Showing papers on "Moiré pattern published in 1983"

Fourier transform profilometry for the automatic measurement of 3-D object shapes

Abstract: A new computer-based technique for automatic 3-D shape measurement is proposed and verified by experiments. In contrast to the moire contouring technique, a grating pattern projected onto the object surface is Fourier-transformed and processed in its spatial frequency domain as well as in its space-signal domain. This technique has a much higher sensitivity than the conventional moire technique and is capable of fully automatic distinction between a depression and an elevation on the object surface. There is no requirement for assigning fringe orders and interpolating data in the regions between contour fringes. The technique is free from errors caused by spurious moire fringes generated by the higher harmonic components of the grating pattern.

Projection moire with moving gratings for automated 3-D topography

Abstract: A method is presented that permits a vast increase in the capability of projection moire topography. It involves simultaneous translation of the reference and object gratings to generate high-definition contour fringes without any of the artifacts associated with ordinary moire. Experimental results are presented for single- and double-projection arrangements for a general 3-D object and an inclined-plane test surface. Clear contouring fringes for angles of inclination up to 80° are shown, and fringe densities higher than the grating frequency are obtained. Coupled with the flexibility of projection moire, this technique is shown to be particularly suited for computer-assisted moire fringe pattern analysis. Means of practical implementation in on-line processing system are proposed.

Projection moire interferometer for vibration analysis.

Abstract: A projection moire interferometer is presented which was developed to study rotating vibrating objects such as turbine blade assemblies. Three methods of moire interferometry were used in this study: pulsed; time-average; and real time. Real-time moire interferometry used in conjunction with image derotation and strobe techniques is shown to be a viable method of studying traveling wave modes on a rotating disk.

Moire technique by means of digital image processing.

Abstract: Moire technique by means of projected fringes is a suitable method for full field measurements of out-of-plane deformations and object contouring. One disadvantage in industrial applications has been the photographic process with the involved time-consuming development of the photographic film. This paper presents a new method using a TV camera and a digital image processor whereby real-time measurements of deformations and comparison of object contours are possible. Also the principles and limitations of the projected Moire method are described.

Real-time analysis keratometer

Abstract: A computer assisted keratometer in which a fiducial line pattern reticle illuminated by CW or pulsed laser light is projected on a corneal surface through lenses, a prismoidal beamsplitter quarterwave plate, and objective optics. The reticle surface is curved as a conjugate of an ideal corneal curvature. The fiducial image reflected from the cornea undergoes a polarization shift through the quarterwave plate and beamsplitter whereby the projected and reflected beams are separated and directed orthogonally. The reflected beam fiducial pattern forms a moire pattern with a replica of the first recticle. This moire pattern contains transverse aberration due to differences in curvature between the cornea and the ideal corneal curvature. The moire pattern is analyzed in real time by computer which displays either the CW moire pattern or a pulsed mode analysis of the transverse aberration of the cornea under observation, in real time. With the eye focused on a plurality of fixation points in succession, a survey of the entire corneal topography is made and a contour map or three dimensional plot of the cornea can be made as a computer readout in addition to corneal radius and refractive power analysis.

Apparatus and method 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.

Automatic topography using high precision digital moire methods

Abstract: Three types of moire topographic methods using digital techniques are proposed. Deformed gratings obtained by projecting a reference grating onto an object under test are subjected to digital analysis. The electronic analysis procedures of deformed gratings described here enable us to distinguish between depression and elevation of the object, so that automatic measurement of 3-D shapes and automatic moire fringe interpolation are performed. Based on the digital moire methods, we have developed a practical measurement system, with a linear photodiode array on a micro-stage as a scanning image sensor. Examples of fringe analysis in medical applications are presented.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

On a curvature based non-destructive moiré technique for detecting defects in plates

Abstract: Curvature contouring of laterally loaded reflective plates is shown to be an effective means of detecting defects. A sensitive moire method is proposed which uses an image-shearing technique to obtain at the image plane a dense slope-modulated virtual grating which, when superposed upon itself with a lateral shift, yields explicit partial curvature fringes. The method enables the determination of the location and also the size and shape of the defect.

Curvature measurement by moiré effect

Abstract: A simple method is proposed for obtaining curvature of plate surfaces. The experimental arrangement is based on the Ligtenberg reflection moire principle. Shifting two identical grating images relative to each other, which are optically superposed, results in moire curvature fringes. The shifting is done with a Wollaston prism which is positioned in front of the camera objective. Because of the simultaneity of the superposition, the method is well suited for dynamic problems.

Digital and optical moiré detection of flaws applied to holographic nondestructive testing

Abstract: Superposition of two double-exposure holographic interferograms creates moire patterns that can be used to detect flaws. Relative magnification can be used to correct for imprecise replication of loading when the second interferogram is formed; it also can be used to detect flaws when only a single interferogram is used if the basic deformation field is radially symmetric. Digital image processing is a rapid and versatile technique for forming such moire patterns.

Fringe addition in moire analysis

Abstract: In this paper, we suggest and demonstrate a technique for summation of moire fringes. We show that summation of fringes requires the formation of a conjugate grating, analogous to a conjugate wave in interferometry. A detailed example of fringe summation in moire deflectometry is presented.

Moire deflectometry with deferred analysis.

Abstract: A simplified version of moire deflectometry for flow visualization is presented. The modification comprises replacement of the second grating, the ground glass screen, and the camera with a plate film holder to obtain a shadow picture. Postanalysis proceeds by placing a grid transparency of the same periodicity of the remaining glass grating on the negative for projection viewing. The rotational angle between the grating and the plate alters the moire fringe periodicity. Use of the method in studying flows is predicted to reveal weak density gradient areas and shocks.

Stereoscopical image fiber

Abstract: PURPOSE:To observe stereoscopically an object in a place where no persons can enter, by transmitting moire stripes generated on the end face of an image fiber and observing moire fringes. CONSTITUTION:The image of a projection grating K1 on an object 3 is focused on the end face of an image fiber 1 by a lens 8. An image G1 of the projection grating K1 and the second grating G2 which is provided from the beginning are superposed on the end face of the image fiber to generate moire fringes q' on the end face of the image fiber 1. The image fiber 1 transmits moire fringes q' to an image receiving part. When the image is observed in the image receiving part, the image of the object and moire fringes are seen well mainly. Since moire fringes reflect the state of ruggedness of the object, three-dimensional information of the object is obtained. Thus, the object is observed stereoscopically in the place where no persons can enter.

Contrast Enhancement in Holographic Moiré Fringes

Abstract: The aim in this paper is to report on the multiplicative holographic moire fringes in quasi-real time. The work overcomes the drawback of low contrast fringes inherent to holographic moire patterns for the measurement of the in-plane displacements. The factors affecting the visibility of the fringes are discussed, and experimental results are presented.

Arrangement for the contactless and artificial determination of the two- or three-dimensional shape of an object.

Abstract: Arrangement for the contactless and artificial determination of the two- or three-dimensional shape of an object (1) by illuminating the object with a light source (2) produced from two coherent illumination points which are separated from each other. As a result primary real interference patterns are produced in the direction of the light beams (5b). The object (1) is observed by means of a primary imaginary interference pattern obtained via two simultaneously-connected coherent observation points (3) which are separated from each other. The combination of the two interference patterns gives a secondary pattern of Moire lines which provides an artificial image (4) which is significant for the shape of the object.

Three-Dimensional Shape Recognition By Moire Correlation

Abstract: This paper presents a new method for pattern recognition of 3-dimensional objects. Three dimensional objects are recognized by means of a moire contour difference technique. The technique utilizes the projection of a grating upon the object. The grating is perturbed according to the topography of the object surface; thus the perturbed grating acts as information carrier about the surface topography. The image of a master part which has been illuminated with a projected grating is stored in a negative photographic transparency, and it is used as a transmission filter when inspecting other parts. The transmitted image contains the correlation information of the part under inspection with the master part. If the two parts are identical, an autocorrelation occurs which results in a minimum level of light transmitted. If the inspected part is different from the reference part, a cross-correlation occurs which results in the presence of moire fringes and causes more light to be transmitted. Missing parts are detected by identifying the presence of moire fringes or simply detection of the level of the transmitted light and decision can be made automatically. The feasibility of the method was verified by a laboratory demonstration.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Moire method to determine separate frequency contributions in vibration patterns

Abstract: Interference holography with a pulsed ruby laser is used as a tool for analyzing complex mechanical vibrations. With the aid of a moire technique, the combination of two interferograms taken in special, electronically controlled conditions yields the contribution to the vibration pattern corresponding to a single frequency. Quantitative analysis then follows the same lines as in ordinary holographic interferometry.

An Analysis of the Effect of Diaphragm Shape on the Contrast of Filtered Moiré Fringes

Abstract: The paper shows that, by suitably selecting the shape, dimensions and orientation of the diaphragm through which the moire fringes formed by crossed gratings are viewed, the contrast of the fringe pattern of interest may be maximised with respect to accompanying noise. Computer simulation is used to give quantitative information regarding the improvement obtained. The results have potential application in the design of transducers for measuring displacement using moire fringes.

Moire fringe multiplication technique for measuring small displacements.

Abstract: It is well known that moire patterns can be produced by a number of ways. These include direct superposition of two gratings and superposition of a grating and the image of an­ other grating. Since Rayleigh first explained how moire patterns are produced by the superposition of two families of equispaced parallel straight lines, moire techniques have been widely used for metrological applications, evaluation of replica gratings, phase object mapping, strain analysis, and refractive index and refractive-index gradient measure­ ments. Recently, Livnat and Kafri suggested a moire technique for liquid level measurements. With their technique, the minimum detectable change in the liquid level is given by

Moire Topography Using A Charge Coupled Device Television Camera

Abstract: A simple and straightforward way to make projection Moire topograms is described. A grating pattern is projected on the object, which is imaged by an interline transfer (ILT) charge coupled device (CCD) television camera. High contrast Moire fringes that can be equal to topographical contours are then obtained. Experiments showing examples of this technique are presented and discussed.

Stereometric Analysis Of The Human Body And Articular Surfaces

Abstract: In this paper we introduce the method of Moir4 contourography to measure human body and animal's articular facies and teeth. The animal facies of articulation is rather compli­ cated. We haven't seen an expression of a complete mathrnatic formula yet. Hence, we adopt Moire contourography to express three dimensions of animal's articular facies.1We show here also the characteristic equation of Moire contourography of irradiation grating, and the relationship of the contour Moire frings and influence coefficients. So it is very useful to measure errors. Then we introduce some of our research on animal's arti­ culation surface and teeth.introductionMoire is an old expression. It means the fabric, especially silk having wavy patterns. It was first used in Europe to describe the fiqure on silk imported from ancient China. But now in technic Moire is generally meant to show the interference fringes which are created by the superposition of two black-white liner gratings. One of these gratings is to^be dis­ torted by an object whose deformation of shape is represented by the resulting Moire fring­ es. Here we shall discuss method whose primary purpos is used to measure the out-of-plane shape of object.We also use two gratings, one as a reference and another for specimen. But specimen grating is not a separate one, rather it is the shadow of the reference grating as cast on the object surface. The specimen grating will be distorted by the out side of plane form of the surface. When they are viewed together with the reference grating by a camera, Moire fringes are created which represent the topology of the surface.^Examine lumbar vertebrae of human bodyMoire contourography is non-contact measurements which can measure three dimensional ob­ jects and rough surfaces. The Moire contourography is not a new measurement method but it was used on human body's examination since 1970 by H. Takasaki.2 Since then many studies have published about application of Moire contourography to examine three dimension of hu­ man body and K. Ashizawa applied it in human trunk and researches on measure errors,3Application of Moire contourography is not only the optical system which can be easily used but it is also the illumination of light which is not harmful to human. It dosn't like x-ray, so it has further development of usage.4 We have shown one of our experiments to examine lumbar vertebrae of human body.sThere are two kinds of grating, one is the grating irradiation type, the other is the grating projection type. The grating irradiation type always measures small objects, the grating projection may be used to measure big objects. But both of the two kinds of grating can examine lumbar vertebrae of human body.Characteristic equation of Moir^ contourography of irradiation gratingFor obtaining the Moire contour lines we always use two kinds of optical systems, one is the parrallel illumination and parrallel receiving. If the object is small enough and the camera is at approximation it can be achieved.The assumption of the camera being at infinity is not a practical one, so it limits the method to small models only. The other system is the point illumination and point receiving.The principle of the grating irradiation type of Moire contourography for point illumunation and point receiving optical system is that both light source and the camera are assumed at a finite distance away from object. Both the light source and the camera lens focal points are located at the same distance away from the grating plane. The re­ ference grating configuation is a transmission section placed immediately before the ob­ ject. The vertical distance from the grating plane to Moire stripe degree of the object is given by

Measuring device for shape by moire

Abstract: PURPOSE:To discriminate the ruggedness of a measuring object and to calculate the sectional shape in arbitrary directions automatically by moving a light source and an image sensing element finely in a horizontal direction, and detecting the directions where the patterns of moire patterns change. CONSTITUTION:A laser light 11 is reflected by a mirror 13a, and is radiated ont a solidified shell 7 which is a measuring object, by a concave lens 14a. The shade of a grating 2 formed on the shell 2 passes through a filter 15 by way of the grating 2 again and is picked up as moire fringes indicating the contour patterns of the shell 7 with a TV camera 16. When the mirror 13a is periodically moved vertically, the beam 11 is reflected alternately by the mirrors 13a and 13b and therefore the spot light sources of the moires move periodically and horizontally. When the light sources move rightward, the distances between the grating 2 and the moire fringes increase and the positions of fringes 20, 21 change to 20', 21'. Then, the moving directions 22...23 22'...23' of the moire fringes viewed from the camera are reversed in the projecting part A and recessing part B of the measuring object, and the ruggedness is discriminated accordingly.