Discrete-time Second Order Sliding Mode Control For Direct Drive NC Rotary Table

In the thesis, Liaoning Province National Nature Science Foundation“Study on DirectDrive Numerical Control(NC) Rotary Table High Stiffness Precision Control Strategy”(No.201133029) as the background, for the characteristic of the ring permanent magnettorque motor used in the direct drive NC rotary table servo system, it is suffered from theeffect of parameters variations and external load disturbances, using discrete-time slidingmode control to improve servo performances for the NC rotary table system.In many numerical control rotary table servo system, the most of tradition drive modewhich is consist of rotary motor plus worm wheel, worm pair and gear pair mechanism,thus mechanical transmission chain leads to slow motion response, bad dynamic stiffnessand other nonlinear errors and achieves high-precision machining difficulty. The rotaryservo system adopting the direct drive technique, abolishing the medium transmission,which has large thrust, quick response, high dynamic stiffness and position precision. Butthe system is more sensitive to uncertainties such as load disturbances and inertiavariations, which greatly reduces servo performances. It is necessary to designing a servocontroller, which is required to improve robustness, tracking performance and dynamicservo stiffness.In the thesis, ring permanent magnet torque motor direct drive servo systemmathematical model is established, expounded the reason of weakening chattering.Discrete second order sliding mode control is employed to realize the dynamia robust ringpermanent magnet torque motor direct drive servo system in the existence of parametersand load disturbances uncertainties. The sliding surfaces of position controller and speedcontroller are independently designed. The control laws are designed by equivalent controlplus switch control. And a robust differentiator is designed to observing the accelerationsignal robustly based on the super twisting algorithm. This strategy has good robustness toload and parameters varations, and simultaneously weakens the chattering effectively.Finally, Type RM410/100ring permanent magnet torque motor is took as thecontrolled object, which is produced by German Cytec Company, then using simulink toestablish mathematical model in the thesis. Using MATLAB7.6software to study andanalyze the proposed control strategy with no-load, load, load and parameters varieties separately, which verify the validity of theory studies and simulation results for theproposed control methods.