Patent ID: 8710945
Filing Date: 2014-04-29
Classification: H01F

Abstract:
1. An electromagnetic actuator comprising: an armature comprising a permanent magnet, wherein the armature is movable between first and second stable positions; two electric coils disposed on opposing sides of the armature along its direction of movement, with their axes substantially aligned with said direction; and a magnetic flux container substantially surrounding the armature and the coils to substantially contain magnetic flux generated thereby and to substantially shield its interior from external magnetic flux, wherein in each stable position magnetic flux generated by the permanent magnet extends around a magnetic circuit path including the container so as to retain the armature in its stable position when the coils are de-energized, energizing the coils causes the armature to move from one stable position to the other, there is a third stable position between the first and second stable positions, and the actuator comprises a pair of resilient devices which are partially compressed or extended when the armature is in the third stable position, with the resilient devices arranged such that as the armature moves from the third stable position to one of the first and second stable positions, one of the pair of resilient devices is compressed or extended further, at least during a final portion of said movement, so as to urge the armature back towards the third stable position, and the degree of partial compression or extension of the other resilient device remains unchanged.