Light source is one of the important components in the machine vision system. It directly affects the quality of input data by at least 30% of the application effect. Therefore, the choice of light source for machine vision systems is very important. The purpose of using a light source is to distinguish the measured object from the background as clearly as possible to obtain a high-quality, high-contrast image; to 'freeze' the moving target on the image; to enhance the edge clarity of the target to be measured; to eliminate shadows; to offset noise and increase target brightness; to overcome the interference of ambient light; and to ensure the stability of the image. Machine vision has three major technologies: imaging technology, processing technology, and motion control technology. Imaging technology is inseparable from light sources. The selection and performance of light sources directly affect the success or failure of the system, affecting processing accuracy and speed. Therefore, the light source plays a decisive role in the machine vision system.
Through appropriate light source lighting design, the target information and background information of the image can be optimally separated, which can greatly reduce the difficulty of segmentation and identification of image processing algorithms, while improving the positioning and measurement accuracy of the system, thereby improving the reliability and comprehensive performance of the system. On the contrary, if the light source is improperly designed, it will lead to half the effort in image processing algorithm design and imaging system design. Therefore, the success or failure of the light source design is the primary factor that determines the success or failure of the visual system.
There are three main types of light sources used by vision systems:
1. High-frequency fluorescent lamps: The fluorescent lamps used in our daily life have a service life of about 1500-3000 hours;
- Advantages: good diffusion, suitable for uniform irradiation of large areas;
- Disadvantages: slow response speed, dim brightness.
2. Fiber optic halogen lamp: It is an effective combination of halogen lamp and fiber optic conduit. The fiber optic conduit transfers the strong light generated by the halogen bulb to the object under test for illumination. The service life is about 1,000 hours;
- Advantages: high brightness;
- Disadvantages: Slow response speed, almost no changes in brightness and color temperature.
3. LED (Light Emitting Diode) light source: It is a way of illuminating the object being tested by combining multiple LED lights in a specific shape. This is a commonly used lighting method with a wide range of applications and a service life of about 10,000-30,000 hours;
- Advantages: Multiple LEDs can be used to achieve high brightness, and different shapes can be combined at the same time; the response speed is fast, and the wavelength can be selected according to the purpose.
- Disadvantages: The temperature resistance of LED chips is relatively weak and the power consumption is relatively large.
Light source comparison chart
In comprehensive comparison, LED light sources have been widely recognized by the industry for their unique technical advantages in machine vision systems. LED light sources have the advantages of long service life, adjustable brightness, low temperature, balance, stability, no flicker, no shadows, consistent brightness and color temperature, etc., which meet the technical requirements of machine vision users for high quality and high precision; in addition, special designs can be made according to customer needs. It is for this reason that LED light sources have brought huge development space to the industry.
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