Automatic demodulation of single-image fringe patterns with application in the evaluation of external defects in aeronautical surfaces by shadow-moire

Abstract

Automatic demodulation of single-image fringe patterns is of great importance in research areas were it is difficult to apply standard phase evaluation techniques such as phase sampling or Fourier transform methods. In this work we will present recent advances in the automatic demodulation of single-image fringe patterns. In particular we have used two methods for the demodulation process: the regularized phase tracker (RPT) and the isotropic quadrature transform (IQT). For a reliable and automatic demodulation of real fringe patterns by means of the RPT and the IQT techniques we have developed strategies for fringe pattern normalization, modulo 2π fringe orientation computation and adaptive processing, which all together configure a reliable and fast demodulation scheme. We have applied these techniques in the evaluation of external defects in aeronautical surfaces by the shadow moire technique and for this purpose a software package has been developed that works together with an in-line inspection system for indentation assessment designed by the company NDT-Expert. Experimental results of the system will be shown and performance will be discussed.