VOLUMETRIC ACCURACY DETERMINATION USING NON-TRADITIONAL DEVICES

摘要

Since the first 3-D Coordinate Measurement Machine was developed over twenty years ago, various devices and techniques have been used to determine their volumetric measuring accuracy. Early machines used calibrated length standards TV determine their linear measuring accuracy. Indicating devices located on the measuring arm, were nulled against each end of the length standard and the measured value was compared against the calibrated value. This, of course, was very time consuming and required a high degree of stability in the artifacts used so that their known length would be maintained. Also, this did not uncover many of the 3D errors such as axis squareness, straightness, or roll. Various parametric measuring devices, such as laser interferometers to measures length, straight edges to measure straightness, levels and autocollimators tom measure angularity changes, are still being used to determine the various translation errors, and utilizing a least squares analysis, an approximation of expected volumetric accuracy can be deduced. The possible problem with this technique, is that the use of indicators against straight edges, and static position measurements referenced to interferometers, autocollimators and precision levels, do not report the actual dynamic errors that the machine experiences when measuring a part, which are absolutely essential when using a dynamic probe such as a touch trigger probe.