Abstract: An electronic commutation circuit for feeding from a direct-current source an electric motor consisting of a stator with a polyphase winding and a magnetized rotor coupled mechanically with a position and angular speed sensor, comprises for each phase of the stator winding a transistor switching circuit, the operation of the switching circuits being sequentially controlled from signals received from the sensor in such a way that the various phases of the stator winding are fed by a system of polyphase bidirectional currents of substantially sinusoidal form rising and falling in steps, the frequency and phase angle of these currents being determined by the speed of the rotor and by its position relative to the stator. Each of the switching circuits is preceded by an electronic trigger with three stable positions and which delivers a positive, zero or negative voltage to provide control of the binary state of the associated commutation circuit.

Abstract: A low-cost electromechanical watch movement comprises a step-by-step motor including a multipolar rotor mounted for rotation within an encased stator and carrying driving pallets operatively engaging with a time-display gear train. The stator and rotor each have a like number of alternate pole pieces disposed on arcuate surfaces concentric to the axis of the rotor and separated radially by arcuate air-gaps of constant section. Small circumferential air-gaps separate the pole-pieces of the stator and, possibly, the rotor. The pole pieces of the rotor are permanently magnetized and those of the stator electromagnetically energizable by a winding supplied with periodic electric pulses from a pulse generator to drive the rotor through an angle less than 15.degree. in response to a pulse. A spring lightly biases the rotor to its initial position.