Critical Technology Of Grating-based Interferometer On Large Range,high Preceision And Miniaturization Design

Precision measurement technology is an important guarantee means of modern ultra precision machining and ultra precision control technology.The precision measurement technology taking into account large range,high precision and miniaturization provides a suitable technical means for ultra precision position positioning in high-end machining equipment.As a kind of measuring equipment based on grating distance,grating displacement measurement system has the advantages of high measurement accuracy and good environmental adaptability,which makes it applied to a variety of high-end processing equipment.In recent years,although scholars at home and abroad have carried out research in various aspects,there are still contradictions between large range,high precision and miniaturization in the grating displacement measurement system,that is,the processing and installation errors of optical elements in the system affect the overall measurement accuracy,the processing and manufacturing errors of measurement gratings are difficult to calibrate,and the processing and manufacturing difficulties of single large-size and high-precision measurement gratings limit the measurement range,The system structure is bloated and is not suitable for the application environment.These problems restrict the application scope of grating displacement measurement system,seriously restrict its development from laboratory technology to product,and can not meet the market demand for ultra precision positioning products.Therefore,starting from the three contradictions of mutual restriction of grating displacement measurement system,this paper aims to find the balance point of contradiction and improve its comprehensive performance;Analyze and solve the difficulties required by the application,so as to make the grating measurement system become a product.The specific research contents of this paper are as follows:Firstly,the diffraction characteristics of grating and the principle of interferometric displacement measurement are studied.The calculation of grating diffraction efficiency by rigorous coupled wave method is described,and the spatial relationship between incident beam and diffracted beam is analyzed;The influence of grating Doppler effect on measuring beam frequency is described;The relationship between phase change and displacement change of interference light in interferometry is analyzed;The commonly used phase extraction methods are listed,such as homodyne four-step phase shift and differential frequency interference phase shift extraction.Secondly,the grating displacement measurement method based on conical diffraction modulation is studied.Using the rigorous coupled wave method,the efficiency change and polarization state change of the measurement beam diffracted by the conical surface are analyzed,the universality of the conical diffraction structure under different grating parameters is analyzed,and the measurement error caused by the motion error of the worktable is analyzed according to the phase change of the diffracted light;The construction and experiment of grating displacement measurement system based on cone diffraction are carried out.The error in repeated measurement is analyzed and compensated,and the measurement accuracy of 43 mm range is 45 nm.The modulation effect of cone diffraction on beam polarization and the high accuracy of cone measurement structure are verified.Thirdly,the research on the elimination of grating shape error based on conical diffraction is carried out.The influence of grating shape error and scribe error on the measurement error in multi-point measurement is analyzed,and the conical diffraction structure is used to realize the single point measurement of symmetrical structure,so as to eliminate the problem that the multi-point measurement is mixed by grating shape error and littero single point measurement stray light;The detection and data processing of the surface shape of the measuring grating are carried out.The measurement error and the scribe error are compared.The two kinds of errors are basically the same.The residual surface shape error caused by the non coincidence of the measuring beam is analyzed,and the residual error of 43 mm measuring range is 0.2nm.The elimination characteristics of surface shape error of conical diffraction measurement method are verified,which also provides the research basis of high-precision reading head for subsequent range expansion and miniaturization design.Fourthly,the large range extended method of grating displacement measurement system is studied.The dynamic error in the switching process of grating measurement system caused by multi grating splicing gap is analyzed,and the methods of measurement data compensation and switching transmission are explored;A grating measurement system with multiple gratings is designed and built.The measurement gratings are placed in a way of partial overlap.The specially designed double-layer reading head can collect the measurement data of two gratings at the same time;The data delay compensation of overlapping area and the error compensation caused by inconsistent attitude in splicing measurement are carried out,and the data loss caused by gap in uniform splicing and the inconsistent attitude error of grating before and after switching are eliminated.The applicability of splicing data compensation and data switching method in larger range expansion is verified.Fifthly,the determination and distribution of structural error in miniaturized measurement are studied.Based on the measurement structure of high-precision conical diffraction grating and combined with the spatial distribution of conical diffraction,a grating displacement measurement structure with high measurement accuracy and high space utilization is designed;The influence of stray light in the measurement structure is analyzed by ZEMAX,and the coincidence degree of interference beam under different errors is analyzed according to the ray tracing program of ray vector,so as to determine the machining error tolerance of optical mechanical components and allocate the error;The assembly steps of the designed miniaturized measuring optical machine structure are designed,and the design and assembly of a 48 mm * 40 MM * 20 MM miniaturized reading head are realized.