Light source selection for visual inspection system

　The characteristic of a robot vision inspection system is to improve the flexibility and automation of production. In some hazardous work environments that are not suitable for manual work or situations where artificial vision cannot meet the requirements, machine vision is commonly used to replace manual detection; At the same time, in large-scale industrial production processes, using artificial vision to inspect product quality is inefficient and inaccurate. Using machine vision inspection methods can greatly improve production efficiency and automation level. Moreover, machine vision is easy to achieve information integration and is the fundamental technology for achieving computer integrated manufacturing. We can measure, guide, inspect, and identify products on a rapid production line, and complete production tasks with quality and quantity assurance.

　In robot vision systems, obtaining a high-quality and processable image is crucial. The reason why the system is successful is to first ensure good image quality and clear features. The reason why a machine vision inspection project fails is mostly due to poor image quality and unclear features. To ensure a good image, it is necessary to choose a suitable light source.

　Basic elements of light source selection
　Contrast:
　Contrast is very important in machine vision systems. The lighting task of machine vision applications is to generate maximum contrast between features that need to be observed and image features that need to be ignored, making it easy to distinguish features. Contrast is defined as having sufficient grayscale differences between a feature and its surrounding area. Good lighting should ensure that the features to be detected protrude from other backgrounds.
　Stability:
　Another way to test a good light source is to see if the light source is least sensitive to the position of the component. When the light source is placed in different areas of the camera's field of view, the resulting image should not change accordingly. A highly directional light source increases the likelihood of specular reflection on bright areas, which is not conducive to subsequent feature extraction.
　Brightness:
　When choosing two light sources, the best choice is to choose the brighter one. When the light source is not bright enough, three bad situations may occur.
　1. The signal-to-noise ratio of the camera is not sufficient;
　2. Due to insufficient brightness of the light source;
　3. The lack of contrast in the image increases the likelihood of noise appearing on the image.

　Secondly, if the brightness of the light source is not enough, it is necessary to increase the aperture, thereby reducing the depth of field. In addition, when the brightness of the light source is insufficient, random light such as natural light has the greatest impact on feature acquisition.
　A good light source needs to be able to make the features you need to look for very obvious. In addition to being able to capture the components with the camera, it can generate maximum contrast, brightness, and is not sensitive to changes in the position of the components. Once the light source is selected, the rest of the work will be much easier.