This paper describes a new method for the adaptive control of imaging parameters in automized machine vision systems. By these new methods even in case of critical objects, which show metal and specular reflections or having polished surfaces, the imaging parameters like illumination can be adjusted optimally without any prior knowledge about the surface characteristics. As a result, an image is generated, which is almost free of irrelevant information in the image. This optimized image only contains the 'real' edges actually found on the object's surface and is free of effects resulting from specular reflections or shadows. Surface inspection for scratches, texture analysis or for dimensional measurements becomes much more reliable now.

In computer vision several views exist how to solve vision problems. The first general methodology was introduced by Marr; he proposed a data-driven and straightforward analysis strategy. Nowadays the concept of active vision introduced by Aloimonos et al. becomes more and more important. In contrast to Marr's philosophy, active vision implies a feedback loop which consists of sensors and active components. In this paper we present a system for the identification of material faults under the surface of a test object. For that purpose the specimen is elastically deformed, then the deformation is made visible using holographic interferometry, and finally flaw parameters are estimated using a model-based approach to analyze interferograms. This is an underconstrained computer vision problem which is regularized using a priori knowledge and an active modification of the experimental setup. More mathematically, this vision task can be seen in the context of inverse problem theory. In this contribution we describe the system and point out how it is related to the methodologies named above. To illustrate the functionality of the system, results are shown from nondestructive testing of satellite fuel tanks.

In this paper, we present a suite of novel speckle based displacement sensors. A laser beam illuminates the optically rough object and the light scattered off the object is collected and processed by various optical elements and, finally, the speckle pattern is detected. A new theoretical tool has been developed in which the speckle dynamics at the detector plane is described for an arbitrary complex optical system simply by means of the ABCD ray-transfer matrix elements for the optical system. Armed with the general theoretical tool, this paper discusses the correlation between object displacement and the speckle dynamics observed at the detector. In particular, the general theoretical tool allows trade-of analyses that are very important for industrial applications. As an example, all the sensors presented here are designed such that they are independent on variations in object distance. A new method is introduced in which rapid prototype optical sensors can be realized with standard optical elements. This facilitates a way of rapid realization of very compact optical sensors.

Today's industry demands high-performance components meeting toughest mechanical features and ultimate safety standards. Especially in automotive and aircraft industry the development focuses on tailor-made design and solutions according to customer specifications. To reconcile economy, light-weight construction has become a key issue. Many companies are looking for new advanced strain/stress analysis techniques to improve cost efficiency and the limitations of classical methods. Detection of weak points and fatigue tests are carried out mainly with strain gauges which need careful application and experience. ESPI (electronic speckle pattern interferometry) allows a rapid, full field and 3D-measurement without contact. This paper presents the principle and application of a new miniaturized laser optical sensor combining contour and deformation measurement. In its basic employment ESPI is an interferometric method measuring deformations at modern working materials with high accuracy. Here also a module for contouring was developed and integrated into a single interferometer. Therefore even at complex components it is possible to measure and display strain-fields and -gradients with respect to the underlying contour. The new sensor is a unique device for flexible strain-analysis at welded-materials, extrusions, engines, car-bodies, etc. Without preparation and due to the full field and 3D- measurement 'hot spots' are shown, reducing the testing procedure and increasing the reliability of the complex component testing significantly. In this paper the recent development of a miniaturized ESPI-interferometer for strain and stress measurement is described. Advanced features according to classical techniques are specified and new applications in material and component testing are presented.

We report on a novel set-up using image shearing speckle pattern interferometry for the determination of 2D strain distributions of an object surface. This system is based on simultaneous illumination of the object with three diode lasers that emit at different wavelengths between 810 nm and 850 nm. Their speckle images are separated within the shearographic set-up, consisting of a special color separation optics and 3 b/w CCD cameras, in such a way that each camera records the speckle image corresponding to one laser source only. Two methods are presented which allow to switch between the two directions of image shear. The shearographic camera in combination with the appropriate illumination geometry allowed us to determine and isolate all six displacement derivatives from phase stepped fringe patterns. The good suitability and accuracy of the system for the determination of 2D strain distributions are demonstrated on the basis of shearographic measurements during tensile testing and comparison with strain gage measurements.

This paper reports a theoretical description of a recently proposed length sensor using the laser-feedback technique. It is found that the optical feedback causes a sinusoidal fluctuation of the emission frequency with respect to time. The amplitude of the fluctuation strongly depends on the power reflectivity of the target and therefore the target distance. For target power reflectivities below 10^-4 stable single-mode laser oscillation is maintained and accurate measurements of target displacement are possible. Good agreement between theoretically calculated device output and measured device output has been obtained. Furthermore typical application examples for dielectric and metallic target materials are presented and some performance characteristics are discussed.

Multiple-wavelength interferometry is a well-known technique which enables to increase the range of non-ambiguity for interferometry and to reduce the sensitivity of the measurement. Moreover, this technique is also applicable to rough surfaces. It is therefore of a great interest for shape measurement. We propose here a multiple-wavelength heterodyne interferometer with two-dimensional detection. Heterodyne technique requires synchronous detection of the heterodyne signal, which is not compatible with standard CCD. We used therefore a new type of CCD smart image sensor for two- dimensional synchronous detection at the heterodyne frequency. By applying an appropriate signal processing, distance measurements on rough surfaces were performed with a resolution of about 10 micrometer. By optimizing the illumination pattern on the target, only a few mW of total optical power is required for the measurements at several meter distance. This is of a great importance for an eye-safe system. Applications of this technique to shape measurements are discussed.

A self-calibrating 3D measurement system using structured- light illumination with a digital-light projection unit (DMD) will be reported, which ensures a high number of object points, quick data acquisition, and a simultaneous determination of coordinates and system parameters (self calibration), making the system completely insensitive to environmental changes. Furthermore, there is no necessity of any marker on the object surface and a subsequent matching of the single views is not required to obtain a full-body measurement. For this reason, the object under test is successively illuminated with two grating sequences perpendicular to each other from different directions resulting in surplus phase values for each measurement point. On the basis of this phase value one can calculate the orientation parameters as well as the 3D-coordinates online. Two different measurement set-ups will be reported, which have the ability to measure the entire surface (full-body measurement).

With optical sensors (mostly working with CCD-cameras), digitizing time could be successfully reduced within the last few years. The result is a dense point cloud which can be used for surface reconstruction, milling, tool manufacturing, etc. The challenge was to further reduce the processing time significantly by an intelligent digitization method which makes enhanced surface generation easier. Now, this great leap forward has been approached with the AutoScan system from Steinbichler Optotechnik adapted to Zeiss measuring machines. In a first step, a new laser scanner captures character lines, edges and borders automatically. The current measurement result is used to control the measuring machine by a computer. Mathematical edges are calculated on-line. Furthermore, also tapes can be digitized automatically. After that, the areas between character lines and borders can be scanned. The sensor system is able to work with 3- or 5-axes machines. A 6^th axis is used for the automatic adjustment of the sensor parallely to character lines or borders. The system's accuracy is better than 30 micrometers, its sample frequency is 32 kHz, and the sensor scans with a frequency of 40 Hz and a speed of up to 2.0 m/min. It is possible to replace the sensor by a touch probe without further calibration. An automatic operating process which does not require user interaction has already been realized.

One of the objectives of surface metrology is to obtain a better and faster assessment of the micro- or nanogeometry of component surfaces. In this way the innovative concept of the profiler is changing towards non-contact modular computer- controlled systems for measuring and analyzing shape and texture of a surface. In this paper we present a new instrument which is based on the concept of confocal microscopy. In this instrument (which may be used for measurements on smooth and rough surfaces) a pattern of slits is imaged by a very high numerical aperture optical system on the surface of the sample to be measured. The reflected or diffused light is observed with a CCD array and analyzed with different digital image processing algorithms. In addition to the replacement of the existing stylus systems there are also important new potential applications for this type of instrument. We present the results obtained in micro- or nanomeasurements of high precision optical surfaces, texture assessment of non-homogeneous liquid depositions and metrology of microstructures such as master gratings and certified calibration standards. The obtained results show that the confocal profiler is robust enough to provide a surface topography with spatial resolution lower than 0.5 micrometer and uncertainty of about 10 nm.

A set-up based on a zoom stereo microscope is presented which can be used for fast and robust microstructure analysis on engineering surfaces. A fringe projection technique with an optimized grating pattern is used to determine the third dimension of the specimen. Due to the zoom objective the set- up can be quickly adapted to different fields of view. The magnification dependent vertical resolution can be as high as 0.1 micrometer with measuring times of less than a few seconds for 768 X 568 pixels. This very high speed together with the flexibility of the set-up is of great advantage for tribological investigations of metal sheets for example. After a brief description of the set-up and the algorithms used for the measurement evaluation, the mains emphasize is given for the application of the fringe projection technique to the determination of roughness parameters. Conditions like the optimal size of the field of view and others are given. In particular we give some studies for the comparability to a tactile sensor and to other optical sensors like white-light interferometry and confocal microscopy and present results of measurements on metal sheets and paper.

A simple system for detecting the rotation in two directions of a reflective ball is presented. The primary goal for the set-up is to realize a simple and compact concept that can be used for PC-cursor control, yet having an adequate precision for cursor control. A slightly diverging beam from a Vertical Surface Cavity Emitting Laser (VCSEL) mounted on a pcb-board with a diameter of 6.8 mm illuminates a reflective ball (0 4 mm) placed at a distance of 15 mm. Light scattered off the rotating ball produces a speckled field, which sweeps across two pairs of elongated photo detectors arranged perpendicular to each other. The four photo detector signals are digitized and fed into an ASIC, which determines the rotation of the ball in two directions including the sign of the rotation.

Applying the pulse laser to speckle methods, nonuniformities of the laser beam profiles and the intensities between each laser pulse have unpleasant consequences on the intensity distribution of the recorded images and following on the expected fringes of the corresponding subtractive result. This contribution introduces a computer based technique for compensating this technical and physical problem, so that the fringe quality is improved, even if the homogeneity of the laser beam profiles is on such low level, that the conventional (subtractive) technique fails. The solution is based on algorithms, which refines each intensity distribution and is comparable with the known shading correction. After this refinement the interferogram can be processed by the well known Fourier transform evaluation of the relative phase distribution. Applying the FFT, practical problems arise when it comes to the step of automatic sign corrections. The contribution will discuss an approach of automatic sign correction. The methods for refinement and automatic sign correction following the Fourier transform evaluation is explained in detail and demonstrated on selected interferograms.

The human hand is a very complex grasping tool to handle objects of different size and shape. A lot of research work has been done to transfer these capabilities to artificial robot hands, called multifinger grippers. The major part of this work describes the controlling of multifinger grippers. Since there is no information about the object's pose available in real-time, the finger joint positions or the fingertip positions of the gripper are position feedback controlled. But the global goal is to handle an object. Therefore, it is more useful to control the object's pose itself. In this paper object pose monitoring by laser scanning is presented. With the help of laser scanning the object's pose is controlled in real-time. Some results of the object pose monitoring show this ability.

Pulsed ESPI techniques have been developed during the last years to replace conventional double pulse holography interferometer for analysis of dynamic behavior of components. The main benefits of holography towards conventional measuring techniques have already been known as field and non-contact measurement results. Recent developments have extended the capabilities of pulsed ESPI techniques to 3D measurement of dynamic behavior. The object under investigation is illuminated with the light of a pulsed laser and simultaneously observed from 3 different directions with 3 ESPI cameras. The measuring results from the 3 cameras are representing the deformation field in the 3 sensitivity directions of the optical set-up. The optical image distortion due to the different viewing angles of the 3 cameras is automatically compensated and the complete 3D-deformation vector is calculated on every point of the inspected surface. Recent industrial applications of the 3D pulsed ESPI technique have been identified and carried out in the field of automotive NVH applications, aerospace and railway technique.

A differential interferometer is used to measure the difference in motion of two points of the diffuse surface. The disadvantage of a differential interferometer is a very small amplitude of the interference signal. The heterodyning with a strong reference beam can be used for optical amplification of weak backscattered light to overcome this disadvantage. In that case the system of two separate reference beam interferometers is used instead of a differential interferometer. In this paper the comparative study of the signal-to-noise ratio of a differential interferometer and of a system of two reference beam Michelson type interferometers is carried out. The investigation is carried out on the assumption that the laser of the same power is used in both interferometers. It is found that when the shot noise is dominant the signal-to-noise ratio of a differential interferometer is practically the same as the signal-to-noise ratio of a reference beam Michelson type interferometer. When the thermal noise is dominant the signal-to-noise ratio of the reference beam interferometer greatly exceeds the signal-to- noise ratio of the differential interferometer for a typically rough surface.

The application of mass spectrometry using resonant ionization by a tunable laser was investigated for analyzing hydrogen isotopes. Resonance ionization mass spectrometry (RIMS) was carried out to detect gas-phase hydrogen isotope atoms. The ionization efficiency was increased more than thousand times that obtained with conventional methods using non-resonant ionization. Resonant laser ablation mass spectrometry (RLAMS) was applied for deuterium detection in solid samples. A graphite substrate implanted with deuterium as used for ordinary laser ablation mass spectrometry (LAMS) and RLAMS. The deuterium signal was observed very clearly by RLAMS, in contrast to LAMS. Mass spectrometry combined with resonance ionization was very useful for hydrogen isotope detection, because components with equal mass numbers were resolved and the method demonstrated higher ionization efficiency.

The depth profile of hydrogen isotope atoms was measured by using mass spectrometry combined with resonant laser ablation. A graphite sample was implanted with deuterium by a cyclotron and was employed for the measurements. The graphite sample was ablated by a tunable laser which wavelength was corresponding to the resonant wavelength of 1S - 2S for deuterium with two- photon excitation. The ablated deuterium was ionized by a 2 + 1 resonant ionization process. The ions were analyzed by a time of flight (TOF) mass spectrometer. The deuterium ions were detected very clearly with resonant ablation contrast to non-resonant measurement. The depth profile was determined from the intensity of the mass spectrum and the etching depth. The depth profile was compared to the simulated profiles. Each profile coincided within the error of the numerical simulation.

For coherence radar measurements of lateral ranges of more than 10 X 10 cm² broadband light sources with average output powers of several 100 mW in the visible spectral range are needed. This micrometer-scale 3D-imaging technique using the Michelson interferometer technique with low coherence light sources is described in recent papers. The depth resolution is limited by the coherence length of the incident light. That is why light sources with a broad emission spectrum are useful. With the commonly used light sources, e.g. conventional lamps and superluminescent diodes, it is not possible to measure dark and strongly curved objects with a large lateral field of view. This problem is solved by a powerful, broadband laser in fundamental mode operation. The method to obtain a light source with a broad emission spectra presented in this paper is by gain switching a Ti:sapphire laser.

AC interferometers based on modificated Michelson's scheme allow to terminate disadvantages of DC interferometers, such as a high level of photo-detector noises, an instability of laser output radiation and other noises of low frequency nature. In the scheme of AC interferometer laser beam in supporting channel is shifted at the rate of frequency relative to laser beam in measuring channel by means of devices, which are shifting frequency or converting one frequency coherent radiation into two frequency ones. They allow to carry the spectrum of interferometer signal to higher frequency region of discrimination of low frequency noises. The main problem of AC laser interferometers is the choice of effective converters, because the characteristics of last ones determine the accuracy, the dynamic range, the overall dimensions and the cost of the first ones. The goal of this paper is to compare metrological features of interferometers with two converters -- piezo-mirror and electro-optical device -- used by us in measuring practice. The questions which are considered: effect of coherent nature of laser radiation, extreme values of measuring frequency and amplitude of vibrations, extreme values of SNR and distance from testing surfaces, restrictions on view field and design parameters, most effective application areas.

The described 3D-measurement system with fringe projection applies the principle of uniform scale representation by the exclusive use of phase-measurement values for the coordinates of each point. The object under test is successively illuminated with a grating structure from at least 3 different directions with a telecentric system, whereas gray-code is combined with four or five 90 degs phase-shifts. A CCD-camera records the intensity distribution of the fringes that appear as intersection lines on the surface of the object. This gives the linearly independent absolute phase values which are necessary for the calculation of the coordinates. It should be pointed out that all coordinates (x, y, z) are determined with the same accuracy. To compensate the influence of specular reflections or shadow areas up to 15 directions of light projection can be used. Moreover, the object can be rotated around a second axis yielding other views of the object. So we get different patches of the object that are transformed into a global coordinate system without any interactive user help. During this procedure correlation methods or special points are not necessary. The calibration of the 3D-orientation of the second axis is realized with a special calibration body.

The laser interferometers are intended for high-precision measurement of distances and displacements. The calibration equipment for the definition of real meaning of the laser radiation wavelength and investigation of wavelength stability and reproducibility of the laser radiation in the laser interferometers is presented in paper. The laser radiation frequency was measured with the heterodyne method using the developed laser frequency iodine standard 633 nm. The system was used for calibration the frequency of the He-Ne Zeeman laser used in the two frequency laser interferometer.

Particle Image Velocimetry (PIV) is a non-intrusive optical measurement method to capture flow velocity fields. It provides the simultaneous visualization of the two-dimensional streamline pattern in unsteady flows and the quantification of the velocity field over a plane. To reveal the flow motion, the flow is seeded by small scattering particles. The instantaneous fluid velocities are evaluated by recording the images of tracers, suspended in the fluid and traversing a light sheet. A PIV system consists of seeding particles, illumination unit, image acquisition system, and a processing computer with appropriate software. For industrial applications a standard PIV system is not suitable, for its costs, sizes and needs of specialized users and work areas. In this paper, the realization of a new PIV system is described and compared with the standard PIV. The solution proposed is a Continuous PIV, CPIV, system: with respect to a standard PIV, it is composed of a continuous laser light source, a low cost standard CCD camera. A specifically new image-processing algorithm has been developed. This studies the gray level distribution in the particle trace image, and indicates those particles moving with an out-of-plane velocity vector component and the measure with a limited error.

Optical inspection is a well-known tool for scientific research and production control since long-time. In its form as visual inspection it is one of the main inspection tools since the beginning of technology. But the amount of data to be processed is very high in common, real time application under changing conditions is usually an industrial requirement, and last not least the recognition ability of human beings is hard to be matched. However, there is a dramatic change in the last one or two decades: the laser was developed to a reliable, easy to use and economical light source. Furthermore, the fast development in computer technology in the last decade opened applications for the improvement of products and production far beyond the possibilities of the first three quarters of this century. The methods can be described in a spanning tree of increasing specialization from the way of evaluation to the application task to be performed with this metrology method. However, all inspection methods follow a fundamental set-up scheme consisting of a loading, the object to be interacted with, the detector system and the evaluation. The approach to practical application will be reported by some example of large components.

A serious problem for the operation of track vehicles, especially trams, is the uneven wear of the wheels caused by a discontinuous driving regime. To maintain the safety and comfort the diameter of the wheels should be closely matched. For this reason the diameter of the wheels must be periodically measured. The measurement has to be carried out automatically when the vehicle is moving slowly across the measurement system. The measurement system is based on triangulation, therefore a laser line is projected onto the wheel's rolling surface orthogonal to the axle, such that an arc of about 400 mm length is marked. The arc is registered using a medium resolution, high speed CMOS image sensor featuring high dynamic range. A two step circle approximation using the minimum squared error criterion is performed. In the first step the circle is approximated including all points of the arc. In the second step points having a larger distance from the estimated circle are discarded, then the approximation is repeated. Initial simulations and tests with a standard CCD image sensor showed a potential measurement accuracy of about 0.1 mm with common wheel diameters.

For the application of interferometric methods in industrial quality control and particularly in non-destructive material testing an extensive analysis of the obtained image data is needed. In the field of optical image processing wavelet transformation has been proved to be a capable tool in the detection of structures with definite spatial resolution. The selection of the analyzing wavelet function and the variation of parameters lead to a wide range of selective wavelet filters, which are able to perform detection and classification of structures. The presented paper demonstrates numerical simulations and their optical realization in an SLM- based correlator. To locate defect patterns of different classes in interferometric fringe patterns, several wavelet functions, which are optically realizable by a transmission distribution, were utilized. The optical experiments indicate a good accordance with the computer simulations.

Detailed characterizations of inhomogeneous material compounds, e.g. welds or composite materials, require extended knowledge about local material properties. However, steep property gradients in the sample under investigation hinder the application of conventional measurement techniques. Adapted methods with high lateral resolution must be applied, which ideally record strain maps in a wide measurement range. The Digital Speckle Photography (DSP) is an optical non- contact measurement technique that fulfills these requirements. This method bases on the well-known Speckle Photography and provides fieldwise in-plane displacements and strains, respectively. DSP can be applied to a large spectrum of measurements in the field of solid and fluid mechanics. Two typical applications of this method are presented in this paper. First, the properties of laser welded steel samples are investigated. Local stress-strain diagrams of each zone of the laser weld are experimentally determined. Typically, these zones have narrow dimensions and steep property gradients. In a second application the local Young's modulus and thermal expansion coefficient of graded materials are measured. These graded materials are produced by means of a laser beam cladding process and consist of a metal matrix with varying percentages of a hard phase. Dependent on the region of the sample different quantities of the material properties are provided, owing to the varied hard phase content.

Introducing into industry numerous mechanical joints produced by new technologies and combining new materials requires careful determination of their properties. In the paper the material constants and residual strain distributions in the analyzed structures are determined and their applying in the hybrid experimental-numerical method is considered. Application of automated moire interferometer for measurement of local Young's module, Poisson ratio and residual stresses released by cutting are described. The process of reduction and transferring of experimental data into FEM model is presented. The examples of laser weldment and ceramic-to metal joint testing are shown.

A shearographic measurement system, named ILIAS, is presented which allows the non-contact large area defect detection and structural analysis of composites and other lightweight structures (e.g. in the field of aerospace) with respect to faulty materials and structural defects. Of main interest are defects which are situated below the surface and are not detectable using visual inspection. The use of pulsed illumination additionally allows the vibrational analysis and detection of constructive weak points. In contrast to conventional methods such as ultrasonic, X-ray or eddy current, the ILIAS system allows a fast and large area survey inspection in industrial environments. Applications are presented for composite structures and materials of aircrafts.

We present a fast inspection method of machine vision for in- line quality assurance of liquid crystal displays (LCD) and plasma display panels (PDP). The method incorporates an optical spatial filter in the Fourier plane of the imaging optics to block the normal periodic pattern, extracting only defects real time without relying on intensive software image process. Special emphasis is on designing a collimated white light source to provide a high degree of spatial coherence for effective real time Fourier transform. At the same time, a low level of temporal coherence is attained to improve defect detection capabilities by avoiding undesirable coherent noises. Experimental results show that the proposed inspection method offers a detection accuracy of 15% tolerance, which is sufficient for industrial applications.

Fluorescence from paper following excitation by either ultraviolet or visible light gives information on the chemical composition of the paper. This can be used for on-line monitoring of the paper during production. Such measurements can be performed non-intrusively at sampling rates high enough to give a sub-millimeter resolution at paper webs moving at velocities higher than 20 meters per second. Two types of fluorescence meters, operating at different wavelengths, have been constructed. Together with an optical speedometer they have been tested at newsprint producing paper mills. A fluorescence based method for scanning cross-directional newsprint profiles in the laboratory has been developed. From these measurements the relative shrinkage of the paper during drying can be calculated using time-frequency analysis.

Shearography has been validated as fast and reliable inspection technique for composite materials in aerospace components. Following a several years phase of evaluation of the technique to show the principal applicability and prove the required sensitivity, now the first production lines for aerospace components have been equipped with automatic shearography inspection systems. In this paper, recent installations of automatic inspection systems in aerospace industries are presented.

An optimum of preparation of the body in white is indispensable for the manufacturing of a customer relevant quality of painted surfaces. For the reduction of the refinishing operations during and after the painting processes, and to guarantee a constant quality level, it is necessary to detect and eliminate surface defects already in the body works finish. Within the project 'Automatic Body Inspection System' (ABIS), a system is developed, which automatically detects, classifies and marks invisible surface defects on bodies in white, so that a propagation of these defects into the painting process can be prevented. For this reason, an optical measuring system for the visualization of sheet metal defects, a sophisticated software package for the recognition of surface defects, and the system technology required for the automation of all functionalities (like measurement, identification, classification and marking) is developed. The system is trainable, hence collects the knowledge of experienced quality testers and translates it into objective judgement criteria to allow for a constant quality level.

In the development of new airplane generations at DaimlerChrysler Aerospace extensive testing of new designs and geometries is performed in the wind tunnel. Models to various scales are built from steel and aluminum by milling. To achieve optimum performance in the airstream, the model surface is hand-finished according to the CAD design geometry. In the past this finishing process was controlled in several measurement loops with a tactile coordinate measurement machine. This was very time consuming and could only be performed at discrete points of the model surface. The optical measurement and inspection system WinGS (Wing Geometry Sensor) was developed to significantly increase the speed of the shape control process and to measure the complete 3D-surface of the model. The system consists of a fringe projection sensor with photogrammetric orientation. The 3D-geometry of the model surface is digitized and the deviation from the designed CAD model is calculated and displayed as a 2D false color map. The complete measurement, analysis and display cycle time is 25 seconds. The accuracy of the system is plus or minus 0.03 mm on whitened surfaces up to 400 X 280 mm². The overall measurement volume is 1.5 X 1 X 0.5 m³.

Basically, optical profilometry has a wide spread application potential in sheet metal forming starting at the design stage when models have to be digitized, followed by needs for shape acquisition in tooling technology, and finally in on-line testing during mass production. In particular, deep-drawing of car body components and surface structures of aircrafts put high demands on metrology. In the past, a number of restrictions caused application limits of optical 3D sensing in this field. The paper will show, that object size greater than 1 m, measuring time less than 1 s, vertical resolution less than 10^-4 of object size and the capability to work on shining, oil-covered metallic surfaces are key criteria for industrial applications. New approaches are described addressing these practical needs. Based upon high brightness, high contrast pixel by pixel projection equipment (Digital Micromirror Device of Texas Instruments Inc.), algorithms have been developed and tested that meet the objectives named above. Multilevel adaption generates near-to- perfect sinusoidal fringes across the field of view and advanced phase analysis improves both, measuring accuracy and reliability of operation. Fast data acquisition has been obtained by development of sophisticated synchronization hardware. An application example will be given showing surface structures on a large sheet metal part at two different scales of height.

The conveying and dumping of earth masses lying over the coal seam in lignite surface mining is done usually by overburden conveyor bridges. The overburden, obtained from connected excavators, is transported over the bridge construction using a conveyor belt system and poured into one front dump and three surface dumps. The shaping of the dump growth is of great importance both to guaranty the stability of the masses dumped to earth stocks as well as the whole construction and to prepare the area for re-cultivation. This article describes three measurement systems: one to determine the impact point of the dumped earth masses, one to determine the shape of the entire mining process and the other a sensor for the loading of the conveyor belt. For the first measurement system, a real-time video system has been designed, set-up and installed that is capable to determine the impact point of all three dumps simultaneously. The second measurement system is a connection of 5 special designed laser distance measuring instruments, that are able to measure the shape of the mining process under unfavorable environmental conditions like dust, high temperature changes, heavy shocks etc. The third sensor is designed for monitoring the transportation of the masses via the conveyor belt system.

The detection and classification of defects is strongly useful for stopping in real time the cloth production when degenerative defects occur; for increasing the efficiency of production by limiting the decrement of price for cloth rolls. The paper describes the work performed for detecting defect of well-known manufacturers of cloths and machine builders for cloths (looms). The main goal has been to obtain a new and innovative production line endowed with a system for detecting defects in real-time. The system is based on image processing techniques with a special attention to the real-time constraints. An architecture separating an on-line defect detection and an off-line classification has been proposed. An intelligent optical head, assembled on the loom, has the duty to acquire images and to detect the defects in real-time. A server has the offline task to classify each defect detected by the head. In the paper, some new algorithms for defect detection have been proposed. These have been compared with a selection of the most interesting algorithms for the same purposed taken from the literature. The comparison has been conducted by on the basis of a large test set with several types of defects and by considering reliability, performance, and complexity.

With this paper we would like to present a high resolution linear sensor system. It has been developed for the sheet fabricating industry. The sensor is a stand-alone system. A Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA) and a Microcontroller (MC) collect and process the data of the linear sensors. The basic elements are six CCD linear sensors. They deliver the required high resolution of the sensor. A multiplexer connects two active linear sensors at a time to the CPU. The switching between the linear sensors is automated by the DSP. Furthermore this paper gives some detailed information about the accuracy, resolution and the measuring range of the sensor. The industrial application is listed at the end of this paper.

The laser diffraction is a robust and precise technique to monitor wire diameters in-line. However, classical Fraunhofer diffraction formulas are not appropriate for 3-dimensional object size determination. The Babinet's principle allow to use such formulas only for angles of diffraction that tend to zero. A real diffraction measurement necessarily takes a finite angular range (approximately 10 degrees) and therefore, an error will be introduced if using classical formulas. The exact electromagnetic formulation is not appropriate to deal with 3-D objects, basically because it does not provide explicit formulas to determine the wire diameter. We have worked a pseudo-empirical approach out to reach simple accurate and reliable diffraction formulas that use exclusively the fringe pattern. To validate the diffraction formulas we need a calibration of the wire diameter. To accomplish this, we have introduced a hybrid set-up which allows interferometric and diffraction measurements over the same area of the wire. Using a He-Ne laser and a plus or minus 10 degree measurement range we observe, typically, a diameter overestimation of approximately 0.5 microns for different metallic wires (approximately 30 - 300 micrometer). From this work, we can also extract a practical physical insight to diffraction phenomena in terms of the Geometrical Theory of Diffraction (GTD). Many optical techniques for metrology of high resolution must take into account diffracted light.

This paper presents an optical method of process control based on the thermographic detection of signals from the process zone. At the Laser Zentrum Hannover e.V., a monitoring system based on a high-temperature camera has been developed to enable on-line monitoring of the cut quality. During the cutting process, the temperature field was observed on-line using a thermocamera. The camera images were analyzed afterwards using specific digital image analysis. The crucial task of the work is the adequate application of analyzing and visualization techniques to extract significant information from the measured signals, and to find correlations to the cutting quality. Investigations have been carried out on cutting metal sheet materials such as steels and titanium. For the investigations, different process parameters such as laser power or process gas pressure were varied. Influences of the optical set-up on the signal were studied. Results show that the temperature distribution in the process zone is strongly connected to the cut quality, e.g. dross attachment, surface roughness of the cut kerf, width of the kerf. Observation of the temperature and temperature gradients at the cutting front allow a determination of the resulting cut quality.

Electronic speckle pattern interferometry (ESPI) is a rapidly developing optoelectronic method of nondestructive laser metrology supported with computer evaluations. It permits measurement of deformations in the micrometer and submicrometer ranges produced by an electrical signal, heating, mechanical stress or another load. Though the method seems very friendly for industrial checks it has several drawbacks which prevent its application in real industrial environment: complexity, bulkiness and high costs of optical setups, difficulties in aligning of the optical elements. There are problems in working outside the laboratory especially due to high sensitivity of ESPI devices against environmental vibrations and daylight. The method of ESPI with holographically stored waves was introduced by these authors in 1995. It permitted to avoid all drawbacks mentioned above and to build an elegant, portable ESPI device with 2 optical components only: a HOE and a plane mirror. The device works very well with different test specimens subjected to deformations and vibrations. It was found that the method and the device also suit well for quasi-real time monitoring of dynamic thermal deformations. Such a novel possibility of ESPI to monitor temporal development of deformations due to electrical heating of electronic components populating a printed circuit board (PCB) and to locate a component subjected to excessive heating is presented in this work for the first time. Temporal development of deformations of the same PCB were monitored in quasi-real time in other innovative ESPI devices also originating from our laboratory. These portable, compact devices utilize alternative physical principles for combining of object and reference ESPI waves and guiding them to the sensor of the CCD camera. Such novel devices also ensure proper acquisition and documentation of temporal development of deformations and dynamics of propagation of thermal waves. Vast experimental data properly illustrating the possibilities of the novel methods are presented.

One of the main ways to develop testing nondestructive devices for fiber communication systems is to use optical reflectometry in frequency domain (OFDR) and LFM-technique. There are some problems in OFDR-systems which are determined by complexity degree of modulation type realization and its law, low energy characteristics of frequency modulators and large scattering losses on reflectometer units in general. In present paper we want to consider some common and special solutions for these problems. Especially a new LFM-technique based on two frequency laser radiation, which can help us to develop compact reflectometer, is presented. Basic consideration of one frequency radiation transformation into two frequency is given. The elements of LFM technique for reflectometers are given. We determined informative parameters of output radiation and their connection with degree of internal and external disturbances and coordinates along the axis of fiber, calculated the accuracy characteristics of system. We showed that two frequency output radiation carried more information and could help us to get results closed to two mode reflectometers. The experimental set-up of structural testing system and first practical results are given.

Carbon fiber technology and other lightweight constructions are used more and more for airplane parts. Modern airliners are already equipped with such components as e.g. in the vertical and horizontal stabilizer, rudder, airbrakes and spoiler. The application of the new materials is accompanied by new requirements for an optimal dimensioning. In this case, the investigation with respect to material and construction imperfections is of high interest. In order to receive a high safety of operation possible damages must be recognized prematurely within control examinations to prevent the total breakdown of the device. For this reason, adapted examination designs and especially developed testing methods are necessary. An appropriate testing method must meet the following requirements: (1) nondestructive evaluation, (2) inspection of large aircraft structures, (3) working with non- cooperative surfaces, (4) non-ambiguous flaw interpretation, (5) flexible and simple in operation. A testing method which can manage such examination designs is the shearography. It is a robust interferometric technique to determine locations with maximum stress on various material structures under an appropriate load. The procedure is also suitable for inspection where only one side of the aircraft-structure to be tested is accessible. This paper describes a complete procedure including loading and image processing facilities for structural testing and flaw recognition on non-cooperative aircraft surfaces.

Particle Image Velocimetry (PIV) is presented as a tool for aerodynamic optimization of a real world complex car cooling system. The method allows to freeze flow structures within a 2-D plane and delivers descriptive velocity vector plots in short time. Vector plots of the flow at different places in the cooling system are shown. How to handle problems like limited optical access and noise caused by surface reflections is demonstrated, too.

In this paper the experimental characterization of a transducer for on line measurement of coating thickness in food industry applications is described, which is composed by a fiber optic probe and by an eddy-current proximity one. The method is based on measuring reflectance by a fiber optic probe of the coating plated on thin steel sheets. The eddy current proximity probe should be used to measure the substrate position. In order to evaluate the feasibility of this approach, a particular attention has been paid to the accuracy of the method, since an accuracy in the order of plus or minus 1 micrometer should be achieved for practical interest. With this aim, the effect of the main interfering and modifying quantities of geometrical (sensor size, probe head angle of incidence, working distance, ...) and optical (light source and photo-detector behavior stability, ...) type has been evaluated both theoretically and experimentally by using a calibration test bench in stationary working conditions. Furthermore, a calibration test bench has been built, where a translating and vibrating steel plate is realized, in order to evaluate the effect of translation velocity of the plate and also of cross vibrations. Results of dynamic calibration are also described and discussed, in order to get information about the final sensor configuration.

A thin rubber plate is circumferentially clamped and centrally loaded with a small constant force. The behavior of this elastic membrane is studied through an out-of-plane sensitive Digital speckle-pattern interferometer. The surface deformations of the plate are revealed by a developed program, realizing the phase determining method of Spatial heterodyning. Simulated noisy speckle patterns are used to test the possibilities of the software. The removal of an arising tilt effect, due to a non-whole number of carrier fringes in the analyzed pattern, is shown and discussed. Experimental results are presented for the rubber surface deflection in several consecutive moments during the application of the force, and after its removal. Trajectories of surface points are plotted. A subtle effects of non-linear behavior are visualized.

Quality checking and part measurement are common needs in confectioning and manufacturing processes especially of electronic components. The complete part inspection of SMD- element, of connectors, of toy buildings blocks are such examples. For all these examples the demand arises to check parameters of different object sides by optical means with extremely high precision. The referred solution performs such inspection tasks from one point of view for (up to) five different sides, whereby four sides must be inspected for coplanarity and for the fifth the imprint quality has to be controlled. The optical set up uses special positioned mirrors combined with a sophisticated lighting system producing back light (coplanarity) as well as direct light (imprint inspection). The measurement procedure contains, of course, a calibration by help of a normal. The high precise measurement, better 10 micrometer, in the acquired image with a relatively low local resolution is reached by a spline based subpixel approach. Introducing cylindrical lenses or parabolic mirrors in the optical way allows to improve the potential accuracy for areas of interest, inside the view available for inspection.

There are applications, where the relative orientation, i.e. the roll-, pitch-, yaw angles, between a reference system and a far distant object system must be known. If the systems are closed together, for example, the rotational encoder is a standard instrument to measure the roll angle. For large distances (up to intersatellite distances) this optical sensor is able to measure the roll angle between both systems with an accuracy of about 1 arcsec within a range of plus or minus 30 degrees. The measurement principle is based on the reception and evaluation of the transmitted polarization plane according to the law of Malus. Replacing one photodiode with a position- sensing detector (PSD), the other two degrees of freedom can be also measured with similar accuracy within a range of about plus or minus 5 degrees. The present sensor principle is characterized by the application of amplitude- and polarization modulation with two perpendicular linear polarized laser diodes in the transmitter and evaluation of the signals with a suitable algorithm. The advantage of the sensor is that it becomes insensitive to stray light, intensity fluctuations of the laser diodes, responsivity fluctuations of the photodiodes and the p-s transmission splitting due to non-perpendicular incident light.