Study On Key Technology Of Heterodyne Grating-based Precision Displacement Measurement System With Littrow Structure

Precision measurement technology is the foundation of modern processing and manufacturing.Precision measurement equipments with large range,high precision and multi-dimensional are very important to promote the development of advanced processing industry and manufacturing industry.Grating-based displacement measurement system as a kind of precision displacement measurement equipment has attracted much attention of researchers because of its high accuracy,large measurement range,simple and compact structure,small environmental impact and other advantages.The related products have been widely used in a variety of precision measurement occasions.At present,although there are many studies on the grating-based displacement measurement system,there are still some sharp problems in the system,such as the contradiction among large range,high resolution and high precision,and the contradiction among multi-dimension,small volume and large range.These problems seriously restrict the application scope and its development towards miniaturization and commercialization.In view of this,this paper studies the key technologies of the heterodyne Littrow grating-based precision displacement measurement system,aiming at solving the above contradictions and laying a solid foundation for the industrialization of grating displacement measurement system.The main work is as follows:Firstly,the measurement theory of grating-based precise displacement measurement system is deeply studied.A theoretical model for analyzing the diffraction efficiency of one-dimensional trapezoidal grating is established by rigorous coupled-wave theory.The basic principle of displacement measurement is deduced by Doppler frequency shift principle,light interference principle and displacement conversion principle.The Jones matrix representation methods of polarized light and common polarized optical elements are enumerated.Secondly,a miniaturized,high precision and heterodyne grating-based displacement measurement system for 2D is proposed.The basic principle of 2D displacement measurement with Littrow structure and the influence of the yaw relationship among grating,reading head and displacement platform on displacement measurement are analyzed theoretically.The principle prototype is built and compared with the dual-frequency laser interferometer.The minimum resolution of 3 nm is achieved in two dimensions and the measurement range is more than 10 mm.The system also has better static stability than the laser interferometer.The two-dimensional displacement measurement system combines Littrow structure and heterodyne measurement principle.The reading head is simple,easy to integrate and install,and has large measurement range and high accuracy.It is of great significance for the development of grating displacement measurement system into products.Thirdly,a grating-based precision measurement system for 5D is proposed.The basic principle of three-dimensional angle measurement using diffraction grating and position sensitive detector is analyzed theoretically.On the basis of the two-dimensional displacement measurement system,a high-precision position sensitive detector is introduced to build a prototype,and the displacement and angle measurements are compared with the dual-frequency laser interferometer and photoelectric autocollimator.The high-precision two-dimensional displacement measurements with resolution of 3 nm and the high-precision three-dimensional angle measurements with resolution better than 1 arcsec realized.The five-dimensional precision measurement system has the advantages of simple structure,easy integration,high resolution and accuracy,wide range of displacement measurement and strong applicability.It is of great significance for the development of multi-dimensional grating displacement measurement system into products.Fourthly,the influence of grating on measurement of displacement measurement system is systematically analyzed.The influence of the position error between the grating and the reading head on the displacement measurement is simulated,and it is revealed that the grating yaw error is the most sensitive error of the system.It has important significance to the installation and adjustment of the system and the selection of measuring environment.Based on the principle of geometric optics,the theoretical model of the influence of grating surface error and groove error on the displacement measurement of the differential Littrow grating displacement measurement system is established,and a fast method of detecting and calculating the error is proposed.The principle prototype of heterodyne Littrow grating displacement measurement system is built and compared with dual-frequency laser interferometer.The experimental results show that the method is correct and has the characteristics of fast speed and high accuracy,which is of great significance to improve the accuracy of the system.The polarization characteristics of optical components of Littrow grating-based displacement measurement system are established by using Jones matrix analysis method.The theoretical model of the relationship between property and signal intensity is used to simulate the influence of diffraction efficiency and polarization characteristics of grating on displacement measurement.It is found that the difference of diffraction efficiency between P-ray and S-ray has the greatest contribution to the non-linear error.It is of great theoretical significance for the design of grating and the improvement of system accuracy.Fifthly,a large range and high precision heterodyne grating one-dimensional displacement measurement system is proposed.The measuring range of the system is expanded by means of interlacing gratings.A miniaturized reading head is designed by using double-layer Littrow structure.A prototype of the principle is built and compared with a dual-frequency laser interferometer.The correctness of the principle is verified.The high-precision displacement measurement with a measuring range of 50 mm and a resolution of 3 nm is realized.In addition,the splicing process of staggered stitching grating is simulated,which lays a foundation for the fabrication of grating.The one-dimensional displacement measurement system has the advantages of large measurement range,high accuracy and simple reading head.It is of great significance for the development of grating displacement measurement system to a large range and high accuracy.