Investigation Of Small Low-Speed Permanent Magnet Servo Motor

With the increasing requirement for the servo system, higher performance requirements have been brought forwards to the servo motor. For a permanent magnet (PM) machine, permanent magnets take the place of field windings on the rotor, which simplifies the motor structure. Benefiting from the absence of the exciting current and the excitation loss, the efficiency and the power density have increased. Permanent Magnet Synchronous Motor (PMSM) has the advantages of low inertia, high efficiency, high torque-current ratio, low noise, no excitation loss, and become a competitive choice for high precision servo system.The motor analyzed in this paper is a Permanent Magnet Synchronous Servo Motor with the rated speed of5rpm and rated torque of0.2Nm. Because of the low speed, the servo system is sensitive to the torque ripple. First, material selection, winding arrangement and initial structure design is finished according to requirement. Then several structures for fundamental index are proposed and compared. Considering that Permanent Magnet Synchronous Motor with one-piece stator structure cannot meet the demand of rated input power, the segmented stator technology, which causes a significant higher copper fill factor and power density, is a key solution to ease the manufacture process, particularly the stator winding process. Several feasible stator segmentations, e.g., uniform segments, and nonuniform segments, are proposed and investigated. A detailed theoretical and experimental study is carried out in this paper to reveal the influence of the gaps in the yoke on the magnetic field symmetry and cogging torque of a Permanent Magnet Synchronous Motor. Given with excellent output performance and simple manufacturing process, the machine with9or18additional gaps are considered the best choices. As the shapes of the tongues and grooves vary with the manufacture techniques and applications, the cogging torque of several Permanent Magnet Synchronous Motors with various kinds of the shapes of the tongues and grooves are analyzed in this paper. Two types of Permanent Magnet Synchronous Servo Motors have been manufactured and experimental performances coincide with the results of finite element analysis (FEA).