Automatic Print Quality Inspection Equipment and Technology (I)

Today, in the printing and packaging industry, more and more manufacturers have the financial ability to purchase various types of advanced printing and post-press processing equipment. With the improvement of printing equipment, various high-grade prints are also increasing. While looking at domestic printing companies, some of them already have advanced and similar equipment and have the same production technology capabilities, but the result is similar products and companies lack competitiveness.

The key to how a printing company can maintain its leading position in the industry and obtain a reasonable profit is whether the company itself can provide non-homogeneous characteristics. For example: unique new technology and good, stable print quality. However, the unique new technology and good and stable quality are difficult to measure with money. Moreover, in terms of quality, the company must have a reasonable and complete quality management system in order to have a good and sustained overall quality for a long time.

Whether it is a manufacturer or an end user, everyone wants a good, stable quality. In theory, the quality of a good print should be an agreement negotiated and confirmed by a manufacturer and end-user for a particular print, and must be clearly and quantifiable and reasonably described. Although there is a certain standard in the definition of "quality" of the domestic brush product at present, because of the different printing standards and the different standards, it is more likely that the inspection results will be affected when the printed matter is actually inspected. Excessive external factors and human factors make it difficult to achieve uniform and quantifiable stability standards. How can we achieve a uniform, quantifiable and stable quality standard? Industry insiders are eager to establish such a quality standard as soon as possible and are actively seeking a reasonable and best way to test it.

In terms of printing quality inspection, countries such as Europe, America and Japan have made great progress. As early as the 1970s, there have been vendors actively working with image processing systems to digitize visual information, achieve "seeing" and "cognition" of print quality through computers, and conduct high-speed, high-precision printing on printed materials. 100% real-time detection completely eliminates human errors and establishes a uniform and quantifiable inspection standard. At present, BOBST in Switzerland, PROIMAGE in the United States, DAC in Japan, and TOKIMEC can provide full automatic print quality inspection equipment.

Automatic Print Quality Inspection Equipment

1. How it works

The detection system used in automatic print quality inspection equipment is to first take a standard image using a high-definition, high-speed camera lens, set a certain standard on this basis, and then shoot the detected image, and then compare the two. The CCD linear sensor converts the change in the light quantity of each pixel into an electronic signal. After the comparison, if the detected image is different from the standard image, the system considers the detected image to be a defective product. The various errors generated in the printing process are only different from the standard image and the detected image for the computer, such as defects such as smudges, ink spots, and the like.

2. Detection accuracy

The earliest used for print quality inspection is the technology of comparing the gray scale of the standard image with the detected image. Now the more advanced technology is based on the RGB three primary colors for comparison. Where is the difference between fully automatic machine detection and human eye detection? Taking human eyes as an example, when we look at a certain printed matter intently, if the contrasting color of the printed matter is relatively strong, the smallest flaw that the human eye can find is a defect with a contrasting color that is not less than 0.3 mm; but it depends on people. It is difficult to maintain consistent, stable visual effects. In another case, if defects are found in prints of the same color, especially in a light color system, the defects that the human eye can detect need at least 20 gray levels. An automated machine can easily detect a 0.10mm defect, even if the defect is only one grayscale difference from the standard image.

However, in terms of practical use, even the same panchromatic contrast system has different ability to discriminate color differences. Some systems can find contours and defects with large variations in color, while others can identify very small defects. For white cardboard and some simple style prints, such as the Japanese KENT cigarette label, the United States Marlboro cigarette label, simple detection may be sufficient, and most of the domestic print, especially various labels, has many characteristics, With too many flash elements, such as gold, silver cardboard, hot stamping, embossing, or polishing prints, this requires that the quality inspection equipment must have sufficient ability to find the smallest grayscale differences, perhaps 5 shades of gray. The difference in level may be a stricter one gray level difference. This point is crucial to the domestic label market.

The accuracy of the comparison between the standard image and the printed matter being examined is a key issue in the detection equipment. Usually, the detection equipment collects the image through the lens. In the middle part of the scope, the image is very clear, but the image at the edge may be false. Shadow, and the detection result of the phantom part directly affects the accuracy of the entire test. From this point of view, if only the comparison of the full width area is not suitable for some fine prints. If the obtained image can be subdivided again, for example, the image is divided into 1024dpi×4096dpi or 2048dpi×4096dpi, the detection accuracy will be greatly improved, and at the same time, because the phantom of the edge portion is avoided, the detection result is more stable.

3. Detection parameters

After setting the quality inspection parameters, will the use of high-speed, automated quality inspection equipment lead to excessive scrap rates? The increase in scrap rates will undoubtedly lead to lower profits. But in fact all quality standards are relative, such as the generally unacceptable minor defects, if it is in certain areas (gluing, subsistence) is acceptable. In the case of manual detection, an appropriately relaxed, flexible standard can be automatically formed. How can rational and data-based detection be completed? It is more reasonable for the printer and the end-user to reach an agreement to adopt a sub-regional and hierarchical quality inspection standard for the printed matter. This is only a rigid rule, but must be a quantifiable standard that can be manipulated and accepted by all parties. And these standards must be all kinds of data set by the user, such as the area to be detected, the detection level of each area, and the testing standards to be performed at each detection level.

First, we partition the detected prints, as shown in Figure 2. In the figure, A is the most rigorous testing area - the most important part of the printed matter (trademarks, products); B is the rigorous testing area - important part (product); C is the general testing area - background; D is the neglected area - concealed Part (glue wing, life part)

Then, set each detection level. This point is very critical, it will directly relate to the ability to find defects, but also directly related to the number of reject rates, so customers will certainly require an acceptable and reasonable range of tolerances, including the setting of acceptable, defect-size Range tolerance, acceptable, defect gray tolerances.

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