The Shadow Moiré method using the phase shifting technique and digital image processing: computational implementation and application to the 3D-reconstruction of a buckled plate

Abstract

The Shadow Moiré fringe patterns are level lines of equal depth generated by interference between a master grid and its shadow projected on the surface. In simplistic approach, the minimum error is about the order of the master grid pitch, that is, always larger than 0,1 mm, resulting in an experimental technique of low precision. The use of a phase shift increases the accuracy of the Shadow Moiré technique. The current work uses the phase shifting method to determine the surfaces three-dimensional shape using isothamic fringe patterns and digital image processing. The current study presents the method and applies it to images obtained by simulation for error evaluation, as well as to a buckled plate, obtaining excellent results. The method hands itself particularly useful to decrease the errors in the interpretation of the Moiré fringes that can adversely affect the calculations of displacements in pieces containing many concave and convex regions in relatively small areas

Acoustic Shadow Moiré Interference, Experimental Proof

“…This technique is cost effective, noninvasive, fast, and nonradiative that can be easily automated. Using phase-shifting technique, shadow moiré can be employed to obtain the 3D image of an object using a software that utilizes isothermic fringe patterns and digital image processing [9]. A comparison between shadow moiré versus projection moiré shows that the projection moiré can provide about 27 times the accuracy of normal shadow moiré or 27 times pixel density [10].…”

An accurate method to calibrate shadow moiré measurement sensitivity

“…Obviously, the contour interval ∆z is a function of fringe order, and is not constant. But, in most cases, d and l are much larger than p and h n, so that equation ( 2) can be simplified to equation ( 4), which is derived based on the parallel lights illumination [14,15].…”