GB2622420A

GB2622420A - Variable aperture assembly

Info

Publication number: GB2622420A
Application number: GB2213593.3A
Authority: GB
Inventors: matthew bunting Stephen; Langhorne Robert; Armstrong Samuel; Farmer Geoffrey; Reynolds Felix
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2022-09-16
Filing date: 2022-09-16
Publication date: 2024-03-20
Also published as: GB202213593D0

Abstract

A variable aperture assembly 1 comprising a plurality of blades 40 which may be driven by a Shape Memory Alloy (SMA) actuator 10 (Fig 7). There is a base 30 and a rotatable part 20 wherein the actuator assembly drives rotation of the rotatable part relative to the base about a primary axis O. The multiple blades are connected to the base via pivot pins or moving pins and are connected to the rotatable part via the other of the pivot pins or moving pins. The arrangement of blades defining a changeable aperture. Preferably the actuator assembly has one or more SMA elements which upon contraction drive the rotation of the rotatable part relative to the base. The actuator assembly may also be driven by a drive chip. The variable aperture assembly may be used in a camera.

Description

VARIABLE APERTURE ASSEMBLY

Field

The present application relates to a variable aperture assembly.

Summary

According to an aspect of the present invention, there is provided a variable aperture assembly comprising: a base; a rotatable part; an actuator assembly configured to drive rotation of the rotatable part relative to the base about a primary axis; a plurality of blades connected to the base via either a plurality of pivot pins or a plurality of moving pins, and connected to the rotatable part via the other of the plurality of pivot pins and the plurality of moving pins, and arranged to define a variable aperture with a central axis which coincides with the primary axis; wherein said rotation of the rotatable part (relative to the base) drives relative movement between the pivot pins and the moving pins, which drives rotation of the plurality of blades about the pivot pins; wherein said rotation of the plurality of blades changes the size of the variable aperture Optionally, the moving pins are configured to rotate (e.g. move in a circular arc) around the pivot pins (when the rotatable part is rotated relative to the base).

Optionally, the moving pins are connected to the base or the rotatable part via connecting arms, wherein the connecting arms are configured to allow (e.g. deform to allow) rotation of the moving pins around the pivot pins.

Optionally, the connecting arms comprise crank arms and/or flexure arms (which e.g. are integrally formed with the base or the rotatable part).

Optionally, the connecting arms are configured to bias the moving pins at least partially towards the pivot pins.

Optionally, the connecting arms are configured to bias the moving pins such that the plurality of blades are bistable, i.e. configured to cause the plurality of blades to have a first stable equilibrium position and a second stable equilibrium position. The first and second stable equilibrium positions may correspond to the ends of the range of possible movement of the plurality of blades.

Optionally, the moving pins are connected to the blades in a manner that prevents relative translational movement between each connected moving pin and blade (but allows each connected moving pin and blade to rotate relative to each other, i.e. the moving pins are rotatably held by the blades). Additionally or alternatively, the moving pins may be rotatably held by the connecting arms.

Optionally, the moving pins and the pivot pins are configured (e.g. are close enough to each other) to provide, per degree of rotation of the rotatable part about the primary axis, at least 5, 10, or 20 degrees of rotation of the blades about the pivot pins.

Optionally, each blade is connected to the base and to the rotatable part via one (e.g. only one) pivot pin and one (e.g. only one) moving pin.

Optionally, the base (e.g. the main body of the base) is (at least partially or fully) provided/nested within a (through) hole that extends through the rotatable part along the primary axis.

Optionally, the plurality of blades (at least partially) overlap with the connecting arms and/or the rotatable part as viewed along the primary axis.

Optionally, the plurality of blades (at least partially) overlap with each other as viewed along the primary axis.

Optionally, the plurality of blades generally lie in a plane perpendicular to the primary axis which sits on top of the rotatable part and the base (e.g. the plurality of blades (at least partially) cover/are provided at sides of the base and the movable part that generally face in the same direction).

Optionally, a bearing (e.g. a sliding bearing) is provided between the base and the rotatable part.

Optionally, the variable aperture assembly comprises a holding arrangement configured to releasably (i.e. temporarily) hold the rotatable part at one or more positions within the range of positions that the rotatable part is capable of being driven to relative to the base by the actuator assembly.

Optionally, the actuator assembly comprises one or more shape memory alloy (SMA) elements configured to, upon contraction, (directly or indirectly) drive the rotation of the rotatable part relative to the base.

Optionally, the actuator assembly comprises: a support structure fixed to the base; and a movable part coupled to the rotatable part; wherein the one or more SMA elements are configured to, upon contraction, drive relative movement between the movable part and the support structure so as to drive the rotation of the rotatable part (relative to the base).

Optionally, the movable part is fixed to the rotatable part; and the one or more SMA elements are configured to, upon contraction, drive rotation of the movable part relative to the support structure (e.g. around the primary axis) so as to drive the rotation of the rotatable part (relative to the base).

Optionally, the variable aperture assembly comprises a holding arrangement configured to releasably (i.e. temporarily) hold the movable part at one or more positions within the range of positions that the movable part is capable of being driven to relative to the support structure.

Optionally, the one or more SMA elements comprise (e.g. a total of) four SMA elements configured to (directly, or indirectly via the movable part) drive the rotation of the rotatable part; wherein, optionally, the four SMA elements are arranged in a loop at different angular positions around the primary axis; and, optionally, wherein successive SMA elements around the primary axis are configured (on contraction) to apply a force to the rotatable part (directly or indirectly via the movable part) in alternate senses around the primary axis.

Optionally, the one or more SMA elements comprise: a first SMA element arranged to (directly, or indirectly via the movable part) rotate the rotatable part about the primary axis in a first sense; and a second SMA element arranged to (directly, or indirectly via the movable part) rotate the rotatable part about the primary axis in a second sense, wherein the second sense is opposite to the first sense.

Optionally, the one or more SMA elements comprise: a first pair of SMA elements, electrically connected together (in series), arranged to apply a torque to the rotatable part (directly, or indirectly via the movable part) for rotating the rotatable part about the primary axis in a first sense; and a second pair of SMA elements, electrically connected together (in series), arranged to apply a torque to the rotatable part (directly, or indirectly via the movable part) for rotating the rotatable part about the primary axis in a second sense, wherein the second sense is opposite to the first sense.

Optionally, the actuator assembly is configured to be controlled by a drive chip via two drive channels of the drive chip (only).

According to another aspect of the present invention, there is provided a camera assembly comprising: a variable aperture assembly as described above; a further actuator assembly; a (single) drive chip operatively connected to the actuator assembly and the further actuator assembly for controlling the actuator assembly and the further actuator assembly; wherein the drive chip comprises at least four drive channels; and wherein the actuator assembly is configured to be (fully) controlled (only) via a first channel and a second channel of the at least four drive channels, and the further actuator assembly is configured to be (fully) controlled (only) via a third channel and a fourth channel of at least four drive channels.

Optionally, the further actuator assembly is a focus (e.g. auto-focus (AF)) actuator assembly (configured to drive movement of one or more lenses along the primary axis, and, optionally, comprising one or more SMA elements configured to drive said movement).

According to another aspect of the present invention, there is provided a camera assembly comprising: a variable aperture assembly as described above; and a lens assembly; wherein the variable aperture assembly (e.g. the base of the variable aperture assembly) is mounted on the lens assembly, and the optical axis of the lens assembly coincides with the primary axis.

Optionally, the lens assembly is (at least partially) provided/nested within a (through) hole that extends through the base along the primary axis.

Optionally, more than 50%, 60%, 70%, 80%, or 90% of the variable aperture assembly overlaps with the lens assembly along the primary axis (i.e. as viewed across the primary axis).

Optionally, the actuator assembly fully overlaps with the lens assembly along the primary axis (i.e. as viewed across the primary axis).

Brief description of the drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic view of a variable aperture assembly in a first position; Fig. 2 is a schematic view of the variable aperture assembly of Fig. 1 in a second position; Fig. 3 is a schematic view of the variable aperture assembly of Fig. 1 mounted on a lens assembly; Fig. 4 is a schematic view of a variable aperture assembly; Fig. 5 is a schematic view of the variable aperture assembly of Fig. 4 mounted on a lens assembly; Fig. 6 is a schematic view of the variable aperture assembly of Fig. 4 mounted on a lens assembly; Fig. 7 is a schematic view of an actuator assembly comprising four shape memory alloy (SMA) wires; Fig. 8 is a schematic illustration of an eight-channel drive chip configured to control three actuator assemblies; Fig. 9 is a schematic illustration of two four-channel drive chips configured to control three actuator assemblies; Fig. 10 is a schematic illustration of an eight-channel drive chip and a four-channel drive chip configured to control three actuator assemblies; and Fig. 11 is a schematic view of a variable aperture assembly comprising folded SMA wires.

Detailed description

Figs. 1 to 6 show a variable aperture assembly 1 comprising: a base 30; a rotatable part 20; an actuator assembly 10 configured to drive rotation of the rotatable part 20 relative to the base 30 about a primary axis 0; a plurality of blades 40 connected to the base 30 via a plurality of pivot pins 31 and connected to the rotatable part 20 via the a plurality of moving pins 21, and arranged to define a variable aperture with a central axis which coincides with the primary axis 0; wherein said rotation of the rotatable part 20 (relative to the base) drives relative movement between the pivot pins 31 and the moving pins 21, which drives rotation of the plurality of blades 40 about the pivot pins 31; wherein said rotation of the plurality of blades 40 changes the size of the variable aperture.

Plurality of blades 40 are distributed around the primary axis a In alternative embodiments, the plurality of blades 40 may be connected to the base 30 via the plurality of moving pins 21 (i.e. pins connected to connecting arms 22), and connected to the rotatable part 20 (i.e. pins about which the plurality of blades rotate about) via the plurality of pivot pins 31.

The variable aperture assembly 1 of Figs. 1 to 3 and the variable aperture assembly 1 of Figs. 4 to 6 differ only in that the variable aperture assembly 1 of Figs. 1 to 3 has the base 30 nested within the rotatable part 20, whereas the variable aperture assembly 1 of Figs 4 to 6 has the rotatable part 20 nested within the base 30.

The moving pins 21 are configured to rotate (e.g. move in a circular arc) around the pivot pins 31 (when the rotatable part 20 is rotated relative to the base 30).

The moving pins 21 are connected to the rotatable part 20 via connecting arms 22, wherein the connecting arms 22 are configured to allow (e.g. deform to allow) rotation of the moving pins 21 around the pivot pins 31. However, in alternative embodiments, the moving pins 21 may be connected to the base 30 via connecting arms 22, wherein the connecting arms 22 are configured to allow (e.g. deform to allow) rotation of the moving pins 21 around the pivot pins 31.

The connecting arms 22 comprise flexure arms 22 which are integrally formed with the base 30 or the rotatable part 20. However, in alternative embodiments, the connecting arms 22 may comprise crank arms.

The connecting arms 22 may be configured to bias the moving pins 21 at least partially towards the pivot pins 31.

The connecting arms 22 may be configured to bias the moving pins 21 such that the plurality of blades are bistable, i.e. configured to cause the plurality of blades 40 to have a first stable equilibrium position and a second stable equilibrium position. The first and second stable equilibrium positions may correspond to the ends of the range of possible movement of the plurality of blades 40.

Although Figs. 1 to 6 only show the plurality of blades 40 being connected to the base 30 via the plurality of pivot pins 31 and connected to the rotatable part 20 via the plurality of moving pins 21, in alternative embodiments the plurality of blades 40 could instead be connected to the base 30 via a plurality of moving pins 21 and connected to the rotatable part 20 via the plurality of pivot pins 31.

The moving pins 21 are connected to the blades 40 in a manner that prevents relative translational movement between each connected moving pin 21 and blade 40, but allows each connected moving pin 21 and blade 40 to rotate relative to each other, i.e. the moving pins 21 are rotatably held by the blades 40. Additionally or alternatively, the moving pins 21 may be rotatably held by the connecting arms 22.

The moving pins 21 and the pivot pins 31 are configured (e.g. are close enough to each other) to provide, per degree of rotation of the rotatable part 20 about the primary axis 0, at least 5, 10, or 20 degrees of rotation of the blades 40 about the pivot pins 31.

Each blade 40 is connected to the base 30 and to the rotatable part 20 via one (e.g. only one) pivot pin 31 and one (e.g. only one) moving pin 21.

In the variable aperture assembly 1 of Figs. 1-3, the base 30 (e.g. the main body of the base 30) is (at least partially or fully) provided/nested within a (through) hole that extends through the rotatable part 20 along the primary axis 0.

In the variable aperture assembly 1 of Figs. 4-6, the rotatable part 20 (e.g. the main body of the rotatable part 20) is (at least partially or fully) provided/nested within a (through) hole that extends through the base 30 along the primary axis 0.

The plurality of blades 40 (at least partially) overlap with the connecting arms 22 and the rotatable part 20 as viewed along the primary axis 0.

The plurality of blades 40 (at least partially) overlap with each other as viewed along the primary axis 0.

The plurality of blades 40 generally lie in a plane perpendicular to the primary axis 0 which sits on top of the rotatable part 20 and the base 30. In other words, the plurality of blades 40 (at least partially) cover/are provided at sides of the base 30 and the movable part 20 that generally face in the same direction.

A bearing (e.g. a sliding/plain bearing, ball bearing, or a roller bearing) may be provided between the base 30 and the rotatable part 20.

The variable aperture assembly 1 may comprise a holding arrangement configured to releasably (i.e. temporarily) hold the rotatable part 20 at one or more positions within the range of positions that the rotatable part 20 is capable of being driven to relative to the base 30 by the actuator assembly 10.

The actuator assembly 10 may comprise one or more shape memory alloy (SMA) elements configured to, upon contraction, (directly or indirectly) drive the rotation of the rotatable part 20 relative to the base 30.

S

An example of an actuator assembly 10 is shown in Fig. 7. The actuator assembly 10 of Fig. 7 comprises (a total of) four SMA elements 11, 12, 13, 14; a support structure 4 fixed to the base 30; and a movable part 3 coupled to the rotatable part 20. The SMA elements 11, 12, 13, 14 are configured to, upon contraction, drive relative movement between the movable part 3 and the support structure 4 so as to drive the rotation of the rotatable part 20 relative to the base 30.

The movable part 3 is fixed to the rotatable part 20; and the one or more SMA elements 11, 12, 13, 14 are configured to, upon contraction, drive rotation of the movable part 3 relative to the support structure 4 (e.g. around the primary axis 0) so as to drive the rotation of the rotatable part 20 relative to the base 30.

The variable aperture assembly 1 may comprise a holding arrangement configured to releasably (i.e. temporarily) hold the movable part 3 at one or more positions within the range of positions that the movable part 3 is capable of being driven to relative to the support structure 4, e.g. by the one or more SMA elements 11, 12, 13, 14.

The four SMA elements 11, 12, 13, 14 are configured to, indirectly via the movable part 3, drive the rotation of the rotatable part 20 relative to the base 30. The four SMA elements 11, 12, 13, 14 are arranged in a loop at different angular positions around the primary axis 0. Successive SMA elements 11, 12, 13, 14 around the primary axis 0 are configured, on contraction, to, indirectly via the movable part 3, apply a force to the rotatable part 20 in alternate senses around the primary axis O. In an alternative embodiment, the four SMA elements 11, 12, 13, 14 may be configured to directly drive the rotation of the rotatable part 20 relative to the base 30. Successive SMA elements 11, 12, 13, 14 around the primary axis 0 may be configured, on contraction, to directly apply a force to the rotatable part 20 in alternate senses around the primary axis 0.

For example, as shown in Fig. 12, the one or more SMA elements 11', 12' may comprise: a first SMA element 11' arranged to (directly, or indirectly via the movable part) rotate the rotatable part 20 about the primary axis 0 in a first sense relative to the base 30; and a second SMA element 12' arranged to (directly, or indirectly via the movable part) rotate the rotatable part 20 about the primary axis 0 in a second sense relative to the base 30, wherein the second sense is opposite to the first sense.

As shown in Fig. 11, the actuator assembly 10 may comprise one or more SMA elements 11', 12' that wound around corner elements 300' such as flexures, pulley wheels, posts or rocking arms.

The one or more SMA elements may comprise: a first pair of SMA elements, electrically connected together (in series), arranged to apply a torque to the rotatable part 20 (directly, or indirectly via the movable part 3) for rotating the rotatable part 20 about the primary axis 0 in a first sense; and a second pair of SMA elements, electrically connected together (in series), arranged to apply a torque to the rotatable part 20 (directly, or indirectly via the movable part 3) for rotating the rotatable part 20 about the primary axis 0 in a second sense, wherein the second sense is opposite to the first sense.

As shown in Figs. 3,5 and 6, the variable aperture assembly 1 (e.g. the base 30 of the variable aperture assembly 1) may be mounted on a lens assembly 50 of a camera assembly, such that the optical axis of the lens assembly 50 coincide with the primary axis 0. The lens assembly SO may be (at least partially) provided/nested within a (through) hole that extends through the base 30 along the primary axis 0. More than 50%, 60%, 70%, 80%, or 90% of the variable aperture assembly 1 may overlap with the lens assembly 50 along the primary axis 0, i.e. as viewed across the primary axis 0. The actuator assembly 10 may fully overlap with the lens assembly 50 along the primary axis 0, i.e. as viewed across the primary axis.

The actuator assembly 10 may be driven/controlled using two drive channels only (and a common). As such, as shown in Fig. 8, a single 8-channel drive chip 101 could be used to drive: (i) the actuator assembly 10, (ii) an optical image stabilisation (015) actuator assembly 51 requiring four drive channels (and a common), and (Hi) a focus (e.g. auto-focus (AF)) actuator assembly 52 requiring two drive channels (and a common). If the 8-channel drive chip 101 has two common channels C, as shown in Fig. 8, one of the common channels C may be shared by e.g. the AF actuator assembly 52 and the actuator assembly 10.

Alternatively, as shown in Fig. 9, a single 4-channel drive chip 102' could be used to drive: (i) the actuator assembly 10, and (ii) the AF actuator assembly 52; and another single 4-channel drive chip 102 could be used to drive the OIS actuator assembly 51. If the 4-channel drive chip 102' has a single common channel C, as shown in Fig. 9, the single common channel C may be shared by the AF actuator assembly 52 and the actuator assembly 10.

Alternatively, as shown in Fig. 10, where a camera assembly comprises a module tilt actuator assembly 53 which requires 8-channels (and a common) to provide 015, a single 4-channel drive chip 102' could be used to drive: (i) the actuator assembly 10, and (H) the AF actuator assembly 52; and a single 8-channel drive chip 101 could be used to drive the module tilt actuator assembly 53. If the 4-channel drive chip 102' has a single common channel C, as shown in Fig. 10, the single common channel C may be shared by the AF actuator assembly 52 and the actuator assembly 10.

The above-mentioned 015 actuator assembly 51 may be an actuator assembly comprising (a total of) four SMA elements such as the one disclosed in WO 2013/175197 or WO 2017/072525. The above-mentioned AF actuator assembly 52 may be an actuator assembly comprising (a total of) two SMA elements such as the one disclosed in WO 2019/243849. The above-mentioned module tilt actuator assembly 53 may be an actuator assembly comprising (a total of) eight SMA elements such as the one disclosed in WO 2011/104518.

SMA element The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions.

The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and/or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and/or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling or deposition and/or other forming process(es). The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field. Other

The primary axis 0 may be the longitudinal axis of the variable aperture assembly 1. The primary axis 0 may be the longitudinal axis of the actuator assembly 10.

Moving pins 21 may be integrally formed with the connecting arms 22 or the blades 40.

The connecting arms 22 may be integrally formed with the base 30 or the rotatable part 20.

The plurality of blades 40 may, for example, comprise five or six blades 40.

Other variations It will be appreciated that there may be many other variations of the above-described examples.

The actuator assembly 10 may, for example, be a voice coil motor (VCM) actuator assembly or a piezoelectric actuator assembly, instead of a SMA actuator assembly.

Claims

Claims 1 A variable aperture assembly comprising: a base;a rotatable part;an actuator assembly configured to drive rotation of the rotatable part relative to the base about a primary axis; a plurality of blades connected to the base via either a plurality of pivot pins or a plurality of moving pins, and connected to the rotatable part via the other of the plurality of pivot pins and the plurality of moving pins, and arranged to define a variable aperture with a central axis which coincides with the primary axis; wherein said rotation of the rotatable part drives relative movement between the pivot pins and the moving pins, which drives rotation of the plurality of blades about the pivot pins; wherein said rotation of the plurality of blades changes the size of the variable aperture.
2 A variable aperture assembly according to claim 1, wherein the moving pins are configured to rotate around the pivot pins.
3 A variable aperture assembly according to claim 1 or 2, wherein the moving pins are connected to the base or the rotatable part via connecting arms, wherein the connecting arms are configured to allow rotation of the moving pins around the pivot pins.
4 A variable aperture assembly according to claim 3, wherein the connecting arms comprise crank arms and/or flexure arms A variable aperture assembly according to claim 3 or 4, wherein the connecting arms are configured to bias the moving pins at least partially towards the pivot pins.6. A variable aperture assembly according to any of claims 3 to 5, wherein the connecting arms are configured to bias the moving pins such that the plurality of blades are bistable.7. A variable aperture assembly according to any preceding claim, wherein the moving pins are connected to the blades in a manner that prevents relative translational movement between each connected moving pin and blade.8 A variable aperture assembly according to any preceding claim, wherein the moving pins and the pivot pins are configured to provide, per degree of rotation of the rotatable part about the primary axis, at least 5, 10, or 20 degrees of rotation of the blades about the pivot pins.9 A variable aperture assembly according to any preceding claim, wherein each blade is connected with the base and the rotatable part via one pivot pin and one moving pin.10. A variable aperture assembly according to any preceding claim, wherein the base is provided within a hole that extends through the rotatable part along the primary axis.11. A variable aperture assembly according to any preceding claim, wherein the plurality of blades overlap with the connecting arms and/or the rotatable part as viewed along the primary axis.12. A variable aperture assembly according to any preceding claim, wherein the plurality of blades overlap with each other as viewed along the primary axis.13. A variable aperture assembly according to any preceding claim, wherein the plurality of blades generally lie in a plane perpendicular to the primary axis which sits on top of the rotatable part and the base.14. A variable aperture assembly according to any preceding claim, wherein a bearing is provided between the base and the rotatable part.15. A variable aperture assembly according to any preceding claim, comprising a holding arrangement configured to releasably hold the rotatable part at one or more positions within the range of positions that the rotatable part is capable of being driven to relative to the base by the actuator assembly.16. A variable aperture assembly according to any preceding claim, wherein the actuator assembly comprises one or more shape memory alloy (SMA) elements configured to, upon contraction, drive the rotation of the rotatable part relative to the base.17. A variable aperture assembly according to claim 16, wherein the actuator assembly comprises: a support structure fixed to the base; and a movable part coupled to the rotatable part; wherein the one or more SMA elements are configured to, upon contraction, drive relative movement between the movable part and the support structure so as to drive the rotation of the rotatable part.18. A variable aperture assembly according to claim 17, wherein the movable part is fixed to the rotatable part; and the one or more SMA elements are configured to, upon contraction, drive rotation of the movable part relative to the support structure so as to drive the rotation of the rotatable part.19. A variable aperture assembly according to claim 17 or 18, comprising a holding arrangement configured to releasably hold the movable part at one or more positions within the range of positions that the movable part is capable of being driven to relative to the support structure.20. A variable aperture assembly according to any of claims 16 to 19, wherein the one or more SMA elements comprise four SMA elements configured to drive the rotation of the rotatable part; wherein, optionally, the four SMA elements are arranged in a loop at different angular positions around the primary axis; and, optionally, wherein successive SMA elements around the primary axis are configured to apply a force to the rotatable part in alternate senses around the primary axis.21. A variable aperture according to any of claims 16 to 20, wherein the one or more SMA elements comprise: a first SMA element arranged to rotate the rotatable part about the primary axis in a first sense; and a second SMA element arranged to rotate the rotatable part about the primary axis in a second sense, wherein the second sense is opposite to the first sense.22. A variable aperture according to any of claims 16 to 21, wherein the one or more SMA elements comprise: a first pair of SMA elements, electrically connected together, arranged to apply a torque to the rotatable part for rotating the rotatable part about the primary axis in a first sense; and a second pair of SMA elements, electrically connected together, arranged to apply a torque to the rotatable part for rotating the rotatable part about the primary axis in a second sense, wherein the second sense is opposite to the first sense.23. A variable aperture assembly according to any preceding claim, wherein the actuator assembly is configured to be controlled by a drive chip via two drive channels of the drive chip.24. A camera assembly comprising: a variable aperture assembly according to any preceding claim; a further actuator assembly; a drive chip operatively connected to the actuator assembly and the further actuator assembly for controlling the actuator assembly and the further actuator assembly; wherein the drive chip comprises at least four drive channels; and wherein the actuator assembly is configured to be controlled via a first channel and a second channel of the at least four drive channels, and the further actuator assembly is configured to be controlled via a third channel and a fourth channel of at least four drive channels.25. A camera assembly according to claim 24, wherein the further actuator assembly is a focus actuator assembly.26. A camera assembly comprising: a variable aperture assembly according to any preceding claim; and a lens assembly; wherein the variable aperture assembly is mounted on the lens assembly, and the optical axis of the lens assembly coincides with the primary axis.27. A camera assembly according to claim 26, wherein the lens assembly is provided within a hole that extends through the base along the primary axis.28. A camera assembly according to claim 26 or 27, wherein more than 50%, 60%, 70%, 80%, or 90% of the variable aperture assembly overlaps with the lens assembly along the primary axis.29. A camera assembly according to any of claims 24 to 28, wherein the actuator assembly fully overlaps with the lens assembly along the primary axis.