Actuators

1 . 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.

2 . The apparatus according to claim 1 , further comprising:

a temperature sensing module configured to determine a temperature corresponding to the first segment of shape memory alloy wire, wherein the controller is configured to:

determine the temperature; and

adjust a distance of the first segment of shape memory alloy wire from at least one of the heat sinks based on the temperature, wherein the adjusting the distance of the first segment of shape memory alloy wire from at least one of the heat sinks based on the temperature comprises:

(i) retrieving, from a look-up table stored by the controller, a pre- calibrated distance which corresponds to the temperature; or

(ii) in response to determining an increase in the temperature, reducing the distance of the first segment of shape memory alloy wire from at least one of the heat sinks; in response to determining a decrease in the temperature, increasing the distance of the first segment of shape memory alloy wire from at least one of the heat sinks.

3 . The apparatus according to claim 1 , wherein the controller is further configured to reduce the distance of the first segment of shape memory alloy wire from at least one of the heat sinks before changing the relative positions of the second part and the first part.

4 . The apparatus according to claim 1 , wherein the controller is further configured to increase the distance of the first segment of shape memory alloy wire from at least one of the heat sinks after changing the relative positions of the second part and the first part.

5 . The apparatus according to claim 1 , wherein;

the controller is further configured to adjust a distance of the first segment of shape memory alloy wire from at least one of the heat sinks based on relative position of the second part within the range of movement; and

the adjusting the distance of the first segment of shape memory alloy wire from at least one of the heat sinks based on relative position of the second part within the range of movement comprises:

in response to the second part moving closer to a centre of the range of movement, increasing the distance of the first segment of shape memory alloy wire from at least one of the heat sinks; and

in response to the second part moving further from the centre of the range of movement, decreasing the distance of the first segment of shape memory alloy wire from at least one of the heat sinks.

6 . The apparatus according to claim 1 , wherein:

the one or more shape memory alloy wires comprise one or more further segments of shape memory alloy wire, each further segment of shape memory alloy wire being identically configured to the first segment of shape memory alloy wire; and

the controller is configured to control each further segment of shape memory alloy wire in the same way as the first segment of shape memory alloy wire.

7 . A method of controlling a shape memory alloy actuator, the method comprising:

controlling a cooling rate of a first segment of shape memory alloy wire by adjusting a tension of the first segment of shape memory alloy wire, wherein:

the shape memory alloy wire is part of the shape memory alloy actuator, the shape memory alloy actuator comprising:

a first part;

a second part;

one or more heat sinks; and

one or more shape memory alloy wires, comprising the first segment of shape memory alloy wire and a second segment of shape memory alloy wire, wherein:

the second segment of shape memory alloy wire is configured to oppose the first segment of shape memory alloy wire;

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; and

a tension of the first and second segments of shape memory alloy wire is variable independently of the position of the second part over at least a portion of the range of movement;

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; and

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;

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.

8 . The method according to claim 7 , wherein the one or more shape memory alloy wires are configured to move at least one of the second part relative to the first part over the range of movement or the first part relative to the second part over the range of movement.

9 . The method according to claim 8 , wherein the second end of the first segment of shape memory alloy wire is connected to the second part by a second resilient element.

10 . The method according to claim 7 , further comprising:

determining, using a temperature sensing module, a temperature corresponding to the first segment of shape memory alloy wire; and

adjusting a distance of the first segment of shape memory alloy wire from at least one of the heat sinks based on the temperature.

11 . The method according to claim 10 , further comprising:

in response to changing the relative positions of the second part and the first part, reducing the distance of the first segment of shape memory alloy wire from at least one of the heat sinks.