Rotation Speed Measurement And Signal Processing Based On Laser Self-mixing Speckle Interference

Optical non-contact measurement is widely used due to its advantages such as low loss and high accuracy.However,when non-contact measurement is performed on the target by traditional methods,the measurement system is often accompanied by problems such as complex equipment,large optical paths,and difficult signal processing.The personnel proposed to analyze the target motion parameters by analyzing the laser self-mixing interference(SMI)signals.The SMI can be described as a laser beam irradiated on the target surface,the target reflects the incident light,and feeds back the laser cavity to modulate the output of the laser,and then obtains the movement state of the measured target by analyzing the SMI signal.In the previous SMI research,there is a high requirement on the surface roughness of the measured target.Usually,the SMI signal generated by laser irradiation on the mirror surface is analyzed to achieve measurement,but there is less research on the measured target surface as a rough surface.In response to this problem,this paper combines SMI with the speckle effect caused by laser irradiation on rough surfaces,and proposes the analysis based on the laser self-mixing speckle interference(SMSI)signal to realize the rotational speed of the rough surface target.The speed measurement methods proposed in this article can reduce the requirements for the surface roughness of the measured target in the SMI field,realize the processing of random signals,solved the problem of complex signal processing,high sampling rate,and signal preprocessing in the past.The method can reduce the cost and expanded into a new type of speed measurement sensor,which is used in various industries for the measurement of speed.The research of this paper is mainly divided into the following four aspects:1.Based on the analysis of SMI theory and SMSI theory,an equivalent physical model Fabry-Perot(FP)model is established to analyze the phase change caused by the laser modulation of the measured target surface.Provide theoretical support for signal processing and speed measurement based on SMSI.2.Based on the theoretical analysis of SMSI,a rotation speed measurement method based on the grating self-mixing speckle frequency shift is proposed.By analyzing the power spectrum of the SMSI signal,the frequency offset of the SMSI signal generated when the object moves is extracted to realize the measurement of the rotational speed of the rough surface target.It is proposed to use the diffraction characteristics of the grating to eliminate the influence of the incident angle of light on the measurement results in the measurement,reduce the influence of the working wavelength on the speed measurement accuracy,and achieve high-precision measurement of low-speed objects.3.In order to improve the speed measurement range and realize the measurement of high speed targets under the condition of low sampling rate,this paper proposes a speed measurement method based on cross-correlation laser SMSI.That is,two semiconductor lasers are used to illuminate the target surface at the same time.When the target moves,any point on the target surface passes through the two lasers,and the two SMSI signals are processed by the cross-correlation algorithm.The delay,combined with the distance traveled,gives the rotation speed of the measured object.This method can solve the problem of higher sampling rate required in the previous high-speed measurement methods,and does not need to pre-process the SMSI signal,which simplifies the experimental process and can realize the measurement of high-speed objects with low sampling rate.4.Rotation speed measurement based on auto-correlation SMSI method is proposed.This method simplifies the experimental system while retaining the advantages of the cross-correlation SMSI rotation speed measurement method.Only a semiconductor laser is used to illuminate the measured target surface.When the target object moves for a period,the SMSI is collected.The signal is subjected to auto-correlation calculation to obtain the rotation speed of the target.