Actuator assembly

Abstract

An actuator assembly comprising: first and second parts that are movable relative to each other; and at least one actuating unit each configured, on actuation, to apply a respective actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; and an SMA wire connected between the body portion and the first part, wherein the SMA wire is arranged, on actuation, to apply an input force to the body portion, thereby causing rotation of the body portion about an effective pivot point defined by the force-modifying flexure such that the actuating force is applied via the coupling flexure to the second part, wherein the angle between i) a notional line between the effective pivot point P and the connection point between the SMA wire and the body portion and ii) a notional line between the effective pivot point P and the connection point between the coupling flexure and the body portion is greater than 135 degrees.

Description

[0001] ACTUATOR ASSEMBLY

[0002] Field

[0003] The present application relates to an actuator assembly with at least one actuating unit including a shape memory alloy (SMA) element.

[0004] Background

[0005] SMA actuator assemblies may be used in a variety of applications for moving a movable part relative to a support structure.

[0006] 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 / 029315 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.

[0007] 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.

[0008] 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.

[0009] Summary

[0010] According to a first aspect of the present invention, there is provided an actuator assembly comprising: first and second parts that are movable relative to each other; and at least one actuating unit each configured, on actuation, to apply a respective actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a forcemodifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; and an SMA wire connected between the body portion and the first part, wherein the SMA wire is arranged, on actuation, to apply an input force to the body portion, thereby causing rotation of the body portion about an effective pivot point defined by the force-modifying flexure such that the actuating force is applied via the coupling flexure to the second part, wherein the angle between i) a notional line between the effective pivot point P and the connection point between the SMA wire and the body portion and ii) a notional line between the effective pivot point P and the connection point between the coupling flexure and the body portion is greater than 135 degrees.

[0011] The angle is preferably greater than 150 degrees, further preferably greater than 170 degrees, most preferably about 180 degrees.

[0012] Arranging the points at which the forces from the SMA wire and the coupling flexure act on the body portion on or close to a notional line intersecting the effective pivot point reduces or avoids undesirable out-of-plane deformation of the force-modifying flexure. This makes movement of the body portion more stable, ensuring more reliable operation of the actuating unit.

[0013] This applies to second- and third-class levers as well as first-class levers. Hence, according to a second aspect of the present invention, there is provided an actuator assembly comprising: first and second parts that are movable relative to each other; and at least one actuating unit each configured, on actuation, to apply a respective actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; and an SMA wire connected between the body portion and the first part, wherein the SMA wire is arranged, on actuation, to apply an input force to the body portion, thereby causing rotation of the body portion about an effective pivot point defined by the forcemodifying flexure such that the actuating force is applied via the coupling flexure to the second part, wherein (i) the effective pivot point P, (ii) the connection point between the SMA wire and the body portion and (iii) the connection point between the coupling flexure and the body portion are positioned on or close to a notional line.

[0014] Further aspects of the present invention are set out in the dependent claims and in the detailed description.

[0015] It will be appreciated that a reference to a component being "connected between" two other components means, for example, that the component is directly or indirectly connected to each of the other components. Such an indirect connection may involve a connection via further component(s) (e.g. a connector) with fixed position(s) relative to one of the other components. Such an indirect connection may involve a connection via further component(s) which is / are movable relative to the other components. For example, an SMA element may be connected to the one of the first and second parts via a further flexure, e.g. as described in WO 2022 / 144541 (which is herein incorporated by reference).

[0016] Brief description of the drawings

[0017] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0018] Figures 1A-E are schematic cross-sectional views of different variations of a camera assembly incorporating an actuator assembly;

[0019] Figure 2 is a schematic perspective view of the actuator assembly;

[0020] 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;

[0021] Figure 4 is a schematic plan view of an arrangement of four actuating units;

[0022] Figure 5 is a schematic perspective view of an arrangement of eight actuating units;

[0023] Figure 6 is a schematic plan view of an actuating unit according to a comparative example;

[0024] Figure 7 is a schematic plan view of an actuating unit according to the present invention;

[0025] Figures 8a-d are schematic views illustrating the forces acting on the actuating units of Figures 6 and 7;

[0026] Figure 9a is schematic view illustrating the forces actuating on a comparative example of an actuating unit that acts like a third-class lever; and

[0027] Figure 9b is schematic view illustrating the forces actuating on an example of an actuating unit that acts like a third-class lever. Detailed description

[0028] Camera assembly

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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).

[0033] 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:

[0034] • Tx and Ty: 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.

[0035] • 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.

[0036] • 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.

[0037] • 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In the ("module-tilt") variation shown in Figure 1C, 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Actuating unit

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 P. Although the effective pivot point P is shown in Figure 3B as being positioned in the middle of force-modifying 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.

[0061] 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.

[0062] 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 of these features, if present, may be formed from different parts or materials.

[0063] 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.

[0064] 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°. 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. 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.

[0065] 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:

[0066] • adjusting the orientation of the SMA wire 34 (and thus of the input force Fi);

[0067] • adjusting the location of the connection point between the SMA wire 34 and 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

[0068] F).

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 (or may not) 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.

[0076] 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.

[0077] Arrangement of four actuating units

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Arrangement of eight actuating units

[0088] Figures 5a-c schematically show perspective views of different versions 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.

[0089] 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 1C).

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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).

[0098] Other variations

[0099] It will be appreciated that there may be many other variations of the above-described examples.

[0100] 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. Improved stability of body portion

[0101] Figure 6 schematically shows an actuating unit 30 according to a comparative example to the present invention. As shown, both the SMA wire 34 and the coupling flexure 33 are connected to the body portion 31 at a point behind the effective pivot point P defined by the force-modifying flexure 32. The line 34a between the effective pivot point P and the point at which the SMA wire 34 connects to the body portion 31 and the line 33a between the effective pivot point P and the point at which the coupling flexure connects to the body portion 31 form an angle therebetween that is less than 135 degrees. As a result, the input force Fi and the actuating force F may apply a torque about the effective pivot point P about an axis in the plane of the actuating unit 30. With reference to Figure 6, the force-modifying flexure 34 may thus undesirably bend out of the plane. Such undesirable out-of-plane deformation may lead to high stresses in the force-modifying flexure 34, risking in fatigue and failure, as well as reducing the performance of the actuating unit 30.

[0102] The inventors have identified this issue of possible undesirable out-of-plane deformation of the actuating unit 30. One solution to address the issue is to provide a bearing or other constraint that restricts the body portion 31 from moving out-of-plane. However, such an approach may lead to additional parts and cost of the actuating unit 30, and lead to additional friction and hence a performance reduction of the actuating unit 30. The present invention aims to address the issue of undesirable out-of-plane deformation without the need of introducing additional components to constrain out-of-plane movement. According to the present invention, the body portion 31 is designed such that any torque on the body portion 31 due to the input force Fi and actuating force F leading to out-of-plane deformation is reduced or avoided.

[0103] Figure 7 schematically depicts an embodiment of an actuating unit 30 according to the present invention. The effective pivot point P, the point at which the SMA wire 34 connects to the body portion 31 and the point at which the coupling flexure 33 connects to the body portion 31 lie on a straight line. As such, forces in the SMA wire 34 and the coupling flexure 33 do not apply an out-of-plane torque about the effective pivot point P to the body portion 31. Undesirable out-of-plane deformation of the forcemodifying flexure may thus be avoided.

[0104] In the embodiment of Figure 7, the angle a between i) the line 34a between the effective pivot point P and the point at which the SMA wire 34 connects to the body portion 31 and ii) the line 33a between the effective pivot point P and the point at which the coupling flexure connects to the body portion 31 is 180 degrees. This is particularly preferable, because it allows undesirable out-of-plane torque to be minimized. The benefits of the invention are also achieved when the angle a is close to 180 degrees. In particular, the angle a is preferably greater than 135 degrees, further preferably greater than 160 degrees, further preferably greater than 170 degrees. Undesirable out-of-plane deformation of the forcemodifying flexure 32 may thus be reduced compared to the comparative example of Figure 6. Angles a that are closer to 180 degrees result in less undesirable out-of-plane deformation.

[0105] The body portion 31 of the actuating unit 30 of Figure 7 is shaped so as to position the point at which the SMA wire 34 connects to the body portion 31 and the point at which the coupling flexure 33 connects to the body portion 31 along a line intersecting the effective pivot point. In Figure 7, the body portion 31 comprises two arms extending from the connection point to the force-modifying flexure. A first arm is arranged between the force-modifying flexure 31 and the SMA wire 34. A second arm is arranged between the force-modifying flexure 31 and the coupling flexure 33. The first and second arms extend, from the connection to the force-modifying flexure, towards the effective pivot point P, i.e. towards the point of connection of the force-modifying flexure to the support structure 10.

[0106] Figures 8a-d further illustrate the technical benefits of the present invention. The figures shows lines through the force-modifying flexure 34 and through the coupling flexure 33 relative to the effective pivot point P defined by the force-modifying flexure 32. Figure 8a shows such lines for the actuating unit 30 of Figure 7 when in a central position (i.e. when not deformed by the SMA wire 34). Figure 8b shows such lines for the actuating unit 30 of Figure 7 when deformed by the SMA wire 34. Figure 8c shows such lines for an actuating unit 30 according to the comparative example of Figure 6 when in a central position (i.e. when not deformed by the SMA wire 34). Figure 8d shows such lines for an actuating unit 30 according to the comparative example of Figure 6 when deformed by the SMA wire 34.

[0107] As shown in Figures 8c and 8d, in the comparative example the angle between the SMA wire 34 and the coupling flexure 33 is relatively large. This may lead to greater gearing, i.e. a larger amount of stroke amplification. However, as described above, the stability of the actuating unit 30 may be undesirably affected. The distances Ds and Dt may vary relatively greatly, resulting in a relatively large difference in amplification between the central position and the edge position of the body portion 31.

[0108] In comparison, Figures 8a and 8b show that the distances Ds and Dt for the actuating unit 30 according to the present invention vary by a relatively small amount. As such, the amount of amplification between the central position and the edge position of the body portion 31 remains relatively similar. Control of the actuating unit 30 is thus made easier. The above examples relate to actuating units that act like first-class levers. Similar principles apply in relation to actuating units that act like second-class levers and (the generally more useful, stroke amplifying) third-class levers.

[0109] Figures 9a illustrates a comparative example of an actuating unit 30 that acts like a third-class lever. In particular, Figure 9a illustrates the positions of the effective pivot point P, the connection point Q. between the SMA element 34 and the body portion (not shown) and the connection point R between the coupling flexure 33 and the body portion. As can be seen, a line L through the connection points R and Q. passes behind the effective pivot point P, enabling undesirable out-of-plane deformation of the force-modifying flexure (not shown) as described above with reference to Fig. 6. In contrast, in the actuating unit 30 illustrated in Figure 9b, the equivalent line L passes through the effective pivot point P and, in such an example, undesirable out-of-plane deformation of the force-modifying flexure can be avoided.

[0110] SMA

[0111] 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

Claims1. An actuator assembly comprising: first and second parts that are movable relative to each other; and at least one actuating unit each configured, on actuation, to apply a respective actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying element connected between the body portion and the first part; a coupling link connected between the body portion and the second part; and an SMA element connected between the body portion and the first part, wherein the SMA element is arranged, on actuation, to apply an input force to the body portion, thereby causing rotation of the body portion about an effective pivot point defined by the forcemodifying element such that the actuating force is applied via the coupling element to the second part, wherein the angle between i) a notional line between the effective pivot point P and the connection point between the SMA element and the body portion and ii) a notional line between the effective pivot point P and the connection point between the coupling link and the body portion is greater than 135 degrees.

2. An actuator assembly according to claim 1, wherein the angle between i) the notional line between the effective pivot point P and the connection point between the SMA element and the body portion and ii) the notional line between the effective pivot point P and the connection point between the coupling link and the body portion is greater than 160 degrees, preferably greater than 170 degrees, most preferably about 180 degrees.

3. An actuator assembly according to any one of the preceding claims, wherein the force-modifying element comprises a force-modifying flexure.

4. An actuator assembly according to any one of the preceding claims, wherein the force-modifying element is arranged to be in tension on actuation of the SMA element.

5. An actuator assembly according to any one of the preceding claims, wherein the force-modifying element is arranged at an angle relative to the SMA element, preferably at an angle in the range from 13 to 77 degrees, optionally from 13 to 40 degrees or from 77 to 50 degrees.

6. An actuator assembly according to any one of the preceding claims, wherein each actuating unit is configured so as to amplify an amount of actuation of the SMA element to a relatively greater amount of movement of the second part relative to the first part, optionally by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3.

7. An actuator assembly according to any one of claims 1 to 5, wherein each actuating unit is configured so as to amplify the input force such that the actuation force is greater than the input force, optionally by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3.

8. An actuator assembly according to any one of the preceding claims, wherein the coupling link comprises a coupling flexure.

9. An actuator assembly according to claim 8, wherein the coupling link is arranged to be in tension on actuation of the SMA element.

10. An actuator assembly according to claim 8 or 9, wherein the angle between the coupling flexure and the SMA wire is in the range from 70 to 110 degrees.

11. An actuator assembly according to any one of the preceding claims, wherein each actuating unit extends substantially in an actuating plane.

12. An actuator assembly according to any one of the preceding claims, wherein the body portion and the force-modifying element are integrally formed from the same material, optionally wherein the coupling link is further formed from the same material.

13. An actuator assembly according to any one of the preceding claims, comprising a total of four actuating units arranged to apply actuating forces such that none of the actuating forces are non-coll inear.

14. An actuator assembly according to claim 13, wherein the four actuating units are arranged such that a first pair of actuating units applies actuating forces in opposite directions parallel to a first axis in a plane and a second pair of actuating units applies actuating forces in opposite directions parallel to a second axis in the plane, wherein the first and second axes are non-parallel.

15. An actuator assembly according to claim 14, wherein the first pair of actuating units is arranged to apply a torque to the second part relative to the first part in a first sense, and the second pair ofactuating units is arranged to apply a torque to the second part relative to the first part in a second sense, wherein the second sense is opposite to the first sense.

16. An actuator assembly comprising: firstand second parts that are movable relative to each other; and at least one actuating unit each configured, on actuation, to apply a respective actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying element connected between the body portion and the first part; a coupling link connected between the body portion and the second part; and an SMA element connected between the body portion and the first part, wherein the SMA element is arranged, on actuation, to apply an input force to the body portion, thereby causing rotation of the body portion about an effective pivot point defined by the forcemodifying element such that the actuating force is applied via the coupling element to the second part, wherein (i) the effective pivot point P, (ii) the connection point between the SMA element and the body portion and (iii) the connection point between the coupling link and the body portion are positioned on or close to a notional line.

17. An actuator assembly according to any one of the preceding claims, comprising an image sensor and / or a lens assembly, wherein the image sensor or the lens assembly is fixed relative to the second part and / or the lens assembly or the image sensor is fixed relative to the first part.

Images