电子散斑干涉法在振动测量中的物光位相调制法

介绍的物光正弦调制法是给振动物体的基座以低频振动,相当于物光位相受到正弦调制,仪器在不“冻结”参考状态(即CCD采样的信号不在帧存器中锁定)时,连续进行相邻两时刻散斑图的“相减”,并在监视器上得到与振型有关的实时图象。当物体达到自振频率时,将出现清楚的振型。因此,本方法可进行频率扫描,通过观察监视器的条纹场确定各阶自振频率及相应的振型,其条纹分辨率高于时间平均法,与相减法比较则可在很宽频率范围内进行频率扫描。 

PHASE MODULATING IN ESPI FOR VIBRATION PATTERN MEASUREMENT

The conventional method of electronic speckle pattern interferometry (ESPI) for vibration pattern measurement is to freeze reference beam.This method enables to sweep over a wide frequence range and to identify resonant modes.However,the obtained fringe contrast is not too fine.In order to eN_hance the visibility of fringe pattern,it is possible to subtract two time average pattern at any given frequancy.In result,the fringe pattern is obtained with high visibility but only valid at the given frequency.A phase shifting technique is adopted to overcome this shortcoming.A time average image is put into processor and frame store(renewed and put into processor per 40ms),then a subsequent image with a phase shift of ΔΦ resulted from sinusoidal modulation in object beam is recorded and subtracted from the first image.This method is similar to modulation of light intensity function of speckle pattern.The advantage of this method is the capabilities of obtaining real time fringe pattern of vibration with high resolution and of performing frequency scanning at a wide range.Its application to the vibration pattern measurement of disk blade coupling in an aeroengine is a great success.