Evaluation Of Fringe Patterns Research Articles

An exact approach for radius of curvature measurement in a calibration test sphere

In this paper we present a technique to measure the radius of curvature of a test sphere based on the relation between acquired images of a circular cosine fringe pattern and size of virtual image formed on the calibration test surface. Radius of curvature is calculated with the exact equation proposed, using the parameters of the optical setup. Fringe pattern evaluation was performed by locating extrema indices. The mathematical formulation as well as the experimental setup and results are presented. After applying a linear fit algorithm to the data as a method of compensation, obtained results show an error within the tolerance established by the ISO 10343 specifications.

Evaluation of fringe pattern magnification for lens dioptric power measurement

Dioptric power measurement is an essential part of the characterization and quality control of lens manufacturing. In this framework, a fairly simple and potentially cost-effective method for lens characterization by interferometric fringe evaluation is reported. This technique consists of acquiring images of straight and parallel fringes projected onto a planar screen through the lens to be tested and in the regions surrounding the lens. Upon phase evaluation procedures, two apparent three-dimensional shapes of the screen are obtained, namely, the background contour and the one visualized through the test lens. The lens power is obtained as a function of the ratio between the two shapes and the parameters of the optical setup. The fringe pattern evaluation was performed by four-stepping and phase unwrapping methods. The results obtained by this technique were compared with the ones obtained by a commercial focimeter in the measurement of unifocal and progressive power lenses.

Multiwavelength electronic speckle pattern interferometry for surface shape measurement

Profilometry by electronic speckle pattern interferometry with multimode diode lasers is both theoretically and experimentally studied. The multiwavelength character of the laser emission provides speckled images covered with interference fringes corresponding to the surface relief in single-exposure processes. For fringe pattern evaluation, variations of the phase-stepping technique are investigated for phase mapping as a function of the number of laser modes. Expressions for two, three, and four modes in four and eight stepping are presented, and the performances of those techniques are compared in the experiments through the surface shaping of a flat bar. The surface analysis of a peach points out the possibility of applying the technique in the quality control of food production and agricultural research.

Temporal evaluation of fringe patterns with spatial carrier with an improved asynchronous phase demodulation algorithm

Temporal evaluation of fringe patterns with spatial carrier with an improved asynchronous phase demodulation algorithm

Temporal evaluation of fringe patterns with spatial carrier with an improved asynchronous phase demodulation algorithm

A method for temporal evaluation of fringe patterns with a spatial carrier is presented. The proposed technique consists in the recording of the temporal irradiance fluctuations obtained when a linear variation of the set-up sensitivity is introduced. In this way, the use of a spatial carrier introduces a linear temporal carrier frequency. This allows the use of fast and low time consuming temporal asynchronous demodulation algorithms, similar to those employed in spatial phase shifting techniques. An existing five-step algorithm has been corrected for asynchronous demodulation. It is shown that it is possible to fix the sensitivity variation in such a way that the algorithm presents optimum behaviour against noise and nonlinearities presented by the temporal irradiance signal. Finally, the technique has been applied to measure the shape of an object, using a fringe projection set-up.

Sinusoidal least-squares fitting for temporal fringe pattern analysis

A sinusoidal least-squares fitting algorithm (SLSF) is applied to temporal evaluation of fringe patterns. The least-squares fitting of a sine function directly with the irradiance fluctuations due to a linear sensitivity variation of the optical set-up avoids the problems inherent to Fourier analysis. Experiments show that the proposed method has a better noise immunity than the temporal Fourier method. An application of this technique to Deflectometry is also presented.

Synchronous detection technique for temporal fringe pattern analysis

An alternative method for temporal evaluation of fringe patterns is proposed. The method is based on the application of a synchronous detection system for processing the temporal irradiance fluctuations generated when the sensitivity of the optical set-up is changed. The technique requires an easy computing implementation and presents good noise rejection characteristics. In particular, the proposed method does not require to store the whole set of fringe images as it happens with Fourier techniques which allows for a faster data processing. Results of this method proved on synthetic fringe images as well as in real experiments are presented.

Temporal phase evaluation by Fourier analysis of fringe patterns with spatial carrier

Abstract A new method is presented for the temporal evaluation of fringe patterns with spatial carrier. The proposed technique involves recording the irradiance fluctuations obtained when a linear variation of the set-up sensitivity is introduced. In this condition, the use of a spatial carrier introduces a linear temporal carrier frequency. In this way, Fourier analysis can be performed to obtain the phase and, finally, the quantity to be measured. The optimum conditions for the sensitivity variation have been studied in order to minimize the errors associated with the Fourier analysis. The technique has been applied to measure the distribution of ray deflections on the surface of two ophthalmic lenses using a deflectometric set-up.

Temporal phase evaluation by fourier analysis of fringe patterns with spatial carrier

A new method is presented for the temporal evaluation of fringe patterns with spatial carrier. The proposed technique involves recording the irradiance fluctuations obtained when a linear variation of the set-up sensitivity is introduced. In this condition, the use of a spatial carrier introduces a linear temporal carrier frequency. In this way, Fourier analysis can be performed to obtain the phase and, finally, the quantity to be measured. The optimum conditions for the sensitivity variation have been studied in order to minimize the errors associated with the Fourier analysis. The technique has been applied to measure the distribution of ray deflections on the surface of two ophthalmic lenses using a deflectometric set-up.

Computer aided evaluation of fringe patterns

The crucial step in computer aided evaluation of interferometric fringe patterns is the determination of the interference phase distribution from the recorded and stored intensity pattern. Methods for determination of the interference phase distributions from fringe patterns are presented and the most important methods, which are skeletonising, temporary heterodyning, phase shifting and Fourier transform evaluation are compared with regard to experimental requirements, achievable resolution and precision, as well as inherent noise suppression and image enhancement. The comparison shows that whenever phase shifting is possible, it is the best choice. If only one interference pattern is offered, Fourier transform evaluation is recommendable. For demodulation of the wrapped phase a path-independent algorithm is presented. Practical examples are given from holographic interferometric measurements.

Application of computer-aided evaluation for holography and similar techniques

The application of computer based evaluation of fringe patterns achieved by holographic interferometry, projected fringes or moiré technics are demonstrated for • - vibration analysis; • - non destructive testing; and • - contour measurements. The vibration analysis is carried out on dynamic stressed parts by impact or operation. Even rotating objects can be investigated. Non destructively tested materials are compound materials like glass or carbon fibre reinforced plastics and honeycomb panels for aerospce application and tires. A different evaluation technique is used in droplet analysis. The 3-dimensional image, stored in the hologram, is automatically evaluated for the investigations of injection sprays.