Optimization of fringe spacing in a digital flatness test.
The optimum condition of fringe spacing in a flatness test using digital fringe analysis is described. This condition is based on information theory and maximizes the amount of measurement information in a fringe image. First, the relationship between resolution and data sampling number is discussed. Then the optimum fringe spacing is derived using the concept of average information--entropy. Numerical analysis to evaluate fringe spacing in FFT fringe analysis is performed using the derived condition. An experiment is carried out with a liquid level flatness tester and its results show high space frequency resolution superiority at the condition.
Hatsuzawa
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National Research Laboratory of Metrology, 1-1-4, Umezono, Sakura-mura, Niihari-gun, Ibaraki 305, Japan.