本文探討應用高速攝影機補捉振動訊號時，改變目標物之明暗對比和攝影機之對焦與否的效應，以測試此種影像數據收集系統的應用範圍。因為是初步研究，本文固定攝影機的焦距於30公分位置，在該位置改變攝影機鏡頭與被測物的距離，以產生失焦效應。針對振動物之影像明暗對比研究，則以改變背景之明暗以襯托影像之明暗效應，以及外加含有黑色十字線之白色紙張兩種方方法測試之。測試時固定攝影機之取樣頻率為232fps，暴光值為2000。本文先在距離激振器0.3、0.6、1、2、和4m位置上放置高速攝影機以掘取影像訊息，測試不會產生殘影之不同頻率之激振器的振動訊號。測試時以灰色和白色兩種背景配合有無外加強化明暗對比之白色紙張，以產生4種不同組合的影像明暗對比。本文從所攝取的連續明暗影像種，選取不同位置之50 X 50像素正方形，將該區域內的灰階值累加，可得到time series訊息，經使用快速疊代型率波器移除time series數據串中的趨勢線後，使用Fourier sine spectrum產生器求取其頻譜。實驗數據顯示不論在有或沒有正確對正焦距的情形下，只要訊號的明暗對比度合理，高速攝影機仍然有機會補捉到振動訊息。加強影像明暗對比例子之數據說明，在較遠的失焦距離下仍可以補捉到振動訊息。但不同距離所攫取的振動數據，因為所涵概的範圍也不同，故需做進一步研究。其後測試一台電動小型直升機的運轉訊息，也得到同樣的效果。本文研究結果顯示，使用高速攝影機攝取振動機件，只要以簡單方式強化目標之影像的明暗對比，即使攝影機對焦不盡理想，仍可忠實的得到振動訊息。故此種遠距離非接觸式的振動數據收集系統，具有很大的潛力應用到不同的自然或實驗場合。

By varying two conditions, the capability of capturing the vibration signal with the image frames grasped by a high speed camera is examined. The first one checks the in or out of focusing state of the camera and the second changes the span of brightness of the image. For the sake of simplicity, this study fixed the focus length to be 0.3m. The image signals were taking at the following distances between the target surface and camera lens: 0.3, 0.6, 1, 2, and 4 meters. Except the 0.3 m case, the high speed camera was out of focus in all the rest of cases. Four different spans of brightness were generated by using a gray and white background shields together with or without attaching a white paper sheet marked a black cross lines. At first, the vibration signals of a vibration exciter with different frequencies were examined. For each image frame captured by the camera, the gray level within a square of 50 X 50 pixels were summed up and were referred to as the vibration signal at the corresponding time. Subsequently, a time series data string of the image signal was obtained. After filtering out the trend via the fast iterative Gaussian smoothing method, the Fourier sine spectrum of the sinusoidal part was obtained in which the vibration modes can be faithfully obtained. Experimental data showed that, when the brightness degree of the image signal is relatively low and the lens is seriously out of focus, the vibration signal may not be captured. After properly enhancing the brightness, the vibration mode can be reflected even when the camera is still out of focus. Notice that, since the region enclosing the image changes as the distance between the target surface and camera lens is changed, the interpretation of the grasped spectral data should be carefully addressed via extensive further study. A series of tests to grasp the operation spectrum of a small electric helicopter also show similar results. All the data show that the non-contact type image data acquisition system can grasp vibration signal in the state of out of focus by properly enhancing the degree of brightness of the target surface. In other words, the image data acquisition system is suitable for a severe environment.

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