Calculation and measurement of radial and axial forces for a bearingless PMDC motor

A bearingless motor is an electromotor without any kind of bearings. Knowing accurately the radial and axial forces applied to the rotor is particularly important to the magnetic suspension control of the rotor. This paper presents the calculation methods of radial and axial force based on 2-D and 3-D finite element analysis for bearingless PMDC motors, a simple and practical method to measure the static radial and axial forces of bearingless motors is introduced. The comparison of the calculated radial and axial forces with the tested results for a 4-pole bearingless PMDC motor is presented in the paper.