Showing papers on "Moiré pattern published in 1977"

Scanning moiré method and automatic measurement of 3-D shapes.

Abstract: A new type of moire and its application to topography are discussed. moire fringes are generated by observing a grating projected on an object under test with a scanning imaging device. The general equations of the projection-type moire topography are given. By controlling the phase, the pitch, or the direction of the virtual grating corresponding to the scanning lines of the imaging device, the automatic sign determination of the contour lines is accomplished. By the use of a high precision flying spot scanner with CRT(DD-tube) and a minicomputer system, an experimental measurement system is developed. Very significant is the fact that a contour line system and a sectional shape of the object are automatically reconstructed and displayed on a color TV monitor.

Varifocal moiré zone plates for straightness measurement

Abstract: A Fresnel zone plate of variable size can be formed as a moire pattern between a suitable pair of identical grids. The focusing power may be varied over a considerable range by relative translation of the grids if their line sbapejs are determined by a combination of cubic and linear functions. Elliptical and hyperbolic patterns are also obtainable. If both grids ae constructed in phase reversal form, the irradiance in the diffraction image due to the zone plate is enhanced substantially. The device may then be used with photoelectric detection to monitor the straightness of a continuous linear motion. A possible application to field widening in interference spectroscopy is also suggested.

Optical differentiation of geometrical patterns

Abstract: Two simple optical methods are presented which can perform direct, real-time differentiation of geometrical patterns by shifting. The first one gives uniform shifting in one direction and the resulting moire fringes are curves of constant partial derivative along the same direction, and the second renders moire fringes of constant gradient modulus of the function represented by the pattern.

Instrument for measuring the amplitude of vibration of a vibrating object

Abstract: An instrument for measuring the amplitude of vibration of a vibrating object consists of a first optical system for periodically projecting the image of a grating onto the vibrating object and second optical system having an optical axis intersecting that of the first optical system in the vicinity of the object, for sharing the image projected on and reflected from the object and recording the shared image on a photographic film. The measurement of the amplitude is obtained in the form of a moire pattern.

The Interrelations between Moiré Patterns, Contour Fringes, Optical Surfaces and Their Sum and Difference Effects

Abstract: A general relationship between potential functions and moire patterns can be realized in a number of forms. The potential function can be worked as an optical surface and combined with other potential functions similarly worked to give the solution to a complex potential problem. Contour fringes can be produced from the optical surfaces or generated on a computer graph plotter directly. When superimposed these contour lines generate moire fringes which are also solutions to potential function problems but with an essential ambiguity of sign. Two circularly symmetrical potential wells have been contoured and moire fringe solutions to simple problems are given.

Moiré microwave holography.

Abstract: A new method for the recording of a microwave field using a moire interference pattern is presented. The moire interference pattern was used to map the thermal expansion of a microwave absorbing slab when irradiated by a microwave field. The technique was evaluated by applying it to the recording of a number of different microwave holograms. The moire recording method is found to be relatively sensitive and usable to produce holographic images of good quality.

Analyzing Rapid Surface Motions With Moire Fringes

Abstract: High speed photography of moire fringes was used to analyze the motion of surfaces subjected to dynamic loadings. The moire fringe device used a high power light source, a pair of Ronchi rulings, and commonly available lenses. One Ronchi ruling was projected at an angle onto the surface to be studied. The projected ruling was then imaged onto the second Ronchi ruling where a fringe pattern was produced which was characteristic of the stationary wall before impact. Any outward displacement of the surface caused a corresponding change in the original fringe pattern. Calculations of wall motion from fringe patterns were greatly simplified by the observation that each fringe can be represented as an ellipse which intersects the target (usually in two places) and both the projection and taking lenses.

Method of forming moire contour lines

Abstract: A light beam is periodically chopped and then converted to a plane of light by a cylindrical lens. As the plane of light is chopped, it is caused to scan an object in the direction normal to the plane of the light to form a grating pattern on the object. The image of the grating formed on the object is superposed with a standard grating to obtain a moire pattern which represents the moire contour lines of the object.

Study Of Combustion Phenomena By Combined Deflexion Mapping And Speckle Superposition Techniques

Abstract: One of the more widely used methods for the study of combustion phenomena is the deflexion-mapping method, in combination with Moire techniques. As combustion phenomena are essentially dynamic, multiple frames are generally needed to record the whole event. An exact superposition of each pair of frames may then be done, in order to deduce from the resulting Moire patterns, the change of the thermodynamic variables in the corresponding time interval. We present here a new technique by means of which the superposition of the pairs of frames can be done exactly. This superposition is obtained by comparing a reference speckle pattern registered in each frame with a standard. The reference speckle pattern is provided by an immobile auxiliary diffuser. After developing, a laser beam is directed through the reference region of the nearly superposed pairs of frames, and these are displaced one respect to the other until Young fringes disappear. This yields the criterion of correct superposition. A major advantage of this technique is that the filtering of the Moire patterns corresponding to each pair of frames, and the control of their correct superposition, are made simultaneously on the focal plane of a single lens in a simple optical setup.

Application Of Moire Method To Measurement Of High Speed Deformation

Abstract: The purpose of the investigation is measurement of a diffusing surface, normal to a certain reference plane, changing rapidly with time. In this paper are, in the first place, described basic study, based on geometrical optics, of Moire topography using an incoherent or a coherent light source in two procesess. The contents are below; (1) generating the best quality of equispacing fringes on the surface, (2) formation of Moire contour lines and height difference between the most adjacent lines. Next is shown a time resolved Moire topography consisting of casting fringe system using Xe-flash as a light source and a high speed framing camera et al, with a ten microseconds of time resolution and about 150 microns of contour sensitivity. As a typical application when a thin plate was received an impact force, the deformations of the surface are shown in a series of contour lines pictures.

On Measurement of Three Dimensional Deformation Using Moire Method and Light Slicing Method

Abstract: Methods of photographing orthographic projections of a grating and a contour on a curved surface were proposed. In photographing a contour, a sheet of light is projected on an object intermittently and the object is moved so that its surface may be swept by the sheet, while a camera is focused at the sheet. The contour obtained in this way corresponds to what would be observed from direction of movement of the object. In photographing a grating, a sheet of light is projected continuously. These methods can be applied to any object regardless of its size, whereas in the usual methods using the tele-centric system, spread of region to be photographed is restricted by the aperture of the field lens. Some related methods of measuring shape using Young's interference fringes were modified in similar way. Further, a procedure of measurement of strain in the three dimensional deformation of sheet bulging was shown.