DEVELOPMENT OF THREE-DIMENSIONAL VIBRATION MEASUREMENT SYSTEM USING LASER DOPPLER VIBROMETERS
DEVELOPMENT OF THREE-DIMENSIONAL VIBRATION MEASUREMENT SYSTEM USING LASER DOPPLER VIBROMETERS
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发表时间：
2005
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通讯作者：
T. Miyashita;Y. Fujino
中科院分区：
文献类型：
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作者：
T. Miyashita;Y. Fujino
This paper presents the development of a high precision three-dimensional measurement system using single point type Laser Doppler Vibrometers. The following fundamental issues were studied and the results presented: measurement principle, accuracy with respect to long distance measurements and laser beam angles. As examples of possible applications of the system, measurements of ground motion and wave propagation in a plate were treated. INTRODUCTION Damage to civil infrastructure has occurred because of aging or deterioration, resulting in a need to develop effective and qualitative structural health monitoring (SHM) techniques. The Laser Doppler Vibrometer (LDV) is an effective device for SHM applications. By utilizing a LDV, non-contact and long distance measurement are possible. Moreover, multiple point measurement is made possible by the use of a scanning unit. Kaito et al. developed a spatial vibration measurement system using a Laser Doppler Vibrometer. Using measured ambient vibration, a damage detection technique was developed in order to assess the structural integrity quantitatively. Using this technique, changes of plate stiffness and mass were detected, including the presence of a void inside a concrete block (Kaito et al., 2001). As an application of the LDV system to real structures, Kaito et al. applied the vibration measurement system to steel and reinforced concrete girders of existing viaducts. The mode shapes were identified and the quality of measurement was quantitatively evaluated (Kaito et al., 2001). In previous studies using the LDV system, only one-dimensional measurements were conducted. The investigations showed the shortcomings present in a one-dimensional measurement system. First, it was observed that for high accurate measurement, compensation of laser beam angles was required. Second, it was impossible to distinguish in-plane vibration components and out-of-plane vibration components. To overcome these shortcomings, three-dimensional measurements using LDVs is being considered. Three-dimensional vibration components of a body are measured by three single point LDVs. The principle of three-dimensional measurement involves a geometrical transformation of coordinates. The rectangular three-dimensional vibration components of the body are determined by multiplying the measured vibration from the three LDVs by a transformation matrix consisting of the direction cosines of the laser beam angles. The objective of this study is the development of a high precision three-dimensional measurement system using LDVs. In this paper, a three-dimensional measurement system using three single point type LDVs is proposed. First, the following fundamental issues were investigated: measurement principle, accuracy of laser beam angles and long distance measurement. Lastly, as possible applications of the measurement system, measurements of ground motion and wave propagation in a plate were also treated. 3D VIBRATION MEASUREMENT USING LASER DOPPLER VIBROMETERS Laser Doppler Vibrometer Laser Doppler vibrometer (LDV) is an optical instrument employing laser technology to measure velocity of points on a vibrating object. Velocity is measured based on the Doppler effect, which induces a frequency change between the radiation laser beam and the reflected laser beam. The characteristics of the LDV are: first, compared with conventional transducers such as accelerometers, non-contact and long distance measurement (up to 30 m) is possible without adding mass or stiffness to an object. Advances in Experimental Structural Engineering Itoh and Aoki (eds.) ISBN 4-901887-19-X 649
