Instantaneous velocity displacement and contour measurement by use of shadow moiré and temporal wavelet analysis

Abstract

A temporal wavelet analysis method is proposed for velocity, displacement, and three-dimensional surface-profile measurement of a continuously deforming object by use of the shadow moiré technique. A grating is placed close to a deforming object, and its shadow is observed through the grating. The moiré fringe patterns, generated by the interference of the grating lines and their shadows, are captured by a high-speed CCD camera with a telecentric gauging lens. Instantaneous frequency of gray-value variation is evaluated point by point with the continuous wavelet transform. From the instantaneous frequency of each point on the object, the velocity, displacement, and high-quality surface profile at different instants can be retrieved. In this application, two specimens are tested to demonstrate the validity of the proposed method: One is a small coin with a rigid body motion, and the other is a simply supported beam subjected to a central point load. The results are compared with those obtained from temporal Fourier-transform and mechanical stylus methods.

Atmospheric Turbulence Characterization and Wavefront Sensing by Means of the Moiré Deflectometry

“…It is used to study numerous static physical phenomena such as refractive index gradient (Karny & Kafri, 1982;Ranjbar et al, 2006). In addition, it has a severe potential to study dynamical phenomena such as atmospheric turbulence (Rasouli & Tavassoly, 2006a;b;2008;Rasouli, 2010), vibrations (Harding & Harris, 1983), nonlinear refractive index measurements (Jamshidi-Ghaleh & Mansour, 2004;, displacements and stress (Post et al, 1993;Walker, 2004) (Tay et al, 2004), acceleration sensing (Oberthaler et al, 1996), etc. The moiré pattern can be created, for example, when two similar grids (or gratings) are overlaid at a small angle, or when they have slightly different mesh sizes.…”

The 2D Continuous Wavelet Transform: Applications in Fringe Pattern Processing for Optical Measurement Techniques

“…In particular, it has been shown that 1-D and 2D continuous wavelet transform (CWT) using Gabor atoms is a natural choice for proper analyses of fringe images. This kind of analysis has been used for fringe pattern denoising and fringe pattern demodulation showing several advantages, for example in laser plasma interferometry [38], in shadow moiré [39][40][41], in profilometry [42][43][44], in speckle interferometry [45], in digital holography [46], and other optical measurement techniques [47][48][49][50][51][52][53][54][55].…”

Sinusoidal phase modulating interferometer for real-time surface profile measurement

“…Surface profile is one of the most important features of objects, and it is the key factor to guarantee and enhance the properties of mechanical, electronic and optical devices. Recently, the surface profile measurement technique becomes a research spot in the field of measurement [1][2][3][4][5][6]. There exist two methods in the surface profile measurement.…”