Research On The Shafting Characteristics Of On-orbit Theodolite Turntable

Theodolite is a kind of equipment used for observation in shooting range.Its main function is to track targets and provide high-definition and intuitive live images of targets.With the development of modern range measurement technology,theodolites are developing towards the direction of high resolution,high tracking accuracy and high pointing accuracy.For the on orbit theodolite,the turntable is the key component.With the increasing demand for space mission,improving the accuracy of the turntable mechanism becomes the key to improve the performance of the theodolite.Compared with the commonly used ground-based theodolite,the space-based theodolite will experience different excitation loads in the process of transportation and use,or in the process of launching.Based on the space-based theodolite,study the static and dynamic characteristics of the turntable.Firstly,propose the static error analysis method of turntable mechanism.That is to find out the error source in the design,production and processing of the mechanism.The error sources are classified and superimposed on pitch axis,azimuth axis and normal axis.Then the static error model of turntable mechanism is established by using matrix.The error model is solved by MATLAB software,and the offset value of random position and attitude change of errors under the action of each error source is obtained,and the influence of each error source on the accuracy of mechanism is analyzed.In order to study the relationship between bearing preload and system stiffness when the structure form of turntable is determined,the relationship between bearing preload,bearing stiffness and shaft stiffness is analyzed.After simplifying the structure,the finite element model of theodolite turntable structure is established by Hyper Mesh software.Through finite element analysis,the static characteristics of shaft system under different conditions are analyzed,and the relationship between bearing pretension and deformation of pitching shaft system of turntable is obtained.The modal analysis of theodolite turntable is carried out by using the finite element software.The modal shapes and natural frequencies of the turntable made of aluminum alloy and aluminum based silicon carbide are obtained,and the influence of different preloads on the mode of pitching shafting is discussed.The first-order natural frequencies under each preload force are obtained by finite element analysis.The natural frequencies of the shafts change with the change of the axial preload force.Finally,according to the test scheme,the theodolite turntable is tested for mechanical vibration,the test results are analyzed,and the modified finite element model is verified.