Showing papers on "Moiré pattern published in 1993"

Handbook of the moiré fringe technique

Abstract: Part 1 Theoretical interpretation of formation of Moire fringes: a Fourier series approach to the description of Moire patterns the parametric equation method description of Moire in terms of vectorial sums in Fourier space Moire as an aliasing phenomenon by undersampling. Part 2 Incoherent methods of superimposition of structures: Moire types - additive, subtractice, multiplicative examples of two-structure superimpositions special techniques - use of structures with orthogonal transmittances. Part 3 Coherent methods of superimposition: fringe pattern formation by filtering of the double diffraction orders overlapping real time interference fringes with a recorded pattern. Part 4 Influence of the type of illumination and separation of gratings on the intensity distribution in Moire fringes: the case of coherent illumination, incoherent illumination, partially coherent illumination. Part 5 Moire displacement transducers: basic concepts grating reading heads accuracy of Moire fringe transducers. Part 6 Moire fringe alignment methods: optical alignment by whole-field detection of Moire fringes Moire patterns for three point alignment technique submicron alignment methods for lithography. Part 7 Moire photography: principles implementation fringe pattern recording and processing examples of applications. Part 8 Moire methods in interferometry: in two-beam interferometry in two-beam interferometry with conjugate wavefronts in grating shearing interferometry. Part 9 Shadow Moire topography: principles theoretical description localization and contrast of Moire fringes fringe order determination - absolute, relative instrumental considerations applications. Part 10 Projection Moire topography: principles and basic configurations configurations with a single projection system systems without grating in the observation system double projection Moire topography off-line demodulation methods contrast of Moire fringes absolute and relative fringe ordering instrumental considerations. part 11 Reflection Moire method: Ligtenberg and Rieder-Ritter configurations refleciton Moire arrangements for studying dynamic events specific experiemntal arrangement for studying the flexure of plates. Part 12 Moire as a graphical solution to physical problems: wave physics field physics interpretation of images formed in the field-ion microscope. Part 13 Automatic fringe pattern analysis: intensity methods phase measuring methods - general considerrations, electronic, analytical comparison of automatic fringe pattern analysis methods future trends.

Electron beam moiré

Abstract: A method of writing very high frequency line and dot pattems, in excess of 10,000 lines/mm, is described. This method uses a very small diameter, 10 to 20 nm, beam of electrons to sensitize a 100-nm thick layer of electron resist. The line and dot patterns are produced by etching the sensitized resist. Moire fringe patterns occur when the line arrays are observed in the scanning electron microscope. Moire fringes with excellent contrast have been produced at magnifications as high as 1900x. This capability permits e-beam moire to be employed in micromechanics. Examples of line arrays, dot arrays and moire fringe patterns on a brass disk and on a tensile specimen fabricated from glass-fiber-reinforced plastic are demonstrated to introduce the possibilities for micromechanics applications.

Shadow moire topography by means of the phase-shift method

Abstract: We propose using the phase-shift technique to improve such shortcomings inherent to conventional shadow moire topography as low sensitivity and difficulties in computational processing. Because in shadow moire the reference grating and the deformed grating are mutually dependent, it is not possible to produce phase shifts of the fringe by moving the grating. However, fringe shifting that is actually constant regardless of fringe orders is achieved by changing both the gap between a specimen and the grating and the angle of illumination. This proposal is justified by a simulation test and some experimental results are shown for the verification of this trial.

Microcreep deformation measurements by a moire method using electron beam lithography and electron beam scan

Abstract: Microcreep deformations in pure copper specimens are studied by a new moire method. In this method, a fine micrograting prepared by electron beam lithography is used as a model grating, and a scanning exposure ofthe primary electron beam in a scanning electron microscope (SEM) as a master grating. The scanning exposure of the electron beam on the specimen with the model grating produces moire fringes of bright and dark lines formed in response to the different amounts of the emitted secondary electrons for each primary electron. This new method makes it possible to obtain a clear and fine moire fringe without an image-processing system and to observe the moire fringe pattern and the SEM image at the same time. By this method, the inhomogeneous microcreep deformations such as grain boundary sliding, coarse slip, and localized strain are measured with high accuracy. It is confirmed that the creep strain is nonuniform even in the same grain and the strain distribution is caused mainly by the grain boundary sliding.

System for determining the topography of a curved surface

Abstract: A system for determining the topography of a curved surface, comprising a device for projecting patterns of lines on the surface to be examined, which device includes two projectors disposed at an angle relative to each other, each provided with a raster of parallel straight lines, which are positioned at right angles to the plane through the projection axes and a rectangular diaphragm, of which the long sides are parallel to the lines of the raster, and a detection device for registering the image formed on the surface. The system is implemented such that an additive moire pattern is produced and that a pilot monitor in conjunction with an electronic filter is provided for real-time visualizing this moire pattern. The detection device is implemented for registering the image without moire interference, suitable for discrete Fourier analysis. The registration of the formed height line map for proper focussing or for obtaining an end product is electronically filtered, with the object of being able to see highly contrasting moire height contours in real time on a monitor. The light source for both projectors is a slit shaped continuous light source combined with a slit shaped flashlamp, which-- by means of synchronization at the end of the first raster period and the beginning of the second raster period respectively--illuminate a complete TV raster in only a few ms, and in which the half rasters can complement each other afterwards through explicit digital analysis.

Scanning moire at high magnification using optical methods

Abstract: Methods of employing scanning moire at high magnification are developed and demonstrated. Modern lithographic techniques for producing custom moire gratings with a frequency up to 250l/mm are described. On a probing station equipped with a video system, pseudo-color moire fringes are produced using the scannning lines of the color charge-coupled-device (CCD) camera. Fringe multiplication from 1 to 5 is possible with correct combinations of magnification and grating pitch. An analysis is given to show that strain sensitivity depends only on the number of scanning lines used to record the image. The grating pitch and the magnification are important because they reduce the gage length of the strain measurement. The high-magnification scanning moire was used to study plastic- strain fields in an aluminum tensile specimen. Local disturbances in the strain field were observed at 2 to 2.5 percent applied strain. These discontinuities became more significant at higher levels of applied strain.

Method and apparatus for generating halftone images by discrete one-to-one dither tile rotation

Abstract: The invention relates to a method and apparatus for automatic high-speed generation of digital angled halftone screens, specially suited for obtaining screens approximating the irrational angles which are generally required by high-quality color reproduction. The method enables color separations to be generated which minimize Moire effects, interferences and artifacts by applying discrete one-to-one rotations to digital halftone screens of the required period in order to reach the final screen angle. Dither tiles incorporating assemblies of the basic screen element are rotated by one-to-one discrete rotation and transformed into a new type of dither array, the scanning dither array. The scanning dither array is composed both of dither thresholds and of displacement vectors, providing the means to scan the dither array at image generation time. Several different discrete one-to-one rotation variants are proposed: a small angle rotation technique valid for a subset of rational rotation angles, a rigid band technique and an improved band technique valid for all rational rotation angles and a technique based on discrete shearing transformations. The high-quality of the so rotated dither tile is due to the fact that discrete one-to-one rotation preserves the exact number of elementary cells per screen element and their exact dither threshold values.

Method and system of color halftone reproduction

Abstract: A method of color halftone reproduction with reduced moire patterns and simplified calculations of color densities is disclosed. The method entails dividing a reproduction surface into an array of abutting halftone cells having centers aligned at a screen angle, preferably 45° , with halftone cells in adjacent rows. The halftone cells each cover an area of M abutting horizontal dots long by N abutting vertical dots wide. The various system colors are applied to the pels, as required, in color patterns centered within the halftone cells. The patterns overlap one another to adjust the hue of the reproduction at the halftone cell location to the desired hue. The method is usable with permanent reproductions, such as printed paper, or with transient reproductions, such as the image on a CRT screen.

Phase stepping in projected-fringe fibre-based moire interferometry

Abstract: An optical fibre based moire interferometer for surface shape measurement is described. The technique uses an optical fibre interferometer to project interference fringes and is readily phase stepped without mechanical movement of components.

Automated fringe pattern analysis for moiré interferometry

Abstract: The theory of an automated fringe-pattern analysis using temporal phase stepping method for moire interferometry is presented. The automated method provides a fast and accurate strain measurement for moire interferometry. Measurements on a tapered composite specimen with a dropped ply are shown to highlight the capability of this technique to obtain the strain distribution, particularly around the region with a dropped ply.

Solder ball connect (SBC) assemblies under thermal loading: II. strain analysis via image processing, and reliability considerations

Abstract: A novel approach to processing interferometric moire images, called computational Fourier transform moire, has been developed. The essential principle of this technique is to automatically calculate a whole-field strain from digitized images of interferometric moire fringes using digital Fourier transform procedures. With the use of this technique, a whole-field strain distribution of a Solder Ball Connect (SBC) interconnection under thermal loading was obtained. The calculated strain field was then used to understand fatigue modes of SBC observed from an accelerated thermal cycling (ATC) test.

Method of and apparatus for recording halftone images

Abstract: The present invention produces a set of improved halftone images which effectively prevents occurrence of rosette moire. A plurality of parallelograms can be formed from three apexes consisting of an arbitrary first apex of a reference triangle RT1, a middle point of the side of the triangle facing to the first apex, and one of the other two apexes of the triangle. One of the parallelograms is selected as a unit area for one halftone dot. The unit area is virtually laid out repeatedly on an image plane, and one halftone dot is located with respect to each unit area. Each halftone dot can be located at the center of the unit area or at any desirable position in the unit area.

Geometric moire methods with enhanced sensitivity by optical/digital fringe multiplication

Abstract: A robust fringe-shifting and image processing scheme is applied to geometric moire experiments. High quality contour maps of U, V and W displacement fields are obtained with sensitivity enhanced by a factor of ten. The method is compatible with complicated intensity distributions, variable bar-to-space ratios of gratings, and optical noise. It is applicable to large fields for both in-plane moire and shadow moire measurements.

Angular distortion measurements by moire fringe patterns

Abstract: A process and apparatus for measuring angular distortion in an optical imaging system in order to provide a mapping that completely characterizes the distortion of the imaging system involves electronically capturing the image of a test pattern at the image plane of the imaging system, superposing a computer generated reference pattern on the test pattern, and measuring the deviation of the test pattern from the reference pattern at selected areas of the reference pattern.

Moire technique utilization for detection and measurement of scoliosis

Abstract: Moire projection method enables non-contact measurement of the shape or deformation of different surfaces and constructions by fringe pattern analysis. The fringe map acquisition of the whole surface of the object under test is one of the main advantages compared with 'point by point' methods. The computer analyzes the shape of the whole surface and next user can selected different points or cross section of the object map. In this paper a few typical examples of an application of the moire technique in solving different medical problems will be presented. We will also present to you the equipment the moire pattern analysis is done in real time using the phase stepping method with CCD camera.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Generation of surface shape from variable-resolution video moire contours

Abstract: Several methods for generation of three dimensional surface shapes from variable resolution video moire contours are described. In a classical moire system, a physical grating is projected on a target and also used to view the target. The moire contours are generated in the plane of the viewing grating. An unambiguous surface shape can then be computed by processing a set of moire images where the grating, target, or both are moved. By using an interferometer to generate and project variable pitch gratings and video technology to generate the moire contours, a 3-D surface can be scanned at different resolutions and used on a wide range of object sizes. The elimination of the physical grating also leads to surface generation techniques that do not use moving parts, increasing reliability. From these video moire contours, it is possible to uniquely reconstruct the 3-D surface, making the distinction between concave and convex surfaces. In one technique, a computer is used to mix digitized images of distorted gratings projected on the object with computer generated gratings, creating the moire patterns. By shifting one grating, it is possible to reconstruct the surface without having to move the object being scanned.

Electronic speckle pattern interferometry with holo-optical element

Abstract: This paper presents the use of holographic optical elements for the measurement of slope and curvature by video techniques. the curvature fringes occur as moire between two speckle slope patterns. A good agreement between theory and experimental results is demonstrated.

Variable-resolution video moire error map system for inspection of continuously manufactured objects

Abstract: Moire techniques can be a powerful tool to determine deviation of a manufactured shape from a desired shape. In a traditional moire system, distorted gratings on an object are viewed through an undistorted grating. The moire contours that result represent equal depth contours over the entire viewed surface. By generating the moire patterns in video, it is possible to view the distorted gratings on a test object through a set of gratings that has been distorted by a similar but perfect object. The output is then a set of moire contours that corresponds to the differences between the two surfaces. This difference or error map eliminates much of the unnecessary information generated in traditional moire inspection and thus becomes a valuable tool for comparisons between an imperfect test object and a manufacturing standard. We have developed a variable resolution video system for creating this error map using a Michelson interferometer to generate the gratings. We have successfully applied this system to damage detection on a long, continuous lengths of pipe by having two side-by-side cameras looking at different sections of pipe and also by having one camera's view filtered with a video-taped recording of an undamaged section of the pipe.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Automated Fourier transform fringe-pattern analysis in holographic moire

Abstract: Fourier transform fringe-pattern analysis is a wide-spread technique with many applications to optical metrology. Introducing a spatial carrier into a holographic moire pattern is also a well-known technique to obtain observable moire fringes. Preprocessing of the holographic moire pattern includes optical or digital Fourier filtering to remove the carrier. The pattern is then processed by employing time-consuming and less accurate fringe-counting algorithms. This work presents a new application of the Fourier transform method to automated analysis of holographic moire fringe patterns. The method has the advantage of instantaneous determination of both phase functions in the fringe pattern. Investigations are carried out on the frequency limitation imposed on the spatial carrier. The technique is demonstrated on computer-generated noisy holographic moire patterns. The technique does not complicate the conventional holographic moire arrangement.

Interference patterns generated by a plane-parallel plate

Abstract: A simple geometrical theory is developed to evaluate the interference pattern that is generated by a plane-parallel plate illuminated with a monochromatic point source. It is shown that a specific tilt of the plate exists with respect to incident illumination, at which the spatial distribution of the interference fringes becomes uniform. Experimental evaluation of the fringe patterns by superposition moire techniques supports the theoretical results.

Encoder and system with encoder

Abstract: PURPOSE:To detect a highly accurate phase difference signal by providing a double refraction element arranged between a light projecting means and a light receiving means, and means for obtaining a plurality of output, signals with a phase difference based on the light passing through the double refraction element. CONSTITUTION:The luminous flux from a semiconductor laser is turned to parallel luminous fluxes by a lens system 2, entering a grating part, G1 of a scale 3 to generate many diffraction lights. Laser beams of the linearly polarized light entering a Savart plate 6 comprised of double refraction elements at right angles are separated to ordinary rays and inordinary rays different in the direction of polarization and projected from the Savart plate 6. A Fourier image A by the ordinary rays and a Fourier image B by the inordinary rays are overlapped at the grating face of a scale 4 and respectively form Moire fringes. The Moire fringes of the ordinary rays and the Moire fringes of the inordinary rays hold such relationship in space that, the phrases are shifted by 14 period. Moreover, the Moire fringes of each of the ordinary and inordinary rays are formed of the P-polarized light and S-polarized light having the 90 deg. difference of the polarization direction. The change of the intensity of light of the Moire fringes is separated by a polarization beam splitter 7, whereby signals with a phase shift are obtained.

Some advances in optical contouring of diffuse objects using moire and speckle techniques

Abstract: Optical contouring is a full field, non-contact technique capable of determining shape and deformation data from 3-D surfaces. The data, which are obtained from the optical contouring system, represent the surface geometry at evenly sampled points. The main objective of this thesis is to report some advances achieved by the author in the optical contouring field. Conditions for the design and construction of optical systems to measure object topography and deformation using the same hardware, as well as the optical working methodology and system parameters, are analysed. The conventional in-plane and out-of-plane optical setups for displacement sensitive ESP I systems are employed to contour. The contour maps are obtained by giving small displacements to optical fibres carrying the object and reference beam illumination. A rigorous mathematical treatment of shape contours generated by ESPI is given. It is experimentally verified that the fringe patterns produced are identical to projected fringe contours, and may be analysed in the same way. Then, practical systems which combine deformation and shape measurement in both in-plane and out-of-plane ESPI configuration are demonstrated. Comparison is made with shape measurement using two fringe projection moire techniques. The first moire technique uses electronic demodulation to obtain the contour maps. This technique encodes and analyses moire contours by using an electronic system similar to that used for Electronic Speckle Pattern Interferometry (ESPI). Hence automatic fringe detection and contour measurement is possible. The Talbot effect, where the self imaging of a periodic object is used as second moire technique. The Talbot image of a linear grating is imaged on the target surface. The grating lines are deformed according to the surface shape. Viewing this deformed grating image through a second reference grating, generates contour maps. A novel on-axis sensor which directly measures distance as a direct colour mapping is introduced. It is emphasized that all the techniques researched here can be extended to be applied as industrial tools for surface inspection or quality control. Phase-shift measurement and digital image processing are employed for data reduction.

Projection type liquid crystal projector

Abstract: PURPOSE:To make a display image easy to see on a screen which varies in screen gain by making moire fringes, generated on the screen, invisible by the projection type liquid crystal projector. CONSTITUTION:In the projection type liquid crystal projector which irradiates a liquid crystal panel 4 with the light from a light source 1 and a reflecting mirror 2 and projects the light passed through the liquid crystal panel 4 on a screen 6 where lenticular parts 7 are arranged by a projection optical system 5 to display an image formed by the liquid crystal panel 4, the liquid crystal panel 4 is vibrated at right angles to the array of the lenticular parts 7; and the amplitude of the vibration is a half as large as the pitch of the moire fringes formed on the screen 6 and the frequency of the vibration is higher than an eye recognizable speed. Consequently, the light and shade of the moire fringes are seen to be uniformed with human eyes and the moire fringes seem to disappear, so that the display image on the screen 6 becomes easy to see.

Phase stepping: application to high-resolution moire

Abstract: The application of phase-stepping to moire is presented. An analysis of the precision attainable with this technique shows that a resolution comparable to that of strain gauges is possible. We present preliminary experimental results from computer aided processing of phase-shifted moire fringe patterns (software FRANGYNE developed in our laboratory). Although this software is not specific, only results from in-plane moire are presented. Our moire setup consists of a CCD camera whose sensor acts as the reference grid. The phase shift is obtained by translating the camera perpendicular to the optical axis. The experimental results concern isotropic and anisotropic materials, and show the potential interest of such a technique in the field of experimental mechanics.

Computer gratings for vibration analysis

Abstract: The reflection moire is a well known method to analyze the out-of-plane slope and curvature of a plate. It has also been applied to obtain the mode shape of a plate vibrating at resonance. The sensitivity of the method depends on the pitch of grating and the set-up parameters. In order to increase the sensitivity, the set-up or pitch of grating needs to be changed. Besides that, patterns produced with ordinary gratings have to be filtered to increase contrast. Using computer grating with image processing, the gratings can be quickly and readily changed and images can be enhanced. In this paper, the reflection moire method using computer grating is proposed to inspect the mode shapes of vibrating plates. A method to calculate the frequency of a vibrating plate using scanning frequency of screen is also introduced. Some of the routines for fringe enhancement are quasi-real-time while other routines are more computationally intensive.

Auto-correlation of measuring inaccuracies in lithography system - forming superimposed images of linear and strip grids on high resolution film, subjecting to effect for set time, and observing using microscopic

Abstract: The method involves illuminating a linear grid with a corpuscular optical beam-system under investigation and using a high resolution recording film. An image of a strip grid of the same grid constant but slightly relatively rotated is superimposed onto the film after a finite period, table movement or other influence on the equipment. The resulting beam position error relative to the first image is magnified in the direction perpendicular to the grid direction by the reciprocal of the rotation angle. It can be directly read off in nanometres from the Moire strips using a microscope after developing the substrate. USE/ADVANTAGE - For quality control of lithographic processes, allowing measurement of position errors, thermal and mechanical instabilities, and image distortion. Accuracy of a few nm is achieved with direct read-out not requiring computer processing.

Mask alignment technique using phase-shifted moire signals

Abstract: Moire technique with different variations has been successfully used for mask alignment, with very high accuracies. In this paper we report a new approach to computer controlled mask alignment using modified moire technique. In this technique alignment is controlled in the higher slope region of the moire signal using a single pair of grating alignment marks. In the present case a phase shifted signal is generated by the computer using the input moire signal. The point at which this phase shifted signal becomes equal to the moire signal is treated as the alignment point. The error signal for controlling alignment is obtained by computing the difference of instantaneous moire signal from the intensity of this point. Computer simulation studies as well as experimental studies were conducted on this approach. The results of these studies are presented.

Hybrid grid-moiré method for measuring strain and displacement

Abstract: A hybrid grid-moire method for measuring strain is presented. The method employs a line grating attached to a plane surface of the specimen. Images of undeformed and deformed gratings are acquired and stored using a video system and a frame digitizer. The magnification is adjusted to record 10 to 30 lines of a grating with a pitch of 4 μm over the frame width. A fast Fourier transform (FFT) of the intensity data gives a close estimate of the spatial line frequency. A moire function is formed as the product of a reference sine function and the image intensity-position function. FFTs of the moire function yield an improved estimate of the line frequency. The line frequency is related to an average strain over the recorded image. The method was demonstrated at a magnification of 1500 x with a grating pitch p s = 4 μm. The accuracy achieved depended on strain. For strains in excess of 0.1%, the errors were usually less than 5% when compared to strain gauge results. For plastic strains, in excess of 1%, the differences between two comparable measurements were less than 3%.

Holographic moire patterns processed by the Fourier transform method

Abstract: Spatial-carrier fringe pattern analysis is a wide-spread technique and has found a lot of applicationsto optical metrology. Introducing spatial- carrier into a holographic moire pattern is also a well-known technique to obtain observable moire fringes. Preprocessing of the holographic moire pattern in- cludes optical or digital Fourier filtering to remove the carrier. The fringe pattern is then processed byusing time-consuming fringe-counting algorithms. The current work presents a new application of theFourier transform method to automated analysis of holographic moire fringe patterns. The method ownsthe advantage of instantaneous determination of both phase functions in the pattern. Investigations are carried out on the frequency restrictions imposed on the phase functions. The technique is demon- strated on computer generated noisy holographic moire patterns. The technique does not complicate theconventional experimental holographic moire arrangement. 1. INTRODUCTIONPrincipal problem in fringe pattern analysis is how to reveal the phase information from a fringepattern by separating it from the background intensity and local contrast variation. One solution to