High Stiffness Control Strategies Of NC Double Swivel Milling Head Driven By Torque Motors

In order to meet requirements of the high speed cutting and high precise cutting technology, a new "zero-transmission" direct drive double swivel milling head feed system driven by PMSM had been developed. Compared with conventional worm gear double swivel milling head system, the direct drive NC double swivel milling head system has outstanding characteristics, such as the simple structure, high acceleration, and high position accuracy.In order to maintain the processing quality when they suffers disturbs from cutting force and make the machine tools have enough processing precision, exploit the high response characteristics of direct drive PMSM servo system in machining process, the servo control system must achieve tracking performance as high as possible a well as good dynamic servo stiffness.The dissertation mainly discusses the servo stiffness of direct drive NC double swivel milling head servo system. Firstly, the merit and the shortcoming of the direct drive and evaluation method is brought foreword since the servo stiffness of the direct drive servo system take on new features. Secondly, the models of this control system and servo stiffness are given. A simulation is performed using software MATLAB to evaluate the influence of control structure,control parameters and mechanical characteristics on the dynamic stiffness direct drive servo system.The robustness of permanent magnet ring torque motor used in the direct drive NC double swivel milling head servo system is measured by H2 and H∞norm. Two methods are combined for control system design, which can improve robustness, disturbance rejection and rapidity. A H2 and H∞, rasped controller is designed by Q Parameter, since the solution to the continuous system and the discrete system is consistency, the continuous problem is transformed into discrete problem to solve, the proposed multi-objective H2/H∞speed control ensure stability, rapidity and robustness of system.Permanent magnet ring torque motor is considered as the controlled object, its mathematical model is established, and it is necessary to simulate and analyze above two control strategies using MATLAB software. Simulation results show that the proposed multi-objective mixed controllers meet the requirement of robustness and rapidity for high response high-precision NC double swivel milling head servo system.