Research On The Vibration Masurement Using Optical Interferometry

Optical interferometry enjoys many unique advantages of being noncontact, nondestructive, high precision and resolution, therefore has the broad and particular application prospect. Generally there are two types of optical interferometry techniques:camera-based whole-field optical interferometry and photodetector-based laser Doppler vibrometry. Vibration measurement using both the two methods are researched in this paper. Digital holographic interferomery is selected as the representative of camera-based whole-field optical interferometry.With the fast-developing computer science and CCD technology, digital holography becomes a focus of attention in optical interferometry field. The factors influencing the resolution of digital holographic interferomery and reconstructed complex amplitude are analyzed. The disadvantages of current processing method in phase domain are analyzed. A new method based on three-dimensional windowed Fourier processing is proposed to extract vibration parameters from the complex amplitude difference sequence. The proposed method can solve many problems in convenient processing method and improve the precision of vibration parameters extraction.Windowed Fourier transform is the core of this proposed new method. Its performance depends on the preset window size. How to select the optimal window size is explored in this paper. The relationship between the optimal window size and frequency is given and verified by both the numerical simulation and experiment.Two experiments are designed and conducted to measure the random vibration of a chloroprene rubber latex membrane and the simple harmonic vibration of a small cantilever. The windowed Fourier processing in complex domain is employed to retrieve the displacement, velocity and acceleration precisely.Compared with the whole-filed optical interferometry, laser Doppler vibrometry provides a extra high temporal resolution but a bad spatial resolution. The multipoint laser Doppler vibrometry with a single light source and photodetector is described in this paper. The vibration sharp is measured and reconstructed by the combination of polynomial interpolation and windowed Fourier transform. The spatial resolution and measurement precision can be improved.The steady-status vibration and transient vibration of a cantilever beam is measured using the multipoint laser Doppler vibrometry. The vibration sharp is reconstructed by the proposed combined method of polynomial interpolation and windowed Fourier transform.