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.
Optical Depth Field
Meaning
Optical imaging attributes represent the axial range in which a camera lens can resolve a target with acceptable sharpness. The optical depth field determines the vertical thickness of the region where features remain in sharp focus simultaneously. This attribute is a critical parameter when designing inspection systems for three-dimensional parts with large height variations.
When parts exceed this thickness, the resulting out-of-focus areas prevent automated algorithms from locating edges with high precision, which introduces unacceptable measurement uncertainty.
Focus Range
Lens magnification and aperture size directly control the span of the focused region. As magnification increases, the optical depth field shrinks, requiring precise z-axis positioning to capture clear images of all features. This physical limitation demands a trade-off between image resolution and the height range of the scan.
Image Quality
Blur occurs when the surfaces of a component sit outside the focus limits of the sensor. For parts with stepped geometries, a narrow optical depth field can result in fuzzy edges that skew measurements. Machine vision engineers often use specialized lenses or focus-stacking algorithms to overcome this issue.
Inspection Throughput
Measuring parts with multiple height levels can require multiple scans at different focal planes. A generous optical depth field allows a system to capture all necessary features in a single scan, increasing the throughput of the inspection line.