Electromagnetic Field Analysis And Improvement Of The Thrust Ripple Of Linear Motor

Currently, the benefit from the traditional motor is unable to meet the requirements, and the linear motor contains potential application along with the future developing of various novel control strategies and power electronic technology as well as high performance magnetic materials. Consequently, linear motor has excellent application perspectives in IC core making, CNC systems and packing equipment, and so on, and is gradually becoming the main function device of high-grade CNC machines. However, in the linear motors, there exists thrust ripple caused by all sorts of internal and external factors(such as the friction disturbance and the perturbation of system parameters and so on), which can not only affect the steadiness at low speed and positioning accuracy of high precision NC machining system, but also become one of important factors interfering with the application prospection of the linear motors in industrial practice.This paper, taking the linear motor of direct-drive technology experiment platform of high speed and precision horizontal machining center of Pu shi Ning jiang machine tool co., LTD., as the research object, in order to weaken the negative influence of thrust ripple, analyzed the occurrence reasons of thrust ripple and servo control system, then put forward the structure improvement measures and the control strategy to restraint thrust fipple.Firstly, the development and research progress of linear motor is analyzed in this paper. Secondly, the structure characteristics and working principle of the permanent magnet linear synchronous motor(PMLSM) are introduced. What’s more, the physical model of the PMLSM was built by means of the mirror image method, and the field distribution of the PMLSM was received. Meanwhile, the transient electromagnetic field of PMLSM is analyzed, and the transient magnetic field distribution of PMLSM is discussed in detail. The precision of analytical method is verified.Then, the thrust ripple and the detent force that is the main reason of thrust ripple was researched based on the electromagnetic field analysis. Combined with the corresponding boundary conditions, the finite element analysis model is built, and the structure improvement measures to improve the thrust fluctuation are put forward. The analysis results showed the correctness of the finite element analysis and the structure improvement measures.Finally, an improved direct thrust control(DTC) system of the PMLSM with sensorless speed estimation is proposed. In this modified DTC control scheme the thrust force and the stator flux are controlled by two PI controllers instead of the conventional hysteresis controllers. The proposed control scheme is based on decoupled control of thrust force and stator flux in the stator flux reference frame by two independent(decoupled) control loops. Practical results prove the robustness of the proposed scheme and a significant reduction in the thrust force ripple.