Active Vibration Isolation of an Unbalanced Machine Spindle

Proper configurations of controls, sensors, and metrology technologies have enabled precision turning machines to achieve nanometer positioning. However, at this level of positioning resolution, vibration sources can become a limiting factor. One of the largest sources of vibration in a turning machine may be an unbalanced rotating spindle. In this paper, a system is implemented to actively cancel spindle unbalance forces. Specifically, to attenuate the spindle housing vibration using an active vibration control system to prevent the unbalance force from disturbing the rest of the machine systems e.g., the slide servo system or the machine metrology frame. The system controls three degrees of motion. An unbalanced spindle creates a rotating force vector with a once per revolution period. The cause and size of this force is a function of the spindle, the part, the part fixturing, the part setup and the spindle speed. In addition, certain spindle speeds coupled with the size of the unbalance force may contain other harmonics that can excite machine structural resonances. The magnitude of the unbalance force increases as the square of the spindle speed. The control algorithm of this system is fully implemented on a commercially available machine tool controller and is sensitive onlymore » to unbalance induced motion. The paper describes in detail the control algorithm and how it is implemented. The system has demonstrated the ability to adapt in real time to remove the fundamental component of the unbalance force to nanometer levels. However, higher-order structural resonance components of the test bed have been observed when the system is active. The control system is stable and the voice coil (VC) excitation is harmonically clean but the high Q of the mechanical test system is apparently excited by energy leakage. Our results indicate the need to carefully examine the dynamics of any spindle system that would take advantage of this active system.« less