Analysis and Design of a High Force Low Torque Ratio Magnetic Field Modulation Screw

This article proposes a magnetic field modulated screw (MFMS), which exhibits high force low torque transmission ratio. Essentially, the proposed MFMS requires less torque to generate a significant thrust force. The “force per torque” ratio is 1.02 kN/N.m, which is 4 times higher than conventional MFMS. The proposed MFMS is analyzed based on three-dimensional (3-D) magnetic field modulation. Then, the uniform analytical expression of the “force per torque” ratio can be derived. The pole-pairs of the proposed MFMS are reasonably selected, resulting in a significant improvement in the “force per torque” ratio. Besides, a discrete analysis method is employed to analyze the circumferential and axial modulation in the MFMS. Based on this, the modulation process and performances of the proposed MFMS is analyzed and compared. Moreover, the 3-D Maxwell tensor method is first used to analyze the contribution of air-gap flux density harmonics to the torque and thrust force. Finally, the 3-D finite element method and experiments are used to validate the theoretical analysis.