Light source selection
LED lights offer the best overall performance and are widely used in machine vision. LED lights have the following advantages:
1. High degree of shape freedom; it can be combined into various shapes and sizes, and the illumination angle can be freely adjusted. It can be customized according to customer needs.
2. It can be made in various colors as needed, and the brightness can be adjusted at any time;
3. The light source has good heat dissipation, stable brightness, and a long service life, capable of continuous use for tens of thousands of hours;
4. It has a fast response time and can reach maximum brightness in a very short period of time;
5. Low operating costs and high cost-effectiveness.
Bright field lighting and dark field lighting
Bright-field illumination refers to light that enters the camera after reflection, while dark-field illumination refers to light that does not enter the camera after reflection. Bright-field illumination typically uses direct light to observe the object as a whole (diffuse light appears black), which is beneficial for creating high contrast, but reflective surfaces will produce specular reflections. Dark-field illumination uses diffuse light to observe the object as a whole (direct light appears white), diffused light is reflected into the camera, but specularly reflected light is reflected away.
In defect inspection, bright-field illumination is primarily used for detecting defects that scatter and absorb light. In most bright-field illumination images, the background is bright and the defects are dark. Dark-field illumination is mainly used for detecting defects on smooth workpiece surfaces that contain scattered light. In most dark-field illumination images, the background is dark, and only the defects are visible. Dark-field illumination is often used to detect surface dirt and surface protrusions.
Backlighting and front lighting
Backlighting places the light source behind the object. This method can highlight the shadows of opaque objects or reveal the interior of transparent objects. Backlighting clearly outlines the edges of the object being measured; in the image, the obscured parts appear black, and the unobscured parts appear white, thus creating a clear black-and-white image. Front lighting is the opposite of backlighting, with the light source placed between the object and the camera. Depending on the angle, it can be further divided into "low angle" (less than 25 degrees) and "high angle" (above 75 degrees).
Auxiliary optical accessories
Polarizing filter: The function of a polarizing filter is to restrict the passage of specific light waves. Using a polarizing filter can eliminate the effects of light reflection, thereby highlighting the details of a surface. Polarizing filters are generally installed on the lens or on one side of the light source.
Anti-scat light filter: The function of the anti-scat light filter is to reduce the influence of external ambient light on the system light source. Using a light filter can filter out diffuse light from outside the system.
Diffuser plate: The function of a diffuser plate is to make light more uniform. A diffuser plate is a type of glass made by polishing one surface of glass with diamond powder to create an uneven surface. Light is refracted by the diffuser plate and then emitted in all directions, thus making the light more uniform.
