Research On Simultaneous Measurement Of Straightness And Displacement Based On Laser Homodyne Polarization Interferometry

Straightness is an important geometric parameter to characterize the performance of precision guide rails or motion stages in various types of high-end equipment.High-precision measurement of straightness is a prerequisite for ensuring the overall performance of high-end equipment.Straightness measurement technology can be used for straightness error detection and calibration in the fields of ultra-precision machining,microelectronics manufacturing,and micro-electromechanical systems(MEMS).With the continuous advancement of the strategic line of manufacturing development,the role and position of measuring instruments are increasingly highlighted.However,there is a gap between our country with industrial developed countries in the latest precision measurement technology and instrumentation.In this dissertation,a method of simultaneous measurement of straightness and displacement based on laser homodyne polarization interferometry is proposed for the demand for high-end equipment manufacturing.It uses laser homodyne interferometry with less nonlinearity to achieve the high-precision measurement of straightness and displacement.A simultaneously measurement mathematical model of six-degree-of-freedom parameters such as straightness,displacement,and rotation errors is established.It makes full use of the high-precision measurement advantages of the laser homodyne interferometry to realize the measurement of four degrees of freedom parameters.Based on the coupling relationship of straightness,displacement and motion errors,the straightness and displacement measurement results can be compensated.From the actual implementation of measurement,the measurement model of straightness and displacement is derived.With the analysis and optimization of the optical configuration from the aspects of the "common path" structure and the influence of air refractive index,a method of simultaneous measurement of straightness and displacement based on laser homodyne polarization interferometry is presented.By demodulating the displacement information of the two measurement beams through laser homodyne polarization interferometry,the straightness and displacement are measured simultaneously.Based on the optical configuration of the simultaneous measurement of straightness and displacement,a method of simultaneous measurement of six-degree-of-freedom parameters is proposed.The two-dimensional small angle measurement method based on homodyne interference fringe pattern analysis is used to detect the pitch and yaw error,and the collimation measurement method is used to detect the roll and horizontal straightness error.The simultaneous measurement of six-degree-of-freedom parameters is achieved,among them four degrees of freedom are obtained by the laser homodyne polarization interferometry.With the analysis of the effect of motion error on the measurement beams,an mathematical model for the motion error of simultaneous measurement of straightness and displacement is established.Combined with the analysis of the measuring beams' optical paths in the Wollaston prism,the straightness and displacement measurement results can be compensated accurately.For interference signals,a laser homodyne polarization interference signal processing method based on signal correction is proposed.The pre-processing and phase delay correction are used to correct the interference signals,and eliminate the effects of phase measurements due to DC bias,amplitude inconsistency,and phase non-orthogonality.With the interference signal integer counting method,a CORDIC fractional counting method is used to achieve high-precision phase detection.For interference fringe analysis,an interference fringe image processing method based on median filter,binarization,fringe separation,straight line fitting and straight line spacing calculation is proposed.For the laser spot position signals,the relationship between the differential current signal and the spot position of the four-quadrant detector is analyzed,and the parameter k used for conversing from the normalized coordinate to the actual coordinate is deduced and simulated.Finally,the software system for signal processing system is given,and each function module is introduced.For the polarization non-linear error of the measurement system,a nonlinear error analysis model based on the optical configuration of the simultaneous measurement of six-degree-of-freedom parameters is established.With the analytical model,the influences of the laser polarization ellipsometry,Wollaston prism installation error,double right-angle reflector roll error,quarter-wave plate installation error,and polarization beam prism installation error on straightness and displacement measurement are analyzed theoretically and simulated.For the environmental disturbance,the laser wavelength is corrected by the indirect air index measurement method(PTF method),and an anti-interference design is used to reduce the impact of external environmental disturbance on experimental measurements.For the straightness assessment,a straightness assessment method based on the least square and the binary search principle is proposed.A measurement system for straightness and displacement simultaneous measurement and motion error detection is constructed,and the feasibility verification experiment,comprehensive performance verification experiment and application verification experiment have been performed respectively.For the feasibility verification experiment,the experimental results show that the repeatability results of the simultaneous measurement of six-degree-of-freedom parameters are in accordance with the specifications of the measured stage.For the comprehensive performance verification experiment,the measurement data of the pitch error,yaw error,horizontal straightness error,vertical straightness error,and displacement are compared with Renishaw's XL80 interferometer measurement data with the standard deviations of 0.353 arcsec,0.414 arcsec,0.882 ?m,0.398 ?m,and 0.320 ?m,respectively.The roll error measurement data is compared with the measurement data of WL11 digital level meter,and the standard deviation is 0.839 arcsec.The experimental results show that the measured data of the proposed measurement system is in agreement with the measured data of the comparison.For the application verification experiment,the calibration of the VM1000 CNC machine tool's Y-axis stage was carried out,and the test results show that the proposed measurement system can be applied to the straightness calibration in the field CNC machine tools.