Dimensional metrology with X-ray CT: A comparison with CMM measurements on internal features and compliant structures
Dimensional metrology with X-ray CT: A comparison with CMM measurements on internal features and compliant structures
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DOI：
10.1016/j.precisioneng.2017.08.021
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发表时间：
2018-01-01
影响因子：
3.6
通讯作者：
Smith, Stuart T.
中科院分区：
文献类型：
--
作者：
Villarraga-Gomez, Herminso;Lee, ChaBum;Smith, Stuart T.
x射线计算机断层扫描（CT）特别适合于具有内部几何形状，难以触及的部件特征以及易于变形或灵活结构的部件的尺寸测量。通过标准的发展，它也被接受为一种计量工具。本研究的目的是比较使用当前最先进的CT和坐标测量机（CMM）技术对包含内部结构和机械顺应性特征的工件的尺寸测量。它还旨在讨论一些问题，与最近制定的标准的测量不确定度估计。为了说明三坐标测量机的挑战和x射线CT在可靠尺寸检测方面的潜力，提出了两个不同的问题：1)具有触觉或基于视觉的测量技术无法达到的特征的金属工件的内部几何特征；2)通过触觉仪器（如三坐标测量机）评估具有机械接触而弯曲的杆的柔性物体部件的直径、形状和相对距离的尺寸测量。此外，讨论了直接应用ISO 15530系列来估计CT测量不确定度的一些问题，并将CT计量中不确定度预算的广义形式（仍然基于ISO 15530指南，但存在一些差异）应用于本文所提供的测量。对于几何特征的尺寸范围从0.6 mm到65 mm， CT和CMM测量之间的比较通常导致大多数测量结果的差异约为5 μ m或更小，而CT测量计算的扩展不确定度范围为1到20 μ m。CT对内部几何形状的测量结果的不确定度与金属工件拆卸后获得的CMM数据相当。然而，在测量柔顺结构的特殊情况下，传统的三坐标测量策略导致测量中的系统误差很大。使用外推方法证明，这两个系统的测量结果收敛到+/- 2 μ m以内。
X-ray computed tomography (CT) is uniquely suited for dimensional measurement of components having internal geometry, difficult-to-reach part features, and easy-to-deform or flexible structures. Through the development of standards it is also becoming accepted as a metrology tool. The objectives of this study are to compare dimensional measurements on artifacts containing internal structures and mechanically compliant features using current state-of-the-art CT and coordinate measure machine (CMM) techniques. It also aims to discuss some of the issues with recently developed standards for CT measurement uncertainty estimation. To illustrate the challenges of CMM and the potential of X-ray CT for reliable dimensional inspection, two different problems are presented: 1) characterization of internal geometry in a metallic artifact that has features inaccessible to tactile or vision-based measurement techniques; and 2) evaluation of dimensional measurement of diameters, form, and relative distances in the components of a flexible object with stems that bend due to mechanical contact by tactile instruments, e.g., CMM. In addition, some issues with the direct application of the ISO 15530 series for the estimation of CT measurement uncertainties are discussed, and a generalized formalism for uncertainty budgeting in CT metrology (still based on the ISO 15530 guidelines but with some differences) is applied to the measurements presented throughout this paper. For dimensions of geometric features ranging from 0.6 mm to 65 mm, a comparison between CT and CMM measurements typically resulted in differences of approximately 5 mu m or less for most of the measurements, while expanded uncertainties computed for the CT measurements ranged from 1 to 20 mu m. CT measurements on the internal geometries resulted in uncertainties comparable to CMM data that were obtained with the metallic artifact disassembled. However, in the particular case of measuring compliant structures, the conventional CMM strategies led to large systematic errors in the measurements. It is demonstrated that using extrapolation methods, measurements from these two systems converged to within +/- 2 mu m.