Effects on the absolute moire contouring systems from using different period and profile gratings and rotating angles are described in this paper. It was found that by choosing a different period of the grating or the rotating angle, different resolution and accuracy of the measurement can be obtained. So, for objects with different height or depth, different period of grating or rotating angle should be chosen to ensure accuracy of the measurement. The square wave intensity grating with small period can be treated as a sinusoidal wave intensity grating in the absolute moire contouring system. A few objects with different shapes and dimensions have been used as samples to verify the above conclusion. (C) 1997 Elsevier Science Ltd.

A novel absolute moire contouring principle and the associated experimental system is described. This system enables the absolute distance from the object point to the reference plane and the height of the object to be measured directly to a high degree of accuracy. It is not necessary to judge the hills or valleys to decide the object's shape. A few objects were used as samples to illustrate the procedure. The objects' height, found by using the moire technique, compares very well with that found by using a mechanical gage. (C) 1997 Elsevier Science Ltd.

If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then the surface acts as a phase modulator, with the amount of modulation at any point depending upon the height of the surface at that point. In recent years considerable effort has been devoted to the problem of fringe demodulation, with prominence given to techniques using fringe-phase stepping and Fourier analysis. It has long been known that phase demodulation is possible using a system of filters, and the technique has been widely used in the related area of frequency demodulation in radio. In this paper the development of phase demodulation using a system of digital filters is considered. For the accurate recovery of image phase it is necessary for the filters to introduce zero phase shift, or to have a phase shift proportional to frequency. The design of the digital filters is considered and their performance is assessed using the signal from a real modulated fringe pattern and a simulated signal. It is shown that the demodulation technique works well, even with a poor signal-to-noise ratio. © 1997 Elsevier Science Ltd. All rights reserved.

In the shadow-moiré system, the period of the grating is varied by rotation of the grating, so the phase of the moiré pattern is changed as well. By the selection of suitable rotation angles, three images at different positions of the grating are acquired to obtain the absolute distance from the object to the grating. A theoretical analysis is presented for the method, and some experiments have been done to verify the theoretical analysis. The results show that the method is fast and the accuracy is better than 10 μm. The measurable range is directly proportional to the period of the grating and inversely proportional to the angles at which the grating is rotated.

A new method of moire contouring, absolute shadow moire contouring by rotating a grating, is described in this paper. In the shadow moire system, the period of the grating is varied by rotating the grating, so that the phase of the moire pattern is changed as well. By selecting suitable rotation angles, four images at different positions of the grating are acquired to obtain the absolute distance from the object to the grating. The theoretical analysis is presented for the method and some experiments have been done to verify the theoretical analysis. The results show that the method is fast and very accurate. The measurable range is directly proportional to the period of the grating and inversely proportional to the angles to which the grating is rotated.

This paper presents a novel application of frequency shifting in the Fourier transform fringe analysis technique applied to surface shape measurement. In recent years little use has been made of frequency shifting, although it was a feature of the method as originally proposed. The paper shows that if the angle between fringe projection and viewing is small, it is possible to employ a frequency shift to effectively eliminate the occurrence of any wraps in the resulting phase distribution. This is obviously of value in cases where the object to be measured contains several discontinuities which would lead to a highly complex, maybe unprocessable, wrapped phase distribution. The technique is presented and analysed, and its effects on measurement resolution discussed. It is illustrated with a measurement made on a populated surface mount technology printed circuit board.

This paper describes research into a non-contact system for the inspection of fine pitch electronic components on manufactured electronic assemblies. A far-field diffraction pattern from the leads of a tape automated bonding component is captured and stored on a frame store. The diffraction pattern is statistically represented and then classified using an artificial neural network. Results from simulation and experimentation show the feasibility of the technique.

The absolute contouring of diffuse objects is considered. Variable index holographic contouring is presented in terms of a thought experiment. Absolute moire contouring is discussed in some detail. Experimental work is presented. This work agrees well with the theoretical analysis outlined.

This paper describes research into a non-contact system for the measurement of components and solder on printed circuit boards (PCBs). The objective of the system is the inspection of the PCB to identify faults in the manufacturing process. Two approaches are described: diffraction pattern analysis and fringe pattern analysis. For the diffraction pattern analysis, a diffraction pattern is formed by the lead array on a component. For fringe pattern analysis, a fringe pattern is generated on the PCB using either interferometric methods or projection of a grating. For both methods, an image of the pattern is captured and stored on a frame store. The pattern is then processed to provide data from which parameters which relate to solder joint integrity can be determined. Results demonstrate the feasibility of the methods.

A technique for the quality assessment of fine-pitch electronic components is described. A system for the capture of Fraunhofer diffraction patterns reflected from the component is presented. The processing of the image to enable classification by a neural network is discussed. Simulation results are presented, showing the feasibility of the technique.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The feasibility of using diffraction pattern analysis for the quality assessment of small components, with a specific application aimed at electronic components, is discussed. An electro-optical system for the capture of reflected diffraction patterns is presented. Preliminary simulation results for simple faults have been obtained and are used to illustrate the described feature vector and neural network classifier.

An automatic computer imaging system for recording body surface topography has been developed on a microcomputer-based image processing system. The computer processes fringe patterns generated on the surface of the trunk and reconstructs the complete 3-dimensional form of the surface. From the topographic reconstruction, clinical parameters of scoliotic deformity such as Angle of Trunk Inclination are calculated at a number of levels from the upper thoracic to the sacral region. These multiple level measurements illustrate the change in deformity over the trunk and correspond to measurements obtained using conventional tactile devices on patients.

Two major developments in interferometry are discussed. One is the availability of cheap reliable He-Ne lasers, which have replaced expensive, unreliable and unwieldy sources with a device with is compact and cheap. The most recent product, coherent laser diodes, give extremely robust and reliable sources in a very small semiconductor package. The other development is the growth of computer technology, which has made high speed digital image processing available at low cost to most workers in the field. The analysis of interferograms is an algorithmic issue

This paper initially describes the principles of laser-based dynamic fringe projection techniques, and more specifically, how these techniques have been exploited in the Dynamic Automated Range Transducer (DART). This instrument employs novel techniques to produce a high accuracy single point range measurement over a wide variety of distances. The latest miniature optical components lend themselves to the production of a small, low-cost, self-contained device, which is easily portable and suitable for use in on-line, automated inspection systems, or in the field. The development of the DART for three- dimensional measurements is described. Two methods are possible, either a single beam or twin-beam system. Using a CCD photodiode array with precise pixel geometry an accurate three dimensional mapping of an object can be achieved. The problems of processing the data from the various DART systems is briefly examined. For multi-pixel measurements a parallel architecture using fast digital signal processing devices is recommended.

The authors describe a method which represents a development of several optical contouring techniques. The authors choose to call it absolute contouring. By absolute range is meant the distance from the hologram or camera to a point in the field; as opposed to the distance between one contour fringe and the next. Absolute contouring is effected in real time by varying the contour depth of a system from infinity to some chosen value. During this continuous variation the intensity output trace is then processed to produce a value for absolute distance

A range evaluation system is presented which uses a unique method of fringe projection to establish the range of points upon the surface of an object, viewed along the optical axis using a high resolution sensor. A range profile is obtained and by computing over a matrix of points, which represent a segment of the surface under view, the topographical form of the object can be determined.

Non-contact optical measurements have been made for acetabular cups of both the Charnley (worn in vivo) and Stanmore (simulator worn) types.

A novel technique using dynamic fringe projection is discussed and the methods of analysis of the waveforms generated by such an instrument are given. An error analysis of the range equation is included to ensure that the design of such a system may be optimised for the minimisation of range errors.