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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386721
An optoelectronic system is presented that is used to measure the 3D vector components of a vibrating object. The complete determination of the vibration occurs by combination of three different measurements. (1) A 3D system based on digital holography for the measurement of the 3D deformation vector along the directions x, y and z is used. Pulses from a ruby laser, with a separation in the range from 1 to 1000 microseconds, are used to record holograms on CCD sensors, which are later digitally reconstructed. (2) The shape of the object is determined. In this case too the ruby laser is used as a light source but now two pulses are emitted with different wavelengths. The wavelength change is produced by changing the distance between the plates of the laser output etalon. The shape is obtained by subtraction of the phases of the wavefronts recorded at the two different wavelengths. (3) For the absolute measurement of a vibration using double exposure holographic techniques, it is necessary to have a reference point where the absolute vibration is known. A precise measurement of the vibrations in a point is done by using a 3D laser Doppler vibrometer.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386728
Using degenerate four-wave-mixing technique the acoustic wave produced in transparent microstructured optical materials can be determined. The light source used in this paper was a mode-locked, Q-switched Nd:YAG laser operated at 532 nm with pulse width of approximately 20 ps. The laser beam was split into three pulses. By spatially overlapping inside the sample with an angle in a backward propagating scheme. A laser induced periodic interference pattern which serves as grating was formed in the sample. The third, `probe', beam incident on the region in the direction satisfied by the Bragg condition. The diffracted signal brings the information of the produced acoustic wave. The incident laser pulses coupled to the acoustic field of the material through effects of thermally induced acoustic strain and electrostrictive coupling. This results in a generation of two counterpropagating ultrasonic acoustic waves in the grating wave vector direction, which is so- called the Laser Induced Phonon Spectroscopy.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386738
For application in on-line control of elastic vibrations, a control feedback is proposed based on distributed measurement of deflection-curvature. This is achieved using modal curvature gauges, one for each dominant vibration mode: each gauge is sensitive to a designated vibration mode while insensitive to other modes of interest. Only distributed measurements can provide such decoupled modal information and, thus, simplify the vibration control. The number of gauges required equals the number of dominant vibration modes of interest. The proposed `modal curvature gauge' is a generalization of the novel `curvature gauge' reported recently. Unlike the established technology of modal strain sensing, this sensor that combines fiber-optics and laser sources, is particularly suitable for thinner structures. For any strain and any curvature sensor, there exists a breakeven structural thickness separating the application domains of the two, such that curvatures should be measured in structures thinner than this breakeven thickness. It is the thinner structures that are most prone to elastic vibrations in mechanical systems. They also have more distinctly dominant vibration modes.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386745
Dynamic parameter measurement is very important for disk- slider interface design. Laser Doppler Vibrometer has been the most favorite instrument for this purpose due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular locate on the entire feature. In order to get the whole field data, a laser beam scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will deteriorate the measurement accuracy. Moreover current scanning LDV can not avoid Pseudo error introduced by the scanning angle. This paper describes a novel scanning LDV optical system embodied an acousto-optic deflector scanning mechanism. It can not only eliminate the Pseudo error, but also improve the measurement accuracy since there is no mechanical motion involved. Promising results have been obtain from the preliminary experiments carried out for measurement of out- of-plane runout of magnetic disk, vibration of slider relative to the surface of the rotating magnetic disk, and flying height along the traveling edge.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386754
In this paper, a two-axis-scanning Laser Doppler Vibrometer for micro-scale object dynamic behavior characterization is described. The system employs a two-axis acousto-optic deflectors and a telecentric lens to achieve high-precision and high-speed scanning. The newly developed vibrometer was used to measure the dynamic behavior of an entire AFM cantilever operated in free air. The 120 micrometers long, 25 micrometers wide micro-cantilever dynamic response was measured at different positions with 2 micrometers spatial resolution.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386770
The statistical properties of photodetector current noise in Doppler and grating schemes are analyzed; in particular, the effect of speckle averaging over the receiving aperture is discussed. It is shown that in the typical configurations of both schemes shot noise prevails over other sources of noise. The dependence of the potential accuracy on the signal-to-noise ratio is established in both schemes. Also, it is shown that the relative frequency spread of the Doppler shifted component and the informational component in the grating scheme can be less than 0.1% with a signal-noise ratio exceeding 100.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386713
This paper presents a method to measure responses for a sinusoidally excited structure using a continuously scanning Laser Doppler Vibrometer (LDV). The LDV output signal is an amplitude-modulated vibration, whereby the excitation signal will be modulated by the response of the excited structure. Using an applicable demodulation the mode shape defined along a scan line can be derived by the envelope of the modulated vibration. By using an adaptable digital low-pass filter and parallel measuring of responses and mirror drive signal in the time domain the mode shape can be directly derived from the measured response. So the demodulation is a fast method to identify the mode shape from the measured response, because of its completion in the time domain. For that purpose the method is capable for using the responses online for normal mode tuning. Furthermore it is necessary for normal mode testing to measure complex responses to make an affirmation about the separation of real mode shapes. The method will match these requirements.
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Alfred Link, Wolfgang Wabinski, Axel Pohl, Hans-Juergen von Martens
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386714
A signal processing method for identifying the input-output behavior of accelerometers is developed. The method is based on the state-space description of the relationship between input, noise and output signals. The accelerometers is modeled as a one-degree-of-freedom system. The acceleration input signal is derived from the interferometrically measured displacement signal by a subroutine for the low- noise estimate of the input acceleration. For observed sequences of input-output data, the parameters of the transfer function of the accelerometer are estimated by minimizing the prediction error sequence of the state-space model. The identification procedure developed was applied to accelerometer input-output data furnished by a shock acceleration standard. The results obtained for pulses with peak values ranging from about 104 m/s2 to 5(DOT)104 m/s2 were in good agreement with calibration results known from sine and shock calibrations for the accelerometer under investigation. The estimated transfer function characterizes the input-output behavior of the accelerometer in the time and frequency domain and allows us to determine the acceleration output signals for non-stationary input signals, for example, the input and output peak values in primary shock calibrations.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386715
The paper describes investigations of vibrations by the laser interferometry where both beams are offset in frequency. This method is called the laser heterodyne vibrometry. The main aim of this investigation was heterodyne detection of a weak laser light scattered from a vibrating object. As a standard surface we used a piece of white zero sheet connected to the vibrating object.
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Steve Vanlanduit, Patrick Guillaume, Johan Schoukens, Eli Parloo
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386716
Because a scanning laser vibrometer can perform vibration measurements with a high spatial resolution it is an ideal instrument to accurately locate damage in a structure. In literature different authors successfully used linear vibration measurements to detect faults with the aid of a scanning vibrometer. In this article we will study the feasibility of using nonlinear vibration features to detect and locate damage in a structure. The nonlinearities will be estimated using both classical and a newly developed technique. A comparison of linear and nonlinear damage detection features will be performed on measurements of a cracked plexiglass panel and a delaminated composite plate.
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Leonid K. Yarovoi, Lubomir I. Robur, Georg Siegmund, Dmitry Tushev
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386717
The implementation of laser vibrometers into various branches of industry solves complex technical problems as well as raising the authority of laser vibrometry as unique measurement tool. From this point of view, the nuclear industry is an interesting and attractive application field with specific and rigorous exploitation conditions of measuring systems. The objective of this work was to evaluate all advantages and disadvantages of the laser Doppler vibrometry with respect to nuclear power plant (NPP) equipment examination. The Chernobyl NPP is the ideal place for these purposes. The diagnostic ability on different Chernobyl NPP systems (e.g. third power unit main circulators, bearing shaft of fifth turbo-generator and various pipelines) has been demonstrated using laser Doppler vibrometers. The measurements performed by laser vibrometers were checked by standard Chernobyl NPP vibration measurement tools. The laser Doppler vibrometers (CLV, Polytec GmbH and LDV, Kiev University) have been tested and have shown full functionality in NPP zone at 0.5 sievert/hour radiation levels, high electromagnetic fields (magnetic component up to 5 kA/m) and significant vibrations.
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Guillermo Silva-Pineda, Luis Gironella Ferrer-Argote
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386718
In practice, traceability leads to improve the accuracy and agreement among the results obtained using different means of measurement. However, in every calibration within the traceability chain there is a certain increment of the uncertainty of measurement. The uncertainty of measurement gives an idea of the length of the traceability chain and the accuracy of the methods used to calibrate the measurement standard. The case when the linear acceleration quantity is measured using a laser interferometer, traceability to length through the calibration of the laser in wavelength, and time and frequency through the calibration of a sine generator and a frequency counter, is discussed. It highlights that an important portion of type B uncertainty related with these reference standards depends on two factors, their traceability chain to basic standards of length and frequency, and the measurement accuracy achieved within the traceability chain.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386719
The biological photoreceptor bacteriorhodopsin (bR) uses light energy to translocate protons across the cell membrane. The bR-films have spatial resolution does not fall below 5000 lines/mm, require no external processing, and may be cycled through the write/erase process more over millions of times without degradation. We have shown in Raman-Nath conditions (thin holographic grating) when the intensities of recording beams are equal, a very drastic increase in the first-order self-diffraction beam occurs under impulse shift. In this work, we propose to apply the kinetic characteristics of the first-order self-diffraction beam in thin holographic grating conditions on bR-film for real-time analysis of small vibrations and shocks. Oscillograms of these rapid vibrations are given. The processing cycle time is less than 1 ms. Detection and analysis of small vibrations and shocks in present method can be directly observed on the oscillograph screen without the need for electrical amplification and computation circuits. Only the He-Ne laser with wavelength 633 nm is used in our system, it makes possible the low-cost diode lasers also to be used.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386720
This paper outlines the current status of measurement standards for vibration and shock at the National Research Laboratory of Metrology of Japan. As for the vibration acceleration standards, two systems have been established. One system is for the middle and high frequency range (20 Hz to 5 kHz) and its acceleration range lies within 1 m/s2 to 100 m/s2. The other system is for the low frequency range (1 Hz to 200 Hz) and its acceleration range lies between 0.1 m/s2 and 100 m/s2. A test facility is under development to evaluate the accelerometers' performance in different temperature and humidity. With this facility, temperature of the test chamber can be varied from -40 degree(s)C to +100 degree(s)C and humidity from 20% to 90%. A calibration apparatus is also under construction to establish the national standard of shock acceleration in the high acceleration range from 102 m/s2 to 105 m/s2.
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Sergio Rojas-Ramirez, Alfredo A. Elias-Juarez, Hans-Joachim Schlaak, Hans-Juergen von Martens
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386722
Measurement results about instant displacement and its associated velocity on an interferometric setup for shock calibration of accelerometers are studied; fitting methods for displacement and velocity from which peak-acceleration shock is computed, are compared using a least squares error criteria. Computation of instant parameters from interferometric signals are based on zero-crossings evaluation and their corresponding time-intervals. Voltage outputs from an accelerometer-amplifier chain are also analyzed.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386723
The ISO 'Guide to the Expression of Uncertainty in Measurement' (GUM, 1993) establishes a unified method for evaluating and stating measurement uncertainties, that has been accepted by nearly all calibration services and most test cooperations in all parts of the world. In vibration measurements and calibrations using laser interferometry, the application of the GUM may be difficult and very time- consuming unless some possibilities of simplification are made use of. After a brief introduction to the basic procedure specified in the GUM for the calculation of the measurement uncertainty, a survey is given of the problems typically encountered in uncertainty calculations when vibrations are measured or accelerometers calibrated by laser interferometry. It is shown how a model function of simple structure can be established for the usually complex relationship between the output quantity (e.g. sensitivity of an accelerometer), the quantity to be measured (e.g. acceleration) and various influence quantities (noise, transverse motion, base strain etc.). Among other things, non-linear effects such as the influences of distortion, hum and noise can be properly taken into account. The uncertainty evaluation is demonstrated and explained by the example of the measurement of the displacement amplitude of a sinusoidal vibration using Michelson interferometry and by the example of the primary vibration calibration of an accelerometer.
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Joseph F. Vignola, Scot F. Morse, Xiao Liu, Lidija Sekaric, Brian H. Houston, Douglas M. Photiadis
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386724
The mechanical motion of a new class of micro-mechanical devices, known as micro electro-mechanical systems oscillators, is examined using the laser Doppler technique. Currently, experimental methods based on capacitance, induction, and Fabry-Perot interferometry are used to find resonance frequencies and to establish quality factors or Q's. The technique described in this paper is capable of distinguishing mode shapes, yielding calibrated displacements, and revealing the existence of flexural modes, in addition to finding resonance frequencies and establishing Q's as the other techniques do. Because full- field laser vibrometry measurements provide an understanding of the modal composition of the systems, it can be used to refine the design and construction of these devices.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386725
As part of a government funded multidisciplinary project, a sensor has been developed to allow the measurement of the ultrasonic amplitude at the tip of the bonding too. A laser interferometer has been designed with a fiber coupled miniature measurement head which can be mounted on the rotating bond head. A modulated visible diode laser is employed to generate a direction-sensitive Doppler signal according to the pseudo-heterodyne principle.
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Vadim S. Gurevich, Mikhail E. Gusev, Igor Begishev, Vyacheslav I. Redkorechev
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386726
In the introduced paper on an example of the mobile pulse holographic set-ups, designed by authors and inserted to the large industrial enterprises of Russia the requirements to the basic units of holographic measurement complex, intended for vibration analysis of large-scale objects under out-of- laboratory conditions are analyzing. It is shown the quality of obtained measurement information depends not only from coherent properties of laser and quality of interferometer, but also from the quality a control system of laser radiation. In particular, for obtaining the reliable and reproduced results of analysis of actual vibration processes (non-stationary, random, multicomponent vibrations) the system of control and synchronization play a major role. The methods of synchronization of laser radiation with the phases of investigated dynamic processes, designed by authors, are considered. The capability of the development the newest mobile holographic complex, including the powerful superstable double-pulse laser, kit of removable digital interferometers with selective sensitivity and unified computer system of control of laser radiation, recording and processing of digital interferograms are considered. The new design solutions of the main unit of a complex are discussed.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386727
New interferometric technique for the linear detection of small out-of-plane vibrations of a rough surface caused by ultrasound is described. The technique is based on the polarization self-modulation effect in photorefractive crystals and does not involve light diffraction. The signal- to-noise ratio of the measured system is approaching to that of the classical homodyne interferometer. The system possesses the large field of view providing the measurements of small phase shift of a speckled wavefront. Moreover, the proposed interferometer is adaptive to slow environment changes with response time about 1 ms keeping ability to measure ultrasonic vibrations of as small amplitude as 0.1 nm. Comparison of the proposed technique with the photorefractive two-wave mixing is given. It is shown that the proposed technique has number of advantages providing higher signal-to-noise ratio and higher sensitivity.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386729
Measurements performed using a double pulse ESPI (Electronic Speckle Pattern Interferometry) are used to estimate the power flow maps in a square plate excited harmonically. The pulse ESPI was equipped with one camera providing no information about the phase of the measured displacement field. A procedure based on the solution of a system of transcendental equations which corresponds to two measurements with a known time delay is used to determine the magnitude and phase. In order to spatially smooth the operational modes and reduce the noise spikes, a smoothing technique and a median filter are used, respectively. The active power flow is estimated for two frequencies. The reactive power flow due to the bending moments, twisting moments and shear forces are obtained separately. A finite element model based on the theory of thin plates is used for qualitative comparison of the reactive power flow maps.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386730
In many vibrometer applications, the measured structure is excited not only by the controlled excitation source, but also by secondary, unwanted excitation sources. The effects of those disturbing excitation sources can often be limited to a small frequency range by windowing. As measurements with multi-sine excitations like periodic-chirp require a rectangular window, which provides very poor leakage reduction, the unwanted excitation sources leak out to a wide frequency range. This leakage can considerably limit the signal-to-noise ratio. The disturbing excitation sources are typically at low frequencies. As velocity is scaled to acceleration by i2(pi) f, low frequencies are better attenuated for acceleration signals than for velocity signals. Therefore it is especially important to reduce the effects of the disturbing excitation sources when measuring with vibrometers. Several methods of reducing the leakage effects of the disturbing excitation have been developed and are compared in this paper.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386731
We present the performance characteristics of a novel laser feedback technique for displacement measurement of moving materials. The approach has been shown to be robust at high temperatures and offer the prospect of remote sensing in harsh environments. The sensor head basically consists of two single laser feedback interferometers which are asymmetrically arranged with a stable intermediate angle. The measurement results indicate that the method offers advantages in ease of alignment, sensitivity and robustness over conventional laser Doppler techniques.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386732
The use of non contact vibration measurements with laser based optical devices is a relatively recent and fairly expensive technique and the more extensive use of this type of measurement is often limited by the high cost of these instruments. Laser vibrometer measurements are therefore generally restricted to single or two point simultaneous measurements or a series of reference single point measurements as the beam is displaced from one point to another. Many optical methods based on interferometry are also difficult to use in industrial environments. To help to resolve some of these problems a simple optical device based on the use of fiber-optics and luminous intensity modulation is presented. The accuracy of the optical vibrometer is not influenced by the industrial environment. The behavior of the fiber optic vibrometer is compared with the response of an accelerometer. This comparison shows that the fiber optic probe has a linear response over a large bandwidth.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386733
A laser sensor using optical feedback interferometry has been designed to measure displacements up to several micrometers. For this purpose a Lithium Niobate crystal generates a phase-shift in order to modulate at a frequency of 580 kHz the optical path difference between the sensor and the target. This setup has been calibrated by means of a commercial optical fiber sensor. The overall accuracy resulted to be up to 40 nm, for a 1 kHz sinusoidal motion of the target at 10 cm away from the sensor.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386734
This paper demonstrates a new method of conducting a non- contacting vibration measurement on light structures. Although laser vibrometry provides a routine method of acquiring response data, the method of achieving non- contacting point excitation of structures remains problematic. This is the primary concern of the paper. There is understandable motivation to develop a viable non- contacting excitation method as exiting methods involve contact thereby altering the structure's in-situ properties.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386735
Structural intensity is a powerful tool which give transfer path of the vibration energy within a structure. Additional data processing allows then to localize sources and sinks of that energy. The measurement of these quantities is possible using classical means (accelerometers, stress gauges, ...) but the data processing is complex and require a lot of accurate sensors because it is based on spatial derivatives of high order. The optical techniques (laser vibrometry, holography, ...) are more suited for that purpose because of the high density of measuring points and because of the well-known advantages of these methods: reduced measurement time and no modification of the mass parameters of the structure as it is the case when using contact sensors.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386736
In the framework of the BRITE EURAM project VIP (BE96-3192), a software for the determination of structural intensity and acoustic radiation of planar structures from holographic interferometry and laser vibrometry measurements has been developed.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386737
The structural intensity gives the information on the vibrating fields of structures, which is different from that provided by the modal decomposition. The divergence of the structural intensity is used for locating injected and dissipated power by external elements such as mechanical excitations, damping, radiation regions. Both the structural intensity and the divergence are expressed in terms of high- order spatial derivatives with respect to the variables of a coordinate system. Two methods, the finite difference approximation and the spatial Fourier transform, have been used to evaluate the structural intensity and its divergence. The limitation of the number of sensors makes it impossible to use the first method in the measurements of the high-order derivatives. The technique of processing in the wavenumber domain, based on the spatial Fourier transform of 2D-vibrating fields has not such a limitation. It has been already used in the near-field acoustic holography and laser vibrometry measurements. It makes it possible to process the massive data measured by the holographic interferometry. However, performing directly the Fourier transform usually results in large distortions if a discontinuity occurs in spatial periodicity (leakage effect) as it the case for a free plate. In this paper new algorithms--mirror processing, are developed. The structural intensity, its divergence and the force distribution in a planar plate are evaluated by processing the normal velocity data measured using the holographic interferometry or laser vibrometry. It is demonstrated that the distortions caused by leakage effects can be removed by using advanced algorithms.
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Sylvain Poggi, Bruno Gazengel, Jean-Christophe Valiere
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386739
Laser Doppler Velocimetry is used here to measure sinusoidal structural velocities. Two systems for signal acquisition and processing, one available commercially and the other being developed in our laboratory, are assessed in detail. Their performance and limitations are evaluated by means of a comparison of the estimated velocities with reference values given by a laser vibrometer. Both systems show close and satisfactory performance up to 2 kHz for rms velocities higher than 1 mm/s.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386740
A time-average DSPI method for nanometer vibration mode measurement is presented in this paper. The phase continuous scan technique is combined with the Bessel fringe-shifting technique to quantitatively analyze the vibration mode by time-average DSPI is used in measurement system. Through the phase continuous scan, the background and speckle items are completely eliminated, which improves the fringe quality and enhances the signal-to-noise ratio of interferogram. There is no need to calibrate the optical phase-shifter exactly in this method. The anti-disturbance capability of this method is higher than that of the phase-stepping technique, so it is robust and easy to be used. In the vibration measurement system, the speckle average technology is used, so the high quality measuring results are obtained.
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Herman Van der Auweraer, Hans Steinbichler, Carsten Haberstok, Raymond Freymann, D. Storer
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386741
The present paper discusses the various critical elements of a modal testing system based on pulsed-laser holographic ESPI measurements. Such system allows making very high spatial resolution measurements on panel-like structures at frequencies which are of relevance for the vibro-acoustic behavior.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386742
Mechanical effects that amy damage tissue were measured by laser doppler vibrometry. The results on the recoil momentum illustrate the laser parameters under which laser survey of organs with delicate structures becomes dangerous. One example is the acceleration of the tiny middle ear bones. In the case of an intact ossicular chain, the motion of a middle ear bone is transferred to the inner ear. The second topic is related to eye surgery. Removing or cutting of membranes, the lens or the vitreous body by pulsed lasers is often associated with the formation of laser induced cavitation bubbles. The collapse of these bubbles generates pressure shock waves propagation through the eye. Laser Doppler vibrometry was used to monitor the shock wave induced velocity of the sclera.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386743
We present a characterize theoretically and experimentally a photorefractive velocimeter. This device, based on two wave mixing in a rapid photorefractive crystal, measures the instantaneous velocity of a vibrating target. It is particularly adapted to the measurement of high amplitude (as high as some mm) low frequency (until some kHz) vibrations. Instantaneous velocity as high as 25 mm.s-1 are expected to be measured with common photorefractive semiconductors and CW lasers.
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Anthony B. Stanbridge, Milena Martarelli, David J. Ewins
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386744
A continuous-scan LDV can be used to give the response mode shape (of a vibrating surface as a spatial polynomial series. Second spatial derivative(s) of the deflection equation are then easily derived, and these should, in principle, give a curvature equation from which, for a beam or plate of known cross-section, stresses and strains can be obtained. Unfortunately, the stress and strain distributions depend critically on higher terms in the series, which are not accurately measured. This problem is avoided by a method described in this paper, which enables accurate stress and strain distributions to be derived for uniform beams, from a straight-line LDV scan, using only five terms in the mode- shape polynomial series. An application to uniform plates is being developed; the analysis in this latter case is rather more complicated.
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Anthony B. Stanbridge, Milena Martarelli, David J. Ewins
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386746
The out-of-plane vibration response mode shape of a vibrating surface may be measured very conveniently using a scanning LDV. Sinusoidal vibration within a rectangular area may be measured by scanning at a uniform rate over the whole area, the mode-shape bering recovered by demodulation. This process may be applied to any vibrating surface, but a large amount of data may be generated, and results may be polluted by speckle noise. Alternatively, the area may be covered by sine-scan inputs, simultaneously applied in x and y directions, at different scan frequencies. The frequency spectrum of the LDV output then contains components at discrete frequencies, from which coefficients in a polynomial expression for the mode shape may be derived directly. Both magnitude and phase data are required for each of the spectrum components. The process is only valid if the mode-shape is spatially smooth without, for example, any apertures within the scanned area. It has the particular advantage of representing the mode-shape by a relatively small data set. Repeat measurements at different test frequencies allow standard modal analysis techniques to be employed.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386747
To investigate the relationship of the motion of the malleus, incus and stapes in the middle ear of cat the 3D vibrations of the three ossicles were measured in the same ear utilizing a confocal heterodyne interferometer. Each ossicle was treated as a separate rigid body and its motion was calculated individually. A micro CT scanner was used to obtain serial sections of the experimental temporal bone. A 3D reconstruction of the three ossicles was made using these sections. The parameters derived from the rigid body motion calculation were combined to animate a 3D model of the complete middle ear. While the malleus vibration changed from simple, nearly hinged motion at low frequencies to very complex at higher frequencies, the stapes moved in a predominantly piston-like way. The incus transforms the complex malleus motion into the simple motion of the stapes. The incudo-stapedial joint plays a major role in this complex transmission mechanism. It is accepted that the ossicles rotate around a fixed axis and function as mechanical levers. Our precise vibration measurements on malleus do not confirm this theory.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386748
In the present investigation, the characteristics of the integrated inner product calculation as a function of Doppler frequency present in signal analysis have been explored. The integrated inner produce is an estimate of the distance measurement in space or time between the reference signal and the target signal. Various techniques have been examined with the underlying goal to increase the speed of the actual calculations and possible interpretations for varying scaling and translation parameters. The integrated linear productor distance measurement as a function of scaling, translation and frequency is shown graphically. All computations and graphical depictions are performed using Mathematica.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386749
We present a new technique for identifying the dynamics of bolted joints. The technique relies on the comparison of the overall dynamics of the bolted structure to that of a similar but unbolted one. The difference in the dynamics of the two systems can be attributed solely to the joint; modeling this different in the dynamics enables us to construct a nonparametric model for the joint dynamics. Noncontacting, laser vibrometry is utilized to experimentally measure the structural responses with increased accuracy and to perform scans of the structural modes at fixed frequency. A numerical algorithm is then developed to post-process the experimental data and identify the joint force. Theoretical calculations are first used to validate the technique, which is then utilized to identify a practical joint. Experimental force-displacement plots at the joint reveal clear hysteresis loops which, in turn, can be used to estimate the damping dissipation at the joint. Moreover, experimental frequency responses and scans of the mode shapes of the bolted structure reveal nonproportional damping and nonlinear effects due to micro-impacts of the connected beams at the bolted joint.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386750
The development of mechanical vibration generators (shakers) used in the precise calibration of accelerometers requires minimizing the amount of distortion and cross (transverse) motion present in the vibration of the moving element of the shaker. It is well known that both distortion and cross motion can introduce significant errors in the calibration of accelerometers. Potential effects on measured sensitivity due to the presence of harmonic distortion were determined experimentally. Varying amounts of harmonic distortion were systematically introduced into the drive signal of a shaker. Changes in the measured sensitivity of an accelerometer were noted for these varied amounts of distortion and compared with theoretical predictions. Measurements of the sensitivity of an accelerometer were also made using moving elements having varying amounts of cross motion in order to experimentally determine potential effects due to the presence of cross motion on measured sensitivity. The results of this study should be helpful in the development of error budgets for accelerometer calibration systems and in the design of shakers used as a part of such systems.
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Steven Pauwels, Nick Boucart, Benoit Dierckx, Pieter Van Vlierberghe
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386751
The use of a scanning laser Doppler vibrometer for vibration testing is becoming a popular instrument. The scanning laser Doppler vibrometer is a non-contacting transducer that can measure many points at a high spatial resolution in a short time. Manually aiming the laser beam at the points that need to be measured is very time consuming. In order to use it effectively, the position of the laser Doppler vibrometer needs to be determined relative to the structure. If the position of the laser Doppler vibrometer is known, any visible point on the structure can be hit and measured automatically. A new algorithm for this position determination is developed, based on a geometry model of the structure. After manually aiming the laser beam at 4 or more known points, the laser position and orientation relative to the structure is determined. Using this calculated position and orientation a list with the mirror angles for every measurement point is generated, which is used during the measurement. The algorithm is validated using 3 practical cases. In the first case a plate is used of which the points are measured very accurately, so the geometry model is assumed to be perfect. The second case is a brake disc. Here the geometry points are measured with a ruler, thus not so accurate. The final validation is done on a body in white of a car. A reduced finite element model is used as geometry model. This calibration shows that the new algorithm is very effective and practically usable.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386752
Laser Doppler Vibrometry is now a well established experimental technique. Single beam and parallel beam instruments for translational and rotational vibration velocity measurements are now commercially available and gaining in popularity. 30 years ago, one of the first reported uses of laser vibrometry concerned rotating turbine blade vibrations. Non-contact operation and inherent immunity to target shape still prompt instrument manufacturers to quote measurement from rotors as a key application area. Success in these early investigations actually relied on the existence of only a single vibration component while significantly more complex motions are encountered in practice. This paper sets out a comprehensive model of the velocity sensed by both a single laser beam and by a pair of parallel beams incident on a rotating shaft element requiring three translational and three rotational co-ordinates to describe its vibratory motion fully. While the intention is obviously to measure the six vibration components, the model reveals how it is instead only possible to measure six vibration `sets', each inseparable combinations of more than one of the vibration components. Arrangements for isolation for each `set' are set out and an essential post-processing technique to resolve translational and rotational vibration components is demonstrated. This paper will prove to be an invaluable guide to the engineer wishing to take advantage of the powerful benefits of laser vibrometry while avoiding the possibility of serious data misinterpretation.
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Franco Alasia, Sergio Baggia, Giuseppe Basile, Galt Booth, Fabrizio Mazzoleni
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386753
In this paper the characteristics of a test bed for checking the theoretical behavior of a multi reflection interferometer are described. This optical interferometer has to be coupled to a shaker for the absolute determination of the vibration amplitudes. Its capability of producing four reflections on the measuring beam on the vibrating table, before its recombination with the reference beam, allows to extend the frequency limit at which the optical signal is still satisfactory. The test bed reproduces the working conditions, including the limitations to tilting, optical path length, alignment... and has the objective of experimentally confirm the feasibility study.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386755
An unbalanced object that rotates may present a characteristic vibration amplitude at an specific frequency. Pulsed electronic speckle pattern interferometry is a non- destructive electro-optical technique well suited to study this rotating-vibrating object. Fringe data is initially qualitatively analyzed while being observed in real time on a TV monitor, and later quantitative data can be extracted using one of several methods reported in the literature. However, if an object derotator is not available the resulting fringes are composed of a mixture of rotation and vibration fringes, making of a qualitative and quantitative analysis an almost impossible task. The present paper proposes a method to separate the fringes due to rotation from those produced solely by vibration. The method is based on a high precision scheme that synchronizes and fixes an object point during rotation, and assumes a resonant mode of object vibration.
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Wojciech Bochenek, Zbigniew Motyka, Henryk Passia, Adam Szade
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386756
Continuous monitoring of long-term and sudden changes of tilt of building structures located in mining areas with various geological-tectonic conditions and forms of effects of underground mining operations, also reveals the influence of a number of other environmental and operational conditions. The following can be counted among them: climatic, road traffic, hydrogeological. They can be distinguished with a relatively high precision. Finally, the recorded changes (reaction of buildings) are the resultant of environmental (mining and others) conditions, type of the structure itself, its appropriation, and technical- operational conditions. High structures, e.g. chimneys, hoisting towers, react in a basically different way than the extended ones such as monumental (as an example) or residential blocks, especially of large-panel construction.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386757
The records of the acoustical holography imaging of 60 cm concrete cube model have been taken with the predetermined model lead intrusions. Both phase and amplitude holograms were obtained. Their numerical reconstruction enabled to visualize the cross-shaped structure of this model intrusion. The records for seismic imaging of near-surface objects were taken in the region of Barbara Experimental Mine, Mikolow, Upper Silesia region, Poland. The method of seismic transmission holography was used. The explosives were detonated at one point on the depth of 40 m and signals were recorded on the surface lattice of 21 X 21 points on 50 m square. These signals were further processed to obtain phase and amplitude holographic data. The seismic holograms synthesized in such a way that were numerically reconstructed. The Z-shaped image of the part of mine's gallery on the depth of 20 m was obtained.
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Paolo Castellini, E. Cupido, Nicola Paone, Enrico Primo Tomasini
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386758
Tracking Laser Doppler Vibrometry is presented. It is applied to track a linear translational motion of a timing belt for automotive applications, so that vibration is measured with respect to a moving reference frame fixed on the belt. Typical vibration signals are amplitude modulated and show vibration frequency modulated by operating deflection shape.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386759
This paper describes the application of a Tracking Laser Doppler Vibrometer to the measurement of side-wall vibration of a tire during its rotation. An optimized version of the TLDV was developed for the specific application. The developed system was therefore applied to a rotating drum bench on automotive tire. The new version of TLDV is presented and some results on real automotive tire are shown.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386760
This work is part of a research devoted to the development of a non-intrusive modal analysis procedure based on laser techniques both for excitation and for measurement. The attention is focused on the experimental evaluation of uncertainty sources in modal parameter measurement, when high energy laser pulses are used to excite the vibration of the structure. The tests were performed on a cantilever beam excited firstly with a hammer and then with laser pulses from a Nd-YAG source (532 nm, 100 mJ/pulse). The problem due to the lack of knowledge on laser-induced input force is here considered. This, in fact, makes the precise quantitative measurement of the mobility functions and of the damping ratio difficult. To this aim, an `equivalent' input force was estimated by solving an inverse problem: the `equivalent' force is useful to determine the features of the laser-induced impulsive excitation. The achieved results are in complete agreement with other characterizations presented in previous studies, in particular in terms of specific impulse, time duration and characteristic frequencies. Finally, several suggestions are given in order to minimize the influence of the problems connected with laser pulse excitation, in particular concerning the limited energy given to the structure under investigation.
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Gianluca Di Giulio, A. Nicolini, Gian Marco Revel, Enrico Primo Tomasini
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386761
In this paper the problem of vibration measurement and testing for quality control of electronic components is approached. In general, many tests are performed on electronic devices (personal computers, power supply units, lamps, etc.), according to international standards (IEC), in order to verify their resistance to shock and vibrations, but these are mainly `go no-go' experiments, performed on few samples taken from the production batches. The idea here proposed is to improve the efficiency of these tests by using electro-optic techniques for the measurement of the vibration behavior of the components under known excitation. This would allow the on-line testing of a high percentage of the production and would be useful to give important feedback to the design process. Scanning laser Doppler vibrometry seems to be a valuable solution for the problem, thanks to its capabilities of measuring several spatially- defined points on a vibrating object with reduced testing time for on-line application, with high sensitivity and accuracy, non-intrusivity and with any kind of excitation signal. Experimental tests are performed on a power supply: the results show the effectiveness of the proposed approach.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386762
In this work the advances of the damage detection and characterization technique based on laser Doppler vibrometer is presented. In particular the algorithms for data processing are analyzed in detail, discussing the advantages and the limitations. Finite element model was employed for the controlled characterization of the procedure. With respect to the previous works, the aim of the present one is to further improve reliability, easiness and readability of the output of the diagnostic procedure and to reduce the amount of the relevant data to be managed. A new algorithm is presented and discussed in detail and numerical and experimental tests are presented.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386763
In this paper, an extremely small, simple and economic laser Doppler sensor is presented. It simply consists of a laser diode and of an optical system composed by two lenses in order to focus the laser light. The sensor is able to measure velocity and it is based on the self-mixing effect that occurs in a semiconductor laser diode when the emitted radiation is back reflected toward the cavity and then re- introduced inside. The velocity is calculated measuring the position of the frequency peak on the frequency spectrum of the intensity signal generated by the photodiode present inside the laser diode when modulated by feedback light coming from the moving scattering particles. The laser Doppler self-mixing velocimeter has been statically calibrated, using a rotating disk covered with white paper. The sensor has then been dynamically characterized using an electro-magnetic shaker and a Laser Doppler Vibrometer as reference.
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M. Gioffre, V. Gusella, Roberto Marsili, Gianluca L. Rossi
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386764
The use of accelerometer based measurement techniques for evaluating bridge forced vibrations or to perform bridge modal analysis is well established. Some of the goals of this experimental approach and typical results are here reviewed. It is well known to all researchers who have experience in vibration measurements that values of acceleration amplitude can be very low at low frequencies and that a limitation to the use of accelerometer can be due to the threshold parameter of this kind of transducer. Under this condition the measurement of displacement seems more appropriate. On the other hand laser vibrometer systems detect relative displacements as opposed to the absolute measures of accelerometers. In this paper the results of some in field measurements on a highway little bridge, excited by traffic, under normal operating conditions, are analyzed. Vibrations have been measured simultaneously by a typical accelerometer for civil structures and by a laser vibrometer equipped with a fringe counter board in terms of velocity and displacements. The accelerations calculated from the laser vibrometer signals and the one directly measured by the accelerometer has been compared. The advantages of the use of a laser vibrometer at low frequency are relevant and it appears possible to open up new possibility to analyze bridge loads in operating conditions, monitoring bridge health state, predict fatigue life and improve the bridge design.
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T. Di Giacomo, Raffaella Di Sante, G. Ferri, Gianluca L. Rossi, Claudio Santolini, Enrico Primo Tomasini
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386765
A major problem in directly measuring synchronous belt noise is that, often, the noise coming from bearings, fans or any type of vibration transmitted through the belt drive may be taken for belt noise. In the automotive field, most of the times, the noise generated by belt drives is estimated using microphones in the proximity of belt, crankshafts, idlers...Such a method can be misleading, since it may easily include the contribution of background noise at some frequency. Moreover, a big amount of data is needed to test different layouts and running conditions. This work aims at developing a tool for estimating the acoustic radiation of synchronous belts during the design stage, one of the main objects being that of reducing the high number of tests currently employed.
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S. Goumas, M. Zervakis, A. Pouliezos, G. S. Stavrakakis, Enrico Primo Tomasini, Nicola Paone, Lorenzo Scalise
Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386766
This paper presents a method for extracting features in the wavelet domain of vibration velocity transient signals of washing machines, that are then used for classification of the state (acceptable-faulty) of the product. The Discrete Wavelet Transform in conjunction with Statistical Digital Signal Processing techniques are used for feature extraction. The performance of this feature set is compared to features obtained through standard Fourier analysis of the stationary part of the signal. Minimum distance Bayes classifiers are used for classification purposes. Measurements from a variety of defective/non-defective washing machines taken in the laboratory as well as from the production line are used to illustrate the applicability of the proposed method.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386767
Almost forty years ago the electric bass was invented and after some years it established itself as the most important source of low frequency sounds in modern music. This work will aim at studying the vibrational behavior of this instrument using, as much as possible, exciting sources related to its normal use, namely acoustical waves and short pulses applied on the strings. A characterization of the forces applied while playing will also be briefly performed along with a description of the basic features of different musical signals.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386768
Sequential double exposure holographic interferometry is employed for examining the mechanical effects induced in the UV ablation of polymers. Deformations, evidenced by changes in the refractive index of the substrate, are observed to develop at unexpectedly long distances (approximately equals 2 - 5 cm) from the irradiation area. The morphology of the induced effects depends on the substrate properties, with the major types observed being tentatively ascribed to delaminations and local fractures. For accounting for the highly delocalized spatial spread of the effects, laser doppler vibrometry was used for monitoring the propagation of the stresses generated by the ablation process. The examination confirms the development of intense vibrations far from the ablation point. The present results suggest that in UV laser processing of molecular substrates, the photomechanical effects can be significant and special attention should be paid in their characterization and their minimization.
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Proceedings Volume Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (2000) https://doi.org/10.1117/12.386769
Laser interferometers are being used to measure a single linear degree of freedom reflecting the motion in a direction of a pointing laser beam. In a recent study, the need to measure both linear and angular transient behavior of a slowly sliding rigid mass has risen. For this purpose a special signal processing method, which is backed by a special hardware, was developed. An experimental system set- up to measure the motion of a mass connected to a cantilever beam sliding upon a rough surface will be described in this work. During sliding, the mass is subject to friction forces that give rise to stick-slip type of motion in the horizontal direction of motion and to vibration of the dragged mass in the vertical and angular directions. The basis of the proposed method is described and the relevant physical assumptions alongside with the mathematical procedure are provided.
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