Contactless measurement of the secondary position in linear reluctance motors

A new method of measuring the position of the secondary in a linear reluctance motor (LRM) is described, based on sampled measurements of the primary phase currents and the airgap flux density at the primary surface. Corrections must be applied for primary slot openings, primary end effects, and currents induced in a conducting barrier between the primary and the secondary. A static positional accuracy of ±1°, representing ±0.55% of the pole pitch, has been achieved in an experimental machine with load angles of up to 30°. The method is particularly suited to applications where the LRM is used for materials handling in a sealed containment system, since the secondary position can be determined from measurements made on the primary side of a conducting barrier. It should be capable of accurate position measurement at speeds of up to 1 m/s, which is the nominal upper limit for systems of this kind