Analysis and reduction of detent effect in magnetic lead screws with parallel magnetized permanent magnet segments

This paper deals with the analysis and suppression of detent effect in the magnetic lead screw (MLS), which is equipped with parallel magnetized permanent magnet (PM) segments to approximate the helical PM for manufacturing simplicity. The detent effect is caused by the non-uniform magnetization along the helical PM, and behaves as both thrust force ripple and torque ripple during the transmission process. In this paper, a three-dimensional (3-D) analytical model of the MLS is established to analyze and predict the air-gap magnetic field, and the thrust force and torque are then derived, as well as their ripple components. It demonstrates that the harmonic order of the ripples is solely dependent on PM segments' quantities per helix turn on both the nut and screw. The analytical analysis is verified by extensive 3-D numerical computations. The impact of load angel and quantities of PM segments on the detent effect are investigated. It's shown that the torque ripple suffers more seriously than thrust force ripple, and both ripple percentages drop with the increase of load angle. And it is highlighted that larger least common multiple of PM segments' quantities on screw and nut is conducive to improving the average values of thrust force and torque, and reducing the detent effect.