Moire Contours Research Articles

Projection-type moiré topography with frequency modulation technique using liquid crystal digital gratings

A projection-type moire topography that uses a frequency modulation technique with two liquid crystal digital gratings (LCDGs) is proposed. In this method, moire contours are filtered to remove the image of the original grating from the moire contours by moving the image created by the LCDGs. The frequency modulation technique can be used to analyze the fringe of step heights or other separate areas by modulating the fringe interval. The experimental results showed the possibility of measuring three-dimensional shapes and step heights.

Application of acousto-optic cells and video processing to achieve signal-to-noise improvements in variable resolution moire profilometry

Moire techniques can be a powerful tool to determine surface shape or deviation of a shape in progress from a final or desired shape. The presence of the high-contrast viewing grating and the distorted grating in the final image plane makes the moire pattern hard to see. Moving grating techniques have been developed to improve the visibility of the moire pattern, but at the expense of complex moving parts. Several variable resolution projection moire techniques have been developed that either move the grating or eliminate its presence electronically, and have neither mechanical moving parts nor any physical gratings. One system uses an acousto-optics cell to generate, project, and move the gratings, while the moire is viewed through a second synchronized A-O cell. The second system uses an interferometer to generate and project variable spacing gratings that are made to move across the target and across a reference surface by an A-O beam deflector. Video processing of the reference image generates the transmissive filter that produces the moire pattern. A third system removes the grating presence electronically but retains high-contrast moire contours. Noise reduction is shown in a series of moire images of targets.

Three-dimensional shape analysis by use of a projected grating image

A grating pattern projected onto an object deforms in accordance with the three-dimensional shape of the surface. This deformed image can be analyzed by detecting the shifted phase of the original grating pattern with the aid of Fourier transformation. The profile of the object is expressed in moire contours as well as in a wire-frame model for the intuitive understanding of the shape. In this procedure, multiplication and visibility enhancement of moir&#233 fringes are performed with an improved result.

人体の図形的特徴とその解析

The shape of the segmental living subjects, viz. right side half trunks of 28 female were measured three-dimensionally using a moiré camera and a mirror unit, and described with aid of geometrical modeling. The surface of the trunk was marked with netted measurement points which covered any anatomical landmarks so as to retain anthropometrical meanings in the following shape analysis. These points also included peak of concavity and convexity on the surface. The whole trunk surface of the marked subjects was measured with moire contours and the coordinates of the netted points were interpolated from the discrete value on the contours. For the description and shape analysis of the trunk, a geometrical model was generated putting measurement points as control points for Bézier paches. The results showed that the geometrical model approximated appropriate aspects of the original shape of the subject.

Generation Of Moire Contours With Acousto Optic Cells

Moire contours are seen on a curved surface viewed through a grating when the surface is illuminated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic (AO) cells and have been able to observe and record moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object when the illuminating laser beam is strobed with 50 ns pulses by means of an AO modulator. We give data showing the variation in grating spacing with AO modulation frequency. Figures show the variation of the moire contour spacing with the AO modulation frequency and with target contour. The results for an angled flat plate target are compared with those in the literature.

Projection moiré for remote contour analysis

Remote projection and viewing of moire contours are examined analytically for a system employing separate projection and viewing optics, with specific attention paid to the practical limitations imposed by the optical systems. It is found that planar contours are possible only when the optics are telecentric (exit pupil at infinity) but that the requirement for spatial separability of the contour fringes from extraneous fringes is independent of the specific optics and is a function only of the angle separating the two optic axes. In the nontelecentric case, the contour separation near the object is unchanged from that of the telecentric case, although the contours are distorted into low-eccentricity (near-circular) ellipses. Furthermore, the minimum contour spacing is directly related to the depth of focus through the resolution of the optics.