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

Based on the considerations of locating the error source and true positioni ng geometric dimensioning and tolerancing (GD/T), this paper presents a loc ating error analysis approach for set-up planning and fixture design. It in cludes three techniques: (1) by synchronizing locating elements with locati ng features, a fixturing coordination system is defined to simulate the act ual locating situation; (2) a vectorial tolerance zone definition is explor ed. Compared with the tolerance zone definition published in ISO and ANSI Y 14.5 standards, the biggest difference is that this definition is built up on the fixturing coordination system. Consequently, it is especially suitab le for locating error analysis; (3) a locating error evaluation algorithm i s developed with sensitivity analysis functions. The proposed models and te chniques have been implemented with commercial CAD systems and have been ap plied to automobile manufacturing companies.