A Comparison of Virtual Condition Cylinder Evaluation Methods in Coordinate Metrology

Abstract

When a cylindrical datum feature is specified at maximum material condition (MMC) or least material condition (LMC) a unique circumstance arises: a virtual condition (VC) cylindrical boundary must be defined [1]. The geometric relationship between a cylindrical point cloud obtained from inspection equipment and a VC cylinder has not been specifically addressed in previous research. In this research, novel approaches to this geometric analysis are presented, analyzed, and validated. Two of the proposed methods are new interpretations of established methods applied to this unique geometric circumstance: least squares and the maximum inscribing cylinder (MIC) or minimum circumscribing cylinder (MCC). The third method, the Hull Normal method, is a novel approach specifically developed to address the VC cylinder problem. Each of the proposed methods utilizes a different amount of sampled data, leading to various levels of sensitivity to sample size and error. The three methods were applied to different cylindrical forms, utilizing various sampling techniques and sample sizes. Trends across sample size were analyzed to assess the variation in axial orientation when compared to the true geometric form, and a relevant case study explores the applicability of these methods in real world applications.