Contactless position sensing in linear reluctance motors

The position of the secondary in a linear reluctance motor can be sensed by monitoring the airgap flux density at regularly spaced points along the primary surface and comparing it with the current density derived from the phase currents. A correction must be applied for the effect of slot openings, derived from a finite-element analysis of the airgap field. A static positional accuracy of ±0.5°, representing ±0.3% of the pole pitch, has been achieved in an experimental machine