Development Of A Straightness And Its Position Measurement System Based On Laser Heterodyne Interferometer

Straightness is a geometric characterization of the parameters of mechanical properties,straightness error detection is one of the most important research field in precision measurementtechnology. The present researches of straightness measurement at home and abroad aresummaried, the advantages and disadvantages of straightness measurement methods arediscussed and the research of the instruments based on laser heterodyne interferometry is done inthis thesis.The method of the two degree freedom measurement and the system based on laserheterodyne interferometry principle are described in this thesis. The measurement error ofstraightness and position of the optical elements are analysed, the corresponding mathematicalmodel is constructed and the Simulation is done, the result of which shows that: Nonlinear errorof elliptical polarization of laser beam is the major one in all kinds of affecting factors instraightness measurement and the value of which is up to1000nm; The error of straightnesscaused by laser beam angle floats, the polarization spectroscope and polarization analyzer isaround50nm; The error produced by inclination angle of Wollaston mirror and the corner cubeis a sinusoidal error, the amplitude of which is about20nm in the position measurement and800nm the straightness measurement.The signal processing system corresponding to the method given in this thesis based onFPGA is designed and a new interferometer signal processing method is proposed. For themethod, one signal delayed45degree is generated besides the original measurement signal, andif the phase displacement between them approaches to0,180and360degree, the phase isdemodulated from the original signal and the delayed signal, otherwise the phase is demodulatedfrom the reference signal and the original measurement singal, which can reduce the measuringerror. The program of FPGA based on Verilog language is written, which is used to do phasedemodulation and communicate with computers. The measurement software based on Visual Basic is designed which is used to analyse the data from signal acquisition system and finallygives the result of straightness and its position.In order to verify the feasibility of the developed interferometer system, the experimentswith the displacement step inscrement of10μm、100μm、250μm、500μm and1000μm are carriedout separately, the displacement error is given by comparing the results from the comparedexperiments between the data of the Interferometer system proposed in this thesis and the data oflinear stage of M-521.DD(Physik Instrumente). The results shows that the average of thedisplacement errors of position is2μm, the mean square deviation of which is1μm, the averageof the errors of straightness is300nm and the mean square deviation of which is900nm.