Optical CMM Gauge Capability Evaluation for Sub Millimeter Molded Features
Optical CMM capability on sub-millimeter molded features requires material-specific bias correction and telecentric backlighting to maintain GR&R under 20%.
Telecentric Lighting
Meaning
Illumination techniques utilize specialized optics to produce parallel rays of light across the entire field of view. Incorporating telecentric lighting in a machine vision system eliminates perspective error and allows for the accurate measurement of three dimensional objects.
Beam Collimation
Lens elements align the photons so that they strike the part surface at a constant angle. This telecentric lighting setup ensures that the size of the object image does not change even if the part moves slightly toward or away from the camera. Shadows produced by this method are sharper and more predictable than those from conventional sources.
Perspective Error
Reduction of magnification changes across the sensor improves the reliability of automated gauging. Because telecentric lighting prevents the side of a tall part from appearing in the image, the software sees only the true profile of the top surface. This property is essential for measuring the diameter of cylinders or the spacing of deep holes.
Shadow Sharpness
Increased edge contrast allows the detection algorithms to work with higher precision. While a standard light might create a fuzzy boundary due to diverging rays, telecentric lighting maintains a crisp transition from light to dark. This clarity supports sub pixel accuracy in high speed production environments where the time for image processing is limited.