The present work deals with the analysis of problems and potentials of laser vibrometer measurements inside vehicle cabins in running conditions, with particular reference to helicopters where interior vibro-acoustic issues are very important. This paper describes the results of a systematic measurement campaign performed on an Agusta A109MKII mock-up. The aim is to evaluate the applicability of scanning laser Doppler vibrometer (SLDV) for tests in simulated flying conditions and to understand how performances of the technique are affected when the laser head is placed inside the cabin, thus being subjected to interfering inputs. First a brief description of the performed test cases and the used measuring set-ups are given. Comparative tests between the SLDV and accelerometers are presented, analyzing the achievable performances for the specific application. Results obtained measuring with the SLDV placed inside the helicopter cabin during operative excitation conditions are compared with those performed with the laser lying outside the mock-up, these last being considered as "reference measurements." Finally, in order to give an estimate of the uncertainty level on measured signals, a study linking the admitted percentage of noise content on vibrometer signals due to laser head vibration levels will be introduced.
This paper describes the design, realization and testing of an optical scanner for real time on-line detection of the shape
of wood-panels entering a sanding machine on a transport belt. The paper describes the options considered for the design
of the triangulation sensor, taking into account target performance specifications and geometrical constraints. Final
design is a folded optical system which employs two laser line projectors and one CMOS camera, operated over a limited
Region of Interest. Sensor calibration is outlined and examples of on-line measurements on moving panels are presented.
The paper presents the analysis of metrologic performance and measurement uncertainty of an optical scanner for the
measurement of surface profile of large size panels designed to operate on-line in real time on moving panels in a noisy
industrial environment.
After a brief discussion of standards relevant to this type of sensor and of sensor specifications, an analytical model
developed for the sensor design and for the uncertainty budget estimation is described.
In addition, rather than presenting the common analysis of uncertainty of laser scanners based on the modelling of the
image formation and processing, this paper addresses this question through a black-box approach, analysing the whole
system as a sensor and therefore performing an experimental evaluation of uncertainty which embodies all possible
sources of uncertainty, according to type A and type B approaches of the ISO-Guide to The Expression of Uncertainty in
Measurement, which is an uncommon approach in the field of laser scanners calibration and represents the main novelty
of this paper.
Deterioration of wood artwork is often connected to mechanical material degradation that starts on microscopic scales. Insight into decay mechanisms can be obtained by monitoring surface microscopic deformation and displacement fields. This paper presents the application of Electronic Speckle Pattern Interferometry (ESPI) to detect invisible on the surface intrinsic defects of a wood samples. The different artificial defects were created under the pine wood surface to simulate "defected" samples. The fiber-optic ESPI set-up based on a He-Ne CW laser has been developed and used for the studying the possibility determination of locations, sizes and shapes of wood defects. For this end two digital holograms of the test object, corresponding to vibrating states of the non-heated and heated states of object, are captured at two video frames of the CCD camera, transferred in a frame-grabber and then processed in a PC. The resulted the fringe pattern has the information about the defects. Obtained fringe patterns of all defects are presented. The purpose of work was determining the sensitivity of ESPI method in application to different sizes and forms of defects.
In this work a procedure for the aero-acoustic characterization of air jets was presented. The ability of a laser vibrometer to assess the changes in the optical path induced by local fluctuation of air refraction index was used to calculate the pressure oscillations produced by turbulence. The signal from the laser must be treated in order to extract the required information. From the pseudo velocity, which represents the integral of the refraction index distribution along the laser beam, it is possible to calculate, by a tomographic algorithm, the volumetric distribution of the refraction index at each frequency, and then the pressure oscillation. Each pressure voxel represents a sound source, i.e. monopole, that gives contribution to the Sound Pressure Level in each point of the surrounding. The uncertainty of the procedure was also evaluated.
In recent years, a great effort has been done to improve damage detection techniques in structures by using vibration measurements. This paper presents a case where a non-contact measurement system, a Scanning Laser Doppler Vibrometer, has been used to detect delaminations in a composite material plate. The diagnostic technique is the evolution of a methodology previously approached by the authors. An in-house made software has been produced for data acquisition and vibrometer control. The maps of the detected defects are presented, thus allowing the assessment of the performances of this methodology to detect damages. This analysis permitted to outline the main points to be improved in the future investigations.
The use of artificial heart valves is more and more diffused in the medical practice in particular in Europe and US where the average age of the people is continuously increasing. In the engineering point of view they present several problems that can be faced by a deep knowledge of the behaviour in operative conditions. Such problems are mainly related to the compatibility with the patient body and the reliability of the valve itself, and both are related to the possibility of a continuative and extended application in real cases. The compatibility is mainly related to the material choice and to the fluid-dynamic behaviour. The reliability can be basically improved by a smart and simplified design of each component, which imposes a really intensive evaluation of the response to operative inputs. Fatigue is one of the most important effects related to reliability. A mechanical valve is subjected to fluid-dynamics forces and repeatable shocks. due the impact on the constraints, which create dangerous vibrations. The analysis of such vibrations by SLDV[1][2] in both free and operative conditions is the main task of the present work. In this paper an experimental and numerical analysis of the vibrational behaviour of a mono-leaflet valve was performed in order to extract useful information on the optimised design. An in vitro test, simulating operative conditions, was performed in order to verify the real behaviour of the valve.
In the present work the development of a customised vibrometer able to work on Microsystems is shown. The system is based on a commercial Laser Doppler vibrometer, in which the optical set-up, the mechanical arrangement and the processing software and hardware were modified and developed to measure vibrations of small object with a resolution in the micro scale. The main characteristics of this system is a very versatile platform, in which laser Doppler Vibrometry, two-axis stages micropositioner, digital signal processing and image acquisition and processing can work together in order to obtain the integration of vibration measurements with other experimental techniques. The system developed, which represents the first step in this project, has been applied to a typical test case in order to verify performances and limits. A discussion about main features and limits is presented.
Red blood cell damage (hemolysis) and thromboemblism are the main complications associated to the implantation of mechanical artificial heart valves. In the last decades a great number of in vitro studies have been conducted to improve the design and to understand the transvalvular flow patterns under steady state and pulsatile conditions. Steady state tests are useful to study the flow established upstream and downstream the valve prosthesis in the moment of the peak flow rate. In the present study, Particle Image Velocimetry (PIV) technique was employed to visualise the flow patterns in a pre-commercial model of bi-leaflet mechanical heart valve prosthesis in a steady state flow. PIV technique and a convenient test rig have provided good conditions to investigate the whole flowfield upstream and downstream the valve.
Laser diagnostic systems based on shearography, vibrometry, and holography principles were employed to investigate the potential implementation of laser techniques in art conservation structural diagnostic field. The employed techniques offered the required measuring variability to allow a first discrimination on complex diagnostic uncertainties encountered often in art conservation. The systems were tested and used to assess the structural condition of well-documented Byzantine icons with known structural problems. Defects and mechanical deformations were identified in various distances from the artworks by alternative employment of techniques. In this way simultaneous eligibility classification of the used systems was also obtained. Results of the on-field application on the XVII century Byzantine icons are herein presented with discussion on the prospects of the techniques in the diagnostic field of art conservation.
During the last years the growing importance of the correct determination of the state of conservation of artworks has been stated by all personalities in care of Cultural Heritage. There exist many analytical methodologies and techniques to individuate the physical and chemical characteristics of artworks, but at present their structural diagnostics mainly rely on the expertise of the restorer and the typical diagnostic process is accomplished mainly through manual and visual inspection of the object surface. The basic idea behind the proposed technique is to substitute human senses with measurement instruments: surfaces are very slightly vibrated by mechanical actuators, while a laser Doppler vibrometer scans the objects measuring surface velocity and producing 2D or 3D maps. Where a defect occurs velocity is higher than neighboring areas so defects can be easily spotted. Laser vibrometers also identify structural resonance frequencies thus leading to a complete characterization of defects. This work will present the most recent results coming out of the application of Scanning Laser Doppler Vibrometers (SLDV) to different types of artworks: mosaics, ceramics, inlaid wood and easel painting. Real artworks and samples realized on purpose have been studied using the proposed technique and different measuring issues resulting from each artwork category will be described.
In this paper an experimental test bench for mechanical heart valve and the procedure for non-invasive optical measurement are reported. Fluidynamic behaviour of a bileafleat mechanical valve in steady state and pulsed flow conditions has been studied. Laser Doppler Anemometry (LDA) is used to access velocity and turbulence values at different distances before and after the mechanical valve. Data obtained can be related, according to the literature, to typical pathologies affecting patients who underwent surgical procedures to implant mechanical heart valves. In particular thrombosis and hemolysis can be related to high levels of shear stress affecting blood cells. Measurements of velocity, turbulence and shear stresses have been performed.
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.
KEYWORDS: Vibrometry, Composites, Damage detection, Data processing, Diagnostics, Data modeling, Signal processing, Doppler effect, Finite element methods, Actuators
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.
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.
KEYWORDS: Doppler effect, Mirrors, Computer programming, Vibrometry, Control systems, Denoising, Sensors, Laser systems engineering, Data acquisition, Signal attenuation
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.
Thermal effects caused by 532 nm Nd:YAG laser pulses on human tooth surface are investigated using an IR high frame rate (60 Hz) detector (256x 256 elements, Indium Antimonide, with 3-5 μm spectral bandwidth). Measurements of the temperature on a reference line of the tooth surface during exposure to laser pulses of 0.5 W of power, with time amplitude of 12 ns and 10 Hz of frequency repetition are performed. Images and maps of temperature of the human to the surface are shown during laser treatment. Results are discussed with particular reference to the possibility to evaluate thermal effects of pulsed lasers of frequent use in dentistry and to the application of such lasers as excitation sources for non- destructive defect analysis of human teeth by laser Doppler vibrometry.
Frescoes, icons and composite materials show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; past experiences demonstrated that the study of surface vibrations could be used to locate defects position and size. At present a non- invasive diagnostic system is under development and the aim of this work is to propose and compare different kinds of structural exciters. After initial measurement set-ups based on accelerometers and impact hammers, a novel system based on laser vibrometers and acoustic stimulation has been assembled; full remote and contactless investigation of detachments and delaminations is thus possible with a very high accuracy. At present three different types of acoustic sources are employed: unbaffled standard loudspeakers, horn loudspeakers and an elliptic mirror sound focuser. The last source has been developed to concentrate sound power in a very small area so to excite only localized defects of the structures and void annoying noises to be propagated around them. A new kind of exciter, namely a piezo actuator, has also been introduced in the measurement chain and its effectiveness in finding defects in icons will be demonstrated. This paper will present experimental result gathered from sample showing differences in data due to different exciting sources. A comparison with results furnished by traditional techniques will be shown.
The use of air compressed, high rotational velocity drill and of ultrasound devices in the dentist practice can cause pain for the patient and damage to the tooth structure. The authors in this paper have investigated the possible cause of these problems: the vibrations caused by the drill exciting the tooth. Particular attention has been dedicated to the frequency behavior of teeth, in order to individualize their frequency resonances. A method for the investigation of human teeth dynamic response, in terms of natural frequencies and modal shapes has been proposed. Very short laser pulses have been used to excite teeth vibrations and a scanning laser doppler vibrometer to measure the dynamic response. An assessment of the amplitude of the characteristics of the excitation has been done using the theory of the impulse response function in such a way as to calculate the frequency response of the teeth. The results measured have been compared. Results permit to extract information extremely useful for the design of devices used in the dentist practice.
In recent years damage detection techniques based on vibration data have been largely investigated with promising results for many applications. In particular, several attempts have been done to determine which kind of data must be extracted for damage monitoring. In this work scanning laser doppler vibrometry (SLDV) has been sued to detect, localize and characterize delaminations in composite materials. In order to improve understanding of the analyzed phenomena and to design efficient post-processing algorithms for experimental SLDV data, a theoretical lumped model has been developed by the authors. The model describes the dynamic behavior of the structure in the delamination zone. Following the model result, an experimental investigation by SLDV has been performed on panels with known detachments. Results have been compared with those achieved by thermal tomography, which at present is one of the most used techniques for monitoring the state of composite materials. The presented methodology has proved to be efficient also to determine the delamination deepness.
Frescoes and icons show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; the aim of this work is to develop a diagnostic system for the measurement of the defects position and size. After initial measurement set-ups based on accelerometers and impact hammers a novel system based on laser vibrometers and acoustic stimulation of structures to allow full remote and contactless investigation of detachments and delaminations has been developed. This paper presents a measurement procedure based on two subsequent scans of the work of art is employed; the first scan aims at finding defects positions the second one to characterize their resonant response. A new kind of exciters, namely piezo actuators, has been introduced in the measurement chain and its effectiveness in finding defects in icons will be demonstrated. Also an on field measurement session on large sample walls will be described along with the result obtained that show how efficient this technique has become.
Frescoes and icons show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; our aim is to develop a diagnostic system for the measurement of the defects position and size. We employ laser vibrometers and acoustic simulation of structures to allow full remote and contactless investigation of detachments and delaminations. The use of advanced measuring devices combined with computer data backup systems allow the restorers to follow damage evolution during time and to verify the effectiveness of their work. A full working experimental measurement set-up is described along with the results obtained. Extensive measurement sessions were performed with on purpose built frescoes and icons samples, presenting a wide range of defects positions and dimensions and different surface finishes and colors; results were then compared with those obtained by professional restorers by manual techniques. Further to this, we demonstrate that the simultaneous use of a complementary technique, IR thermography, allows also the measurement of complex defect structures, especially of superimposed defects at different layers interfaces.
A powerful technique for monitoring and analyzing mechanical systems is the application of laser Doppler vibration measurements. When the object to be analyzed rotates, the measurement becomes difficult. That is, when a steady laser beam is used, the presence of a tangential motion of surface determines a noisy disturbance. The speckle pattern produced by the roughness of the analyzed surface is moving with the surface itself, and this phenomenon is observed as a signal with a frequency depending on the rotational speed. For these reasons, the aim of the present work is to show the possibility of Eulerian approach to the vibration measurement of rotating objects. A Laser Scanning Vibrometer has been used for the tracking of the same point in the complete circular motion. The capabilities of this system are tested on the measurement of vibration map of blades of a model of naval propeller working in water: a comparison has been found with the static analysis, in water and air, of the same propeller. Some results are shown.
The paper presents the application of a laser Doppler vibrometer as a nonintrusive measurement technique to detect damage of frescoes paintings. Experimental verification is carried on a wall where detachment of the external layer from the inner substrate is artificially introduced. Impulse excitation shows that frequency response functions identify the presence of any damage. Laser beam scanning provides a way to remotely investigate large areas of paintings. Acoustic excitation is also tested; it allows to excite resonant vibrations on detached areas. A measurement procedure is proposed and tested on the experimental wall and on field tests performed on a real fresco inside a church.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.