Overview
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Coreless linear motors are used for linear motor stages and electronic
packaging machines. Generally, the thrust force of a coreless linear motor
is smaller than that of an iron core linear motor. Since a coreless linear
motor has no cogging, its thrust force variation is much less than an iron
core linear motor. This note presents the use of magnetic field analysis
to obtain the thrust force of a coreless linear motor. |
Lorentz Force Density Distribution
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Figure 1 shows the Lorentz force density distribution at the translation
distance of 21 mm. When the current flows in the coils, Lorentz force is
produced by the magnetic field of the magnets. The strength of Lorentz
force is determined by the amount of the current and the strength of the
magnetic field. The direction of Lorentz force is determined by the direction
of the current and the direction of the magnetic field. At the translation
distance of 21 mm, the current flows only in the U-phase and W-phase coils.
So, Lorentz force density is higher in those coils facing the magnets.
The Lorentz force produced in the translation direction is thrust force.
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Thrust Force
| Figure 2 shows the thrust force waveform. Since a coreless linear motor
has no cogging, the thrust force variation is about 6.0 % relative to the
average thrust force. |
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