Actuator assembly

Abstract

An actuator assembly 2 comprises first and second relatively moveable parts, and a plurality of actuating units 30a-h each configured to apply an actuating force to one of the first and second parts. At least one of the actuating units 30 comprises a force modifying mechanism with a body portion, an SMA element 34 connected between the body portion and the other of the first and second parts, a force-modifying element connected between the body portion and the other of the first and second parts, and a coupling link 33 connected between the body portion and the one of the first and second parts. The coupling link is compliant in a direction perpendicular to the actuation force. Each actuating unit 30 comprises an SMA element 34 arranged along a first side of the actuator assembly 2 and a coupling link 33 arranged along a second, adjacent, side of the actuator assembly 2. The plurality of actuating units 30a-h are arranged such that, for each direction along each axis of a Cartesian coordinate system (+x, -x, +y, -y, +z, -z), there is at least one actuating force with a non-zero component along that direction.

Description

Field The present application relates to an actuator assembly with one or more actuating units, each of which includes a shape memory alloy (SMA) element. Background SMA actuator assemblies may be used in a variety of applications for moving a movable part relative to a support structure. For example, WO 2013 / 175197 Al describes a camera in which four SMA wires are arranged to move a lens element relative to an image sensor in a plane that is perpendicular to the optical axis of the lens element, thereby effecting optical image stabilization (OIS). WO 2010 / 029316 Al describes SMA actuator wires used to provide OIS in a camera by tilting a camera module. WO 2011 / 104518 Al describes an actuator assembly having eight SMA wires capable of effecting positional control of a movable element with multiple degrees of freedom. Typically, the range of movement (also known as "stroke") of such SMA actuator assemblies is limited by the maximum contraction of the SMA wires, and the actuating force is limited by the maximum force that can be generated by the SMA wires. To increase the movement range or the actuating force, longer or thicker SMA wirescan be used, but this may be at the expense of increased cost, size and / or power, which may not be practical in miniature applications. WO 2022 / 084699 Al discloses an actuator assembly comprising at least one actuating unit (incorporating an SMA wire) that, on actuation, moves a movable part relative to the support structure. The actuating unit may be configured to amplify the movement range of the movable part, to amplify the actuating force acting on the movable part, or to re-direct the force applied by the SMA wire. Summary According to an aspect of the present invention, there is provided an actuator assembly comprising: a first part; a second part arranged to be movable relative to the first part; a plurality of actuating units each configured to apply an actuating force to one of the first and second parts capable of moving the second part relative to the first part, wherein at least one of the actuating unit comprises: a body portion an SMA element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts and configured to modify the input force so as to give rise to the actuating force; and a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force; wherein each actuating unit comprises an SMA element arranged along a first side of the actuator assembly and a coupling link arranged along a second side of the actuator assembly, wherein the second side is adjacent to the first side; and wherein the plurality of actuating units are arranged such that, for each direction along each axis of a Cartesian coordinate system (+x, -x, +y, -y, +z, -z), there is at least one actuating force with a non-zero component along that direction. Further features are specified in the dependent claims. 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: Figures 1A-E are schematic cross-sectional views of different variations of a camera module incorporating an actuator assembly; Figure 2 is a schematic perspective view of the actuator assembly; Figures 3A and 3B are perspective and plan views of an actuating unit forming part of the actuator assembly, and Figure 3C is a plan view of another such actuating unit; Figure 4 is a schematic plan view of an arrangement of four actuating units; Figures 5 is a schematic perspective view of an arrangement of eight actuating units; Figure 6 is a perspective view of an actuator assembly according to the present disclosure; Figure 7 is a schematic perspective view of the actuator assembly of Figure 6; 5 Figure 8 is another view of the actuator assembly of Figure 6; Figure 9 is a perspective view of another actuator assembly according to the present disclosure; Figure 10 is a schematic perspective of the actuator assembly of Figure 9; 10 Figure 11 is another view of the actuator assembly of Figure 9; Figure 12 is a schematic perspective view of another actuator assembly according to the present disclosure; and 15 Figure 13 is an alternative perspective view of the actuator assembly of Figure 6. Detailed description Camera module Figures 1A-E schematically show different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera module 1. Generally, the apparatus 1 is to be incorporated in a portable electronic device such as a smartphone. Thus, miniaturisation can be an important design criterion. Figure 2 schematically shows the actuator assembly 2. The actuator assembly 2 includes a support structure 10 and a movable part 20. The movable part 20 is movable relative to the support structure 10. When the actuator assembly 2 is included e.g. in the apparatus 1, the support structure 10 may be fixed relative to the main body of the apparatus 1. However, in general, the support structure 10 need not be stationary and may be movable relative to or within the apparatus 1. The actuator assembly 2 includes one or more actuating units 30. Each actuating unit 30 is configured to apply an actuating force to the movable part 20 capable of moving the movable part 20 relative to the support structure 10. The movable part 20 may be supported (i.e. suspended) on the support structure 10 exclusively by the actuating units 30. Alternatively, the actuator assembly 2 may include a bearing arrangement 40 that supports the movable part 20 on the support structure 10. The actuating units 30 and the bearing arrangement 40 may together support the movable part 20 on the support structure 10. The bearing arrangement 40 may have any suitable form for allowing movement of the movable part 20 with respect to the support structure 10 with one or more degrees of freedom (DOFs). The actuating units 30 and / or the bearing arrangement 40 may constrain, i.e. reduce or prevent, other DOFs of movement of the movable part 20 relative to the support structure 10. For this purpose, the bearing arrangement 40 may, for example, include one or more of the following bearings: a rolling bearing (such as a ball bearing), a flexure bearing (i.e. an arrangement of flexures or other resilient elements that guide movement), or a plain (i.e. sliding contact) bearing. A primary axis P can be defined with reference to the actuator assembly 2 and / or the support structure 10. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2. In some examples, the actuator assembly 2, the support structure 10 and / or the movable part 20 extends predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 2, the support structure 10 and / or the movable part 20 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. The primary axis P may be the longitudinal axis of the actuator assembly 2 and / or the support structure 10. Alternatively or additionally, the support structure 10 and / or movable part 20 may include a planar component that extends perpendicularly to the primary axis P. Alternatively or additionally, in examples in which the apparatus 1 includes an optical element (such as a lens assembly 3) with an optical axis, or an imaging element (such as an imager sensor 4) with an imaging axis, the primary axis P may be parallel to such an axis and / or may coincide with such an axis when the movable part 20 is in a central position or orientation (for example, see Figure 1A). In general, the movable part 20 may be movable relative to the support structure 10 with up to six degrees of freedom (DOFs). In the context of describing the DOFs of movement, the primary axis P may also be referred to as the z axis, and two further axes that are perpendicular to the primary axis P and to each other may be referred to as the x and y axes. The movable part 20 may be movable relative to the support structure 10 in all or in any subset (including only one) of the following DOFs: TxandTy: Translational movement in the x-y plane. In other words, the movable part 20 may be independently movable along the x and y axes. The movable part 20 may be movable to any position in the x-y plane within a range of movement. Instead of such planar movement, the movable part 20 may be movable linearly, e.g. along the x or y axis. Rx and Ry: Rotational movement (or simply rotation or tilting) about the x and y axes. In other words, the movable part 20 may be rotated about any line perpendicular to the primary axis P. The movable part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement. Instead of such two-axis rotation, the movable part 20 may be rotatable about a single axis, e.g. about the x or y axis. Tz: Translational movement along the z axis. The movable part 20 may be movable to any translational position along the z axis within a range of movement. Rz: Rotational movement (or simply rotation) about the z axis. The movable part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement. In some examples, the movable part 20 may be supported, e.g. by the bearing arrangement 40, so as to allow translational movement in the x-y plane (Tx, Ty) and / or rotational movement about the z axis (Rz). Translational movement along the z axis (Tz) and rotational movement about the x and y axes (Rx, Ry) may be constrained. Such support may be provided, for example, with a bearing arrangement 40 with a suitable arrangement of ball bearings or plain bearings which produce bearing forces in the +z direction and a biasing arrangement which produces a biasing force in the -z direction. Examples of actuator assemblies with such a bearing arrangement are disclosed in WO 2013 / 175197 Al and WO 2017 / 072525 Al, each of which is herein incorporated by reference. In some examples, the movable part 20 may be supported so as to allow tilting about the x and y axes (Rx, Ry) and optionally rotation about the z axis (Rz). The other DOFs of movement (i.e. Tx, Ty, Tz, Rz, or Tx, Ty, Tz) may be constrained. Such support may be provided by the bearing arrangement 40, for example in the form of a gimbal. Examples of such a bearing arrangement 40 are disclosed in WO 2021 / 209770 Al, which is herein incorporated by reference. Alternatively, such support may be provided exclusively by the actuating units 30, similarly to WO 2011 / 104518 Al which discloses an actuator assembly with 8 SMA wires connected between the support structure 10 and the movable part 20. WO 2011 / 104518 Al is herein incorporated by reference. In some examples, the movable part 20 may be supported so as to allow three-dimensional translational movement (Tx, Ty, Tz), while rotational movement (Rx, Ry, Rz) may be constrained. Such support may be provided by the bearing arrangement 40, for example in the form of nested linear bearings. Examples of such a bearing arrangement 40 are disclosed in WO 2021 / 209769 Al, which is herein incorporated by reference. Alternatively, such support may be provided exclusively by the actuating units 30, similarly to WO 2011 / 104518 Al. The movable part 20 may, alternatively or additionally, move in other DOFs. The movable part 20 may move in DOFs that are a combination of any two or more of Tx, Ty, Tx, Rx, Ry and Rz. For example, the movable part 20 may move along a helical path (i.e. move helically) about the z axis, and so concurrently move along the z axis and rotate about the z axis. In other words, Tz and Rz movement may be coupled. An example of such a helical actuator assembly is disclosed in WO 2019 / 243849 Al, which is herein incorporated by reference. The actuating units 30 are connected between the support structure 10 and the movable part 20. The actuating units 30 are arranged to apply actuating forces F (see e.g. Figs. 4 and 5) between the movable part 20 and the support structure 10. Selectively varying the actuating forces F may cause the movable part 20 to move relative to the support structure 10, for example within the DOFs allowed by the bearing arrangement 40. The actuating units 30 are thus capable of driving movement of the movable part 20 relative to the support structure 10. The bearing arrangement 40 may cause the movable part 20 to move in directions which differ from the directions of the actuating forces F. In simple examples of this, one component of each actuating force F causes the movement of the movable part 20, and another component of each actuating force F acts against the bearing forces produced by the bearing arrangement 40. Referring back to Figure 1, the camera module 1 also includes a lens assembly 3 and an image sensor 4. The lens assembly 3 includes one or more lenses configured to focus an image on the image sensor 4. The lens assembly 3 defines an optical axis O. The lens assembly 3 may include a lens carrier, for example in the form of a cylindrical body, supporting the one or more lenses. The image sensor 4 captures an image and may be of any suitable type, for example a charge coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. The camera module 1 may be a compact camera module in which each lens has a diameter of 20mm or less, for example of 12mm or less. In the ("sensor-shift") variation of the camera module 1 shown in Figure 1A, the movable part 20 includes the image sensor 4. The lens assembly 3 may be fixed relative to the support structure 10 or may be movable relative to the support structure 10 along the optical axis O, as described below. In the ("lens-shift") variation shown in Figure IB, the image sensor 4 is fixed relative to the support structure 10 and the movable part 20 includes the lens assembly 3. The lens assembly 3 may be movable relative to the movable part 20 along the optical axis O, as described below. In both of these variations, the actuator assembly 2 is configured to move the lens assembly 3 relative to the image sensor 4 in any direction in the plane perpendicular to the primary axis P and hence the optical axis 0. Such movement has the effect of moving the image on the image sensor 4 and enables optical image stabilisation (OIS) to be implemented in the camera module 1. In the sensor-shift variation, the movable part 20 may also be rotatable about the primary axis P so as to also enable compensation for roll. In the ("module-tilt") variation shown in Figure IC, the movable part 20 includes both the lens assembly 3 and the image sensor 4. Again, the lens assembly 3 may be movable relative to the movable part 20 along the optical axis O, as described below. The actuator assembly 2 is configured to tilt the movable part 20 about two axes perpendicular to the primary axis P and to each other, and optionally rotate the movable part 20 about the primary axis P, enabling OIS to be implemented in the camera module 1. In the ("autofocus") variation shown in Figure ID, the movable part 20 includes the lens assembly 3, and the actuator assembly 2 moves the movable part 20 relative to the support structure 10 along the primary axis P and hence the optical axis O. Such movement has the effect of adjusting the focus of the image on the image sensor 4. So, auto-focus (AF) or zoom functionality can be implemented in the camera module 1. In some examples (not shown), the camera module 1 may include a first actuator assembly for providing OIS as illustrated in Figures 1A-C, and a second actuator assembly for providing AF as illustrated in Figure ID. One or both of the first and second actuator assemblies may correspond to actuator assemblies 2 as described herein. One of the first and second actuator assemblies may be another type of SMA actuator assembly or may be a non-SMA actuator assembly, e.g. a voice-coil motor (VCM) actuator assembly. As will be appreciated, in the lens-shift and module-tilt variations, the support structure 10 of the second actuator assembly 2 is fixed to (or corresponds to) the movable part 20 of the first actuator assembly 2. In the ("AF+OIS") variation shown in Figure IE, the movable part 20 includes the lens assembly 3, and the actuator assembly 2 produces three-dimensional translational movement of the movable part 20 relative to the support structure 10, enabling both AF and OIS to be implemented using one actuator assembly 2. Other variations are also possible. For example, in the autofocus variation or the AF+OIS variation, the movable part 20 may include the image sensor 4 rather than the lens assembly 3. The camera module 1 may include combinations of the above-described features, e.g. (a) lens shift and sensor shift, (b) module tilt and lens shift or sensor shift and autofocus, or (c) module tilt and AF+OIS. The camera module 1 also includes a controller 8. The controller 8 may be implemented in an integrated circuit (IC) chip. The controller 8 generates drive signals for the actuating units 30, in particular for SMA wires 34 forming part of the actuating units 30. SMA material has the property that, on heating, it undergoes a solid-state phase change that causes the SMA material to contract. Thus, applying drive signals to the SMA wires 34, thereby heating the SMA wires 34 by causing an electric current to flow, will cause the SMA wires 34 to contract and thus actuate the actuating unit 30 so as to move the movable part 20. The drive signals are chosen to drive movement of the movable part 20 in a desired manner, for example so as to achieve OIS by stabilizing the image sensed by the image sensor 4 or to achieve AF / zoom by adjusting the focus of the image sensed by the image sensor 4. The controller 8 supplies the generated drive signals to the SMA wires 34. Optionally, the camera module 1 also includes a motion sensor (not shown), which may include a 3-axis gyroscope and a 3-axis accelerometer. The motion sensor can generate signals representative of the motion (specifically vibrations or "shake") of the camera module 1, which can be processed so as to produce signals representative of the required movement of the movable part 20 to compensate for such shake. The controller 8 receives such signals and can generate the drive signals for the SMA wires 34 to achieve OIS. Although the actuator assembly 2 is described in connection with a camera module 1, it will be appreciated that the actuator assembly 2 may be used in any device in which movement of a movable part 20 relative to a support structure 10 is desired, e.g. to provide haptic feedback in a haptic feedback device or to move a projector or display in an augmented reality (AR) or virtual reality (VR) device. Actuating unit Figure 3A shows a perspective view of an example of the actuating unit 30. Figure 3B shows part of the actuating unit 30 in plan view. A single actuating unit 30 is shown in Figures 3A and 3B, but it will be appreciated that the actuator assembly 2 generally has multiple actuating units 30, each of which may include the same components described with reference to Figures 3A and 3B. The actuating unit 30 includes a body portion 31 to which several other components of the actuating unit 30 are connected as described below. Typically, the body portion 31 is relatively rigid compared to the other components of the actuating unit, and does not deform significantly on actuation of the actuating unit 30. In some examples, the body portion 31 is not a distinct part of the actuating unit 30. For example, the body portion 31 may be defined as part of one of the other components of the actuating unit 30 or simply as a connection point between other components of the actuating unit 30. The actuating unit 30 also includes a force-modifying flexure 32, also known as a force modifying element. The force-modifying flexure 32 is connected between the body portion 31 and the support structure 10. One end of the force-modifying flexure 32 is connected to the body portion 31. The other end of the force-modifying flexure 32 is connected to the support structure 10, e.g. via a foot portion 36. The foot portion 36 is fixed relative to the support structure 10. The force-modifying flexure 32 allows the body portion 31 to pivot relative to the support structure 10 about an effective pivot point P. Although the effective pivot point P is shown in Figure 3B as being positioned in the middle of forcemodifying flexure 32, the effective pivot point P may have a different position and also need not lie on the force-modifying flexure 32. Such pivotal movement of the body portion 31 relative to the support structure 10 is initially in a direction that is substantially perpendicular to the force-modifying flexure 32. The actuating unit 30 also includes an SMA element 34. In this example, the SMA element 34 is an SMA wire 34. The SMA wire 34 is connected between the body portion 31 and the support structure 10. One end of the SMA wire 34 is connected to the support structure 10, e.g. by a crimp 15. The other end of the SMA wire 34 is connected to the body portion 31, e.g. by a crimp 35. The actuating unit 30 also includes a coupling link 33. In this example, the coupling link 33 is a coupling flexure 33. The coupling flexure 33 is connected between the body portion 31 and the movable part 20. One end of the coupling flexure 33 is connected to the body portion 31. The other end of the coupling flexure 33 is connected to the movable part 20, optionally via connection portion 21a. The coupling link 33 transfers or transmits an actuating force F from the body portion 31 to the movable part 20. The coupling link 33 is compliant (i.e. deformable) in a direction (or in multiple directions) perpendicular to the actuating force F. This allows the movable part 20 to move in directions other than the direction of the coupling flexure 33 and actuating force F. This can be needed, for example, where different actuating units 30 cause the movable part 20 to move in different directions. In this example, the body portion 31, the force-modifying flexure 32, the coupling flexure 33 and the foot portion 36 are integrally formed, for example from a single sheet of material (such as metal). In other examples, one or more or these features, if present, may be formed from different parts or materials. The SMA wire 34 is arranged, on contraction, to apply an input force Fi on the body portion 31. The input force Fi acts parallel to the length of the SMA wire 34. The force-modifying flexure 32 and the body portion 31 are arranged to modify the input force Fi so as to give rise to the actuating force F, which is transmitted from the body portion 31 to the movable part 20 by the coupling flexure 33. In particular, the input force Fi deforms the force-modifying flexure 32, thereby causing the body portion 31 to pivot about the effective pivot point P. In simple terms, the force-modifying flexure 32 and the body portion 31 act like a lever. The force-modifying flexure 32 and the body portion 31 may modify the direction and / or the magnitude of the input force Fi so as to give rise to the actuating force F. In the example illustrated in Figures 3A and 3B, the coupling flexure 33 is at an angle of -90° relative to the SMA wire 34. Also, in this example, the force-modifying flexure 32 is arranged at an angle a of -30° relative to the SMA wire 34, and the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. Hence, on contraction of the SMA wire 34 and on resulting deformation of the forcemodifying flexure 32, the body portion 31 initially moves at an angle of -60° (90°-a) relative to the length of the SMA wire 34. Thus, it will be appreciated that, in this example, the force is de-amplified and the stroke is amplified, while the direction of the forces / movements is changed by an angle of -90°. In more detail, a de-amplification of force means that the magnitude of the actuating force is less than that the magnitude of the input force that causes the actuating force. The amplification of stroke means that the amount of movement of the coupling link along the length of the coupling link is greater than the amount of contraction of the SMA wire that causes the movement of the coupling link. In other examples, the input force may be amplified (meaning that the actuating force is greater than the input force) whilst stroke may be de-amplified (the amount of movement of the coupling link is less than the amount of contraction of the SMA wire). More generally, the change in direction of the force depends on the angle between the SMA wire 34 and the coupling flexure 33. Also more generally, the change in magnitude of the force is dependent on the ratio of i) the distance Ds from the effective pivot point P to the line on which the SMA wire 34 lies and ii) the distance De from the effective pivot point P to the line on which the coupling flexure 33 lies, where Ds is the shortest distance from the pivot point to the line along which the SMA lies, and De is the shortest distance from the pivot point to the line along which the coupling link lies. In particular, F / Fi is proportional to Ds / Dc. If the SMA wire 34 lies on a line that is closer to the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is de-amplified. At the same time, the movement of the movable part 20 is amplified, i.e. increased relative to a change in length of the SMA wire 34. Alternatively, if the SMA wire 34 lies on a line that is further away from the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is amplified. At the same time, the movement of the movable part 20 is de-amplified, i.e. decreased relative to a change in length of the SMA wire 34. The actuating unit 30 can thus be configured to amplify movement or to amplify force due to contraction of the SMA wire 34. The actuating unit 30 can also be configured to change the direction of the input force Fi. In some examples, the actuating unit 30 is configured to change the direction of the input force Fi without changing the magnitude of the force or movement. The ratio Ds / Dc is dependent on the location of the end of the SMA wire 34 that is connected to the body portion 31, and on the location of the end of the coupling flexure 33 that is connected to the body portion 31. By way of example, the distance De could be increased by connecting the coupling flexure 33 further to the left of body portion 31 shown in Figure 3B, thereby decreasing Ds / Dc and so increasing the amount of stroke amplification. The ratio Ds / Dc is also dependent on the orientation of the SMA wire 34, and on the orientation of the coupling flexure 33. Such orientations can be defined with reference to the forcemodifying flexure 32 (as above) or any suitable reference line. By way of example, the distance Ds could be decreased by angling the SMA wire 34 shown in Figure 3B so that it passes closer to the effective pivot point P, thereby decreasing Ds / Dc and so increasing the amount of stroke amplification. In summary, the amount by which the force-modifying flexure 32 amplifies or de-amplifies the force / stroke of the SMA wire 34 may be tailored by: adjusting the orientation of the SMA wire 34 (and thus of the input force Fi); adjusting the location of the connection point between the SMAwire34and the body portion 31 (and thus the location at which the input force Fi acts on the body portion 31); adjusting the orientation of the coupling flexure 33 (and thus of the actuating force F); and / or adjusting the location of the connection point between the coupling flexure 33 and the body portion 31 (and thus the location from which the body portion 31 applies the actuating force F). In some examples, at least one actuating unit 30 (preferably each actuating unit 30) is configured such that the force-modifying flexure 32 and the body portion 31 amplifies an amount of contraction of the SMA wire 34. Such amplification, for example, may be by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3. For this purpose, in the example illustrated in Figures 3A and 3B, the angle a between the SMA wire 34 and the force-modifying flexure 32 may be in the range from 0 to 45 degrees, preferably from 13 to 40 degrees. However, in general, the angle a may have other values and the connection points of the SMA wire 34 and / or coupling flexure 33 to the body portion 31 may be adjusted to achieve a desired amount of amplification. As described above, in the example illustrated in Figures 3A and 3B, the coupling flexure 33 is at an angle of about 90 degrees relative to the SMA wire 34. This allows the actuating unit 30 to fold around a corner of the movable part 20 in a compact manner. The angle between the coupling flexure 33 and the SMA wire 34 may be in the range from 70 to 110 degrees, preferably from 80 to 100 degrees. However, in general, the angle between coupling flexure 33 and SMA wire 34 may be outside these ranges. For instance, in the actuating unit 30 illustrated in Figure 3C, the force-modifying flexure 32, the coupling flexure 33 and the SMA wire 34 are substantially parallel to one another. In the above-described examples, the actuating unit 30 is arranged in a plane. In particular, the SMA wire 34, the coupling flexure 33 and the force-modifying flexure 32 are arranged so as to substantially extend in a common plane, at least when the actuator assembly 2 is in an initial configuration. This allows for a compact configuration of the actuating unit 30. The body portion 31, when embodied by a plate, may further be arranged to extend in the plane. However, in general, the components of the actuating unit 30 need not be arranged in a common plane. The SMA wire 34 and / or the coupling flexure 33 may be angled relative to the plane, for example. In the above-described examples, the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. This reduces the risk of buckling of the force-modifying flexure 32, reducing the risk of damage to the actuator assembly 2 and making the actuator assembly 2 more reliable. However, the force-modifying flexure 32 could instead be arranged so as to be placed under compression on contraction of the SMA wire 34. With reference to Figure 3B, for example, the force-modifying flexure 32 could extend to the bottom-right from the connection point between the body portion 31 and the force-modifying flexure 32, and so be placed under compression on contraction of the SMA wire 34. An arrangement in which the force-modifying flexure 32 is placed under compression is disclosed in WO 2022 / 084699 Al, which is herein incorporated by reference. In the above-described examples, the force-modifying flexure 32 and the SMA wire 34 connect at one end to the support structure 10, and the coupling flexure 33 connects at one end to the movable part 20. In general, this arrangement may also be reversed, with the force-modifying flexure 32 and the SMA wire 34 connecting at one end to the movable part 20, and the coupling flexure 33 connecting at one end to the support structure 10. In the above-described examples, the actuating unit 30 includes a coupling link 33 in the form of a coupling flexure 33. The purpose of the coupling link 33 is to allow movement of the movable part 20 in directions perpendicular to the actuating force F. In general, however, the actuating unit 30 need not include a coupling link 33, e.g. in examples in which there is no movement of the movable part 20 in directions perpendicular to the actuating force F. Furthermore, the coupling link 33 may be embodied by components other than the coupling flexure 33, for example by a ball bearing or plain bearing configured to transmit the actuating force F to the movable part 20 while allowing movement of the movable part 20 in directions perpendicular to the actuating force F. Such alternative examples of the coupling link 33 are disclosed in WO 2022 / 084699 Al. The coupling link 33 may be formed by an SMA wire, which may (or may not) be integral with the SMA wire 34 and may (or may not) be driven together with the SMA wire 34. Furthermore, instead of the force-modifying flexure 32, the actuator assembly may include a different type of force-modifying element configured to enable the above-described movement of the body portion 31 relative to the support structure 10. Such a force-modifying element may include, for instance, a rigid member with one end connected to the support structure 10 via a suitable pivoting connection (e.g. a pin joint) and the other end connected to the body portion 31. Arrangement of four actuating units Figure 4 schematically shows a plan view of an example of the actuator assembly 2, showing an arrangement of actuating units 30. In this example, the actuator assembly 2 includes a total of four actuating units 30. The four actuating units 30 may apply actuating forces F between the movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10. The arrangement of actuating units 30 of Figure 4 may be used, for example, in examples in which the movable part 20 is movable relative to the support structure 10 in a movement plane. So, Tx, Ty and optionally Rz movement of the movable part 20 may be allowed. The four actuating units 30 of Figure 4 are in an arrangement capable of applying actuating forces F so as to move the movable part 20 relative to the support structure 10 to any position within a range of movement. The range of movement may be within a movement plane that is perpendicular to the primary axis P. In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a first axis (e.g. the x axis). The other two actuating units (e.g. the left and right actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a second axis (e.g. the y axis), perpendicular to the first axis. By appropriately varying the difference in actuation amount between the opposing actuating units 30, the movable part 20 may thus be moved independently along the first and second axes. The opposing actuating forces Fare not colinear, but offset from each other in a direction perpendicular to the actuating forces F. Providing opposing actuating units 30 allows the tension in the SMA wires 30 of the respective actuating units 30 to be controlled, allowing for more accurate and reliable positioning of the movable part 20 compared to a situation in which actuating units 30 do not oppose each other. In some examples, none of the actuating forces F are collinear. This allows the arrangement of actuating units 30 to translationally move the movable part 20 without applying any net torque to the movable part 20. So, the movable part 20 can be moved translationally in the movement plane without rotating the movable part 20 in the movement plane. In general, the arrangement of actuating units 30 is capable of accurately controlling a torque or moment of the movable part 20 about the primary axis P. So, the actuating units 30 are capable of rotating (or not rotating) the movable part 20 relative to the support structure about the primary axis P. In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a first sense (e.g. clockwise) around the primary axis P. The other two actuating units 30 (e.g. the left and right actuating units 30 in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a second, opposite sense (e.g. anti-clockwise) around the primary axis P. This allows the movable part 20 to be rotated by simultaneously increasing or decreasing the tension of SMA wires in any of the two actuating units 30. As shown, two actuating units 30 may be arranged to apply actuating forces F in a corner of the actuator assembly 2. The other two actuating units 30 may be arranged to apply actuating forces F in another, opposite corner of the actuator assembly 2. The actuator assembly 2, and in particular the movable part 20 and / or the support structure 10, may have a square or rectangular footprint. Each actuating unit 30 may be provided on one of the four sides of the actuator assembly 2. In particular, each actuating unit 30 may bend around a corner of the movable part 20 such that the SMA wire 34 and the coupling flexure 33 of each actuating unit 30 extend along adjacent edges of the movable part 20. So, the actuating unit 30 may be as configured in Figures 3A and 3B, for example. The four SMA wires 32 of the four actuating units 32 may extend along the four different edges of the movable part 20. The arrangement of actuating forces F applied between movable part 20 and support structure 10 corresponds to the arrangement of SMA wires 30 described in WO2013 / 175197 Al, which is herein incorporated by reference. In this example, the actuating forces F are perpendicular to the primary axis P, and may be parallel to the movement plane. However, in general the actuating forces F may be angled relative to the movement plane. The actuating forces F may thus have a component along the primary axis P. This component along the primary axis P may be resisted by the bearing arrangement 40, for example, to provide movement of the movable part 20 in degrees of freedom allowed by the bearing arrangement 40. In some examples, it may even be desirable for actuating forces F to have a component in parallel to the primary axis P, for example so as to load plain or rolling bearings arranged between the movable part 20 and the support structure 10. Although, for illustrative purposes, the arrangement of actuating units 30 was described as moving the movable part 20 in the movement plane (e.g. translationally along the x and y axis, or rotationally about the primary axis P), in other examples the movable part 20 may be moved differently. For example, the same arrangement of actuating forces F may be used to tilt the movable part 20 relative to the support structure 10 about axes perpendicular to the primary axis P, due to appropriate movement constraints provided by the bearing arrangement 40. For example, the bearing arrangement 40 may include a plurality of flexures for guiding tilting of the movable part 20 about the axes perpendicular to the primary axis P. Examples of such bearing arrangement 40 are described in WO2022 / 029441 Al, which is herein incorporated by reference. Although the actuator assembly 2 is described herein in the context of four actuating units 30, in general the actuator assembly 2 may include fewer actuating units 30. For example, the actuator assembly 2 may include two actuating units 30, e.g. the two actuating units 30 depicted in the top left of Figure 4. The forces applied to the movable part 20 by the two actuating units 30 may be opposed by a biasing force of one or more resilient elements, such as springs. With reference to Figure 4, the two actuating units 30 in the bottom right corner may be replaced with springs applying biasing forces along the corresponding depicted arrows, for example. Arrangement of eight actuating units Figure 5 schematically shows a perspective view of an actuator assembly 2 with a total of eight actuating units 30. The eight actuating units 30 may apply actuating forces F between the movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10. The arrangement of actuating units 30 of Figure 5 may be used, for example, in examples in which the movable part 20 is movable relative to the support structure 10 in three translational degrees of freedom (Tx, Ty, Tz) (see Figure IE) or in two or three rotational degrees of freedom (Rx, Ry or Rx, Ry, Rz) (see Figure IC). The eight actuating units 30 may be arranged such that their actuating forces F are oriented or arranged in a manner equivalent to the orientation or arrangement of the forces applied by the eight SMA wires in the actuator assemblies disclosed in WO 2011 / 104518 Al. More specifically, the actuating forces F (e.g. when visualised as vectors at particular positions in space) are arranged on each of four sides (i.e. a first side, a second side, a third side and then a fourth side) around the primary axis P. The two actuating forces F on each side are inclined in opposite senses relative to a plane perpendicular to the primary axis P, when viewed perpendicular from the primary axis P. The four sides on which the actuating forces F are arranged extend in a loop around the primary axis P. In this example, adjacent sides are perpendicular to each other, and the sides form a square when viewed along the primary axis P, but alternatively the sides could take a different e.g. quadrilateral shape. In this example, the actuating forces F are parallel to the outer faces of the square envelope of the movable part 20 but this is not essential. Four actuating forces F, including one actuating force F on each of the sides, form a 'first' group that have a component in one direction ('upwards' or +z) and the other four actuating forces F form a 'second' group that have a component in the opposite direction ('downwards' or -z). Herein, 'up' and 'down' refer to opposite directions along the primary axis P. The actuating forces F have a symmetrical arrangement in which their magnitudes and inclination angles are the same, so that both the first group of actuating forces F and the second group of actuating forces F are each arranged with two-fold rotational symmetry about the primary axis P. As a result of this symmetrical arrangement, different combinations of the actuating forces F are capable of driving movement of the movable part 20 with multiple degrees of freedom, as follows. The first group of actuating forces F, when generated together, drive upwards (+z) movement, and the second group of actuating forces F, when generated together, drive downwards (-z) movement. Within each group, adjacent pairs of actuating forces F, when differentially generated, drive tilting about a lateral axis perpendicular to the primary axis P (Rx or Ry). Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes. Sets of four actuating forces F, including two actuating forces F from each group, when generated together, drive movement along a lateral axis perpendicular to the primary axis P (Tx or Ty). Movement in any arbitrary direction perpendicular to the primary axis z may be achieved as a linear combination of movements along the two lateral axes. The actuator assembly 2 may have other specific arrangements of actuating units 30 to those shown in Figure 5. For example, strict symmetry is not required. Furthermore, instead of there being an up-pulling actuating unit 30 and a down-pulling actuating unit 30 on each side, there may be two up-pulling actuating units 30 on each of two opposite sides (e.g. the first and third sides) and two down-pulling actuating units 30 on the other two sides (e.g. the second and fourth sides). Embodiments of an actuator assembly Figure 6 shows a perspective view of an actuator assembly 2 according to an embodiment of the present disclosure. In this embodiment, the actuator assembly 2 comprises eight actuating units 30a-h, although it will be appreciated that at least some of the functionality of the actuator assembly (described below) can be achieved with more or fewer actuating units. Similar to the actuator assembly shown in Figure 5, the actuating units 30 may apply actuating forces F between a support structure (not shown), and a movable part. The actuating force F applied by each actuating unit 30 is capable of moving the movable part relative to the support structure. Figure 7, which is described in more detail below, schematically illustrates the directions of the actuating forces F applied by each of the actuating units 30 shown in Figure 6. The arrangement of actuating units 30 of Figure 6 may be used, for example, in examples in which the movable part is movable relative to the support structure in three translational degrees of freedom (Tx, Ty, Tz) (see Figure IE) or in two or three rotational degrees of freedom (Rx, Ry or Rx, Ry, Rz) (see Figure 2). As can be seen from Figure 8, each actuating unit 30a - 30h of the actuator assembly 2 is similar in some respects to the actuating units 30 depicted in Figures 3A and 3B. In particular, each actuating unit 30a -30h of the actuator assembly 2 depicted in Figure 6 comprises a respective body portion 31, SMA element 34 connected between the body portion 31 and the support structure, a force-modifying element 32 (e.g. a force modifying flexure) connected between the body portion and the support structure, and a coupling link 33 (e.g. a coupling flexure) connected between the body portion and the movable part. Each actuating unit is connected to the support structure at the distal end of the forcemodifying flexure via a foot portion (such as foot portion 36 shown in Figure 3A) connected to the body portion of the actuating unit. Additionally, each actuating unit is connected to the support structure at the distal end of the SMA element (for example using a crimp such as crimp 15 shown in Figure 3A). Each actuating unit is further connected to the movable part via the distal end of the coupling link (in particular via connection portion 21a), as described above in relation to Figures 3A and 3B. It is generally described herein that the force modifying flexure 32 and SMA element 34 are connected to the support structure 10, whilst the coupling link (e.g. coupling flexure 33) is connected to the movable part 20. However, in some embodiments, some of the actuating units may be connected in the opposite sense between the support structure and the movable part. In other words, in at least some of the actuating units, the SMA element 34 and the force-modifying flexure 32 may be connected to the movable part 20, and the coupling link / flexure 34 may be connected to the support structure 10. For instance, some or all of the first set of actuating units may be connected in the opposite sense and / or some or all of the second set of actuating units may be connected in the opposite sense. As described in more detail above with respect to Figures 3A - 3C, the SMA element is configured, on actuation, to apply an input force Fi to the body portion. In turn, the force-modifying element is configured to modify the input force so as to give rise to the actuating force F through the coupling link. In other words, the force-modifying element is configured to amplify or de-amplify the input force / stroke of the SMA element according to the physical arrangement of the SMA element, forcemodifying element, and the coupling link, which is described in more detail above with reference to Figures 3A - 3C. The coupling link is configured to transmit the actuating force from the body portion to the movable part in order to move the movable part relative to the support structure. The actuator assembly 2 may have a square or rectangular (or more generally quadrilateral) footprint, similar to the actuator assemblies shown in Figures 4 and 5. In the particular example of Figure 6, the actuator assembly has a square footprint, with four sides corresponding to four sides of the support structure. The four sides are arranged around a primary axis P extending through the actuator assembly, similar to the primary axis depicted in Figures 1 and 2. It will be appreciated that in other examples, the actuator assembly may have a differently-shaped footprint, with a corresponding different number of sides. Moreover, the sides on which the actuating units 30, 31 are arranged need not correspond to sides of the support structure 10 or the movable part 20. In other words, the sides may be defined merely by the presence of the actuating units 30, 31. Furthermore, in some other embodiments, the sides on which the actuating units 30, 31 are arranged need not be parallel to the primary axis and / or need not all have the same extent along the primary axis. In general, the plurality of actuating units may be arranged in any suitable manner such that each actuating unit comprises an SMA element arranged along a first side of the actuator assembly and a coupling link arranged along a second side of the actuator assembly, wherein the second side is adjacent to the first side and wherein the plurality of actuating units are arranged such that, for each direction along each axis of a Cartesian coordinate system (+x, -x, +y, -y, +z, -z), there is at least one actuating force with a non-zero component along that direction. As can be seen in Figure 6, each actuating unit 30 extends along two adjacent sides of the actuator assembly. In particular, each actuating unit has its SMA element arranged along a first one of the four sides, and its coupling link arranged along a second side that is adjacent to the first side. In other words, each actuating unit is arranged such that it bends around a corner of the actuator assembly so that the SMA element and the coupling link of each actuating unit 30 extend along adjacent sides of the actuator assembly. With respect to the input and actuation forces of each actuating unit, this means that, in some examples, input force applied by the SMA element of each actuating unit may be generally perpendicular to the respective actuating force, when the actuator assembly is viewed along the primary axis. Each actuating unit extending along two adjacent sides of the actuator assembly can also be described in terms of an angular extent of the actuating unit about the primary axis. In particular, when viewed along the primary axis, the maximum angle subtended by the actuating unit from the primary axis is at least 90°, and may be between 90° and 180° (since in a square arrangement, an actuating unit extending along two adjacent sides will subtend a maximum angle of 180° between opposite corners of the actuator assembly). The maximum angle subtended by the actuating unit is determined between the most distal point (away from the body portion 31) along the SMA element and the most distal point along the coupling link. Reference is now made to Figure 7, which schematically depicts the actuating forces F that can be applied by the actuating units 30a - 30h of the actuator assembly 2 shown in Figure 6. The perspective view of Figure 7 corresponds to Figure 6. Figure 7 shows that, among other things, the actuating units of Figure 6 are arranged such that, for each direction along each axis of a Cartesian coordinate system (+x, -x, +y, -y, +z, -z), there is at least one actuating force F with a non-zero component along that direction. The arrangement of the actuating units 30a - 30h, is capable of moving the movable part relative to the support structure in three translational degrees of freedom (e.g. independent movement along each of the x, y and z axes) as well as rotation in three rotational degrees of freedom (e.g. independent rotation about each of the x, y and z axes), although, as will be appreciated, the movable part 20 may move with fewer degrees of freedom in specific examples because of the way in which the controller 9 controls the actuating units and / or because of constraints due to a bearing arrangement 40, etc. In more detail, and treating each actuating force as a vector in the cartesian coordinate system, Figure 7 shows that each actuating force has a component parallel to either the x or y axis, and a component parallel to the z axis. In other words, given that the primary axis P extending through the actuator assembly is parallel to the z axis, each actuating force has a first component that is perpendicular to the primary axis, and a second component that is parallel to the primary axis. The component that is perpendicular to the primary axis may be referred to herein as the lateral component, whilst the component that is parallel to the primary axis may be referred to herein as the vertical component. The actuating units of the embodiment shown in Figure 6 and 7 may be considered to be arranged in four pairs, where, for each pair, the lateral components of the actuating forces are in the same direction. In other words, for the eight actuating units depicted, there is a pair of actuating units that provide actuating forces with a component along each of the +x, -x, +y and -y directions. In particular: o 30a and 30b are arranged in a first pair, since both units apply an actuating force with a component in the +x direction. o 30c and 30d are arranged in a second pair, since both units apply an actuating force with a component in the -x direction. o 30e and 30f are arranged in a third pair, since both units apply an actuating force with a component in the +y direction. o 30g and 30h are arranged in a fourth pair, since both units apply an actuating force with a component in the -y direction. In addition to applying an actuating force in a lateral direction, i.e. perpendicular to the primary axis, the actuating forces F applied by each actuating unit also has a vertical component that is parallel to the primary axis. In the particular embodiment shown in Figures 6-8, the units 30a-d of both the first and second pairs of units apply an actuating force with a vertical component in the +z direction, whilst the units 30e-h of the third and fourth pairs of actuating units apply an actuating force with a vertical component in the -z direction. In other embodiments, as described in more detail below, different actuating units within a given pair of actuating units may have an actuating force with the same lateral component but opposite components along the primary / z axis. Figure 8 depicts an alternative view of the actuator assembly shown in Figures 6 and 7, and shows that the actuating units are arranged such that, the SMA elements of any given pair of actuating units are arranged along the same one of the four sides of the actuator assembly. The SMA elements 34a and 34b of the first pair 30a and 30b are arranged along the same first side. Similarly, the SMA elements 34c and 34d of the second pair 30c and 30d are arranged along a second side, which in this embodiment is opposite to the first side. The SMA elements 34e and 34f of the third pair 30e and 30f are arranged along a third side, which is adjacent to the first and second sides in this embodiment, whilst the SMA elements 34g and 34h of the fourth pair 30g and 30h are arranged along a fourth side, opposite to the third side. In some embodiments, the SMA elements of each pair may be generally parallel to each other, but this is not essential. Advantageously, the SMA elements for a given pair may be arranged in parallel and adjacent to one another, so as to minimise the space occupied by the SMA elements in a camera module designed to be used in a smartphone or other application where space is at a premium. Whilst the SMA elements are arranged along the same side of the actuator assembly for each pair of actuating units, the coupling links 33a-h of any given pair may be arranged on opposite sides of the actuator assembly, as can be seen in Figure 8. The arrangement of the actuating units in each pair is such that, on actuation, the SMA elements arranged along the same side of the actuator assembly apply input forces towards opposite ends of that side, which, through the force-modifying elements 32a-h, give rise to a pair of actuating forces transmitted through the coupling links along opposite sides of the actuator assembly. As noted above, the lateral component of each actuating force in the pair of actuating forces is in the same direction. In the particular embodiment shown, the component of the actuating force that is parallel to the primary axis is also in the same direction. In general, the pair of actuating forces may be parallel, although this is not essential. In other examples (see discussion below), the vertical components the pair of actuating forces may be in opposite directions. When viewed along the primary axis, there is an angular overlap between each actuating unit in any given pair due to the SMA elements in a pair being arranged on the same side of the actuator assembly. In other words, the angular extent of a first actuating unit in a pair of actuating units about the primary axis overlaps with the angular extent of a second actuating unit in the pair. In a square arrangement, such as in the example depicted in the figures, the amount of overlap between the actuating units in a pair, i.e. the angle subtended by the overlapping portions of the pair of actuating units, is 90° or less due to the square geometry. If the SMA elements in the pair of actuating units extends along the full length of the side on which they are arranged, then the overlap between the actuating units is exactly 90°. However, typically, the SMA elements extend along less than the full length of the side on which they are arranged, meaning that the angle subtended by the overlap of the SMA elements when viewed along the primary axis is less than 90°. In addition to pairs of actuating units angularly overlapping with one another as described above, in some examples, each actuating unit also angularly overlaps with at least one other actuating unit (in addition to the corresponding actuating unit in a pair) when viewed along the primary axis. In other words, the angular extent of any given actuating unit about the primary axis overlaps with the angular extent of two or more other actuating units about the primary axis, wherein one of those two or more other actuating units is in a pair with the given actuating unit. Considering the embodiment depicted in Figures 6 - 8 in more detail, the eight actuating units of the actuator assembly can be divided into two groups. The first group is a "top" group and includes the actuating units which provide an actuating force with a component in the +z direction, which, in this embodiment includes the actuating units 30a-d of the first and second pairs. The second group is a "bottom" group and includes the actuating units which provide an actuating force with a component in the -z direction, which, in this embodiment includes the actuating units 30e-h of the third and fourth pairs. With reference to Figure 13, an alternative perspective view of the actuator assembly of Figures 6- 8 is provided. In this particular view, only the first group of actuating units (i.e. 30a - 30d) are shown with the support structure 10 and movable part 20. As shown in this figure, the actuating units of the first group may be arranged along one or more surfaces of the support structure of the actuator assembly that face generally in the +z direction. For example, the one or more surfaces of the support structure may be planar, and the normal to each of those surfaces may point generally towards the +z direction, or may at least have a larger component in the +z direction than in any lateral (x or y) direction. Similarly, although not shown in the figure, it will be appreciated that the actuating units of the second group may be arranged along one or more surfaces of the support structure of the actuator assembly that face generally in the -z direction. For example, the one or more surfaces may be planar, and the normal to each of those surfaces may point generally towards the +z direction, or may at least have a larger component in the +z direction than in any lateral (x or y) direction. In this way, the actuating units that provide actuating forces with a component in the +z direction are arranged on a top side of the actuator assembly (i.e. at the top of the actuator assembly as shown in Figure 13), wherein the top side also faces generally in the +z direction, whilst the actuating units that provide actuating forces with a component in the -z direction are arranged on a bottom side (the side that is not shown in Figure 13) of the actuator assembly, wherein the bottom side also faces generally in the -z direction. It will be appreciated that the bottom side of the actuator assembly may look identical to the top side, subject to a 180 degree rotation of the actuator assembly about the x or y axis, and a 90 degree rotation about the z axis. More generally, the one or more surfaces along which the first group of actuating units are arranged may substantially correspond to the one or more surfaces along which the second group of actuating units are arranged. Referring now to Figure 9, a perspective view of an alternative arrangement of actuating units 30a-h in an actuator assembly 2 is depicted. As with the embodiment described above with reference to Figures 6-8, the eight actuating units are divided into four pairs, where each pair includes actuating units that both provide an actuating force F with a component in the same lateral direction (either +x, -x, +y or -y). The actuating forces provided by each actuating unit in this arrangement is depicted in Figure 10, which is the equivalent of Figure 7 but corresponds to the alternative embodiment of Figure 9. In this alternative embodiment, the actuating units are arranged such that: o 30a and 30b are arranged in a first pair, since both units apply an actuating force with a component in the +x direction. o 30c and 30d are arranged in a second pair, since both units apply an actuating force with a component in the -x direction. o 30e and 30f are arranged in a third pair, since both units apply an actuating force with a component in the +y direction. o 30g and 30h are arranged in a fourth pair, since both units apply an actuating force with a component in the -y direction However, in contrast to the preceding embodiment in which pairs of actuating units also provide actuating forces with the same vertical component, in this embodiment pairs of actuating units provide actuating forces with opposite vertical components. Taking the first pair as an example, actuating unit 30a provides an actuating force with a component in the +z direction, whilst actuating unit 30b provides an actuating force with a component in the -z direction. More generally, each pair of actuating units has a first actuating unit arranged to apply an actuating force with a component along the +z direction, and a second actuating unit arranged to apply an actuating force with a component along the -z direction. In more detail, each of the first actuating units of each pair is arranged generally along a top side of the actuator assembly (i.e. along one or more surfaces that face generally in the +z direction). Each of the second actuating units of each pair is arranged generally along a bottom side of the actuator assembly (i.e. along one more surfaces that face generally in the -z direction). This arrangement is similar to that described with respect to Figures 6 to 8 in that the actuating units that provide actuating forces with a component in the +z direction are arranged on a top side of the actuator assembly, wherein the top side also faces generally in the +z direction, whilst the actuating units that provide actuating forces with a component in the -z direction are arranged on a bottom side of the actuator assembly, wherein the bottom side also faces generally in the -z direction. As can be seen from Figures 6 and 8, each pair of actuating units (30a and 30b, 30c and 30d, 30e and 30f, 30g and 30h) have SMA elements 34a-h arranged along the same one of four sides of the actuator assembly, whilst the coupling links in any given pair are arranged along opposite sides. As with the preceding embodiment, the arrangement of the actuating units in each pair is such that, on actuation, the SMA elements arranged along the same side of the actuator assembly apply input forces towards opposite ends of that side, which, through the force-modifying elements 32a-h, give rise to a pair of actuating forces transmitted through the coupling links along opposite sides of the actuator assembly. Referring now to Figure 12, a schematics of an alternative arrangement of actuator units is shown. In this particular embodiment, as with the other embodiments, the actuating units are arranged in pairs, where the actuating units of each pair provide actuating forces with lateral components along the same direction. The SMA elements of each pair are arranged along the same side of the actuator assembly in the same manner to the other embodiments described above, whilst the coupling links of each pair are also arranged on the same side (unlike the embodiments described above). For any given pair of actuating units, the side along which the coupling links are arranged is adjacent to the side along which the SMA elements are arranged. Thus, in these embodiments, the SMA elements of any given pair of actuating units apply input forces towards the same longitudinal end of the side along which the SMA elements are arranged, which, through the respective force-modifying elements, give rise to a pair of actuating forces transmitted through the coupling links along an adjacent side of the actuator assembly. The pair actuating forces have the same lateral component and opposite components along the primary axis. Other variations It will be appreciated that there may be many other variations of the above-described examples. For example, the actuator assembly may include different types of actuating units to those described above. Examples of such actuating units include a folded SMA wire arrangement as disclosed in WO 2021 / 111131 Al, a V-shaped SMA wire with a compliant connector as disclosed in WO 2013 / 121225 Al, a scissor jack arrangement as disclosed in WO 2021 / 156458 Al, a two-stage arrangement as disclosed in WO 2021 / 111181 Al, or simply an SMA wire connected between the support structure 10 and the movable part 20. The documents referred to in the preceding sentence are each herein incorporated by reference. The actuator assembly may have any number of different types of actuating units, and may have any suitable number of actuating units of each type. SMA The above-described SMA actuator assemblies comprise at least one 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, deposition, sintering or powder fusion. 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.

Claims

1. An actuator assembly comprising:a first part;a second part arranged to be movable relative to the first part;a plurality of actuating units each configured to apply an actuating force to one of the first and second parts capable of moving the second part relative to the first part, wherein at least one of the actuating unit comprises:a body portionan SMA element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; anda force-modifying element connected between the body portion and the other of the first and second parts and configured to modify the input force so as to give rise to the actuating force; anda coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force;wherein each actuating unit comprises an SMA element arranged along a first side of the actuator assembly and a coupling link arranged along a second side of the actuator assembly, wherein the second side is adjacent to the first side; andwherein the plurality of actuating units are arranged such that, for each direction along each axis of a Cartesian coordinate system (+x, -x, +y, -y, +z, -z), there is at least one actuating force with a non-zero component along that direction.

2. The actuator assembly of claim 1, wherein the actuator assembly comprises a primary axis extending through the actuator assembly, and wherein the sides of the actuator assembly are arranged around the primary axis.

3. The actuator assembly of claim 1 or 2, wherein the actuator comprises four sides arranged around the primary axis, optionally wherein adjacent sides are perpendicular and so the four sides form a quadrilateral shape as viewed along the primary axis.

4. The actuator assembly of claim 2 or 3, wherein the input force applied by each SMA element of each actuating unit is in a direction generally perpendicular to the primary axis, and wherein the actuating force of each actuating unit has a first component that is parallel to primary axis, and a second component that is perpendicular to primary axis.

5. The actuator assembly of any one of claims 2 to 4, wherein the input force of each actuating unit is in a direction generally perpendicular to the respective actuating force when viewed along the primary axis.

6. The actuator assembly of any preceding claim, comprising eight actuating units.

7. The actuator assembly of claim any preceding claim, wherein the actuating units are arranged in pairs and wherein, for each pair of actuating units, the SMA elements are arranged along the same side of the actuator assembly8. The actuator assembly of claim 7, wherein, for each pair of actuating units, the SMA elements are configured, on actuation, to apply input forces towards opposite longitudinal ends of the side along which the SMA elements are arranged.

9. The actuator assembly of claim 7, wherein, for each pair of actuating units, the SMA elements are configured, on actuation, to apply input forces towards the same longitudinal end of the side along which the SMA elements are arranged.

10. The actuator assembly of claim 7 or 8, wherein, for each pair of actuating units, the coupling links are arranged along opposite sides of the actuator assembly.

11. The actuator assembly of claim 10, wherein, for each pair of actuating units, the coupling links are configured to transmit generally parallel actuating forces to the one of the first and second part.

12. The actuator assembly of claim 9, wherein, for each pair of actuating units, the coupling links are arranged along the same side of the actuator assembly.

13. The actuator assembly of claims 7 to 12, when dependent on claim 2, wherein:a first pair of actuating units are each arranged to apply an actuating force with a component along a first direction along a first lateral axis, wherein the first lateral axis is perpendicular to the primary axis;a second pair of actuating units are each arranged to apply an actuating force with a component along a second direction, opposite the first direction, along the first lateral axis;a third pair of actuating units are each arranged to apply an actuating force with a component along a first direction along a second lateral axis, wherein the second lateral axis is perpendicular to the primary axis and the first lateral axis; anda fourth pair of actuating units are each arranged to apply an actuating force with a component along a second direction, opposite the first direction, along the second lateral axis.

14. The actuator assembly of claim 13, wherein:the first and second pairs of actuating units are each arranged to apply an actuating force with a component along a first direction along the primary axis;the third and fourth pairs of actuating units are each arranged to apply an actuating force with a component along a second direction, opposite the first direction, along the primary axis.

15. The actuator assembly of claim 13, wherein each pair of actuating units comprises a first actuating unit and a second actuating unit, and wherein:the first actuating unit of each pair is arranged to apply an actuating force with a component along a first direction along the primary axis; andthe second actuating unit of each pair is arranged to apply an actuating force with a component along a second direction, opposite the first direction, along the primary axis.

16. The actuator assembly of claim 13 or 14; wherein:the body portions, SMA elements, and force-modifying elements of the actuator units of the first and second pairs are arranged along one or more surfaces facing generally in the first direction along the primary axis; andthe body portions, SMA elements, and force-modifying elements of the actuator units of the third and fourth pairs are arranged along one or more surfaces facing generally in the second direction along the primary axis.

17. The actuator assembly of claim 13 or 15, whereinthe body portions, SMA elements, and force-modifying elements of each of the first actuator units of each pair are arranged along one or more surfaces facing generally in the first direction along the primary axis; andthe body portions, SMA elements, and force-modifying elements of each of the second actuator units of each pair are arranged along one or more surfaces facing generally in the second direction along the primary axis.

18. The actuator assembly of claim 2 or any of claims 3 to 17 when dependent on claim 2, wherein each actuating unit has an angular extent about the primary axis that is greater than 90°.

19. The actuator assembly of claim 18 when dependent on claim 7, wherein a portion of each actuating unit in each pair of actuating units overlap one another when viewed along the primary axis.

20. The actuator assembly of claim 19 wherein the angular extent of the overlap about the primary axis is less than 90°.

21. The actuator assembly of any of claims 18 to 20, wherein the angular extent of each actuating unit about the primary axis overlaps with the angular extent of two or more other actuating units about the primary axis.

22. The actuator assembly of claim 2 or any of claims 3 to 21 when dependent on claim 2, wherein the SMA element and coupling link of any given actuating unit are arranged in a plane with a normal that lies at an oblique angle relative to the primary axis.

23. A camera assembly comprising:an actuator assembly according to any one of claims 1 to 22;one or more lenses comprised in one of the first and second parts of the actuator assembly; andan image sensor comprised in the other of the first and second parts of the actuator assembly;wherein the actuator assembly is configured to move the one or more lenses and the image sensor relative to each other in three translational degrees of freedom.

24. A camera assembly comprising:an actuator assembly according to any one of claims 1 to 22; anda support structure comprising one of the first and second parts of the actuator assembly;a module comprised in the other of the first and second parts of the actuator assembly, whereinthe module comprises one or more lenses and an image sensor;wherein the actuator assembly is configured to rotate the module relative to the support structure in two or more rotational degrees of freedom.Application No: GB2317082.2Claims searched: 1-24Examiner: Mr Peter MiddletonDate of search: 11 March 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-24 WO 2023 / 209404 Al (CAMBRIDGE MECHATRONICS LTD) see figures 3 and 5: SMA actuator may use force modifying mechanism and provide force in + / - X, Y, Z directions Y 1-24 WO 2019 / 034860 Al (CAMBRIDGE MECHATRONICS LTD) see abstract and figures: example of SMA actuator assembly with force components in all +1- X, Y, Z directions Y 1-24 CN 116648650 A (CAMBRIDGE MECHATRONICS LTD) see abstract and figures: example of SMA actuator assembly with force components in all +1- X, Y, Z directions Y 1-24 WO 2024 / 188234 Al (HUAWEI TECH CO LTD) see abstract and figures: example of SMA actuator assembly with force components in all +1- X, Y, Z directions Y 1-24 WO 2022 / 084699 Al (CAMBRIDGE MECHATRONICS LTD) see abstract and figures: example of SMA actuator with force modifying arrangement, with SMA and compliant coupling link arranged on adjacent sides of assembly Y 1-24 WO 2022 / 219354 Al (CAMBRIDGE MECHATRONICS LTD) see abstract and figures: example of SMA actuator with force modifying arrangement, with SMA and compliant coupling link arranged on adjacent sides of assembly Y 1-24 CN 111552092 A (DONGGUAN YADENG ELECTRONICS CO LTD) see abstract and figures: example of SMA actuator with force modifying arrangement, with SMA and compliant coupling link arranged on adjacent sides of assembly Y 1-24 WO 2023 / 135432 Al (CAMBRIDGE MECHATRONICS LTD) see abstract and figures: example of SMA actuator with force modifying arrangement, with SMA and compliant coupling link arranged on adjacent sides of assemblyCategories:___________________________________________________________________________________|xDocument indicating lack of novelty or inventive A Document indicating technological background and / or state30•cstep of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From F03G 0007 / 06 01 / 01 / 2006

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