Actuators

An apparatus comprising:

• a shape memory alloy actuator comprising:
• a first part;
• a second part;
• one or more heat sinks;
• one or more shape memory alloy wires comprising a first segment of shape memory alloy wire, wherein:
• the one or more shape memory alloy wires are configured to move the second part relative to the first part over a range of movement;
• the one or more shape memory alloy wires include the first segment of shape memory alloy wire and a second segment of shape memory alloy wire;
• the first segment of shape memory alloy wire is connected to the first part by a first resilient element at a first end, and a second end of the first segment of shape memory alloy wire is connected to the second part;
• the second segment of shape memory alloy wire is configured to oppose the first segment of shape memory alloy wire;
• tension of the first and second segments of shape memory alloy wire are variable independently of the position of the second part over at least a portion of the range of movement;
• the first resilient element is configured such that in response to a change in tension of the first segment of shape memory alloy wire, a first distance between the first segment of shape memory alloy wire and at least one of the heat sinks is increased or decreased by an amount greater than a change in a second distance between the first and second ends;
• and
• a controller configured to:
• control the relative positions of the first part and the second part;
• and
• control a cooling rate of the first segment of shape memory alloy wire by adjusting the tension of the first segment of shape memory alloy wire, wherein:
• moving the first segment of shape memory alloy wire towards at least one of the heat sinks increases the cooling rate;
• and
• moving the first segment of shape memory alloy wire away from at least one of the heat sinks decreases the cooling rate.