Electromagnetic lock

An electromagnetic lock for locking together two relatively movable members in a predetermined relative position, comprising:

• electromagnet means,
• a magnetisable member,
• means to energise the electromagnet means to cause an electromagnetic field,
• magnetic flux cancelling means for cancelling the magnetic flux in the electromagnet means when the electromagnet means is switched off, said flux cancelling means including a circuit including charge storage means connected so that, when the electromagnet is switched off, the electromagnet discharges through itself and then charge from the charge storage means is applied to the electromagnet means to neutralise the residual magnetic flux, and
• mounting means for mounting the electromagnet means and magnetisable member each to a respective one of two relatively movable members in such a position that, as the relatively movable members move to the predetermined position, the magnetisable member and the electromagnet means move towards one another generally transversely of the axis of the electromagnetic field, whereby, when the two relatively movable members are in said predetermined position, said movable magnetisable member may move towards said electromagnet means generally along the axis of the electromagnetic field under the action of the electromagnetic field to normally hold said two relatively movable members in said predetermined relative position,
• shoulder means being provided on or connected with said magnetisable member and said electromagnet means whereby when said relatively movable members are in said predetermined position and said movable magnetisable member and electromagnet means are moved relatively axially towards one another said shoulders may engage to retain the two relatively movable members in said predetermined position even if the two relatively movable members are forced in such a manner to overcome the electromagnetic attraction between said magnetisable member and said electromagnet means.