When designing and optimizing a stepping motor, accurately predicting its performance is crucial. However, due to the complex structure and operating conditions of such motors, engineers often make simplifying assumptions during calculations—such as ignoring magnetic saturation or assuming that the magnetic pressure drop in the core is independent of rotor position. These approximations can introduce errors into the results. To address this, this paper focuses on the BF36 magnetoresistive stepping motor and uses finite element analysis to account for magnetic saturation effects more accurately. By applying mesh auto-splitting technology, the entire motor’s magnetic field is analyzed to calculate the magnetic co-energy and, subsequently, the static torque.
The difference in tooth shapes between the stator and rotor in a reluctance stepping motor significantly impacts the magnetic conductance and the overall magnetic field distribution, which directly affects the motor's performance. In this study, we analyze the static torque characteristics using numerical methods, specifically by calculating the electromagnetic torque based on the magnetic co-energy. The formula used is derived from the angular displacement of the rotor, θr, and the change in angle, radθ. This allows us to evaluate how different current levels and rotor positions influence the motor’s magnetic field distribution.
To simplify the analysis, only half of the motor is considered due to symmetry. The solution area is chosen based on the motor’s structure, mode of excitation, and magnetic field symmetry. Figure 2 shows the meshing of this region. When a specific current is applied to the stator coil at a given rotor position, the two-dimensional magnetic field is calculated using finite element analysis. This provides the vector magnetic potential at internal nodes, the magnetic flux density in each unit, and the distribution of magnetic field lines.
By repeating this process for various current values and rotor positions, we can determine the relationship between current and flux linkage for the motor. This data is then used to compute the magnetic co-energy through integration, leading to the calculation of static torque. Figures 5 and 6 show the static torque characteristics under single-phase and two-phase energization at rated current. Comparing these with measured results, the maximum error was found to be 5.41% for single-phase and 7.34% for two-phase energization.
Additionally, the impact of stator and rotor tooth profiles on the maximum static torque was studied. It was concluded that rectangular stator teeth are ideal, but optimal dimensions exist for tooth height, pitch, and width. Using different ratios of tooth height to pitch and tooth width to pitch, the maximum static torque was calculated. The results showed that when the tooth height is close to the pitch and the tooth width is about 37.5% of the pitch, the motor achieves higher static torque, which is valuable for manufacturing purposes.
In conclusion, this research demonstrates that accounting for magnetic saturation improves the accuracy of static torque predictions. The proposed method proves effective and reliable, offering practical insights for industrial applications.
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