External sensorless adaptive chatter avoidance in NC machining by applying disturbance observer using high resolution linear encoder

The productivity of numerical control (NC) machining is highly limited by the occurrence of chatter vibration. Chatter stability analyses are widely studied to predict chatter vibration. However, these analyses often fail to provide reliable prediction results because the parameters in the vibration model are sensitive to identification errors, mechanical deterioration and thermal changes. On the other hand, to implement robust avoidance of chatter vibration to process changes, additional external sensors have been used, e.g. accelerometers and force sensors. However, this results in increase in cost and decrease in rigidity of the installation site. Meanwhile in recent years, there has been a growing trend toward including a high resolution linear encoder as a standard equipment for a NC machine. In this paper, by applying a disturbance observer using a high resolution linear encoder, an external sensorless adaptive spindle speed selection method is proposed for the robust chatter avoidance. The proposed method is verified by experimental studies on a NC end milling machine.