Study of Image Enhancement for Capturing Vibration Signal of System in Operation
| Autor: | Yao-WenHsu, 許耀文 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 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. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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