Moiré topography using developed recording methods

Where moiré topography is used to record the shape of objects of approximately cylindrical form or that of a series of such objects, a scanning method with a slit camera can be employed. One such method takes photographs by combining conventional shadow type and projection type moiré topography with a slit camera. Laser methods of line projection combined with a scanning method developed from the projection type of moiré topography are also utilised. The main features of the latter method are that it is not affected by any diffraction effect caused by the grid and that highly accurate recording can be achieved with excellent image quality using the properties of the laser beam. Another distinct advantage is that it is capable of recording the shape of a self-luminous object without contacting by selection of laser wavelenghts and matching optical filters. The laser scanning method can therefore be considered to have considerable potential for future applications.     

Formation of unsymmetric moiré fringes and their use in moiré topography

An analytical method of predicting the intensity profile of the moiré fringes formed by a three-dimensional grating is proposed. The proposed method is proved to be effective in determining the appropriate structure of the grating and the experimental conditions for directional moiré topography.     

Computer Aided Moiré Methods

Computer aided moiré methods (CAMM) use the versatility of the computer to manipulate gratings rapidly, the basis of all moiré methods. Application of CAMM to moiré teaching, in-plane moiré, shadow and projection moiré and reflection moiré are reviewed in this paper.     

Moiré topography: alternative technique in health care

The instrumentation and application of moiré topography in the diagnosis of corporal asymmetries associated to different illnesses of the osseous-muscular system in early ages is presented in this paper. A sample comprising 203 adolescents ranging between 12 and 15 years were studied. Some moiré topography analysis of human legs and the sole of the foot are also given as examples of moiré applications. The results show the advantages of using this technique in the health care and treatment of different illnesses in adolescents. Some of these advantages are provided by the easy diagnosis and the low cost of the moiré technique.     

Analysis of CCD moiré pattern for micro-range measurements using the wavelet transform

A new approach based on the moiré theory and wavelet transform (WT) is proposed for measuring the micro-range distance between a charge-couple-device (CCD) camera and a two-dimensional reference grating. The micro-range distance is determined by measuring the pitch of the moiré pattern image, which is digitized by a CCD camera. A one-dimensional WT algorithm is applied to estimate the pitch of the moiré pattern. Experimental results prove that this technique is very efficient and highly accurate. The moiré range finder is an economic technique for measuring a micro-range distance.     

Enhancement of visibility of fringes and exposure time for moiré topography

The aperture filtering of lenses for the purpose of moiré topography is described. By replacing the circular iris of a lens with a rectangular one whose long side is parallel with the bars of the grating, both the visibility of the fringes and the exposure condition are greatly enhanced. Using this technique, it becomes possible to take pictures of moiré fringes on a moving, living human body.     

Phase shifting nano-moiré method with scanning tunneling microscope

In this paper, a new nano-moiré method using scanning tunneling microscope (STM) is proposed. This method is capable of measuring nanoscopic deformation of matter. The formation mechanism of the STM moiré fringe and the phase shifting technique used in STM moiré fringes are explained in details. Typical experiments are conducted with the crystal lattices of freshly cleaved highly oriented pyrolytic graphite, are used as specimen grating, to generate STM moiré fringe patterns. Phase shifting is realized in four steps from 0 to 2π by controlling the PZT in the STM system to shift the specimen in the vertical direction. This method provides a new way for disposal of moiré fringes pattern in the nano-moiré measurement.     

Automatic fringe analysis for moiré topography

Two digital systems are developed for the automatic measurement of 3-D shapes using moiré techniques—an automatic 3-D shape measuring system using the scanning moiré method and an interactive fringe analysing system for moiré fringe photographs. In the automatic 3-D shape measuring system, a deformed grating is scanned and sampled with an electronic image scanning device so that moiré fringes are generated in a computer. This technique of electronic fringe generation eliminates ambiguity with regard to the sign of the moiré fringes. The interactive fringe analyser provides a flexible and versatile tool for moiré fringe analysis. Medical applications of these analysing systems are discussed.     

Moiré topography in odontology

For several decades, measurement of optical techniques has been used in different branches of science and technology. One of these techniques is the so-called moiré topography (MT) that enables the accurate measurement of different parts of the human body topography. This investigation presents the measurement of topographies of teeth and gums using an automated system of shadow moiré and the phase shift method in an original way. The fringe patterns used to compute the shape and the shape matrix itself are presented in the article. The phase shift method ensures precisions up to the order of microns. Advantages and disadvantages of using the MT are included. Besides, some positive and negative aspects concerned with the implementation of this technique in odontology are shown in the article.     

A study on the 3-D measurement by using digital projection moiré method

Moiré topography method is a well-known non-contacting 3-D measurement method. Recently, the automatic 3-D measurement technique by moiré topography has been developed in order to apply to the engineering and medical fields. The projection moiré topography is very attractive because of its high measuring speed and high sensitivity. In this paper, using the two-wavelength methods of projection moiré topography was investigated to measure the 3-D shape of an object with 2π-ambiguity problems. 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 2π-ambiguity problems can be effectively overcome so as to treat large step discontinuities in measured objects.     

Moiré fringes in metrology

Moiré fringe phenomena have been exploited in a wide range of transducers, particularly in the field of engineering metrology. Paying particular attention to developments which have taken place during the last 15 years, the paper presents a cross-section of moiré techniques for the measurement of displacement, surface topography, deformation, vibration and refractive index gradient.     

A study on the digital moiré technique with circular and radial gratings

A digital moiré technique with circular and radial gratings is proposed to measure in-plane displacement and strain distributions of soft materials in a polar coordinate system. By introducing the coordinate-transform technique, the concentric circles and radial lines in the Cartesian coordinate system are converted to cross gratings in a polar coordinate system. Then, the digital moiré fringes are generated using logical and filter operations on the one-bit binary images. Finally, the in-plane displacement distributions are obtained by means of the four step phase-shifting procedure. Also, the measurement principles and the basic procedures of the new digital moiré technique are explained in detail. An application for rubber sheet with a single-edge crack is studied, and the experimental results show that the presented method is feasible.     

Contribution to analysis of the reflection grating method

The reflection grating method is a special case of the well-known reflection moiré principle. Whereas this moiré effect is suitable for measurement of the slope and curvature of deformed object surfaces by superposition of at least two grating images, the same results can be determined using only one reflected grating image without moiré lines.Some fundamental relationships between grating lines, optical setup and the desired deformation are developed and compared with the simplifications that are known from the moiré principle. The theory is tested using a circular plate, uniformly loaded and clamped at the circumference.     

Geometric micron-moiré

A high spatial resolution and high-sensitivity geometric micron-moiré method is presented. The method is based upon classical geometric moiré method and microscopic principle, the frequency of the specimen and reference gratings used in this method can be higher than 1000 lines/mm. By a microscopic moiré system, the high-frequency gratings could be magnified to a low-frequency level, so geometric moiré patterns can be formed. Experiments show that both the spatial resolution and the sensitivity can reach or exceed micron-level.     

Moiré fringes

This review paper clarifies the characteristics of the incoherent-and-multiplicative type moiré fringe phenomenon, presents examples of the application of these characteristics to measurement and explains the profile prediction method and the sharpening conditions of moiré fringes formed by two binary gratings.     

Holographic implementation of holographic moiré inspection

Implementation of holographic moiré inspection is demonstrated using one hologram to project the reference grating and a further hologram to produce moiré patterns. Well contrasted moiré fringes are obtained. Results of calibration tests are reported and an example of object contouring is presented.     

Phase shifting SEM moiré method

A new phase shifting scanning electron microscope (SEM) moiré method is proposed in this paper. The phase shifting technique is realized in four steps from 0 to 2π by shifting electron beam in the y-axis direction controlled by the SEM system. It is successfully applied to determine the residual strain of a deformed holographic grating with a frequency of 1200 lines/mm in an electronic package. As a further application, it is used to measure the virtual strain of a MEMS structure with a 5000-line/mm grating and to determine the phase distribution of a SEM moiré formed with a 6000-line/mm grating fabricated by electron beam lithography. The experiments show the feasibility of this method. It provides a new way for disposal of fringes pattern in sub-micro moiré method.     

Experimental tire mechanics by moiré

Tires and their component parts are made from various low modulus rubbers and cord/rubber laminates. In service they typically undergo large deformations of about 1–30%. The accurate measurement of these deformations by either pointwise (strain gage) or full-field (optical) techniques is rendered difficult in these circumstances. Ordinary strain gages reinforce these soft structures and inhibit their deformation, whereas most optical methods are too sensitive to measure large motions. These difficulties can be overcome by the judicious use of various moiré methods: moiré interferometry, geometric moiré and shadow moiré.Several applications of moiré methods to tire mechanics problems are presented. The emphasis is on the range of problems that has been successfully approached and on the results obtained. Examples are drawn from work on belt-edge strains, tread groove strains, sidewall strains, dynamic sidewall deformations and material properties determination. Proprietary details of technique are not included.     

Electron moiré method and its application to micro-deformation measurement

In this paper, the single and two deposited metal layers method were proposed to produce the model grating for electron moiré method. The measurement principle of electron moiré method and the techniques for manufacturing model grid are expounded in detail. The accuracy of measuring strain using this method is discussed. The gratings with single deposited layer and two deposited layers with high frequency up to 5000 lines/mm were produced on different substrates. From the experimental results, both single deposited metal layer and two deposited metal layers gratings showed their heat resistance ability. Using the gratings produced and a replicated model grid, the electron moiré method was applied to measure the deformation of the strain around holes in a polyimide resin substrate, thermal strain of electronic packaging component and tensile creep around grain boundary in a pure copper specimen.     

Investigation of dynamic displacements of lithographic press rubber roller by time average geometric moiré

Geometric moiré fringe formation method is a classical well-established experimental technique with numerous practical applications. This paper proposes the application of time-average geometric moiré analysis for the determination of dynamic displacements of the lithographic press rubber roller. This optical measurement technique is a natural extension of double-exposure geometric moiré for the identification of dynamic displacements of vibrating elastic structures. Experimental investigations prove the validity and effective practical applicability of the method.