Method and apparatus for registering color in a printing press

A method and apparatus for determining color registration in a multi-color printing press having a plurality of printing stations. A process black registration mark is formed in an identified area by positioning a plurality of color registration marks on top of each other. The process black registration mark is position in a portion of the image that is intended to be printed black, and preferably adjacent to a black ink image. The identified area is examined to determine whether the process black registration mark is properly positioned.

FIELD OF THE INVENTION 
The invention relates generally to color registration in a multi-color 
printing press. 
BACKGROUND OF THE INVENTION 
In multi-color printing, colors are laid down on a moving web by separate 
printing units which print in different colors such as cyan, yellow, 
magenta, and black. The images printed by the separate printing units must 
be printed one on top of the other. This is known as color registration. 
Closed loop control of color registration has been previously proposed. 
See, for example, U.S. Pat. No. 4,546,700, issued to Kishner et al. and 
incorporated herein by reference. Kishner et al. discloses a method and 
apparatus for automatically sensing and maintaining registration of each 
of the color cylinders in a multi-color printing press. Predetermined 
register marks are printed in non-image areas on the sheet to be printed. 
A register mark for each process color is printed in the same location as 
a corresponding black reference register mark. The reference register 
marks are configured such that the average reflectance of the printed 
overlay will change as the registration of the color image changes with 
respect to the black image. The reflectance of each printed overlay is 
measured on the printing press, while the sheet is moving. One type of 
sensor that can be used for this measurement is an on-press densitometer. 
If desired, the reflectance information obtained thereby can be converted 
to a registration error signal and used to achieve automatic, closed-loop 
control of the position of each of the color cylinders. 
See also, for example, U.S. Pat. No. 4,534,288, issued to Brovman and 
incorporated herein by reference. Brovman proposes a unified system for 
detecting misregistration and for ink density control in a four color 
printing press. A color bar having 136 square fields is printed in a 
non-image area normally trimmed or otherwise removed from the finished 
product. The color bar includes register fields. The percentage of non 
print area in register indicia is detected and used to control register 
adjustment mechanisms of the press. 
As evidenced by the Kishner et al. and Brovman patents, closed loop color 
registration systems typically require marks to be printed outside the 
image areas of a sheet, usually in a margin. In addition, closed loop 
color registration systems typically require a separate registration mark, 
spaced from the other registration marks, for each color. 
SUMMARY OF THE INVENTION 
The inventor of the present invention has recognized that much waste is 
produced by color registration systems that require registration marks 
outside printed areas of a sheet, and that require separate, spaced 
registration marks for each color. The margin containing the registration 
marks must be removed from the image area, requiring an additional step in 
the printing process, and further resulting in wasted paper. In addition, 
use of separate and spaced registration marks for each color utilizes 
excess space on the web. 
The invention provides a method for determining color misregistration in a 
multi-color printing press having a plurality of printing stations that 
each include a plate cylinder and that each prints a color image on a web 
with a predetermined color of ink. The colors printed by the plurality of 
printing stations cooperate to produce process black. The method includes 
the steps of identifying an area of the desired image that is intended to 
be printed in black, and forming registration images on the plate 
cylinders of the printing stations. The registration images are positioned 
on the plate cylinders such that, during subsequent printing operations, 
they will produce color registration marks that cooperate to print a 
process black registration mark on the web in the identified area when the 
printing stations are in registration. The method further includes the 
steps of applying ink to the plate cylinders, forming the color images on 
the web, examining the identified area with an apparatus capable of 
distinguishing the colors printed by the printing stations, and generating 
an error signal if the examining apparatus senses that the color 
registration marks are not in a desired registration to form the process 
black registration mark. 
The invention further provides a multi-color printing press including a 
plurality of printing stations, each printing station including a plate 
cylinder that prints a color image on a web with a predetermined color of 
ink. The plate cylinders of the printing stations include registration 
images that are positioned on the plate cylinders such that they will 
produce color registration marks that cooperate to print a process black 
registration mark on the web in an identified area when the printing 
stations are in registry. The printing press further includes examining 
means capable of distinguishing the colors printed by said printing 
stations, and means for generating an error signal if the examining means 
senses that the color registration marks are not in a desired registration 
to form the process black registration mark. 
The invention further provides a method of determining color registration 
in a multi-color printing press having a plurality of printing stations. 
The method includes the steps of passing a web through the plurality of 
printing stations, printing color registration marks that cooperate to 
print a process black registration mark on the web when the printing 
stations are in registration, examining the process black registration 
mark, generating an output signal corresponding with a color variation of 
the process black registration mark, and generating an error signal if the 
output signal indicates that the color registration marks are not in a 
desired registration to form the process black registration mark. 
The invention further provides a method comprising the steps of passing a 
web through the plurality of printing stations, printing a process black 
registration mark on the web, printing a black ink image on the web 
adjacent to the process black registration mark, examining the process 
black registration mark and the black ink image, and generating an error 
signal if the process black registration mark is not in desired 
registration relative to the black ink image. 
Other features and advantages of the invention will become apparent to 
those of ordinary skill in the art upon review of the following detailed 
description, claims, and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Shown in the various figures is a multi-color printing press 10 embodying 
various features of the invention. The printing press 10 includes a spool 
support 12 which supports a spool 14 of web material 16 such as paper. 
The printing press 10 includes printing stations 18, 20, 22, and 24, each 
of which prints in a different color. In the illustrated embodiment the 
first printing station 18 encountered by the web 16 prints with black ink, 
and the other printing stations 20, 22 and 24 print with other colors. For 
example, in the illustrated embodiment, the printing station 20 prints in 
magenta ink, the printing station 22 prints in cyan ink, and the printing 
station 24 prints in yellow ink. It should be understood, however, that 
the invention is capable of being carried out with printing stations that 
print in different colors, or with more printing stations. The printing 
press 10 includes a drive system 26, including drive rollers 28, that 
moves the web material 16 from the spool 14 through each of the printing 
stations 18, 20, 22, and 24. The images printed by the printing stations 
overlap to define composite multi-color images on the travelling web 16. 
Each printing station 18, 20, 22, and 24 includes a pair of parallel 
rotatable blanket cylinders 30 and 32 that nip therebetween the web 16. 
Each printing station 18, 20, 22, and 24 further includes a plate cylinder 
34 which has a printing plate thereon, and which applies an ink image to 
the blanket cylinder 30. Optionally, if it is desired to print both sides 
of the web 16, each printing station 18, 20, 22, and 24 will further 
include a plate cylinder 36 which has a printing plate thereon, and which 
applies an ink image to the blanket cylinder 32. The blanket cylinders 30 
and 32 transfer the ink images, received from the plate cylinders 34 and 
36, to the web 16. 
After exiting the printing stations 18, 20, 22, and 24, the web 16 is 
guided through various components as desired, such as a dryer 38, a chill 
stand 40, a coating machine 42, and a former/folder 44. 
For simplicity, registration control for images on only one side of the web 
16 will be hereinafter described. It should be understood, however, that 
registration control for images on the other side of the web 16 can be 
carried out by simply duplicating structure and the steps that will be 
hereinafter described. 
The printing press 10 further includes a registration control system 46 
which maintains registry of the images printed on one side of the web 16 
by the separate printing stations 18, 20, 22, and 24. The registration 
control system 46 determines the extent of misregistration between the 
images printed by the printing stations 18, 20, 22, and 24, and generates 
signals for appropriately adjusting the printing stations 18, 20, 22, and 
24, as described in more detail below. 
Instead of printing registration marks in a margin or non-image area that 
is normally separated from the finished printed product, a novel 
registration mark 48 is printed in the image portion of the web. An area 
or spot in the image portion that is normally printed with black ink is 
identified and is instead printed with process black. For example, a 
portion of the printed letter or character is printed with process black 
(see FIG. 3) instead of black, as would normally be expected. Process 
black results from printing colors, such a cyan, yellow, and magenta, over 
one another. Thus, to define the registration mark 48, the printing 
stations 20, 22, and 24 print marks 50, 52, and 54, respectively, one over 
the other. 
More particularly, during press set up, respective mark images are formed 
on the respective plate cylinders 34 of the printing stations 20, 22, and 
24. The mark images are positioned on the plate cylinders 34 such that 
they will print registration marks 50, 52, and 54, respectively, one on 
top of the other to define the process black composite registration mark 
48 on the web 16 in the identified area when the printing stations 18, 20, 
22, and 24 are in registry. Further, the mark images are positioned on the 
plate cylinders 34 of respective printing stations 20, 22, and 24 such 
that the printing stations 20, 22, and 24 will print the registration 
marks 50, 52, and 54 one on top of the other so that the process black 
registration mark 48 is aligned and continuous with a mark 55 printed in 
black ink by the printing station 18 when all of the printing stations 18, 
20, 22, and 24 are in registry with one another. 
A human observer of the finished product is not able to distinguish the 
process black registration mark 48 from the black ink. This is 
particularly true because only a small portion of the image area is 
printed with process black (e.g., only a portion of one alpha-numeric 
character on a page of a magazine, book, or newspaper, is printed with 
process black). 
The registration control system 46 further includes an electronic viewing 
device 56 which is capable of distinguishing the colors printed by the 
printing stations 20, 22, and 24, and which is capable of distinguishing 
process black from black ink printed by the printing station 18. The 
viewing device 56 could be a color camera such as a color video camera, a 
densitometer, a spectrograph or other device employing a CCD array or 
photodiodes, or other appropriate viewing device. In the preferred 
embodiment, the viewing device 56 is a combination color and infrared 
camera utilizing CCD arrays. Such a camera can be produced by adding an 
infrared channel to a standard color CCD camera. For example, a dichroric 
mirror can be used to pass visible light to a standard CCD array, and to 
reflect infrared light to an appropriate infrared CCD array. In some cases 
the infrared filter from the camera may need to be removed and an infrared 
pass filter may need to be added. The viewing device 56 is positioned to 
view the area containing the registration marks printed by the printing 
stations 20, 22, and 24 after the web 16 exits all of the printing 
stations. A system capable of performing the functions of the present 
invention is set forth in U.S. Pat. No. 5,412,577, which is incorporated 
herein by reference in its entirety. 
Each printing station further includes adjusting mechanisms 58, 60, and 62 
for adjusting the plate cylinder 34 of that printing station in 
longitudinal, circumferential, and skew directions, respectively. The 
longitudinal, circumferential, and skew directions are indicated by arrows 
64, 66, and 68, respectively. Each adjusting mechanism 58, 60, and 62 
includes a motor, hydraulics, or other suitable movement effecting 
structure for adjusting the plate cylinder 34. Such adjusting mechanisms 
are well-known in the art, as evidence by U.S. Pat. No. 3,806,012 to Roch, 
which is hereby incorporated by reference in its entirety. 
The registration control system 46 includes a computer or microprocessor 
70, that receives image data from the viewing device 56 and that 
calculates or determines by how much the plate cylinder 34 of each 
printing station 18, 20, 22 or 24 that is out of register should be 
adjusted in the longitudinal, circumferential, and skew directions 64, 66, 
and 68, respectively. More particularly, the computer determines whether 
the viewing device 56 indicates a color (i.e., something other than 
process black) where the process black composite registration mark 48 is 
expected. If so, appropriate calculations are made for adjusting the 
printing station 20, 22, or 24 that prints in the color (magenta, cyan, or 
yellow) that is not lined up with the other registration marks 50, 52, or 
54. The computer 70 also determines whether the viewing device 56 
indicates that the process black registration mark is aligned and 
contiguous with black ink printed by the black printing station 18. If 
not, the computer 70 makes appropriate calculations for adjusting the 
black printing station 18. 
One method and apparatus for making calculations for adjusting a printing 
station is disclosed in U.S. Pat. No. 4,887,530, issued to Sainio on Dec. 
19, 1989, assigned to the assignee of the present invention, and 
incorporated herein by reference. In order to make appropriate 
calculations for adjusting the printing station 18, the computer or 
microprocessor 70 determines the center 72 of the process black area where 
the register marks 50, 52, and 54 overlap, determines the width w and 
length of 1 of the process black area where the register marks 50, 52, and 
54 overlap, and determines the distance d from the center 72 to the black 
ink mark 55. If the measured values for width w, length 1 and distance d 
fall outside of a predetermined tolerance from a predetermined value, the 
microprocessor will know that corrections need to be made. 
The computer or microprocessor 70 communicates with the adjusting 
mechanisms 68, 58, and 62 of each printing station 18, 20, 22, or 24 to 
move the plate cylinder 34 of each out of register printing station in the 
longitudinal, circumferential, and skew directions 64, 66, and 68, based 
on the calculated amounts, so as to bring the printing stations 18, 20, 
22, and 24 in registry with one another. For example, if based upon 
information received from the viewing device 56, the microprocessor 70 
determines that the cyan mark 52 is only present at one of the four 
corners of the identified area, as shown in FIG. 4, then the 
microprocessor will know that the printing press that prints the cyan 
color will need to be adjusted to move the cyan mark 52 appropriately. The 
same process can be performed for each of the colors until the values for 
w, 1 and d are within the predetermined acceptable range. 
It should be appreciated that, once the specifics of the error are 
detected, the method for correcting the error can be performed in many 
different ways and using many different apparatuses, as is generally known 
in the art, and as evidenced by the patents incorporated by reference into 
this patent application. 
Thus, the invention provides a color registration system wherein it is not 
necessary to provide a margin for registration marks, and wherein a human 
viewer of the final printed product is not aware that the final printed 
product contains a registration mark. 
While a preferred embodiment of the invention has been described, various 
modifications are possible. Thus, the scope of the invention is to be 
limited only by the scope and spirit of the following claims.