associated with a given color is less than the average gray scale or intensity for that color at each pixel or position of the datar then a minimum value of gray scale zero is assigned to this pixel. Iff however, the intensity or gray scale is greater than the average intensity or gray scale for the given color of ink, the pixel or position of the data is assigned a maximum value of intensity. T1;-s procedure is repeated for each of the 14.

images formed corresponding to the different colors of ink at each of the data points or pixels corresponding to the given image. In this manner, a Kodalith image is formed corresponding to the recorded images of the printed sheet 26.

Next, the data of maximum and minimum values is processed by the CPU in order to form an outline of the image for each color of ink corresponding to the printed image on the printed sheet 26. The outline images are preferred for further processing of the data, since 1) the correct registration is largely noted at the points of high contrast, and 2) the outline provides the critical information and discards all other unneeded information which produces a dramatic increase in the signal to noise ratios, and a more accurate comparison, which will be described below.

Next, one of the outline images is used as a reference image, such as the image corresponding to the ink of color cyan, and the other outline images, such as the magentat yellowl and black images are sequentially superimposed on the reference image, i.e., cyan in this case. After separate superimposition of the images on the reference images, each of the superimposed images is compared to the reference image by subtracting the outline values of the first colors from each of the second images t C.

15.

of other colors at each pixel or position, and the differences are summed, in order to obtain a total value of gray scale or intensity for each of the comp ared images. Hence, the CPU determines the total gray scale obtained by subtracting the outline images of magenta, yellowf and black from the reference image cyan, in order to obtain three different totals for the three comparison of images with the cyan outline image.

Next, further comparisons for the three colors magenta, yellow, and black are made at different displacements or increments longitudinally along the paper web 26, and laterally across the paper web 26, corresponding to the x and y axes, respectively. In one form, the positions may be sequentially displaced a distance of.001 inches along the x and y axes until a total distance of.2 inches is reached in a plus and minus direction along the x axis, and a total distance of.1 inches is reached in a plus and minus direction along the y axis. Hence, an image is formed lor the ink colors magenta, yellow, and black at each of the increments taken along the x and y axes, the additional images are stored in the memory of the CPU, and the outline images are formed, as previously described, corresponding to each of the inks of different colors at each of the increments along the x and y axes. Each of the outline images taken along the x and y axes are compared to the reference 1 6.

outline image (cyan), in order to form differences of the images for each of the inks of different colors at each of the displacements along the x and y axes, as previously described.

As the comparisons are made for each of the inks along the x and y axes, the CPU determines the smallest difference of comparisons along the x and y axes for each of the different inks, and the absolute value of the minimum difference values is retained while making the comparisons in order to form a minimum difference value of absolute value for each of the comvarisons between the magenta, yellow, and black inks, which represents the closest fit between the reference colored image (cyan), and each of the other colored images (magenta, yellow, and black), and which also represents the lowest total of gray scale or intensity determined from the comparisons. In this manner, the best fit of the shifts of minimum absolute value taken along the x and y axes are determined for use in displacing the cylinders to achieve registration for each of the compared images of different colored inks.

As shown in Fig. 3, the CPU utilizes this data representing the beet fit in order to correct the cylinders of the press 10, such an by modifying each of the cylinders separately through a lateral.and 17.

circumferential shift or suitable correction to the cylinders associated with the printed images o.f different colored inks. In this manne!r# registration is obtained between the superimposed images of the different inks through correction of the press 10, as controlled by the CPU or computer 44.

At this time, the press 10 may be started in order to print the web 26 with the press corrected as it passes through the viewing field of the cameras 28. If desired, viewing of the paper web 2.6 by the cameras 28 and correction of the press 10 may be continued during movement and printing of the web 26 by the press 10.

In this manner, the device 12 of the present invention automatically obtains and maintains registration of all the printed images having inks of different colors. The registration may be obtained without the tedious adjustments which were previously required by the operator of the press in order to approximate registration of the press 10. The press 10 is more accurately registered by the present invention, and also eliminates the paper waste previously produced by the prior registration procedures.

Another embodiment of the present invention is illustrated in Fig. 4, in which like reference numerals designate like parts. in this embodiment a skew.angle -18.

theta is determined between the desired x and y axes, and the rotated axes x, and y' due to skewing of one or more plates of the cylinders of the press for each color of ink in the press 10, with the angle theta being enlarged for purposes of clarity. The-translated axes x' and y' may be determined according to the following relationships:

1. x'=x(cos (theta))-y(sin (theta)), and 2. yl=x(sin (theta))+y(cos (theta)), where x and y are the original axes, and x' and y' are the translated axes. A motorized cocking adjustment may be added to the press, and corrections to the press 10 may be made according to relationships 1) and 2) in order to adjust the plates to correct skewing on the cylinders for each of the inks of different colors.

The foregoing detailed desc-ription has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

T.7 'm ":t 19.

CLAimg 1. A device for obtaining registration in a multi-colored printing press, comprising:

means for forming a first image of an ink from a printed sheet having a first color; means for forming a second image of at least one other ink from the printed sheet having a second color; means for comparing the first and second images; and means responsive to the comparing means for correcting the press such that the first and second images are registered an the printed sheet.

-he second forming 2. The device of claim I wherein 1. means forms an image of four colors in a four-color printing press.

1 3. The device of claim 2 wherein the colors comprise cyan, magenta, yellow, and black.

4. The device of claim 1 including means to illuminating said sheet.

7 70.

5. The device of claim 4 wherein the illuminating means illuminates the sheet separately with light and infrared rays.

6. The device of claim 5 wherein the forming means comprises a video camera, and in which the camera determines the colors of the inks.

7. The device of claim 6 wherein the camera has a plurality of filters to determine the different colors of inks.

8. The device of claim 1 wherein the correcting means comprises means for modifying the position of a plurality of cylinders in the press.

9. A device for obtaining registration in a multi-color printing press, comprising:

means for determining a first outline of an image of an ink having a first color from a printed sheet; means for determining a second outline of an image of an ink having a second different color from the printed sheet; means for comparing the outlines of the first and 21.

second images; and means responsive to the comparing means for correcting the press to obtain registration of the first and second images.

10. A device for obtaining registration in a multi-color printing press, comprising:

means for determining a first outline image of an ink having a first color from a printed sheet of the press; means for determining a second outline image of an ink having a second color from the printed sheet of the press; means for comparing the first and second images at a plurality oú different relative locations of the images on the sheet; means responsive to the comparing means for ascertaining the position of the closest match between the first and second images; and means responsive to the ascertaining means for correcting the press to superimpose the first and second images at the position of the closest match to register 22.

the press.

11. The device of claim 10 wherein the ascertaining means forms the closest matches between outline images of a plurality of inks of different colors from the printed sheet, and in which the correcting means modifies the press to obtain registration between the plurality of printed images of dilferent colors.

12. The device of claim 10 wherein the determining means comprises a camera to view the images on the printed sheet.

13. The device of claim 12 wherein the camera determines the light intensity at a plurality of locations on the printed sheet.

14. The device of claim 10 wherein the comparing means comprises means for subtracting the values associated with the images at a plurality of locations on the printed sheet.

15. The device of claim 10 wherein the comparing means compares the first and second images at a plurality of positions on the printed sheet.

16. The device of claim 15 wherein the comparing 23.

means compares the first and second images at a plurality of spaced positions laterally and longitudinally along the printed sheet.

17. The device of claim 10 wherein the correcting means comprises means for changing the position of a plurality of cylinders in the press.

18. A device for obtaining registration in a multi-color printing press, comprising:

means for viewing a printed web in the press; means for stopping the web at a position for viewing an image on the web by the viewing means; and means for correcting the press responsive to the viewing and stopping means.

19. A device for obtaining registration in a multi-color printing pressf comprising:

means for viewing a printed web in the press; means for determining the skew of a plate an a cylinder of the press; and 24.

means for correcting the skew of the plate in the press.

20. A device for obtaining registration in a multi-color printing press, comprising:

means for viewing an image on a printed sheet of the press, and for forming signals proportional to the light intensity of the image for a plurality of inks having different colors at a plurality of positions of the image on the printed sheet; means for determining the average light intensity of the viewed images at the plurality of positions on the nrinted sheet; means for determining the light intensity of the images at the plurality of positions; means for comparing the light intensity for the plurality of colors at the plurality of positions on the printed sheet with said average intensity, for assigning a minimum intensity to the values of light intensity less than the average intensity, and for assigning a maximum intensity to the values of light intensity greater than the average intensity; M 2 5.

means responsive to the comparing means for forming an outline image for each of said colors; means for comparing one of said outline images with an outline reference image.at a plurality of laterally and longitudinally displaced positions of the two images on the printed sheet, and for determining the position of the smallest value between the compared images; means responsive to the comparing and determining means for correcting the relative position of the compared images from the smallest determined value between the compared images; and means responsive to the correcting means for correcting the press to obtain registration of the images of different colors on the printed sheet.

21. The device of claim 20 wherein the viewing means comprises a camera.

22. The device of claim 21 wherein the light intensity comprises a gray scale at a plurality of positions of the camera.

23. A device for obtaining registration in a multi-color printing press, comprising:

96 f o r C2 leans deter.mining a first outline image of an ink having a first color from, a printed sheet of the press; ,leans for determi-ning a plurality of second outline images of a plurality of inks having a plurality of second dififerent colours from the printed sheet of the press; a .leans for separately comparing the first and plurality of second images at a plurality of different relative locations of the ima-es on the sheet; 0 means responsive to the comparing means for ascertaining the positions of the closest matches between the first image and plurality of second images; and 0 m .ea.is responsive to the ascertaining means for correcting the press to superimpose the first image and C2 0 plurality of second images at the positions of the 0 closest matches to register the press. 74. A device for obtaining registration in a multi- W coloured printing

press substantially as hereinbefore described and as shown in the aCCOITIDanying, drawings.

25. A nulti-colour printing press including a device as in any preceding claim.