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Here is a probing routine in which a machining center performs its own first-article inspection. The machine first probes a known reference to overcome measurement error. The difference between the known measurement and the measured value becomes the offset that will correct the probe measurement. This difference also serves as an offset for correcting the machining moves for the next workpiece in this setup.

This video was shot at Renishaw, and shows an actual part of the company’s automated production process. Renishaw offers these additional comments about the “reference comparison” or “artifact comparison” technique:

• The probe is calibrated against an artifact that has been calibrated at 20°C with uncertainty traceable to NPL.

• The artifact is the same material as the workpiece.

• It has geometry and features similar to the part.

• Comparative measurement gives traceability, and is independent of machine tool measurement accuracy.

• The part is measured using gaging points on the surfaces.

• Thermal effects determined from the artifact measurement are compensated when updating the process variables.