Light source selection for visual inspection system

The characteristic of robot vision inspection system is to improve the flexibility and automation level of production. In some hazardous work environments that are not suitable for manual operation or where artificial vision is difficult to meet requirements, machine vision is commonly used to replace manual inspection; At the same time, in large-scale industrial production processes, using manual 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 realizing computer integrated manufacturing. It can measure, guide, detect, and identify products on a fast production line, and can complete production tasks with quality and quantity assurance.

In robot vision systems, obtaining a high-quality and processable image is crucial. The success of the system depends first on ensuring good image quality and distinct features. The reason why a machine vision inspection project fails is mostly due to poor image quality and unclear features. To ensure good images, 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 create a large contrast between the features that need to be observed and the image features that need to be ignored, making it easy to distinguish the features. Contrast is defined as the sufficient grayscale difference between a feature and its surrounding area. Good lighting should ensure that the features to be detected stand out from other backgrounds.

Stability: Another way to test a good light source is to see if the light source is less 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 in bright areas, which is not conducive to subsequent feature extraction.

Brightness: When selecting two light sources, choose the brighter one. When the light source is not bright enough, there may be three bad situations.

1. The signal-to-noise ratio of the camera is insufficient;

2. Due to insufficient brightness of the light source;

3. The contrast of the image is not sufficient, and the possibility of noise appearing on the image increases accordingly.

Secondly, if the brightness of the light source is not sufficient, it is necessary to increase the aperture, thereby reducing the depth of field. Additionally, when the brightness of the light source is insufficient, random light such as natural light has a significant 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 the camera being able to capture the components, it should be able to produce high contrast and brightness, sufficient and insensitive to changes in the position of the components. Once the light source is selected, the remaining work becomes much easier.