A Magnetic Journal Bearing

Abstract

This report is related to the development of a magnetic journal bearing which can support a rotating shaft without any mechanical contact. A complete levitation is successfully achieved by means of a combination of permanent magnets and servo-controlled electromagnets. The principle and the characteristics of this bearing are as follows. The greater part of the rotor weight is supported by repulsion forces of like-poles of permanent magnets (barium ferrite) which are magnetized in the axial direction. Therefore, as indicated by the Earnshaw's theorem, there appears a strong unbalance force, but this can be prevented by attractive forces of direct current electromagnets which are servo-controlled. Owing to the use of the two control circuits which drive the two electromagents independently, the influence of current drifts of electromagnets upon the stability is made extremely low. The brake torque induced by eddy currents is made negligibly small by the use of ferrite.