Showing papers on "Moiré pattern published in 1990"

The physics of moire metrology

Abstract: Historical background introduction to Moire metrology techniques used in Moire metrology limitations on accuracy due to the use of light holographic vs Moire contouring of three-dimensional diffusive objects Moire analysis of strain Moire deflectometry applications of Moire deflectometry.

Fast profilometer for the automatic measurement of 3-D object shapes.

Abstract: A fast technique for automatic 3-D shape measurement is proposed and verified by experiments. The technique, based on the principle of phase measurement of the deformed grating pattern which carries the 3-D information of the measured object, can automatically and accurately obtain the phase map or the height information of a measured object at every pixel point without assigning fringe orders and interpreting data in the regions between the fringe orders. Only one image pattern is sufficient for obtaining the phase map. In contrast to the fast Fourier transform based technique, the technique processes a fringe pattern in the real-signal domain instead of the frequency domain by using demodulation and convolution techniques, can process an arbitrary number of pixel points, and is much faster. Theoretical analysis, simulation results, and experimental results are presented.

Scanning apparatus for halftone image screen writing

Abstract: Moire patterns in raster-scanned halftone dots image screens generated by multi-element line scanner devices are rendered imperceptible to the human eye by selecting the number of elements in the line scanner device to be that number which makes the "once-around" scanner frequency an integral multiple of the halftone dot screen frequency and makes the beat frequencies between the scanner and frequencies either fall outside the nominal visible spatial frequency range of about 2.5 to 250 lines per inch or fall on the screen frequency.

Imaging system having a blurring optical element for minimizing moire phenomenon

Abstract: An image pickup device using a solid-state image sensor adapted to provide an optical component having a multiple curved surface, polyhedral surface, symmetric cylindrical surface, axially symmetric aspherical surface or asymmetric refracting surface in an objective lens system, or lengthen a shape of an image formed on an exit end face of an illuminating optical system in a direction parallel to a scanning direction of the solid-state image sensor, or select an angle made by a line segment connecting between the centers of individual exit end faces of two illuminating optical systems with the scanning direction of the solid-state image sensor to ±40° or less, or extend a shape of an aperture of a stop in a direction parallel to the scanning direction of the solid-state image sensor, in order to make it possible to fabricate the device in a small size and at a low cost and eliminate moire and false color without reducing resolving power.

Moire distance measurement method and apparatus

Abstract: A Moire distance measurement technique for measuring the distance that a diffusely reflecting surface moves involves projecting a first grating onto the surface, imaging the projected grating onto a second grating to form a Moire pattern, and measuring a change in the Moire pattern as the surfaces move to determine the distance that the surface has moved

Automatic fringe detection algorithm used for moire deflectometry.

Abstract: An automatic fringe detection algorithm applied to moire deflectometry is presented. This algorithm is based on a set of points linked together and with a behavior similar to a rubber band, in which these points are attracted to fit the moire fringes. The collective behavior of these points gives rise to a final state which is their regularly spaced alignment along the fringe pattern. The algorithm is dynamic in the sense that it tracks the fringe even when it suffers continuous deformations. Once the rubber band is adapted, the rubber band’s points coordinates are obtained and their distance to the starting straight line is found, as required by moire deflectometry.

Imaging optical system having a moire elimination effect

Abstract: An imaging optical system for forming images of objects on an image surface. The optical system includes an aspherical surface that functions to reduce spatial frequency response of the optical system when aperture size of the optical system is reduced within a variable range and adapted so as to eliminate spurious signal by the aspherical surface.

Moire contouring camera

Abstract: A moire contouring imaging device for small field moire imaging in which both the illumination and viewing optical beam paths pass through a common primary lens and optical grating. The use of such common optical elements improves optical stability and accuracy since magnification and focal length and other mismatching between discrete optical elements in the viewing and illumination paths are avoided. The device is assembled in a rugged elongated housing. Additional features are provided to avoid the effects of unwanted stray light reflected off rear surfaces of optical elements within the system.

Polarization phase shifting method for moire interferometry and flatness testing

Abstract: Described in this short paper is an implementation of the phase shifting technique for computer-aided processing of interference fringes obtained by the moire interferometry method for in-plane displacement measurements or in a similar arrangement used for out-of-plane displacement (flatness) determination. The polarized light approach was selected because of the common path propagation of the interfering beams. The experimental verification is presented.

Non-destructive testing of aircraft for structural integrity using holographic moire patterns

Abstract: A method of using the classic principles of moire patterns and holography to provide defect analysis of variable sensitivity on structures of various sizes, including large aircraft. By taking several holograms (usually a series of four) of the structure which has been illuminated with dual (or multiple) beams of coherent illumination (e.g. laser), each hologram will record an image of the test object which includes an interferometric fringe pattern on the surface. The spacing and orientation of the fringe pattern can be varied by the arrangement and nature of the dual illumination beams.

Strain analysis by mismatch moire method and grid method using Fourier transform

Abstract: We have formerly presented a new method of the moire analysis of strain using the Fourier transform. It uses the phase information of the moire fringe brightness. By shifting the Fourier spectrum of the image of deformed grating lines, we obtain the “complex moire pattern”. Strain distribution is given as the derivatives of the phases of the complex moire fringes. The analysis is completely automated by digital image processing. All of the laborious and subjective procedures required in the conventional analysis such as fringe sign determination, fringe ordering and fringe interpolation are thus eliminated, and objective, fast and accurate analysis can be made.

Optical pickup device

Abstract: PURPOSE:To integrate luminous fluxes of forcusing and tracking by a moire fringe into the same optical system without allowing them to interfere with each other by placing the direction of the fringe of two pieces of gratings for generating the moire fringe of focusing and the direction of the fringe of a diffraction grating for generating three beams of tracking so as to be roughly orthogonal to each other. CONSTITUTION:A diffraction grating 3 for generating three beams and a first and a second gratings 8, 9 for generating a moire fringe are provided so that the directions of the respective fringes are roughly orthogonal to each other. Accordingly, it does not occur that between the diffraction grating 3 for generating three beams and the gratings 8, 9 for generating the moire fringe, the moire fringe is generated due to interference, and there is no possibility that a pseudo focus signal generated at the time placing the gratings in parallel is generated. In such a way, a compact optical pickup device which can obtain a focus error signal and a tracking error signal by the same optical system is obtained, and also, a first grating 8 and a second grating 9 are provided by separating them by a Talbot distance, therefore, the moire fringe becomes distinct and the optical pickup device having high detection accuracy is obtained.

Cellular neural network application to moire pattern filtering

Abstract: The moire effect, i.e. the intermodulation of signal frequencies, is generated by superposition of two or more periodic and/or quasi-periodic functions. It occurs as distortion in printing and displaying, and can be used for measurement (moire topography, stress and strain analysis). This paper describes the moire technique for medical spinal curvature estimation. Two approaches are presented: classical 2D sequential digital filter, and a cellular neural network. >

Refractive power mapping of progressive power lenses using Talbot interferometry and digital image processing

Abstract: A method of refractive power mapping of a lens is presented which is based on Talbot interferometry and utilizes a digital image processor. By adding a digital image processing system, fast measurement of a lens power distribution is feasible. A test lens is placed in front of two collinearly arranged gratings. The light passing through the test lens produces a shifted Talbot image of the first grating on the second grating and generates moire fringes. Given the inclination angle of moire fringes, the refractive power of the lens can be calculated. The calculation is performed using a digital image processor. This method is effective in finding the refractive power distribution of progressive power lenses.

Video Applications to Moiré Metrology

Abstract: Video technology is applied to the problem of moire metrology. In the past, moire metrology seemed a promising yet limited method in the measurement and comparison of surface shape. The use of video technology has widened the area of application of moire metrology by reducing the complexity of the optical set up and providing real time information on surface shape and deformation. A continuously variable grating projector and analog video circuitry are used to generate real time additive (bright line) and transmissive (dark line) moire patterns. These patterns are used to compare a test object against a “perfect” reference object. This is done in both real time and through the use of computer image processing. Depth resolutions on the order of 0.3 mm are obtained on a cone 25.4 mm high and 50.8 mm wide. The projection system allows easy expansion to large objects. Because of the use of video technology moire metrology can now be more readily applied to robotic vision and factory assembly line quality control over a wide range of scales.

Moire deflectometry with a focused beam: radius of curvature, microscopy, and thickness analysis.

Abstract: Three uses of moire deflectometry employing a focused beam are described. A microscopic mode provides inspection of magnified images of the test object. The moire fringes are used as a noncontact tunable caliper for measuring the dimensions of small imperfections and other features of the surface. The tunable scale is independent of the zooming ratio. The spherometer mode measures the radius of curvature of concave or convex spherical objects. Deviations from spherical shape are measured with variable sensitivity. The thickness of transparent objects is measured by focusing the beam on each face in turn.

Holographic Moire Contouring

Abstract: Theoretical analysis and experimental results on holographic moire contouring (HMC) of difussely reflecting objects are presented. The sensitivity and application constraints of the method are discussed. A high signal-to-noise ratio and contrast of the fringes is achieved through the use of high quality silver halide holographic plates HP-650. A good agreement between theoretical and experimental results is observed.

Moire distance measurements using a grating printed on or attached to a surface

Abstract: Method and apparatus are disclosed for providing Moire distance and displacement measurements of a diffusely reflective surface of an object or support. More particularly, a first grating is physically located, formed, or printed on the diffusely reflective surface. An image of the first grating is formed on a second grating by an imaging means for generating a Moire pattern behind the second grating. At an initial position of the diffusely reflective surface relative to the imaging means, the periods of the image of the first grating and the second grating match. Movement of the diffusely reflective surface in a direction normal thereto and away from the initial position produces a spatially varying intensity pattern caused by the Moire between a shifting and changing magnified pattern of the image of the first grating and a pattern of the second grating. The temporal intensity changs in the Moire pattern are detected and are used to produce information related to the instantaneous distance and displacement of the diffusely reflective surface from the initial position.

Constructing pure digital secondary moiré patterns

Abstract: A new method of constructing pure digital secondary moire patterns of equal-strain fringes is proposed in this paper. By this method, a pure secondary moire pattern, without trace of primary moire fringes, is obtained directly from common digital moire patterns regardless of how low or high the fringe density. The pure secondary moire patterns eliminate the backnoise of primary fringes and give the strain value at every point over the whole strain field. This technique can significantly increase the measurement accuracy and the range of moire techniques.

Analysis of Superposed Moiré Patterns in Halftone Screen

Abstract: In the multicolor printing process, moire patterns appear in a printed image due to the superposition of two or more screens. This is called superposed moire and is distinguished from the moire that appears in the sampling or modulating process. It is necessary to suppress this kind of moire as well as other kinds. However, the fundamental properties of the superposed moire, such as their shapes and amplitude, has not been analyzed in detail. Therefore, suppression of the superposed moire have not yet been considered. This paper proposes an analytical method to determine the fundamental properties of the superposed moire. This method can estimate the frequency, direction, profile and amplitude caused by arbitrary halftone, screen-dot functions.

Screening and Moiré Suppression in Printing and Its Analysis by Fourier Transform

Abstract: Moire patterns are often observed in printing when the image is reproduced as a bilevel image with halftone A Fourier transform analysis of screening a picture by an optical method or an ordered dither method is presented Conventional moire—suppressing techniques are discussed considering the human visual system The moire fringes are explained as aliasing and visible moire fringes are especially due to high-frequency spectra with high power From this viewpoint, a screening method is proposed which uses the Fourier transform for moire suppression This method has the additional advantage that any pitch and any screen angle may be selected

Automatic focusing apparatus with moire fringes

Abstract: An automatic focusing apparatus having an objective lens for forming a beam from a semiconductor laser as a spot image on an image subjecting face, a driving unit for driving the objective lens in a direction parallel to an optical axis thereof, a beam splitter disposed between the semiconductor laser and the objective lens, a pair of grids for generating a moire image displaced in a travelling path of a beam returning from the image subjecting face and reflected by an inclined prism face of the beam splitter, a photo detector for detecting the moire image generated by the grids and an control unit for evaluating a focusing error based on a variation in the moire image pattern and for controlling the driving unit so as to correct the focusing error. The first grid and the second grid are interspaced in parallel to each other along a beam axis and angularly displaced from each other about the beam axis.

Deformations in glass-fiber woven composite using moiré interferometry

Abstract: Moire interferometry is used to study the deformations around a small hole in a glass-fiber woven epoxy composite material Variation of principal material direction and its influence on the deformation are described The high sensitivity of the moire interferometric method in some instances provides too many fringes A moire of the moire interferometric method is used to subtract some of the uniform fringes to present the nonuniformities as bold variations

Fringe pattern analysis using hybrid image processing.

Abstract: Hybrid image processing using optical defocusing and digital computing techniques is investigated for use in the analysis of interferograms or moire fringes. The optical thickness distribution of a glass plate is measured from the interferogram, and the power distribution of an eyeglass lens is tested from the moire pattern. The optical defocusing technique is also used for preprocessing of the input image to suppress high frequency noises. The optimum defocus amount relating to the processed result is discussed.

A novel technique for X-ray laser beam characterization

Abstract: The use of a novel diagnostic based on the Moire effect, known as Moire deflectometry, to characterize X-ray laser beams is described. This technique is purely geometric in nature and does not require coherent radiation for its operation. The unique feature of Moire deflectometry is that it provides a fully quantitative laser beam diagnostic which can be operated in any wavelength region of the spectrum. This technique allows the number of transverse modes present in the beam to be determined from the inherent beam divergence. The latter is measured from the degree of reduction in the contrast of the Moire fringes. From the same deflectogram the geometrical-beam behaviour can be determined. This includes both geometrical-beam divergence and ray-aberrations which lead to wavefront distortions.

Shock Waves in Plates under Elastic and Viscoelastic Conditions -Optical Measurement by Combining Photoelasticity and Moiré

Abstract: A hybrid optical measuring technique is introduced to measure the whole-field state of stresses and strains under dynamic loads. Using a combined optical bench the displace-ments are recorded by in plane Moire technique and synchronously the isochromatics by photoelasticity. To separate the Moire deformation data white-light processing is applied which also serves to multiply the Moire fringes and to encode the data for archival storage in color films. The application of the technique is demonstrated for the example of stress waves in plates to simulate solid-sound propagation in machine parts.

Measurement of the face's topography by digitally enhanced shadow Moire

Abstract: In order to adapt the pilot's pressure mask individually there is a need to evaluate the topography of the human face. Classical shadow moire technique was combined with modern digital image processing to insure the capability of the developed system to automatically trace the location of the full and half multiples of moire fringes. Use of digital image processing allows depth measurements not only at those fringe locations, but also at the fractional fringe position, thus one can use less dense fringe patterns. Such patterns are more easily adapted for automated processing. The developed software and hardware are capable to acquire the image, digitize it and calculate the 3D location for any point in the area of interest, with plane resolution of 0.5 mm and depth resolution of 0.3 mm. The developed approach can be modified to work on a variety of surface topologies, which require fast and automated analysis with the digital output transferred to a cutting device.