Research On The Control Technology And Dynamic Performance Of Linear Motor Direct Drive Feed System In CNC Machine Tools

With the rapid development of high-speed cutting technology and multifunctional CNC machine center, feed system with high rigidity, high accuracy, high speed and high responsiveness was required. While the traditional ball-screw feed system can not satisfy the high-performance requirements. In comparison with the ball-screw drive, the direct drive feed system by linear motor has the advantages of less friction, no backlash, less mechanical limitations on acceleration and velocity, higher accuracy and speed, higher reliability and dynamic performance. The direct drive feed system by linear motor is regarded as the most promising high-performance feed system of CNC machine tools.The performance of Linear motor direct drive feed system is largely determined by linear servo control technology. The more simplify of mechanical transmission structure, the more difficulty of electrical control. Disturbance variations, without any attenuation of the transmission mechanism, directly impose on the motor shaft, leading to significant effect on the linear servo system performance. Meanwhile, the end effect, force ripple, cogging and other nonlinear factors have increased the difficulty of control. In order to satisfy the requirements of speed tracking performance and eliminate the influence of disturbance, an appropriate controller and research on dynamic performance are necessary and important for linear servo system of CNC machine tools. This paper focuses on the control technology and dynamic characteristics of Linear motor direct drive feed system, to improve disturbance rejection abilities and dynamic stiffness of Linear motor direct drive feed system, ensure all kinds of dynamic and static performance index, meet the requirements of high-performance CNC machine tools.The research works were as follows:(1) The basic structure and working principle of linear motor were introduced. The mathematics model and transfer function were established. The key parameters of Linear motor direct drive feed system were analyzed. In comparison with the ball-screw drive, It is realized the advantages and control difficult of linear servo system. The nonlinear and uncertain factors of Linear motor direct drive feed system were summarized.(2) Digital control technology of Linear motor direct drive feed system was introduced and the cascaded-loop structure of servo system, which contains current, velocity and position loops, was constructed according to the engineering design method. The pole placement controller was researched in detail including the basic principle, specific design process and digital realization method. The effectiveness of the proposed schemes was verified by simulation and experiment. The performance of two algorithms was compared finally.(3) According to characteristics of nonlinear, uncertainty and dynamic complexity in Linear motor direct drive feed system, the linear servo system based on neural network with the abilities of non-linear approximation, learning and adaptive were designed. CMAC adaptive neural network controller with the characteristic of rapid response and partial approximation was designed to meet the requirement of real-time. The tracking performance and disturbance resistance abilitie of the Linear motor direct drive feed system were improved by dynamic recurrent Elman neural network. An improved Elman neural network with spares memory was proposed and rapid associate theory based on table-look up was introduced to enhance learning speed and generalization capability of neural network. The information of neural network was classified, stored and selected to use. Compound controller with feedforward and feedback comprehensive compensation was proposed. The disturbances were compensated by feedback component and reference speed input signal was preview controlled by feedforward component. The tracking performance and respect speed of linear server system were improved.(4) The structure of linear servo system was constructed. The hardware of system including driver, detection and controller and so on was introduced in detail. The software was designed according to the principle of space-vector control and the important problems were discussed. The debugging test of servo controller was carried out.(5) The linear servo system test platform, the performance parameters and measure method were introduced. The parameters of friction and thrust coefficients were obtained and the dynamic performances of Linear motor direct drive feed system based on PID and pole placemen controller were researched by experiment. The key parameters which influence the performance of system in controller were analyzed. The position tracking performance and dynamic stiffness of Linear motor direct drive feed system were studied.