Design and Realization of a Miniature Milling Spindle with Active Magnetic Bearings

This paper describes the design of two active magnetic bearing spindle systems. A miniature active magnetic bearing spindle, with two radial bearings, one axial bearing and a permanent magnet synchronous motor has been built. The spindle is controlled by five, decentralized PID controllers. The closed loop bandwidth of the system is 380 Hz. The static positioning error was measured to be below 45 nm (1sigma). This spindle has been tested with rotational speeds up to 120.000 rpm. To reach higher rotational speeds a second miniature active magnetic bearing spindle has been designed. The rotor dimensions are smaller than in the first generation in both length and diameter. The basic design concept is a small disk shaped rotor, which eliminates the passing of one rigid mode and several flexible body modes during startup. The gyroscopic coupling in a disk shaped rotor is larger when a relatively short rotor is applied. In this research, the aim is to use resistance of a gyroscope against tilting to an advantage.