Analysis method for motor characteristics with three-dimensional flux distribution

This paper investigates the static torque characteristics of a two-phase pancake-type DC brushless motor for DVD-ROM spindles or chip coolers to control their driving speed. The novel spindle motor is of the axial-winding and radial-air-gap type, which has inherent three-dimensional (3-D) flux distribution and therefore requires excessive computation time for computer-aided design and analysis. The paper describes an analytical method based on an equivalent magnetic circuit, where the permeance distribution per salient pole is calculated by the boundary-element method. The method is particularly suitable for solving partial differential equations, and since the basic voltage equation can be deduced, the detent torque can be calculated analytically by using the energy method. This approach is computationally efficient and useful in the optimal design of a motor whose flux distribution is inherently three-dimensional. The Maxwell 3D Field Simulator has verified the numerical results. Tests of a prototype of the newly designed two-phase spindle motor for CD/DVD-ROM drives have demonstrated the performance and illustrated potential applications.