Acceleration Feedforward for Increase of Bearing Stiffness - Application for Very Small AMBs

The achievable dynamic stiffness of active magnetic bearings (AMBs) is typically quite low compared to ball bearings or hydrodynamic bearings. For many applications this is not a problem, or even a favorable characteristic. In the case of non-stationary bearings, however, base vibrations will cause large amplitude responses relative to the base due to the limited stiffness. Acceleration feedforward control is a method that helps to reduce these amplitudes considerably. This paper presents the functional prototype of an AMB that meets the space requirements of commercial hard disk drives (HDDs). The work was carried out in the scope of a feasibility study, investigating a possible application of AMBs in HDDs. It is shown how acceleration feedforward improves the dynamic performance and that the dynamic specifications of modern disk drives can practically be satisfied with AMBs.