The hammering method used by inspectors is generally applied to inspection of looseness of bolted parts. This method entails active sensing through the input of an excitation signal produced by the inspectors, and has the advantage of practical experience acquired over many years. The sound (vibration) and sensation produced upon excitation by a hammer can be used as indices, but also leads to the disadvantage of unavoidable qualitative testing and human error. Laser remote sensing (LRS) uses the same diagnostic principle as the hammering test for remote, high-speed, and quantitative inspection. However, the accuracy of LRS must be improved and the required pulse energy must be reduced. Hence, we propose the sweep pulse excitation method, which realizes LRS with low pulse energy through the resonance oscillation caused by sweeping the laser irradiation frequency. A performance test on bolted joints was conducted with regard to bolt loosening diagnosis using two methods, namely, the conventional single-pulse excitation method and the sweep pulse excitation method. With the sweep pulse excitation method, the laser-induced vibration is produced only by absorbing the laser pulse energy which is caused by thermo-elastic waves and without using the elastic wave induced by the laser ablation. The experimental and calculation results reveal that, with the proposed method, the measurement accuracy improved by 10 4 times, while the required pulse energy decreased by 10 2 times. The adaptability of the low-pulse energy laser contributes toward the development of inspection systems because it achieves size and cost reduction, and inspection convenience.

中文翻译：

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基于扫描脉冲激励的高灵敏度低能激光传感用于螺栓松动诊断

检验员使用的锤击法一般用于检验螺栓连接件的松动。这种方法需要通过输入检查员产生的激励信号进行主动感应，并具有多年积累的实践经验的优势。锤子激发时产生的声音（振动）和感觉可以用作指标，但也导致不可避免的定性测试和人为错误的缺点。激光遥感 (LRS) 使用与锤击测试相同的诊断原理进行远程、高速和定量检测。但是，必须提高 LRS 的精度并降低所需的脉冲能量。因此，我们提出了扫描脉冲激励方法，通过扫描激光照射频率引起的共振振荡，实现低脉冲能量的LRS。采用常规单脉冲激励法和扫描脉冲激励法两种方法对螺栓连接处的螺栓松动诊断进行了性能测试。采用扫描脉冲激发法，只吸收热弹性波引起的激光脉冲能量，不利用激光烧蚀引起的弹性波，产生激光诱导振动。实验和计算结果表明，采用所提出的方法，测量精度提高了10 4 倍，而所需脉冲能量降低了10 2 倍。