Showing papers on "Moiré pattern published in 2000"

Moiré Methods for Engineering and Science — Moiré Interferometry and Shadow Moiré

Abstract: Moire interferometry and shadow moire are extraordinarily versatile and effective methods for determining in-plane and out-of-plane displacement fields, respectively. The basic concepts are reviewed for both methods, topics on practice and analysis are addressed, and numerous examples of important applications are presented.

Shadow moire profilometry using the phase-shifting method

Abstract: Two-stages are planned to measure the 3-D profile of objects by using the phaseshifting method, based on shadow moiretopography. The stages essentially consist of moving the grating vertically, which produces a change in the moirepattern, and rotating the grating, which results in a constant phase shift regardless of the moirefringe order. In practice, an additional stage of moving the grating horizontally has to be added, which averages the grating period and yields a better moirepat- tern. We aim to improve the shortcomings inherent in the conventional method, such as complicated operation of the optical arrangement, and our emphasis is on describing the novel methodology and justifying it by an error simulation test. The experimental results show that this tech- nique is available for practical applications. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00408-6)

Fourier transform method of fringe analysis for moiré interferometry

Abstract: An automated Fourier-transform method of phase retrieval of moire interferometric fringe pattern is presented. The method is shown to provide fast and accurate determination of the phase information by removing the carrier without shifting in frequency domain the filtered Fourier spectrum of the carrier-modulated moire fringe pattern. The principle of the method is described and moire interferometric measurements with submicron sensitivity of the in-plane displacement fields of thick carbon-fibre/PEEK composite laminates are analysed as an example of the application of the technique.

Reducing tilt errors in moiré linear encoders using phase-modulated grating

Abstract: A new hardware compensation method reducing displacement measurement errors, caused by tilt of the index scale in a moire linear encoder, has been developed. In conventional moire linear encoders, the detectors are aligned perpendicular to the line of the moire fringes and this structure is very sensitive to an unwanted tilt of the gratings. In this article, a newly designed grating, called a phase-modulated grating, is developed to compensate for nonorthogonal errors. By using the phase-modulated grating instead of a conventional index, it is possible to reduce nonorthogonal errors of the moire linear encoder.

Fringe analysis for moiré interferometry by modification of the local intensity histogram and use of a two-dimensional Fourier transform method

Abstract: A noise-immune method for phase retrieval of a single moire interferometric fringe pattern is presented and discussed. The method is shown to provide accurate recovery of the phase information by a combined method based on modification of the local intensity histogram and use of a two-dimensional Fourier transform of the enhanced moire fringe pattern. The principle of the method is described and the experimental results of moire interferometric measurements with submicrometre sensitivity of the in-plane displacement fields of thick carbon fibre/PEEK composite laminates are presented as an example of the application of the technique.

Generation of carrier fringes in holography and shearography.

Abstract: Double-exposure holography and double-exposure shearography are often used together with the carrier fringe technique, which requires additional shifting of the light source in a prescribed manner between exposures. In the holographic carrier fringe technique, difficulty in prescribing a suitable movement of the light source may be alleviated through visualization of the moire fringes that are reconstructed by slight displacement of two overlaid families of ellipsoids in a holodiagram. Because shearography is the first differential of holography, it is often impractical to perform two successive optical differentiations on the ellipsoids to visualize the shearographic carrier fringes. A simple method of discerning holographic and shearographic carrier fringes is described. The method is based on the hyperboloids in a holodiagram that represent Young’s (interference) fringes produced by the interference of two point sources. The hyperboloids are analogous to holographic carrier fringes, whereas the moire patterns reconstructed from two overlaid hyperboloids are analogous to shearographic carrier fringes. Use of this method for explaining the formation of deformation fringes in plate bending, as well as the effect of light-source movement on the deformation fringes, is also illustrated.

Combining interference fringe patterns to a moire fringe pattern

Abstract: An interferometer (1) is arranged to form a first interference fringe pattern comprising at least ten interference fringes; recording an image of said first interference fringe pattern; perturbing an optical path in the interferometer (1) to form a second interference fringe pattern comprising at least ten interference fringes; and combining an image of said second interference fringe pattern with the recorded image of the first interference fringe pattern to produce a further image comprising a moire fringe pattern arising from a difference or differences between the first and second interference fringe patterns. The combining step involves subtraction (4) of digital images. Different wavelengths and interferometers are used: Michelson, Mach-Zehnder, Fizeau, Twyman-Green. In this new approach, all the errors of a poor quality, misaligned system are accepted and then eliminated by the combination process, producing a moire fringe pattern. The method enables very large aperture optical systems for traditional and engineering interferometers to be constructed from inexpensive and basic components.

Digital Processing and Evaluation of Fringe Patterns in Optical Metrology and Non-Destructive Testing

Abstract: The basic principle of modern optical methods in experimental solid mechanics such as holographic interferometry, speckle metrology, fringe projection and moire techniques consists either in a specific structuring of the illumination of the object by incoherent projection of fringe patterns onto the surface under test or by coherent superposition (interference) of light fields representing different states of the object. A common property of the methods is that they produce fringe pattern as output. In these intensity fluctuations the quantities of interest — coordinates, displacements, refractive index and others — are coded in the scale of the fringe period. Consequently the task to be solved in fringe analysis can be defined as the conversion of the fringe pattern into a continuous phase map taking into account the quasi sinusoidal character of the intensity distribution. The course starts with a physical modeling of the image content that contains the relevant disturbances in optical metrology. After that the main techniques for quantitative phase reconstruction together with the most commonly used image processing methods are presented. Because image processing is an important prerequisite for holographic non-destructive evaluation (HNDE) an overview of modern approaches in automatic flaw detection based on knowledge assisted and neural network techniques is given. Finally modern software tools for digital processing of fringe patterns are presented.

Measurement of residual stress using interferometric moiré: A new insight

Abstract: The use of interferometric moire and hole drilling to determine residual stress has been well reported and accepted for stress fields whose principal directions can be predicted well enough to permit the moire grids to be aligned with the principal strain axes. When the principal strains do not align themselves with the grid axes, a third strain component can be obtained by working with the diagonal pitch of the moire grid, but this requires resetting the optical bench to the lower frequency. Diffraction efficiency is lost, with an additional loss in sensitivity. In this paper, the authors determine the shear strain component by observing the rotation of the moire fringes in close proximity to the hole. The results of experiments on a specimen containing a model residual stress distribution are presented and compared with the theoretical prediction. Finally, the isothetic contours, based on elastic theory, were computed and plotted for several cases to verify this proposition. These results and the expected residual stress distribution are also compared to the experimentally obtained moire fringes.

The Shadow Moiré method using the phase shifting technique and digital image processing: computational implementation and application to the 3D-reconstruction of a buckled plate

Abstract: The Shadow Moire fringe patterns are level lines of equal depth generated by interference between a master grid and its shadow projected on the surface. In simplistic approach, the minimum error is about the order of the master grid pitch, that is, always larger than 0,1 mm, resulting in an experimental technique of low precision. The use of a phase shift increases the accuracy of the Shadow Moire technique. The current work uses the phase shifting method to determine the surfaces three-dimensional shape 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 in the interpretation of the Moire fringes that can adversely affect the calculations of displacements in pieces containing many concave and convex regions in relatively small areas.

Method for adjusting exposing device and exposing device

Abstract: PROBLEM TO BE SOLVED: To provide a method for adjusting exposing device by which an optical system can be adjusted easily with high accuracy in a short time. SOLUTION: The arrangement and direction of the constituents of the optical system are adjusted so that the pattern of Moire fringes, which are generated due to the superposition of a reference groove pattern and the interference fringe pattern between two fluxes of laser light upon another on the lattice surface of a reference plate 18a having a reference surface on which the reference groove pattern is formed when the reference plate 18a is arranged on an exposed surface, may become coincident with the pattern of Moire fringes theoretically found from the design parameter of the optical system. COPYRIGHT: (C)2001,JPO

Scanning projection grating moire topography

Abstract: One problem with moire topography for 3D surface metrology is the so-called 2(pi) -ambiguity limiting the maximum step height difference between two neighboring samples points to be less than half the equivalent wavelength of moire fringes. To cope with the ambiguity problem, a special scheme of scanning moire technique is proposed by resorting to the frequency domain fringe analysis that is in fact originated from white light scanning interferometry. This new more principle of 3D measurement allows determining the absolute height of the surface without information on absolute fringe orders so that largely stepped surfaces are measured with a great improvement in accuracy.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Shadow moiré profilometry by the frequency sweeping

Abstract: The frequency sweeping technique is proposed to measure the shape of objects with discontinuous height steps and / or spatially separated surfaces, which have been impossible to measure with conventional shadow moire topography. By controlling the amount of the rotation angle of the grating, the spatiotemporal moire patterns are produced with different contour intervals. The Fourier transform technique has been applied to analyze these patterns and obtain the temporal carrier frequency in which the height distribution of the object is involved. Experimental results show the validity of this method.

Measurement of bending stresses in shells of arbitrary shape using the reflection moiré method

Abstract: The basic equation for fringe formation in the case of reflection moire applied to surfaces of arbitrary curvatures is derived. A practical point-by-point solution for the application of this method is introduced, and the corresponding simplified equations are given. The technique is applied to an industrial problem, the stress analysis of a shell-shaped door.

An absolute depth range measurement of 3-D objects based on modulation Moire topography

Abstract: It is the foundation that the absolute fringe order is discerned in 3-D image measurement methods, such as spatial pattern projection technique and Moire topography. The reason is that the depth range of the object is computed from the correspondence relation between the fringe order of a reflective pattern and the depth of an object. Multiple images are need by the conventional method for discerning the fringes order. Moreover, it has a problem of phase unwrapping in the phase analysis method of a Moire pattern or other interfering pattern. So it is difficult to calculate the absolute phase or to discern the relation between the fringes, especially in cases of which the fringes are discontinuous or the objects are isolated, and so forth. The technique of using modulation projection with 3-D information is presented. A new fringes pattern whose fringe intensity or color changes with its order is produced. Thus the fringe order can be extracted easily from the fringe intensity or color, and then the absolute phase and the absolute depth range can be obtained also. This technique needs only a single image or double images.

Document image segmentation and quality improvement by moiré pattern analysis

Abstract: Moire patterns are distortions on the results of scanning printed documents. However, the patterns can be utilized in document image segmentation and quality improvement. The moire phenomenon comes from sampling periodical structures in images, such as halftone screens, color components, and text galleys which often appear in printed magazines and newspapers. The generated moire patterns appear in the scanning result in the form of obvious periodical patterns, color skew, and color noise on the edges of artworks. The moire pattern degrades the scanning result and makes document analysis more difficult. A new approach to document image segmentation and quality improvement by moire pattern analysis is proposed. A scanning resolution, called the conductor of screen sharing, is proposed to control the moire pattern. With the resolution, moire patterns are generated and enhanced in certain designed areas in the frequency domain. Then, a logical filter, called the comb filter, is proposed to detect the moire pattern. The new method, which is based on the sampling theory and moire analysis in the frequency domain, is actually performed in the spatial domain by re-sampling and logical filtering. The proposed method can efficiently extract gray or color pictures, artworks, and text paragraphs in printed documents. Moreover, the moire patterns on the segmented document components can be easily suppressed. The suppression yields better image quality for further analysis and image compression. Experimental results are shown to demonstrate the feasibility of the proposed approach.

New digital subdividing and rester- sensing technique for moire fringes of grating

Abstract: A novel digital subdividing technique for Moire fringes is put forward in this paper. The digital signal processing method and its software implementation is carried out in a single chip microprocessor. First, the two digitized sine signals from the two measuring channels are processed by the seuse finding circuit to generate a interrupt pulse signal whose frequency is four times as that of the sine signal. Then in the interrupt service routine, the measured angles are calculated to implement four folds Moire fringes subdivision. At the same time, with the aid of CPU and A/D convertor, a triangular wave signal is calculated based on the two sine signals. Then a novel subdividing technique is utilized to realize twenty folds subdivision. Finally, eighty folds subdivision is applied to the Moire fringes, and the angular measuring precision is up to 1″.

Automated In-Plane Moiré Techniques and Grating Interferometry

Abstract: Several problems in experimental solid mechanics and material engineering require determination of in-plane displacement / strain fields It is especially true if we consider flat samples under simple loading arrangement The effective experimental tools working under these assumptions are in-plane grid / moire technique and high sensitivity grating (moire) interferometry Below the principles of both techniques and modern solutions of grating / grid technology and design of moire and interferometric systems are presented As the fringe patterns obtained at the output of the systems require automatic analysis, the overview of the phase methods of fringe pattern analysis especially suited for various opto-mechanical configuration of the systems are described Also the interaction of the results with FEM is presented, while referring to various concepts of hybrid experimental-numerical analysis The result advances in measurement technology expand significantly the applications of the in-plane moire and grating interferometry techniques The numerous examples refer to the most challenging applications including local material constant determination, micromeasurements, residual stress analysis and monitoring of various engineering structures

A moiré microscope for finite deformation micro-mechanical studies

Abstract: A new version of a moire microscope is presented that embodies the theory of optical moire interferometry. To interrogate the deformed specimen grating, the device uses a transmission diffraction grating that allows for a simple and quick change of the virtual reference grating vector without disturbing the optical alignment of the other components in the optical train. To analyze deformation from the acquired moire interference fringe patterns, the displacement light-itensity moire optical law introduced by Sciammarella is revisited. The analysis of deformation is consistent with the continuum principles of finite deformation and can readily be used to obtain micro-mechanical quantities of interest such as the local strains, stretches and rotations.

Phase-shifting method for circular grating moire technique

Abstract: A phase-shifting method for circular grating Moire technique is introduced in this paper. The phase-shifting technique and the polarization method are combined to develop the phase- shifting of the circular grating Moire pattern, which is formed by Michelson interferometer through a series of simple components with some necessary polarization sections in the light path. It is a precise and applicable method and it can be performed in an ordinary situation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Measurement of thermal deformation of IC packages using the AFM scanning moire technique

Abstract: The scanning moire method was suggested in 1980s. A scanning moire method using optical method was proposed in 1993. The scanning lines in the SEM monitor or CCD video camera were utilized as the reference grating to form a scanning moire pattern. The available results are limited to the deformation measurement by using a grating with a frequency less than 250 lines/mm. Thus it is impossible to apply this method to measure deformation in nanometer scale. With the development of micro-mechanics and the appearance of nanometer mechanics, new techniques for deformation measurement form micrometer to nanometer scales are in urgent need.

Moire measurement method and moire measurement device using it

Abstract: PROBLEM TO BE SOLVED: To measure a shape of an object to be measured with high precision by using convolutional integration as a filtering method for removing a carrier component in a moire fringe. SOLUTION: As an object to be measured is an aspherical shape in a virtual screen data determined by a virtual interference fringe calculator 13, a space frequency of a carrier component has a band width. An interference fringe including a light wave surface data is fetched from a CCD camera 10 as a measured image data and converted into a digital data by a capture board 11. The measured image data fetched into the board 11 and a virtual image data of an initial phase written in a frame memory 14 are multiplied by a multiplier 18. A kind of moire fringe with a low space frequency that means an error shape of the object to be measured and a high carrier with high frequency is generated by this calculation. If a carrier component is cut off with a convolutional integrator 19 being a filtering function, a sharpened moire fringe with the low space frequency generated by an electronic moire can be obtained.

Dynamic holographic moiré patterns in photorefractive Bi12TiO20 and small-angle measurements

Abstract: A procedure for obtaining real-time holographic moirelike patterns and measuring small angles is proposed. Two rotated sinusoidal phase gratings are superposed, and the result represents a promising technique for making small-angle measurements in metrological applications. The experiments are performed with a diffusion-only recording mechanism in the photorefractive crystal Bi12TiO20 illuminated by lambda = 0.633 microm light from a He-Ne laser.

Period measuring method of diffraction grating

Abstract: PROBLEM TO BE SOLVED: To precisely measure a period of a diffraction grating even when the period of the diffraction grating is modulated in a minute area. SOLUTION: In this period measuring method, a photoresist film 10a is formed on a semiconductor substrate 10 on which the diffraction grating is formed, and an interference pattern is formed by exposing it by a two-luminous flux interference exposure method. At this time, moire fringes are generated by the interference pattern by an incident light beam and the interference pattern by a diffracted light beam. By measuring the angle of the moire fringes, the period of the diffraction grating is calculated and obtained.

Adaptive hierarchical-filtering technique for high-quality magazine image reproduction

Abstract: This paper describes a novel adaptive-hierarchical-filtering technique to achieve high-quality magazine image reproduction on computer peripherals such as color copier, or scanner plus printer. Commercial magazine images are halftoned images. Unacceptable noises and moire distortion may result when halftone images are copied (i.e., scanned and printed). In this paper, we analyze moire patterns formation characterized by the following factors: Moire patterns formation depends on the following factors: (1) halftone screen frequency, how many lines per inch (i.e., lpi) (2) scan frequency, how many dot per inch, (dpi) (3) screen angle which is the screen orientation against the scan direction, (4) scanner aperture (i.e., scanner characteristics), (5) halftoning and printing mechanisms, (6) viewing conditions. Error diffusion tends to randomize the moire patterns, and cluster-dot or line screen show more moire distortion. We developed a set of variable- length low-pass filters that have a nice inheritance of canceling aliased low frequency components (moire distortion). High pass filtering is also applied to sharpen image edges. A hierarchical filter classifier was developed to determine that an edge is either a global true edge (for sharpening enhancement) or a local halftone's micro-structural edge (for LPF for moire reduction). Depending on the classifier, adaptive LPF is applied to achieve the smooth transition between sharp edges and smooth halftone regions. Thus, we achieve overall high-quality output images. Experimental results have been shown the effectiveness of the presented technique that works well on wide combinations of above- mentioned 6 factors for high-quality magazine image reproduction.

Image forming device and method for controlling same

Abstract: PROBLEM TO BE SOLVED: To achieve highly accurate color slip correction at a low cost, in accurately detecting a deviation of the scanning width for each photoreceptor by adopting an inexpensive sensor with relatively low accuracy, instead of the expensive sensor with high accuracy that is conventionally used for the color slip detection. SOLUTION: This controlling method is, allowed to detect density of a composite pattern formed on a recording medium by overlapping the specified pattern on respective photoreceptor in the scanning direction by means of a line sensor part 109, to detect a gap between moire occurring on the composite pattern by means by moire gap detecting means 110, based on cycle of the density of the composite pattern detected in that scanning direction, and to calculate a difference of the scanning width of respective image carrier by calculating means 111, based on this detected moire gap.