Research On Anti-load Disturbance Of Direct Drive NC Rotary Table Servo System

Due to the elimination of the adverse effects of middle transmission on the system accuracy and control performance, direct drive NC rotary tables have the advantages of simple structure, high acceleration, fast response and high positioning accuracy when compare with traditional drive NC tables. Thus, direct drive NC rotary tables have become the inevitable trend of NC rotary tables. Because of zero-transmission, direct drive NC rotary tables are more sensitive to load disturbance, inertia change and motor torque fluctuation. In order to exert the advantages of direct drive technology, the paper tries to find suitable control strategies to improve the anti-load disturbance ability of direct drive NC rotary tables. The main work of the paper is as follows:(1) The paper analyzes the control principles of two main types of permanent magnet synchronous torque motors and studies the sinusoidal pulse width modulation technology and the space vector pulse width modulation technology used in modern AC variable speed control system. Besides, simulation models of direct drive NC rotary table servo system are built in Simulink.(2) An integral type sliding mode speed controller based on new reaching law is proposed to improve the anti-load disturbance ability of direct drive NC rotary tables. Simulation on RM166/100 permanent magnet ring torque motor shows that the proposed controllers could reduce speed drop and speed recovery time from 18r/min and 0.25 s to 12 r/min and 0.035 s, respectively. Simulation results also show that the new reaching law can effectively restrain the inherent chattering problem of sliding mode control.(3) A feed-forward compensation method based on novel reduced order load torque observer is proposed to improve the anti-load disturbance ability of direct drive NC rotary tables. The novel reduced-order load torque observer uses motor rotation instead of motor speed as input, hence avoids the introduction of differential mutation. Simulation on RM166/100 permanent magnet ring torque motor shows that this method could achieve similar anti-load disturbance ability with sliding mode control. Besides, this method can also improve the startup performance.(4) An experimental platform based on DSP and magnetic powder brake is designed and constructed. Preliminary experiments show that the experimental platform can run reliably. The experimental platform provides the foundation for further research.