Inspection of scratches on metal plate object

Scratches on the surface of a flat metal plate are inspected. Typically, highly parallel coaxial lighting is employed so that scratches appear black and the surrounding area appears white. However, when the scratches are shallow (or thin or fine), they can be captured in white along with the surrounding area. This occurs because the light emitting surface of the coaxial lighting is large, and when the installation height (LWD) is low, light strikes the object from an oblique angle and scatters at scratches. For such scratches, light with higher parallelism is required. Using an OPF-50x15W-PS backlight with narrow directivity angle and arranging the camera and lighting in a V shaped configuration allows the scratches to be captured in black and the surrounding area in white.

Imaging example

Not acceptable: Coaxial lighting

The large emitting area and oblique illumination cause the scratch to reflect light, making it appear white in the image. Note: The scratch was made for testing purposes.

✓ Back lighting (50 x 15 ㎜）

By illuminating the workpiece with higher-parallelism light, the undamaged areas produce specular reflection and appear white, while the scratched areas are captured as black.