Research On The Comprehensive Vibration Measurement Of Shaft System Based On Laser Doppler Effect

Rotating machinery is widely used in industrial compressors, aircraft engines, turbines and motors of various mechanical devices, and the rotary shaft is the key to ensure the normal operation of the equipment. The monitoring of the bending vibration and torsional vibration of rotating shaft system is an important means to identify and determine the reliable mechanical equipment. Currently,the flexural and torsional vibration of shafting are generally measured by the independent method, but due to the bending and torsional vibration coupled with each other, and the measurement information is difficult to accurately characterize the vibration characteristic of the shaft. In this paper, a method for measuring the comprehensive vibration of the rotating shaft is proposed, based on the laser Doppler vibration measurement technology, in order to realize the shaft bending vibration and torsional vibration are measured simultaneously.A kind of bending and torsional vibration measurement system is designed based on laser Doppler vibration measurement technology. That is, using the same laser source to generate double beams through a multi beam splitter, for acquiring the instantaneous speed of different measuring points on the same cross section of the shaft, the different direction vibration interference are eliminated by the double photoelectric detector, and realizing the measurement of bending and torsional vibration finally. Combining with the optical beat and the reference light technology, a mathematical model of the optical system is built, and the theoretical derivation is carried out at the same time.The experimental platform of this measurement system is built and the corresponding experiments are completed. The AC component of the coherent optical frequency difference is obtained by the preprocessing of signal denoising and amplification. And the Doppler shift value is obtained by the method of spectrum rearrangement in time frequency analysis, which is based on the data processing platform of MATLAB software. the accurate measurement of the torsional vibration is realized by calculating the instantaneous speed and the shaft bending vibration value. In addition, the on-line vibration measurement of the cutting spindle of the CNC milling machine is carried out, and combiningwith the set speed, it shows that: the instantaneous velocity measurement error of this system is less than±2 r/min, which can satisfy the comprehensive measurement of shaft vibration in high speed rotating state.The influence of glass micro beads and micro prism reflecting film on Doppler signal of shaft vibration is explored, and the test and comparison of different reflective films are carried out. The results showed that: using a reflecting characteristic of glass microsphere reflection film on the measured shaft can effectively improve the rough of shaft, which formed on the surface of the speckle interference and the rotating shaft is not sensitive to laser reflection on the measurement result influence. Finally, the measurement uncertainty of torsional vibration measurement system is analyzed, which proved the feasible and reliable of the system, and also provided a reference for the measurement of high speed and precision.