Precise Measurement of Suspension Force in Two-Axis Actively-Positioned Bearingless Motor for a Comparison to 3D-FEM Analysis

Bearingless motors are required in centrifugal pumps, reaction wheels and artificial hearts for the applications in semiconductor manufacturing, space applications and medical devices, respectively. Two-axis actively regulated bearingless motors have the advantages of low cost and compactness. Only two degrees of freedom are actively regulated in the radial x-ydirections. Thus it is known that tilting motion causes seriousinterference to the radial position regulation. The interference occurs when the following three positions are not exactly corresponding; (i) the center of gravity of the rotor, (ii) the application point of the suspension force, and (iii) the position of the displacement sensors. A discrepancyin these positions causes tilting and axial displacements, which results in a reduction of radial suspension force. In this paper, a 3D-FEM analysis of the radial suspension force is carried out taking into account the rotor tilting displacement. A precise measurement method of the static radial suspension force is proposed and tested. The experiment results indicate a good correspondence to the finite element analysis.