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Position Error in Assemblies and Mechanisms:
Statistical and Deterministic Methods

Jon Wittwer, Brigham Young University
Presented June 15, 2001 at the ADCATS 2001 Conference

A common misconception in tolerance analysis is that the circular tolerance zone is the best representation of position error.  While this is true for simple two-dimensional features with location dimensions that have equal standard deviations, for assemblies and mechanisms the position error is best described as elliptical. 

Both deterministic and probabilistic methods have been used to determine the effects of manufacturing tolerances on position error. This presentation demonstrates the use of the direct linearization method to estimate the position error, and compares this method to other deterministic and probabilistic methods. The generalized Bivariate normal model is shown to be an accurate representation of position error in two-dimensional assemblies and mechanisms.

Bio
Jon Wittwer is a graduate student at Brigham Young University researching tolerances in compliant mechanisms and micro-electro-mechanical systems. He received a National Science Foundation graduate research fellowship for work in these areas in 2000 after graduating summa cum laude with a degree in Mechanical Engineering.

 

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