Printing – Planographic – Processes of lithographic printing
Patent
1995-05-09
1996-10-29
Fisher, J. Reed
Printing
Planographic
Processes of lithographic printing
101148, B41F 724, G01B 1100
Patent
active
055687695
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for influencing or affecting the ink density of a printing ink layer on a printing substrate or a print carrier.
DESCRIPTION OF THE PRIOR ART
A process for monitoring the moistening supply in offset printing presses is known from DE 38 30 732 A1, by means of which not yet printed or printed surfaces, in the area of the edges of, or on predetermined colored surfaces are scanned by means of an opto-electrical converter and the signals generated in the course of this scanning are evaluated.
This process is disadvantageous in that the signals for changing the amount of moistener are only triggered when scumming occurs on a full-tone surface of the measuring field. This has the result that the quality of the pieces printed up to the removal of the printed control sheet is already reduced.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a process for evaluating fluctuations in the ink density in an offset rotary printing press.
The ink density or colorimetric value of a plurality of coloration and position defined ink spots on a printed surface is measured. This ink density or colorimetric value for each spot is then stored in a microprocessor as a plurality of set values which will define a good or acceptable level of ink density. During the operation of a printing press, the ink density or colorimetric values of the selected, positions defined measuring spots on the substrate to be checked, are measured. These production values are also entered into the microprocessor and the differences between these production values and the previously supplied set values are compared. If it is determined that the deviation of the production values from the set values has exceeded a certain level, the microprocessor will generate a signal that is used to control the rotational speed of a motor driving a moistener. The speed of rotation of the moistener will thereby be increased or decreased to decrease or increase the ink density or colorimetric value of the printing ink applied to the substrate.
The following advantages in particular ensue from the attainment of the object in accordance with the invention. As a result of the determination of the ink density over several adjoining zones, it is possible to maintain the ink density values constant or to evaluate these ink density values in a downstream-connected logical device, by means of which the amount of moistener can be continuously regulated. A signal for changing the amount of moistener is generated in this way prior to reaching the scumming threshold, so that for this reasons a lack in quality is avoided during printing. It is possible to give the operators or the automatic ink density control a hint or a signal whether and in which direction it is necessary to change the amount of moistener or the amount of ink in order to achieve a desired ink density again. Thus the process makes the detection of reasons for ink density changes in the coloration on a printing substrate easier.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in detail below by means of an exemplary embodiment. The associated drawings show in:
FIG. 1, a block wiring diagram of the arrangement of the device; and,
FIG. 2, a process flow chart in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The ink density of a printing ink layer of, for example an ink color control strip applied to a printing substrate 1, for example a printed sheet, and which may extend crosswise to the direction of movement of the printing substrate 1 and which has a plurality of measuring fields (measuring spots=with a standardized measuring surface) is measured by means of a densitometer or colorimetric measuring device 2. However, these can also be suitable measuring spots from the subject which may be printed crosswise to the direction of rotation of the printing substrate 1. A coloring zone of the colorization involved, for example "magenta", is produced in full tone and in seve
REFERENCES:
patent: 4881182 (1989-11-01), Hank et al.
patent: 4972774 (1990-11-01), MacPhee
patent: 5090316 (1992-02-01), Rodi et al.
Fisher J. Reed
Koenit & Bauer Aktiengesellschaft
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