Showing papers on "Moiré pattern published in 1987"

Method and apparatus for digital morie profilometry calibrated for accurate conversion of phase information into distance measurements in a plurality of directions

Abstract: Projectors and cameras disposed about an object under test obtain digital moire information of overlapping aspects (views) of the object. The system is calibrated using a calibration pattern of straight lines on a flat reference surface and a projected pattern of lines which are perpendicular to the lines of the calibration pattern and contain marker fringes between predetermined lines. Each aspect is calibrated individually by stepping the calibration pattern along the axis of each camera so as to obtain a plurality of tables which relate phase information to distance in each of a plurality of planes spaced successively closer to the camera. The calibration tables define a calibrated volume in space between the cameras and projectors. When the object under test is located in this volume, the video signals from the camera are converted into digital moire information. This information is directly related to the calibration information and is converted with the aid of the calibration information into absolute distance measurements along the perimeters of cross-sections through the object.

Measurements of the small tilt-angle variation of an object surface using moire interferometry and digital image processing.

Abstract: A method of measuring the small tilt-angle variation of an object surface by using moire interferometry based on the Talbot effect and a moire technique is described. The object surface is placed in the middle of a set of two gratings. A monochromatic plane wave illuminates the first grating producing the magnified Talbot image. The moire fringe is generated by superimposing this Talbot image on the second grating. The inclination angle of the moire fringes is a measure of the tilt angle of the object surface. The inclination angles are measured with a digital image processor.

Least-Squares Penalty-Constraint Finite Element Method For Generating Strain Fields From Moire Fringe Patterns

Abstract: An essential phase in moire techniques is the generation of strain fields from optical fringe patterns. In this effort we explore a finite element method based upon a new least-squares penalty-constraint variational principle, which will be shown to be extremely effective in producing accurate, two-dimensional displacement and strain fields over the full-fringe domain. The approach encompasses the full-field analyses of optical fringes, which include: (1) an effective and theoretically sound noise filtering/smoothing and differentiating of the optical intensity fringes, from which displacement fringes are accurately determined, (2) subsequent smoothing/differentiating of the displacement fringes, producing continuous displacement and strain fields of high quality, (3) computational efficiency, (4) the ability to routinely process distorted mismatch fields which occur, for example, with large fields of view, avoiding the need for any special care to eliminate such distortion, (5) ease of implementation within a conventional finite element program. Several examples are carried out which demonstrate the attractiveness of the methodology.

Real-time optical differentiation for moire interferometry.

Abstract: Real-time methods for differentiation of in-plane displacement fields produced by the moire interferometry technique are introduced. Two approaches are developed: (1) optical shearing of displacement patterns and (2) superposition of two lateral shear interferograms of wavefronts from 2 diffraction orders of the specimen grating. Coherence problems are circumvented by polarization effects. In both cases additive-type moire fringes give the map of displacement derivatives of the object under load. The issue of carrier patterns and extraneous fractional fringe order is clarified. Experimental verification of the principle is presented.

Device for measurement of the surface of an object

Abstract: For scanning an object surface (1) a moire fringe pattern is generated grid by combining two stroke and at the object surface (1) DEFOR-optimized strip images are evaluated captured with a television camera (4) and with an electronic circuit (16). A case required movement of the stripe pattern is in a simple manner by a Ver of the grating shift generated to each other, and the period of the stripe pattern is determined by the Neigungswin the graduations of the grating angle to each other adjustable.

Moire Topography With Large Contour Intervals

Abstract: One of the widely recognised limitations of moire topography is its inability to provide unambiguous data from objects which have discontinuities in their shape. Similar limitations arise when two parts of an object are separated by a region which is in shadow. This feature of moire topography has limited its use to the measurement of objects which have continuous surfaces. With the development of phase measuring techniques for fringe pattern analysis, moire fringe contour patterns can now be analysed to high levels of accuracy, the contour interval being subdivided into, perhaps, 200 increments of measurement by the phase calculation procedure. This paper describes a modified version of moire topography in which the contour interval has been greatly increased so that, in some cases, the entire depth of the object lies within one fringe. By applying high accuracy phase measuring techniques to the analysis of these moire fringe patterns, sub-millimetre accuracy can be obtained in measurements of objects which would normally be thought of as unmeasurable by moire topography.

Straigtness measurement using a heterodyne moiré method

Abstract: Optical heterodyne interferometry is a new interference technique, allowing quick and accurate measurements of dimension A similar technique can determine the fringe phase of the moire method as intensity is modulated by movement of the reference grating The phase difference between certain points in the moire pattern is detected automatically The interference fringes generated by laser are used to measure straightness Small displacement of fringes is detected with the heterodyne moire method Generally, beam flutter caused by air disturbance becomes a serious problem in systems using long beam paths, though it can be reduced by controlling the air flow

Performance of moiré deflectometry with deferred electronic heterodyne readout

Abstract: The effects of diffraction and nonlinear photographic emulsion characteristics on the performance of deferred electronic heterodyne moire deflectometry are theoretically and experimentally investigated. The intensity transmission distribution of the transparency, the moire image, the heterodyne readout, and the spatial and angular resolution are analytically discussed. The deferred electronic heterodyne technique is evaluated by measuring small fringe shifts caused by a weak phase object. It is found that this technique can be applied for accurate and sensitive readout of moire fringes of unsteady phase objects. The theoretical study shows that the accuracy and sensitivity of the system are weakly affected by diffraction and nonlinear photographic emulsion characteristics. Nonlinear recording does not affect the spatial resolution of the system.

Automated Contour Ordering In Moire Topograms

Abstract: A method is described for ordering the fringes in an ordinary moire topogram. It requires no a priori shape information and resolves "hill-or-valley" ambiguities using local surface reflectance properties. The theoretical and practical constraints of this method are discussed, and analyzed examples are presented as experimental evidence.

The Magic of Carrier Patterns in Moire Interferometry

Abstract: : Practical applications in which carrier patterns are used with moire interferometry for strain measurements are presented. Examples of typical experimental analyses illustrate how moire carrier patterns are applied to obtain the desired data in complex laminated composite specimens. In many cases, carrier patterns permit extraction of much more detailed information, with procedures that are easier and more accurate than those using load-induced fringes alone. In moire interferometry, the carrier patterns can be introduced easily by adjustments of optical elements that control the virtual reference grating.

Analysis of periodic motions using moire fringes

Abstract: periodic movements are analyzed by generating moire fringe images in real time. A network line attached to the surface of the object (1) is photographed by means of an apparatus (4) to the rigid support, since an oblique angle with respect to the lattice plane. A negative slide of the line network is placed inside the apparatus (4) supported by a glass plate and the valve being opened, the slide is first aligned with the instantaneous image of the landline network and then inclined to create misaligned fringes. A television camera (6) control the subsequent interaction between the negative slope and the instantaneous image of the line network on the moving object (1) seen on the glass plate at the image plane of the camera, and this interaction is displayed on a monitor screen (10). The image is characterized by the presence of a phenomenon of secondary fringes revealing the movements of the object.

Moire interferometric focusing system for optical microlithography.

Abstract: An interferometric apparatus for detecting axial and angular misalignments of the film plane in a photolithographic camera is proposed. The misalignments are observed as moire interference fringes created by the superposition of a reference interferometric fringe pattern representing the focused camera and a perturbed fringe pattern produced when the camera is misfocused. The theory and results of a simple experimental implementation are described.

Displacement and strain calculations by the phase shift method.

Abstract: The phase shift method, well known in holographic interferometry, is applied to the deformation of line gratings. The method uses the moire effect but it determines local displacement or strain from the grey values of three shifted images instead of the coordinates of the fringes. The basic equations are derived from the transmittance function. The theoretical error with respect to a given displacement field is calculated by simulation. Real errors are investigated by related plotter-generated line gratings. The phase shift method is especially suitable for automatic digital image processing.

Method and instrument for measuring strain distribution in real time

Abstract: PURPOSE:To measure the strain distribution of a body to be measured almost in real time by delaying the image pickup output signal of a deformed grating pattern corresponding to the parallel movement of the grating pattern and then superposing it on the original image signal, and thus forming moire fringes. CONSTITUTION:A deformed grid is moved longitudinally in parallel and superposed upon the grid before the movement to form the moire fringes (a). When this parallel movement is performed by using an image processor, the movement is attained easily and accurately and the absolute value of the difference in density value between two grids is easily found. The arithmetic result is outputted as an image (b) to increase the contrast ratio of the moire fringes, thereby making it easy to see. Further, only the moire fringes can be extracted by smoothing and binarization of the image (b). The more fringes are made into thin lines and lines of equal distortion are found in the image (d). Further, a shearing strain distribution is also moved laterally in parallel to easily find images (e) and (f). Thus, the need for a master grid is eliminated, processing is easy, and an analysis is taken at an extremely high speed.

Multifunctional moire fringes camera

Abstract: The utility model discloses a multifunctional moire fringes camera, belonging to the key instrument of the strain field of the measure material of a moire fringes method in experimental mechanics. The multifunctional moire fringes camera is formed by four sections of metallic cylinders. The multifunctional moire fringes camera can freely flex. A distance between the shot and the image surface of the camera can be changed between 360 mm to 740 mm, and imaging ratio can be changed according to needs. The multifunctional moire fringes camera can shoot vivid specimen gratings by once focusing. An analyzer grating can be rotated 90 DEG, which obtains the goal of separating the displacement fields of U and V. The camera can be used as the cameras of speckle and defocusing speckle, and can accurately measure defocusing amount.

Phase-Measuring Moiré Topography

Abstract: A number of full-field optical methods which exploit interferometric, holographic, speckle or moire fringe phenomena have been developed for the measurement of surface form and deformation. Between them, these methods offer a wide range of sensitivities together with the ability to visualize the quantity of interest through a fringe pattern which describes the height or deformation contours of the surface.

A Computer Based Moire Technique To Measure Very Small Displacements

Abstract: The accuracy that can be achieved in the measurement of very small displacements in techniques such as moire, holography and speckle is limited by the noise inherent to the utilized optical devices. To reduce the noise to signal ratio, the moire method can be utilized. Two system of carrier fringes are introduced, an initial system before the load is applied and a final system when the load is applied. The moire pattern of these two systems contains the sought displacement information and the noise common to the two patterns is eliminated. The whole process is performed by a computer on digitized versions of the patterns. Examples of application are given.

Moire deleting method

Abstract: PURPOSE: To delete the moire when a halftone dot picture is read by a large sensor like a linear image sensor. etc., by using only a sheet of double refraction element. CONSTITUTION: The light received from a halftone original 1 put on an original surface is divided into two beams by a double refracting optical element 3 after passing through a lens 2 and projected onto a linear color image sensor 4 in the form of a double image. Then the position of the sensor 4 is adjusted so that the double image overlaps the adjacent picture elements by half value. Thus the misreading rate and the blur degree are reduced for the image. Then the floating extent of the sensor 4 can be controlled at a state where a desired blur degree is substantially secured by substituting a blur distance (z) for a formula ▵a=f*(b-z)/(b-z-f)-a to obtain a position where an in-focus state is secured at the floating position of the sensor 4 and then setting the original 1 at this position. Thus it is possible to reduce the moire including the blur by controlling the positional relation between the element 3 and the sensor 4. COPYRIGHT: (C)1988,JPO&Japio

Moire topograms: a simple method for their evaluation.

Abstract: Pacific University, College of Optometry, Forest Grove, Oregon 97116 Received 8 December 1986. 0003-6935/87/071166-02$02.00/0. © 1987 Optical Society of America. We have found that moire fringes can be easily evaluated by using the fringe spacing without knowing the dimensions of the actual experiment involved. That is similar to interferometry where the depth of a defect or other surface irregu­ larities can be found directly from the fringe distortions. Consequently, determining the magnification, or the rota­ tion of one grid relative to the other, and calibration of the apparatus in general, are not much of a problem anymore. Following Rayleigh's first observation, the evaluation of moire fringes is easy when one of two identical linear grids is rotated through an angle θ. If the separation of the lines in the original grids is d, the spacing M of the resulting moire fringes is

Moire topography camera

Abstract: PURPOSE:To obtain a TV image which has no extra moire fringes except contour lines by making the direction of straight lines of a reference grating projected on an object parallel to the direction of scanning lines of a device which picks up the image of an object where the reference grating is projected. CONSTITUTION:The image of the reference grating 101 is projected on the object 102 by a light source 103 and then the projection image 106 of the reference grating 101 becomes a grating deformed according to the surface shape of the object 102. The image of the object 102 where the deformed grating is projected on the surface is formed on the image pickup surface 110 of the image pickup device 109 and photographed to generate a video signal. At this time, the direction (X direction) of scanning lines of the image pickup device 109 is coincident with the direction of straight lines of the reference grating 101, so the contour lines are formed on the image of the object 102 as moire fringes formed by the interference between the projection image 106 of the reference grating on the object and the scanning lines of the image pickup device 109.

Moire -Holographic Analysis Of Bent Plates With Non-Uniform Thickness

Abstract: The moire-holographic technique utilized for this investigation basically consists of filtering, in a Fourier optical system, pairs of wave-fronts diffracted by the model grating and of reconstructing the interference fringes frozen in the holograms obtained by double exposure, i.e. before and after the defor-mation [1],[2]. It has been shown that moire holograms can even be reconstructed with white light; furthermore, optical differentiation of the fringes is readily accomplished, during the reconstruction process, by direct observation of the shapes taken on by the strain components [3]. This paper describes a new extension of moire-holography to the analysis of plates with non-uniform thickness, in particular orthotropic plates. It is known that with transparent models of variable thick-ness, through which a beam of light passes, it is necessary to reconstruct the flatness of the optical surface by immersing them in auxiliary liquids with corresponding refraction indices. The authors observed, however, that moire-holographic analysis resolves this problem also, simply and rapidly, provided the surface containing the grating is uniformly flat (Fig.l).

New Methods for Recording and Processing High Frequency Moire Patterns

Abstract: : Two techniques for enhancing the potential of high frequency moire interferometry are investigated. A high frequency Ronchi grating is transferred from a suitably processed silicon wafer to a test specimen. Results indicate that the grating can be used to vary sensitivity, and that gratings of nearly any shape and size can be deposited on the surface of specimen. Further work is suggested to refine the technique. In addition, an automated approach for measuring surface displacement using moire interferometry is described. The method relies on the introduction of a carrier fringe pattern to achieve fringe linearization, and the application of image digitization and computer analysis to determine the magnitude and direction of a specific displacement component. (Reprint)

Applications Of Photoelasticity To Elasto-Dynamics

Abstract: The use of methods of experimental mechanics to study physical behavior in elasto-dynamic problems requires high speed photographic recording systems capable of storing images of optical fringe patterns where features often propagate at or above the dilatational wave velocity. This paper discusses the requirements of a very high speed recording system for the dynamic photomechanics class of experiments. The requirements include: exposure time, framing rate, field size, image size and light intensity. The design of a new Cranz-Schardin photographic recording system which has recently been completed at the University of Maryland is described in some detail. The camera system incorporates a novel spark gap design with a reflecting and focusing mirror and a fiber optic output. The fiber-optic bundle adds considerable flexibility in adapting the optical system to a large number of different experiments. The optical system has been designed for operation in both the transmission and reflection modes. In the transmission mode the system records conventional photoelastic fringe patterns, moire and caustic images of transparent media. In reflected light the specimen is mirrored and the system records fringe patterns from birefringent coatings, moire and caustic images from opaque materials.

Stage noise detection of electron beam exposure device

Abstract: PURPOSE:To facilitate detection of distribution and oscillation frequency of stage noise in exposure region by a method wherein the cyclic interval of compression waves due to Moire's phenomenon and the feed speed of stage measured by pattern arrays comprising multiple array element with different overall length are detected. CONSTITUTION:Multiple detecting patterns comprising linear pattern elements arranged in one line at the same interval are formed on overall surface of a mask or a wafer by electron beam exposure. The cyclic interval of compression waves due to Moire's phenomenon is read by scale pattern. Pattern arrays comprising multiple array elements with different overall length are formed on a mask for simultaneous electron beam exposure using a mask while the feed speed of stage is detected by measuring the stage shifting distance in each array element and the exposure time required. Through these procedures, the oscillation frequency of stage noise can be detected by measuring the cyclic interval of compression waves and the feed speed of stage.

Application Of Moire And Speckle Techniques To Curved Surfaces Using A Periphery Camera

Abstract: By using aoperiphery camera which is capable of 360° viewing we have extended the in-plane, shadow and reflection moire methods and laser and white light speckle methods to cylindrical surfaces without the perspective effect.

Application Of Moire Analysis Of Strain Using Fourier Transform

Abstract: By shifting the discrete Fourier spectrum of the image of a deformed grating, we can obtain "the complex moire pattern", from which strain distribution is given as the derivatives of the phases of the complex moire fringes. The analysis is completely automatized by introducing the digital image processing. All of the laborious and subjective procedures required in the conventional analysis such as fringe sign determination, fringe ordering, fringe interpolation are so eliminated that objective, fast and accurate analysis can be made. Some applications for rubber plates are shown.

Moire Contouring Of Objects Generated By CAD

Abstract: Moire technique using projected fringes is a suitable method for full field measure­ ments of out-of-plane deformations and object contouring. In this paper a system using a TV-camera combined with a digital image processor is described. In this way a real-time system with the inherent possibilities of fringe interpolation for improving the accuracy and sensitivity is obtained. This system is very suitable for comparing the shape of dif­ ferent objects, e.g. for measuring the surface profile difference between a product speci­ men and a master object. An attractive alternative would be to measure the surface profile compared to a master object generated by means of CAD. An example of this method is pre­ sented. This technique offers a powerful tool for industrial production control. 1. INTRODUCTION In recent years, moire topography has attracted the attention of a lot of workers as an attractive alternative for measuring the shape of 3-D objects 1~10. ^^\e methods employed have been several variations of the principles of shadow moire and projected fringes. One reason for the renewed interest in these fringe techniques is the increasing capacity and decreasing prices of digital image processing plug-in modules for personal computers. In combination with electronic imaging devices, these modules offer a very convenient means for image processing and fringe analysis.In this paper a system based on moire technique with projected fringes is presented. This method is very suitable for comparing the shape of different objects and therefore offers a powerful means for measuring the surface profile difference between a product spe­ cimen and a master object. This is obtained by subsequent recordings of the master and the product, resulting in a moire pattern which maps the difference between the two objects due to e.g. manufacturing defects.This technique prompts the need for a physical master object to be available in the first recording. In many cases however, the manufacturing of an ideal master can be very expensive or even impossible. An attractive alternative would be to generate the master object with projected fringes by means of a computer. After describing the principle of the moire system, an example of this approach will be presented.

On the Suppression of Unwanted Moiré Patterns in Half-tone Images Generated by a Scanning System with a Periodic Displacement Defect

Abstract: Arrays of motifs, such as are found in half-tone images, may exhibit unwanted moire fringes when they are generated by a scanning system which introduces a periodic displacement defect. It is shown that the fringes may be eliminated in the continued presence of the defect when it is in the direction of the scan lines, but cannot be suppressed when the displacement is perpendicular to this direction. The appropriate Fourier theory is presented and suppression of the moire fringes for one particular defect is illustrated.

Measurement Of Surface Profile Changes By The Use Of Moire Fringes With Particular Application To Mass Transfer

Abstract: The use of Moire fringes for the measurement of mass transfer is reported. In this application, changes in surface profile on a naphthalene plate due to mass transfer take place. The profile changes are measured using Moire fringes and the results are compared with an existing measuring device which uses a height sensitive stylus. Fringe patterns are illustrated on both flat and cylindrical surfaces.

Development of several ohp equipment of physics using moiré patterns

Abstract: This paper reports on several simple OHP equipments for education using Moire patterns. The first equipment is concerned with centrifugal waves. The Moire pattern is produced by superposing two specified patterns composed of straight lines and curves. The two patterns are determined as functions of the wave propagation velocity. The second is the fluid model used in demonstrating such notions in vector analysis as divergence. The spiral travelling wave is simulated using the reverse Moire, which is a counterpart of the Moire technique. The third is the equipment to simulate the electric lines of force produced by a pair of point charges and is used in teaching electromagnetics. The patterns are designed also for easy understanding of Moire phenomena. This paper describes the design procedures for the patterns, indicating several points to be noted in the actual application of the equipments.