Study On Multi-Objective Robust Control Of Permanent Magnet Ring Torque Drive NC Rotary Table Servo System

Based on the project supported by National Natural Science Foundation of China "Study on Numerical Control(NC) Machine Tool Rotary Feeding Precision Direct Drive Technique and Its Control Strategy",for the characteristic of the permanent magnet ring torque motor used in the direct drive NC rotary table servo system suffering from the effect of external disturbances and parameters variations,multi-objective mixed control strategies was designed to solve the contradiction between rapidity and robustness to enhance servo performances of the rotary table system in this dissertation.Direct drive technique of NC rotary tables break through limitation of the traditional drive mode,which is generally the rotating servo electrical machine with worm wheel, worm pair and gear pair mechanism,but has large thrust,quick response,high dynamic stiffness and position precision.Direct drive technique make rigid connection between servo drive motor and the load,mechanical transmission and transformation links are eliminated,external load disturbances and parameters variations have no-bufferaction on motor axle,which greatly reduces servo performances.Designing a servo controller is required to improve robustness,disturbance rejection and rapidity.The robustness of permanent magnet ring torque motor used in the direct drive NC rotary table 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/H_∞speed 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.A multi-objective mixed L₁/H₂ controller was designed to solve the contradiction between rapidity and robustness,and a rational mixed L₁/H₂ control problem was introduced to replace the primal mixed L₁/H₂ control problem,the solution for the rational L₁/H₂ control problem was obtained via EAS.Compared with conventional H_∞speed controller,the proposed multi-objective L₁/H₂ speed control enables the NC rotary table rotary feeding system to be better in robustness against external disturbances and parameters variations.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 highresponse high-precision rotary table servo system.