EP1767364A1

EP1767364A1 - On-line method and system for monitoring and adjustment of printing conditions and materials of a press field of the invention

Info

Publication number: EP1767364A1
Application number: EP06396015A
Authority: EP
Inventors: Ulla c/o Oy Keskuslaboratorio - Mattila; Heidi c/o Oy Keskuslaboratorio - Reinius; Andrew Ytkemiska Institutet Ab Fogden; Joakim Ytkemiska Institutet Ab Voltaire
Original assignee: Keskuslaboratorio - Centrallaboratorium Oy AB
Current assignee: Keskuslaboratorio - Centrallaboratorium Oy AB
Priority date: 2005-09-22
Filing date: 2006-09-08
Publication date: 2007-03-28
Also published as: FI20050945A; FI20050945A0

Abstract

The invention relates to an on-line method for monitoring the printing conditions and materials of a press, in which method an acoustic signal is gathered from the printing nip of a printing unit; the acoustic signal is divided into a signal of a non-image area and image area; the acoustic signal of the non-image area and/or image area is analyzed; the analysis results and/or their changes are followed; and when necessary, the measures required by the analysis results and/or their changes are taken. Moreover, the invention relates to an on-line system for monitoring the printing conditions and materials of a press.

Description

The present invention relates to an on-line method and system for monitoring the printing conditions and materials of a press.

BACKGROUND OF THE INVENTION

On-line acoustic measurement can be used to monitor ink film layer splitting and characterize the properties of the ink layer in an offset nip of an offset press. It has been shown that when the amount of fountain solution in the ink increases, the intensity of an acoustic signal decreases indicating lower film splitting force at a nip exit. Likewise, the signal decreases when changing from high to low tack ink. Moreover, due to weaker cohesive forces, a non-image area produces typically a significantly lower sound intensity than an image area. This prior art is described e.g. in articles Voltaire et al.: Acoustic characterization of film splitting in a HSWO printing nip, International Printing and Graphic Arts Conference, Vancouver, British Columbia, Canada, October 4-6 2004 (pages 21-27) and Iwasaki et al.: Study of paper releasing phenomena in offset printing by acoustic approach, 45th Annual TAGA Conference, April 25-28, 1999, Minneapolis (pages 238-253).
Publication JP 2003-072036 discloses a monitoring system of a press based on acoustic measurement. To optimize the print quality of a press, the system uses printing sound gathered from a press and caused by an unfavorable change in the balance of the feeds of the ink and fountain solution. The optimization is performed by adjusting the feed units of ink and fountain solution.
A problem with known monitoring systems of a press is that it reacts poorly to changes that do not occur until in the printing nip as the ink is transferred to the printing substrate. A prior-art system uses sound gathered from the feed rollers of ink and fountain solution, and cannot observe, for example, the changes in sound which are caused, for example, by the printing substrate and correlate with the changes in the print quality.

OBJECTIVE OF THE INVENTION

It is an objective of the invention to eliminate the disadvantages referred to above.
One specific objective of the invention is to disclose a novel on-line monitoring method of a press that is susceptible to changes occurring in the printing conditions and materials and can be used to closely monitor the printing conditions and materials and the changes occurring in them. One further objective of the invention is to disclose an on-line monitoring method and system of a press that is well suited for controlling the accumulations of the non-image area of a printing unit and for closely optimizing the washing cycles of the blanket.

SUMMARY OF THE INVENTION

The monitoring method of a press, according to the invention, is characterized by what has been presented in claim 1.
The monitoring method of a press, according to the invention, is characterized by what has been presented in claim 13.
The invention is based on research work which studied the acoustic on-line measurement occurring in the printing nip of a press and in which it was surprisingly found out that it is possible to divide the acoustic signal gathered from the printing nip into parts corresponding to the different areas of the printing area. After the division of the signal, it was found out that the sound intensity produced by the non-image area and the image area changes as a function of the number of copies printed. A novel feature in the invention is, in particular, the fact of linking the increase in the intensity of a sound produced by the non-image area and the decrease in the intensity of a sound produced by the image area to all types of accumulations being formed on a blanket.
In the invention, a non-image area is used to mean an area whose dot percentage on the press plate of a printing unit is less than 50%. An image area is used to mean an area whose corresponding dot percentage is over 50%.
According to the method of the invention, an acoustic signal is gathered from the exit of the printing nip of a printing unit; it is divided into a signal of a non-image area and image area; and the acoustic signal of a non-image area and image area is analyzed. Further, the method follows the analysis results and/or changes in them and, finally, where necessary, the measures required by the analysis results and/or their changes are taken.
An acoustic signal can be gathered from the exit of the printing nip using any sensor suitable for gathering an acoustic signal, such as a microphone. By means of a sensor, the sound being produced at the exit of the printing nip is transferred to a converter such as an A/D converter and is digitized. Thereafter, the converted signal is divided into a signal of a non-image area and image area and is analyzed. To divide and analyze the signal, known processing algorithms of an acoustic signal are used, and they are implemented on a computer.
The signals of a non-image area and image area are separated from one another and analyzed using a suitable signal processing method. The separation can be performed by means of an image area and/or triggering. The analysis can be made by converting the signal into a frequency presentation using a suitable algorithm, e.g. an FFT or Wavelet conversion.
At the step of gathering and/or prior to the division and/or analysis of the acoustic signal, other disturbing factors such as vibration of the press or background noise can be eliminated from the acoustic signal to strengthen the right signal gathered from the printing nip that represents the sound of the non-image area and/or image area and that of the accumulations. An acoustic signal can be filtered using, for example, band-pass filtering and/or processed by using, for example, time frequency analyses and/or other suitable signal processing methods. A filtered signal can be strengthened when necessary.
In the method in accordance with the invention, it is possible to analyze any parameters of describing the variations of an acoustic signal of a non-image area or image area. These parameters can include power, intensity, power spectrum density, signal variance, mean value or median of an absolute value, or other corresponding parameters describing the variation of a signal. Known algorithms are used for the analysis of the parameters describing the variations of an acoustic signal.
It is also possible to analyze just a part of a signal that is above or below a given limit value.
In one preferred embodiment, the method analyzes the power and/or intensity of an acoustic signal of a non-image area using known algorithms. Sound power and/or intensity produced by a non-image area changes as a function of the number of copies printed. The increase in the power and/or intensity of the sound frequencies corresponding to the sound of the accumulations of a non-image area is associated with the formation of all types of accumulations on the blanket.
In another preferred embodiment, the method analyzes the power spectrum density of an acoustic signal of a non-image area, the power spectrum density being also linked to the formation of all types of accumulations on the blanket.
In still another preferred embodiment, the method analyzes the intensity of an acoustic signal of an image area using known algorithms. The intensity of a sound produced by an image area changes as a function of the number of copies printed. The decrease in the intensity of an image area is associated with the formation of accumulations on the blanket.
In the method of the invention, the starting point of the signal being analyzed can be any point in the non-image or image area. Usually, the starting point of a signal is selected by using triggering at the step of gathering the signal and/or by means of the periodic nature of the print pattern and that of the signal.
An acoustic signal is continuously gathered and analyzed during the running of the press. The changes in the analysis results are followed by comparing the results to the results after the starting moment of printing and/or after the washing, whereby the non-image area and image area of the blanket represent pure accumulations. The comparison uses a change value representing the formation of accumulations, the change value being a quotient of the results obtained from the moment of time of analyzing and starting/washing.
The changes of the analysis results can also be followed by comparing the changes to the results given by a reference sample which is used to obtain a good printing result. The printing conditions of a good reference sample can be reset by adjustment of the settings of the press. The comparison uses a change value which is a quotient of the analysis results and the results given by the reference sample.
The changes in the analysis results given by the non-image area can also be followed by comparing the results to the results of the image area.
Similarly, the changes in the analysis results given by the image area can also be followed by comparing the results to the results of the non-image area.
The change value depends on several different factors affecting the printing process and materials, including the press, printing conditions, the intended print quality, paper, ink, etc. The change value is specific to each printing process.
Measures are taken usually when the change value of the non-image area, which is to be followed, is over 3, usually about 3-5, times bigger than the reference value.
Measures are taken usually when the change value of the image area, which is to be followed, is smaller than the reference value of the starting point.
In one embodiment, the power and/or intensity of the acoustic signal of the non-image area and image area is analyzed simultaneously. The power and/or intensity of the acoustic signal of the image area gives additional information on the print quality.
Measures required by the analysis results and/or their changes include adjustment of the process conditions or materials. The signal level of a non-image area and image area is typical of the given process conditions and materials. The feed level of fountain solution has a great influence on the process conditions, and its addition decelerates the formation of accumulations. Also, the ink and its tackiness, as well as the paper to be used have an effect on the signal level of the non-image area. The formation of accumulations is slower with a lower-tack ink. Other factors having an effect on the process conditions include the printing speed.
In one embodiment, the accumulations of the non-image area and image area of a printing unit are controlled based on the analysis results by adjusting the process conditions. The adjustment can be a manual or an automatic adjustment based on the feedback of the press. Preferably, the adjustment is made by adjusting the amount of fountain solution to a level that prevents the formation of accumulations on the blanket.
In another embodiment, the washing cycles of the printing unit are optimized based on the analysis results. A washing cycle can be started when one exceeds the change value of the power and/or intensity of an acoustic signal of a non-image area and/or when one goes below the change value of the intensity of an acoustic signal of an image area. The washing cycle is started either manually or with an automatic adjustment based on the feedback of the press.
The method of the invention can be used in presses operating with different printing methods, such as in printing units operating with the offset, flexography, gravure printing and/or electrophotography principle.
The invention also relates to an on-line system for monitoring the printing conditions or materials of a press. The system comprises a printing unit, means for gathering and analyzing an acoustic signal, as well as means for dividing the acoustic signal into a signal of a non-image area and image area, and means for following the analysis results and/or changes.
In one embodiment of the invention, the printing unit is a part of an offset press. The means for gathering an acoustic signal can be a microphone (1), and the means for analyzing the acoustic signal and for following the analysis results and/or changes can be an algorithm such as an FFT or Wavelet conversion that converts the signal into a spectral form. Prior to the signal analysis, an acoustic signal can be converted into a digital form using an analog-to-digital converter. A suitable signal processing program can be used as a means of signal division into a signal of a non-image area and image area. Preferably, the means for signal analysis, division and follow-up of results and/or changes are located on the same computer.
The system can comprise means for filtering and/or strengthening the signal.
The system can also comprise a feedback mechanism for adjusting the printing conditions of the printing unit. The system typically adjusts the amount of fountain solution and/or ink and/or it can start the washing of the blanket.
Moreover, the system can comprise an alarm mechanism that alarms the operator when one exceeds the change value of the non-image area or goes below the change value of the image area. The operator makes the necessary adjustments and/or starts the washing.
Thanks to the invention, the printing conditions or materials of a press can be controlled and, when necessary, continuously adjusted so that no accumulations are formed on the non-image area or image area, and that the print quality remains uniformly good during the entire printing process.
Further thanks to the invention, the washing cycles of the blanket can be optimized. This also improves the print quality and decreases the amount of waste paper.
Moreover, the method and system of the invention can detect changes in all types of processes in which uncoated or coated paper is attached to a roller.

LIST OF FIGURES

Fig. 1 illustrates gathering and analyzing of an acoustic signal at the exit of a printing nip of a printing unit.
Fig. 2a represents the differences of an acoustic signal in a non-image and image area, as well as the effect of accumulations on the variations of the signal.
Fig. 2b represents the effect of the formation of accumulations and the washing on the power spectrum density of an acoustic signal in a non-image and image area.
Fig. 2c represents the change of the power of an acoustic signal as a function of time in a non-image and image area in normal printing conditions, in conditions in which the print density has been increased, as well as in conditions in which the print density and feed of fountain solution have both been increased simultaneously.
Fig. 3 represents the effect of ink and paper on the power of an acoustic signal gathered in a non-image and image area.
Fig. 4 represents the effect of a good sample, toning and water marking on the power of an acoustic signal gathered in a non-image and image area.
Fig. 5 represents the effect of the number of copies on the power spectrum density of an acoustic signal in a non-image and image area.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The test studied the effect of the formation of accumulations and washing on the power spectrum density of an acoustic signal in a non-image and image area. Moreover, the test studied the effect of the printing conditions on the power of the signal in a non-image and image area by increasing the print density and by increasing both the print density and the feed of fountain solution.
The test was carried out using a heat-set press, as shown in Fig. 1. The acoustic signal was gathered by a microphone (1) which was placed at the exit of the printing nip of the printing unit as close as possible to the non-image and image area of the blanket (2) and the paper (3). The signal was digitized using an analog-to-digital converter (4) and divided into signals of a non-image and image area and analyzed by the aid of a computer (5). The frequency range of the microphone being used was 10 to 100 kHz.
Fig. 2a shows the acoustic signal gathered as the accumulations are being formed and after the washing, whereby there are no accumulations. In the figure, the signals have been shifted in the vertical direction for the purposes of imaging. The signal parts used in the analyses are denoted by a line. A distinct difference in the variations of an acoustic signal is detected in the non-image area as the accumulations are being formed and as the signal changes from a signal of a non-image area into a signal of an image area.
Fig. 2b shows the power spectrum densities (PSD) of the signals (see Fig. 2a) of the image area and non-image area. The figure shows that the power spectrum density of the image area is susceptible to the formation of accumulations in the frequency range 6 - 35 kHz. On the other hand, the power spectrum density of the non-image area considerably changes at the frequencies of about over 6 kHz, the change being the biggest at high frequencies.
Fig. 2c shows the power of an acoustic signal in a non-image and image area when using frequency filtering. In the figure, the power of the non-image area is denoted by squares and the power of the image area by triangles. The tests were carried out 1) in normal printing conditions (dashed line), ii) in conditions in which the print density had been increased by 0.2D units compared to normal conditions (unbroken line), and iii) in conditions in which the print density had been increased by 0.2D units compared to normal conditions and the feed of fountain solution had been increased (dotted line). After the washing of the blanket, the powers of the acoustic signals always returned to the same level.
In Fig. 2c, the acoustic powers of a non-image area and image area are compared at frequencies over 35 kHz. The power from the non-image area clearly monitors the build-up of accumulation, whereas the power from the image area is less affected by it. The printing conditions have a major effect on the build-up of accumulation, which can be clearly seen in the power monitored from the non-image area. Thus, in practice, the press or the control system of the press can adjust the conditions in which the build-up of accumulation is insignificant using the measurement of acoustic power.

Example 2

The test studied the effect of the surface texture of paper and the tackiness of ink on the average acoustic powers measured from a press a) from an image area and b) from a non-image area.
As the ink, low-tack and high-tack cyanic color was used and as the paper six different sorts of paper. The test was carried out using a press, as shown in Example 1. In addition, the signals were filtered using a high-pass filter at the frequency of 8 kHz prior to the analysis.
The results of the test are shown in Fig. 3. The circled points indicate the reference points of the test at the beginning and end points of the trial run. A trial using paper sort 1 shows an increase in signal level in a non-image area, which is due to the build-up of accumulation on the blanket.

Example 3

The test studied the effect of a good printing sample, toning and water marking on average acoustic powers measured from a press a) from an image area and b) from a non-image area.
The tests used low-tack ink (Hydrophilic 2) and paper A. The acoustic signal was gathered from the printing nip of the lower printing unit of a heat-set press.
The results are shown in Fig. 4. The results show that toning causes a clear increase in the signal level of a non-image area. Addition of fountain solution decreases the signal level.
The printing conditions of a good printing sample can be reset by settings of the press.

Example 4

The test studied the effect of the accumulations being formed on a blanket on the power spectrum density of an acoustic signal in an image area and non-image area when printing uncoated paper. The test was carried out using a heat-set press. As the ink, high-tack heat-set ink was used, and the build-up of accumulation was monitored using acoustic measurement at the exit of the printing nip in the first printing unit.
The results of the test are shown in Fig. 5. The results show that in this case, the build-up of accumulation, as the number of copies increases, causes a clear decrease in the acoustic signal level gathered from the image area. The test shows that depending on the quality of the accumulation, the signal level can thus also decrease. In this test, the build-up of accumulation was best represented by a signal gathered from the image area. A change in an acoustic signal correlates well with the amount of accumulation.
The invention is not limited merely to the examples of its embodiments referred to above; instead many variations are possible within the scope of the inventive idea defined by the claims.

Claims

An on-line method for monitoring the printing conditions and materials of a press, the method comprising the steps of:
gathering an acoustic signal from the exit of the printing nip of a printing unit;

analyzing the acoustic signal;

characterized in that the method further comprises the steps of:
dividing the acoustic signal into a signal of a non-image area and image area;

analyzing the acoustic signal of the non-image area and image area;

following the analysis results and/or their changes;

if necessary, taking the measures required by the analysis results and/or their changes.
The method as defined in claim 1, characterized in that the acoustic signal is gathered by means of a microphone and digitized.
The method as defined in claim 1 or 2, characterized in that the acoustic signal is filtered at the step of gathering and/or prior to the division and/or analysis of the signal.
The method as defined in claim, characterized in that the power and/or intensity of the acoustic signal is analyzed.
The method as defined in any one of the preceding claims, characterized in that based on the analysis results of the non-image area, the change value describing the accumulations of the non-image area is determined.
The method as defined in claim 5, characterized in that in case the change value is more than 3 times bigger than the reference value, adjustment of the process conditions and materials is made.
The method as defined in any one of claims 1 to 4, characterized in that based on the analysis results of the image area, the change value describing the accumulations is determined.
The method as defined in claim 7, characterized in that in case the change value decreases, adjustment of the process conditions and materials is made.
The method as defined in any one of the preceding claims, characterized in that the analysis results and/or their changes given by the non-image area or image area are followed simultaneously.
The method as defined in any one of the preceding claims, characterized in that the accumulations of the non-image area and/or image area of a printing unit are controlled based on the analysis results.
The method as defined in any one of the preceding claims, characterized in that the wash cycles of the printing unit are optimized based on the analysis results.
The method as defined in any one of the preceding claims, characterized in that the printing unit operates with the offset, flexography, gravure or electrophotography principle.
An on-line system for monitoring the printing conditions and materials of a press, the system comprising:
a printing unit;

means for gathering an acoustic signal from the exit of a printing nip;

means for analyzing the signal;

characterized in that the system further comprises:
means for dividing the acoustic signal into the signal of a non-image area and image area;

means for following the analysis results and/or their changes.
The system as defined in claim 13, characterized in that the means for gathering an acoustic signal comprise a microphone and an analog-to-digital converter.
The system as defined in any one of claims 13 or 14, characterized in that the means for analyzing and dividing the signal and for following the results and/or changes comprise signal processing algorithms/programs preferably on the same computer.
The system as defined in any one of claims 13 to 15, characterized in that the system comprises means for filtering the signal.
The system as defined in any one of claims 13 to 16, characterized in that the system comprises means for adjusting the printing conditions of the printing unit.