Irradiation solid angle When the object surface is uneven, the following patterns can be used for imaging. (1) When you want to make the unevenness stand out as a defect. (2) When you do not want the unevenness to stand for defects, but want to detect other stains, etc. It is necessary to obtain completely different results for (1) and (2), which can be achieved by adjusting the "irradiation solid angle". The irradiation solid angle is the angle of incident light to a point on an object, and the size of the irradiation solid angle controls the appearance of unevenness. (1) To make texture stand out → Place lighting at a distance with a small light-emitting surface. ( Smaller irradiation solid angle ) (2) To minimize the visibility of uneven surfaces → Use lighting with a large light-emitting surface at a closer distance to minimize the visibility. ( Larger irradiation solid angle ) This is also an essential factor to consider when using a backlight to capture the silhouette of the object.
Bright field and dark field A rough, low-reflective object such as paper or untreated wood will appear equally bright no matter where the light is projected. On the other hand, a object that is shiny and highly reflective, such as a mirror, polished metal or glass, is captured in a completely different image depending on where the light is projected from. It is necessary to change the lighting method based on whether the inspecting defects are to be captured brightly (white) or darkly (black). Bright field: Capturing the positive reflection of light irradiated on a object. It also captures the positive transmitted light that passes through a transparent object such as glass. Dark field: Capturing the diffuse reflection of light irradiated on a object. It also captures diffuse transmitted light transmitted through a translucent object such as an acrylic plate.
Bright field / Lighting: Spot light
Dark field / Lighting: Low-angle ring light
Large irradiation solid angle Cannot see the strike-conformity of the metal object.
Small irradiation solid angle Unevenness is emphasized, and the dents can be extracted.
Object 1. Smartphone screen (highly reflective and shiny) What you want to capture: flaws on the panel
Dome light + co-axial light at close proximity to the object
Co-axial light at a distance from the object
Bright field / Lighting: Direct flat light
Dark field / Lighting: Low-angle ring light
Large irradiation solid angle Unevenness makes it difficult to see foreign objects.
Small irradiation solid angle Remove unevenness and extract foreign objects
Object 2. Glasses (transparent and light-transmitting).
Narrow bar light from an angle
Dome light close to the object
What you want to capture: Fingerprints and smudges on the glass part
Large irradiation solid angle Image captured with a backlight does not capture the silhouette well due to light diffusion.
Small irradiation solid angle Suitable for dimensional measurement, etc., as light diffusion is minimal and the silhouette can be clearly recognized.
Dark field / Lighting: Diffused ring light
Bright field / Lighting: Co-axial box light
Backlight slightly larger than the object positioned at a distance from the object
Backlight larger than the object at close proximity to the object
Object 3. Cap of resin material. What you want to capture: Surface flaws
Dark field / Lighting: Bar light (VBA)
As described above, the color, type, size, and installation method of lighting can change the way an object is seen. The selection of the lighting is essential together with the camera and lens. VS Technology offers verification with actual objects, so please contact us for more information.
Object 4. Ballpoint pen What you want to copy: How cleanly is the logo printed?
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