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.