Considerations for low inertia AC drives in machine tool axis servo applications

Advances in permanent magnet materials have allowed construction of AC permanent magnet servo motors that have one-tenth of the shaft inertias of their torque-equivalent predecessors. The differences encountered in applying these generation motors to machine tool axis servo applications are discussed. Experimental results demonstrating the differences and corroborating the conclusions drawn are provided. Experimental testing was accomplished on a motor test stand and on a machine tool axis servo application. The test stand had two AC servo motors coupled in a motor/dynamometer configuration. Analytical and experimental results demonstrate that, in addition to affecting the acceleration, or command-following capabilities of the servo motor, reduction of shaft inertia affects the controller tuning robustness, bandwidths, and dynamic stiffness characteristics, and has implications for the drive/controller sampling rate. The process of selecting an appropriate servo motor for such axis servo applications is reviewed, and tie factors that are affected by motor/magnet technology are summarized.<>