Evaluating Optical CMM Accuracy for Micro Molded Features
Evaluating optical CMM accuracy for micro molded features requires quantifying optical lens resolution, polymer light dispersion, and sensor thermal drift.
Coaxial Illumination
Meaning
Optical lighting configurations designed for machine vision systems project light along the same optical axis as the camera lens to eliminate shadows on reflective surfaces. A beam splitter redirects light from a side source down onto the target, allowing coaxial illumination to capture fine surface detail on polished metals or silicon wafers. The technique is restricted to flat, specular parts and becomes ineffective when used on highly contoured or diffuse objects.
Lighting Mechanism
Internal beamsplitters divide the incoming light path to align the illumination source with the receiver optics. When light travels through the beamsplitter, it strikes the specimen perpendicularly and returns directly to the sensor. By employing this configuration, systems prevent the shadowed edges common in off-axis lighting, delivering a bright, uniform background.
Inspection Domain
Surface inspection of silicon wafers relies on precise alignment of the light path. Microscopic diagnostics often use coaxial illumination to resolve multi-layered circuit patterns. The technique succeeds in revealing shallow relief across planar structures, but it fails to define boundaries on rounded objects.
Contrast Limitation
Highly reflective materials disperse the directed light if they have curved geometries. Because the light must return along the optical axis, coaxial illumination generates blind spots on curved chamfers. Manufacturers must select alternative ring lights when profiling cylindrical pins or hemispherical contacts.