Application of machine vision technology in printing inspection

With the increasingly stringent requirements of users for product exquisiteness and the continuous self-upgrading of the packaging and printing industry, manufacturers' requirements for printing quality have become more and more refined, which has also put forward new requirements for visual inspection, prompting us to find new and better Programs to help users solve difficulties.

In this article, WeiShang image uses a company's inspection requirements for printed matter as an example to carry out detailed solution decomposition.

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Sample: 800mm x 500mm printed matter, made of hard paper, with hot stamping pattern and surface coating.

User requirements: detection of missing prints, multiple prints, contamination, coated wrinkles, etc.

Problems encountered by customers in the early stages of seeking solutions:

1. Due to the thick paper, when the light is considered from the front, the sample has serious reflection and uneven light.

2. The detection accuracy of missing prints or defects in the area is micron level, and the low pixel solution cannot find the defects well;

3. The size of the sample provided by the user is large, and the entire sheet needs to be tested at one time, so the field of view is too large, resulting in extremely high accuracy requirements;

4. The wrinkles of the transparent film on the surface of the sample are very small, which is not easy to check;

5. The user budget is limited and the cost of line scan cameras is too high.

The solutions we provide:

1. Because the paper is relatively large and requires high detection accuracy, after testing, we finally selected the MV-E series 29 megapixel gigabit network camera, combined with the AFT series 10 megapixel fixed-focus lens, which can meet the testing needs of customers;

2. Due to the unsatisfactory lighting effect on the front, we tried a variety of other lighting methods, and finally found that the user sample was transparent, so we chose a stable and uniform LED backlight to supplement the light from the back of the sample. The lighting effect of this solution is very good. Not only can defect detection be performed, but also transparent film folds can be clearly found.

The following figure is a partial effect map:

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3. Because the customer has strong software development capabilities, we have not provided a detection software solution, so I won't explain too much here.