线切割机电极丝动态稳定性的主动控制研究

分析了国产快走丝线切割机床加工精度差的运动学和动力学原因。导出了电极丝的运动方程和各种激励下的强迫响应解，指出丝架的振动和转动元件的动不平衡是影响电极丝稳定性和加工质量的主要因素。由于电极丝细而柔，结构振动和动不平衡在制造中难以完全消除，着重研究了利用主动控制方法提高电极丝动态稳定性和加工质量的理论原理和技术方法。通过理论分析，指出主动控制不应采用传统的模态控制，而应为远低于首阶模态的强迫响应控制

Active Control of Dynamic Stability for Moving Wireof Wire-Cut Electric Discharge Machine Tool

The kinematics and dynamic reasons for poor machining quality of home-made High Speed Wire-CutElectric Discharge Machine (WEDMHS) are analyzed. A segment of the moving wire is taken from thesystem and then studied independently,the equation of motion of this part wire is given and its forced resPOnses to the excitations coming from other parts of the system and cutting reaction are analyzed,fromwhich it is shown that the vibration of the wire-frame and the dynamic unbalance of rotational parts drivingthe wire to move dominate the resPOnse of the wire and the machining quality. The theoretic ptinciple andthe technical method for improving the dynamic stability of the wire and the machining quality by using active control are emphatically stated since the excitations from the structures are difficult to remove by traditional passive methods. It is shown that the active control to be adopted should not be the traditionalmode control,but the control of forced response with the upper frequency much lower than the first naturalfrequency of the wire,because the low frequency excitations almost dominate the total response of thewire. In such cases,the placement of sensors and actuators is free from the nodes of modal shapes. Becausethe wire is too thin and flexible,direct measurement and control is difficult. Therefore,an indirect method,named 'lightly pressing and touching" or 'vibration transformation",is developed,in which a metal sheet isfixed to the machine at one end,lightly touching the wire. Piezoelectric ceramic elements are used as thesensor and actuator to the metal sheet. A simple control system is designed and cutting tests are carried outon a practical machine. Experimental results show that the vibration amplitude of the moving wire is largely reduced;the dynamic stability of the moving wire and the machining quality are considerably improvedby using the active control method developed in this paper.