Patent ID: 8395855
Filing Date: 2013-03-12
Classification: F03G,G02B,G03B

Abstract:
1. A shape memory alloy actuation apparatus comprising: a support structure; a movable element supported on the support structure by a suspension system which guides movement of the movable element along a movement axis; a shape memory alloy actuator biassed against contraction by a resilient biassing arrangement and arranged on contraction to drive movement of the movable element relative to the support structure, the shape memory alloy actuator under the influence of the resilient biassing arrangement having a property that resistance varies with decreasing length on contraction, and in the absence of end-stops limiting movement, along a curve passing through a local maximum resistance and thereafter through a local minimum resistance; and an end-stop arranged to limit movement of the movable element on extension of the shape memory alloy actuator at a position where the shape memory alloy actuator has a predetermined length that is above the length corresponding on said curve to the local maximum resistance by an amount not greater than 15% of the difference between (i) the length corresponding on said curve to the local maximum resistance and (ii) the length corresponding on said curve to the local minimum resistance.