Research On Inhibiting Low-Speed Torque Ripple Of Direct Drive Rotary Table

NC rotary table servo system is an important part of NC machine tool. It plays a vital role in the mechanical processing and manufacturing. The precision of the position, speed and the stability of speed are the key indexes in NC rotary table servo system.For high-precision mechanical processing and manufacturing, the minimum stable speed and high-precision are needed. So, the low speed jitter problem has been the central task in the rotary table servo system research. The improvement of the working precision at low speed is hindered by the disturbances of the friction moment and the motor torque waveforms, while the decrease of the disturbances is restricted by the making technology. For the reason, the research of the low speed properties and corresponding compensation methods means a lot for the manufacture.Taking the RTD-500 NC rotary table as an object, the paper focuses on the influences of the nonlinear friction moment and the motor torque fluctuation to the system precision at low speed first. Then, the theoretical analysis and simulation was made. The experimental verification is carried out in RTD-500 NC rotary table servo system for the effectiveness and feasibility.The control method and the principle of the RTD-500 rotary table motor have no difference with general PMSM in essence, so the paper explains the theory of PMSM vector control, analyzes the control principle of field oriented control(FOC) of PMSM and proposes the PMSM mathematical model at first.Then the low-speed properties and the main reasons of jitter were analysed theoretically. After that, the main factors of the impact of low-speed characteristics-friction torque and motor torque fluctuation were analysed in qualitative. Based on this, the paper introduces the disturbance observer method to curb disturbances of the friction moment and the motor torque fluctuation, and simulates it.In order to verify disturbance observer's effectiveness at low-speed, the hardware and software of NC rotary table servo system was designed.Hardware includes design of the main power circuit, voltage and current detection circuit, position and speed detection circuit design, control and drive circuit and protection circuit. Software includes current sample, coordinate convert, digital PID regulator.Finally, based on the hardware platform, the experiments were done and the experimental results were analyzed.