Electromagnetic motor rotatable in either direction

Abstract

An electromagnetic stepping motor has a stator with an armature having the shape of an isosceles trapezoid the base of which is interrupted by a central gap and which is provided with three pole faces. The rotor comprises a permanent magnet. The stator comprises two coils one of which is located between a pole face opposite said gap and one of the other two pole faces. The other coil is located between the pole face opposite said gap and the other of said other two pole faces. When a current passes through the coils, the rotor is subjected to magnetic fields having directions which are oblique to each other and which are symmetrical with respect to a diameter of the rotor. The sense of the coil currents determines the sense of the fields. The arrangement is such that one can create in the zone of the rotor a resultant magnetic field which can extend in any one of four different directions dependent on the sense of the currents passing through the coils. By appropriate commutation of the sense of each of the two coil currents, one can cause the resultant magnetic field to rotate in one direction or in the other, to drive the rotor in one or the other directional sense, but always in the same direction for a given field rotation. Thus, the rotor rotates always in the desired direction, even if a rotational step is missed or if the rotor makes one rotational step too many.