Research On Self-Turning Control Of Direct Drive Low Speed Precision NC Rotary Table

With the development of manufacturing, the requirement to high grade precision processing center is improved continuously, especially to the multi-axial linkage processing center. As the important part of Numerical Control (NC) machine tool, the NC rotary table becomes more and more important in the whole machine industry.The change of inertia directly influences the stability, positioning accuracy, dynamic response of ring permanent magnet torque motor servo system used in NC rotary table, and the problem of inertia seems more outstanding on the mode of direct drive. The ring permanent magnet torque motor is three phase permanent magnet synchronous motor specially designed for direct drive NC rotary table, its servo system requires the minimum stable speed and high precision. So it is necessary to analyze and compensate the disturbance torque especially cogging wave torque that influences the low speed performance of rotary table servo system.The thesis studies NC rotary table servo control system based on theoretical analysis and computer simulation. First, the mathematical model of PMSM and basic theory of vector control are analyzed, the vector control scheme (i_d =0) is confirmed, and current controller and speed controller are designed respectively. Besides, the principle and specific realization method of SVPWM are discussed and current and speed double loops control system emulation model are founded using MATLAB/SIMULINK to validate. Then the identification algorithms commonly used presently are preliminary studied, a technique of the identification using Extended Kalman Filter (EKF) is presented to identify inertia, load torque and speed, and the influence to identification process of the selection of parameters (Q, R, P) are analyzed. The parameters of speed controller are adjusted online using inertia identification value, so a series of problems caused by manual adjusting parameters of PI controller brought by the change of inertia. The anti-jamming performance of speed loop and robustness of system are upgraded. Lastly, the theory model of motor wave torque caused by slot effect is mainly studied. The design of position controller based on repetitive control theory is to improve the stability and tracking accuracy. The simulation results show that the ability of tracking sine signals adopting repetitive control in the system is better than adopting the traditional PID control. A summery of whole thesis is given in the end.