Analysis and control/monitoring of the direct linear drive in end milling

To meet the requirements of higher speeds, greater accuracies and improved reliability, direct linear drives are increasingly employed in new machine tools. In this paper, the modelling, control and monitoring of a direct linear drive for end milling are studied. First, a direct linear drive and its advantage are addressed; then, a dynamical model of the direct drive for end milling is proposed. Second, the friction and damping characteristic of the guideways and its relation to axis velocity and temperature as well as the cogging force of the drive resulting from the interaction of the primary (active) and secondary (passive or stator) part are analysed in detail. Third, possibilities to improve the motion behaviour of the direct linear drive by compensation of disturbances, friction and cogging forces are discussed, and a self-adjusting compensation controller and a state-space controller are proposed. Finally, a practical case demonstrates that the high-frequency cutting force can be tracked by the linear motor current. Then a tool breakage monitoring method by sensing linear motor current with a smoothing non-linear energy operator is proposed and tested with the practical case.