Study On Ultra-Precision Turntable For Micro-Nano CT And Method Of Indexing Correction

Micro-nano CT technology visually displays the three-dimensional structure,density distribution and defect information of the object,and is not limited by the material and structure of the object.With its high image resolution,it has been widely used in aviation,aerospace,national defense,military project,materials,automotive industry,microelectronics,biomedical science and other fields.Ultra-precision turntable is one of the key components in CT equipment.It is also an indispensable part of micro-nano CT device to realize the spatial precise location of the detected object.Low speed stable operation,high precision technical index,precision detection and error separation method and indexing error correction technique are the focus of research on ultra-precision turntable.The project is funded by the major national science equipment development special project.The key technologies of ultra-precision turntable are studied.The problem of precise positioning of the detected objects in micro-nano CT systems is solved.The main work and innovations of this thesis are as follows:The electron beam linear CT scanning method applied in micro-nano CT system on is studied.The requirements of the micro-nano CT system to the performance indexes of the ultra-precision turntable are analyzed emphatically.Through analysis,the main technical indexes of the ultra-precision turntable,which meets the requirements of micro-nano CT system detection,are proposed.Starting from the basic equation,the basic theory of gas lubrication and the theory of aerostatic bearing are studied.The stability of aerostatic bearing is analyzed,and the stability criterion is deduced.The method of improving the rotary accuracy of aerostatic bearing is studied emphatically.On the basis of the research,a precision aerostatic bearing is designed.By ANSYS,the static bearing capacity,static stiffness and gas mass flow of the aerostatic bearings,under different air supply pressure,different film thickness and different number of gas supply holes,are simulated and analyzed.A precision aerostatic bearing is made and the ultra-precision turntable is assembled and debugged.The radial runout detection and error separation technique of ultra-precision turntable are mainly studied.Based on the minimum cost,the single-probe,three-point and two-transposition radial runout error detection and separation technique is presented.By simulation,the method can separate random errors.The method combines the characteristics of the reverse method,which makes the result more accurate than the single reverse method.It saves more preparation and detection time than the two reverse method.The cost is lower and it is more simple and easier.On the experimental platform,the ultra-precision turntable is tested and compared with the reverse method.The test results show that the error detected by reverse method is 50 nm,but the singleprobe,three-point and two-transposition radial runout error detection and separation technique is used,the radial runout error of detection and separation is 67 nm,the latter method can reflect the real radial runout error of ultra-precision turntable better.It can evaluate the radial runout precision of ultra-precision turntable more effectively.The correction technique of indexing error is mainly studied.Combined with the sparse decomposition idea and harmonic analysis,indexing error compensation model is established,and the correcting method of indexing error based on sparse decomposition is proposed.In the process of processing the indexing error data,the method can filter out the noise in the signal and obtain more accurate harmonic components.The error compensation function is synthesized by the harmonic component obtained by the decomposition,and the indexing error is compensated.The proposed method is validated on the experimental platform and compared with harmonic analysis and correction technique.The experimental results show that an error compensation method,based on sparse decomposition,acquires data by using a single reading head to compensate the angular indexing error of turntable,the method can improve the positioning accuracy of the turntable angle without increasing the cost.The maximum indexing error of the turntable is 90.85 ",after the error is compensated,the error of angle measurement can be reduced to 0.64",which is nearly twice as high as the error compensation result of 1.22 " by using harmonic analysis,the correction technique.According to the GB/17421.2-2000 standard and the uncertainty,the positioning accuracy of the developed ultra-precision turntable is 4.47".At the same time,the axial runout,swing error,rate fluctuation,static bearing capacity and static stiffness test are carried out on the developed ultra-precision turntable.Finally,this paper summarizes the work of this paper,and looks forward to the next research plan and direction.