Design And Analysis Of Static And Dynamic Performance Of An Ultra-precision Air Bearing Turntable

Ultra-precision machining technology is an important part of modern manufacturing technology.It affects the development of the National defense and civilian processing technology.For decades,all the powerful industrial countries of the world have conducted extensive research and have made great achievements.Ultra-precision machine tools is an important mean of ultra-precision machining.Rotary table system is one of the key equipment to ensure the quality of machine tool processing,so it is of great significance to do some research on the rotary table system.Closed gas hydrostatic bearing is chosen as the support component according to the specific requirements.The design of the support system and the control system is the key.The structure of small hole throttling is determined based on the principle of air bearing.The layout of the bearings is the combination of journal bearing and bidirectional thrust bearing.The detailed dimensions of the bearings are designed by the gauge pressure ratio method.The bearing capacity,static stiffness and air cons?mption of the rotary table under certain working pressure are obtained by engineering calculation.In order to improve the control accuracy of the turntable,UMAC controller,linear driver,DC brushless torque motor and high precision round grating are applied to form closed loop control system.According to the basic principle of the gas lubricated bearing,the Reynolds equation of the thrust bearing in the cylindrical coordinate is established.The influence of the average thickness of the film and the pressure of the air supply on the static characteristics of the thrust bearing is studied by software Fluent.The static stiffness of the turntable is measured,and the result of the measurement is compared with the theoretical calculation result and the simulation result.The results show that the design of the rotary table system is reasonable.The modal analysis of the turntable is carried out by using WORKBENCH,and the natural frequency and mode shapes of each stage are obtained.The results show that the axial error of the turntable is relatively small but the radial error is slightly larger.The improvement measures are proposed by analyzing the rotation error of the rotary stage.The control system is built based on the UMAC and the drive,and the mathematical model of the torque motor movement is established on the basis of the control system.The best PID parameters are obtained by Simulink simulation.The optimal control parameters of the turntable are obtained by debugging the control system based on the UMAC controller.The accuracy of the initial position of the turntable is measured by the laser interferometer and error compensation is done based on the error compensation function of UMAC.The result shows that the positioning accuracy of the rotary stage achieves the design target.