Basic knowledge of machine vision light sources

The basic components of visual inspection hardware include: processor, camera, lens, and light source. Through appropriate light source lighting design, the target information and background information in the image can be optimally separated. This can not only greatly reduce the algorithm difficulty of image processing, but also improve the accuracy and reliability of the system. Unfortunately, there is currently no universal machine vision lighting system that can cope with different detection requirements. Therefore, for each specific case, it is necessary to design an adapted lighting device to achieve the best effect. Inappropriate lighting will cause many problems. Machine vision light sources are so important, but they are often ignored by many people. At present, machine vision light sources mainly use LEDs (light-emitting diodes).

Machine vision light source

Machine vision illumination methods include:

• Direct light: The incident light basically comes from one direction and has a small angle of incidence. It can cast the shadow of the object.
• Diffuse light: The incident light comes from multiple directions, or even all directions, and it does not cast obvious shadows.
• Polarized light: In a plane perpendicular to the direction of propagation, the light vector vibrates only in a certain fixed direction.
• Parallel light: light with the same illumination angle, such as sunlight. The narrower the luminous angle of LED direct light, the closer it is to parallel light.

Machine vision light source basics:

1. Shape freedom An LED light source is composed of many individual LEDs. Therefore, compared with other light sources, it can be made into more shapes, and it is easier to design the shape and size of the light source according to the user's situation.
2. Long service life In order for the image processing unit to obtain accurate and repeatable measurement results, the lighting system must ensure that it can provide stable image input for a long period of time. The brightness of LED light sources decreases after 10,000 to 30,000 hours of continuous operation, but the effect is far better than other types of light sources. In addition, using a control system to make it work intermittently can suppress the heating of the luminous tube and double its life.
3. Fast response speed The response time of the LED light-emitting tube is very short. The real meaning of the response time is to ensure the working switching between multiple light sources or between different areas of a light source as required. When a special controller is used to power the LED light source, the time to reach the maximum illumination is less than 10s.
4. Various colors In addition to the shape of the light source, another aspect of obtaining stable image input is the choice of the color of the light source. Even for light sources of the same shape, the images obtained will be very different due to different colors. In fact, how to use the technical characteristics of light source color to obtain the best contrast image effect has always been the main direction of light source development.
5. Low comprehensive operating costs If you choose a product that is cheap but has no guaranteed performance, the initial investment savings will soon be offset by the daily maintenance and repair costs. Other light sources not only consume 2-10 times more power than LED light sources, but also need to be replaced almost every month, which wastes a lot of valuable time for maintenance engineers. Moreover, the more light sources that are put into use, the greater the cost of device replacement and labor. Therefore, it is very economical to choose long-life LED light sources in the long run.

When designing optical systems for machine vision applications, the most important concern is the reflected light from the surface of the object. The geometric shape, gloss and color of the surface of the object determine how light is reflected on the surface of the object. The trick to applying light sources in machine vision boils down to how to control the light reflection of objects. As long as the reflected light is better controlled, the collected images will be easier to control.