Overview
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Linear motors have been used in carrying devices and tooling machines for
their capability for high-speed performance, high acceleration/deceleration,
and accurate positioning.
While the key issue is to increase the thrust force, reducing variations
in thrust force and magnetic attraction are also required.
This note presents a case study of calculating the cogging and evaluating
the thrust force. |
Cogging Ripple
Fig.1 shows the cogging force waveform. To examine the cause of the cogging
force, the flux density distribution at the position (timing) circled in
blue in Fig. 1 is shown in Fig. 2.
Fig. 2 shows that the flux density at the end of the mover is not evenly
distributed. This imbalance of the magnetic circuit is the key factor causing
large cogging forces. |
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Thrust Force and Magnetic Attraction
The position versus thrust force is shown in Fig.3, and the position versus
attraction force is shown in Fig.4.
The graphs show the periods of thrust and attraction have the same interval
as the period of cogging. The cogging force must be made smaller if the
thrust variation is to be reduced. To reduce the attraction force variation,
it is necessary to reduce the flux perpendicular to the gap, which might
be done by changing the shape of the slot. The attraction force is caused
by perpendicular flux in the gap, in a manner similar to the radial force
of a rotating machine. |
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