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The Importance of Light Sources in Machine Vision Systems

A machine vision system mainly consists of three parts: image acquisition, image processing and analysis, and output or display. Image acquisition is the core of machine vision, and the image acquisition system is composed of three parts: light source, lens, and camera. The selection and lighting of the light source can directly affect at least 30% of the imaging quality. So the light source is a very important part of the machine vision system.

Ⅰ. The role of the light source of the machine vision system

Through appropriate light source lighting design, the target information and background information in the image can be optimally separated, which can greatly reduce the difficulty of image processing algorithm segmentation and identification, and at the same time improve the positioning and measurement accuracy of the system, so that the reliability and comprehensive performance of the system can be improved. 

Conversely, if the light source is not properly designed, it will result in twice the effort in the image processing algorithm design and imaging system design. Therefore, the success or failure of light source and optical system design is the primary factor that determines the success or failure of the system.

1. Illuminate the target and improve the brightness of the target;

2. Highlight measurement features and simplify image processing algorithms;

3. Overcome the interference of ambient light, ensure the stability of the image, and improve the signal-to-noise ratio of the image;

4. Improve the positioning, measurement and recognition accuracy of the machine vision system, as well as the running speed of the system;

5. Reduce the complexity of system design and form the most favorable imaging effect for image processing;

Ⅱ. Light source classification and application of machine vision system

1. Ring light source

The ring light source provides different illumination angles and different color combinations, which can better highlight the three-dimensional information of the object; high-density LED array, high brightness; various compact designs save installation space; solve the problem of diagonal illumination shadows; optional diffuser guide light, the light spreads evenly.

Application areas: PCB substrate inspection, IC component inspection, microscope lighting, liquid crystal calibration, plastic container inspection, integrated circuit printing inspection.

2. Backlight

The high-intensity backlight illumination provided by the high-density LED array surface can highlight the contour features of the object, and is especially suitable as a microscope stage. Red and white dual-purpose backlight, red and blue multi-purpose backlight, can be deployed in different colors to meet the multi-color requirements of different measured objects.

Application areas: measurement of mechanical parts size, appearance detection of electronic components and ICs, film stain detection, transparent object scratch detection, etc.

3. Strip light source

The strip light source of the machine vision system is the preferred light source for the larger square structure measured object; the colors can be matched and combined freely according to the needs; the illumination angle and installation can be adjusted at will.

Application areas: metal surface inspection, image scanning, surface crack detection, LCD panel inspection, etc.

4. Coaxial light source

The coaxial light source can eliminate the shadow caused by the uneven surface of the object, thereby reducing interference; some use a beam splitter design to reduce light loss, improve imaging clarity, and evenly illuminate the surface of the object.

Applications: The series of light sources are most suitable for objects with extremely high reflectivity, such as scratch detection on the surfaces of metals, glass, films, wafers, etc., damage detection of chips and silicon wafers, Mark point positioning, and packaging barcode identification.

5. AOI special light source

Three-color light illumination at different angles highlights the three-dimensional information of the solder; additional diffuser plate guides light to reduce reflections; different angles are combined.

Application field: used for circuit board solder inspection.

6. Sphere integral light source

The hemispherical inner wall with integral effect uniformly reflects the light emitted from the bottom 360 degrees, so that the illumination of the whole image is very uniform.

Application field: suitable for curved surface, surface unevenness, curved surface detection, or surface detection of objects with strong reflection on metal and glass surfaces.

7. Linear light source

Ultra-high brightness, using cylindrical lens to condense light, suitable for various pipeline continuous detection occasions.

Application field: dedicated for matrix camera lighting, dedicated for AOI.

8. Point light source

High-power LED, small size, high luminous intensity; substitute for fiber optic halogen lamps, especially suitable as a coaxial light source for lenses, etc.; efficient heat dissipation device, greatly improving the service life of the light source.

Application field: suitable for telecentric lens, used for chip inspection, Mark point positioning, wafer and liquid crystal glass substrate correction.

9. Combined strip light source

The four sides are equipped with strip lights, and the lighting on each side is independently controllable; the required lighting angle can be adjusted according to the requirements of the measured object, and the applicability is wide.

Application cases: CB substrate inspection, IC component inspection, solder inspection, Mark point positioning, microscope lighting, packaging barcode lighting, spherical object lighting, etc.

10. Alignment light source

Fast alignment speed; large field of view; high precision; small size, easy to detect and integrate; high brightness, optional auxiliary ring light source.

Application field: VA series light source is a special light source for automatic circuit board printing machine alignment.