Overview
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A coreless motor provides advantages, such as a reduction in torque ripple
and inertia, because the rotor does not have an iron core. A coreless motor
can also reach higher speeds because there is no iron loss.
While a coreless motor has both superior response and control, the manufacturing
costs increase to improve miniaturization and performance as they require
materials such as costly magnets.
Therefore, examination through the magnetic field analysis becomes more
advantageous as various innovations to lower the costs of manufacturing
small, high-performance motors are necessary.
This example presents the use of the magnetic field analysis to obtain
the torque waveform amplitude of a coreless motor. |
Torque Waveform/Current Waveform
| The torque waveform is indicated in Fig. 1, and the current waveform is
indicated in Fig. 2. A smooth rotation can be achieved because the rotor
doesn't have an iron core as indicated in Fig. 1. The average torque is
also indicated at 0.022 mN•m. A ripple has occurred in the torque
waveform calculated by this analysis, but this is caused by the varying
contact of the brush and commutator as indicated in Fig. 2. |
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Closeup |
Current Density Distribution/Lorentz Force Density Distribution
Closeup |
The current density distribution of the coil for 360 degrees of rotation
is indicated in Fig. 3, and the Lorentz force density distribution is indicated
in Fig. 4. A current flows in coil 1 and coil 3 without flowing in coil
2, when the rotation angle is 360 degrees, as indicated in Fig. 3. The
currents also flow in opposite directions of one another. The enlarged
view in Fig. 4 indicates the force produced in the rotation direction for
coil 3, but the force produced for coil 1 goes with, as well as against,
the rotation direction. This occurs because the direction of the current
differs while the directions of the magnetic fields for each phase coil
are the same. |
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