AMB controller design for a machining spindleusing mu-synthesis

Control of an AMB supported machining spin-dle was explored to determine the potential advantages of µ-synthesis relative to more a conventional strategy based on PID with notch filters. The spindle was manufactured by Revolve Magnetic Bearings, Inc. and adapted to permit control using a dSpace real time digital controller. This very open platform enabled introduction of arbitrary control algorithms, synthesized in MatLab(TM) . The study compares the performance of a carefully de-signed PID + notch compensator to that of aµ-synthesized controller. The main finding is thatµ-synthesis is better able to reduce tool tip compliance than is PID+notch and that this improvement was a factor of at least 2 over a wide range of frequencies for the spindle examined.