Comparison of the influence of CMM measurement strategies on uncertainty evaluation

Abstract

In the present application of Coordinate Measuring Machines (CMMs), generally only the estimated value of the measured quantity can be computed while its corresponding measurement uncertainty can not. It is well known that a result without its uncertainty is incomplete. However, uncertainty evaluation has always been one difficult issue in application of CMM because error sources causing measurement uncertainty of CMM are very complex. Based on Geometrical Product Specifications (GPS), the three measurement strategies of CMM application, i.e. conventional measurement, substitution measurement and compensation measurement strategies, are studied in this paper. For each measurement strategy, the uncertainty sources are analyzed, and the corresponding task-oriented uncertainty evaluation model is established. In this paper, the hole diameter measurement of one workpiece is taken as an example. The uncertainty is evaluated respectively according to the three different strategies, and the results are compared. The comparison result shows that the influence of different measurement strategy on measurement result is different, the maximum difference is about 2 times, and the accuracy of measurement can be improved through selecting proper measurement strategy for specific measurement task.