Velocity Measurement Based On Laser Self-mixing Interference And Its Application

Laser self-mixing interference(SMI)originates from optical feedback effect.Compared with traditional interference technology,it has the advantages of simple optical path,self-collimation,and compact structure,and can be applied to the measurement fields such as vibration,displacement,speed,and distance.The fluctuation frequency of SMI is the Doppler shift of the laser after the light interacts with an external object,and thus SMI can be used to measure the velocity of light.In this paper,SMI and MSMI are used to measure the velocity and reconstruct the velocity of the object movement.At the same time,velocity measurement based on SMI is applied to the bearing fault diagnosis to expand the application scope of the technique.First of all,this paper introduces the theory of SMI and uses the three-mirror cavity model to discuss in detail and explains the effects of SMI from several aspects,including different feedback levels,different linewidth enhancement factors,different amplitudes of object,and different movements of object.The above analysis laid the theoretical foundation for subsequent research.Secondly,based on the relationship between Doppler effect and SMI,the basic principle of SMI velocity measurement is studied.In order to solve the problem that the Fourier transform can only analyze the velocity of the object globally,the method of segmental Fourier transform is adopted to obtain the relationship of the frequency and with time,and the reconstruction of the object velocity is achieved.Then,the forming process and the theoretical model of Multiple Self-Mixing Interference(MSMI)are analyzed.According to the feature of doubled fringe resolution,a method of velocity measurement using MSMI is proposed and its calculation formula is deduced.Then the reconstruction of the object's velocity is achieved through Fourier transform.This algorithm is not only suitable for objects with different reflection surfaces,but also has lower measurement error than SMI.Finally,according to the advantages of MSMI,such as simple structure,easy alignment of light path and non-contact,a method of judging bearing fault signal based on MSMI is proposed.Compared with the traditional contact-type measurement of the acceleration sensor,the measurement error caused by the increase of the overall mass of the measured object caused by the contact can be avoided.