Electronic shearography, a variation of electronic speckle pattern interferometry (ESPI), is a promising new technology for non-contacting, full-field optical nondestructive inspection. In this technique, the shearographic fringe pattern is generated electronically and updated at the video frame rate of the camera. Therefore, the results of an inspection procedure may be viewed in real time, offering a significant advantage over film-based interferometric techniques such as holographic interferometry. This work examines several opportunities to adjust system parameters to optimize the detection resolution of electronic shearography when used for nondestructive flaw detection. For any application, the required detection resolution must be balanced against the practical need to maximize the field of view of the inspection window, and thus the speed of the inspection. The magnitude of the image shear also plays an important role, because it controls the measurement sensitivity of shearography. The interaction of these principles is demonstrated for the detection of disbonds behind thin aluminum face sheets using vacuum stressing. The experimental results were obtained using a compact, portable electronic shearography system which incorporated a skewed-Michelson interferometer configuration. This arrangement allowed easy adjustment of both the direction and magnitude of the image shear at any working distance.

The use of charge-coupled devices (CCDs) for imaging in digital shearography necessitates the knowledge of their electronic (signal-independent) noise level, as the visibility of fringes produced is dependent on this factor. A method based on measuring the experimental CCD noise variance to construct a linear equation system is presented. From the solution of this equation system, the electronic noise level of a particular CCD used for imaging can be determined. Evaluation of CCDs based on this noise factor allows the performance of each CCD used in digital shearography to be compared.

With the growing number of aging passenger aircraft in the fleet, improve nondestructive inspection (NDI) techniques are being investigated to insure the reliability of the fuselage structures of these aircraft. The Boeing Commercial Airplane Group is evaluating nondestructive testing techniques for detecting disbonds in aircraft structures. One of the techniques under evaluation is electronic shearography. This paper describes the disbond inspection of aluminum lap joint coupons with electronic shearography. Inspection results from the simulated lap joint coupons, containing programmed defects, are reported.

This paper describes a novel application of a laser-based vibration measuring system and finite element modeling to evaluate the bond condition of Space Shuttle thermal protection system tiles. This application is based on characterizing the vibrational response of tiles when excited by an audible acoustic energy. Finite element models for tile assemblies which are comprised of tiles, SIP, and RTV layers attached to the Orbiter aluminum skin are first developed. The mathematical model considered the actual orthotropic material properties, different geometrical configurations as well as different bond conditions. The tiles' natural frequencies and mode shapes are then determined and their frequency responses due to simulated sound pressure are computed. The computed frequency response of a tile having a disbond indicates a decrease in its natural frequencies. This can be used to quickly identify the disbonded tiles. However, the exact size and location of the disbond are determined from the computed rigid- body vibrational modes. The finite element results are compared with experimentally determined frequency responses of a 17-tile test panel, where a rapid scan laser system was employed. An excellent degree of correlation between the mathematical simulation and experimental results is realized. The paper also reports on laser-based modal and shearographic testing performed on tiles of Space Shuttle Columbia. Again, the results demonstrate that experimental modal analysis, when combined with finite element modeling, can be successfully used as a reliable nondestructive, non-contact technique for tile bond verification.

To provide an improvement of vibrotest process of the small-sized units and systems the optic method of determination of resonance frequencies, quality and oscillation amplitudes has been developed. Sensitivity of the method can be compared with the sensitivity properties of the well known interference- holographic-vibration methods. The typical for resonance of oscillation phenomena of amplitude increasing has been used for oscillation parameter determination.

Photothermal measurement techniques offer sensing methods for the determination of material properties and for a contactless and non-destructive identification of subsurface defects and hidden structures. Our special interest in these fields is focused on the non-destructive parameter evaluation of coatings, of disturbed zones and surface layers after manufacturing processes (e.g. grinding, hardening, or cutting). Our aim is to present some theoretical aspects and experimental results of the photothermal measurement techniques with respect to a non- destructive and reliable thermal material characterization and to an identification of subsurface defects and hidden structures. Two different photothermal detection techniques have been used: the optical beam deflection and the radiometric method. The results combined with image processing routines and numerical data analysis may be used in order to characterize the materials' properties and their response to different kind of loadings.

Using photoelasticity, isochromatic and isoclinic fringe patterns can be generated in a model specimen with an applied load. The isochromatic fringes are related to the difference between the two principal stresses and the isoclinics give the direction of the principal stresses of any point in the model. However, the isoclinics give the principal stress directions in a form that is not well suited for direct interpretation. A more useful representation is the isostatic or stress trajectory diagram where the principal stresses are tangent or normal to the isostatic lines at each point. Since the isoclinic patterns identify the direction of the principal stresses, therefore the isostatic diagram can be constructed directly from the composite isoclinic pattern. Usually this method is done by hand and involves some tedious curve fitting techniques. This paper describes the implementation of a computer program that we developed to carry out this procedure efficiently. The image of the isoclinic pattern is digitized into a database using video processing equipment and used as input to the program. The output of the program is a diagram showing the isostatic pattern.

A new Electronic Shearing Speckle Pattern Interferometer (ESSPI) with continuously variable sensitivity is described. This new instrument not only provides variable sensitivity and improved shearing range but it also increases the maximum shearing sensitivity. It will be well suited to nondestructive testing applications in industry.

A new computer-controlled Phase-shifting apparatus based on polarization techniques is developed. This apparatus changes the phase only by rotating a polarizer using a precision step motor. The precision of this method can be higher than other methods due to the accurate control of rotating angle. Several applications of this technique to optical interferometry and 3D shape measurements are presented.

Among optical strain measurement methods, the grid method is a powerful one. Progresses in the technique of information processing have contributed to develop classical analysis (optical and numerical Fourier transform). We propose a new optical device that allows the interference of diffracted beams from two crossed gratings of parallel lines marked on the specimen surface. The analysis of the interference fringes during loading provides the geometry of the gratings and so leads to the strain determination. The proposed method is insensitive to the specimen translations and presents a range from 10⁵, with the use of a phase-shifting technique, to a few 10². Using experimental traction tests, we compare this method with the classical ones and we develop the performances of the proposed method (sensitivity and large measurement range).

Young's modulus, shear modulus and cylindrical stiffness of the steel plate have been experimentally determined by method of a stroboscopic holographic interferometry. Photothermoplsstic carrier was used as a recording media and pulse Q-switched ruby laser was used as a radiation source. The maximum contra.st of interferometric bends is 0.5.

A common problem in fabrication and welding of complex structures is that there is no simple way to determine where to cut one part so that it will fit another part unless both parts designed and built on a CAD/CAM system. Particularly in prototype or retrofit work, cutting and fitting parts for welding is more of an art than a science. We have developed a unique video moire system that generates the intersection contour in near real time with the contour superimposed on a video image of the part, allowing the cut line to be marked while following the contour on the video monitor.

This paper describes a displacement measuring technique using a laser-beam scanner for detailed non-contact mapping of the interior geometry of pipes. The technique, which is based on optical measurement using triangulation, measures radial displacement with an accuracy of +/- 0.2 mm for radii between 33 and 42.5 mm. A mapping system using this technique with automated data-acquisition and three-dimensional rendering of the interior is also described and its effectiveness is illustrated with experimental results. This paper also describes an automated system for detecting pipe wall deformation and presents preliminary results using this system.

In this paper we propose a practical approach to apply range imaging technology in machine automation. The applications we are especially interested in are industrial heavy-duty machines like paper roll manipulators in harbor terminals, harvesters in forests and drilling machines in mines. Characteristic of these applications is that the sensing system has to be fast, mid-ranging, compact, robust, and relatively cheap. On the other hand the sensing system is not required to be generic with respect to the complexity of scenes and objects or number of object classes. The key in our approach is that just a limited range data set or as we call it, a sparse range image is acquired and analyzed. This makes both the range image sensor and the range image analysis process more feasible and attractive. We believe that this is the way in which range imaging technology will enter the large industrial machine automation market. In the paper we analyze as a case example one of the applications mentioned and, based on that, we try to roughly specify the requirements for a range imaging based sensing system. The possibilities to implement the specified system are analyzed based on our own work on range image acquisition and interpretation.

The wear of 3D surfaces of a metallurgical vessel can be monitored with a commercial laser measuring device specially designed for this purpose. This paper describes two procedures for locating (fixing) this device, i.e., methods for finding the position and the orientation of the device with respect to the monitored vessel. The first procedure is based on strictly fitting coordinate frames on three 3D fixing points. The other procedure uses three or more points and minimizes the square sum of these distances. The locations of the fixing points in relation to the monitored surface are not affected by the wearing process. The uncertainty of the result is investigated using Monte-Carlo simulation. Random errors are included in the simulated range measurement and two orientation angles of the measuring device. The uncertainty is also estimated with linearized models of the locating procedures. The uncertainty estimation is a potential method to design the optimal on-site measurement configuration (device locations, point locations, etc.) and to improve computer algorithms for locating computations.

A fine wire diameter measurement system, for on-line monitoring, has been proposed by using a Machine Vision System and a visible diode laser. The system uses the Fraunhofer diffraction principle. The diffraction pattern, generated by a small wire exposed to a collimated laser beam, is acquired by a CCD industrial camera that is connected to a processing board inside a PC computer. Two different methods of measuring the diameters, static and dynamic, have been proposed in order to get high precision and high measurement rate. Wires with diameter from 10 to 350 micrometers have been measured by this system with 0.06% resolution. The accuracy is less than +/- 0.5% over a range of 90 - 350 micrometers diameter. For thinner wires, the measurement system should be calibrated to eliminate the systematic errors. The estimate random errors are +/- 0.25%. The instrument can measure the wire diameter at a 1000 Hz rate and allows it to move laterally in a 1 mm square window, maintaining the above accuracy. The system is compact and there are no moving parts.

The purpose of this paper is to describe a new precision displacement sensor--Multi-Beam Holographic Optical Sensor (MBHOS) for control of diamond turning--with the use of holographic optical element (HOE) technology. MBHOS is actually an integrated sensor which serves as three sensors. It can be used with the function of a single sensor to be a feedback component in closed loop control system and it can be used in the differential mode to detect the angular components of the micro-tool servo motion and to eliminate or to minimize the vibration errors with the function of three sensors. The ir HOEs are made by using a computer generated hologram (CGH) method. A computer simulation method is used to analyze the performances of this integrated sensor system. The initial experimental results of the MBHOS are obtained. The MBHOS is both compact and inexpensive.

In this work a prototype of a flexible electro-optical measuring machine suitable for dimensional quality control of inner and outer diameters of mechanical workpieces, is presented. Two measuring probes are displaced by means of motorized slides over a range of +/- 100 mm enabling the measurement of diameters from 0 up to 200 mm. The position of the probes is gauged by a double interferometer designed for the application. The characterization of the prototype has shown that repeatability and accuracy are better than +/- 0.16 micrometers .

The particle size distribution is important to today's material industry. The author will introduce his work on cement production line. The measurement principle, sample and dispersion system and multi-diffraction and its restrain technique are discussed briefly in this paper.

An optical heterodyne system for the measurement of profile and roughness has been developed. Several improved techniques are employed. The optical system was designed with entire common path. The effect of sample vibration and the thermal drift could be eliminated. A modified objective was used to perform respectively the measurement beam and the reference beam. The detected signals were processed with phase comparison technique to give a high accuracy. The optical system can be developed to an accessory of the Zeeman laser interferometers.

Velocity measurements and monitoring of atmospheric inhomogeneities have been provided by an optical system, incorporating image detector and supporting hardware. Two-dimensional intensity distributions have been digitally recorded after capturing successive images. The relevant software has been designed to operate the system for different purposes. In-plane velocity measurements of atmospheric clouds have been conducted in different weather conditions. Two methods for data processing have been applied to obtain the main drift velocity. Air turbulence estimations by registration of laser spot fluctuations and its geometry changes have also been considered.

A frequency-modulation absolute distance measurement techniques using a external-cavity semiconductor laser is proposed. A reference interferometer was adopted in order to reduce the effect of the central frequency drift of the laser on the measurement accuracy. The principle of the measurement is described and the experimental setup is introduced. The measurable range is as large as ten meters.

A new testing method of the surface roughness of transparent and reflecting objects is discussed. The method is based on the usage of the probing laser beam with spatial modulation in the form of a regular interference pattern, and of the contrast change effect of the pattern in the scattered light depending on the tested surface roughness parameters. A theory of the technique is presented. Various types of devices for the dynamic interference field formation in the probing laser beam (on the basis of interferometers, acoustic-optical modulators, optical and holographic elements with a piezoelectric deflector) are considered. A specialized processor of dynamic interference signals has been used to convert the measured contrast values. The experimental results of surface roughness testing of television screens are presented. The possibility of the technique usage in small angle scattering investigations is discussed. Consideration is also given to the feasibility of the technique industrial application in the rapid testing of the products surface quality while in production.

A travel sensor detects a motion of a mechanical part of a circuit breaker and checks its condition of the operation mechanism. We have developed a new optical travel sensor which measures a motion of a sealing rod with no contact. The design of the travel sensor and its fundamental inspections will be mentioned in this report. In our proposed sensor, the silhouette of the sealing rod is detected optically, and the motion of the rod is detected with no contact. Using optical fiber sheets, electric components such as the light source, the image sensor, and signal processing circuits are located remotely from the circuit breaker. As a result of this construction, the sensor is not affected by electro-magnetic noise. The travel sensor is constructed with two mirrors retro-reflecting illuminating light and prisms inverting the rod image. It is easy to adjust the mirrors according to the retro-reflecting construction. As the prisms compensate for the inverting effect of the lenses, intensity fluctuation of the rod image decreases. As a result of our fundamental inspections, we confirmed that the travel sensor had the detected range of 125 mm and the position resolution of 1 mm.