Actuator assembly

Abstract

An actuator assembly comprises a first part, a second part movable relative to the first part, and one or more actuating units 30 each configured to apply an actuating force to the second part. At le

Description

Field The present application relates to an actuator assembly with at least one actuating unit including 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 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 wires can 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 increase the stroke or the actuating force and / 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 that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part. At least one of the actuating units comprises: a body portion; an SMA (shape memory alloy) element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion; a force-modifying element connected between the body portion and the first part, 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 second part, wherein the coupling link is configured to transmit the actuating force from the body portion to the second part, wherein the coupling link is compliant in a direction perpendicular to the actuating force, and wherein the coupling link forms part of at least one conductive path via which the first and second parts are electrically connected. The second part may carry an electronic component (e.g. an auto-focus (AF) actuator) and the at least one conductive path may be for electrically connecting (e.g. a control circuit, a printed circuit board, and / or a power supply) to the electronic component. This may e.g. remove the need to provide a FPC (flexible printed circuit) for electrically connecting to the electronic component, or may allow a reduction in the number of conductive paths required in such an FPC so that it can be reduced in size. Optionally, the at least one actuating unit comprises a flexible conductive component electrically connecting the coupling link and the first part. Optionally, the flexible conductive component forms part of the at least one conductive path via which the first and second parts are electrically connected. Optionally, the flexible conductive component is or comprises a flexible conductive flexure. Optionally, the flexible conductive flexure is compliant in a direction perpendicular to the actuating force and compliant a direction parallel to the actuating force. Optionally, the flexible conductive flexure is elongate and is stiff along its length and compliant in a direction perpendicular to its length. Optionally, the flexible conductive flexure extends from a first end, electrically connected to the coupling link, to a second end, electrically connected to the first part, in a serpentine manner. Optionally, the flexible conductive component and the coupling link are integrally formed. Optionally, the flexible conductive component and / or the coupling link are / is electrically insulated from the body portion. Optionally, the coupling link is or comprises a coupling flexure. Optionally, the coupling link is elongate and is stiff along its length and compliant in a direction perpendicular to its length. Optionally, the force-modifying element forms part of a second conductive path via which the SMA element and the first part are electrically connected. Optionally, the second conductive path is insulated from the at least one conductive path. Optionally, the force-modifying element is or comprises a force-modifying flexure. Optionally, the force-modifying element is elongate and is stiff along its length and compliant in a direction perpendicular to its length. Optionally, the second part comprises an electronic component electrically connected to the first part via the at least one conductive path. Optionally, the electronic component comprises an auto-focus actuator, an image stabilisation actuator, an image sensor, a variable aperture actuator, an emitter, a display, an actuator for moving an emitter, an actuator for moving a display, or a part thereof. Optionally, the one or more actuating units comprise four actuating units arranged so as to be capable of moving the second part relative to the first part in any direction in a movement plane without applying any net torque to the second part about a primary axis perpendicular to the movement plane. Optionally, a first pair of actuating units are each configured to apply a torque to the second part in one sense about the primary axis, and a second pair of actuating units are each configured to apply a torque to the second part in the other sense about the primary axis. Optionally, the one or more actuating units are configured to tilt the second part relative to the first part about an axis perpendicular to a primary axis. Optionally, the one or more actuating units comprise two or more actuating units configured to tilt the second part relative to the first part about two axes perpendicular to a primary axis and to each other. Optionally, the two or more actuating units comprise four or eight actuating units. Optionally, the first part or the second part comprises one or more lenses and / or an image sensor. Optionally, the primary axis is parallel to the optical axis of the one or more lenses and / or is perpendicular to a light-sensitive region of the image sensor. Optionally, the first part or the second part comprises an emitter, a display, or a part thereof. Optionally, the primary axis is perpendicular to a plane defined by the display and / or is parallel to the general direction in which radiation is emitted from the emitter. 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 assembly incorporating an actuator assembly; Figure 2 is a schematic perspective view of the actuator assembly; Figures 3A and 3B are plan views of an actuating unit; Figure 4 is a schematic plan view of an arrangement of four actuating units; Figure 5 is a plan view of an arrangement of four actuating units; Figure 6 is a perspective exploded view of the arrangement of Figure 5; Figure 7 is a plan view of an alternative actuating unit; Figure 8 is a plan view of an arrangement of four actuating units; Figure 9 is a perspective exploded view of the arrangement of Figure 8. Detailed description Camera assembly Figures 1A-E schematically show different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera assembly 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 (herein also referred to as a first part 10) and a movable part 20 (herein also referred to as a second 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 to the maximum extent permissible by law. 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 to the maximum extent permissible by law. 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 to the maximum extent permissible by law. 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 to the maximum extent permissible by law. 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, Tz, 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 to the maximum extent permissible by law. 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. Fig. 4) 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. The camera assembly 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 assembly 1 may be a compact camera assembly 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 assembly 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 O. 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 assembly 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 assembly 1. In the ("autofocus" or "zoom") 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 optical axis O. Such movement has the effect of adjusting the focus of the image on the image sensor 4 or providing zoom functionality. So, auto-focus (AF) or zoom functionality can be implemented in the camera assembly 1. In some examples (not shown), the camera assembly 1 may include a first actuator assembly for providing OIS as illustrated in Figures 1A-C, and a second actuator assembly for providing AF or zoom 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 assembly 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 assembly 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 drive relative movement of the movable part 20. The drive signals are chosen to drive relative 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 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 assembly 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 assembly 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 assembly 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 Figures 3A and 3B show plan views of an example of the actuating unit 30. 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. The actuating unit 30 also includes a force-modifying flexure 32. 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. 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. 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. The coupling link 33 forms part of at least one conductive path 301 via which the first part 10 and second part 20 are electrically connected. The second part 20 may carry / comprise an electronic component (e.g. an auto-focus (AF) actuator) and the at least one conductive path 301 may be for electrically connecting, e.g. a control circuit / controller, a printed circuit board, and / or a power supply, to the electronic component. This may e.g. remove the need to provide an FPC (flexible printed circuit) for electrically connecting to the electronic component, or may allow a reduction in the number of conductive paths that needs to be provided by such an FPC such that the FPC can be reduced in size. The electronic component may comprise an auto-focus actuator, an image stabilisation actuator, an image sensor, a variable aperture actuator, an emitter, a display, an actuator for moving an emitter, an actuator for moving a display, or a part thereof. The actuating unit 30 also includes a flexible conductive component 37 electrically connecting the coupling link 33 and the first part 10. One end of the flexible conductive component 37 is connected to the coupling link 33. The other end of the flexible conductive component 37 is connected to the first part 10 e.g. via a foot portion 38. The flexible conductive component 37 forms part of the at least one conductive path 301 via which the first part 10 and second part 20 are electrically connected. In this example, the flexible conductive component 37 is a flexible conductive flexure 37. The flexible conductive flexure 37 is compliant in a direction perpendicular to the actuating force F and compliant a direction parallel to the actuating force F. In this example, the flexible conductive component 37 and the coupling link 33 are integrally formed, for example from a single sheet of material (such as metal). In other examples, these features may be formed from different parts or materials. In this example, the flexible conductive component 37 and the coupling link 33 are electrically insulated from the body portion 31. In the example of Figures 3A and 3B, the flexible conductive flexure 37 is elongate and is stiff along its length and compliant in a direction perpendicular to its length. However, as shown in Figure 7, alternatively the flexible conductive flexure 37 may extend from a first end, electrically connected to the coupling link 33, to a second end, electrically connected to the first part 10, in a serpentine manner. The actuating unit 30 of Figure 7 only differs from the actuating unit 30 of Figures 3A and 3B in that the flexible conductive flexure 37 extends from a first end, electrically connected to the coupling link 33, to a second end, electrically connected to the first part 10, in a serpentine manner. The force-modifying element 32 forms part of a second conductive path 302 via which the SMA element 34 and the first part 10 are electrically connected. This second conductive path 302 is for electrically connecting, e.g. a control circuit / controller, a printed circuit board, and / or a power supply, to the SMA element 34. The second conductive path 302 is insulated from the at least one conductive path 301. 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 parallel to the SMA wire 34. Also, in this example, the force-modifying flexure 32 is perpendicular to the SMA wire 34, and the forcemodifying flexure 32 is placed in tension on contraction of the SMA wire 34. In the illustrated 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 forcemodifying flexure 32 could instead be arranged so as to 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 to the maximum extent permissible by law. In the illustrated 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 the illustrated 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. Instead of the force-modifying flexure 32, the actuator assembly may include a different type of forcemodifying element 32 configured to enable the above-described movement of the body portion 31 relative to the support structure 10. Such a force-modifying element 32 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 F are 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. Figure 5 shows a plan view of four of the actuating units 30 of Figures 3A and 3B arranged as shown in Figure 4. Similarly, Figure 8 shows a plan view of four of the actuating units 30 of Figure 7 arranged as shown in Figure 4. 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. anti-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. 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. 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 to the maximum extent permissible by law. 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 to the maximum extent permissible by law. 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 right 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 left corner may be replaced with springs applying biasing forces along the corresponding depicted arrows, for example. In alternative arrangements, one or more actuating units 30 may be configured to tilt the second part 20 relative to the first part 10 about an axis perpendicular to a primary axis P. Where this is the case, the one or more actuating units 30 may comprise two or more actuating units 30 configured to tilt the second part 20 relative to the first part 10 about two axes x, y perpendicular to a primary axis P and to each other. The two or more actuating units 30 may comprise four or eight actuating units. The first part 10 or the second part 20 may comprise one or more lenses and / or an image sensor. Where this is the case, the primary axis P may parallel to the optical axis of the one or more lenses and / or is perpendicular to a light-sensitive region of the image sensor. The first part 10 or the second part 20 may alternatively comprise an emitter, a display, or a part thereof. Where this is the case, the primary axis P may be perpendicular to a plane defined by the display and / or is parallel to the general direction in which radiation is emitted from the emitter. As shown in Figures 6 and 9, within each actuating unit 30, the body portion 31 may be bonded B to the flexible conductive flexure / component 37 and the coupling link 33, such that the body portion 31 is mechanically coupled and electrically insulated from the flexible conductive flexure / component 37 and the coupling link 33. Moreover, within each actuating unit 30, the body portion 31 may be welded W to the force-modifying flexure / element 32, such that the body portion 31 is mechanically coupled and electrically connected to the force-modifying flexure / element 32. 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 to the maximum extent permissible by law. 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 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 that is movable relative to the first part; andone or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part, wherein at least one of the actuating units comprises:a body portion;an SMA (shape memory alloy) element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion;a force-modifying element connected between the body portion and the first part, 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 second part, wherein the coupling link is configured to transmit the actuating force from the body portion to the second part, wherein the coupling link is compliant in a direction perpendicular to the actuating force, and wherein the coupling link forms part of at least one conductive path via which the first and second parts are electrically connected.

2. An actuator assembly according to claim 1, wherein the at least one actuating unit comprises a flexible conductive component electrically connecting the coupling link and the first part.

3. An actuator assembly according to claim 2, wherein the flexible conductive component forms part of the at least one conductive path via which the first and second parts are electrically connected.

4. An actuator assembly according to claim 2 or 3, wherein the flexible conductive component is or comprises a flexible conductive flexure.

5. An actuator assembly according to claim 4, wherein the flexible conductive flexure is compliant in a direction perpendicular to the actuating force and compliant a direction parallel to the actuating force.

6. An actuator assembly according to claim 4 or 5, wherein the flexible conductive flexure is elongate and is stiff along its length and compliant in a direction perpendicular to its length.

7. An actuator assembly according to claim 4 or 5, wherein the flexible conductive flexure extends from a first end, electrically connected to the coupling link, to a second end, electrically connected to the first part, in a serpentine manner.

8. An actuator assembly according to any of claims 2 to 7, wherein the flexible conductive component and the coupling link are integrally formed.

9. An actuator assembly according to any of claims 2 to 8, wherein the flexible conductive component and / or the coupling link are / is electrically insulated from the body portion.

10. An actuator assembly according to any preceding claim, wherein the coupling link is or comprises a coupling flexure.

11. An actuator assembly according to any preceding claim, wherein the coupling link is elongate and is stiff along its length and compliant in a direction perpendicular to its length.

12. An actuator assembly according to any preceding claim, wherein the force-modifying element forms part of a second conductive path via which the SMA element and the first part are electrically connected.

13. An actuator assembly according to claim 12, wherein the second conductive path is insulated from the at least one conductive path.

14. An actuator assembly according to any preceding claim, wherein the force-modifying element is or comprises a force-modifying flexure.

15. An actuator assembly according to any preceding claim, wherein the force-modifying element is elongate and is stiff along its length and compliant in a direction perpendicular to its length.

16. An actuator assembly according to any preceding claim, wherein the second part comprises an electronic component electrically connected to the first part via the at least one conductive path.

17. An actuator assembly according to claim 16, wherein the electronic component comprises an auto-focus actuator, an image stabilisation actuator, an image sensor, a variable aperture actuator, an emitter, a display, an actuator for moving an emitter, an actuator for moving a display, or a part thereof.

18. An actuator assembly according to any preceding claim, wherein the one or more actuating units comprise four actuating units arranged so as to be capable of moving the second part relative to the first part in any direction in a movement plane without applying any net torque to the second part about a primary axis perpendicular to the movement plane.

19. An actuator assembly according to claim 18, wherein a first pair of actuating units are each configured to apply a torque to the second part in one sense about the primary axis, and a second pair of actuating units are each configured to apply a torque to the second part in the other sense about the primary axis.

20. An actuator assembly according to any of claims 1 to 17, wherein the one or more actuating units are configured to tilt the second part relative to the first part about an axis perpendicular to a primary axis.

21. An actuator assembly according to any of claims 1 to 17 and 20, wherein the one or more actuating units comprise two or more actuating units configured to tilt the second part relative to the first part about two axes perpendicular to a primary axis and to each other, optionally wherein the two or more actuating units comprise four or eight actuating units.

22. An actuator assembly according to any preceding claim, wherein the first part or the second part comprises one or more lenses and / or an image sensor.

23. An actuator assembly according to claim 22 when dependent on any of claims 18 to 21, wherein the primary axis is parallel to the optical axis of the one or more lenses and / or is perpendicular to a light-sensitive region of the image sensor.

24. An actuator assembly according to any of claims 1 to 21, wherein the first part or the second part comprises an emitter, a display, or a part thereof.

25. An actuator assembly according to claim 24 when dependent on any of claims 18 to 21, wherein the primary axis is perpendicular to a plane defined by the display and / or is parallel to the general direction in which radiation is emitted from the emitter.

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