本文研究使用數位攝影機透過一對Ronchi 光柵，拍攝振動物件表面之連續影像，經由累加某一指定區塊的灰階值以獲得一時變訊號，同時也用加速規量測振動數據以茲驗證。
為了增強訊號強度並增加數據的可靠性，本文應用疊紋技術(Moire)對被測物體進行處理。考慮單、雙光柵以及不同的條紋間距，以分析不同的疊紋狀況下對時頻訊號的影響；並以游標尺量測振幅數據，藉此分析振幅對疊紋系統所得數據的影響程度。影像方面則討論不同條件下灰階累加法所得數據，以分析此系統的限制條件。
透過討論激振器的不同輸入頻率對影像數據捕捉頻率的影響，以期界定數位高速攝影機之殘留影像之時間常數。實驗結果顯示在輸入頻率為70Hz以下，不致於對頻率解析有太大影響，超過70Hz的輸入頻率則會產生與輸入頻率不相關的訊息。判斷本文所用的高速攝影機的殘像常數約為1/70秒。比較單、雙光柵的結果，發現雙光柵可以強化輸入數據，而降低殘像的影響。實驗也證明當振動器的振幅增大或者光柵條紋間距縮小時，會增加殘像的影響。而累加灰階值之像素區域也需要仔細選擇，否則會影響頻率判別。本文也以一架小型電動搖控直升機的訊號，說明影像數據系統可以補捉到低頻固定和變化的頻率訊號。

By accumulating grayscale data over all the pixels within a region of an image frame, a time series data string is referred to as the vibration signal of a vibration excited shaker. The image frame is captured by a digital video camera by attaching a Ronchi ruling gate on the surface of the shaker and/or putting another gate between target and camera. The signal of accelerometer is simultaneously taken to verify the image data.
The Morie pattern produced by the Ronchi ruling gate is applied to strengthen vibration signal and to identify the time constant of afterimage decay. The test of using a single Ronchi ruling gate shows that, for input frequency greater than and equal to 70Hz, the dominant mode of the image signal is not related to the input frequency of the shaker. If the frequency is less than 70Hz, the dominant mode’s frequency is almost equal to accelerometer signal. Therefore, it is identify that the time constant of the high speed video camera is around 1/70 second. This study also shows that images generated by two Ronchi gates can effectively suppress the negative effect of afterimage in capturing the dominant mode. The shaker’s amplitude, pitch of the ruling gates, and the region of accumulating the grayscale data can affect the capability of capturing the dominant mode. This study also employed the image system to identify the operation frequencies of a small electrical remote controlled helicopter. The image signal can faithful reflect the dominant and harmonics in the low frequency region (<70Hz) for both fixed and variable frequencies.

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