3D shape measurement is one of the growing industrial applications of the Texas Instruments DLP® micro-mirror device. This paper presents investigations on precision and repeatability of that spatial light modulators output when it is driven up to its high-speed limit. The study concerns the basic switching behavior of the individual micro-mirror at different frame rates ranging over three orders of magnitude. The 3D shape measuring methodologies are focused on phase encoded triangulation, i.e. the projection of sinusoidal patterns. The DLP chip is a bi-stable device providing an on/off pattern at each certain moment in time, i.e. it has a native binary output. Sinusoidal patterns are the result of either a temporal integration of multiple on/off patterns or a spatial integration within one on/off pattern. Both approaches are studied experimentally with respect to precision and stability of the pattern output. The STAR-07 industrial projection unit, based upon the 0.7” DLP Discovery™4100 chipset, has been used for this work and the pattern frame rates cover the range from 225 frames per second (fps) to 50,000 fps. The STAR-07 output is detected by a photodiode, amplified, and analyzed in a Yokogawa digital storage oscilloscope. All results prove the very high precision and repeatability of the STAR-07 pattern projection, up to the extreme speed of 50,000 fps.
Deterioration of artwork, in particular paintings, can be produced by environmental factors such as temperature
fluctuations, relative humidity variations, ultraviolet radiation and biological factors among others. The effects of these
parameters produce changes in both the painting structure and chemical composition. While well established analytical
methodologies, such as those based in Raman Spectroscopy and FTIR Spectroscopy require the extraction of a sample
for its inspection, other approaches such as hyperspectral imaging and 3D scanning present advantages for in-situ, noninvasive
analysis of artwork. In this paper we introduce a novel system and the related methodology to acquire process,
generate and analyze 4D data of paintings. Our system is based on non-contact techniques and is used to develop
analytical tools which extract rich 3D and hyperspectral maps of the objects, which are processed to obtain accurate
quantitative estimations of the deterioration and degradation present in the piece of art. In particular, the construction of
4D data allows the identification of risk maps on the painting representation, which can allow the curators and restorers
in the task of painting state evaluation and prioritize intervention actions.
The SYDDARTA project is an on-going European Commission funded initiative under the 7th Framework Programme. Its main objective is the development of a pre-industrial prototype for diagnosing the deterioration of movable art assets. The device combines two different optical techniques for the acquisition of data. On one hand, hyperspectral imaging is implemented by means of electronically tunable filters. On the other, 3D scanning, using structured light projection and capturing is developed. These techniques are integrated in a single piece of equipment, allowing the recording of two optical information streams. Together with multi-sensor data merging and information processing, estimates of artwork deterioration and degradation can be made. In particular, the resulting system will implement two optical channels (3D scanning and short wave infrared (SWIR) hyperspectral imaging) featuring a structured light projector and electronically tunable spectral separators. The system will work in the VIS-NIR range (400-1000nm), and SWIR range (900-2500nm). It will be also portable and user-friendly. Among all possible art work under consideration, Baroque paintings on canvas and wooden panels were selected as the project case studies.
The use of computer generated sinusoidal fringe patterns has found wide acceptance in optical metrology. There are
corresponding software solutions that reconstruct the phase field encoded in the fringe pattern in order to get 3D-shape
data via triangulation and deflection measuring setups, respectively. Short recording time is a common issue of high
importance for all tasks on the factory shop floor as well as in medical applications and for security. Recent high-speed
implementations take advantage of MEMS based spatial light modulators and the digital micro mirror chipset DLP
Discovery<sup>TM*</sup> is the fastest proven component currently available for this aim. Being a bi-stable on-off-state system, the
sinusoidal gray level pictures are generated by controlling the mirrors ON-time period during which an analogue
detector is exposed. This digital generation of light intensity distributions provides outstanding precision and long-term
stability. It is used in leading edge technology solutions that produce video type streams of 3D surface data with a
sustained repetition rate of 40 Hz. A new proposal is discussed in this paper that goes beyond this state of the art by
considering the optical encoding of the surface as an all-digital communication link. After a brief classification of state-of-
the-art systems, the authors describe how future all-digital encoding leads to extremely high speed and precision in
3D shape acquisition.
The methodology of phase encoded reflection measurements has become a valuable tool for the industrial inspection of components with glossy surfaces. The measuring principle provides outstanding sensitivity for tiny variations of surface curvature so that sub-micron waviness and flaws are reliably detected.
Quantitative curvature measurements can be obtained from a simple approach if the object is almost flat. 3D-objects with a high aspect ratio require more effort to determine both coordinates and normal direction of a surface point unambiguously.
Stereoscopic solutions have been reported using more than one camera for a certain surface area. This paper will describe the combined double camera steady surface approach (DCSS) that is well suited for the implementation in industrial testing stations
The paper describes methodology, instrumentation, and experiments for the study of the mechanical behavior of MEMS, especially active micromembranes. The technique of speckle interferometry is extended to high microscopic magnification and short wavelength of laser light and two corresponding interferometric solutions are discussed. Challenging issues for the optical measurement are the micrometer lateral size of the details, the nanometer deflection, and the Megahertz frequencies of resonant vibrations. Micromembrane arrays different in size and shape were analysed with respect to piezo response, resonance, and cross-talk. Systematic investigations revealed the complex micromechanical behavior of the microstructures.
In the last decades, electronic speckle pattern interferometry (ESPI) was successfully used for detecting deformation, vibration, and strain on specimens and components with dimensions on the macroscopic level. The outstanding features of ESPI are it's ability for fully automatic operation combined with the excellent sensitivity controlled by the wavelength of laser light. In the field of MEMS' (MicroElectroMechanicalSystems) testing, however, where the object size scales down below one millimeter, a number of problems arises when speckle techniques are to be applied. On the other hand, speckle solutions sound really promising to satisfy certain demands in MEMS technology. In this situation, some recent research concentrated on the further development of speckle interferometry to serve best for the specifics of MEMS characterization and quality assurance. The paper explains the benefits and the application limits of micro speckle interferometry (MSI) and it shows the potential for improvements when a deep UV laser source is used. For the experiments, a new deep ultraviolet micro speckle interferometer (DUV-MSI) was designed operating at 266 nm of wavelength. The implemented optics enables for the measurement of both, in-plane and out-of-plane movements on the microparts. In this way, a complete motion analysis can be performed with nanometer accuracy.
The paper explains the benefits and the application limits of micro speckle interferometry (MSI) and it shows the potential for improvements when a deep UV laser source is used. For the experiments, a new deep ultraviolet micro speckle interferometer (DUV-MSI) was designed operating at 266 nm of wavelength. The implemented optics enables for the measurement of both, in-plane and out-of-plane movements on the microparts. A number of practical examples are shown in the paper in order to illustrate the advantages of a shorter wavelength in speckle interferometry.
Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The microvibrations have nm amplitudes and are detected by electronic speckle pattern interferometry (ESPI). A specific signal processing technique (moving phase reversal reference) has been applied to make the solution robust. Comprehensive numerical simulations provide the theoretical base for estimating the frequencies and mode shapes expected for perfect MEMS as well as for typical faults. The complete wafer ensemble was modeled to gain knowledge about best suited wafer clamping and about interactions between the microparts vibrating. A laboratory system for 4' wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly by means of the hybride approach. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level.
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<SUP>-4</SUP> 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.
Design, manufacturing and test of microcomponents generate new challenges for measurement techniques in general. The non- contacting operation of optical metrology makes it attractive to solve the task of measuring geometric quantities of microparts. So far, speckle interferometry (ESPI) is well established as a measuring tool for analyzing deformation, vibration and strain on a macroscopic level. This paper deals with possibilities and application limits of ESPI in the case of scaling down the object size below one millimeter. In a first part, both spatial resolution and displacement sensitivity of the technique are discussed. Theoretical considerations are shown together with experimental verification. Secondly, a micro speckle interferometer will be presented that has been built for the use with different microscopes. Its capabilities are demonstrated by a practical application. The microcomponent under investigation is a bulk micromachined gyroscope, a demanding object with respect to its multilayer design. Developments aim at increasing the spatial resolution step by step and results obtained with different field of view will demonstrate the progress. Finally, the deformation behavior of an X-shaped torsional spring with a width of 100 micrometer could be characterized.
Design, manufacturing and test of microcomponents generate new challenges for measurement techniques in general. The non-contacting operation of optical metrology makes it attractive to solve the task of measuring geometric quantities of microparts. So far, speckle interferometry (ESPI) is well established as a measuring tool for analyzing deformation, vibration and strain on a macroscopic level. This paper deals with possibilities and application limits of ESPI in the case of scaling down the object size below one millimeter.
The thermally induced deformation of anisotropic composite tubes with different thicknesses is studied by means of Finite-Element-Analyses and interferometric measurement techniques. Of particular interest are the differences in the deformation behavior in comparison to isotropic tubes. It is shown that characteristic bending phenomena appear at the shell surfaces of the tubes, due to the three-dimensional stress state near the edges. The simulated thermal deformation is experimentally verified by means of holographic as well as speckle interferometry. The results of this work show that the implemented micro- and macromechanics of both used Finite- Element systems enables to predict the thermal deformation of composite tubes properly, if a suitable model is used. Nevertheless, especially for thin tubes significant discrepancies between the simulated and the measured deformation could appear, due to the disregarding of the complex microscopic structure in the simulation. Thus experimental verifications with fullfield measurement techniques should generally be performed.
Deformations of thermally loaded composite tubes are studied by means of Finite-Element-Analyses and interferometric measurement techniques. Of particular interest are the differences in the deformation behavior of the two investigated anisotropic tubes in comparison to isotropic tubes. Two characteristic bending phenomena appear at the frontal and the shell surface of the tubes, owing to the three-dimensional stress state near the edges. These simulated phenomena are experimentally verified by means of holographic as well as speckle interferometry. The results of this work show that in most cases the implemented micro- and macro- mechanics of the used Finite-Element models enable to properly predict the thermal deformation of composite tubes. Nevertheless, especially for very thin tubes, significant discrepancies between the simulated and the measured deformations could appear, due to the disregarding of the complex microscopic structure in the simulation. Thus, experimental verifications of the simulated thermal deformation of composite tubes are necessary. Generally, these verification measurements should be performed with fieldwise experimental methods, like the presented interferometric measurement techniques.
This paper gives an account of the first application of a high-power diode laser system for laser bending of sheet metals. The applied diode laser has an power output of 100 Watt at a wavelength of 810 nm. Sheet metals of AlMg3, St 14 and stainless steel have been investigated. The results show that it is possible to bend sheets with a thickness of up to 2 mm. The paper shows the correlation between the obtained bend angle and the investigated parameters like path feed rate, number of irradiations, sheet material and sheet thickness. An estimate of the range of application of the diode laser for laser bending has been derived from the determined results.
This paper describes a systematic study of influences that have to be overcome for the application of interferometry in the high temperature range. A specially designed test facility including an optical arrangement is used for the investigation of CMC specimens. Verification tests are performed up to 1500 degree(s)C with combined thermal-mechanical load sets. The fringe quality achieved allows to evaluate a field of displacement and strain data. Experimental experience gained is convincing to reach even higher temperatures and to test CMC components as well.
During the preparation of HNDT applications, it is common practice to carry out a number of experiments in order to gain knowledge about detectable and nondetectable flaws, and to select optimum testing conditions. In many cases, considerable effort is necessary especially for advanced materials with anisotropic properties. This paper proposes an alternate approach: completely simulating the component behavior as well as the HNDT process. Considerable savings occure in both time and cost items, and in addition a direct relationship can be established between the damage significance of a flaw and its visibility by interferometric techniques.
This paper presents qualitative and quantitative results obtained from measurements on specimens of different composite materials and one ceramic-ceramic joint. Characterizing anisotropic material properties, extensive investigations have been carried out to measure effective thermal coefficients of expansion and to determine thermal shear based on correlation fringe patterns. Carbon-fiber materials reinforced with epoxy and metal matrix have been subjected to thermal cycles. A further DSPI application concerns residual stress analysis on a ceramic pipe that is laserbeam welded.