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A new method for processing impact excited continuous-scan laser Doppler vibrometer measurements

机译：一种处理冲击激发连续扫描激光多普勒测振仪测量的新方法

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摘要

A scanning laser Doppler vibrometer (LDV) can acquire non-contact vibration measurements from a structure with high spatial detail in an automated manner; one only need redirect the laser via computer-controlled mirrors to acquire measurements at additional points. However, since most LDV systems are only capable of measuring one point at a time, conventional scanning vibrometry cannot be effectively employed in some situations, for example when the time record is long at each measurement point or when the structure changes with time. Conventional scanning LDV systems are also difficult to employ with impact excitation because there is considerable variation in the impact location, angle and the character of the impacts, which leads to errors in the mode shapes that are extracted from the measurements. This paper presents a method by which one can determine the mode shapes, natural frequencies and damping ratios of a structure from as little as one response record by sweeping the laser continuously over the vibrating structure as the measurement is acquired. A novel resampling approach is presented that transforms the continuous-scan measurements into pseudo-frequency response functions, so they can be processed using standard identification routines to find the modal parameters of the structure. Specifically, this work employs a standard multi-input-multi-output identification routine and the complex mode indicator function to the continuous-scan laser Doppler vibrometry (CSLDV) measurements. The method makes no assumptions regarding the shape or properties of the surface and only requires that the laser scan periodically and that the structure vibrate freely. The method is demonstrated experimentally on a free-free beam, identifying the first nine mode shapes of the beam at hundreds of points from a few time histories. For this system, this represents a two-order of magnitude reduction in the time needed to acquire measurements with the LDV.
机译：扫描激光多普勒振动计（LDV）可以自动从具有高空间细节的结构中获取非接触式振动测量值；只需通过计算机控制的反射镜重定向激光，即可在其他点进行测量。但是，由于大多数LDV系统一次只能测量一个点，因此在某些情况下，例如在每个测量点的时间记录较长或结构随时间变化时，常规的扫描振动测量法无法有效使用。传统的扫描LDV系统也难以与冲击激励一起使用，因为冲击位置，角度和冲击特性存在相当大的变化，这导致从测量中提取的模态形状中的误差。本文提出了一种方法，通过将激光连续扫描到振动的结构上，就可以从一个响应记录中确定结构的模态形状，固有频率和阻尼比，从而获得测量结果。提出了一种新颖的重采样方法，该方法将连续扫描的测量值转换为伪频率响应函数，因此可以使用标准识别例程对其进行处理，以找到结构的模态参数。具体来说，这项工作采用了标准的多输入多输出识别例程和复杂模式指示符功能来进行连续扫描激光多普勒振动测量（CSLDV）测量。该方法不对表面的形状或特性做任何假设，只要求激光扫描定期并且结构自由振动。该方法在自由光束上进行了实验验证，可以从一些时间历史中的数百个点识别出光束的前九种模式形状。对于该系统，这代表用LDV进行测量所需的时间减少了两个数量级。

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  • 来源
    《Mechanical systems and signal processing》 |2010年第3期|721-735|共15页
  • 作者

    Matthew S. Allen; Michael W. Sracic;

  • 作者单位

    Department of Engineering Physics, University of Wisconsin-Madison, 535 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706, USA;

    Department of Engineering Physics, University of Wisconsin-Madison, 535 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706, USA;

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