Locating error analysis and tolerance assignment for computer-aided fixture design

Based on the considerations of locating the error source and true positioning geometric dimensioning and tolerancing (GD/T), this paper presents a locating error analysis approach for set-up planning and fixture design. It includes three techniques: (1) by synchronizing locating elements with locating features, a fixturing coordination system is defined to simulate the actual locating situation; (2) a vectorial tolerance zone definition is explored. Compared with the tolerance zone definition published in ISO and ANSI Y14.5 standards, the biggest difference is that this definition is built up on the fixturing coordination system. Consequently, it is especially suitable for locating error analysis; (3) a locating error evaluation algorithm is developed with sensitivity analysis functions. The proposed models and techniques have been implemented with commercial CAD systems and have been applied to automobile manufacturing companies.