Study On Measurement Algorithm Of Vibration Parameters Based On Self-mixing Interference System

Since the discovery of laser self-mixing interference in 80 s of last century,as a new sensing principle,it has been applied to measurement of physical quantities such as mechanical quantities,geometric parameters,material parameters,laser parameters and so on.Especially in recent years,more and more domestic and foreign researchers have invested in the research of laser self-mixing interference sensing system,and have made fruitful achievements in measuring algorithm design,measuring system hardware structure design and application.Vibration and displacement measurement is a classic application of laser self-mixing interference system.There have been a large number of research results,some commonly recognized measurement algorithms have been designed,however,there are still many improvements in the existing algorithms in the theoretical model,resolution and accuracy.In this paper,the self-mixing interference signal filtering algorithm,vibration frequency measurement algorithm and vibration trajectory reconstruction algorithm are studied in the laser self-mixing interference micro vibration measurement system.The main works are as follows.In the laser self-mixing interference system,the self-mixing interference signal has different characteristics due to the change of the measured object and the measured parameters,and the different measuring environment.This requires that the filter should automatically adjust the filter parameters to achieve the best filtering effect when the signal is changed.In this paper,aiming at the characteristic of selfmixing interference signal and considering the realization of hardware,an adaptive filter is designed.Secondly,the measurement algorithm of the vibration frequency is studied in this paper.Two algorithms of frequency measurement are designed,which are simple,real-time and easy to implement.The first method is called the feature point method.It is based on the self-mixing interference signal adaptive filtering,differential,shaping,feature extraction and then calculate the vibration frequency.The secondmethod is an autocorrelation function method with strong anti-interference ability.This method is based on the relationship between the fundamental frequency of the autocorrelation function and the vibrational frequency.Through collecting the data of the interference signal,calculating the autocorrelation function and detecting the peak value,the cycle of the autocorrelation function is determined,and the vibration frequency is obtained.Finally,in order to obtain the more vibration parameters of the measured object,based on the characteristics of self-mixing interference signal under the moderate light feedback level,this paper design the vibration trajectory reconstruction algorithm.Based on the mathematical model of the self-mixing interference displacement measurement system,the data dictionary and the vibration direction function of the measured object is constructed.According to the linear relationship between the displacement of the object and the initial phase of the interference signal,the initial phase of the acquisition of the interfered signal is collected.Thus the displacement is obtained in real time and the vibration trajectory is reconstructed.The validity of the algorithm is verified by simulation and experiment.The results verify the effectiveness of the algorithm.