Diamagnetic suspension system for small rotors

Abstract

A novel frictionless motor-bearing combination, featuring a passive five degrees of freedom (DOF) suspension system is presented in this paper. In conventional frictionless systems, levitation is achieved by means of feedback controlled electromagnetics or electrostatics (active bearings), permanent magnets in combination with displacement (passive bearings) or by superconductive repulsion of permanent magnets. Earnshaw's theorem discards the possibility of passive static magnetic levitation, but by taking advantage of the diamagnetic effect, a passive magnetic system can be stabilized. In the proposed system, all the degrees of freedom of a disc-shaped magnetic rotor, except its rotation around the main axis, are stabilized using the diamagnetic properties of materials such as bismuth and graphite. As the weight of the rotor is compensated with a permanent magnet, the proposed system can make use of the weak diamagnetic repelling forces, presenting the only known principle for 'real' levitation (no energy input) at room temperature. The presented approach leads to very compact energy-saving solutions. The principle of diamagnetic levitation is well known and understood. The presented experimental work adds radial stiffness to the classic three degrees of freedom suspension and powers the rotor using an induction motor. The realized motor is hardly bigger than one cubic centimeter and turns with up to 800 rpm. This paper intends to draw attention to this uncommon method of levitation and to show that it could be used to design micro-mechatronical actuators.