The machine vision inspection system mainly includes industrial cameras, industrial lenses, machine vision light sources and image analysis parts. The light source is an important part of it, which directly affects the imaging quality of the image. Through appropriate light source lighting design, the target information and background information in the image can be optimally separated, which not only greatly reduces the algorithm difficulty of image processing, but also improves the accuracy and reliability of the system.
A good image should have conditions such as high contrast, good uniformity, high authenticity, moderate brightness, and as little background as possible. Overexposure will hide a lot of important information; shadows will cause edge misjudgment; image unevenness will make threshold selection difficult. Therefore, to ensure a better image effect, it is necessary to choose a suitable light source.
However, there is currently no general machine vision lighting system that can cope with different inspection requirements, so for each specific case, it is necessary to design an adaptive lighting device to achieve the best effect. There are many types of machine vision light sources, and there are many types of light sources for each type. After the type is determined, it is necessary to select the type. The following describes the selection methods of different types of light sources.
Selection of bar light source
1. The illumination width of the light source is preferably greater than the detection distance, otherwise it may cause poor brightness or insufficient radiation area;
2. The length of the strip light can be enough to illuminate the position that needs to be illuminated. Too long may cause installation inconvenience and increase the cost at the same time;
3. If the lighting target is a highly reflective object, it is best to add a diffuser plate. If it is a dark non-reflective product such as black, you can also remove the diffuser plate to increase the brightness.
Ring light source selection
1. Understand the installation distance of the light source and filter out some angle light sources;
2. The target area is small, and the main characteristics are in the middle of the surface, you can choose a small size 0-angle or small-angle light source;
3. If the feature that the target needs to show is on the edge, you can choose a 90-degree angle ring light, or a large-size high-angle ring light;
4. To detect scratches on the surface, you can choose a 90-degree angle ring light, and try to choose a light source with a short wavelength.
Coaxial optical selection
1. According to the size of the target, select the coaxial light with the appropriate light-emitting area;
2. The light-emitting area of the coaxial light is preferably about 1.5~2 times larger than the target size to avoid uneven light from left to right;
3. When installing, try not to be too high from the target. The higher the height, the larger the coaxial light required to be selected, in order to ensure uniformity.
Selection of parallel coaxial light
1. The design of the parallel coaxial optical path is unique, which is mainly suitable for detecting various scratches;
2. The characteristics of parallel coaxial light and coaxial light are different and cannot be used as a substitute for coaxial light;
3. For products such as scratches detected by parallel coaxial light, try not to choose a light source with a long wavelength.
When selecting other light sources, it is necessary to understand the size of the feature point area, the characteristics of the product, the material of the product, the installation space and other conditions that may cause obstacles, so as to select the appropriate light source.
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