自己制御型八極磁気軸受方式の理論解析

Abstract

High precision inertial sensors such as gyros and accelerometers are necessary to launch a space vehicle successfully. The gimbls of these inertial sensors which had been developed were floated in damping oil whose density was equal to their average density and the output axes of the sensors were supported by means of high precision jewel-pivot bearings. This type of bearings cannot help having a small clearance between jewel and pivot, therefore the bearings may sometimes occur frictional torque which is uncertain torque about the axes. In order to develop preciser sensors, the axes of the sensors are necessary to be provided with suspension systems which are free from uncertain torque about the axes. A magnetic suspension system is one of the systems which have the above mentioned capability.Formerly, R. H. Frazier had derived an expression of a magnetic suspension force neglecting the leakage of the magnetic flux which may occur in the gaps between rotor and stator of the magnetic suspension system and neglecting the components of the magnetically nonrestorative force which acts on the gaps' surface. Because the expression had been reasonable only within a small displacement of the output axis, unstability of the magnetic suspension force could not be discussed which exists with the output axis largely displaced in the gaps.From this point of view, a passive magnetic suspension system with an eight-pole stator is theoretically analyzed, which can be applied to supporting the output axes of the sensors. In this theoretical analysis, the above mentioned analytical imperfections is taken into consideration, and the equation of the magnetic suspension force is directly derived from an equation of the magnetic energy which exists in the gaps, and then static characteristics of the magnetic suspension systems obtained by means of digital computation are discussed. Consequently it is proved that authors' equation can discuss the unstable region of the magnetic suspension force. And then it is shown that authors' analytical results with relation to the magnetic suspension force are in close accordance with Frazier's results within a small displacement of the output axis.