Abstract: An electromagnetic actuator is described in which a rotor comprising permanent magnet means is rotatable in a stator which is magnetisable by causing an electric current to flow through at least one winding associated with the stator. The rotor has at least two stable rest positions, each defined by spring and/or magnetic forces acting on the rotor. Spring means stores energy during part of the movement of the rotor and provides kinetic energy for accelerating the rotor during subsequent movement thereof away from rest in one position towards another. A magnetic torque is exerted on the rotor when a current flows in said at least one winding which is sufficient to overcome the force(s) holding the rotor in that rest position, to cause the rotor to rotate in a direction from that rest position towards another a rest position. The rotor is connected to a thrust member by a mechanical linkage by which the rotational movement of the rotor is converted into substantially linear movement.

Abstract: An electro-magnetically operated device is described in which a magnetisable armature, typically a length of thin naturally resilient mild steel, is sandwiched between, and extends from, two parts of a magentic circuit which contains an air gap into which the armature extends. An electromagnet polarizes the armature along its length so as to cause the end thereof in the air gap to be attached to one or the other of the two poles of the magnetic circuit defining the gap. The armature is designed so as to be capable of adopting a mid-position between the poles of the air gap if the curent flowing in the electromagnet is reduced to zero. Equalising the air gaps and adjusting the size of the gap relative to the resilience of the armature will produce a bistable characteristic in which the armature will not remain in the mid-position, but will always remain in contact with one pole or the other, and is shifted from one to the other by a pulse of current of appropriate polarity.

Abstract: A magnetic device is formed from a permanent magnet (12, 14) generating magnetic flux, and an armature (10) which can occupy either a first air gap in which the flux is in one direction, or a second air gap in which the flux is in the opposite direction, with a region of flux cancellation between the two air gaps. At least one electromagnet winding (36, 38) may be provided to which current can be supplied which when energised produces a magnetic flux in one direction or the other, depending on the direction of the current, the flux from the winding increasing the flux density in one of the air gaps and reducing the flux density in the other air gap. This effectively shifts the flux cancellation region towards or into one of the two air gaps so as to produce a flux density gradient extending from one air gap to the other, which will cause the armature to move into (or remain in) the air gap having the higher flux density, and continue to remain in that air gap after the current flow ceases.