Research On Simultaneous Measurement Of Straightness And Displacement Using A Modified Wollaston-prism-sensing Heterodyne Interferometer

As an important support for the development of advanced manufacturing,precision measurement technology and instruments are necessary guarantees to promote the development of advanced manufacturing technology.Straightness is a significant parameter of various motion platforms or guide rails in precision instruments and equipment,and directly affects the performance and quality of the equipment.Based on the development needs of precision instruments and equipment,this paper proposes a heterodyne interferometer for simultaneous measurement of straightness error and displacement using a Wollaston prism as the mobile sensor.The dual quadrature phase-locked amplification is used in signal processing to achieve phase demodulation,and the phase difference method is adopted to compensate for periodic nonlinear errors,which effectively improve the straightness and displacement measurement accuracy.Through the research on high-precision measurement technology,a heterodyne interferometer for simultaneous measurement of straightness error and displacement is proposed.A modified mobile sensor composed of a Wollaston prism and a semi-transmissive plane mirror is adopted to obtain straightness and displacement information simultaneously.The phase information is demodulated by the double phase-locked amplification method.Finally the straightness error and displacement can be measured with high accuracy.After the research and analysis of the periodic nonlinear error and the influence of the Wollaston prism’s roll angle on the nonlinearity,the phase-differential measurement model of straightness error and displacement is established.By obtaining the straightness and displacement phase differential signals at the same time,the periodic nonlinear error compensation of the measurement system is realized.Through the simulation analysis of the measurement model,it is verified that the phase difference method is effective in compensating the nonlinear error,and the straightness nonlinear compensation effect is not affected by the roll angle of the measuring mirror.Based on the principle of double phase-locked amplification,a signal processing method is designed.The design of the signal processing hardware system is completed based on FPGA and Quartus II development environment.The software of the measurement system is designed based on the Lab VIEW development platform.The phase demodulation,data calculation and processing can be accomplished in the signal processing system.The signal processing method verification experiment has proved the effectiveness of the dual phase lock-in amplification phase demodulation method.In the 0.1μm step straightness and displacement measurement experiments,the standard deviations are 4.511 nm and 3.245 nm,respectively.An experimental device of the proposed heterodyne interferometer is set up,and three kinds of experiments have been conducted,including the viability verification experiment,the Wollaston prism’s roll angle error influence experiment and the application verification experiment.The viability verification experiment has proved the effectiveness of phase differential measurement method for compensating periodic nonlinear errors.In the 0.01μm step phase-differential displacement measurement experiment,the nonlinear compensation effect can be effectively improved by appropriately adjusting the position of the optical axis of the quarter-wave plate.The minimum nonlinear error of the phase differential displacement measurement is 2.154 nm.In the 0.15μm step phase-differential straightness error measurement experiment,the nonlinear errors of the single-channel measurement type are16.960nm～19.754 nm and 11.281nm～13.325 nm,respectively,and the nonlinear error of the phase-differential type is less than 5nm.In the experiment of Wollaston prism’s angle-error influence,the linearity of the single-channel measurement is affected by the roll angle.The nonlinear error of the phase-differential method is about 5nm,and the compensation effect is not affected by the roll angle error.The application verification experiment has proved the practicability of the proposed measurement system.In the millimeter stepping experiment,comparing the measured data of the Renishaw interferometer and the developed measurement system,the standard deviations of straightness error and displacement are 0.231μm and 0.258μm,respectively.