A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Fringe projection techniques: Whither we are?

Phase shifting algorithms for fringe projection profilometry: A review

A new phase-unwrapping algorithm is described that uses two phase images with different precision in the unwrapping; this technique can produce an approximately correct unwrapping in the presence of discontinuities. We introduce it into the measurement of a three-dimensional object shape and also present the experimental results.

Phase-unwrapping algorithm for the measurement of three-dimensional object shapes.

Automatic analysis technique of spatial carrier-fringe patterns

A new method of 360 degree turning 3D shape measurement in which light sectioning and phase shifting techniques are both used is presented in this paper. A sine light field is applied in the projected light stripe, meanwhile phase shifting technique is used to calculate phases of the light slit. Thereafter wrapped phase distribution of the slit is formed and the unwrapping process is made by means of the height information based on the light sectioning method. Therefore phase measuring results with better precision can be obtained. At last the target 3D shape data can be produced according to geometric relationships between phases and the object heights. The principles of this method are discussed in detail and experimental results are shown in this paper.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

360-degree 3D profilometry

Two new and simple methods for measuring the 3D rigid body line displacements and 3D rigid body angle displacements are proposed. And at the same time, two laser diodes and two new CMOS image sensors are used as light sources and photodetectors, respectively. Moreover, the experimental results are presented, which demonstrate the new methods have high accuracy, high processing speed, high reliability, and are easily realized.

Three-dimensional rigid body line displacement and 3D rigid body angle displacement measurements

A new method for measuring 3-D rigid body angle micro-displacements is proposedCorresponding to the method a laser diode(LD) and a new CMOS image sensor(CIS) are used as alight source and a photodetector, repectively. The method can also be used to measure 1-D or 2-Ddisplacements when required . Moreover , the paper also presents the experimental results , which demonstrate the new method has high accuracy ,easily. high processing speed , high reliability , and isKey words : 3-D rigid body angle displacements CMOS image sensor correlation 1. INTRODUCTION There are many methods[lI to measure the 3-D angle displacements of a rigid body , such asDiffraction, Interferometry , Moireand so on. In this paper, a new simple method is proposed tomeasure 3 -D rigid body angle Corresponding to the method a LD is used toproduce two beams which reach the same target in a distance of 1 . 5 — 2 meters , and a CIS is usedto detect the spot position on the target . The method can also be used to measure the 1-D or 2-Drigid body angle displacements when required ,

Wenyi Chen

Papers

Phase-unwrapping algorithm for the measurement of three-dimensional object shapes.

Automatic analysis technique of spatial carrier-fringe patterns

360-degree 3D profilometry

Three-dimensional rigid body line displacement and 3D rigid body angle displacement measurements

Double beams to measure 3-D rigid body angle displacements