Shadow Moire as a Tool for Measurements and Tridimensional Quality Control in Curved Surfaces 2000-01-1334
The Shadow Moiré fringe patterns are level lines of equal depth generated by interference between a master grid and its shadow projected in the surface. By a simple approach, the minimum error is of the order of the master grid pitch, that is, always larger than 0,1 mm resulting in a experimental technique of low precision. The introduction of a phase shift increases the accuracy of the Shadow Moiré technique. The current work uses the method of phase sifting to determine the three-dimensional shape of surfaces 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 due to 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. This contribution presents a method for whole-field shape measurements on large curved surfaces and a tool for tri-dimensional quality control based on the well known Shadow Moiré technique and proves it feasibility.