Study On Key Technologies Of Angular Metrology Turntable With High Subsecond Precision

Angular metrology is widely used in various areas of science and technology.With the development of technology,the requirement of accuracy of metrology becomes higher and higher.In particular,in the development and production process of some high-accuracy equipment,the circular degree of the measurement accuracy is extended to subsecond level.Traditional mechanical calibration tools such as the block gauge,scale gauge and index plate have already not satisfied the needs of the development of modern science and technology.The combination of the optical,mechanical,electronic,computer and other multidisciplinary advanced technology has become a new type of angular measurement platform.This study focuses on the key technologies such as the supporting and driving technologies considering the system requirement of the angular metrology turntable with high subsecond precision.Firstly,based on the special structure of vacuum preload aerostatic bearing(VPL pad),a mathematical model is obtained according to the outflow function method,which can effectively improve the calculation efficiency of the static characteristics of the aerostatic bearing.Stiffness volatility is proposed to descript the performance of the rotary table consistency.The influences of volatility on load,stiffness and stiffness variation are analyzed.Using the orthogonal method and the optimization of the stiffness and stiffness variation range,the optimization of the structure of VPL pad is realized.Secondly,on the basis of the static characteristic analysis,the dynamic characteristic analysis of VPL pad is carried out.Based on the small disturbance method,the dynamic characteristics of the VPL pad is analyzed,and the stability of the bearing is confirmed.The influences of different parameters on the stability of VPL pad are studied.This provides a theoretical support for stable design of the VPL pad.Thirdly,to achieve fast angle positioning and high stability of the pneumatic bearing turntable with vacuum preloading,a multi-mode control strategy based on a linear extended state observer(LESO)is proposed.On the speed mode(AC),the turntable runs to a specified target position at a fast speed.When it reaches the target position,a smooth transition to another non ultrasonic control mode(DC)is made to achieve a precise adjustment in a small range.Based on LESO,the mathematical model of the turntable is analyzed and identified,and the AC and DC control algorithms are designed,and the multi-mode control algorithm based on MATLAB is simulated.According to the result of the experimental analysis,the AC model can run to a specified target position at a faster speed,and then switch to another control mode DC mode.The DC mode can precisely adjust the position in a small range,and finally the turntable realizes the highly stable precision of 0.003 angular seconds.Finally,based on the above study,a prototype of the sub-second angular metrology was made and the measurement system of circular indexing error was built up.Using the closed circle principle and the least square principle,this study analyzes the measurement algorithm of circular indexing error based on non-physical data.The influence of the installation error,the installation environment,and the instrument on the measurement results and the error control method are discussed.The calibration of the angular metrology error was conducted on the new built measurement system.The comparison of the calibration error results using the prototype with the results obtained from,China Institute of Metrology(NIM),and the manufacturer was carried out,which confirms that the effectiveness of the developed device achieves the subsecond level.