| dc.description.abstract | Moiré technology has been proven to be an excellent non-destructive method
of experimental mechanics for contour mapping or surface topography in recent years.
Wavelet transformation has been known as a novel tool for signal processing (or the
image data analysis) since the late of 1980s. Appling wavelet analysis on moiré
fringes analysis in modern optical system to measure the optical parameters was
explored in this dissertation. In this study, different wavelets (i.e. the Mexican hat
wavelet, the Daubaches’ wavelet, the Harr wavelet, and the Morlet wavelet) are
chosen under the requirement for analyzing different types of moiré patterns.
The Mexican hat wavelet is the one used to filter out the noise in moiré fringes
for focal length measurement of lens. The image of a Ronchi ruling (i.e. a grating)
arranged in front of the lens under test is superimposed with pixel arrays of the CCD
camera, a moiré pattern on CCD camera formed and captured into computer for
further processing. Since the pitch of the grating image depending on the power of the
testing lens, the power of testing lens can be determined by the moiré fringe changes
without or with testing lens. The experimental data show that this new method is
simple and reliable for focal length measurement.
Moiré deflectometry provides the lateral gradients of the optical path difference
and is suitable for analysis of phase objects. The Morlet and Harr wavelets are
respectively proposed to act as bases to reconstruct the phase functions form the
fringes which are superposition of wave front of lens under test and it’s shearing. In
moiré deflectometry, two matched transmitting gratings placed apart from each other
are used, and the lens under test is placed before the gratings in the path of collimated
beam. Numerical simulations are conducted in the wave front determination of optical
lens with Seidel aberrations.
Thirdly, wavelet analysis is used to improve the accuracy of the alignment
angle between LCD panels and x-cubes in the of LCD projector arrangement
processes which is the bottle neck for automatic alignment. Two straight parallel
gratings are projected from different panels, and moiré patterns would be observed
when panels are aligned properly. We find that Daubaches’ wavelet transformation
with muti-resolution analysis is a lucid and reliable methodology to analyze the
pitches of moiré patterns on the screen for estimating the angle of misalignment.
From the study for the focal length measurement using moiré technology with
wavelet, the setup is simpler than other methods based on interferometry, and the
accuracy is compatible with theirs. The technology developed in finding the
misaligned angle of LCD panels is adaptable for automatic control system in the
assembly line. The Seidel aberration determination by wavelet bases is proved more
stable than other polynomials. Hence, the combination of wavelet and moiré
techniques in optical system metrology is promising and shows fully potential in the
application of modern optical system | en_US |