Industrial light source selection skills in machine vision

1. The main function of the light source

1. Illuminate the target and increase the brightness. In industrial vision systems, natural light is generally insignificant, and the formed images are often dark and dark. 2. Form an
imaging effect that is conducive to image processing, reducing the complexity of the visual system and the requirements for image processing algorithms
3. Ensure the stability of the image and improve the accuracy and efficiency of the system

2. Classification of light sources

1. Classify according to color

White (composite light), red, blue, green, infrared, ultraviolet

2. Classification according to shape

(1) Coaxial light source
(2) Ring light source
(3) Ring low-angle light source
(4) Bar light source
(5) Dome light source (bowl light source/dome light source)
(6) Surface light source

3. Bright field and dark field

1. Bright field is the most commonly used lighting scheme, which is formed by direct frontal light irradiation.
2. The dark field is mainly formed by low-angle or backlighting.
3. Generally speaking, the dark field will make the background appear dark, while the detected object appears bright.

4. Light source selection criteria

1. Choice of lighting method

(1) Observe the characteristics of the detection part, whether there is damage, shape, presence, etc.
(2) Observe the surface, whether it is flat, curved or uneven

2. The method and shape of lighting

(1) polarized light

It is used to reduce specular reflection or glare, and the light is changed through the polarizer to change the propagation direction, and the polarizer in front of the lens is used together.

3. Choose the color of the lighting

There are generally three types of LED lighting.

(1) Specular reflection type

The light received by the lens comes from the specular reflection of the object
. The character inspection on the metal surface can be extended to the detection of concave and convex objects on the metal surface. The metal surface is easy to reflect light, and the reflective ability of the concave and convex engraved places is poorer, which is easy to cause differences.
The low-angle shadowless light source adopts a unique illumination structure, and the light emitted from the LED is evenly diffused and irradiated. The flexible linear circuit board is fixed at a 90-degree illumination angle, and is refracted by a diffuse reflection plate to irradiate the measured object at a low angle. to enhance surface features.
The flat shadowless light applied to the metal surface has two effects: it can shoot the concave-convex surface into a plane to eliminate reflections and background interference, such as wrinkles, which is convenient; 2. It is similar to coaxial light after being pulled up

(2) Diffuse reflection type

Avoids specular light from the subject and receives an overall, uniform light
Ideal for products with a thin film surface

(3) Transmission type

Receives light from the subject's background. It is a lighting method for detecting contours.
The foreign matter is similar to the workpiece in color, and it is difficult to distinguish from the surface. Therefore, it is necessary to emphasize the contrast between the foreign matter and the surface of the workpiece. Although it is difficult to observe the foreign matter with reflected light, as long as the thickness and color of the foreign matter are consistent with the workpiece If there is a difference between them, the black shadow of the foreign object can be revealed by using the transmitted light from the back of the workpiece.