Abstract
The authors propose the new brushless DC motor without stator slots as a servo motor. The conventional motor has a lots of stator slots, and the stator coils are placed in the slots. In the new motor, the stator has no slots. Accordingly, the stator coils are fixed along the inside of the stator cores, and the coils are molded by a thermosetting resin. Therefore, the magnetic airgap is very large. Generally, as leakage fluxes increase in response to the size of the airgap, output torque decreases. But the new motor improves characteristics of torque by using a new magnet having high magnetic energy. And the new motor without slot does not produce cogging torque and electromagnetic noise and torque ripples of harmonic magnetic fluxes caused by stator slots. In this paper, calculated characteristics analyzed by flux density using FEM and experimental result is described. It is confirmed that the analyzed results agreed with experimental results with good accuracy. In the experimental results using a 4-pole 0.4kW test motor and high-efficiency drive inverter with power factor control, the motor efficiency is about 83.7%, the motor power factor is about 96.9%, and cogging torque is zero.
