By Jon M. Baldwin, Kim D. Summerhays and Daniel A. Campbell
Comprehensive tools for evaluating the uncertainty of measurements made with coordinate measuring machines (CMMs) have been available for several years, yet their widespread application generally has lagged the existing technology, presenting significant problems for producers and consumers of CMM measurement results as well as for auditors of CMM measurement operations. In searching for reasons for this slowness to embrace currently available tools, we regularly come upon two factors. The first of these is confusion about the significance and applicability of various indices of CMM measurement uncertainty. Secondly, the depth of understanding of CMM measurement strengths and weaknesses, and their impact on product profitability, which can be developed from a comprehensive investigation of CMM measurement uncertainty, are not widely understood. We hope to clarify some of these issues and to encourage both producers and users of CMM results as well as auditors to enhance the value and significance of CMM data by application of these now technically mature tools.
Computer simulation techniques excel in offering the best combination of thorough coverage of measurement influence factors, defendability of results and general applicability for complex measurement systems such as CMMs. In this presentation, we briefly discuss the principles of computer simulation methods and the concept of task-specific measurement uncertainty as it applies to CMMs. Following this, we present several practical examples, adapted from real-world measurement problems, of the use of simulation methods in CMM uncertainty evaluation, ranging from traceability demonstration and measurement process optimization to analysis of measurement uncertainty impacts on product profitability.
