BECKHOFF AL2000 - Manual (Page 8)

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8
3 Phase Linear Motor AL2000
Different techniques can be applied in order to get an accurate and smooth motion of the slide. The permanent
magnets are fixed on the magnetplate. So the phase of the magnetic force of each magnet is invariable. For the
coils on the other hand the phase is adjustable. The slide is propagated by commutating the phase of the cur-
rent. Providing each coil with a suitable phase displacement is one of the appropriate techniques for linear mo-
tors. Another point of concern is the position of the coils in respect to the permanent magnets.
Erroneous postioning and phasing
Placing the coils in the same pattern and mutual distance as the magnets, as shown in the figure is problematic.
When in addition the coils are provided with equally phased current, the slide won’t move at all. Considerations
like these should be faced when designing a linear motor of series AL2000.
Postioning and phasing for a 3 phase linear motor AL2000
The principle of the three phase linear motor AL2000 comes to meet the mentioned problems. In the example
here discussed, the coils are equally positioned in the slide with a ratio 3 to 4 compared to the magnets of the
magnetplate (see figure ). As a result three different groups of coils can be distinguished. Coil 1 will continu-
ously have a comparable position as coil 4. Coil 2 and 5 are also comparably positioned as well as coil 3 and 6.
Smooth and accurate motion is now obtained by providing a three phase rotary current to the coils, one phase
to each group. The phase angle depends on the position of the slide. Information about this position is provided
by a linear encoder.