XtremeFringe is a new library for fringe pattern processing which incorporates modern methods for automatic
analysis including fringe pattern demodulation, fringe pattern filtering and phase unwrapping methods. XtremeFringe
is written in C# and is usable as an assembly from any .NET language (C#, C++ .NET, J#) and additionally as a
Matlab toolbox, which ensures an easy adaptation in custom applications, providing the user with a versatile and
powerful tool for fringe pattern analysis in a flexible way. The functions of XtremeFringe are suitable to be employed
in metrological applications such interferometry, photoelasticity, Moire techniques, holography, etc. supplying the user
with up-to-date fringe analysis tools.
In this work, we demonstrate the capabilities of the XtremeFringe library, processing different examples showing the
ability of the library to analyze complex fringe patterns in a fast, reliable and automatic way.
Phase detection is an important issue when dealing with optical metrology techniques for which the magnitude to be
measured is encoded through the phase of a given fringe pattern. Asynchronous phase detection techniques are
employed when the rate of phase change (frequency) it is not known. These techniques always present a variable
frequency response, in other words, their ability to recover properly the phase depends strongly on the local frequency.
In many experiments, it is possible to have a rough knowledge about the range of frequencies involved. Therefore, it
constitutes a great advantage to have a procedure to design an asynchronous demodulation method which is suited to a
particular frequency response for a given experiment. In this way, we get a better behaviour against noise which leads to
more accurate and reliable phase extraction.
In this work we present a technique to design asynchronous demodulation algorithms with a desired frequency response
using a Fourier-based technique. The method allows the design of algorithms with a limited algebraic error in the
recovered phase which have better properties than standard asynchronous phase detection techniques as it is shown in
numeric and real experiments.
We present a high-speed 3-D spatiotemporal shape measurement technique by means of structured light. Current methods use a constant number of images that do not take into account the available temporal continuity of the measured object. That is, they focus on acquiring and processing as quickly as possible a fixed number of images to solve for the correspondence problem and later obtain the 3-D shape by triangulation. The number of images used imposes the use of some spatial support. The major contribution of our research is a new spatiotemporal scheme that, depending on the object's movement, adaptively uses the maximum number of projected images consistent with the local temporal continuity, therefore solving the correspondence problem with the minimum possible spatial support for each position. This is achieved by the use of a hybrid color pattern composed of an analog sinusoidal periodic code in the red channel and a digital binary spatial code in the blue channel that is cyclically displaced. No subpixel calculation is used and it is possible to implement error correction strategies that make the method fast and reliable, enabling dynamic online 3-D measurement of objects in movement.
A new method for 3-D shape registration of prismatic objects is presented. The term prismatic object denotes any object with sharp boundaries on its surface. These kinds of objects cannot be correctly registered with typical existing methods, which require smooth overlapping of the whole surface. The method presented here is based on the use of reference marks, placed on a planar glass plate that is attached to the prismatic object. Two 3-D range measurements of the object are then acquired, before and after rotating the object by approximately 180 deg. Using the reference marks on the glass and two different calibrations of the 3-D range scanning system, these two range measurements can be correctly merged to provide a full 3-D range scan of the prismatic object.
In this work, an optoelectronic device that provides the absolute position of a measurement element with respect to a pattern scale upon switch-on is presented. That means that there is not a need to perform any kind of transversal displacement after the startup of the system. The optoelectronic device is based on the process of light propagation passing through a slit. A light source with a definite size guarantees the relation of distances between the different elements that constitute our system and allows getting a particular optical intensity profile that can be measured by an electronic post-processing device providing the absolute location of the system with a resolution of 1 micron. The accuracy of this measuring device is restricted to the same limitations of any incremental position optical encoder.
An all optical autofocus has been designed and tested for tight line width control in a high NA laser photoplotter system. The laser system is based in a GaN semiconductor laser with power 30 mW and wavelength 405 nm. The advantage of using this laser, despite the relatively long wavenlength, is compactness and easy for high frequency modulation. The autofocus system is based in a secondary 635 nm GaAlAs laser without need for wavelength, neither power stabilization. The two beams are delivered coaxially through the focusing lens by means of a dichroic beamsplitter. Focusing lens need no correction for chromatic aberration, as this is compensed by appropriate autofocus beam divergence. After reflection in the sample, the autofocus beam is separated from the returning writing beam and then guided to a collimation sensor, in which defocus of about 1/20 of the Rayleigh range of the writing beam can be detected and compensated by an analogue PID electronic control. Stable linewidth within 5% is achieved with different numerical aperture focusing lenses.
In this work, we present a method for the asynchronous direct demodulation of spatiotemporal fringe patterns by the estimation of the quadrature sign (sign of the fringe pattern quadrature signal) from one of the irradiance gradient components. The technique is based in the normalization of one plane of a spatio-temporal fringe pattern, an arcos demodulation and a final sign correction by means of the estimated quadrature sign. We present two experimental applications of the direct demodulation method presented. The first application is the measurement of surface topography by RGB Shadow-Moire. The second application is isochromatics retardation measurement by load stepping photoelasticity. In both cases good results are obtained confirming the suitability of the presented technique.
In this work we present two methods for the analysis of moire deflectograms. The first method is a Fourier-transform technique. The second method uses a regularization based method. Both methods are applied to realistic deflectograms and their performances are discussed.