Showing papers on "Moiré pattern published in 1985"

Halftone dot formation

Abstract: In reproducing halftone dot images, the appearance of moire effect is suppressed by slightly and randomly disarranging the positions of halftone dots to be recorded from the normal position in each unit halftone dot area, or by slightly and randomly distorting the halftone dots.

Effect of diffraction on the moiré image. I. Theory

Abstract: The effect of diffraction on the transmission pattern of an infinite Ronchi grid and the moire image of two equal Ronchi grids was studied. Transmission patterns and moire images of two equal Ronchi grids with and without a phase object, at a wide range of conditions, are presented. Diffractional phenomena were found to affect the transmission pattern and the moire image significantly. In order to minimize their effect, the distance between the grids must be exactly one of the Fourier-image planes of the grid. The moire image of a given phase object, even under these conditions, has an inherent error that can be precisely calculated. Deflection mapping and the uncertainty (because of diffraction) of lenses were calculated.

The governing equations for moire interferometry and their identity to equations of geometrical moire

Abstract: The equations prescribing the gradient and inclination of fringes in moire interferometry are derived from the basic laws of diffraction and interference. A vectorial representation of three-dimensional diffraction employs incidence and emergence vectors in the plane of the grating; the representation is especially well suited for this type of analysis. The corresponding equations for geometrical moire are derived by a remarkably direct vectorial method. The analyses prove that the patterns of moire interferometry and geometrical moire are governed by identical relationships.

Electronic heterodyne readout of fringes in moiré deflectometry.

Abstract: An electronic heterodyne technique is described for the readout of fringes in moire deflectometry The technique is based on phase measurements of signals generated by a photodetector observing the light transmitted through a traveling moire fringe pattern The phase of the signal is proportional to the fringe deviation and thus to the deflection angle of the light ray The phase is measured on line by a standard phase meter with an accuracy of 1 deg or 1:360 of a fringe The technique, which is precise and sensitive, is demonstrated by detecting and measuring a fringe shift of 015 mm corresponding to 0029 of a fringe

Methods and apparatus for avoiding moire in color scanners for graphic art

Abstract: Methods and apparatus for avoiding moire occurring in color scanning for graphic art, wherein light rays from a color original are passed through a pick-up lens, and prior to starting the color scanning, are modulated by means of a low-pass filter, which modulated rays are branched into two optical paths, on one of the paths a lattice plane is provided so as to project the modulated rays thereon, the lattice plane being beforehand selected in accordance with various conditions for scanning. A possible moire on the lattice plane is observed thereby to adjust the low-pass filter by replacement or displacement until the moire disappears on the lattice plane. Finally the light rays from the color original are modulated by the selected low-pass filter.

Optical differentiation of displacement patterns using moire interferometry.

Abstract: New methods of optical differentiation of fringe patterns obtained by the moire interferometry method are presented. They provide spatial derivatives of in-plane and out-of-plane displacements of the specimen under load in the form of moire or two-beam interference fringes. Either the uniform or finite fringe detection mode can be used. Simulation experiments using specially prepared transmission-type gratings are given to verify the principles.

Effect of diffraction on the moiré image. II. Experiment

Abstract: The best mode of experimental operation for creating moire images was determined. The effect of diffraction on the transmission pattern of a commercial Ronchi grid and the moire image of two equal Ronchi grids was measured. Transmission patterns and moire images at a wide range of conditions of two equal Ronchi grids with and without a phase object are presented. Deflection mapping of lenses by the moire method was carried out.

Two-Frequency Moiré Topography

Abstract: Moire topography visualizes the contour lines of an object, but it requires the absolute order of the fringe to be analyzed, and cannot distinguish the concavity and convexity of a portion of an object showing closed moire fringes. The two-frequency moire topography technique proposed here readily gives the absolute order of a fringe, and gives oblique intersection lines which help in identifying the concavity and convexity of local curvature. The technique is especially suitable for collecting data on unknown shapes such as a deformed human body.

A New Interferometric Alignment Technique with Holographic Configuration

Abstract: A new interferometric alignment technique using a holographic configuration with a precision of the order of tens of nm has been developed for registering a grating on a substrate to an interference fringe of two conjugate beams in a space. The alignment between a grating and a fringe was determined from the moire image generated by the beams diffracted from the grating, and a theoretical analysis was performed to calculate the intensity of the moire image. The experimental results were in good agreement with the calculations. The application of the method to a wafer stepper with submicron resolution is proposed.

Composites Analysis by Fractional Moiré Fringe System

Abstract: There is a need for a high resolution method for the full field measurement of sur face displacements and strain on FRM components. This paper describes a technique for utilizing low density moire gratings to obtain high resolution fringe data through the use of digital image analysis procedures. The technique is illustrated by determining displacement and strain data in the neighborhood of a central hole in a composite ten sile plate.

Straightness measurement using heterodyne moire method.

Abstract: Heterodyne moire method is applied to the displacement measurement of the interference fringes, which act as the normal lines in the straightness measurement. As the phase difference of the moire fringes is detected that are transformed into time frequency by the tranferring reference grating with a constant speed, the measurement is done with short time and high accuracy, and also continuously. Further, it is confirmed that the flutter of the laser beam can be controlled by sending the air flow to the beam.

Moire Evaluation Of Pulse Illuminated Interferograms By Synchronized Video Recording

Abstract: Moire analogy is advantageously used to explain aspects of interferometry, in particular, holography and derived techniques. Transposition of concepts from moire methods to fringe pattern processing proved to be of merit and capable of producing development of new features of practical interest. It is proposed the exploration of the concepts of moire reference change, differential moire, integrative moire and moire derivation. Examples are given to present envisaged advantages particularly for application on the study of dynamical events where pulsed illumination with synchronized video recording is proposed for extended range analysis.

High-sensitive moire method by phase detection.

Abstract: A technique has been developed for capturing fractional-fringe informations in moire measurements, by detecting the phase of fringes. Since moire fringes are produced by superimposing a reference grating on a deformed pattern, fringes move if the reference moves. Then, the varying intensity of fringes received by two electric detectors reveals moire information on each point of the specimen as the phase difference between these inspection points. Using this principle an improvement in sensitivity was tried successfully in various moire applications.

Method for and apparatus of line pattern analysis

Abstract: The disclosure herein describes an apparatus and a method of analysis of line patterns such as fingerprints, ideograms, or the like, which comprises the steps of superimposing a centrosymmetric reference pattern of lines over the line pattern to be analyzed to form an interferometric pattern of the moire type, positioning the reference pattern on a characteristic element of the line pattern to be analyzed, and enlarg­ing it until the lines of the reference pattern fill the space between adjacent lines closest to the character­istic element to thereby translate the superimposed line patterns into a field pattern of different optical densities.

Application Of High Speed Moire' Photography To Dynamic Measurement

Abstract: A simple method for obtaining moire' patterns sequence of aluminium plate at high strain rate and large flexivity is presented. At different instant full field flexivity and three dimensional coordinates of all interested points on the plate are obtained by the moire' fringes. Thus displacement and strain components may be deduced. Possible errors are also estimated.

Stresses in Thin Films by Optical Techniques

Abstract: Residual stresses present in thin films can be rpecisely measured by optical techniques. Four different techniques, namely (1) Reflection Moire, (2) Reflection Moire with shift, (3) Holographic Moire with shift and (4) Interferometry were evaluated. Based on the accuracy, sensitivity and simplicity, interferometry was chosen and applied in a practical investigation. The deflection fringe pattern was processed along principal directions. Slopes, derivatives and hence stresses wee evaluated using cubic spline numerical technique. The departure from isotropic nature of stresses, as clearly depicted by the fringe pattern, is analysed and the error introduced by the assumption of isotropic state is shown to be only about 8.33%.

High Speed Photography On Moire Pattern Masked Flight Target

Abstract: The fleight target painted with moire pattern to be tracked by a high speed camera through a transparent grid give us a very high precision method for the measurement of target displacement. The film unflatness, air fluctuation and the vibration of the high speed camera are also effected on the shape change of the moire. The small amount change of the pitch, yaw, rotation and the direction of the fleight target can be easily measured by this method.

Simple OHP equipment for demonstrating centrifugal spherical waves and group of minute articles by using moiré and reversal moiré and their evaluation

Abstract: This paper describes simple OHP equipment as an aid in the teaching of physics, for example, electromagnetics by demonstrating centrifugal spherical waves and a group of minute articles radially progressing. A Moire pattern is produced by using two grated transparencies having certain lattices, one fixed, and the other rotated. In this paper, rotating type Moire patterns are used since they are easy to operate. Each lattice is designed as a function of the propagation velocity of each phenomenon to be demonstrated. The model of the movements of a group of minute articles is used for the divergence in a vector analysis. A reversal Moire is used for this model. This paper discusses the method of designing the grated transparencies required for these models. Another model for demonstrating the electric force around a dipole is described, formed by overlapping two identical transparencies in a slightly shifted position. It is proven in this paper that this overlapped pattern agrees with the pattern of an electric field formed by a set of parallel lines charged positively and negatively, respectively, and with a homogeneous density. The responses of students to this equipment are analyzed via factor analysis, and the factor axis representing “idea” gains a relatively high mark.

Optical differentiation of displacement patterns obtained by double-exposure Moiré-holographic method

Abstract: Double diffraction and spatial filtering is used for coherent processing of two identical copies of the doubly exposed image of the grating photorecorded on a transparent model. Proper orientation of the copies in space yields high-contrast two-beam shearing interference fringes after single-order spatial filtering. The fringes correspond to partial derivatives of in-plane displacement components.