Printing – Multicolor – Rotary machines
Patent
1998-07-16
1999-11-30
Fisher, J. Reed
Printing
Multicolor
Rotary machines
101DIG45, B41F 3316, B41F 3100, G01J 346
Patent
active
059923180
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to maintaining the densities of inks put down on a paper web as same is being fed from a multi-color printing press.
2. Description of the Prior Art
In a typical printing press, multi-colored data is printed repetitively on a web of paper fed from the press using a plurality of zone controlled inking units. The number of inking units corresponds to the number of different colors that may be applied to the web while the number of zones in a unit corresponds to the number of patches of ink that can be put down by a given inking unit.
The density of each patch is dependent on the amount of ink deposited on the paper during printing. Ordinarily, the amount to be deposited is preset prior to the commencement of a run.
From a quality standpoint, proper color density must be established and maintained throughout the run. In the past, there have been systems to monitor the quality of the print and correct it when there is a variation from a preset standard. This is accomplished by adjustment of the inking elements to change the amount of ink being deposited.
Prior art teaches some methods to detect the density of the ink laid down on the paper by evaluating a color bar with some type of detector means. Variations in density are noted and ink adjustments are made to correct for the variation. Examples of same are found in: Schramm, et al., U.S. Pat. No. 4,200,932; Lecha, U.S. Pat. No. 4,752,892; Brunner, U.S. Pat. No. 4,852,485; Keller, et al., U.S. Pat. No. 4,975,862; Pfeiffer, U.S. Pat. No. 5,122,977; Kipphan, et al., U.S. Pat. No. 5,182,721; and, Christie, Jr., et al., U.S. Pat. No. 4,003,660.
It is also known that video inspection is an important part of some process controls. A key element of the inspection of a high speed object, such as a printed web, is the synchronization of a stroboscopic light source and video source. This is done in such a way as to stop the action of motion with the area or object of interest in the field of view of the video source. An example of same is found in Gneuchtel, et al., U.S. Pat. No. 4,794,453.
SUMMARY OF INVENTION
The present invention differs from the known prior art, as typified by the above, in that, among other things, a standard RGB (red, green, and blue) CCD (charge coupled device) camera is utilized to translate what is seen in an image of the color patch to density. This achieves higher quality print. The invention further differs from the prior art by providing greater precision of synchronization of the stroboscopic light source and video acquisition relative to the color bar. This allows for acquisition of color bars with widths of 2 mm or greater to be scanned at press speeds in excess of 3,000 feet per minute. A still further distinction is that in our present invention, lateral movement of the web, web shrinkage, distortion and changes in position of the printed data on the web relative to the centerline of the moving web are compensated for dynamically. This allows for precise lateral positioning of the scanning head relative to the color patch. Another difference is our unique stroboscopic light source assembly including its light guide system to provide even illumination across the area of interest without producing electromagnetic interference which would degrade the video signals.
Accordingly, an object of the invention is an improved system for establishing and maintaining ink density of inks put down on a paper web as it is being fed from a printing press with press speeds in excess of 3,000 feet per minute.
Another object of the invention is a system that will scan both sides of the web independently to establish correct ink density quickly upon press start up. This reduces the time it takes to produce acceptable impressions.
Still another object of the invention is to minimize encroachment on the usable portion of a paper web by decreasing the width of the color bar to 2 mm.
A further object of the invention is to use a unique method to dynamically synchronize the strob
REFERENCES:
patent: 4003660 (1977-01-01), Christie, Jr. et al.
patent: 4681455 (1987-07-01), Jeschke et al.
patent: 4794453 (1988-12-01), Gnuechtel et al.
patent: 5029527 (1991-07-01), Jeschke et al.
patent: 5122977 (1992-06-01), Pfeiffer
patent: 5128879 (1992-07-01), Greve et al.
patent: 5141323 (1992-08-01), Kipphan et al.
DiBello Dominick J.
Ham, Jr. Thomas J.
McKenna Bruce
Fisher J. Reed
Perretta Graphics Corporation
Spiegel Joseph L.
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