Direct detection of back EMF in permanent magnet step motors

Abstract

By choosing the winding and drive circuit configuration of a conventional two phase step motor so that during any one step time, a drive current pulse in one winding is not magnetically coupled to the other winding, then the back EMF induced in this other winding by the permanent magnet of the motor can be used to generate a feedback emitter pulse. The zero crossings of the induced EMF coincides with the detent positions in a conventional two phase step motor. Only one winding of the two phase step motor is driven during any step time. In order to use this same winding as an emitter signal source during the next step time, the drive current in this winding is reduced to zero before the zero crossing of the EMF waveform which is induced in this winding by the permanent magnet of the motor. The drive current is quickly reduced by using a supply voltage substantially higher than the rated motor voltage.

Dependencies are inferred from the claim text.