Digital Moire Research Articles

A digital moiré fringe method for displacement sensors

In this study, a displacement measurement method based on digital moire fringe is described and experimentally demonstrated. The method is formed by only one grating with a constant pitch. First, the magnified grating image is received by an imaging array and is sent to a computer. Then, the digital moire fringes are generated by overlaying the grating image with its mirrored one. Finally, a specifically designed algorithm is used to obtain the fringes’ phase difference before and after movement and calculate the displacement. This method has the effects of amplifying displacement and averaging the grating lines error, the same as the traditional moire technique using two pieces of gratings. At the same time, the proposed system is much easier to assemble and the measurement resolution can be set more flexibly. One displacement measuring system based on this method was built up. Experiment results show that its measurement errors are less than 0.3 μm and less than 0.12 μm at the resolutions of 0.1 μm and 0.03 μm, respectively.

Implement of Digital Moire technique on DSP for alignment of partial compensation interferometer

Digital Moiré technique is adopted in partial compensation interferometer (PCI) for high-precision testing of figure error of the aspheric surfaces. The figure error of the measured aspheric is obtained by a series of calculation with the real interferogram and ideal interferograms generated by computer. The dense interference fringes at the exit pupil make it difficult to align the PCI. On the contrary, digital Moire fringes composed from real and ideal interferograms are sparse and corresponding to the figure error of the measured aspheric, making it easier to align the PCI. Generally, digital Moire technique is processed on the computer, resulting in slow processing speed and difficult display in real time. Digital Signal Processor (DSP) can be used to implement digital Moire technique and display digital Moire fringes in real time with its powerful processing capacity. In this paper, digital Moire technique is implemented on the TMS320C6455 DSP. The hardware system consists of a DSP module, a CCD camera and a monitor. Finally we experimentally obtain the digital Moire image, and further analyze how to align the PCI theoretically.

INTERFEROMETRY METHOD USING TWO WAVELENGTHS FOR ANGULAR DISPLACEMENT MEASUREMENT

At the present time moire interferometry is commonly used for control of objects attitude position and their geometric shape. Method of angular displacement measurement using moire is offered in this research. The method is based on use of digital moire fringes which are formed by subtraction of interference patterns intensity. Laser source with different wavelengths were used for creation of these interference patterns. Moire fringes are formed from fringe patterns by means of Hilbert transform. Using moire fringes result precision and sensitivity increase because small shift of the interference fringes result large shift of moire fringes. Consequently, there is a possibility to make measurement with submicron resolution if conversion coefficient of the moire pattern has large value. Experimental setup using the digital moire pattern for angular measurement was made and tested. It has displayed feasibility of the offered method. Measurement error of experimental setup is equal to 0.8% in the range ± 2.5 ' then laser sources with wavelength 632 nm and 532 nm are used. For accuracy increasing laser sources with wavelength difference 5-10 nm are necessary.

OS1-9 Full-field Deformation Measurement Using Random and Repeated Patterns : a Comparison Study on Digital Image Correlation and Sampling Moire Method(Fringe analysis,OS1 Advances in optical methods and techniques,MEASUREMENT METHODS)

OS1-9 Full-field Deformation Measurement Using Random and Repeated Patterns : a Comparison Study on Digital Image Correlation and Sampling Moire Method(Fringe analysis,OS1 Advances in optical methods and techniques,MEASUREMENT METHODS)

Mathematical Model and Simulation for Testing Aspheric Surface Using the Digital Moiré Patterns by Circular Sub-Region Stitching Method

sub-region stitching measurement of asphere by using the combination of digital moire patterns without compensator, auxiliary mirror and other assistant modules. This paper illustrated the principal theory. And use of digital filtering, phase shifting, the least square method and Zernike polynomial fitting to establish the reasonable mathematical model. Meanwhile the computer simulation experiment was carried on. the PV and RMS of the full aperture phase distribution residual error are 0.058λand 0.0087λ After this method processing.

Structural Analysis of a Micro Hexagonal Mesh Using a Three-way Grating by Hexagonal Digital Moire Method

Structural Analysis of a Micro Hexagonal Mesh Using a Three-way Grating by Hexagonal Digital Moire Method

Experimental Analysis of the Damage Zone around Crack Tip for Rubberlike Materials under Mode-I Fracture Condition

Studying the deformation and fracture properties of soft materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of rubberlike materials. In this paper, an application of the experimental digital moire method to determine the damage zone around crack tip for rubberlike material is presented. The measurement principles and the basic procedures of the method are explained in detail. The deformation of crack tip fields in the damage zones is analyzed using the sector division mode. Finally, an analysis of the damage zone is proposed to describe crack-tip fields in rubber-like materials with large deformation.

Experimental Analysis of the Damage Zone around Crack Tip for Rubberlike Materials under Mode-I Fracture Condition

Studying the deformation and fracture properties of soft materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of rubberlike materials. In this paper, an application of the experimental digital moire method to determine the damage zone around crack tip for rubberlike material is presented. The measurement principles and the basic procedures of the method are explained in detail. The in-plane defomation distributions of crack tip fields under Mode I fracture condition are measured. In addition, the deformation of crack tip fields in the damage zones is also analyzed using the sector division mode. Finally, an analysis of the damage zone is proposed to describe crack-tip fields in rubber-like materials with large deformation.

Experimental analysis of crack tip fields in rubber materials under large deformation

A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformation. The inplane displacement of crack-tip fields under both Mode I and mixed-mode (Mode I–II) fracture conditions is measured by using the digital Moire method. The deformation characteristics and experimental sector division mode are investigated by comparing the measured displacement fields under different fracture modes. The out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method.

Solving the Two-Objective Shop Scheduling Problem in MTO Manufacturing Systems by a Novel Genetic Algorithm

With the characteristics of un-touching, high-automatic and high-speed, we measured 3D shape by digital moiré patterns. And it can measure 3D shape without compensator, auxiliary mirror, hologram and other assistant modules. So it is widely used in measurement of 3D shape. But with the negative effect of grating area and CCD resolution of the camera, it has some problems in large aperture, steep aspheric surface, even off-axis aspheric testing. Focus on these problems; this paper established a sub-region splicing measurement of aspheric surface by using the combination of digital moire patterns and digital phase shifting technology. This paper also illustrated the basic theory, and the mathematical implementation procedure. In all, sub-region splicing digital moiré patterns can be considered as another method, which beyond compensation tests to measurement of aspheric surface.

Displacement and Strain Measurement by Circular and Radial Gratings Moiré Method

Direct digital moire method of circular and radial gratings with its phase shifting technique is proposed and applied in a mixed-mode fracture problem of large deformation materials. Circular and radial curves are used as both reference and specimen gratings in this digital moire method for deformation measurement. And phase shifting technique is automatically implemented directly on circular and radial fringes, which facilitates obtaining displacement fields in polar coordinate system, radial ur and circumferential uθ, and strain fields er, eθ, erθ are calculated subsequently. Application of the direct digital moire method of circular and radial gratings in a mixed-mode fracture problem with large deformation illustrates the process of this method, and also demonstrates its feasibility and validity for large deformation materials.

OS1-3-2 Digital moire technique of circular and radial gratings and its application

OS1-3-2 Digital moire technique of circular and radial gratings and its application

Application of the digital moiré method in fracture analysis of a cracked rubber sheet

This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moire technique. Through the four step phase-shifting method of automated fringe analysis, the displacement fields in the Cartesian coordinate system are given. By the coordinate-transform equation, the radial and circular displacement distributions in the polar coordinate system are obtained. The displacement isoline distributions and displacement vector distributions near the crack tip are discussed. The strain isoline distributions near the crack tip are also analyzed in this paper. Finally, the distribution rules for the mechanical fields near the crack tip are discussed with the sector division method.

Investigations on the dynamics of water in the macrostructural dentine

The purpose of this study was twofold: (1) to investigate the nature and degree of water loss at 21 degrees C, 60% relative humidity (dehydration) and at 105 degrees C (desiccation), and to relate these findings with (2) the strains produced in the dentine structure during dehydration and rehydration processes. In stage 1, digital moire interferometry (DMI) was used to study the strain distribution pattern during dehydration and rehydration at 21 degrees C. In stage 2, the nature and degree of water loss was determined using gravimetric analysis and nuclear magnetic resonance spectroscopy. DMI showed that dehydration produced strains in the dentine structure after an initial latent period. Gravimetric analysis showed that dentine exhibited an initial rapid water-loss phase followed by a slow and steady water-loss phase. Though the major portion of water loss occurred in the initial 2 h of dehydration (rapid water-loss phase), no obvious strains were produced during this period. Rehydration lead to the major reversal of dehydration-induced water loss and strains in dentine. Heating at 105 degrees C resulted in further substantial loss of water from dentine. These experiments highlighted that the free water in the dentine surface, porosities and tubules are lost rapidly and constitute the major water lost when dehydrated at 21 degrees C.

Experimental investigation on the role of water in the mechanical behavior of structural dentine

Dentine is a porous hydrated composite structure that forms the major bulk of the human tooth. The aim of this study was to investigate the role of free water on the in-plane, mechanical strain response in dentine structure. A digital moire interferometry was used for this purpose. It was observed from this experiment that structural dentine demonstrated distinct strain gradients in the axial (perpendicular to the dentinal tubules) and lateral (parallel to the dentinal tubules) directions. The hydrated dentine displayed significant increase in strain with stress in the direction perpendicular to the dentinal tubules, and this response was characteristic of a tough material. On the contrary, the dehydrated dentine, which was dehydrated at 24 degrees C, 55% relative humidity for 72 h showed a strain response characteristic of a brittle material. The strains formed in the direction parallel to the dentinal tubules for hydrated dentine were consistent and did not vary much with increase in applied loads. Upon dehydration, the outer dentine experienced higher strains, and the difference between the outer and inner dentine became more conspicuous with increase in loads. This experiment highlights hydration-induced, distinct in-plane strain gradients in the directions perpendicular and parallel to the dentinal tubules in the dentine structure.

Photomechanical investigations on the stress-strain relationship in dentine macrostructure

In this study photomechanical experiments were carried out to examine the relationship between macroscopic mechanical stress and strain gradients within the root dentine structure. Three-dimensional digital photoelasticity was used to study the stress distribution patterns in tooth models, while digital moire interferometry was used to study the strain gradients within the natural teeth. The stress analysis showed a distinct bending stress distribution, along faciolingual plane in the coronal and cervical regions of the tooth. There was a reduction in bending towards the apical third of the tooth model. The strain analysis displayed strain gradients in the axial (along the long axis of the tooth) and lateral (perpendicular to the long axis of the tooth) directions in dentine. There was a conspicuous reduction in strains from the cervical to the apical third of the root dentine. The root dentine displayed uniform distribution of normal strains. Although there was a steep increase in stresses from the inner core region to the outer surface of an isotropic tooth model, there were more uniform strain gradients in the natural dentine structure. It is apparent from these observations that complex organization of material properties facilitated distinct strain gradients in dentine structure during mechanical functions.

Optical measurement of the specimen deformation at high strain rate

During recent years, the investigation of the strain-rate-dependent properties of materials has become more and more important. The experimental techniques used to establish the specific dynamic behavior of materials all have in common that the acquisition of information concerning the deformation of the specimen is cumbersone and often questionable. Mostly, only limited information on the spatial distribution and time evolution of the deformation in specimen can be obtained. In this paper, a non-contact, optical technique is presented, providing the time evolution and spatial distribution of the axial deformation in specimens during a high strain rate test. The deformation of a line grid attached to the specimen is recorded during an experiment by means of a rotating drum camera. The time history of the axial displacements is subsequently derived by an advanced technique based on digital geometric moire combined with a phase-shift method, specially developed to this purpose. The technique can be applied to a wide range of materials and high strain rate tests, and is illustrated by means of a split Hopkinson tensile bar experiment on a steel sheet specimen.

Liquid diffusion coefficients by digital moire´

In studying hydrodynamic instabilities between two miscible fluid mixtures, one often faces the problem of assigning a reliable value to very small diffusion coefficients. It is also difficult that for diffusion between two binary mixtures, such as water and glycerin, water and salt, etc., no complete data are available in the literature. To measure the isothermal diffusivity of liquid binary mixtures, we propose an improved version of digital projection moire. The system uses a simple and flexible fringe generator realized with a diffractive optical element (DOE). The fringe patterns are projected onto the bottom of a ground glass plate. The phase object (diffusion cell) is placed in front of the ground glass (in other words, in front of the fringe pattern), which is imaged by a digital video camera. Grating patterns, during the evolution of diffusion phenomena, are captured by a charge-coupled device (CCD) camera and stored in a computer at different times. With the aid of fast Fourier transform (FFT) and signal demodulating techniques, the images are processed to obtain the diffusion coefficients. The theoretical basis of the technique is presented. We also report experiments conducted for validating the system.

OS1(P)-2(OS01W0218) A Study on the Rapid 3D measurement by Using Digital Projection Moire

OS1(P)-2(OS01W0218) A Study on the Rapid 3D measurement by Using Digital Projection Moire

OS01W0218 A study on the rapid 3D measurement by using digital projection moire

Moire topography method is a well-known non-contacting 3-D measurement method. Recently, the automatic 3-D measurement by moire topography has been required since the method was frequently applied to the engineering and medical fields. The 3-D measurement using projection moire topography is very attractive because of its high measuring speed and high sensitivity. In this paper, using the two-wavelength methods of projection moire topography was tested to a measuring object with 2pi-ambiguity problems. Also, rapid measurement can be accomplished by the synchronization between CCD camera and projector. The experimental results prove that the proposed scheme is capable of finding absolute fringe orders, so that the 2pi-ambiguity problems can be effectively overcome so as to treat large step iscontinuities in measured objects.