| In recent years, the drive system with high-speed, high-precision, high stiffness and high dynamically responding has been a new trends for high-end CNC machine tools. There are two ways used in the traditional drive systems: one is the linear feed servo system driven by the rotating motor plus linear ball screw and nut assembly; the other is the rotary drive servo system driven by the rotating motor plus precision gear or worm transmission. However, both of them cannot meet the requirements of the high-speed and high-precision performance for CNC machine tools. Therefore, the direct-drive technology has been paid more and more attention for CNC system. And there are two kind of direct drive systems used in the CNC machine tool drive systems, one is the rotating direct drive system driven by torque motor or high-speed spindle motor, and the other is the linear direct drive system driven by permanent magnet linear synchronous motor. Direct-drive system eliminates the intermediate mechanical transmission links to the execution unit directly, so it has the advantages of fast dynamic response, high precision, high acceleration, and high stiffness.However, the simplification of the mechanical transmission mechanism will make the system be more sensitive to the load disturbances, parameter changes and thrust ripple. so it will increase the difficulty to control the system control and reduce the servo system performance. Meanwhile, the nonlinear factors, such as the end effect and cogging force l will greatly increase the difficulty for the system. And the uncertainties, including the nonlinear modeling errors, position and speed detection errors, and noise will also affect the control accuracy and stability of the system.The research is supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China “High Speed Horizontal Machining Center”(NO:2009ZX04001-013-04). High speed horizontal machining center THMS6340/THMS6350 are selected as the specific objective to research the control methods for the permanent magnet linear synchronous motor direct drive system. In order to achieve high-accuracy control of speed and position for permanent magnet linear synchronous motor servo system, it is necessary to research the dynamic performance of the system, and then effectively compensate and control of the parameter uncertainties and all kinds of disturbances. Take into account the aforementioned issues, the main research work are as follows:(1) Two kinds of the integrated speed and current control strategy are proposed for permanent magnet linear synchronous motor servo system with the uncertainties. Most of the control strategies for the linear motor only design the controller for speed and position loop. It is not take into account the impact of changes of electrical parameters in the system, but it is necessary to consider these impacts in designing the controller for high precision servo system. Two kinds of nonlinear speed controller are designed, namely robust adaptive speed controller and adaptive fuzzy sliding-mode controller. In the designed controllers, the the speed loop and current loop is considered together, and adaptive theory and fuzzy control method are employed, respectively.(2) Research on sensorless control technique for permanent magnet linear synchronous motor servo system. There are lots of problems in the traditional sliding observer for speed and position estimation of permanent magnet linear synchronous motor, including amplitude and phase error, poor steady-state performance. So, a new siding mode observer is presented. In the proposed sliding mode observer, the sigmoid function is employed instead of the sign function used in the is raditional sliding observer. It is not necessary to introduce the low-pass filter for the proposed observer. Therefore, it will completely solve the problems of the amplitude and phase difference caused by the low-pass filter, and achieve the accuracy estimation of the speed and position for the linear motor.(3) High-precision position control for permanent magnet linear synchronous motor servo system. A sliding-mode adaptive position control strategy is proposed by using the sliding mode control and adaptive control. The proposed control strategy takes the advantage of the strong robustness of sliding control, and employs the adaptive method to estimate the uncertain parameters in the system. Using the proposed method, it can effectively reduce the impact of the nonlinear factors in the linear motor servo system, such as thrust fluctuations, friction and uncertain parameters.(4) Improved direct thrust control strategy for permanent magnet linear synchronous motor servo system. In the traditional direct thrust control method, there are some problems, such as high thrust, flux and current ripple, which will degrade the performance of the system. To solve those problems, a back-stepping direct thrust control strategy is proposed for permanent magnet linear synchronous motor servo system. Moreover, space vector modulation scheme is also employed to ensure the inverter switching frequency to be fixed.(5) Research on nonlinear chaos control method for permanent magnet synchronous motor. Permanent magnet synchronous motor servo system for CNC machine is a complex nonlinear system, and chaos is one of the important characteristics of nonlinear systems. The chaotic phenomena will happen in the permanent magnet synchronous motor if its parameters fall into certain area. And the existence of chaotic behavior in permanent magnet synchronous motor will seriously degrade the performance of the system, enven cause the system to crash. Nonlinear control theory is used to suppress the chaos in permanent magnet synchronous motor, and four chaos control approaches are investigated to stable the system, including finite-time chaos control, partial-state finite-time chaos control, control Lyapunov function based chaos control, and nonlinear observer based chaos control. The uncertain parameters is considered only in the first three approaches, and in the last method, both the parametric uncertainties and external disturbances are considered for permanent magnet synchronous motor chaotic system. |
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