Open Access Dissertation
The need for reliable and consistent measurement has become more acute with the use of statistical process control (SPC), gage repeatability and reproducibility (Gage R&R) assessment, and high precision, computer-controlled gaging systems. Although it is often overlooked, the inspection methodology under which various features are inspected has an impact on Gage R&R results. This notion was confirmed when a 1993 thesis study substantiated inspection methodology as a source of measurement variability in direct computer-controlled, coordinate measuring machines (DCC/CMMs). Although this study explored a methodology to bring measurement variability under statistical control, the tested assessment methodology--single baseline repeatability assessment--was not validated. This study was initiated to assess the effectiveness of multi-baseline repeatability assessment (MBRA) in (a) identifying diameter/probe hit categories with inherent stability in measurement repeatability on the XY, XZ, and YX planes and (b) generating planar inspection programs that yield improvements in diameter measurement repeatability on each of the three planes. The methodology of this study was based on a Brown & Sharpe Xcel $7\cdot 6\cdot 5$ CMM, twenty-three circular test specimens of different diameters, an inspection methodology varying from 3-10 probe hits, and two repeatability determination methods--range and standard deviation. The results of this study indicated: (a) in general, diameter measurement repeatability can be improved by increasing the number of contact probe hits; (b) MBRA is an effective methodology for quantifying stability in measurement repeatability; and (c) MBRA is not an effective methodology for improving measurement repeatability (diameter/probe hit categories with the greatest stability did not necessarily possess the "best" repeatability). The principle implication presented by this study is that multi-baseline repeatability assessment gives CMM users an assessment tool that can be used to establish (a) inspection methodologies under which different features can be inspected with high precision, (b) part orientations (planes) under which circular features can be inspected with high precision, (c) machine signatures upon which machine wear can be monitored and tracked, and (d) machine signatures upon which repeatability comparison studies can be conducted.
Year of Submission
Department of Industrial Technology
Ahmed Elsawy, Advisor
1 PDF file (x, 249 pages)
©1996 Bruce Marsh
Marsh, Bruce, "An investigation of diameter measurement repeatability using a coordinate measuring machine and a multi-baseline repeatability assessment methodology" (1996). Theses and Dissertations @ UNI. 905.