Optimal tooth-geometry for specific performance requirements of a hybrid stepper motor

The design of a hybrid stepper motor for achieving a specific performance necessitates the choice of appropriate tooth geometry. In this paper, a detailed account of the results of two-dimensional and three-dimensional finite-element (FE) analyses, conducted with different tooth width/tooth pitch ratios (t/(lambda)) and also with various tooth/slot shapes such as rectangular, trapezoidal, triangular, and circular, is presented. The study has shown that the rectangular tooth/slot shape is better with respect to torque density. The best results are obtained when t/(lambda) lies between 0.38 and 0.4. The use of equal tooth pitch on the stator and rotor structures provides nearly 10% more torque than the case with unequal tooth pitch, but with corresponding increase in detent torque. For the requirements of maximum torque density, high-detent torque, and better positional accuracy, equal pitch slotting with equal tooth widths has to be adopted. Instead, for maximum torque density, less detent torque, better positional accuracy, and smooth static torque profile, different pitch slotting with equal tooth width has to be provided.