| With the rapid development of precision manufacturing industry,it is an urgent problem to realize nano-scale manufacturing accuracy in micro-electronic integrated circuit manufacturing technology and ultra-precision machining technology.Therefore,precision displacement measurement technology emerges as the times require.Laser interferometry displacement measurement technology,represented by homodyne interferometer and heterodyne interferometer,is widely used in the precision manufacturing field because of its advantages of large measurement range,high accuracy,fast measurement speed,non-contact measurement and meter traceability.Combining the advantages of homodyne interferometer and electro-optic phase modulation technology,based on the phase-modulated homodyne interferometry,a phase-modulated homodyne interferometric nano-displacement measurement system is designed and its performance is evaluated by some experiments.In this thesis,the performance of a phase-modulated homodyne interferometer with different structures is tested from two aspects of static stability and periodic nonlinear error.The structure of the interferometer is further optimized through the test results.Finally,the common optical path structure with good static stability and small periodic nonlinear error is selected as the optical path design scheme of the phase-modulated homodyne interferometer.The influence of polarizer installation error on the periodic nonlinearity error of the interferometer is verified by experiments.It is shown that the periodic nonlinearity error of the interferometer is the smallest when the laser beam is vertical linear polarized light,and the precision displacement measurement can be realized.Based on the principle of phase-modulated homodyne interferometric nano-displacement measurement,combined with the design of some common optical path structure,a four-in-one instrumental design of phase modulation homodyne interferometric nano-displacement measurement system is presented,which integrates signal processing hardware,upper computer operating software,hardware circuit and optical element mechanical structure.According to the need of interferometer signal processing,the signal processing board Redpitaya of FPGA+ARM is used to complete the signal processing process of modulation signal generation,PGC-Arctan signal demodulation and least square ellipse fitting correction of demodulated signal,and the real-time communication with host computer software is realized.On the basis of virtual instrument development platform LabVIEW,the upper computer operation software adopts modular design scheme and realizes the functions of PI guideway control,Renishaw contrast interferometer data processing and display,and reading,processing,displaying and saving the measurement results of phase modulation homodyne interferometer by serial communication.The hardware circuit consists of three parts: power supply circuit based on switching power supply and DC step-down dual output module,modulation signal amplifier circuit based on single operational amplifier and high voltage amplifier module and photodetector circuit.Based on the three-dimensional structure design software Solidworks,the design,simulation,processing and assembly of the components and the whole structure of the phase modulation homodyne interferometer are completed,and the rationality of the mechanical structure design is verified.In order to evaluate the performance of the phase-modulated homodyne interferometer,static stability measurement experiment,nonlinear error measurement experiment and displacement measurement experiment are designed.The static stability comparison experiment shows that the phase-modulated homodyne interferometer is more stable than Renishaw interferometer,and the drift is only 5.5 nm in 10 min test time.The experimental results of nonlinear error measurement show that the periodic nonlinear error of phase-modulated homodyne interferometer is less than 0.1 nm and repeatability.The average and standard deviation of the phase-modulated homodyne interferometer and PI-753.1CD guideway measurement errors are all within 1 nm through nanometer displacement measurement experiments.The average error of the phase-modulated homodyne interferometer is in the range of 0.73 nm~5.51 nm and the standard deviation of the error is in the range of 0.51 nm~2.25 nm in the micrometer displacement measurement experiments,which shows that the phase-modulated homodyne interferometer can reach nanometer level in micro-nanometer displacement measurement.Compared with a Renishaw interferometer in the experiments of millimeter displacement measurement,it is shown that the phase-modulated homodyne interferometer can achieve large-scale displacement measurement.The average displacement error is in the range of 6.58nm~163.85 nm,and the standard deviation of displacement error is in the range of 33.55 nm~ 62.24 nm.The above measurement results show that the phase-modulated homodyne interferometer developed in this thesis has high stability,small periodic nonlinear error and can achieve nanometer-scale accuracy measurement. |
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