Design of a Novel Miniature Spindle Concept with Active Magnetic Bearings using the Gyroscopic Stiffening Effect

A high speed spindle will be designed for micro fabrication applications. The aim is to reach 0.1 µm accuracy with a rotational speed of at least 300.000 rpm. A study is done into the behavior of different rotor shapes. A short rotor and a long rotor are modeled by solving the non linear Newton and Euler equations numerically. The short rotor tilts much less under the influence of the cutting forces than a long rotor. The short rotor is thus much stiffer around the rotational axis than a long rotor. Short rotors are easier to bring up to speed. The gyroscopic coupling between the two vertical planes is much stronger in case of a short rotor. This can cause instability and must be taken into account in the design of a control system. The possibility to use this gyroscopic stiffening to our advantage will investigated. Two active magnetic bearing systems will be built. The performance of a long rotor and the performance of a short rotor, both magnetically levitated, will be compared. The design of a magnetic bearing system for a prototype with a long rotor is described in this paper. This prototype is built to gain experience in the design of small magnetic bearings, with permanent magnets for bias. The setup will be used to test the performance of a long rotor.