Experiments on the lateral stabilisation and levitation of linear induction motors

Conventional linear motors always have a component of force which acts at right-angles to the normal (levitation) and longitudinal (traction) forces, and which attempts to expel the secondary side-ways from under the primary. This paper describes some different types of machine in which these lateral forces always act inwards, i.e. attempt to align the primary with the secondary. The first machines described rely upon an application of either the shaded-pole principle, or the reluctance principle, to produce a lateral stability which is conditional on the relative widths of the primary and secondary. A later development was the double-skewed or 'herringbone' motor, in which inwards-travelling fields are set up by appropriate skewing of the primary slots. This machine is shown to be somewhat disappointing, in that stability was once again restricted to very narrow secondaries. Transverse-flux geometry has led to the introduction of a large number of devices which are much simpler in construction than their longitudinal-flux counterparts, but which will stably levitate, guide, and propel a sheet secondary. Difficulty is encountered in maintaining stability when iron is introduced into the secondary iron circuits, but the paper shows how stability can be restored by using a double U-core construction.