Showing papers on "Moiré pattern published in 1980"

Vibration analysis of plates by a time-averaged projection-moiré method

Abstract: A time-averaged moire principle is described that is appropriate for vibration analysis of plates. If the projected grating, deformed by the vibrating object, is superposed upon a reference grating in the area of the screen of the projector and observed on a ground-glass plate for more than one period, moire patterns can be seen without the interfering gratings, depicting the nodal lines and the slope contours in the extreme deflected positions of the plates.

Measurement of strain fields near coldworked holes: High resolution grating photography, optical data processing, and digital data reduction extend power and simplicity of moiré study of elastic-plastic problem

Abstract: Residual strains near coldworked holes were measured for several degrees of radial expansion. Moire-grating photography created magnified replicas of deformed gratings. Fringe patterns with sensitivity multiplication and S/N improvement were obtained by optical data processing and by using slotted apertures for photography. Computer data reduction and plotting provided the required strain maps.

A geometrical approach to holographic interferometry

Abstract: Geometrical considerations are used to obtain quantitative data for the components of the displacement vector. Use is made of a dual-beam illumination and a variant is described, using point light sources and a single point of observation. Contour lines for the displacement vector in the viewing direction and in a perpendicular direction are obtained as the algebraic sum and difference of two interference patterns. Densification of the initial pattern is used to obtain moire patterns for the out-of-plane and in-plane displacements of flat Surfaces and for the derivatives of these displacements. To determine the complete displacement field of objects of arbitrary shape, one holographic plate is sufficient, using two times two-point light sources.

Simple optical processing of moiré-grating photographs

Abstract: The three fundamental optical phenomena of diffraction, two-beam interference, and transformation by a lens form the basis of modern moire strain-measurement techniques. The improved understanding of diffraction by superimposed gratings and optical spatial filtering leads to a general gain of freedom in designing moire experiments. Benefits characteristic of refined but very simple optical-data-processing techniques include simpler apparatus, less-demanding procedure, possible large gains in sensitivity, and the ability to choose certain moire parameters, such as sensitivity,after an experiment is concluded and the raw data stored. Sample results from a study of strains near cold-worked holes demonstrate that acceptable results can be had with elementary apparatus and systematic exploitation of optical-data processing.

Imaging system and method with reduced moire interference

Abstract: System and method for forming a halftone image by scanning without visible moire interference. Alternate scan lines are sampled with clock signals of different phases to produce a displacement between adjacent scan lines in the output image. This displacement reduces the increase in spot width which would otherwise produce moire interference, with no increase in the rate at which the video signal is sampled.

Apparatus for measuring surface shape by utilizing moire method

Abstract: PURPOSE:To enable arbitrarily setting of the measuring sensitivity of an apparatus for measuring the surface shape utilizing moire method and improve the measuring accuracy of the apparatus by constructing the apparatus with an illuminating and observing unit movable on the same plane and a camera having a vertically movable standard lattice rotatable on the same plane within the plane. CONSTITUTION:An illuminator 7, an observing unit 8 and a camera 9 on a base 2 are set to an article 1 to be measured to illuminate the surface of the article 1 through a standard lattice 13 with light and observe through the lattice 13 by the unit 8, interfered moire pattern is obtained. In this method, the illuminator 7 or the unit 8 can be moved along a groove 4 around a rotary shaft 3 as a center to alter the measuring sensitivity thereof. That is, the larger the angle theta between the illuminator and the unit 8 is increased, the better the measuring sensitivity can be improved. The measuring sensitivity can be altered by rotating the lattice 13 of the camera 9 within the plane. The pattern of phase displacement can also be created by controlling the interval between the surface of the article and the lattice 13.

Automatic measurement of 3‐D shapes using scanning moiré method

Abstract: A new type of moire topography called scanning moire method is proposed. Moire fringes are obtained by electronic scanning and sampling techniques, instead of superimposing a reference grating in the conventional projection type moire topography. The electronic technique enables us to distinguish between a depression and an elevation of an object under measurement, and also interpolate moire fringes automatically. By controlling the phase of the virtual grating corresponding to the scanning lines of the image sensors, the automatic sign determination of the moire contour lines is accomplished. We have developed a practical system, in which a 1728‐element linear photodiode array on a micro‐stage is employed as a scanning image sensor. Some examples of analysis are presented.

Moire fringe measuring device

Abstract: PURPOSE:To change the space between contour line Moire fringes arbitrarily and quickly by using an image converting element, which is capable of rewriting the grid image, as a reference grid and by writing various grid images in the image converting element to form a reference grid. CONSTITUTION:The object 26 to be measured is placed at a fixed position on the sample bed 25, the desired contour line Moire fringes is fed from the keyboard 12 to the CPU14. When the measurement is directed from the keyboard after the required grid image is written in the image converting elements 21, 30 as the distribution of refractive indexes, the CPU14 controls the light source controller 15 to make the laser 16 emit laser rays, the grid image written in the image converting element 21 is projected on the object 26 and becomes a deformed grid image. The deformed grid image is formed on the image converting element 30, the contour line Moire fringes formed by the said image is photographed by the TV camera 41 and is converted into a diagram by the CPU.

Focusing point detecting method of optical device

Abstract: PURPOSE:To detect focusing of an optical device promptly and accurately from the appearing moire image interference fringe, by placing first and second charts having regular pattern on the imaging lens focal plane and subject position. CONSTITUTION:A first chart 6 and a second chart 7 are placed on a focal plane 4 of an imaging lens 2 and a subject position 5. The respective charts are provided with regular patterns 61, 71, which should cause moire interference phenomenon when they are overlapped. A moire image 9 of good contrast appears when the two regular patterns to be overlapped are formed in the same pitch. There fore, since the moire image 9 appears only when correctly focused, the range finding precision similar to the required precision of the imaging lens may be obtained, so that the focusing of the optical device may be detected promptly and accurately.

Biostereometrical Application Of Moire Fringe Method With Special Reference To Our Optical Device In Aid Of Parallel Light

Abstract: Biostereometrical approach in aid of moire interference fringe has an advantage in that the contour fringes on the surface of an object are promptly visible to the naked eye and are recorded photographically. Even the movement of these fringes concomitant with the motion of the human body can be recorded by movie camera or video TV. One of the limitations of this moire method using radiating light is that the value of contour interval is obliged to increase gradually with the advancement of the ordinal number of fringes counted from the grating. To cover this demerit, a new moire technique with parallel light has been developed at our laboratory. The parallel light is provided by an optical system including a field lense. Our optical apparatus makes it possible to get equal intervals of the succeeding contour fringes, irrespective of the fringe order. Any requested contour intervals are attained by choosing a grating with suitable pitch and/or an appropriate incidence angle of the parallel light at the grating. The automatic input of analogue data of moire patterns into the central processing unit is accomplished by a TV camera and A/D converter. Examples of line printer output through this conversion system are given.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Flatness accuracy meter

Abstract: PURPOSE:To make it possible to highly accurately meter the flatness accuracy by using both an optical wave interference fringe, which is generated by a reference flat plane a plane to be metered, and a Moire fringe which is generated by a straight lattice. CONSTITUTION:Generally speaking, if the pitch of interference fringe is not coincident with that of a transparent lattice, there appear a number of Moire fringes. A wedge angle is adjusted by angle adjusting screws 8 and 9 so that the pitch of the interference fringe is coincident with that of the lattice. Then, the numerous Moire fringes disappear so that the whole field of view become uniformly bright. In case, at this time, there is no difference in the flatness accuracy between the plane 7a to be metered and a reference plane 6a, the interference finges become completely equidistant straight lines so that they can be completely coincident with a straight lattice 12.

Fringe method measuring deformations over large surface area - involves projection of two coherent beams onto grating on object surface

Abstract: Deformations over a large surface area are measured from Young's or Moire's fringes to a very high degree of sensitivity This is obtained by projecting two coherent light beams onto a grating and frequency modulating one of the beams A grating (2) is mounted on an object (1) and is illuminated by two coherent waves (3, 4) having angles of incidence symmetrical about the normal The Fourier spectra of amplitude sharing of the grating is observed in the focal plane of a lens (5) A screen (6) receives uniform illumination when the incident angles are adjusted A birefringent element (7), comprising a quarter wave blade, provides modulation of the frequency from one source (51) This causes the fringes to travel and they are then sensed by photodetector elements