RU2775537C1 - Method for quality assessment of laser printing samples - Google Patents

Abstract

FIELD: printing.

SUBSTANCE: present invention relates to a method for quantitative and quality assessment of laser printing samples. The method contains following stages: provision of a laser printing sample; generation of a digital raster image of part of laser printing of the laser printing sample, and creation of digital graphic information, which forms a digital raster image; identification of at least one individual part within digital graphic information; generation of at least one image histogram for identified at least one individual part of digital graphic information; approximation of a probability density function for obtained at least one image histogram; and determination of at least one parameter of the probability density function.

EFFECT: provision of the possibility of automatic detection of optimal laser setting by examination and optical assessment of markings on a product.

13 cl, 7 dwg

Description

The present invention relates to a method for objectively quantifying the quality of laser printing on injection molded plates.

The marking of cast products is constantly used to indicate the serial number and additional information. Those skilled in the art are aware of appropriate methods for marking molded articles made from polyolefin compositions, for example based on polyethylene or polypropylene: for example, these are conventional printing methods such as inkjet printing, embossing, etc. In the field of communications and power cables, marking is necessary to provide the installer with information so that the installation can be carried out correctly and efficiently. Similarly, in the automotive industry, markings are necessary to provide information about the manufacturer of a part, since often a particular part that is used, for example, in a car, is manufactured by several suppliers. In addition, additional information is often required on the manufactured part, such as date of manufacture, expiration date, barcode, and company logo.

However, for many applications, conventional printing methods such as inkjet, embossing, etc., are not suitable because the outer surface of the formed product is not large enough to be imprinted using conventional methods, or because the shape of the manufactured product does not allow printing. conventional methods, for example, because the corresponding part of the surface of the product is not flat.

Therefore, the use of laser printing methods is becoming increasingly important. In particular, for fiber optic microcables (FOC), conventional printing methods are not suitable due to the very small outer surface of such microcables. The increasing demand for microcables has also increased the use of laser printing. One of the advantages of laser printing is that it can be printed at a higher line speed than alternatives, which improves cost efficiency. Another advantage is that the resulting laser print is not as easily rubbed off by rubbing or rubbing, as opposed to an inkjet print.

Significant progress has now been made in laser printing on polyolefin compositions, for example in improving the contrast between the black color of the manufactured product and the light inscriptions obtained by laser printing. This process includes the development and production of new polyolefin compositions for specific applications, which provide, for example, such increased contrast after laser printing. Of course, the type and parameters of the laser beam are also being improved for specific polyolefin compositions in order to obtain better contrast.

In this regard, inspection of laser print samples, usually injection-molded plates, and evaluation of print quality are of paramount importance. Until now, this examination has been performed using the human eye. In reality, however, this is not a completely objective and quantitative way to obtain reproducible results.

An example of a typical human eye print is shown in FIG. one.

In FIG. 1 shows squares laser-printed on an injection-molded polyolefin composition, these squares are ordered nine in a column and fourteen in a row, for a total of 126 squares, each corresponding to a specific laser beam setting.

From FIG. 1, it can be concluded that there are relatively good print parameter settings (center) and relatively imperfect settings (left side bars and bottom rows) for a given injection molded sample, but no quantitative information about print quality or print contrast can be obtained. given.

Therefore, there is still a need to provide an objective and quantitative method for evaluating the quality of laser printing on injection molded plates of polyolefin compositions, such injection molded plates being a model for molded articles of general type polyolefin compositions.

The present invention is based on the discovery that this goal can be achieved by taking a digital image of a laser print sample, obtaining an intensity distribution for several different parts of the image, identifying the center of a normal distribution curve approximating each of the obtained intensity distributions, and recording the intensity values at the centers normal distribution curves as a function of the different parts of the image for which these intensity distributions were obtained. The display of this information provides a quantitative assessment of the quality of the laser print sample and, accordingly, a comparison with other samples.

Accordingly, in its first aspect, the present invention relates to a method for quantitative and qualitative evaluation of laser print samples, comprising the following steps:

a) providing a laser print sample,

b) obtaining a digital raster image of the laser print part of the laser print sample and providing digital graphic information based on it, which forms a digital raster image,

c) identifying at least one distinct part within the digital graphic information,

d) obtaining at least one image histogram for the identified at least one distinct piece of digital graphics information,

e) approximating the probability density function for the obtained at least one image histogram, and

f) determining at least one probability density function parameter.

According to one embodiment of the invention, the laser print sample is an injection molded plate from a polyolefin composition. This means that the injection molded plate consists of a polyolefin composition.

According to another embodiment of the invention, the polyolefin composition contains at least 90 wt%, preferably at least 95 wt%, more preferably at least 98 wt%, even more preferably at least 98.5 wt% of an ethylene homopolymer or copolymer, or a propylene homopolymer or copolymer, or a mixture thereof. The content of ethylene homopolymer or copolymer, or propylene homopolymer or copolymer, or blends in the polyolefin composition is generally not higher than 99.5 wt%.

The terms "ethylene homopolymer" and "propylene homopolymer" in the context of the present description refer to polyethylene or polypropylene, respectively, which consists essentially, that is, at least 99.5 wt.%, more preferably, at least 99.8 wt. %, from units of ethylene or propylene, respectively. In a preferred embodiment of the invention, only ethylene or propylene units, respectively, are used in the polymerization. In a preferred embodiment of the invention, only ethylene or propylene units, respectively, can be found in the ethylene homopolymer or propylene homopolymer.

The term "copolymer" in the context of the present description covers polymers obtained by the copolymerization of at least two, i.e. two, three or more different monomers, i.e. the term "copolymer" in the context of the present description does not exclude, for example, the so-called trimers obtained by copolymerization three different monomers.

Suitable ethylene homopolymers are low density polyethylene (LDPE, with a density of 0.910-0.940 g/cm ³ ) and high density polyethylene (HDPE, with a density of at least 0.941 g/cm ³ ).

The melt flow rate of the respective ethylene homopolymers is preferably 0.2 to 3.0 g/(10 minutes), more preferably 0.2 to 2.0 g/(10 minutes).

Suitable ethylene copolymers are linear low density polyethylene (LLDPE, with a density of 0.915-0.925 g/cm ³ ) and very low density polyethylene (VLDPE, with a density of 0.880-0.915 g/cm ³ ). Suitable copolymers are C ₃ -C ₁₂ alpha-olefins, preferably 1-butene, 1-hexene, 4-methyl-1-pentene and/or 1-octene.

Suitable propylene homopolymers are highly isotactic propylene homopolymers.

Suitable propylene copolymers are copolymers, i.e. random and block copolymers, with ethylene and/or C ₄ -C ₁₂ alpha-olefins, preferably with ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene and/ or 1-octene. Suitable propylene copolymers include block copolymers having a matrix that is a propylene homopolymer or a propylene random copolymer in which ethylene-propylene rubber (EPR) is dispersed.

According to another embodiment of the invention, laser printing on the sample contains at least one separate area, which contains a congruent form, which is congruent with at least one of these separate parts.

According to another embodiment of the invention, said at least one distinct part identified within the digital image in step c) corresponds to at least one distinct laser printable area on the sample.

According to another embodiment of the invention, the laser print on the sample comprises a plurality of distinct regions that are at least partially matched in size and/or shape.

According to another embodiment of the invention, the specified set of individual areas is a set of squares, at least partially ordered in the form of a matrix.

According to another embodiment of the invention, said plurality of individual parts identified within the digital image in step c) correspond to a plurality of discrete laser print areas on the sample.

According to another embodiment of the invention, said digital bitmap has a size of 300 pixels x 300 pixels to 2000 pixels x 2000 pixels.

According to another embodiment of the invention, for a plurality of discrete pieces of digital image information, a plurality of image histograms are obtained for each of the plurality of discrete pieces of digital image information.

According to another embodiment of the invention, a digital bitmap image of the laser print part of the laser print sample is obtained in step b) such that the magnification is in the range of 30 to 150 times, preferably 40 to 100 times.

According to another preferred embodiment of the invention, a digital bitmap image of the laser print part of the laser print sample is obtained in step b) such that the magnification is in the range of 30 to 90 times, preferably 40 to 80 times, more preferably 40 to 70 times, even more preferably in the range of 40 to 60 times.

According to another embodiment of the invention, said laser print part of the laser print sample has a flat surface.

According to a second aspect of the present invention, there is provided a computer program product comprising instructions that, when the program is executed by the computer, causes the computer to perform the steps of the method according to the first aspect or any of the embodiments of the invention relating to the first aspect.

According to a third aspect of the present invention, there is provided a computer-readable storage medium containing instructions that, when executed by a computer, cause the computer to perform the steps of the method according to the first aspect or any of the embodiments of the invention relating to the first aspect.

According to a fourth aspect of the present invention, there is provided a data processing system comprising means for performing the steps of a method according to the first aspect or any of the embodiments of the invention relating to the first aspect.

The computer program executing the method of the present invention may be stored on a computer-readable medium. Computer-readable media can be a floppy disk, hard disk, CD, DVD, USB (Universal Serial Bus) device, random access memory (RAM), read only memory (ROM), and erasable programmable read only memory (EPROM).

The computer-readable medium may also be a data network, such as the Internet, that allows downloading of program code.

The methods, systems, and apparatus described above may be implemented as software in a digital signal processor (DSP), microcontroller, or any other auxiliary processor, or as hardware circuitry within an application-specific integrated circuit (ASIC) complex field-programmable logic integrated circuit (CPLD) or field-programmable gate array (FPGA).

The present invention may be embodied in digital electronic circuitry or in computer hardware, firmware, software, or combinations of the foregoing, such as available conventional mobile device technology or new hardware suitable for implementing the methods described herein.

Brief description of the drawings

The invention can be more fully appreciated and its advantages can be understood from the following schematic drawings, not to scale, where:

in fig. 1 schematically shows an example of a flat plate printed with 126 different settings for different squares according to an exemplary embodiment of the invention;

in fig. 2 is a schematic snapshot of a graphical user interface of a computer program product according to an exemplary embodiment of the invention;

in fig. 3 schematically shows an example in which regions of interest automatically generated within squares are colored black according to an exemplary embodiment of the invention;

in fig. 4 schematically shows an example of the results, keeping the square and the corresponding intensity distribution according to the exemplary embodiment of the invention;

in fig. 5 shows an example of a final result according to an exemplary embodiment of the invention;

in fig. 6 shows a comparison of a good sample and a bad sample according to an exemplary embodiment of the invention, and

in fig. 7 shows a flowchart of a method for quantitative and qualitative evaluation of laser print samples according to an exemplary embodiment of the invention.

Detailed description of embodiments of the invention

The illustrations in the drawings are shown schematically and not to scale. In the various drawings, like or identical elements are identified by the same reference numbers.

In the general case, in the drawings, identical parts, blocks, objects or steps are indicated by the same positions.

In FIG. 1 schematically shows an example of a flat plate printed with 126 different settings for different squares according to an exemplary embodiment of the invention.

An example of a quantitative method is given in FIG. 1 where 126 squares are printed, for example in a 14x9 matrix, with different print mode settings. It is possible to evaluate generally good or good (center) and bad settings (bars on the left and bottommost squares), but no quantitative information can be obtained directly from the image. According to one of the embodiments of the invention, the laser printing of the sample contains at least one separate area, which contains a congruent form, which is congruent to at least one separate part. For example, laser printing on a sample contains a plurality of individual squares that at least partially match each other in size and/or shape.

The laser print sample is, for example, an injection molded plate from a polyolefin composition. According to an embodiment of the invention, the laser print part of the laser print sample has a flat surface, for example, with a flatness of less than 2.0 µm.

A sufficiently high magnification is required to display each square in detail, but still not too high for practical purposes. For example, a magnification of 50 is used, but a magnification of 20 can also be used, which is not enough, and a magnification of 100 and 150, which also gives a good image, however, the stored data is approximately 1 gigabyte, and a set of 126 squares has to be divided by a set of four large images, which is inconvenient in practice.

Particular attention should be paid to all additional fine adjustments, as the appearance of the image in an optical microscope can vary significantly. The setting of all possible parameters is especially important for describing the method in order to disclose it as separately as possible and to allow everyone to repeat the experiment properly. All these details are listed in the description of the method.

In addition, the analysis should be carried out independently of the operator. Therefore, a program code was written for automatic sequential analysis of 126 squares. The use of automatic analysis also provides the advantage that many records can be analyzed in a short amount of time, while in the case of manual evaluation, this task would be extremely laborious.

The computer program code has been written in such a way that the analysis can be easily carried out in any laboratory and thus distributed to, for example, customers. In FIG. 2 shows a menu where the steps to be performed are highlighted.

In FIG. 2 is a schematic snapshot of a graphical user interface of a computer program product according to an exemplary embodiment of the invention.

At step 0. Instructions” prints details and instructions for performing the analysis and is therefore intended to be a quick learning and reminder.

At step "1. Screen Clearing closes any windows that may have been open during a previous analysis, allowing the user to get started.

At step "2. Initialization" creates two windows that are saved during subsequent analysis, namely: analyze the image of the square and show the intensity distribution, as shown in Fig. 4. In addition, the user is prompted to upload an image with squares for further analysis. At this point, the software is ready to run.

At step "3. Input Information" enter the name of the sample, the magnification used, and two parameters for finding the correct settings for automatic square detection.

This step also allows the user to enter information whether the analyzed image is the first or second part of the 126 squares currently being examined.

At step "4. Test of squares" runs a piece of code to automatically find squares and display a copy of the original image with an overlay of automatically found squares, painted in black. This is done as a precaution to make sure the code recognizes squares correctly before doing a full parse. If the squares are not correctly identified, the user can return to step 3 and enter the additional parameters listed above, which are the horizontal and vertical shifts for the squares.

Specifically, in step 4, the written code loads the images of interest and automatically creates an area of interest in each square (500×500 pixels over a total area of 2000×2000 pixels), see FIG. 3.

In FIG. 3 schematically shows an example in which various auto-generated areas of interest within squares are colored black according to an exemplary embodiment of the invention.

This smaller area is chosen because sometimes the borders of the squares are not very sharp, and it allows the different squares to be automatically captured while retaining enough information, since 250,000 pixels is enough to create an intensity distribution as discussed below. The digital bitmap, for example, in this example has a size of 300x300 pixels to 2000x2000 pixels.

At step "5. Start in automatic mode” analyze each single square. For each square, a histogram of the intensity distribution is constructed. This distribution is finally fitted with a normal distribution curve and the central value of this curve is recorded. It corresponds to the "whiteness level" of the square.

Therefore, the result of the analysis will be 126 different files, for example, written in PDF format, as shown in the example of FIG. four.

In FIG. 4 schematically shows an example of the results when the square and the corresponding intensity distribution are maintained according to the exemplary embodiment of the invention.

This drawing shows the three most common pictures. The squares may be filled with single dots, light lines interspersed with black lines, or may be more orderly filled with printed areas.

This process is carried out automatically for all squares, however, in case of a more detailed analysis, it is possible to show and analyze each individual square by selecting the option “5b. Square by square.

After analyzing all 126 squares, the program saves the results in a .csv file with the same name that the user gave to the analyzed sample, so that analysis and comparison can be resumed later.

Additionally, there are two more items on the menu: “A. Erase everything from memory, which actually erases all memory information in the software used at the beginning of the analysis, and, most importantly, point "C. Automatic" which automatically performs steps 1-5 above, and the user only has to click once to select an image for analysis and enter the name of the sample.

In FIG. 5 shows an example of a final result according to an exemplary embodiment of the invention.

The center points of the fitting bell curve for 126 squares are plotted on the same graph, where squares "1-9" belong to the first column, squares "10-18" to the second column, and so on. It can be seen that after the fourth column, starting with square 27, the squares are bright and "good".

In FIG. 6 shows a comparison of a good sample with a bad sample according to an exemplary embodiment of the invention.

The images were taken using a Keyence VHX-5000 microscope with a 50 magnification objective, namely: Z20:X50. The exposure time has been set to 14 milliseconds, which allows this microscope to unambiguously determine the lighting settings that should be used. In particular, the standard LED ring supplied with the microscope was used. The images were collected in monochrome, i.e. black and white, in order to obtain an image with a unique amount of intensity. The diffuser was not used.

Additional settings in the microscope software, such as increasing contrast or sharpness or enhancement, have been disabled as this may cause uncontrolled image changes. For each laser printing setup, a 500×500 pixel square was selected within the printable area. Then the intensity distribution histogram was calculated and processed with a median filter 3 for smoothing. This distribution was approximated by a bell curve and the center of this bell curve was recorded for each square.

In FIG. 6 compares good and bad samples. As shown in the example in FIG. 6, after the third column of the good sample (N22225-CM1), there are squares with a relatively high center point of the bell curve. The bad sample (N22225-CM4) has a small range between 9 and 50 squares with roughly constant center dots, indicating normal printing, but not as good as the previous sample, as the centers are around 100, meaning they are dark. Also, after square 50, the centers "crumble" and drop, which is in agreement with the visual observation that these squares look "burnt out".

In FIG. 7 shows a flow chart of a method for quantifying and qualifying a laser print sample according to an exemplary embodiment of the invention.

The method for quantitative and qualitative evaluation of a laser print sample may include at least the following steps:

In the first step S1 of the method, a laser print sample is taken.

In the second step S2 of the method, a digital raster image of a part of the laser print pattern is obtained and, on its basis, digital graphic information is created, which forms a digital raster image.

In the third step S3 of the method, at least one distinct piece within the digital graphics information is identified to obtain at least one image histogram for the identified at least one distinct piece of digital graphics information.

In the fourth step S4 of the method, the probability density function is approximated for the obtained at least one image histogram.

In the fifth step S5 of the method, at least one probability density function parameter is determined.

The computer program may be stored and/or downloaded on an appropriate medium, such as an optical storage medium or solid state media supplied with or forming part of other hardware, but may also be downloaded in other forms, such as via the Internet or other wired or wireless communication systems.

However, the computer program may also be present on a network, such as the World Wide Web, and may be loaded into the working memory of the processor from such a network.

According to yet another exemplary embodiment of the invention, there is provided a storage medium or data storage medium for making a downloadable computer program element, which computer program element enables the implementation of a method according to one of the previously described embodiments of the invention.

It should be noted that embodiments of the invention are described in relation to various aspects of the invention. In particular, some embodiments of the invention are described as elements of a method, while other embodiments of the invention are described as elements of a device.

However, it should be apparent to a person skilled in the art from the above description that, unless otherwise stated, in addition to any combination of features relating to one type of subject matter, any combination of such features relating to other subject matter is also within the scope of inventions. In this case, all features can be combined, providing synergistic effects that are more than a simple summation of features.

Although the invention has been shown and described above with reference to the drawings, such drawings and their description are to be considered illustrative or exemplary only and not limiting; therefore, the invention is not limited to the disclosed embodiments of the invention. Those skilled in the art may propose and make other modifications to the disclosed embodiments of the present invention based on the drawings, description, and claims.

In the claims, the term "comprising" does not exclude other elements or steps, and the singular does not exclude the plural. A single processor, controller or other unit may perform the functions of several elements listed in the claims. The fact that certain features are disclosed in different dependent claims does not mean that a combination of these features cannot be used to advantage. Any reference designations in the claims should not be construed as limiting the scope of the invention.

Claims (19)

1. A method for quantitative and qualitative evaluation of laser marking samples, containing the following steps: a) providing (S1) a molded article of the polyolefin composition as a laser marking pattern, wherein the laser marking pattern has a plurality of separate laser marking portions, each laser marking portion being formed with a different laser setting used to form that laser marking portion, b) obtaining (S2) a digital bitmap of each of the plurality of laser marking parts of the laser marking sample using an optical microscope, and based thereon providing digital graphic information that forms a digital bitmap image of each laser marking part; c) identifying (S3) at least one separate part within the digital graphic information of each part of the laser marking, d) obtaining at least one image histogram for the identified at least one separate piece of digital graphic information of each piece of laser marking, e) an approximation (S4) of a probability density function for the obtained at least one image histogram, and f) determining (S5) at least one probability density function parameter. 2. The method of claim 1, wherein step d) is performed by evaluating a plurality of small areas selected within said identified at least one distinct part. 3. A method according to claim 1 or 2, wherein the laser marking pattern is an injection molded plate from a polyolefin composition. 4. The method of claim 3, wherein said polyolefin composition contains at least 90 wt % of an ethylene homopolymer or copolymer or a propylene homopolymer or copolymer. 5. The method according to any one of paragraphs. 1-4, in which each part of the laser marking has a congruent shape that is congruent to said at least one separate part. 6. The method of claim 5, wherein said at least one distinct part identified within the digital image in step c) corresponds to one of the parts of the laser marking on the sample. 7. Method according to claim 5 or 6, wherein the portions of the laser marking on the sample are at least partially matched in size and/or shape. 8. The method of claim 7, wherein the laser marking portions are a plurality of squares at least partially arranged in a matrix. 9. The method according to any one of paragraphs. 1-8, in which the digital bitmap has a size of 300×300 pixels to 2000×2000 pixels. 10. The method according to any one of paragraphs. 1-9, wherein a digital raster image of said portion of the laser marking of the laser marking sample is obtained in step b) with an optical microscope magnification in the range of 30 to 90 times, or in the range of 40 to 80 times, or in the range of 40 to 70 times , or in the range of 40 to 60 times. 11. The method according to any one of paragraphs. 1-10, wherein the laser marking portions of the laser marking pattern have a flat surface. 12. A computer-readable storage medium containing instructions that, when executed by the computer, cause the computer to perform the steps of the method according to any one of paragraphs. 1-11. 13. The data processing system containing means configured to perform the steps of the method according to any one of paragraphs. 1-11.

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