How to Test UV-A Fluorescence for a Machine Vision Inspection

YOYO UV

A camera can use UV-induced fluorescence to check whether a fluorescent adhesive bead or printed mark is present. Before choosing a light, capture a small set of images that show how consistently the target separates from the background.

Start with known samples

Collect parts with a complete bead or mark, parts with a missing section, and parts without the feature. Include ordinary lot-to-lot variation in the substrate. Keep the camera position, exposure and gain fixed during comparisons. Capture an image with the UV source off to reveal ambient light and any bright reflections that could be mistaken for the target.

Match the light and filter to the material

Ask the material supplier which excitation wavelengths to test. If 365 nm is a candidate, evaluate it on actual parts at the intended working distance. Select a camera filter that passes the fluorescence you want to detect and attenuates reflected UV and unwanted ambient wavelengths. Check the response of the whole camera and lens assembly. For an example of an emitter assembly with configurable board, lens and mounting options, see YOYO UV’s customizable 365 nm LED module.

Check the usable margin

Compare brightness in the expected bead or mark area with adjacent background. Repeat across part positions, production speeds and lighting conditions. Look for overlap between the readings from acceptable and defective parts. If they overlap, revisit the lighting geometry, filter or exposure before setting a pass threshold. Keep representative images and the capture settings so you can repeat the test after a material or fixture change.

Further reading · NI’s practical guide to machine vision lighting