The final inspection of manufactured goods is a labour intensive activity. The use of human inspectors has a number of potential disadvantages; it can be expensive, the inspection standard applied is subjective and the inspection process can be slow compared with the production process. The use of automatic optical and electronic systems to perform the inspection task is now a growing practice but, in general, such systems have been applied to small components which are accurately presented. Recent advances in vision systems and robot control technology have made possible the installation of an automated paint inspection system at the Austin Rover Group's plant at Cowley, Oxford. The automatic inspection of painted car bodies is a particularly difficult problem, but one which has major benefits. The pass line of the car bodies is ill-determined, the surface to be inspected is of varying surface geometry and only a short time is available to inspect a large surface area. The benefits, however, are due to the consistent standard of inspection which should lead to lower levels of customer complaints and improved process feedback. The Austin Rover Group initiated the development of a system to fulfil this requirement. Three companies collaborated on the project; Austin Rover itself undertook the production line modifications required for body presentation, Sira Ltd developed the inspection cameras and signal processing system and Unimation (Europe) Ltd designed, supplied and programmed the robot system. Sira's development was supported by a grant from the Department of Trade and Industry.

This paper will describe the design of a number of coherent light measurement systems which use a combination of active control and passive design principles to compensate for the effects of random system perturbation.

As part of the research in optical techniques for non-destructive evaluation (NDE), we have considered the reception of elastic waves with no contact via a heterodyne detection wideband laser interferometer. The purpose of this article is to present the performances of the model. We have included the operating principles of laser interferometry, the reasons for the technological choices made, the electronic reception system and signal demodulation. The performances of the transient microdisplacement measurement are depicted with few experiments in the field of NDE.

This paper reviews work at Marchwood Engineering Laboratories to provide a range of optical instruments in support of the CEGB reactor inspection, maintenance and repair programme, and in associated programs where similar problems are encountered.

In this paper recent developments in the production of a rotating radial diffraction grating are presented. A diffraction grating is in general an optical component that can be used as a wavelength dependant laser beam splitter. However, when a radial diffraction grating is rotated, the diffracted beams are in addition shifted in frequency. These properties make the rotating grating suitable for application in interferometric systems, such as laser Doppler velocimeters (LDV). A rotating radial grating, driven by a small electronic motor, is a simple and a multifunctional component with small dimensions. Therefore it has substantial advantages over other types of beamsplitting/frequencyshifting equipment, which are usually complex, relatively large in size and more expensive. Rotating gratings however can only be used for limited frequency shifts and they cause larger instabilities of the frequency shift. The application of a new type of driving motor system and other recent improvements have made the disadvantages of a rotating grating relative to other frequency shift equipment smaller. At the moment there is a tendency towards the development of smaller and simpler LDV systems for industrial applications. Especially for this kind of applications the rotating diffraction grating is well suited.

A novel technique for visualizing and measuring an entire velocity field with only one photograph has been developed by taking "Doppler-pictures" with a Michelson interferometer. The Doppler-picture gives information, either about the instantaneous velocity distribution of a fast moving and/or deforming solid reflecting surface, or about the instantaneous and local velocities of tracers passing through a light sheet that cuts the flow field under investigation. The light sheet is produced by a widened laser beam. The Doppler-shift of the frequencies of the light scattered by the tracers is transformed by a Michelson interferometer into varying light intensities, thereby shifting a given initial interference fringe pattern. Generally, the interference fringes are adjusted to a constant frequency of the scattered light, which must be straight, parallel and equi-distant. The light intensities also depend on the intensity of the scattered light, but this occurs only in the illuminated fringe regions. The dark fringe areas with no light remain practically uninfluenced by the varying intensities of the scattered light. That is why, it is only the dark fringes that can be used for determining the measured velocity field distribution in the evaluation of Doppler-pictures. The tracer velocities along the dark fringes can be obtained by simply measuring and comparing the shift of the dark fringes with the initial fringe pattern. This new visualization method will be described in principle, and the use of our Doppler-picture camera will be demonstrated with Doppler-pictures of (a) circular supersonic free air jets coming out of a Laval-nozzle, (b) a cutting torch outflow, (c) vortices, (d) moving shock waves showing the velocity rise across it and (e) a fast rotating solid drum.

The interferometric testing of a stretchable, variable focus, concave imaging mirror is described. The mirror is a very thin plastic membrane, with a metallised mirror finish on the front surface. The mirror curvature is determined by either the strength of a vacuum applied to the rear surface of the membrane, or by a pressure applied to the front surface. High resolution images have been obtained from observed components. The mirrors have been used in conjunction with an all reflective surfaced image derotator, in order to render visible on stationary sheets of cholesteric liquid crystals, the radiated heat patterns from high speed rotating components.

The studied object is illuminated by a light sheet. The fringe produced on its surface is distorted proportionally to the local depth. Scanning the whole surface and integrating the values of the depth provides the total volume. The automation of the process includes the reduction of the fringe width to one pixel, the calibration of the magnification and the completion of the fringe discontinuities.

The diamond turn process affects the metal-surface in a complex way. The knowledge of the relevant mechanisms (influence of polycrystallinity, crystal structure, grain size, mechanical behaviour) shows a new way to optimize optical metal surfaces by using micro-crystalline metals.

The efficiency of gas turbine engines is strongly affected by the clearance between the rotating compressor or turbine blades and the stationary annulus around them. The most critical area is the high pressure turbine which, unfortunately, is the area where it is most difficult to make measurements, as the turbine blades run at temperatures in the region of 1000°C with hot gases containing unburnt fuel, soot etc., flowing over them at high pressure and speeds approaching sonic. The current trend is towards unshrouded blades, the efficiency of which is more strongly affected by tip clearance as the absence of the shroud creates overtip leakage (figure 1).

White light transmission holograms have been made using revolutionary flexible membrane concave mirrors of variable focal length. These mirrors are used as collimators to produce and project conjugate imagery for making white light holograms. The era of super large scale white light holography with undistorted imagery and large angular field of view is predicted, based on current results and the availability of very wide plastic sheets suitable for use as the reflective membrane of the flexible mirrors.

The quantitative evaluation of interference patterns consists of the two steps of determining the interference phase at the points of interest and of combining the phase data with the geometry data. For each of these steps global and local or pointwise methods are presented and compared. Although the methods are applicable to the diverse types of interference patterns, they are presented here for the typical case of holographic interference patterns.

In optical sensor systems for guiding a welding robot along a seam a "look-ahead" or "preview" distance is necessary. The look-ahead-time is used to advantage in control algorithms which can compensate for delay times in the robot controller. Simple and sophisticated control methods are described. With the so-called delayed shift method, originally intended for globally straight sections, it appears to be possible to track more complicated trajectories, without the requirement of a two-way interface between sensor and robot.

An optical heterodyne profilometer has been develooped to get parameters of profiles such as roughness, skewness... Now, it is associated with image processings for automated pattern recognition. Their applications, either on calculated profiles or interference patterns, yield to characteristics of defects on a surface. This device can be a useful tool for the study of erosion phenomena.

Micro-topographic analysis of surfaces, particularly of the non-optical type are of great interest in various areas of science and technology. A technique and results on topographic mapping of surfaces are presented. Essentially, the method uses advanced software for image processing of the pattern of the contouring fringes resulting on the surface from illumination by collimated interference fringes. Inherent noise inconvenients are overcome by specially conceived algorithms leading to a best fit symbolic fringe pattern (ideal contouring fringes). From the topological map, statistical parameters are evaluated to characterize the surface. These include: range and distribution of surface heights, average roughness and the auto-correlation function of the surface.

There are various methods for the data reduction from interferograms. At present the fringe method and the phase-shifting method are widely used. In the fringe method a skeleton of the fringe pattern is derived automatically and the phase distribution and the dis-placement field, respectively, is evaluated interactively from that skeleton. In the phase-shifting method a set of phase-shifted interferograms is used for the calculation of a relative phase at any point of the object under test. Both methods are implemented on a commercial image processing system, including a video processor, that enables to process images at video rate. Due to some practical experiences in holographic and speckle-inter-ferometry the advantages and disadvantages of both methods are discussed and their ranges of application are considered.

The scanning electron microscope (SEM) JSM-T300 was modified to give an outiput signal of the average line signal display of any surface to a resolution of about 10A, which is in reality an average three-dimensional representation of the surface topography. The output signal was recorded and analyzed by an FFT narrow band spectrum analyzer coupled to HP disktop computer, for which a computer program based on a frequency spectrum analysis was developed for surface texture assessment , the computation of its different parameters; Ra, Rq, Rz,etc..... Two standard test specimens were used to calibrate the SEM measurements at any speci-fic operating conditions. Machined brass test specimens were made to give a wide range of surface finish of Ra range of 1.5 to 59 μm, and then used to correlate the SEM results with those obtained by the conventional stylus-tracing equipment such as Surtronic-3, and Talysurf-5 of RTH. The correlation was accomplished between the different parameters of the surface texture stylus-traced profiles "across + along" the lay of the tested surfaces and the corresponding parameters of the profile of the average line signal display of SEM. The results obtained were found to be in very good correlation and the small diffe-rences found are attributed to the influence of the micrometerology of the high resolution SEM. The technique adopted for SEM micrometerology could be classified as an automated procedure for the three-dimensional assessment of surface texture.

A heterodyne interferometer is described for measuring transient flow field phenomena. Data are acquired through up to 64 channels in parallel with a dedicated phase meter, digitizer and buffer memory for each channel. Data frame rates can be as high as 100 KHz with instrumental background levels less than 0.8 nm rms. Measured data of an electron-beam or e-beam pumped flow fields will be presented and discussed.

The introduction of compact, robust and stable ESPI-instruments has opened for new applications of the technique outside the laboratory environments. We briefly describe a typical system and discuss how it may be used in hostile environments to measure on difficult objects.

It was of course Dennis Gabor who, as long ago as 1948, published the fundamental work the principle of holography. But it was not until Theodore Maiman's invention of the laser in 1960 that the practical realisation of holography became possible. This was achieved by Leith and Upatnicks between 1962 and 1964, with the crucial impetus being provided by Vander Lugt (the author wishes to acknowledge the assistence of A. Vander Lugt, who, while performing work of a relatet nature, showed him the value of the gas laser as a light source). 1964 was the year in which Denisyuk presented his first portrait holograms in Leningrad. The many publications of Stroke of the University of New York were a source of numerous impulses. It is to this period, too, that my own first experiences date back. Together with my teacher. Ulrich Grigull, whom I hold in the highest regard, I constructed the first laser interferometer for the study of heat transfer and developed the initial ideas for holo-graphic interferometry. Then, in 1965, came the work of Hildebrandt and Haines and of Powell and Stetson in the United States in this field, and it was around this time, too, that Nassenstein and his colleagues Riek and Bestenreiner began their work in this new area in Germany.

The present paper introduces a double exposure photographic technique that displays, on a single film frame, speckle (addition) correlation fringes identical to those obtained (on substraction) with ESPI. This double exposed photograph is later spatially Fourier filtered to elminate the optical noise giving, as a result, an image of holographic quality. The information given by the Fourier spatial spectrum of the deformed object is at present being studied with the aim of introducing an electronic filter into ESPI. A theoretical account of the above process is given.

A holographic arrangement using two holograms symmetrically placed to the perpendicular of the component under investigation will be introduced. By means of a simple difference method using an image processing system, the relative in-plane-displacement and corresponding strain in a defined direction can be determined. The effects of other directional movements (e.g. tilting) will be fully compensated.

A theoretical investigation of the signal processing by Electronic Speckle Pattern Interferometry ESPI is presented. Both optical and electronic noise are considered, and the optimum S/N ratio of ESPI with respect to a new reference/object ratio is obtained. The technique of ESPI is applied to study rough object deformation. We assume that the 1st signal representing one state of the object is recorded on a high resolution film while the 2nd signal representing another state of the object is recorded in real time through TV camera. Making use of coherent beam behaving as a carrier wave interference pattern will form over a TV monitor. Experimental results of interference images from the TV screen are photographed showing the validity of the technique.

Many historically valuable buildings are in extreme danger due to permanently growing deterioration. For centuries many of these natural stones have been exposed to the weather. Permanently changing conditions of humidity, aridity, frost and wind cause chemical and mechanical processes which influence the properties of the microstructure of the natural stones. The properties may change until damages are macroscopically visible. In addition to environmental stresses caused by weather conditions, increasing stresses due to pollution like SO₂, NO_x, CO₂ etc. act on the stone in recent years. Some of the deterioration effects are accelerated by these additional stresses. The investigation of causes and mechanisms of the destructive processes is of great importance for the development of preservation- and protection-methods which will counteract further decay of the monuments. Up to now characteristic mechanical data of natural stones, especially related to weathering, have barely been investigated. Moreover, the strong inhomogenities of natural stones restrict the application of some parameters like elasticity module for their description. Within the scope of a joint project on monument preservation the mechanical properties of a variety of natural stones shall be investigated. In addition to informations obtained by established methods of material testing, position- and time-resolved data on deformation processes up to crack development are required. The latter suggests the introduction of optical methods which allow the observation of even small deformations on the whole stone surface during a test cycle. Thus a quick interpretation of the observed process is possible.

The Aerospatiale Aquitaine plant implements optical techniques using coherent light for its own activities or for research financed by government authorities. This paper gives two examples of that. The first one concerns two optical measurement systems used to improve the knowledge of the composite materials behavior under space environment : - a facility based on two interferometers to measure the thermal expansion coefficient, - and an optical device to follow the evolution of the composite material's mechanical characterics submitted to accelerated ageing in a space environment (ultra violet, protonic, and electronic rays). The second example presents an ophtalmological study where we implement optical methods in order to characterize a shock wave in a liquid initiated with an YAG laser : schlieren's optoelectronic technique based on a deflection of a test laser beam that depends on the index variation as the wave passes ; otherwise a shadowscopy technique and a Mach Zehnder interferometric technique are implemented to obtain the shape of the wave. For each example some results are given to show the performances of these optical measurement methods. We think that this large field of applications illustrates the interest in suitable optoelectronic tools.

Many of the torsional problems shown in the following can hardly or even not at all be calculated mathematically to a sufficiently accurate degree. Currently by the appropriate physical knowledge is still missing. In the following it has been described in which way holographic measures can be or better must utilized as there are no alternate measuring methods available, yet. Holographic measurements at orginal components as well as at models or by means of analogy procedures are performed. It will be shown that holography is in a position to fill in currently still missing pieces in case of calculating e.g. torsional problems. Furthermore, methods are elaborated which may accurately show deformations under torsion within the relevant model components and allow for appropriate measurements. New up to now unknown phenomena as e.g. in case of torsional notches have been established.

A new system of holography is presented. This modular testing equipment fulfils the performance requirements for industrial measuring equipment. A holographic camera-head module with the approximate dimensions of a television camera is installed close to or actually on the object to be tested. For holography using a continuous wave laser it is necessary only to secure the object to a base-plate mounted on vibration insulators. This is not necessary if pulse holography is used. Because of its small size, the measuring head can also be attached directly to the test object. This largely eliminates the effects of movements of the whole body of the objects. The technical realization of modular holography was made possible by the use of glass fibres. A rigid connection between the laser and the measuring apparatus is no longer necessary. The necessary light for the recording of the hologram is provided by the laser-base module and fed to the measuring head via a glass fibre cable. The hologram recorded by the measuring head is transmitted directly by means of a television camera to the computer-analyzer module, where it is evaluated and presented in user-friendly form. An example from industry is taken to demonstrate the use of the modular holography system.

Moire deflectometry allows one to measure minor angular deflections experienced by light beams, previously collimated, in general,for an easier metrologic decoding. A novel technique is presented aiming at the measurement of curvature radius of polished spherical surfaces. Theoretical studies and experimental results are presented revealing satisfactory agreement, while the sources of errors of the measuring technique are analyzed in detail. The theoretical model is extended to cover the measurement of the focal distance in lenses.

The incorporation of monomode fibre optics into an argon ion powered Electronic Speckle Pattern Interferometer ( ESPI ) is reported. The system. consisting of an optics assembly linked to the laser and a TV camera tranceiver, flexibly connected by 40m of fibre optic cable to the optics, has been used to analyse the modal behaviour of structures up to 5m X 3m X 2m in size. Frequency modulation of the reference beam phase in order to operate in a heterodyne mode has been implemented using a piezo-electric crystal operating on the monomode fibre. A new mode of operation - Sequential Time-average Subtraction - and the results of a new processing algorithm are also reported. Their impementation enables speckle free, time-average vibration maps to be generated in real-time on large, unstable structures. Example results for a 4 cylinder power train, a vehicle door and a whole vehicle floorpan and bulkhead are included. In all cases the analysis was conducted in a general workshop environment without the need for vibration isolation facilities.

Pulsed Laser Electronic Speckle Pattern Interferometry (ESPI) has been shown to be a technique which permits the measurement of in-plane displacements and hence strain under dynamic conditions, in particular radial displacements on rotating components. Conventional optics initially showed the limiting tangential velocity to be of the order of 60 ms^-1 for a reasonable area of interference fringe information. Novel optics increases the tangential velocity range to that in excess of 150 ms^-1. Use of a pulsed laser removes the otherwise rigorous stability requirement of c/w systems including holography and would allow measurements to be made in an industrial environment. Recent preliminary tests using fibre optics indicate that they may be used for components with limited optical access.

Current methods and equipment developed for computer automated holometry are described. Several applications including holo-photoelasticity of planar models, holographic interferometry of crankshaft bearing cap distortion due to bolt torquing and cylinder bore distortion due to head bolt torquing are discussed. Comments are made on future automotive applications.