Study On Nanometer Displacement Measurement Based On Differential Michelson Interferometer

With the rapid development of precision machining, microelectronics and other industries,high-precision displacement measurement techniques and their performance have becomeincreasingly demanding. In this thesis, relying on the National Natural Science Foundation ofChina (NO.51205365), a nanometer displacement measurement method based on differentialMichelson interferometer is designed. And the key technologies of this nanometer displacementmeasurement method are studied in this paper. By constructing a complete measurement system,nanometer-precision displacement measurement is achieved ultimately.The research status of nanometer displacement measurement technology at home andabroad is introduced in this thesis. Then a nanometer displacement measurement method basedon differential Michelson interferometer is proposed. And the principle of nanometerdisplacement measurement method based on differential Michelson interferometer is describedin detail. Then the structure of optical measuring system is designed. The mechanical supportstructure of the system is designed while the finite element stress analysis is completed. Thesignal pre-processing circuit and the voltage conversion circuit are designed, which is forimproving the quality of the interference signal and adjusting the signal voltage range. Ahigh-precision interference signal phase difference measurement method is designed, and thephase measurement accuracy and resolution were verified by experiments. Phase compensationmethod is designed to compensate phase measurement error which is caused by the changingspeed of moving. The measuring principle for counting integer numbers is introduced, and themethod for determining the moving direction of the reference mirror is designed. In addition, theDSP software is designed with C language and the PC system control software is designed withVB language.To confirm the feasibility and effectiveness of nanometer displacement measuring systembased on differential Michelson interferometer constructed in this thesis, by building anexperimental platform, the following experiments are carried out：(1) Interference signal phase difference compensation comparative experiments. Displacement measurement comparativeexperiments were carried out with50nm,200nm as steps respectively. After compensation, thestandard deviation of the measurement error reduced from1.0108nm to0.5686nm and theaverage deviation of the measurement error reduced from0.7648nm to0.4616nm when the stepsize is50nm. After compensation, the standard deviation of the measurement error reduced from1.4188nm to0.5687nm, the average deviation of the measurement error reduced from1.1115nmto0.4838nm when the step size is200nm.(2) The fractional count displacement measurementexperiments. The fractional count displacement measurement experiments were accomplishedwith5nm,10nm,20nm,50nm as steps respectively. And the corresponding standard deviationsof error were0.4697nm,0.6317nm,0.7594nm,0.6644nm.(3) Integer count displacementmeasurement experiment. Experiments were carried out in both positive and negative directions.It verified the correctness of the integer count in the range0-7μm with0.5μm as step. The resultsshow that the whole count error is less than half wavelength which is consistent with theinterference fringe displacement measurement theory and indicates the correctness of integercount.(4) Combining experiment of integer and decimal displacement. The repeatabilityexperiments of displacement measurement with steps of1μm and7μm were carried outrespectively. The corresponding standard deviations of measurement error were1.3199nm and0.9184nm and the average deviation were1.1057nm and0.9179nm. The above experimentalresults show that the proposed method can achieve nanometer accuracy of displacementmeasurement with good reliability and stability.