Actuator assembly

Abstract

An actuator assembly (2) comprising: a first part (10); a second part (20) that is movable relative to the first part; and one or more actuating units (30) each configured, on actuation, to apply an actuation force F capable of moving the second part relative to the first part, each actuating unit comprising: an intermediate part (31); a bearing (32) between the intermediate part and one of the first and second parts that is configured to guide translational movement of the intermediate part along a movement path relative to the one of the first and second parts; a shape memory alloy, SMA, element (34) connected between the intermediate part and the one of the first and second parts and configured, on actuation, to apply an input force Fi to the intermediate part capable of translationally moving the intermediate part relative to the one of the first and second parts, wherein the input force is at an angle to the movement path, and a coupling (33) configured to couple the intermediate part to the other of the first and second parts so as to apply, on application of the input force on the intermediate part by the SMA element, the actuation force to the other of the first and second parts on actuation of the SMA element, wherein each actuating unit is configured to amplify an actuation amount of the SMA element to a relatively greater amount of relative movement between the first and second parts.

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 / 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.

[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 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, on actuation, to apply an actuation force capable of moving the second part relative to the first part, each actuating unit comprising: an intermediate part; a bearing between the intermediate part and one of the first and second parts that is configured to guide translational movement of the intermediate part along a movement path relative to the one of the first and second parts; a shape memory alloy, SMA, element connected between the intermediate part and the one of the first and second parts and configured, on actuation, to apply an input force to the intermediate part capable of translationally moving the intermediate part relative to the one of the first and second parts, wherein the input force is at an angle to the movement path, and a coupling configured to couple the intermediate part to the other of the first and second parts so as to apply, on application of the input force on the intermediate part by the SMA element, the actuation force to the other of the first and second parts, wherein each actuating unit is configured to amplify an actuation amount of the SMA element to a relatively greater amount of relative movement between the first and second parts.

[0011] Each actuating unit is configured such that the amount of movement of the other of the first and second parts is greater than the actuation amount (e.g. contraction) of the SMA element on actuation of the SMA element. The actuating unit may thereby achieve stroke amplification, in that the other of the first and second parts is moved by a greater amount using the actuating unit than in an actuator assembly using a comparable SMA element that is directly connected between the first and second parts. Using bearings to guide translational movement of the intermediate part at a (non-zero) angle to the input force may provide for a particularly compact actuating unit compared to an actuating unit having a flexure allowing pivotal movement of an intermediate part, for example. The bearing angle may further be adjusted without significant rearrangement of the layout of components of the actuator assembly, allowing a variety of stroke amplification factors to be achieved without significant redesign of the actuator assembly.

[0012] In some embodiments, the bearing comprises a rolling bearing (sometimes also referred to as a rolling-element bearing) configured to guide the translational movement of the intermediate part relative to the one of the first and second parts. The rolling bearing may comprise a ball bearing or a roller bearing. The rolling bearing may comprise a first bearing surface on the intermediate part and a second bearing surface on the one of the first and second parts. The bearing may further comprise a rolling bearing element, such as a ball or a roller, between the first and second bearing surfaces. Alternatively, the bearing may comprise a plain bearing.

[0013] In some embodiments, the rolling bearing comprises a rolling bearing element arranged, on actuation of the SMA element, to roll along a first bearing surface on the one of the first and second parts and along a second bearing surface on the intermediate part, wherein the second bearing surface is configured such that a bearing reaction force applied by the bearing on the intermediate part changes in direction as the rolling bearing element rolls along the second bearing surface.

[0014] Put another way, at least a portion of the second bearing surface may be curved. Allowing the bearing reaction force applied by the bearing on the intermediate part to change in direction may achieve variable stroke amplification of the actuator assembly. Alternatively, the second bearing surface may be flat. Stroke amplification may remain constant on actuation of the SMA element.

[0015] In some embodiments, the second bearing surfaces is configured, e.g. curved, such that the ratio of the input force to the actuating force decreases on actuation of the SMA element.

[0016] In some embodiments, the rolling bearing comprises at least two rolling bearing elements arranged between the intermediate part and the one of the first and second parts and configured to roll relative to the intermediate part and the one of the first and second parts on actuation of the SMA element.

[0017] Providing two rolling bearing elements may reduce the risk of undesirable rotation of the intermediate part relative to the one of the first and second parts. The two rolling bearing elements may be offset from each other in a direction along the movement path.

[0018] In some embodiments, the SMA element is configured to apply the input force to the intermediate part at a position between the at least two rolling bearing elements.

[0019] In some embodiments, the intermediate part overlaps with the or each ball bearing when viewed orthogonally to a plane spanned by the input force and the actuating force. The actuating unit may thus be made compact.

[0020] In some embodiments, i) the input force exerted by the SMA element on the intermediate part, ii) a force exerted by the coupling on the intermediate part and iii) a force exerted by the bearing on the intermediate part are concurrent. The forces may be concurrent at at least one position of the intermediate part relative to the one of the first and second parts, for example at a starting position or central position of the intermediate part. The risk of inadvertent rotation of the intermediate part may thus be reduced. The bearing may comprise a single ball bearing. The actuating unit may thus be made compact.

[0021] In some embodiments, the coupling comprises a flexure connected between the intermediate part and the other of the first and second parts. The flexure may be elongate and connect at one end to the intermediate part and at another end to the other of the first and second parts. The flexure may flex in a direction orthogonal to its length. The coupling may apply the actuating force along the length of the flexure. Alternatively, the coupling may comprise a ball bearing or a plain bearing.

[0022] In some embodiments, the flexure is configured to be in tension on actuation of the SMA element.

[0023] In some embodiments, the coupling is configured to transmit the actuating force to the other of the first and second parts and to allow movement of the other of the first and second parts relative to the intermediate part in a direction that is perpendicular to the actuating force.

[0024] In some embodiments, the coupling is configured such that the actuating force is angled relative to the translational movement of the intermediate part, preferably by an angle that is less than 20°.

[0025] In some embodiments, the coupling is configured to constrain rotation of the intermediate part relative to the other of the first and second parts.

[0026] In some embodiments, the coupling comprises at least two flexures connected between the intermediate part and the other of the first and second parts, wherein the at least two flexures are parallel to each other.

[0027] In some embodiments, the SMA element is configured such that the input force is angled relative to the translational movement of the intermediate part, preferably by an angle that is in the range from 60° to 85°.

[0028] In some embodiments, the SMA element and the coupling are configured such that the input force is angled relative to the actuating force, preferably by an angle that is in the range from 75° to 90°.

[0029] In some embodiments, the intermediate part is integrally formed with a connection element configured to mechanically couple the SMA element to the intermediate part. The connection element may be a crimp. In some embodiments, the intermediate part is formed from a sheet material, preferably from sheet metal. The sheet material may be cut and / or deformed so as to form the intermediate part.

[0030] In some embodiments, the ratio of the input force to the actuating force is greater than 2, preferably greater than 3.

[0031] Some embodiments comprise at least two actuating units arranged to apply opposing actuating forces that are capable of moving the second part relative to the first part in opposite directions.

[0032] Some embodiments comprise multiple actuating units arranged in a loop around a primary axis, wherein two adjacent actuating units are configured to overlap when viewed along the primary axis.

[0033] In some embodiments, the SMA elements of the at least two actuating units are configured to overlap when viewed along the primary axis.

[0034] Some embodiments comprise at least four SMA elements arranged to apply actuating forces that are non-colinear and capable of moving the second part relative to the first part in a movement plane and / or rotating the second part relative to the first part about an axis that is perpendicular to the movement plane.

[0035] Some embodiments comprise a further bearing between the first and second parts, wherein the further bearing guides movement of the second part relative to the first part in a movement plane. The further bearing may allow translational movement in two orthogonal directions in the movement plane and rotation about an axis perpendicular to the movement plane.

[0036] Some embodiments comprise a further bearing between the first and second parts, wherein the further bearing guides movement of the second part relative to the first part in a single degree of freedom. The single degree of freedom may comprise translation along a movement axis.

[0037] Further aspects of the present invention are set out in the dependent claims and in the detailed description.

[0038] 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:

[0039] Figures 1A-E are schematic cross-sectional views of different variations of a camera module assembly incorporating an actuator assembly;

[0040] Figure 2 is a schematic perspective view of the actuator assembly that may be incorporated in the camera module assembly of Figures 1A-E;

[0041] Figures 3A and 3B are a plan view and a close-up view of an actuating unit that may form part of the actuator assembly of Figure 2;

[0042] Figures 4A to 4C are close-up plan views of another type of actuating unit that may form part of the actuator assembly of Figure 2;

[0043] Figure 5 is a close-up plan view of another type of actuating unit that may form part of the actuator assembly of Figure 2;

[0044] Figure 6 is a schematic plan view of an arrangement of four actuating units; and

[0045] Figures 7A and 7B are plan views of actuator assemblies comprising four actuating units, respectively according to Figures 3 and 5, in the arrangement of Figure 6.

[0046] Detailed description

[0047] Camera assembly

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 image 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).

[0052] 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:

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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. 3 to 8) 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Actuating unit

[0075] Figure 3A shows a plan view of an example of the actuating unit 30 and Figure 3B shows a close-up plan view of an intermediate part 31 of the actuating unit 30. A single actuating unit 30 is shown in Figure 3A, 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.

[0076] The actuating unit 30 comprises an intermediate part 31 to which several other components of the actuating unit 30 are connected as described below. The intermediate part 31 is typically relatively rigid compared to the other components of the actuating unit 30 and does not deform significantly on actuation of the actuating unit 30.

[0077] The actuating unit 30 also includes a bearing 32, embodied by a rolling bearing 32 in the actuating unit 30 of Figure 3A. The bearing 32 is arranged between the intermediate part 31 and the support structure 10. The bearing 32 guides translational movement of the intermediate part 31 relative to the support structure 10, in particular along a movement path M. In Figure 3B, the movement path M extends along a straight line such that the intermediate part 31 is movable along a movement axis M, but alternatively the movement path M may be curved, as will be described in relation to Figures 4A to 4C.

[0078] With particular reference to Figure 3B, the rolling bearing 32 may also be referred to as a rollingelement bearing 32 and comprises a first bearing surface 321 on the support structure 10 and a second bearing surface 323 on the intermediate part 31. A rolling bearing element 322, in particular in the form of a ball or a roller, is arranged between the first and second bearing surfaces 321, 323. The rolling bearing element 322 is configured to roll along the first and second bearing surfaces 321, 323 on relative movement between the first and second bearing surfaces 321, 323 to thereby guide the movement of the intermediate part 31 relative to the support structure 10 along the movement path M. The first and second bearing surfaces 321, 323 are typically urged together by a biasing force (not shown), for example by a resilient element or magnetic arrangement between the support structure 10 and the intermediate part 31. The first and second bearing surfaces 321, 323 are flat in the view of Figure 3B such that the rolling bearing element 322 rolls along a straight path to guide linear movement of the intermediate part 31 along the movement axis M relative to the support structure 10.

[0079] The intermediate part 31 of Figure 3B is formed from a sheet material and comprises a main body (generally in the plane of Figure 3B) as well as a folded-up tab (out-of-plane in Figure 3B and highlighted by dashed lines). The second bearing surface 323 of the bearing 32 is formed on the folded-up tab (as shown in Figure 3B) and optionally additionally on the main body, such that the rolling bearing element is arranged in a V-shaped groove formed by the intermediate part 31.

[0080] In the view of Figure 3B, the rolling bearing element 322 overlaps with the intermediate part 31, in particular the main body thereof. So, the intermediate part 31 overlaps with the rolling bearing element 322 when viewed orthogonally to a plane spanned by the input force Fi and the actuating force F. This allows the actuating unit 30 to be more compact compared to a situation in which such overlap is not allowed, for example if the intermediate part 31 was moved to the top of the rolling bearing element 322 (and the second bearing surface 323 moved to the bottom of the intermediate part 31) in Figure 3B.

[0081] The actuating unit 30 also includes an SMA element 34. In this example, the SMA element 34 is elongate and thereby embodied by an SMA wire 34. The SMA wire 34 is arranged, on contraction, to apply an input force Fi on the intermediate part 31, where the input force Fi acts parallel to the length of the SMA wire 34. In the depicted embodiment, the SMA element 34 is arranged to load the bearing 32 on actuation, i.e. the input force Fi comprises a component orthogonal to the movement path M that urges the bearing surfaces 321, 323 towards each other.

[0082] As shown in Figure 3A, the SMA wire 34 is connected between the intermediate part 31 and the support structure 10. One end of the SMA wire 34 is connected to the support structure 10, e.g. by a static crimp 15. The other end of the SMA wire 34 is connected to the intermediate part 31, e.g. by a movable crimp 35. Alternatively, connection elements other than crimps 15, 35 may be used. In the depicted example, the movable crimp 35 is formed integrally with the intermediate part 31. In particular, the movable crimp 35 and the intermediate part 31 are formed from a single sheet of material, e.g. from sheet metal. Alternatively, the movable crimp 35 may be a separate part to the intermediate part 31 and be fixedly connected to the intermediate part 31.

[0083] The actuating unit 30 also includes a coupling 33, herein also described as a coupling link 33. The coupling 33 couples the movable part 20 to the intermediate part 31. In the depicted example, the coupling link 33 is a coupling flexure 33. The coupling flexure 33 is connected between the intermediate part 31 and the movable part 20. One end of the coupling flexure 33 is connected to the intermediate part 31. The other end of the coupling flexure 33 is connected to the movable part 20 (only shown schematically in Figure 3A). The coupling 33 transfers or transmits an actuating force F from the intermediate part 31 to the movable part 20. The coupling 33 may be 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.

[0084] In the depicted example, the intermediate part 31 and the coupling flexure 33 are separate components that are connected to each other. Alternatively, the coupling flexure 33 and the intermediate part 31 may be integrally formed, for example from a single sheet of material (such as sheet metal).

[0085] In the depicted example, the bearing 32 comprises a single rolling bearing element 322 arranged between the two bearing surfaces 321, 323. Providing such a single bearing element 322 allows for a particularly compact actuating unit 30 to be provided. Figure 3B also shows the three forces that typically act on the intermediate part 31 on actuation of the SMA element 34, in particular the input force Fi applied to the intermediate part 31 by the SMA element 34, a bearing reaction force Fb applied by the bearing 32 on the intermediate part 31 and a coupling force Fc (equal and opposite to the actuating force F) applied by the coupling 33 to the intermediate part 31. Although not shown in the schematic of Figure 3B, the actuating unit 30 may be configured such that these three forces intersect at a common point, i.e. the forces are concurrent such that the intermediate part 31 is in a force equilibrium. The forces may be concurrent for at least one position (e.g. a starting position or central position) of the intermediate part 31 relative to the support structure 10. Ensuring that the three forces are concurrent reduces the risk of inadvertent rotation of the intermediate part 31 on actuation of the SMA element 34.

[0086] Alternatively or additionally, the coupling 33 may constrain rotation of the intermediate part 31 relative to the movable part 20 and / or support structure 10 (e.g. when the movable part 20 is not rotatable relative to the support structure 10). The coupling 33 may thereby be designed to allow translational movement of the movable part 20 relative to the intermediate part 31 in a direction perpendicular to the actuating force F but constrain relative rotation of the movable part 20 and the intermediate part 31. Although not shown in the Figures, the coupling 33 may, for example, comprise at least two coupling flexures 33 connected between the intermediate part 31 and the movable part 20, wherein the at least two coupling flexures 33 are parallel to each other and offset in a direction orthogonal to the actuating force F. With particular reference to Figure 3B, for example, a second coupling flexure 33 could be connected to the bottom-left of the main body of the intermediate part 31 and extend parallel to the depicted coupling flexure 33 towards the left. Such an arrangement may reduce the risk of inadvertent rotation of the intermediate part 31.

[0087] The actuating unit 30 (preferably each actuating unit 30 of an actuator assembly 2) is configured to amplify an amount of contraction (i.e. stroke) or actuation amount of the SMA wire 34. Such stroke 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 input force Fi may be angled relative to movement path M and the actuating force F. The movement path M may further be angled relative to the actuating force F.

[0088] With particular reference to Figure 3B, the bearing 32 and the intermediate part 31 are arranged to modify the input force Fi so as to give rise to the actuating force F, which is transmitted from the intermediate part 31 to the movable part 20 by the coupling flexure 33. Application of the input force Fi by the SMA element 34 further causes a bearing reaction force Fb to be applied to the intermediate part 31 by the bearing 32. The bearing reaction force Fb is typically perpendicular to the instantaneous direction of movement of the intermediate part 31 along the movement path M, i.e. perpendicular to the movement axis M in Figure 3B assuming friction in the rolling bearing is negligible. The input force Fi and the bearing reaction force Fb combine to give rise to the actuating force F, so the actuating force F is a composite force of the input force Fi and the bearing reaction force Fb. As shown in Figure 3B, for example, the input force Fi is angled relative to the actuating force F (extending along the coupling flexure 33) by an angle a and the bearing reaction force Fb is angled relative to the actuating force F by an angle p. Each of the input force Fi and the bearing reaction force Fb thus has a force component (the horizontal arrows in Figure 3B) parallel to the actuating force F (i.e. parallel to the extent of the coupling flexure 33). These force components add up to the actuating force F applied to the movable part 20, such that F = Fi * cos(a) + Fb * cos(P).

[0089] The input force Fi and the bearing reaction force Fb each have a further force component (Fi * sin(a) and Fb * sin(P), a vertical force component not shown in Figure 3B) that is orthogonal to the actuating force F. The further force component of the bearing reaction force Fb is equal and opposite to the further force component of the input force Fi, such that the further force components of the input force Fi and the bearing reaction force Fb cancel each other out.

[0090] As further apparent from Figure 3B, the actuating force F is smaller than the input force Fi, such that the actuating unit 30 effectively de-amplifies the input force Fi applied by the SMA wire 34. The force amplification factor F / Fi is less than 1. The stroke amplification factor, i.e. the ratio of the movement amount of the movable part 20 to the actuation amount of the SMA wire 34, may be estimated to be the reciprocal of the force amplification factor and calculated using standard trigonometry, as sin(P) / sin(a+P) for acute angles a and p.

[0091] The angles a and p thereby both contribute to the stroke amplification achievable by the actuating unit 30. The angle p may be adjusted relatively easily without changing the layout of the actuator assembly 2 (i.e. the location and general alignment of the SMA wire 34, intermediate part 31 and coupling 33 may remain unchanged), allowing stroke amplification to be adjusted without requiring significant redesign of the actuator assembly 2. Compared to other types of stroke amplification mechanisms which require more substantial changes to the layout and components to achieve different stroke amplification factors, the actuator assembly 2 may thus be more easily be applied to a wider range of possible applications.

[0092] In the particular example of Figure 3B, the angle a is approximately 80° and the angle p is approximately 80°. The stroke amplification factor is thus approximately 2.9. For every 1 millimetre of contraction of the SMA wire 34, the movable part 20 is thus expected to be moved by 2.9 millimetre. To illustrate the ease of adjusting the stroke amplification factor, changing of the angle p to 70° results in a stroke amplification factor of 1.9 and changing the angle p to 85° results in a stroke amplification factor of 3.85. The stroke amplification factor may thus be readily adjusted to a desired value by adjusting the angle .

[0093] In general, the angle may be in the range from 60° to 90°, preferably in the range from 70° to 90°. Put another way, the angle between the actuating force F and the movement path M may be less than 30°, preferably less than 20°. The angle a may be in the range from 60° to 90°, preferably in the range from 75° to 90°. The angle between the input force Fi and the movement path M may be in the range from 60° to 85°, for example. These angles may be in the described ranges at any position of the intermediate part 31 during normal operation, i.e. due to actuation of the depicted actuating unit 30 or another actuating unit 30.

[0094] Figures 4A to 4C are close-up plan views of another example of an actuating unit 30 that may form part of the actuator assembly 2. Only a portion of the SMA wire 34 and coupling flexure 33 are shown in Figures 4A to 4C, and it will be appreciated that the SMA wire 34 and the coupling flexure 33 are typically longer than depicted in Figures 4A to 4C.

[0095] Although depicted in more schematic manner, the actuating unit 30 of Figures 4A to 4C operates generally in the manner of the actuating unit 30 described in relation to Figures 3A and 3B and may be configured as described in relation to Figures 3A and 3B, except that the second bearing surface 323 on the intermediate part 31 comprises a curved portion. Figures 4A to 4C show the rolling bearing element 322 of the bearing 32 are three different positions relative to the second bearing surface 323, corresponding to three different actuation amounts of the SMA wire 34.

[0096] The curvature of the second bearing surface 323 may be constant or variable along the extent of the second bearing surface 323. The second bearing surface 323 may also comprise multiple straight portions that are angled relative to each other, such that an edge (i.e. a relatively sharp curved portion) is formed between the multiple straight portions. In general, at least a portion of the second bearing surface 323 is curved such that the direction of the bearing reaction force Fb is different for at least two different positions of the rolling bearing element 322 along the second bearing surface 323. The rolling bearing element 322 typically applies the bearing reaction force Fb to the intermediate part 31 in a direction orthogonal to the second bearing surface 323. The direction of the bearing reaction force Fb, and thereby the angle p, thus changes on actuation of the SMA element 34. Figure 4A depicts a situation in which the rolling bearing element 322 is in the centre of the second bearing surface 323 across a range of movement of the rolling bearing element 322 relative to the second bearing surface 323. On extension of the SMA wire 34, for example due to actuation of an opposing actuating unit 30 not shown in Figures 4A to 4C, the rolling bearing element 322 rolls towards a first limit of the range of movement of the rolling bearing element 322 relative to the second bearing surface 323, as shown in Figure 4B. The direction of the bearing reaction force Fb changes so as to increase the angle p and thereby increase the amount of stroke amplification. On contraction of the SMA wire 34, as shown in Figure 4C, the rolling bearing element 322 rolls towards a second limit of the range of movement of the rolling bearing element 322 relative to the second bearing surface 323. The direction of the bearing reaction force Fb changes so as to decrease the angle and thereby decrease the amount of stroke amplification.

[0097] As such, the second bearing surface 323 is configured (in particular curved) such that the stroke amplification factor decreases on actuation of the SMA element 34, i.e. so that the ratio of the input force Fi to the actuating force F decreases on actuation of the SMA element 34. The actuating force F thus increases on actuation of the SMA element 34, which may be particularly useful in actuator assemblies 2 that drive movement of an external load applying a centring force to the movable part 20. The resistance to motion of the movable part 20 may increase, e.g. due to such an external load or otherwise, with displacement from a central position relative to the support structure 10, such that it is desirable to provide an increased actuation force F to achieve continued movement of the movable part 20.

[0098] Although not shown in Figures 4A to 4C, endstops may be provided to limit the range of movement of the rolling bearing element 322 along the second bearing surface 323. The support structure 10 may, for example, comprise two endstop surfaces arranged such that the rolling bearing element 322 contacts one of the endstop surfaces when in the position of Figure 4B and contacts the other of the endstop surfaces when in the position of Figure 4C. Such endstop surfaces may ensure that the rolling bearing element 322 remains within a desired range of movement and reliably rolls on the bearing surfaces 321, 323.

[0099] The first bearing surface 321 on the support structure 10 is not shown in Figures 4A to 4C but may generally be curved in complementary manner to the curved second bearing surface 323 on the intermediate part 31, such that a line passing through the contact points of the rolling bearing element 322 with the first and second bearing surfaces 321, 323 also passes through the centre of the rolling bearing element 322 at any position of the rolling bearing element 322 on rolling across the bearing surfaces 321, 323. The tangent to the first and second bearing surfaces 321, 323 at these contact points may be perpendicular to the line passing through the centre of the rolling bearing element 322. Inadvertent frictional forces or shear forces between the rolling bearing element 322 and the bearing surfaces 321, 323 may thus be avoided or minimized.

[0100] Figure 5 is a close-up plan view of another example of an actuating unit 30 that may form part of the actuator assembly 2. Only a portion of the SMA wire 34 and coupling flexure 33 are shown in Figure 5, and it will be appreciated that the SMA wire 34 and coupling flexure 33 are typically longer than depicted in Figure 5. A number of actuating units 30 of the type of Figure 5 are shown in their entirety in Figure 7B, for example.

[0101] The actuating unit 30 of Figure 5 operates generally in the manner of the actuating unit 30 described in relation to Figures 3A and 3B and may be configured as described in relation to Figures 3A and 3B except for the provision of two pairs of first and second bearing surfaces 321a, 323a, 321b, 323b and two rolling bearing elements 322a, 322b. Each rolling bearing element 322a, 322b is arranged between a respective pair of first and second bearing surfaces 321a, 323a, 321b, 323b. Each rolling bearing element 322a, 322b applies a respective bearing reaction sub-force to the intermediate part 31 on actuation of the SMA element 34. The bearing reaction force Fb corresponds to the sum of the bearing reaction sub-forces and is illustrated in Figure 5 approximately halfway between the two rolling bearing elements 322a, 322b, although in general the bearing reaction force Fb may act elsewhere on the intermediate part 31. Providing the two rolling bearing elements 322a, 322b reduces the risk of undesirable rotation of the intermediate part 31 on actuation of the SMA element 34, thereby ensuring a more reliable stroke amplification factor and performance of the actuator assembly 2.

[0102] The SMA wire 34 applies the input force Fi at a position between the two rolling bearing elements 32a, 32b. Put another way, the input force Fi acts on the intermediate part 31 at a position that is between two planes (illustrated by dashed lines in Figure 5) that are orthogonal to the movement path M and intersect the points on which the bearing reaction sub-force act on the intermediate part 31. The input force Fi may thereby reliably sandwich both two rolling bearing elements 322a, 322b between the respective bearing surfaces. In the above-described examples, the coupling flexure 33 is placed under tension on application of the input force Fi so as to transmit the actuating force F to the movable part 20. Placing the coupling flexure 33 in tension reduces the risk of buckling of the coupling flexure 33. Simultaneously, the bearing 32 is placed under compression so as to urge the bearing surfaces 321, 323 towards each other, thereby reducing the risk of the bearing 32 coming apart during actuation.

[0103] Arrangement of four actuating units

[0104] Figure 6 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.

[0105] The arrangement of actuating units 30 of Figure 6 may be used, for example, in apparatus 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.

[0106] The four actuating units 30 of Figure 6 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.

[0107] In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 6) 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 6) 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 34 of the respective actuating units 30 to be controlled, allowing for more accurate and reliable positioning of the movable part 20 compared to a situation in which actuating units 30 do not oppose each other. In some examples, none of the actuating forces F are collinear. This allows the arrangement of actuating units 30 to translationally move the movable part 20 without applying any net torque to the movable part 20. So, the movable part 20 can be moved translationally in the movement plane without rotating the movable part 20 in the movement plane. In general, the arrangement of actuating units 30 is capable of accurately controlling a torque or moment of the movable part 20 about the primary axis P. So, the actuating units 30 are capable of rotating (or not rotating) the movable part 20 relative to the support structure about the primary axis P.

[0108] In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 6) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 10 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 6) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 10 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.

[0109] 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 Figure 3A, 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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 6. 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 6, 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.

[0114] Figures 7A and 7B show plan views of actuator assemblies 2 having four actuating units 30 arranged in the manner described in relation to Figure 6. The actuator assembly 2 of Figure 7A has four actuating units 30 of the type described in relation to Figures 3A and 3B and the actuator assembly 2 of Figure 7B has four actuating units 30 of the type described in relation to Figure 5.

[0115] As shown, each actuating unit 30 folds around a corner of the actuator assembly 2. The support structure 10 and / or movable part 20 typically comprise four sides that extend in a loop around the primary axis P. The SMA element 34 of one actuating unit 30 and the coupling flexure 33 of an adjacent actuating unit 30 are arranged on the same side, such that one SMA element 32 and one coupling flexure 33 is arranged on each side of the actuator assembly 2. In the depicted examples, the coupling flexure 33 is at an angle of about 100° relative to the SMA wire 34. An added advantage of such an arrangement is that the actuating unit 30 may fold around a corner of the movable part 20 in a compact manner, as shown in Figures 7A and 7B. The angle between the coupling flexure 33 and the SMA wire 34 may be in the range from 70° to 110°, preferably from 80° to 100°. However, in general, the angle between coupling flexure 33 and SMA wire 34 may be outside these ranges.

[0116] In the depicted embodiments, the SMA element 34 of each actuating unit 30 overlaps or crosses with both the SMA element 34 and the coupling flexure 33 of an adjacent actuating unit 30 when viewed along the primary axis P. The SMA elements 34 may thus be made longer compared to an actuator assembly 2 in which such overlap is not allowed, extending the stroke capabilities of the actuator assembly 2. Any components of adjacent actuating units 30 that overlap or cross over when viewed along the primary axis P may be spaced apart in a direction along the primary axis P so as to avoid direct contact therebetween.

[0117] As also apparent from Figures 7A and 7B, the maximum extent of the SMA element 34 and / or the maximum extent of the coupling flexure 33 is greater than the maximum extent of the intermediate part 31. This ensures that the actuating unit 30 remains relatively compact while achieving relatively large stroke due to the long SMA wires 34 and / or low undesirable lateral forces (orthogonal to the actuating force F) due to the long coupling flexures 33. The ratio of the maximum extent of the coupling flexure 33 to the maximum extent of the intermediate part 31 may be greater than 1, preferably greater than 1.5. The ratio of the maximum extent of the SMA element 34 to the maximum extent of the intermediate part 31 may be greater than 2, preferably greater than 3.

[0118] Modifications and Alternatives

[0119] In the above-described examples, the actuating unit 30 includes a bearing 32 in the form of a rolling bearing 32. In general, the actuator assembly may include a different type of bearing 32 configured to enable the above-described movement of the intermediate part 31 relative to the support structure 10. The bearing 32 may, for example, comprise a plain bearing or sliding bearing. Such a plain bearing or sliding bearing comprises the pair of bearing surfaces 321, 323 depicted in Figure 3B, for example, but without a rolling bearing element 322 arranged therebetween. The bearing surfaces 321, 323 slide relative to each other relative movement of the intermediate part 31 and support structure 10 to thereby guide the movement of the intermediate part 31 relative to the support structure 10 along the movement path M. Such bearing surfaces 321, 323 may optionally comprise a low-friction and / or wear-resistant material (e.g. in the form of a coating).

[0120] In the above-described examples, the bearing 32 is placed under compression, i.e. the bearing surfaces 321, 323 of the bearing 32 are urged towards each other, on contraction of the SMA wire 34. This reduces the risk of the bearing 32 coming apart, improving the reliability of actuation of the actuator assembly 2. However, the bearing 32 could instead be arranged so as to be placed under tension on contraction of the SMA wire 34. With reference to Figure 3B, for example, the bearing 32 could extend to the top-right from the intermediate part 31. A further element may be included to retain contact of the bearing 32 on SMA wire contraction, for example a resilient element or a magnetic arrangement urging bearing surfaces of the bearing 32 together.

[0121] In the above-described examples, the bearing 32 and the SMA wire 34 are arranged between the intermediate part and 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 bearing 32 and the SMA wire 34 arranged between the intermediate part 31 and the movable part 20, and the coupling flexure 33 connecting at one end to the support structure 10. Actuator assemblies 2 comprising multiple actuating units 30 may comprise some actuating units 30 with the depicted arrangement and some actuating units 30 with a reversed arrangement.

[0122] 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 flexible 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. Instead, a fixed coupling 33 could be arranged between the intermediate part 31 and the movable part 20 such that the intermediate part 31 and movable part 20 are fixed in position relative to each other. 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. 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 movement path M 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 intermediate part 31, when embodied by a plate, may further be arranged to extend generally 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.

[0123] The present invention has been described in connection with SMA wires. The term 'SMA wire' may refer to any element comprising SMA. The SMA wire may have any shape that is suitable for the purposes described herein. The SMA wire 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 wire. It is also possible that the length of the SMA wire (however defined) may be similar to one or more of its other dimensions. The SMA wire may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two elements, the SMA wire can apply only a tensile force which urges the two elements together. In other examples, the SMA wire may be bent around an element and can apply a force to the element as the SMA wire tends to straighten under tension. The SMA wire may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA wire may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA wire may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA wire' may refer to any configuration of SMA wire acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA wire may comprise two or more portions of SMA wire that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA wire may be part of a larger piece of SMA wire. Such a larger piece of SMA wire might comprise two or more parts that are individually controllable, thereby forming two or more SMA wires.

[0124] The foregoing has described some embodiments of the present invention, but the present invention is not limited to these embodiments. The scope of the invention is defined in the appended claims.

Claims

1. Claims1. 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, on actuation, to apply an actuation force capable of moving the second part relative to the first part, each actuating unit comprising: an intermediate part; a bearing between the intermediate part and one of the first and second parts that is configured to guide translational movement of the intermediate part along a movement path relative to the one of the first and second parts; a shape memory alloy, SMA, element connected between the intermediate part and the one of the first and second parts and configured, on actuation, to apply an input force to the intermediate part capable of translationally moving the intermediate part relative to the one of the first and second parts, wherein the input force is at an angle to the movement path, and a coupling configured to couple the intermediate part to the other of the first and second parts so as to apply, on application of the input force on the intermediate part by the SMA element, the actuation force to the other of the first and second parts, wherein each actuating unit is configured to amplify an actuation amount of the SMA element to a relatively greater amount of relative movement between the first and second parts.

2. An actuator assembly according to claim 1, wherein the bearing comprises a rolling bearing configured to guide the translational movement of the intermediate part relative to the one of the first and second parts.

3. An actuator assembly according to claim 2, wherein the rolling bearing comprises a rolling bearing element arranged, on actuation of the SMA element, to roll along a first bearing surface on the one of the first and second parts and along a second bearing surface on the intermediate part, wherein the second bearing surface is configured such that a bearing reaction force applied by the bearing on the intermediate part changes in direction as the rolling bearing element rolls along the second bearing surface.

4. An actuator assembly according to claim 3, wherein the second bearing surfaces is configured such that the ratio of the input force to the actuating force decreases on actuation of the SMA element.

5. An actuator assembly according to any one of claims 2 to 4, wherein the rolling bearing comprises at least two rolling bearing elements arranged between the intermediate part and the one of the first and second parts and configured to roll relative to the intermediate part and the one of the first and second parts on actuation of the SMA element.

6. An actuator assembly according to claim 5, wherein the SMA element is configured to apply the input force to the intermediate part at a position between the at least two rolling bearing elements.

7. An actuator assembly according to any one of claims 2 to 6, wherein the intermediate part overlaps with the or each ball bearing when viewed orthogonally to a plane spanned by the input force and the actuating force.

8. An actuator assembly according to any one of the preceding claims, wherein i) the input force exerted by the SMA element on the intermediate part, ii) a force exerted by the coupling on the intermediate part and iii) a force exerted by the bearing on the intermediate part are concurrent.

9. An actuator assembly according to any one of the preceding claims, wherein the coupling comprises a flexure connected between the intermediate part and the other of the first and second parts.

10. An actuator assembly according to claim 9, wherein the flexure is configured to be in tension on actuation of the SMA element.

11. An actuator assembly according to any one of the preceding claims, wherein the coupling is configured to transmit the actuating force to the other of the first and second parts and to allow movement of the other of the first and second parts relative to the intermediate part in a direction that is perpendicular to the actuating force.

12. An actuator assembly according to any one of the preceding claims, wherein the coupling is configured such that the actuating force is angled relative to the translational movement of the intermediate part, preferably by an angle that is less than 20°.

13. An actuator assembly according to any one of the preceding claims, wherein the coupling is configured to constrain rotation of the intermediate part relative to the other of the first and second parts.

14. An actuator assembly according to any one of the preceding claims, wherein the coupling comprises at least two flexures connected between the intermediate part and the other of the first and second parts, wherein the at least two flexures are parallel to each other.

15. An actuator assembly according to any one of the preceding claims, wherein the SMA element is configured such that the input force is angled relative to the translational movement of the intermediate part, preferably by an angle that is in the range from 60° to 85°.

16. An actuator assembly according to any one of the preceding claims, wherein the SMA element and the coupling are configured such that the input force is angled relative to the actuating force, preferably by an angle that is in the range from 75° to 90°.

17. An actuator assembly according to any one of the preceding claims, wherein the intermediate part is integrally formed with a connection element configured to mechanically couple the SMA element to the intermediate part.

18. An actuator assembly according to any one of the preceding claims, wherein the intermediate part is formed from a sheet material, preferably from sheet metal.

19. An actuator assembly according to any one of the preceding claims, wherein the ratio of the input force to the actuating force is greater than 2, preferably greater than 3.

20. An actuator assembly according to any one of the preceding claims, comprising at least two actuating units arranged to apply opposing actuating forces that are capable of moving the second part relative to the first part in opposite directions.

21. An actuator assembly according to any one of the preceding claims, comprising multiple actuating units arranged in a loop around a primary axis, wherein two adjacent actuating units are configured to overlap when viewed along the primary axis.

22. An actuator assembly according to claim 21, wherein the SMA elements of the at least two actuating units are configured to overlap when viewed along the primary axis.

23. An actuator assembly according to any one of the preceding claims, comprising at least four SMA elements arranged to apply actuating forces that are non-colinear and capable of moving the second part relative to the first part in a movement plane and / or rotating the second part relative to the first part about an axis that is perpendicular to the movement plane.

24. An actuator assembly according to any one of the preceding claims, comprising a further bearing between the first and second parts, wherein the further bearing guides movement of the second part relative to the first part in a movement plane.

25. An actuator assembly according to any one of the preceding claims, comprising a further bearing between the first and second parts, wherein the further bearing guides movement of the second part relative to the first part in a single degree of freedom.

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