A miniature milling spindle with Active Magnetic Bearings

This paper describes the design and realization of a miniature milling spindle with Active Magnetic Bearings (AMBs). Permanent magnet biased, reluctance type actuators position the rotor in five Degrees of Freedom (DOF), leaving the rotation unconstrained. A rotordynamic model was developed to expedite the controller design, and enabled modeling of the spindle’s performance under the influence of cutting forces. A modal controller, including a negative stiffness compensation scheme, was implemented. A cross-feedback controller partly compensates the gyroscopic effect. The spindle with these controllers has a maximum speed of 150.000 rpm.