A miniature milling spindle with Active Magnetic Bearings

Limits, Modeling and Design of High-Speed Permanent Magnet Machines

“…Their stiffness declines with the operating frequency [162] and they have limited control bandwidth [164] due to presence of coils and sensors and limited processing power of controllers. Gyroscopic effect and/or non-linearities can destabilize the rotor-bearings system at high speeds [165] and more complex control methods are needed such as cross-feedback [165] or non-linear feedback control [161].…”

“…Nevertheless, AMB technology is advancing and the bearings appear in many precision and high speed applications [167]. Improvements have been made in design of specialized power amplifiers and their integration with AMB [163], control algorithms [168] and design of AMB for high speed [164].…”

“…Considerable research on AMB for machining applications has been conducted at University of Virginia [172] and at TU Delft [164]. Hybrid solutions have also emerged in high-speed machining spindles where AMB have been combined with other types of bearings and actuators to take advantage of certain virtues of AMB such as accurate positioning during rotation [15].…”

“…In the Microfactory project a small spindle in active magnetic bearings (AMB) was realized by M. Kimman [164,175]. A relatively slender rotor is supported by two radial bearings and an axial bearing which exerts force over a small rotor disc (Figure 7.1).…”

“…The maximum attained speed of the spindle is 150.000 rpm. It was shown that miniaturization of a spindle has positive effects on actuation and cutting force monitoring [18,164]. The first flexural critical speed (approximately 180000 rpm) of the spindle has represented an obstacle of utilizing the motor up to its maximum speed constrained by the structural limit of the PM rotor (250000 rpm).…”