Investigation of permanent magnet magnetization for a bearingless servomotor

High-precision servomotors, such as galvano scanner motors, have serious bearing problems due to nonuniform lubricant distribution resulting from the repetitive pivoting motion. One possible solution is to use a bearingless drive. However, a conventional bearingless drive has limited motion range because of the narrow initial clearance for magnetic suspension. To extend the initial clearance, a variable permanent magnet (PM) is used in the motor part of a bearingless drive system. The research objective is to realize a multiple-degree-of-freedom bearingless servomotor with a wide range of motion using a variable PM force. As the first step in the present study, PM magnetization and its influence on the torque ripple with several pole/slot combinations in the motor are investigated based on three-dimensional finite element method analysis.