A Tool for Determining Task-Specific Measurement Uncertainties in GDT Parameters Obtained from Coordinate Measuring Machines

摘要

Measurement uncertainty plays a vital role in establishing measurement traceability to national and international standards. Likewise, it is a critical factor in the arbitration of issues pertaining to product conformance. For dimensional metrology, it is necessary to associate with each GD&T parameter an estimate of its uncertainty at a specified level of confidence. As a result, for manufacturers to adhere to current standards, inspection reports must be supplemented with statements like, "The uncertainty of the diameter of this nominally 1/4-inch diameter hole is 0.0008 inches, at 95% confidence." Obtaining uncertainty statements for measurements derived from a coordinate measuring machine (CMM) is not trivial. This stringent requirement is not satisfied by merely reporting the CMM manufacturer's estimate of the single point uncertainty, or by B89 test suite results, or even by a full parametric characterization of the CMM. All potential sources of error must be considered and must be propagated in a statistically valid way to yield an uncertainty on each measurement result.