低頻振動之頻譜分析及其對高科技廠房精密儀器之影響

The Spectral Analysis of Low Frequency Vibration and Impact on Precision Tools of High Tech Fab

陳錦村(Chin-Tsun Chen)

指導教授 ： 張陸滿

共同指導教授 ： 羅俊雄(Chin-Hsiung Loh)

國立臺灣大學/工學院/土木工程學研究所/博士(2020年)

https://doi.org/10.6342/NTU202004190

摘要

許多精密內儀器，為了降低微振動的干擾，裝設了主動隔振系統，而依照隔振理論，在頻率小於√2倍系統自然頻率的振動是會被放大的，反而讓精密儀器對低頻振動更加敏感，低頻振動雖然不會造成破片等直接損失，但可能造成生產良率降低、儀器當機等之間接損失。由於低頻振動對高科技產業越來越重要，所以有必要對傳統頻譜分析方法和低頻振動來源重新檢視。作者發現頻譜分析所取的時間長度(頻率解析度)，會影響頻譜分析的結果，尤其是低頻暫態振動，然而，對進行頻譜分析所取的時間長度，目前並沒有標準或規範可供依循，例如造成當年台南科學園區高鐵振動的議題，各家顧問公司的分析沒有共同的基準，分析結果的比較各說各話，導致不少爭議。本研究旨在探索頻譜分析所取的時間長度(頻率解析度) 如何影響頻譜分析的結果，並深入討論其理論基礎和詳述頻譜分析的步驟，以及透過補零(zero-padding)的方式進行頻譜分析。本研究同時以高鐵在高架橋上行駛和車輛在平面道路上行駛所引起的暫態振動，和環境背景微振動進行不同方法的分析比較，分析結果驗證了利用補零(zero-padding)的方式獲得較細的頻譜分佈寬度，可以提高低頻振動分析的精確度，可為不同研究者之間建立共同比較的基礎。
另外，來自遠方且規模大地震可能包含長週期的地震波，週期可能長達10秒以上(0.1 Hz以下)，此種遠域地震並不會造成建築物的損壞或讓人員產生不適，然而當震幅達一定大小，可能會對高科技廠房內的振動敏感機台產生影響。本研究利用台灣的強地動觀測網的地震紀錄和高科技廠房內的地震觀測系統，分析了10個遠域地震的震波內涵特性，利用奇異譜(Singular Spectrum Analysis)分析萃取地震波特性，同時藉由探討高科技廠房關鍵機台掃描機(scanner)的動力行為特性，使用0~0.7 Hz間的累積功率頻譜密度(accumulative power spectral density)和低頻加速度(low frequency acceleration)計算震幅，然後討論震波週期和震幅與掃描機當機的關聯，最後對遠域地震所引起的低頻振動的防治對策提出了可行的方法。

關鍵字

頻譜分析 ； 低頻振動 ； 車輛引起之振動 ； 補零 ； 1/3八倍頻 ； 遠域地震 ； 高科技廠房

並列摘要

The precision tools equipped with active vibration isolation platform in high-tech facilities are sensitive to low frequency vibration. Currently, there is neither standards nor rules to select the time period of vibration data for conducting the spectral analysis of low frequency vibration, and none of the analyses can be used to compare and discuss the differences of spectral amplitude generated by the selection of different time periods. Therefore, the spectral analysis at low frequency range is a crucial issue to estimate the amplitude of low frequency vibration. This thesis is to elaborate the spectral analysis procedures on the vibration signal with various band widths by using zero-padding on the vibration signal in low frequency band. The mechanism not only facilitates obtaining more reliable result but also laying a common base for comparison among various users. Finally, the in-situ measurement data, including high-speed train induced low frequency vibration, will be used to exemplify the length of time period affects the results of spectral analysis, either on narrowband or one-third octave band analysis.
Besides, the vibration of long period signal and seismic records collected from far distant and large magnitude earthquake may also induce long period seismic waves. These long period seismic waves may have dominant period up to 10 sec but with small amplitude which may cause the shut-down of high precision tools in high-tech fab. For general type of structures this kind of seismic waves may not endanger the safety of the structural system or cause any uncomfortable for human activity. On the contrary, for those far distant earthquakes, the long period seismic waves may induce significant damage for some crucial tools in high tech Fab if the amplitude generates resonant effect on the fab structure and/or tools. In this study, the characteristics of long period seismic wave for the pre-event data from each seismic event was investigated. The dominant frequencies of these data were extracted by using singular spectrum analysis (SSA) and multivariate singular spectrum analysis (MSSA). Through the investigation of the dynamic behavior characteristic of crucial tool scanner of high-tech Fab, cumulative PSD (Power Spectral Density) and low frequency acceleration between 0 and 0.7 Hz was used to estimate the amplitude. Discussion on the proposed two features, dominant frequencies and amplitude, among recorded seismic events and the damage severity to the high tech facilities will be made. Finally, the countermeasure of slope index which could provide earthquake early warning to avoid the impact of far distant earthquake induced low frequency vibration will be recommended.

並列關鍵字

spectral analysis ； low frequency vibration ； traffic-induced vibration ； zero-padding ； 1/3 octave band ； far distant earthquake ； high-tech Fab

參考文獻

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