Printing – Inkers – Fountains
Reexamination Certificate
2000-09-15
2002-09-10
Eickholt, Eugene (Department: 2854)
Printing
Inkers
Fountains
C101S211000, C101S484000, C101S350100, C382S112000
Reexamination Certificate
active
06446555
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to an apparatus for the densitometry measurement of printed products.
BACKGROUND OF THE INVENTION
Densitometers are used to control the quality of printing products by, for example, providing density values to control the feeding of ink by metering devices. To measure the density values, a measurement strip comprising a series of measurement fields assigned to different colors is printed alongside the printed image on the same sheet. In products printed by sheet-fed offset printing, the strips are printed at the beginning or the end of the printing procedure. In addition to being inspected visually as it is removed from the deliverer and placed on an underlay, a printed sheet with a measurement strip is also measured by a traversing densitometer. Thus, the ink density values associated with different colors in the measurement fields are measured and accumulated.
The structure of the measurement strips comprises zones that correspond to zones of ink metering in a printing machine. In general, an ink-metering zone marks a section comprising a series of measurement fields. The structure of a measurement strip provides information of the number of measurement fields in each ink-metering zone and the arrangement of the color densities in the zone.
For a given measurement strip, the pattern of colors in the series of measurement fields in an ink-metering zone may vary from zone to zone. For example, in one ink-metering zone the color cyan is assigned the third measurement field and in another zone the color cyan is assigned to the fifth measurement field. In this case, the measurement field for cyan may be located at the edge in one ink-metering zone and close to the center in the other zone.
The primary colors (cyan, magenta, yellow and black) are formed as either full-tone or halftone. Special colors can also be assigned to the measurement fields in the same ink-metering zone.
To measure the measurement strips described above, automatic densitometers with traversing measurement heads are employed. Densitometers of this type have been known for a long time, such as for example the CCI product from the Man Roland Druckmaschinen A G. With these automatic densitometers, a sheet to be measured is laid on the desk and aligned with stops. In a traversing of the strip, the positions of the measurement fields in each of the zones are determined and memorized. In a second traversing of the strip, the densitometry values obtained by corresponding densitometry filters are recorded and stored. The measured densitometry values are compared to predefined values. The results of the comparison are used to automatically adjust the ink-metering elements, each of which are associated with one of the ink metering zones.
The length of the measurement strip, especially the measurement fields assigned with individual colors within an ink-metering zone, extends to the maximum printing format (printing width). If the measurement strip is used for printed products having a format smaller than the maximum, the starting point of the measurement strip, which is the position from the center of the printing machine, does not coincide with the first ink-metering zone. Instead the strip may align its measurement field in such a way that the order of the colors are different than that expected, assuming the maximum format. In this situation, the limits of measurement fields with different colors and the optimum measurement position in the measurement fields can be determined by comparing the ink density values obtained from corresponding filters in a measurement run. But it still cannot determine which ink metering zone is assigned to the first measurement field.
Without additional information about the location of the fields, the densitometer and its associated control system for controlling the ink metering devices cannot determine the format width to use with the measurement strip. For this reason, known ink density measuring systems, in particular the densitometry system described above, have different modes of arranging the colors of the measurement fields between ink-metering zones, which can be taken into account in evaluating the measured data. One possibility for this is the identification of a field by analyzing the ink density values obtained by the various filters. As is known from the German Patent No. EP 0 370 126 B1, measurement fields of different color orders can be distinguished by comparing the ink density values obtained by the various filters (sensor channels). On the basis of this principle, it is possible to determine the structure of an unknown measurement strip by means of one measurement run, but this presupposes a previous detection run. One method for determining the optimum measurement position within a measurement field is described in European Patent No. EP 0274 061 B1.
One further possibility for taking into account the different arrangments of measurement fields in individual metering zones, which arises in the case of different formats, is to manually input where or in which zone the first (e.g., the cyan-colored) measurement field is located. For example, before measuring a first sheet, the operator inputs to the measurement system, via an appropriate input device, the fact that in the given format and in the measurement direction of the densitometer, the cyan measurement field is located in the first zone of the sheet at position 3 or that, in the measurement direction of the densitometer, the first measurement field of the zone on the extreme left has, for example, the color magenta. By way of this information, which has to be manually input, it is possible, taking into account the known measurement-strip structure (i.e., the arrangement of the individual measurement fields of different colors in the various metering zones) to determine the metering zone in which the measurement strip begins.
The possibilities outlined above for manually taking into account color measurement strips arranged in accordance with the printing-material format has the drawback that, as a result of incorrect input, incorrect measured values are obtained, or the measured values obtained cannot be assigned to the corresponding ink-metering zones. The derivation of actuating commands for controlling the zonal ink feeding is then not possible. In addition, any detection runs that may be needed are disadvantageous because of the additional expenditure of time.
SUMMARY OF THE INVENTION
The object of the present invention is, therefore, to expand a device for the densitometer measurement of printed products to the effect that a simple and fail-safe assignment of the measurement-field colors arranged in the individual ink metering zones is possible.
The invention provides for an evaluation unit that is connected downstream of the densitometer and comprises a computing device to compare the ink density values from one measurement field with the neighboring measurement fields of the same color and type (full-tone or half-tone) of measurement field. At the same time, it is taken into account that, within one measurement strip of known structure, the arrangement of the measurement fields assigned, for example, to the printing ink color cyan is known over the entire maximum format width and is different from zone to zone. On the basis of the knowledge of the structure of the measurement strip for the maximum format, the ink density value obtained on one measurement field of the color cyan is compared with the ink density value from the cyan measurement field in the zone N+1. The ink density profile runs smoothly over the width of the strip because of the ink cross-flow and in particular the ink distribution in offset printing machines. In other words, the ink density values of the cyan measurement fields in the metering zones N−1, N, N+1 do not exhibit any large steps in relationship to one another.
According to the invention, then, for the existing measurement fields in the metering zones, in conjunction with the known structure of the measur
Muller Joachim
Schramm Peter
Eickholt Eugene
Leydig , Voit & Mayer, Ltd.
Man - Roland Druckmaschinen AG
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