Research On Signal Detection And Nonlinear Calibratiao Algorihtm Optimization Of Homodyne Laser Vibrometer

The homodyne laser vibrometer has the advantages of simple optical path,high measurement accuracy and high integration.It can realize accurate measurement of engineering quantities such as vibration,displacement and acceleration,which is widely used in scientific research and precision industrial production.In recent years,the rapid development of ultra-precision manufacturing and micro-electromechanical system engineering has raised higher measurement speed and accuracy requirements for homodyne laser interferometers.First,in high-speed vibration measurement applications,due to the bandwidth limitation of the signal detection unit,homodyne laser interferometers cannot effectively measure high-speed vibrations.Second,due to the low robustness of existing nonlinear error correction algorithms,In the actual measurement,it is difficult to effectively correct the nonlinear errors in the actual measurement,so that the vibration measurement cannot meet the high precision requirement.This dissertation,“Homodyne laser vibrometer signal detection and nonlinear correction algorithm optimization research” mainly focuses on the two issues above: implementing high-bandwidth and low-distortion detection of optoelectronic signals through studying-the experimental design and theoretical analysis,identifying the main factors influencing the bandwidth of the signal detection unit,and optimizing the design of detection unit pointedly;proposing a nonlinear correction optimization algorithm with high robust by deeply analyzing the defects and deficiencies of existing nonlinear error correction algorithms and agreeing the vibration characteristics with the actual measurement target.Finally,a homodyne laser vibrometer was designed and developed.The main research work of this dissertation is as follows:In view of the current problem that homodyne laser vibrometer cannot measure highspeed vibration,three main defects in the current photoelectric detection module is pointed out through experimental analysis: low bandwidth of trans-impedance amplification circuit,inconsistent phase characteristics between measurement channels,and harmonic distortion remaining in output signal of photodetectors.-To overcome these defects,firstly,based on the original design of the trans-resistance circuit,a high-gain,high-bandwidth trans-impedance amplification function is realized by optimizing the chip selection and resistance-capacitance matching;Secondly,the symmetry among the detection channels of each circuit is improved to maintain the same phase characteristics among multi-channel detections.At the same time,additional phase delays introducing by differences among the phase characteristics of high-speed signals are reduced by a reasonable PCB design;Finally,a high bandwidth and low distortion photoelectric detection performance is achieved by eliminating the output distortion of the photodetectors with analyzing the relationship between linearity of photodetector and output beam diameter as well as designing a reasonable beam diameter relative to the problem of harmonic distortion of the photoelectric signal in the measurement process.In view of the problem that the low robustness of the existing nonlinear calibration algorithms and the difficulty in effectively correcting nonlinear errors in actual measurements,firstly,it is thoroughly analyzed that the imperfect interference signal,which means when the amplitude of the interference signal changes,defects existing correction algorithm;Secondly,links targeting to affecting the correction result are optimizing designed in order to improve the accuracy of the DC offset calculation,enhance the stability of the output signal amplitude and eliminate the data overflow during the correction process,which effectively improve the robustness of the nonlinear correction algorithm.Based on the above research,this article developed a high bandwidth and high robust homodyne laser vibrometer.Equivalent experiment and actual test results show that the signal bandwidth of the homodyne laser vibrometer developed by this project is 5MHz,and the harmonic rejection ratio is 55 d B.It is proved that the robustness of the nonlinear correction algorithm is improved.Also,a residual nonlinear error less than 2 nm is obtained with the interference signal with an amplitude modulation depth of 0.8.