Machine vision light source is a part of machine vision imaging, machine vision, light source mainly plays the following roles:

1. Illuminate the target to improve the brightness formation; Conducive to the effect of image processing

2. Overcome ambient light interference to ensure image stability; Used as a measuring instrument or reference.

3. Through appropriate light source lighting design, the target information and background information in the image can be best separated, which can greatly reduce the difficulty of image processing algorithm segmentation and recognition.

4. At the same time, improve the positioning and measurement accuracy of the system, so as to improve the reliability and comprehensive performance of the system. On the other hand.

If the light source selection design is not appropriate, it will lead to the image processing algorithm design and imaging system design may do things to achieve the effect. Therefore, the success or failure of light source and optical system design is the primary factor that determines the success or failure of visual system.

In the machine vision system, the target information and background information of the measured object can be distinguished by appropriate light source illumination, so as to obtain high-quality, high-contrast images, so as to reduce the difficulty of image processing algorithm, and improve the accuracy and reliability of the system.

In practical projects, the image imaging effect is closely related to the light source condition. It is no exaggeration to say that it can directly affect the quality of input data and application effect.

Good light source conditions can achieve good imaging effect, so that the object and background can be effectively distinguished from the target, reduce the difficulty of recognition.

As shown in the picture:

It is conceivable that for specific applications, choosing the best lighting system from many schemes is the key to the stable work of the whole image processing system. So how to choose the right light source? In fact, at present, there is no general optical design system can adapt to various occasions, but because of the characteristics of LED light source, such as multi-shape and multi-color, we can still find some methods of light source selection through analysis.

To choose a good light source, first we need to understand the main types of light sources:

Annular light source: providing different irradiation angles and different color combinations to directly illuminate the measured object, which can highlight the three-dimensional information of the object, avoid the shadow phenomenon of Angle irradiation, highlight the imaging characteristics, and can be used in combination with the diffuse plate to make the light more uniform and soft to expand the heat dissipation area, and improve the heat dissipation performance of the light source. Application :PCB substrate detection; Plastic container detection; Detection of electronic components; Integrated circuit character detection; Semiconductor product appearance character detection; Product packaging appearance and label inspection; Broken pills, lack of testing; Spherical object lighting; Pin location of components.

Point light source: high-power LED, small size, high luminous intensity; Fiber halogen lamp substitute, especially suitable for lens coaxial light source; Efficient heat dissipation device, greatly improve the service life of light source. Application: For chip detection; Mark point positioning; Wafer and liquid crystal glass substrate correction; Image scanning.

Square light source: LED irradiation can form a large square field of view, through the light guide plate at a low Angle to achieve uniform diffusion of the measured object, different working distance can form different lighting environment, can be used for different types of detection. Application: Surface bruise, scratch and other defects detection; Print character, fingerprint, graphic recognition.

Strip light source: high intensity LED array. Large area lighting is preferred and can be freely combined to provide illumination to the object surface from multiple angles. Application cases: IC component detection; Welding inspection; Glass based original detection; Connector detection; Plane defect detection.

Coaxial light source: the good illumination directivity of the coaxial light source can eliminate the shadow caused by the uneven surface of the object, so as to reduce the interference, suitable for high working distance and obvious image characteristics; High density LED arrangement, scientific heat dissipation design, part of the spectrometer design, reduce light loss, improve imaging clarity, uniform irradiation of the object surface. For reflective workpiece surface detection, can highlight the surface detection. Application: THE SERIES LIGHT SOURCE is MOST suitable FOR highly reflective objects, such as metal, glass, film, wafer surface scratch detection, chip and silicon wafer damage detection, Mark point positioning, packaging bar code recognition.

AOI light source: through multi-color and colorful Angle irradiation, highlight the product surface three-dimensional information; Plus diffuse plate to guide light, reduce reflection; Different Angle combination; Application: Used for solder inspection of circuit boards.

Surface light source: High-density LED array arrangement, providing high intensity uniform diffusion light irradiation. Maximum effective use area of luminous surface, suitable for use in compact space environment. Flexible installation mode. Application: Dimension measurement of mechanical parts; Electronic components; IC shape detection; Film stain detection.

In addition, we should also consider the following points, the choice of light source should pay attention to:

1. Clear contrast, clear boundary between target and background

2. The overall brightness is uniform, and the overall uneven gray difference affects image processing

3. The background should be diluted and even as far as possible, without interfering with image processing

4. Real color, moderate brightness, no overexposure

5. Infrared light has the characteristics of long wavelength and strong penetration. Infrared light can filter the interference of organic coatings on the surface of products, detect scratches on the surface, and also detect internal impurities through dark oral liquid.

Ultraviolet light has the characteristics of short wavelength, high diffusivity and excitation fluorescence, which is suitable for Mark point positioning on the surface of transparent objects. Router character detection, the ink has low reflectivity to short-wavelength ultraviolet; UV colloid detection; Invisible code reading and so on.

6. Complementary colors: symmetrical colors in the color ring are superimposed on the black and white camera to show dark color

Adjacent color: Adjacent or the same color in the color ring superimposed on the black and white camera to appear light

7. In addition, different materials of metal to different bands of light source reflectance is different; Copper and gold are weak to the light source of wave length; The reflective difference between silver and aluminum is the largest at the wavelength of 850nm. The blue light source is better able to show the difference between copper, gold and aluminum

Through these understanding analysis, we should almost understand how to choose the light source, if you still do not understand then you can try to go to the following two methods:

1. Observation test method (most commonly used)

Try shining different types of light at different locations and then looking at the image through the camera

2. Scientific analysis (the most effective)

Analyze the imaging environment and recommend the best solution.

The test samples should be rich, with different kinds of intact samples and problematic samples. Try to make the sample as problematic as possible, especially if the sample is the most difficult to detect.

There are a number of standby test light sources,LED light sources are common categories, and different colors should be available.

Analyze the operating environment of the system, understand the requirements of the system structure and operation from customers, and determine the spatial structure relationship between camera, light source and measured object.

To sum up, sometimes a complete machine vision system can not support the work, just optimize the light source can make the system work properly.