How to Select the Appropriate Light Source for a Machine Vision System

Introduction: In a machine vision system, the role of the light source is similar to the 'light' in human vision, directly affecting the imaging quality and detection accuracy. Selecting the appropriate light source requires a comprehensive consideration of the characteristics of the detection target, environmental conditions, and technical requirements. Starting from practical applications, this article will sort out the core logic of light source selection for you.

When selecting a light source, it is necessary to clarify the characteristics of the detection target.

I. Material and Surface Characteristics:

1. Highly Reflective Objects (such as metals and glass): It is necessary to avoid specular reflection, and low-angle ring lights or coaxial light sources should be preferentially selected.

2. Transparent/Semi-transparent Objects (such as plastic bottles and films): Backlights or transmission light sources are suitable to highlight the outline or internal structure.

3. Color and Texture:

For detecting color defects (such as color differences in printed products): Select a light source with a wavelength complementary to the target color (for example, a red light source enhances the green contrast).

For surface texture detection (such as scratches and dents): Use low-angle bar lights or dome lights to enhance the texture details through shadows.

II. Selection of Light Source Types, Common Light Source Types and Applicable Scenarios:

1. Ring Light Source: Provides uniform illumination and is suitable for objects with a flat surface (such as PCB board detection).

2. Bar Light Source: Can be combined at multiple angles and is suitable for long strip workpieces or edge detection.

3. Backlight Source: Used for contour and dimension measurement (such as screw pitch detection).

4. Coaxial Light Source: Eliminates reflections and is suitable for mirror surfaces or highly reflective materials (such as scratch detection on mobile phone screens).

5. Point Light Source/Line Laser: Used for 3D contour reconstruction or high-precision positioning.

III. Matching of Wavelength and Brightness:

1. Wavelength Selection:

Short Wavelengths (blue light, ultraviolet): Have weak penetrability and are suitable for detecting fine surface defects (such as metal scratches).

Long Wavelengths (red light, infrared): Have strong penetrability and can detect internal structures (such as foreign objects inside food packaging).

2. Brightness Adjustment:

Excessive brightness will lead to overexposure of the image, and insufficient brightness will increase noise. It is necessary to adjust dynamically according to the camera's exposure time.
IV. Consideration of Environment and Cost:

3. Adaptability to the Industrial Environment: In high-temperature and vibrating environments, anti-interference LED light sources should be selected.

4. Cost-effectiveness: On the premise of meeting the accuracy requirements, give priority to light sources with a long lifespan and low energy consumption.

Conclusion: The essence of selecting a light source is to 'tell a story with light' - highlighting the target features through light and hiding the interference information. Only by flexibly combining the types, wavelengths, and angles of light sources can the machine 'see' more clearly.