Rotational Speed Measurement Based On Laser Self-mixing Speckle Interferometry

With the rapid development of the petroleum industry,the requirements for the stability and service life of petroleum equipment for oil well operation are becoming stricter and stricter in industry.The rotating speed of rotating parts in petroleum equipment has become an important factor affecting the stability and service life of the equipment.Therefore,it is particularly important to calibrate and test the rotating speed of rotating parts before and during the operation of petroleum equipment.At this time,there is an urgent need for a non-destructive and high precision rotating speed measuring device.In this paper,the rotation speed measurement based on laser self-mixing speckle interferometry is proposed.By processing the self-mixing speckle signal,the rotation speed measurement of the rotating object with rough surface can be completed.It is hopeful that the rotation speed monitoring and calibration of the rotating device in petroleum equipment can be realized.Laser self-mixing speckle interferometry combines self-mixing interferometry with speckle effect.When the speckle signal carrying the motion information of rough object surface is fed back into the laser cavity,a self-mixing speckle interferometry is formed,which can measure the velocity of rough object.By processing the self-mixing speckle interferometric signal,the physical properties of objects are measured,which overcomes the complexity of traditional contact measurement and reduces the cost of devices by using fewer components.The speed measurement method based on self-mixing speckle interferometry has the advantages of compact,simple,non-contact and easy collimation.At the same time,it has high accuracy for object measurement.In this paper,the theoretical model of self-mixing speckle interferometry is established based on the F-P cavity model of three-cavity mirror,and the formation mechanism of self-mixing speckle interferometry signal is explained.Based on the analysis of the theory of self-mixing speckle interferometry,two signal processing methods,fast Fourier transform and autocorrelation spectrum solution,are proposed to extract the frequency shift of the collected self-mixing speckle signal.By analyzing the frequency shift,the rotation speed of the object can be determined.Firstly,the validity of the two methods is proved theoretically.Secondly,based on the two methods,a platform for measuring the rotational speed of rough objects is built.The rotational speed of rough turntable is measured in the speed measurement experiment,which shows the feasibility and validity of the two methods.Finally,a method of measuring the rotational speed of double turntables based on self-mixing speckle interferometry with single optical cavity and double cavities is proposed,which uses a laser to measure the rotational speed of two independent turntables.In this paper,the feasibility of this method is proved theoretically and experimentally.The self-mixing speckle pattern interferometry with single light and double cavities not only simplifies the experimental device,but also can measure the speed of two rotating objects.The device has a certain application prospect in the speed measurement and calibration of petroleum equipment.