While tracking the periodic input signal, the position-dependent periodic thrust ripple caused by ending effect, load disturbance and the friction of the permanent magnet linear synchronous motor (PMLSM) will reduce the servo performance of the system. Especially when the periods of the reference input signal and thrust fluctuation interference signal are not synchronous, the precision of periodic signal tracked by the servo system is reduced, which lead to the reduction of the servo system’s periodic signal tracking precision. Therefore, a multi-period discrete repetitive controller using two improved prototype repetitive controllers which are incomplete parallel to restrain\track the multi-period input signal was designed. Theoretical analysis and simulation results show that the proposed scheme can improve the precision of the system tracking periodic signals and restrain the periodic thrust fluctuations effectively.
In view of the characteristics of numerical control turntable servo system directly driven by permanent magnet ring torque motor, which is susceptible to load disturbance and parameter variation, a dynamic-integral sliding mode position controller is designed. Dynamic sliding mode control means making differential operation to switching function of conventional sliding mode control, thus, a new switching function can be obtained. The discontinuous terms are transferred to first or higher derivative of control quantity. Therefore, the dynamic sliding mode control law is continuous timely, and then the chattering can be effectively reduced. Meanwhile, in order to ensure the steady-state accuracy of system, the integral term is introduced in the switching function to realize dynamic integral sliding mode control. The simulation results indicate that dynamic-integral sliding mode control of permanent magnet ring torque motor has favorable dynamic response and strong robustness, and it is effective to weaken the chattering.
The contour accuracy of XY table directly driven by two linear motors was influenced by the complicated reel-time contour error model of free-form curves, uncertainty external disturbance and dynamic matching between X axis and Y axis. To establish XY table model that easily calculated and suitable for free-form curves, real-time contour error estimate method was adopted. In order to reduce uncertainty external disturbance and dynamic matching between X axis and Y axis, the iterative learning cross-coupled controller (ILCCC) was designed for current compensation on X axis and Y axis. Simulation results show that the control scheme can enhance the robustness of the system, and effectively improve the XY table of contour precision.
Permanent magnet linear synchronous motor (PMLSM) suspension system has the merits of no friction, high-speed, high response and so on, using the normal force achieve the mover suspension. The servo performance is affected by the nonlinear coupling between the horizontal trust and vertical normal force, parameters uncertainties and load disturbances. The feedback linearization method is used to achieve the dynamic decoupling of the PMLSM suspicion system and decoupling it Into two linear subsystems; to solve the conflict between disturbance restraint and fast tracking performance, increase the robustness and dynamic stiffness for system, H∞ speed controller based on PDFF and position proportional controller are designed. Simulation results show that the proposed control strategy guarantees the high speed and high precision positioning performance for horizontal axis; the good rigidity and stability for normal suspension length and the strong robustness against load disturbances and parameters variations for the two axes.
The direct-drive ring permanent magnet torque motor is easily affected by parameters changes and the load torque disturbances, which reduces the servo performance of the system. In order to enhance the robustness of the servo system, the super twisting algorithm based on the second order sliding mode control (SMC) is proposed as the speed controller of the direct-drive servo system. The super twisting algorithm need not know the information of the sliding mode time derivative, which through the continuous control measure the sliding mode and its derivative approach zero in finite time. This method not only guarantees the robustness of the servo system and eliminates chatting, but also enhances the static precision of the servo system. The simulation results show that the servo system of the direct-drive NC rotary table has a very strong robustness by adopting the control method against parameters changes and the external disturbances.
For the characteristics of direct drive NC rotary table servo system using ring permanent magnet torque motor being influenced by varying of external disturbance, parameters varieties and load disturbances, the desired compensation adaptive robust position controller based on projection algorithm is designed to achieve high performance and parameters estimation. The desired compensation adaptation law based on projection algorithm for uncertainties off-line estimation is calculated by desired information only to achieve high requirement of the servo system of the ring permanent magnet torque motor. Compared with adaptive robust controller, the controller can reduce the effect of measurement noises. Therefore the process of uncertainties estimation is faster and the estimators are more accurate. Simulation result shows that the designed method enables the system to be better in robustness in general.
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