Development of a continuous scanning laser Doppler vibrometer with bow scanning compensation

This paper addresses a vibration mode shape measurement technique utilizing a continuous scanning laser Doppler vibrometer (SLDV). The scanning capability is added to the conventional discrete laser Doppler vibrometer by reflecting the laser beams on the surface of the object using two oscillating mirrors. The bow scanning resulted from the proposed scanning mechanism is compensated by using the geometrical relation between the bow scan beam trajectory and perfect sinusoidal beam trajectory. If a continuous sinusoidal scanning method is used, it can be shown that the velocity output signal from the SLDV is modulated to give the spatial velocity distribution in terms of coefficients which are obtained from the Fourier transformation of the time dependent velocity signal. Using the Chebyshev series form, the analysis of the vibration mode shape technique for 2 dimensional area scanning are presented and discussed. The performance of the proposed SLDV is presented using the experimental results of the vibration mode shape of a plate.