Study On Laser Heterodyne Interferometric Straightness Measurement And Compensation For Long-travel Precision Stage Metrology

Straightness error is an essential parameter in the field of geometric measurement,and plays an important role in the modern precision equipments and instruments manufacture.Among various straightness measurement methods,laser heterodyne interferometric method has been widely used due to its advantages of high accuracy of nanometer level,long travel of meters range and direct traceability to the definition of the meter and so on.However,except the error sources such as optical non-linearity,interference signal processing error and laser wavelength stability,the laser beam drift is a key factor that affects the accuracies of laser heterodyne interferometric straightness or displacement measurement,especially in the long travel measurement.In this thesis,the influence of the laser beam drift is analysed in detail,and a compensation method for straightness and displacement measurement of laser beam drift is proposed to reduce the influence of the laser beam drift,which aims to improve the straightness and displacement measurement accuracy for long travel precision stage.This thesis analyzes the development of present research on the straightness measurement as well as the determination and compensation method of laser beam drift.The method for straightness error and displacement measurement by combination of detecting the Doppler shift difference of two measuring beams and Doppler shift of one measuring beam is proposed.The optical layout of the measurement and compensation method for straightness and displacement in long travel precision stage based on laser heterodyne interferometry is designed.The mathematical model of separately detecting laser beam drift,yaw and pitch is established.The relationship between the laser beam angular deflection and the light spot position on the position sensitive detector during the measurement is analyzed.The laser beam drift on the horizontal and vertical directions as well as yaw and pitch are obtained.Then the influence of the laser beam drift on the measurement of straightness and displacement is analyzed and the compensation method of laser beam drift for straightness and displacement is proposed.At last,the signal processing system is designed and the measurement software is programmed based on the Visual Basic language.In order to verify the feasibility of the proposed system,an experimental setup was constructed and several experiments were conducted as follows:(1)The experiments of laserbeam stability show that the position stability of laser beam spot in x and y directions after compensation can be improved by more than 50%.(2)The determination and compensation experiments of yaw and pitch by testing a linear stage at different distances show that the yaw and pitch obtained from the proposed system after compensation are in agreement with those obtained from the Renishaw interferometer.(3)The measurement and compensation experiments of straightness error and displacement by testing a linear stage at different distances show that the straightness error and displacement obtained from the proposed system after compensation are in agreement with those obtained from the Renishaw interferometer and the measured stage.