Design Of Robust Controller For Direct Drive Rotary Feeding System

This research is based on the project "Study on Numerical Control (NC) Machine Tool Rotary Feeding Precision Direct Drive Technique and Its Control Strategy" (No.50375102), which is supported by National Natural Science Foundation of China. The ring permanent magnet torque motor used in the direct drive Double-swivel milling heads servo system usually suffers from the effect of parameters variations and external load disturbances, which reduce the system servo performances largely. In order to improve the servo performance of Double-swivel milling heads system, the L₁/l₁ robust control theory is adopted and two control strategies are proposed in this dissertation.The feeding system adopting ring permanent magnet torque motor cancels the mechanical transmission components and eliminates the limitation of velocity and acceleration caused by mechanical factors, which enhances the position precision and dynamic performance. However, in this case, the load disturbance is applied directly on motor. Also, the effects of parameters variations become notable on the performance of control system. Therefore, it is necessary to design a suitable servo controller used for direct drive rotary feeding system.For real systems, L₁/l₁ robust control is an important control strategy used in complex cases such as uncertainties. Since the direct drive servo system suffers from the load disturbances and uncertain parameters that reduce the system servo performances greatly, a L₁ sub-optimization controller based on the fuzzy T-S model is designed in this study firstly. Then, a l₁ norm of mixed sensitive function is considered as the performance index with respect to the conservation of L₁/l₁ robust control theory. Furthermore, in order to obtain better interference rejection and tracking performance, the system controller is optimized to minimize the peak-peak value error of the worst case, as well as weaken the effects involved by mode uncertainties on system stability. The RM166/100 ring torque motor from Germany Cytec Company is adopted as the controlled object in this study. Based on its mathematical model, two proposed control strategies are investigated by simulation using MATLAB software. The simulation results show that the designed L₁ sub-optimization controller is not only effective in robustness against the load disturbances and uncertain parameters of the direct drive servo system but also obtains better tracking performance and guarantees the servo precision.