Moiré pattern

About: Moiré pattern is a research topic. Over the lifetime, 1917 publications have been published within this topic receiving 27176 citations. The topic is also known as: moiré fringes & moire pattern.

Calibration method for angular measurement of moiré patterns

Abstract: In this paper, a high-accuracy calibration method for angular measurement of deformed and curved Moire patterns, based on template matching algorithm, is presented. We report a feasible and accurate method, based on Talbot interferometry and Moire deflectometry, to measure long focal-length lenses. Theoretical analysis indicates that the precision of this method is mainly influenced by the angle of Moire patterns. However, it’s difficult to obtain high-accuracy angle of Moire patterns, since the Moire patterns derived from experiment are constantly deformed or curved. We demonstrate a method, based on template matching algorithm, to calibrate deformed and curved Moire patterns, thus their angle can be calculated fast and accurately in sub-pixel domain. Numerical analysis and simulation prove that the method mentioned above demonstrates high precision and stability, and experiment results show that the accuracy of the long focal lengths measurement is improved obviously.

Color-encoded single-shot computer-generated Moiré profilometry.

Abstract: A color-encoded single-shot computer-generated Moire profilometry (CSCGMP) is proposed. Two sinusoidal gratings with a π phase difference are encoded in red and blue channels respectively to combine a composite color grating. While this composite color grating is projected onto the measured object, the corresponding color deformed pattern can be captured. So two deformed patterns with a π phase difference are separated from its red and blue components respectively. After normalization and subtraction, the AC component of both separated deformed patterns can be extracted. If this AC component respectively multiplied by the two AC components of fringe patterns of reference plane with a π/2 phase difference prepared and saved on the computer in advance, two computer-generated Moire fringes just respectively standing for sine and cosine of phase which is modulated by the height of the object relative to the reference plane are figured out. So the 3D shape of the measured object can be reconstructed with normal computer-generated Moire profilometry. Both simulation and experimental results show the feasibility and validity of the proposed method. It has potential in real-time 3D measurement due to its single-shot feature.

Optical distortion evaluation based on the Integrated Colour CCD Moiré Method.

Abstract: Camera calibration is an important part of high-precision optical measurement, which is especially difficult in the micro-nano field. Based on the integrated correlation calculation and CCD moire method, this paper describes the development of a lens calibration technique called the Integrated Colour CCD Moire Method (ICCM). The CCD moire fringes, formed by superimposing a periodic optical signal of a specimen grating with a CCD target array or a Bayer filter array, significantly enlarges the deformation modulated by lens distortion and the calibration plate attitude (i.e. the rotation angle relative to the camera coordinate system). To measure lens distortion using CCD moire, the deformation pattern that is governed by the lens distortion, specimen grating attitude and carrier was used to construct a CCD fringe image. If the constructed CCD fringe image based on the trial lens distortion and rotation angles have a maximum similarity to the captured CCD moire image, the lens distortion and rotation angles are correctly inversed. Particle swarm optimisation algorithm was selected to search for the true value so that the accuracy and robustness could be improved. Numerical experiments verified that the ICCM method developed in this work can simultaneously inverse the lens distortion, rotation angle and the grating pitch with high precision. The lens distortion of the metallographic microscope has been successfully characterised by the developed method with an 833 nm pitch grating. Simulations and experiments showed that ICCM is an intuitive, accurate, anti-noise and robust distortion calibration method.

Focus detecting device based on double-grating moire fringes

Abstract: The invention relates to a focus detecting device based on double-grating moire fringes. The focus detecting device comprises an incident beam, an extender lens, an object grating, wedge-shaped plates, 4f projection systems, rhombic prisms, a detecting grating and a detector, wherein incident light is perpendicularly projected on the object grating by the extender lens; the 4f systems couple an image of the object grating with the detecting grating to form the moire fringes; the height of a silicon wafer can be obtained by detecting movement of the moire fringes; and inclination of the two gratings in the imaging process can be compensated by matching of a double-wedge mirror. The focus detecting device can achieve high-precision and non-contact measurement of the defocusing amount of the silicon wafer.