Over-load capacity of tubular permanent magnet linear motors

The magnetic limit on the force produced by a tubular permanent linear motor can be taken to be reached when the armature mmf is sufficient to reduce the magnet flux to zero in one area of the magnet. It is shown that this limit is greater when the construction uses embedded magnets than when surface magnets are used. In both cases the limit may be extended by the use of quadrature-axis flux barriers. These reduce the armature flux and therefore the demagnetizing effect whilst leaving the permanent magnet field largely unaffected.