Accuracy and noise analyses of 3D vibration measurements using laser Doppler vibrometer (original) (raw)
Related papers
Journal of Sound and Vibration, 2000
This paper builds on a previous study of the velocity sensed by a single laser vibrometer beam incident on a target in an arbitrary direction to predict the velocity sensed by multiple laser beams with arbitrary orientations. The usefulness of parallel beam arrangements is demonstrated and a concise new theory for the di!erence velocity sensitivity for two parallel beams is presented. Parallel beam arrangements for virtually unambiguous measurement of torsional vibration are presented along with arrangements that allow measurement of the pitch and yaw vibration to be derived. Resolution of individual pitch and yaw motions is shown not to be possible by any geometrical arrangement of the beams but a post-processing technique that enables the genuine pitch and yaw vibrations to be estimated from the measurements of the pitch and yaw vibration sets is demonstrated and validated experimentally in the laboratory. Measurements of pitch and yaw vibration are, for the "rst time, obtained from the crank-shaft of a running diesel engine, enabling identi"cation of the "rst natural frequency of the crank-shaft in bending.
Measurement Science and Technology, 2003
This paper builds on a previous study in which the theoretical description of the velocity sensed by a single laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary vibration was extended to continuous scanning laser vibrometer measurements on targets with flexible cross sections. The velocity sensitivity model was written in terms of either laser beam orientation angles or deflection mirror scan angles, with the latter found to be the most useful for continuous scanning applications. The model enables the prediction of the laser vibrometer output for any measurement configuration on any target. The experimental validation presented in this paper confirms that additional components appear in rotating target measurements that are associated with both the scanning system configuration and any misalignment between the scanning system and target rotation axes. This paper will show how use of the velocity sensitivity model enables the vibration engineer to make laser Doppler vibrometry measurements with confidence.
Optics and Lasers in Engineering, 2017
Laser Doppler vibrometers (LDVs) are now well-established as an effective non-contact alternative to traditional contacting transducers. Despite 30 years of successful applications, however, very little attention has been given to sensitivity to vibration of the instrument itself. In this paper, the sensitivity to instrument vibration is confirmed before development theoretically and experimentally of a practical scheme to enable correction of measurements for arbitrary instrument vibration. The scheme requires a pair of correction sensors with appropriate orientation and relative location, while using frequency domain processing to accommodate inter-channel time delay and signal integrations. Error reductions in excess of 30 dB are delivered in laboratory tests with simultaneous instrument and target vibration over a broad frequency range. Ultimately, application to measurement on a vehicle simulator experiencing high levels of vibration demonstrates the practical nature of the correction technique and its robustness in a challenging measurement environment.
An international review of laser Doppler vibrometry: Making light work of vibration measurement
Optics and Lasers in Engineering, 2016
In 1964, just a few years after the invention of the laser, a fluid velocity measurement based on the frequency shift of scattered light was made and the laser Doppler technique was born. This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments. Consideration is first given to the challenges that continue to be posed by laser speckle. Scanning LDV is introduced and its significant influence in the field of experimental modal analysis described. Applications in structural health monitoring and MEMS serve to demonstrate LDV's applicability on structures of all sizes. Rotor vibrations and hearing are explored as examples of the classic applications. Applications in acoustics recognise the versatility of LDV as demonstrated by visualisation of sound fields. The paper concludes with thoughts on future developments, using examples of new multi-component and multichannel instruments.
Journal of Sound and Vibration, 2000
This paper presents a comprehensive analysis of the velocity sensed by a single laser vibrometer beam incident in an arbitrary direction on a target that is of substantial interest in engineering * a rotating shaft requiring three translational and three rotational co-ordinates to describe its vibratory motion fully. Six separate &&vibration sets'', each a combination of motion parameters, appear in the full expression for vibration velocity sensitivity and it is shown not to be possible to resolve individual motion components within each set by arrangement, or even manipulation, of laser beams. To place this non-contact transducer velocity sensitivity model in its proper context, the velocity sensitivity of a contacting transducer under identical conditions is also derived and comparison is made between non-contacting and contacting transducer performance. Speci"c applications of the laser vibrometer theory to radial and axial vibration measurements are set out and it is shown how estimation of radial vibration components is only possible by post-processing. The theory is easily extended to include measurements made with multiple beams, underlining the model's versatility in enabling determination of the vibration component sensitivity of a measurement with any beam orientation or combination of beam orientations. This will prove bene"cial in devising further optical con"gurations for the measurement of torsional, pitch and yaw vibrations.
Measurement Science and Technology, 2002
This paper describes the application of a tracking laser Doppler vibrometer (TLDV) for vibration measurements on automotive components and the advances in data processing. A Lagrangian approach is adopted: the target point moves continuously and it is tracked by the measurement laser spot, thus no relative velocity between the target and the laser spot exists. By eliminating the relative motion of the laser beam on the surface, speckle noise is drastically reduced. Measuring on a moving reference frame opens an innovative way to look at automotive component vibrations, because the space-time evolution of the vibration can be measured under simulated operative conditions. After a presentation and discussion of the measurement technique, attention is focused on three different applications in the automotive field: the side-wall vibration of a rolling tyre, the out-of-plane vibration of a timing belt and the rubber blade vibration of complex motion windscreen wipers. The development of optimized TLDV measurement systems for each specific application is shown and some results are presented.
XI International Conference on Structural Dynamics, 2020
Despite widespread use in a variety of areas, in-field applications of laser Doppler vibrometers (LDVs) are still somewhat limited due to their inherent sensitivity to vibration of the instrument sensor head itself. Earlier work, briefly reviewed herein, has shown it to be possible to subtract the instrument vibration via a number of means, however, it has been difficult up to now to truly compare the performance of these. This is compounded by the constraint that a frequency domain based approach only holds for stationary vibration signals while, particularly for in-field applications, an approach that is also applicable to transient signals is necessary. This paper therefore describes the development of a novel time domain post-processing based approach for vibrating LDV measurement correction and compares it with the frequency domain counterpart. Results show that, while both techniques offer significant improvements in the corrected LDV signal when compared to a reference accelerometer measurement, the time domain based correction outperforms the frequency domain based method by a factor of eight.
Measurement of trajectories of piezoelectric actuators with laser Doppler vibrometer
2011
Various measurement techniques have been developed f r analyzing performance of piezoelectric devices. Recently laser Doppler vibro meter (LDV) has become a widely applied instrument for vibration measurements both in scien tif c studies and industry. The most common type of LDV is a single-point vibrometer. In this article we propose a system consisting of the single-point LDV, beam deflector and mirrors, which enable automated 2D/3D trajectory or 2D vibration measurements, where a hi gh number of target points can be measured with a very high spatial resolution. We used two te st objects to demonstrate the performance of the system: piezo-actuator, which transforms vibrat ons to the rotational movement and a micrometric screw with piezo-adjustment.
2003
It is readily accepted that a Laser Vibrometer measures target velocity in the direction of the incident laser beam but it is essential that, for correct measurement interpretation, the target velocity be considered in terms of the various target motion components. This paper begins with a review of the theoretical description of the velocity sensed by a single laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary motion. For continuous scanning Laser Doppler Vibrometry, the velocity sensitivity model is shown formulated in two useful ways. The first is in terms of the laser beam orientation angles, developing the original model to incorporate time dependency in the angles, whilst the second is expressed in terms of the scanning mirror angles, since it is these that the operator would seek to control in practice.