Actuator assembly

Abstract

An actuator assembly comprising: first and second parts that are movable and / or tiltable relative to each other along and / or about two orthogonal axes that are perpendicular to a primary axis; and a total of four actuating units each configured, on actuation, to apply a respective actuating force to one of the first and second part capable of moving the first and second parts relative to each other, wherein the four actuating units are arranged such that none of the four actuating forces are colinear and are capable of moving and / or tilting the first and second parts relative each other to any position within a range of movement along and / or about the two orthogonal axes; wherein each actuating unit comprises: a body portion; a shape memory alloy, SMA, element connected between the body portion and the other of the first and second part, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts, and configured to modify the input force so as to give rise to the actuating force; wherein the SMA element is connected by connection elements between the body portion and the other of the first and second parts, wherein the length of the SMA element between the connection elements is less than half of the extent of the actuator assembly in a direction parallel to the SMA element, and wherein the four actuating units do not overlap when viewed along the primary axis.

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 an aspect of the present invention, there is provided an actuator assembly comprising: first and second parts that are movable and / or tiltable relative to each other along and / or about two orthogonal axes that are perpendicular to a primary axis; and a total of four actuating units each configured, on actuation, to apply a respective actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein the four actuating units are arranged such that none of the four actuating forces are colinear and are capable of moving and / or tilting the first and second parts relative each other to any position within a range of movement along and / or about the two orthogonal axes; wherein each actuating unit comprises: a body portion; a shape memory alloy, SMA, element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts, and configured to modify the input force so as to give rise to the actuating force; wherein the SMA element is connected by connection elements between the body portion and the other of the first and second parts, wherein the length of the SMA element between the connection elements is less than half of the extent of the actuator assembly in a direction parallel to the SMA element, and wherein the four actuating units do not overlap when viewed along the primary axis.

[0011] By providing relatively short SMA elements, the power consumption of the SMA elements may be reduced. Providing short SMA elements also facilitates avoiding overlap of the actuating units, such that the assembly of the actuator assembly is simplified and the risk of clashing of components of adjacent actuating units is reduced.

[0012] In some embodiments, the length of the SMA element between the connection elements is less than 5mm, preferably less than 4mm, further preferably less than 3mm. The SMA element is elongate. The SMA element may be an SMA wire.

[0013] In some embodiments, the length of the SMA element between the connection elements is less than a third of the extent of the actuator assembly in a direction parallel to the SMA element.

[0014] In some embodiments, none of the actuating units overlap when viewed along the primary axis. There may be no overlap, when viewed along the primary axis, of any components of any of the actuating units. So, none of the force-modifying elements, body portions, SMA wires and optionally coupling links may overlap.

[0015] In some embodiments, the force-modifying element comprises a force-modifying flexure. The forcemodifying flexure is elongate and compliant in a direction perpendicular to its length. On actuation of the SMA element, the force-modifying flexure may flex so as to provide an effective pivot point about which the body portion is configured to rotate.

[0016] In some embodiments, imaginary lines along the actuating force, along the input force, and along a force exerted by the force-modifying element on the body portion are concurrent, i.e. intersect at a common point. For example, the imaginary lines along the length of the SMA element, the length of the force-modifying flexure and the length of the coupling flexure may be concurrent. In some embodiments, each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

[0017] In some embodiments, the coupling link comprises a coupling flexure. The coupling flexure is elongate and compliant in a direction perpendicular to its length.

[0018] In some embodiments, the force-modifying element is arranged between the SMA element and the coupling link when viewed parallel to the primary axis. The actuating unit may make use of a first-class lever. The body portion may, in use, act as a first-class lever.

[0019] In some embodiments, actuating units are arranged on four sides of the actuator assembly, wherein two actuating units on opposite sides are arranged such that the SMA wires of the two actuating units face each other when viewed along the primary axis, and the other two actuating units are arranged such that the coupling flexures of the other two actuating units face each other when viewed along the primary axis. The coupling flexures, or more generally the actuating forces, may be equidistant to the primary axis. In particular, the perpendicular distances of the coupling flexures, or more generally the actuating forces, to the primary axis may be the same. The perpendicular distance is the distance of a line extending along the actuating force in a direction orthogonal to the actuating force. The four sides of the actuator assembly may extend in a loop around the primary axis. Adjacent sides of the four sides may be perpendicular.

[0020] In some embodiments, the actuating units are arranged, when viewed along the primary axis, not to be mirror symmetric about an axis perpendicular to the primary axis. So, the arrangement of actuating units may not be mirror symmetric. The arrangement of actuating units may be asymmetric about any mirror plane encompassing the primary axis.

[0021] According to another aspect of the present invention, there is provided an actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein at least one of the actuating units comprises: a body portion; an SMA element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element arranged to guide rotation of the body portion about an effective pivot axis relative to the other of the first and second parts to thereby modify the input force so as to give rise to the actuating force; wherein, when viewed along the effective pivot axis, the input force and the actuating force are on the same side of the effective pivot axis; and wherein imaginary lines extending along the input force, along the actuating force and along a force exerted by the force-modifying element on the body portion are concurrent lines or parallel lines.

[0022] Providing the input force and the actuating force are on the same side of the effective pivot axis reduces the size of the actuating unit compared to providing these forces on opposite sides. By providing the input force and the actuating force on the same side of the effective pivot axis, the angle between i) a first notional moment arm between the effective pivot axis and the input force and ii) a second notional moment arm between the effective pivot axis and the actuating force may be acute, for example when viewed along the effective pivot axis. The angle may be in the range from 0 degrees up to but excluding 90 degrees, for example. The angle may be in the range from 0 degrees to 45 degrees, preferably in the range from 0 degrees to 20 degrees. The first notional moment arm is the perpendicular distance between the effective pivot axis and the input force, i.e. the distance between a line along the input force in a direction orthogonal to the input force. The second notional moment arm is the perpendicular distance between the effective pivot axis and the actuating force, i.e. the distance between a line along the actuating force in a direction orthogonal to the actuating force.

[0023] By ensuring that the forces acting on the body portion are concurrent or are parallel, the forces on the body portion naturally balance and undesired rotation of the body portion away from a predetermined initial position is avoided. The actuating unit may thus work more efficiently and reliably. The imaginary lines may be concurrent or parallel when the first and second parts are at an initial position relative to each other, for example when each actuating unit is actuated by the same amount or when each actuating unit is unactuated. The input force acts directly on the body portion. The actuating force is in the opposite direction to a force acting on the body portion, so is along the same axis as a force acting on the body portion. Only three forces may act on the body portion in directions orthogonal to a plane of movement of the body portion.

[0024] In some embodiments, the body portion acts as a third-class lever so as to amplify the amount of actuation of the SMA element to a relatively greater amount of movement of the second part. Alternatively, the body portion may act as a second-class lever so as to amplify the input force to a relatively greater actuating force. So, the body portion may act as a second-class lever or third-class lever. When acting as a third-class lever, the input force acts in a region in between the effective pivot axis and the actuating force. When acting as a second-class lever, the actuating force acts in a region in between the effective pivot axis and the input force. In some embodiments, the force-modifying element comprises a force-modifying flexure arranged to flex so as to guide the rotation of the body portion about the effective pivot axis, and wherein the force in the force-modifying element is in a direction along the length of the force-modifying flexure. Alternatively, the force-modifying element may comprise a bearing (such as a rotating bearing or pivot bearing) guiding the rotation of the body portion about the effective pivot axis. The force exerted by the bearing on the body portion may be a normal force in the bearing, in particular a normal force between two bearing surfaces of the bearing.

[0025] In some embodiments, the SMA element is connected to the body portion at a connection point that is located, relative to a line that intersects the pivot axis and is perpendicular to the input force, in a direction opposite to the direction of the input force. On actuation, the connection point may move towards the line that intersects the pivot axis and is perpendicular to the input force.

[0026] In some embodiments, each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force. The coupling link may comprise or be a coupling flexure.

[0027] In some embodiments, the coupling link is connected to the body portion at a connection point that is located, relative to a line that intersects the pivot axis and is perpendicular to the actuating force, in a direction along the direction of the actuating force. On actuation, the connection point may move away from the line that intersects the pivot axis and is perpendicular to the actuating force.

[0028] In some embodiments, the imaginary lines are angled relative to each other so as to intersect at a point located, relative to the body portion, in a direction along the input force. The imaginary lines may intersect at a point along the SMA element.

[0029] In some embodiments, the three imaginary lines are angled relative to each other so as to intersect at a point located, relative to the body portion, in a direction opposite to a direction of the input force. The imaginary lines may intersect at a point along the coupling link.

[0030] In some embodiments, the one or more actuating units comprises two actuating units, wherein a first of the two actuating units is arranged to apply a respective actuating force in a first direction and a second of the two actuating units is arranged to apply a respective actuating force in a second direction that is at an angle to the first direction. The first and second directions may be perpendicular to each other.

[0031] In some embodiments, the force-modifying elements (e.g. force-modifying flexures) of the two actuating units are connected to a common element on the other of the first and second parts. The force-modifying elements (e.g. force-modifying flexures) of the two actuating units and the common element may be integrally formed. The common element may be fixedly attached to (and so form part of) the other of the first and second parts.

[0032] In some embodiments, the force-modifying elements of the two actuating units are integrally formed.

[0033] In some embodiments, the coupling links (e.g. coupling flexures) of the two actuating units are connected to a common element on the one of the first and second parts. The coupling links (e.g. coupling flexures) of the two actuating units and the common element may be integrally formed. The common element may be fixedly attached to (and so form part of) the one of the first and second parts.

[0034] In some embodiments, the coupling links of the two actuating units are integrally formed.

[0035] In some embodiments, the one or more actuating units comprises a total of four actuating units arranged such that none of the four actuating forces are colinear and such that the four actuating forces are capable of moving and / or tilting the first and second parts relative to each other to any position within a range of movement along and / or about two orthogonal axes that are perpendicular to a primary axis.

[0036] In some embodiments, none of the actuating units overlap when viewed along the primary axis.

[0037] In some embodiments, the actuating units are each arranged to be planar within a plane that is perpendicular to the primary axis. The actuating units may be provided in the same plane. The actuating units may overlap when viewed orthogonally to the primary axis. Alternatively, the actuating units may stand up and extend in a direction along the primary axis. For example, each actuating unit may extend in a plane spanned by the respective actuating force and an axis that is parallel to the primary axis.

[0038] In some embodiments, the one or more actuating units comprises a total of eight actuating units arranged to apply actuating forces capable of moving the first and second parts relative to each other along three orthogonal axes and / or tilting the first and second parts relative to each other about three orthogonal axes.

[0039] According to another aspect of the present invention, there is provided an actuator assembly comprising: firstand second parts that are movable and / or tiltable relative to each other along and / or about two orthogonal axes that are perpendicular to a primary axis; and a total of four actuating units each configured, on actuation, to apply a respective actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein the four actuating units are arranged such that none of the four actuating forces are colinear and are capable of moving and / or tilting the first and second parts relative to each other to any position within a range of movement along and / or about the two orthogonal axes; wherein each actuating unit comprises: a body portion; shape memory alloy, SMA, element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts, and configured to modify the input force so as to give rise to the actuating force; wherein the actuator assembly comprises four sides extending in a loop around the primary axis, wherein the four sides meet at four corners, and wherein the body portion and the force-modifying element of each of the four actuating units is arranged in a different one of the four corners and each actuating unit is arranged to apply an actuating force at an angle to the four sides.

[0040] Providing components of each actuating unit in a different corner allows more space for each actuating unit compared to an arrangement in which actuating units share a corner or overlap. Applying the actuating forces at an angle to the four sides facilitates the arrangement of actuating units in different corners. Adjacent sides of the four sides may be perpendicular to each other, such that the four sides form a rectangle or square. The actuator assembly, in particular the first and / or second part thereof, may have a generally rectangular or square footprint. The four sides may be sides of the generally rectangular or square footprint. The four sides may be sides of the smallest notional rectangle or square capable of encompassing the actuator assembly, and in particular the first and / or second part thereof, when viewed along the primary axis.

[0041] In some embodiments, the angle between each actuating force and the four sides (for example each of the four sides) is in the range from 30 to 60 degrees. The angle between each actuating force and the four sides may be between 40 and 50 degrees, preferably about 45 degrees. In some embodiments, the SMA elements of the four actuating units extend along at least two of the four sides. So, the SMA elements may extend along the sides, allowing for longer SMA elements compared to SMA elements provided in the corners.

[0042] In some embodiments, each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

[0043] In some embodiments, the coupling link of each actuating unit comprises a coupling flexure.

[0044] In some embodiments, the coupling link of each of the four actuating units is arranged in a respective one of the four corners.

[0045] In some embodiments, the coupling link of each of the four actuating units is arranged between the primary axis and the body portion when viewed along the primary axis.

[0046] In some embodiments, the force-modifying element comprises a force-modifying flexure arranged to flex so as to guide rotation of the body portion relative to the other of the first and second parts.

[0047] In some embodiments, the force-modifying element comprises a bearing arranged to guide rotation of the body portion relative to the other of the first and second parts.

[0048] In some embodiments, the body portion is arranged so as to rotate about an effective pivot point on actuation of the SMA element, wherein, when viewed along the effective pivot axis, the input force and the actuating force are opposite sides of the effective pivot axis.

[0049] In some embodiments, the body portion is arranged so as to rotate about an effective pivot point on actuation of the SMA element, wherein, when viewed along the effective pivot axis, the input force and the actuating force are on the same side of the effective pivot axis.

[0050] 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).

[0051] Brief description of the drawings

[0052] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0053] Figures 1A-E are schematic cross-sectional views of different variations of a camera assembly incorporating an actuator assembly;

[0054] Figure 2 is a schematic perspective view of the actuator assembly;

[0055] 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;

[0056] Figure 4 is a schematic plan view of an arrangement of four actuating units;

[0057] Figure 5 is a schematic perspective view of an arrangement of eight actuating units;

[0058] Figure 6 is a schematic plan view of a compact arrangement of four actuating units in line with the arrangement of Figure 4;

[0059] Figure 7 is a schematic plan view of another compact arrangement of four actuating units in line with the arrangement of Figure 4;

[0060] Figure 8 is a schematic plan view of a compact arrangement of four actuating units with a rectangular footprint, in line with the arrangement of Figure 4;

[0061] Figure 9 is a schematic plan view of another compact arrangement of four actuating units with a rectangular footprint, in line with the arrangement of Figure 4;

[0062] Figure 10 is a schematic plan view of another compact arrangement of four actuating units, in line with the arrangement of Figure 4;

[0063] Figure 11A-C are schematic plan views of different actuating units making use of a third-class lever; Figures 12A and 12B are schematic plan view of an arrangement of four actuating units in line with the arrangement of Figure 4, respectively making use of third-class levers and first-class levers;

[0064] Figure 13 is a view of a pair of actuating units making use of third-class levers and suitable for use on one of four sides of an actuator assembly with a total of eight actuating units;

[0065] Figure 14 is a plan view of an arrangement of four actuating units in line with the arrangement of Figure 12A and making use of third-class levers;

[0066] Figures 15A and 15B show the space available for each actuating unit for different layouts of actuating forces;

[0067] Figures 16A and 16B are plan views of arrangements of four actuating units making use of first-class levers and provided in corners of the actuator assembly, respectively with a force-modifying flexure and a pivot bearing;

[0068] Figures 17A and 17B are plan views of arrangements of four actuating units making use of third-class levers and provided in corners of the actuator assembly, respectively with a force-modifying flexure and a pivot bearing;

[0069] Figure 18 is a plan views of an actuator assembly showing an asymmetric space envelope available for accommodating actuating units;

[0070] Figure 19 is a plan view of an arrangement of four actuating units in line with the arrangement of Figure 4, for being accommodated by the asymmetric space envelope of Figure 18; and

[0071] Figures 20A and 20B are respective perspective and plan views of another arrangement of four actuating units in line with the arrangement of Figure 4, for being accommodated by the asymmetric space envelope of Figure 18.

[0072] Detailed description

[0073] Camera assembly

[0074] Figures 1A-E schematically show different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera assembly 1. Generally, the apparatus 1 is to be incorporated in a portable electronic device such as a smartphone. Thus, miniaturisation can be an important design criterion. Figure 2 schematically shows the actuator assembly 2. The actuator assembly 2 includes a support structure 10 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.

[0075] 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.

[0076] A primary axis P can be defined with reference to the actuator assembly 2 and / or the support structure 10. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2. In some examples, the actuator assembly 2, the support structure 10 and / or the movable part 20 extends predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 2, the support structure 10 and / or the movable part 20 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. The primary axis P may be the longitudinal axis of the actuator assembly 2 and / or the support structure 10. Alternatively or additionally, the support structure 10 and / or movable part 20 may include a planar component that extends perpendicularly to the primary axis P. Alternatively or additionally, in examples in which the apparatus 1 includes an optical element (such as a lens assembly 3) with an optical axis, or an imaging element (such as an imager sensor 4) with an imaging axis, the primary axis P may be parallel to such an axis and / or may coincide with such an axis when the movable part 20 is in a central position or orientation (for example, see Figure 1A). In general, the movable part 20 may be movable relative to the support structure 10 with up to six degrees of freedom (DOFs). In the context of describing the DOFs of movement, the primary axis P may also be referred to as the z axis, and two further axes that are perpendicular to the primary axis P and to each other may be referred to as the x and y axes. The movable part 20 may be movable relative to the support structure 10 in all or in any subset (including only one) of the following DOFs:

[0077] • 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.

[0078] • 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.

[0079] • 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.

[0080] • 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] Although the actuator assembly 2 is described in connection with a camera assembly 1, it will be appreciated that the actuator assembly 2 may be used in any device in which movement of a movable part 20 relative to a support structure 10 is desired, e.g. to provide haptic feedback in a haptic feedback device or to move a projector or display in an augmented reality (AR) or virtual reality (VR) device. Actuating unit

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 axis (out of the plane of Figure 3B), depicted herein as 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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°.

[0108] 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.

[0109] 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:

[0110] • adjusting the orientation of the SMA wire 34 (and thus of the input force Fi);

[0111] • 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);

[0112] • adjusting the orientation of the coupling flexure 33 (and thus of the actuating force F); and / or

[0113] • adjusting the location of the connection point between the coupling flexure 33 and the body portion 31 (and thus the location from which the body portion 31 applies the actuating force F).

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] In the above-described examples, the force-modifying flexure 32 and the SMA wire 34 connect at one end to the support structure 10, and the coupling flexure 33 connects at one end to the movable part 20. In general, this arrangement may also be reversed, with the force-modifying flexure 32 and the SMA wire 34 connecting at one end to the movable part 20, and the coupling flexure 33 connecting at one end to the support structure 10. In the above-described examples, the actuating unit 30 includes a coupling link 33 in the form of a coupling flexure 33. The purpose of the coupling link 33 is to allow movement of the movable part 20 in directions perpendicular to the actuating force F. In general, however, the actuating unit 30 need not include a coupling link 33, e.g. in examples in which there is no movement of the movable part 20 in directions perpendicular to the actuating force F. Furthermore, the coupling link 33 may be embodied by components other than the coupling flexure 33, for example by a ball bearing or plain bearing configured to transmit the actuating force F to the movable part 20 while allowing movement of the movable part 20 in directions perpendicular to the actuating force F. Such alternative examples of the coupling link 33 are disclosed in WO 2022 / 084699 Al. The coupling link 33 may (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.

[0120] 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. The force-modifying element may guide rotation of the body portion 31 about the effective pivot point P.

[0121] Arrangement of four actuating units

[0122] 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.

[0123] 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.

[0124] The four actuating units 30 of Figure 4 are in an arrangement capable of applying actuating forces F so as to move the movable part 20 relative to the support structure 10 to any position within a range of movement. The range of movement may be within a movement plane that is perpendicular to the primary axis P. In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a first axis (e.g. the x axis). The other two actuating units (e.g. the left and right actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a second axis (e.g. the y axis), perpendicular to the first axis. By appropriately varying the difference in actuation amount between the opposing actuating units 30, the movable part 20 may thus be moved independently along the first and second axes. The opposing actuating forces F are not colinear, but offset from each other in a direction perpendicular to the actuating forces F. Providing opposing actuating units 30 allows the tension in the SMA wires 30 of the respective actuating units 30 to be controlled, allowing for more accurate and reliable positioning of the movable part 20 compared to a situation in which actuating units 30 do not oppose each other.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] Although the actuator assembly 2 is described herein in the context of four actuating units 30, in general the actuator assembly 2 may include fewer actuating units 30. For example, the actuator assembly 2 may include two actuating units 30, e.g. the two actuating units 30 depicted in the top left of Figure 4. The forces applied to the movable part 20 by the two actuating units 30 may be opposed by a biasing force of one or more resilient elements, such as springs. With reference to Figure 4, the two actuating units 30 in the bottom right corner may be replaced with springs applying biasing forces along the corresponding depicted arrows, for example. Arrangement of eight actuating units

[0132] Figure 5 schematically shows a perspective view of an actuator assembly 2 with a total of eight actuating units 30. The eight actuating units 30 may apply actuating forces F between the movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10.

[0133] 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).

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] As a result of this symmetrical arrangement, different combinations of the actuating forces F are capable of driving movement of the movable part 20 with multiple degrees of freedom, as follows. The first group of actuating forces F, when generated together, drive upwards (+z) movement, and the second group of actuating forces F, when generated together, drive downwards (-z) movement.

[0139] 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.

[0140] 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.

[0141] 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).

[0142] Other variations

[0143] It will be appreciated that there may be many other variations of the above-described examples.

[0144] 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.

[0145] Compact arrangement of four actuating units

[0146] The SMA wire arrangement described in WO 2013 / 175197 Al allows the implementation of OIS by lateral movement of a lens assembly and an image sensor relative to each other. The stroke achievable by the four SMA wires may be sufficient for existing OIS applications. So, there may not be a need to amplify the stroke using the actuating units 30. However, the inventors have found that the use of actuating units 30 may be advantageous even when there is no requirement for increased stroke. The present invention relates, in particular, to using actuating units with relatively short SMA wires so as to achieve the same or similar amounts of stroke as the actuator assembly of WO 2013 / 175197 Al. Using relatively short SMA wires has the benefit of reducing power consumption of the actuator assembly, thus making the actuator assembly more efficient. In addition, the use of relatively short SMA wires in an actuating unit may allow for more a compact layout of the actuator assembly 2.

[0147] Figure 6 schematically depicts an arrangement of four actuating units 30. The four actuating units 30 are arranged to apply forces to the movable part 20 as described in relation to Figure 4.

[0148] The length of the SMA wire 34 of the actuating unit 30 may be relatively short. The length of the SMA wire 34 is, in particular, the length of SMA wire 34 extending between the connection elements 15, 25, e.g. the length of SMA wire 34 extending between crimps. In the embodiment of Figure 6, the length of the SMA wire 34 is less than half of the extent of a side of the actuator assembly 2, i.e. less than half of the largest extent of the actuator assembly 2 along an axis parallel to the SMA wire 34. In some embodiment, the length of the SMA wire 34 may be less than a third of the extent of a side of the actuator assembly 2, i.e. less than a third of the largest extent of the actuator assembly 2 along an axis parallel to the SMA wire 34. So, the SMA wire 34 is shorter than an SMA wire 34 in an arrangement of SMA wires disclosed in WO 2013 / 175197 Al. The SMA wire 34 is deliberately shorter than allowed by the extent of the SMA actuator assembly.

[0149] The SMA wire 34 may have a length of less than 5mm, preferably less than 4mm, further preferably less than 3mm. The lateral extent of the actuator assembly 2 may be more than 10mm, or more than 15mm. The SMA wire 34 may thus be much shorter than the lateral extent of the actuator assembly 2.

[0150] The actuating unit 30 may be configured so as to amplify contraction of the SMA wire 34 to a relatively greater movement of the movable part 20. The actuating unit 30 may be configured to amplify the contraction of the SMA wire 34 by an amplification factor, where the amplification factor is the ratio of i) movement of the movable part 20 (in a direction parallel to the actuating force) to ii) the amount of contraction of the SMA wire 34. The amplification factor may be equal to or similar to (i.e. within 50% of, preferably within 20% of) the ratio of i) the largest extent of the actuator assembly 2 along an axis parallel to the SMA wire 34 to ii) the length of the SMA wire 34. So, the stroke of the actuating unit 30 may be similar to that achievable by a single SMA wire 34 arranged along the entire extent of the actuator assembly 2. The plural actuating units 30 may generally be co-planar. The actuating planes within which the plural actuating units 30 actuate (i.e. within which the body portion 31 of the plural actuating units 30 may move on actuation) may coincide. The body portion 31, force-modifying flexure 32, coupling flexure 33 and SMA wire 34 of the plural actuating units 30 may overlap when viewed perpendicularly to the primary axis P. None of the plural actuating units 30 may overlap when viewed parallel to the primary axis P. This allows the height of the actuator assembly 2 to be reduced compared to a situation in which the actuating units 30, or any components of different actuating units 30, are allowed to overlap. Furthermore, assembly of the actuator assembly 2 is easier, because (due to the lack of overlap) all actuating units 30 may be assembled concurrently in one step.

[0151] The SMA wire 34, the coupling flexure 33 and the force-modifying flexure 32 may extend in similar directions, as shown in Figure 6. For example, the largest angle between SMA wire 34, the coupling flexure 33 and the force-modifying flexure 32 (in particular between the lengths thereof) may be less than 45 degrees, preferably less than 30 degrees, further preferably less than 20 degrees. As a result, the extent of the actuating unit 30 in a direction orthogonal to the lengths of the SMA wire 34, the coupling flexure 33 and the force-modifying flexure 32 may be reduced. The actuating unit 30 is thus compact, allowing for a more compact actuator assembly 2. In the depicted exemplary embodiment, the force-modifying flexure 32 is arranged between the SMA wire 34 and the coupling flexure 33. So, the effective pivot point P is arranged between the actuating force and the input force. The body portion 31 acts as a first class lever on rotation about the effective pivot point P.

[0152] As shown in Figure 6, the four actuating units 30 may be arranged with mirror symmetry, for example about two orthogonal mirror planes that are parallel to the primary axis P. Such an arrangement of actuating units 30 is particularly preferably when the actuator assembly 2 (and in particular the movable part) has a square footprint, for example when the movable part 20 is configured to receive a lens assembly. The coupling flexures 33 of the four actuating units 30 may be equidistant from a centre of the movable part 20 of the actuator assembly 2. So, the actuating forces applied by the actuating units 30 may be equidistant from the centre. The actuating units may be driven with similar drive signals so as to achieve the same amount of movement of the movable part 20.

[0153] In the particular exemplary embodiment of Figure 6, the body portion 31 comprises cut-outs. The cutouts reduce the mass of the body portion 31 compared to a situation in which the cut-outs are not provided. As a result of the reduced mass, less energy may be required to move the body portion 31. The risk of damage to the SMA wire 34 due to impact events may be reduced by reduction of the mass, and hence inertia, of the body portion 31. Furthermore, material costs may be reduced. With reference to the actuating unit 30 provided at the top of Figure 6, the force-modifying flexure 32 may be arranged to extend in a first direction (leftwards) from an end connected to the support structure 10 to an end connected to the body portion 31. The body portion 31 extends in a second direction (rightwards) opposite to the first direction from an end connected to the force-modifying flexure 32 to an end connected to the SMA wire 34. The body portion 31 curves, when viewed along the pivot axis, around the force-modifying flexure 32. The force-modifying flexure 32 is arranged in a space formed by the body portion 31 when viewed along the pivot axis. The SMA wire 34 extends in the first direction (leftwards) from an end connected to the body portion 31 to an end connected to the support structure 10. The force-modifying flexure 34, and thus the effective pivot point P, is arranged between the body portion 31 and the SMA wire 34. The coupling flexure 33 extends in the first direction (leftwards) from an end connected to the body portion 31 to an end connected to the support structure 10. The force-modifying flexure 34, and thus the effective pivot point P, is arranged between the coupling flexure 33 and the SMA wire 34.

[0154] Figures 7 to 9 show different arrangements of the actuating units 30 described in relation to Figure 6.

[0155] Figure 7 shows an embodiment in which the four actuating units 30 are not arranged with mirror symmetry. The four actuating units 30 may be arranged with two-fold rotational symmetry. Such an arrangement allows for a more compact actuator assembly when the actuating units 30 surround an asymmetrically shaped space, such as a rectangle. For example, in may be desirable to move a rectangular image sensor using the actuator assembly 2.

[0156] In a preferred embodiment, the coupling flexures 33 of the four actuating units 30 are equidistant from a centre of the movable part 20 of the actuator assembly 2. The actuating forces applied by the actuating units 30 are equidistant from the centre. This ensures that the torque applied by the two pairs of opposite actuating units 30 may naturally balance, making control of the actuator assembly 2 simpler. In the embodiment of Figure 7, the actuating units 30 surround a rectangular footprint. Each of the actuating units 30 is arranged such that the same component faces the rectangular footprint. In Figure 7, the SMA wire 34 of each actuating unit 30 faces the rectangular footprint. The actuating units 30 arranged along the shorter sides of the rectangular footprint are relatively closer to the rectangular footprint and the actuating units 30 arranged along the longer sides of the rectangular footprint are relatively further away from the rectangular footprint. The actuating force applied by the actuating units are equidistant from the centre of the rectangular footprint.

[0157] Figure 8 shows another preferably embodiment in which the four actuating units 30 surround a rectangular space, when viewed along the primary axis. As shown, two actuating units 30 that are arranged on opposite sides of the actuator assembly 2 (in particular the top and bottom actuating units 30, i.e. the actuating units 30 arranged on the longer sides of the rectangular space) are arranged such that the SMA wires 30 face each other. The other two actuating units 30 that are arranged on opposite sides of the actuator assembly 2 (in particular the left and right actuating units 30, i.e. the actuating units 30 arranged on the shorter sides of the rectangular space) are arranged such that the coupling flexures 33 face each other. The actuating units 30 may thus be packed more compactly around the rectangular space, while keeping the coupling flexures 33 of the four actuating units 30 equidistant from the centre of the movable part 20 of the actuator assembly 2.

[0158] Figure 9 shows another preferably embodiment in which the four actuating units 30 surround a rectangular space, when viewed along the primary axis. The embodiment of Figure 9 is similar to the embodiment described in relation to Figure 8, except that the actuating units 30 are arranged closer to the centre of the actuator assembly 2. The actuator assembly 2 may thus be made even more compact. As shown, two actuating units 30 that are arranged on opposite sides of the actuator assembly 2 (in particular the top and bottom actuating units 30, i.e. the actuating units 30 arranged on the longer sides of the rectangular space) are arranged at least partially in a space between two other actuating units 30 that are arranged on the other opposite sides of the actuator assembly 2 (in particular the left and right actuating units 30, i.e. the actuating units 30 arranged on the shorter sides of the rectangular space). So, when viewed in a direction orthogonal to the primary axis P (in particular in the left-right direction), three actuating units 30 may overlap.

[0159] In the arrangements described in relation to Figures 6 to 9, the coupling flexures 33 of the actuating units 30 all connect to the movable part 20. In alternative embodiments, the coupling flexures 33 of two actuating units 30 arranged on opposite sides of the actuator assembly 2 (for example the top and bottom actuating units 30 shown in the Figures) connect to the movable part 20 and the coupling flexures 33 of two other actuating units 30 arranged on other opposite sides of the actuator assembly 2 (for example the left and right actuating units 30 shown in the Figures) connect to the support structure 10. So, the actuating units 30 are mounted alternately to the movable part 20 and to the support structure 10.

[0160] Figure 10 shows another embodiment of the actuator assembly 2 with a compact arrangement of actuating units 30. The actuating units 30 are depicted schematically only. The body portion 31 is depicted as two lines extending around the force-modifying flexure 34, but it will be appreciated that in practice the body portion 31 may be embodies by a single part. The actuator assembly 2 is similar to that described in relation to Figure 6, expect that the actuating units 30 are arranged closer to the corners of the actuator assembly 2. The space in the corners of the actuator assembly 2 may thus be used more efficiently. Such an arrangement may reduce the footprint of an actuator assembly 2 used to drive movement of a lens assembly, for example.

[0161] Actuating units comprising third-class lever

[0162] Figures 11A to 11C schematically depict actuating units 30 making use of a third-class lever arrangement. The body portion 31 acts as a third-class lever, in particular on rotation of the body portion 31 about the effective pivot point P. The SMA wire 34 and the coupling flexure 33 are arranged on the same side of the force-modifying flexure 32. More generally, the input force (applied by an actuator, such as an SMA element 34) and the actuating force (applied to the movable part, for example by a coupling link 33) are arranged on the same side of the pivot point P (provided generally by a force-modifying element). The input force and the actuating force are parallel or at an acute angle to each other. The SMA wire 34 is arranged between the force-modifying flexure 34 and the coupling flexure 33. More generally, the input force (applied by an actuator, such as an SMA element 34) is arranged between the pivot point P (provided generally by a force-modifying element) and the actuating force (applied for example by a coupling link 33).

[0163] With reference to Figure 11A, for example, the distance Ds between the effective pivot point P and the input force (i.e. the distance between the effective pivot point P and the SMA wire 34) and the distance De between the effective pivot point P and the actuating force (i.e. the distance between the effective pivot point P and the coupling link 33) are on the same side of the effective pivot point P. The distances Ds and De are the perpendicular distances of the respective forces to the pivot point P, so the distance in a direction that is perpendicular to the respective force. The extent of the actuating unit 30 in a direction orthogonal to the input force and / or actuating force is thus approximately equal to the distance De.

[0164] By comparison, Figure 3C shows an actuating unit 30 making use of a first-class lever arrangement. The body portion 31 acts as a first-class lever. The SMA wire 34 and the coupling link 33 are provided on opposite sides of the effective pivot point P. The input force Fi and the actuating force F are in opposite directions or at an obtuse angle to each other. The distance Ds and the distance De are on opposite sides of the effective pivot point P. The extent of the actuating unit 30 in a direction orthogonal to the input force and / or actuating force is thus at least the sum of distances Ds and De. The actuating unit 30 making use of a first-class lever arrangement is less compact than the actuating unit 30 of Figures 11A-11C making use of a third-class lever arrangement when achieving the same amount of stroke amplification.

[0165] Although not specifically shown, the actuating unit 30 making use of a first-class lever arrangement is also less compact than an actuating unit 30 making use of a second-class lever arrangement when achieving the same amount of force amplification. A second-class lever may be used instead of a third-class lever when it is desirable to amplify the input force to a relatively greater actuating force. Similarly to the third- class lever arrangements described herein, in a second-class lever arrangement the SMA wire 34 and the coupling link 33 are arranged on the same side of the force-modifying flexure 32. So, the input force and the actuating force are arranged on the same side of the pivot point P. Unlike the third-class lever arrangements described herein, in a second-class lever arrangement the coupling flexure 33 is arranged between the force-modifying flexure 34 and the SMA wire 34. More generally, the actuating force (applied for example by a coupling link 33) is arranged between the pivot point P (provided generally by a force-modifying element) and the input force (applied by an actuator, such as an SMA element 34). The extent of the actuating unit 30 in a direction orthogonal to the input force and / or actuating force is approximately equal to the distance Ds.

[0166] In a second- or third-class lever arrangement, the distances Ds and De may be at an acute angle to each other, for example at an angle of less than 90 degrees, optionally of less than 45 degrees, further optionally of less than 20 degrees. The distances Ds and De may overlap, so be at an angle of 0 degrees to each other.

[0167] Figure 11A schematically depicts an actuating unit 30 making use of a third-class lever arrangement. Components of the actuating unit 30 are shown schematically as lines, and in practice may be embodied as described in relation to the actuating units 30 of Figures 3A-C and 6 to 9. As shown, both the SMA wire 34 and the coupling link 33 are provided on the same side of the force-amplifying flexure 32. The SMA wire 34 is arranged between the force-modifying flexure 32 and the coupling flexure 33 when viewed orthogonally to the length of the SMA wire 34. The connection point of the SMA wire 34 to the body portion 31 is arranged between the connection point of the coupling flexure 33 to the body portion 31 and the effective pivot point P. So, the input force is arranged between the pivot point P and the actuating force when viewed orthogonally to the input force.

[0168] As shown in Figure 11A, the input force preferably acts on the body portion 31 at a point behind the effective pivot point P. The point at which the input force acts on the body portion 31 (in the depicted actuating unit 30 the connection point between SMA wire 34 and body portion 31) is behind the effective pivot point P when viewed in a direction along the input force. On contraction of the SMA wire 34, the connection point between SMA wire 34 and the body portion 31 moves towards a line that goes through the effective pivot point P and is perpendicular to the SMA wire 34. With particular reference to Figure 11A, for example, the crimp 35 is located above the effective pivot point P and moves downward on contraction of the SMA wire 32. Arranging the connection point between SMA wire 34 and body portion 31 behind the effective pivot point P allows the SMA wire 34 to be made longer compared to a situation in which the connection point is in front of the effective pivot point P.

[0169] As further shown in Figure 11A, the coupling flexure 33 is preferably connected to the body portion 31 at a point in front of the effective pivot point p. The connection point between coupling flexure 33 and body portion 31 is in front of the effective pivot point P when viewed in a direction along the actuating force. On contraction of the SMA wire 34, the connection point between coupling flexure 33 and the body portion 31 moves away from a line that goes through the effective pivot point P and is perpendicular to the coupling flexure 33. With particular reference to Figure 11A, for example, the connection point between body portion 31 and coupling flexure 33 is located below the effective pivot point P and moves further downward on contraction of the SMA wire 32. Arranging the connection point between coupling flexure 33 and body portion 31 in front of the effective pivot point P allows the coupling flexure 33 to be made longer compared to a situation in which the connection point is in front of the effective pivot point P.

[0170] The SMA wire 34, the force-modifying flexure 32 and the coupling flexure 33 of the actuating unit 30 of Figure 11A are parallel to each other. More generally, the input force (acting in a direction parallel to the SMA wire 34), the actuating force (acting in a direction parallel to the coupling flexure 33) and the force exerted by the force-modifying element on the body portion 31 (acting in a direction parallel to the forcemodifying flexure 32) are parallel to each other. The forces may be parallel when the movable part 20 is at an initial position or starting position relative to the support structure 10. The forces may be parallel for each of the actuating units when the movable part 20 is at an initial position relative to the support structure 10. The initial position may be one predetermined position within the range of movement of the movable part 20 relative to the support structure 10. The movable part 20 may be at the initial position when the actuating units 30 are actuated by the same amount and / or when the actuating units 30 are unactuated. The initial position may be a central position within the range of movement.

[0171] Figure 11B schematically depicts another actuating unit 30 making use of a third-class lever arrangement. The embodiment of Figure 11B differs from that of Figure 11A in that the force-amplifying flexure 32, the SMA wire 34 and the coupling flexure 33 are angled relative to each other. In particular, the forceamplifying flexure 32, the SMA wire 34 and the coupling flexure 33 are angled such that imaginary lines along the lengths of the force-amplifying flexure 32, the SMA wire 34 and the coupling flexure 33 intersect at a common point. In other words, the imaginary lines are concurrent. More generally, imaginary lines along the input force (acting in a direction parallel to the SMA wire 34 in Figure 11B), along the actuating force (acting in a direction parallel to the coupling flexure 33 in Figure 11B) and along the force in the force-modifying element (acting in a direction parallel to the force-modifying flexure 32 in Figure 11B) are concurrent. The imaginary lines may be concurrent specifically when the body portion 31 is positioned at an initial position, i.e. prior to movement of the body portion 31 due to actuation of the SMA wire 34. The imaginary lines may be concurrent in at least one position of the body portion 31. Arranging the components of the actuating unit such that forces acting on the body portion intersect at a common point ensures that the forces naturally balance. The actuation efficiency of the actuating unit 30 may thus be improved compared to a situation in which the forces do not intersect at a common point.

[0172] In the actuating unit of Figure 11B, the force-modifying flexure 32 (or more generally a force in the forcemodifying element), the SMA wire 34 (or more generally the input force) and the coupling flexure 33 (or more generally the actuating force) are angled such that the imaginary lines intersect at a point arranged, relative to the body portion, in a direction along the input force. The point of intersection may, for example, be along the SMA wire 34. In Figure 11B, the point of intersection is at the connection element 15 of the SMA wire 34 to the support structure 10. The arrangement of Figure 11B may have particular layout advantages for a lens shift actuator by allowing the SMA wires 34 to fit more efficiency around a lens.

[0173] Figure 11C schematically depicts another actuating unit 30 making use of a third-class lever arrangement. In the embodiment of Figure 11C, the force-amplifying flexure 32, the SMA wire 34 and the coupling flexure 33 are angled relative to each other in the opposite sense to that in Figure 11B. The forcemodifying flexure 32 (or more generally a force in the force-modifying element), the SMA wire 34 (or more generally the input force) and the coupling flexure 33 (or more generally the actuating force) are angled such that the imaginary lines intersect at a point arranged, relative to the body portion, in a direction opposite to the direction of the input force. The point of intersection may, for example, be along the coupling flexure 33. In Figure 11B, the point of intersection is at the connection point of the coupling flexure 33 to the movable part 20. The arrangement of Figure 11C may have particular layout advantages in an "AF +OIS" actuator assembly, or generally an actuator assembly with eight actuating units 30 as described in relation to Figure 5, by allowing a reduction in extent along the primary axis P while maintaining a relatively long coupling flexure 33 within the limited extent along the primary axis P.

[0174] In the embodiments of Figures 11B and 11C, the forces may be concurrent when the movable part 20 is at an initial position or starting position relative to the support structure 10. The forces may be concurrent for each of the actuating units 30 when the movable part 20 is at an initial position relative to the support structure 10. The initial position may be one predetermined position within the range of movement of the movable part 20 relative to the support structure 10. The movable part 20 may be at the initial position when the actuating units 30 are actuated by the same amount and / or when the actuating units 30 are unactuated. The initial position may be a central position within the range of movement. Figures 12A and 12B schematically show the space advantage achievable by actuating units 30 making use of a third-class lever arrangement compared to those making use of a first-class lever arrangement. Figure 12A shows an arrangement of four actuating units 30 making use of third-class lever arrangements. Figure 12B shows an arrangement of four actuating units 30 making use of first-class lever arrangements. The actuating units 30 are arranged to apply forces to the movable part 20 as described in relation to Figure 4. The actuating units 30 of Figures 12B may achieve similar stroke amplification to those of Figure 12A. The actuating units 30 of Figure 12A take up significantly less space around an object to be moved (such as an image sensor or lens) compared to the actuating units of Figure 12B.

[0175] As further shown in Figure 12A, the force-modifying flexures 34 of adjacent actuating units 30 may be connected to the support structure 10 at the same point, in particular in the same corner of the actuator assembly 2. The force-modifying flexures 34 of adjacent actuating units 30 may connect to the same element on the support structure 10, and / or be integrally formed with the same element on the support structure 10. The force-modifying flexures 34 of adjacent actuating units 30 may be integrally formed, for example from the same piece of sheet metal. Assembly of the actuating units 30 on the actuator assembly 2 may thus be simplified, and the number of discrete components may be reduced.

[0176] The coupling flexures 33 of adjacent actuating units 30 may be connected to the movable part 20 at the same point, in particular in the same corner of the actuator assembly 2. The coupling flexures 33 of adjacent actuating units 30 may connect to the same element on the movable part 20, and / or be integrally formed with the same element on the movable part 20. The coupling flexures 33 of adjacent actuating units 30 may be integrally formed, for example from the same piece of sheet metal. Assembly of the actuating units 30 on the actuator assembly 2 may thus further be simplified, and the number of discrete components may be reduced.

[0177] In total, as apparent from a comparison of Figure 12A with Figure 12B, the number of connection points of the force-amplifying flexures 32 and of the coupling flexures 33 may be reduced from eight to four.

[0178] Figure 13 shows an embodiment of an arrangement of two actuating units in a layout suitable for the arrangement of eight actuating units 30 described in relation to Figure 5. The actuating units 30 are similar to those depicted schematically in Figure 11C. The depicted arrangement of two actuating units 30 may be arranged on each of four sides of the actuator assembly. In particular, the depicted arrangement may be provided as shown on two opposing sides of the actuator assembly 2, and it may be provided up-side- down (so flipped along the horizontal axis in Figure 13) on two other opposing sides of the actuator assembly 2. The primary axis P corresponds to the vertical axis in Figure 13. So, the actuating units 30 may extend along the primary axis P.

[0179] Figure 14 shows an embodiment of an arrangement of four actuating units 30, in particular using actuating units 30 depicted schematically in Figure 11B in the arrangement depicted schematically in Figure 12A. The embodiment of Figure 14 makes use of third-class levers, thereby allowing a compact arrangement of actuating units 30. None of the actuating units 30 overlap when viewed along the primary axis P, thereby simplifying assembly and reducing the height of the actuator assembly 2 along the primary axis P. The force-modifying flexures 34 and the coupling flexures 33 of adjacent actuating units 30 of the actuator assembly 2 of Figure 14 are suitable connected together to further simplify assembly. The embodiment of Figure 14 may be particularly suitable for lens shift actuators due to the space available in the corners of such lens shift actuators.

[0180] Although the actuating units 30 described in relation to Figures 11 to 14 comprise force-modifying flexures 32 as a force-modifying element 32, the third-class lever designs or the second-class lever designs described herein may alternatively comprise force-modifying elements 32 in the form of any bearings that guide rotation of the body portion 31 relative to the support structure 10 about the effective pivot point P. The bearing may be a rolling bearing or pivot bearing, such as rolling or pivot bearings described in relation to other embodiments.

[0181] Although the actuating units 30 described in relation to Figures 11 to 14 comprise coupling flexures 33 as a coupling links 33, the third-class lever designs or the second-class lever designs described herein may alternatively comprise any other coupling link 33 capable of transmitting the actuating force while allowing compliance in a direction orthogonal to the actuating force. The coupling link 33 may, for example, comprise a plain or ball bearing described in relation to other embodiments.

[0182] Actuating units for diagonal drive

[0183] The arrangements of four actuating units 30 described in relation to Figures 4, 6 to 10 and 12 are used to apply actuating forces along the four sides of generally rectangular or square actuating units. The four actuating units may be arranged in two opposite corners, as for example shown in Figures 10, 12 and 14. The space available for the actuating units 30 is limited by arranging two actuating units 30 in the same corner. Figure 15A schematically shows the limited space available to each actuating unit 30 when arranging two actuating units 30 in the same corner so as to apply the actuating force along the sides of a generally rectangular footprint.

[0184] Figure 15B shows an arrangement of four actuating units 30 allowing for more space for each actuating unit 30. As shown, each actuating unit is arranged in a respective corner of the actuator assembly 2. In general, the actuator assembly 2 (in particular the support structure 10 and / or the movable part thereof) comprises four sides that extend in a loop around the primary axis P. The footprint of the actuator assembly 2 (in particular the support structure 10 and / or the movable part thereof) may be substantially rectangular or square. The four sides meet at four corners. Each of the four sides may be at an angle of 90 degrees to an adjacent side.

[0185] Each actuating unit is further arranged to apply the actuating force at an angle to the four sides. So, unlike the arrangement shown in Figure 15B, the actuating forces F are not along the four sides. Each of the actuating forces may be at an angle in the range from 30 degrees to 60 degrees, preferably in the range from 40 to 50 degrees, for example about 45 degrees to one or more (e.g. each) of the four sides.

[0186] As such, more space is available for each of the actuating units 30, alleviating space constraints and layout difficulties when arranging four actuating units 30 around a movable part 20.

[0187] Figures 16A, B and 17A, B show, viewed along the primary axis, embodiments of an actuator assembly 2 comprising an arrangement of four actuating units 30. The four actuating units 30 apply actuating forces F generally as described in relation to Figure 4, except that the actuating forces F are not directed along the sides of the actuator assembly 2. None of the four actuating forces F are collinear. The four actuating units F are capable of moving the movable part 20 relative to the support structure 10 to any position within a range of movement along two orthogonal axes, or of tilting the movable part 20 relative to the support structure 10 to any position (or orientation) within a range of movement about two orthogonal axes.

[0188] Each of the actuating units 30 shown in Figures 16A, B and 17A, B is arranged in a respective corner. Each actuating unit 30 may be arranged in a substantially triangular space in a respective corner, when viewed along the primary axis P. As shown, the coupling flexure 33 of each actuating unit 30 extends at an angle to the four sides (in particular to the two vertical sides and the two horizontal sides in Figures 16A, B and 17A, B). Each actuating unit 30 may be arranged such that the coupling flexure 33 of the actuating unit 30 faces towards the primary axis P when viewed along the primary axis P. So, the coupling flexure 33 is arranged between the body portion 31 and the primary axis P when viewed along the primary axis P. The body portion 31 of the actuating unit 30 is arranged in the space behind the respective coupling flexure when viewed radially outward from the primary axis P.

[0189] The SMA wires 34 may be arranged on the sides of the actuator assembly 2, in particular may extend along the sides of the support structure 10 and / or movable part 20 thereof. This allows the extent of the SMA wires 34 to be increased within the available footprint. In the depicted embodiments, the SMA wires 34 of two actuating units 30 are arranged on one side of the actuator assembly 2 and the SMA wires 34 of the other two actuating units 30 are arranged an opposite side of the actuator assembly 2. In general, each SMA wire 34 could also be arranged on a different one of the four sides.

[0190] The actuating units 30 may be arranged so as not to overlap when viewed along the primary axis P. In particular, none of the body portions 31, force-modifying elements 32 or coupling links 33 overlap when viewed along the primary axis P. Some overlap may be allowed between an SMA wire 34 of one actuating unit 30 and components of another actuating unit 30. In the depicted embodiments, for example, two SMA wires 34 cross over when viewed along the primary axis P.

[0191] Each of the actuating units 30 of the arrangements of Figures 16A, B and 17A, B may be used to amplify the amount of actuation of the SMA wire 34 to a relatively greater amount of movement of the movable part 20. As shown, the distance De is greater than the distance Ds. However, in general, the actuating units 30 may be modified to amplify the input force to a relatively greater actuating force. So, the actuating units 30 may be configured such that the distance Ds is greater than the distance De.

[0192] Figure 16A depicts an embodiment with actuating units 30 comprising first-class levers arranged to rotate about an effective pivot axis P provided by a force-modifying flexure 34. The input force Fi is applied on an opposite side of the effective pivot point P compared to the actuating force F. The input force Fi may be applied to the body portion 31 at a point behind the effective pivot point P, as described in relation to the third-class lever designs of Figures 11A-C. As shown in the first-class lever design of Figures 16A, the coupling flexure 33 may also connect to the body portion 31 at a point behind the effective pivot point P. The lengths of the SMA wire 34 and of the coupling flexure 33 may thus be increased.

[0193] Figure 16B depicts an embodiment with actuating units 30 comprising, compared to the embodiment of Figure 16A, a force-modifying element 34 other than a force-modifying flexure 34. In particular, the force-modifying element 34 comprises a pivot bearing providing the effective pivot axis P. The pivot bearing may comprise a first surface arranged on the body portion 31 and a second surface arranged on the support structure 10. The first and second surface are arranged, on actuation of the SMA wire 34, to rotate relative to each other so as to guide rotation of the body portion 31 about the effective pivot point P. The particular pivot bearing shown in Figure 16B comprises a pin protruding from the support structure 10 in a direction along the primary axis P, and a hole in the body portion 31 surrounding the pin when viewed along the primary axis P. In general, any bearing between the support structure 10 and the body portion 31 capable of guiding rotation of the body portion may be used instead of the depicted pivot bearing.

[0194] Figure 17A depicts an embodiment with actuating units 30 comprising third-class levers arranged to rotate about an effective pivot axis P provided by a force-modifying flexure 34. So, the input force Fi is applied on the same side of the effective pivot point P as the actuating force F. The actuating unit 30 may be configured as described in relation to the actuating units 30 comprising third-class levers of Figures 11A-C. For example, the input force may be applied to the body portion 31 at a point behind the effective pivot point P. The coupling flexure 33 may connect to the body portion 31 at a point in front of the effective pivot point P. The lengths of the SMA wire 34 and of the coupling flexure 33 may thus be increased.

[0195] Figure 17B depicts an embodiment with actuating units 30 comprising, compared to the embodiment of Figure 17A, a force-modifying element 34 other than a force-modifying flexure 34. In particular, the force-modifying element 34 comprises a pivot bearing providing the effective pivot axis P. The pivot bearing may be as described in relation to Figure 16B. In general, any bearing between the support structure 10 and the body portion 31 capable of guiding rotation of the body portion may be used instead of the depicted pivot bearing.

[0196] Asymmetric arrangement of actuating units

[0197] The arrangements of actuating units described in relation to Figures 6 to 10, 12, 14, 16 and 17 generally benefit from a substantially equal amount of space on each side of the actuator assembly. The actuating units in these arrangements may all be the same or mirror symmetric to each other.

[0198] In some actuator assemblies, the space envelope available for the actuating units is asymmetric and may not be rectangular. Figure 18 shows an example such an asymmetric space envelope. In particular, the space on the support structure 10 around a movable part 20 (including for example an image sensor) along arrow A is considerably less than the space along arrows B or C. The space along arrow A may not be large enough to accommodate an actuating unit 30. Such asymmetric space envelopes may typically be found in telephoto or periscope cameras, for example. In such cameras, the space on one side of the image sensor may be restricted due to the proximity of the lens and the need for the light path to be unobstructed.

[0199] As such, it is desirable to provide asymmetric arrangements of actuating units 30 capable of being included in actuator assemblies 2 having asymmetric space constraints. Figures 19 and 20 show examples of such asymmetric arrangements of actuating units 30. The arrangements of actuating units 30 comprises a total of four actuating units 30 for applying actuating forces in the manner described with reference to Figure 4.

[0200] Figure 20 shows, viewed along the primary axis P, an actuator assembly 2 with an arrangement of actuating units 30 in a flat configuration. The actuating units 30 are generally provided in a common plane that is perpendicular to the primary axis P.

[0201] The actuator assembly 2 has four sides arranged in a loop around the primary axis P. Adjacent sides are perpendicular to each other. Two different types of actuating units 30 are provided, in particular a first type of actuating unit 30a and a second type of actuating unit 30b. The actuator assembly 2 comprises two actuating units 30a of the first type and two actuating units 30b of the second type.

[0202] The two actuating units 30a of the first type are arranged to apply actuating forces in two opposite directions along a first axis (the horizontal axis in Figure 19). The two actuating units 30a of the first type are arranged with two-fold rotational symmetry about the primary axis P. The actuating units 30a of the first type comprise an SMA wire 34 and a coupling flexure 33 that are perpendicular, or close to perpendicular, to each other. The SMA wire 34 and the coupling flexure 33 may be at an angle of about 90 degrees to each other, for example at an angle in the range from 80 to 100 degrees. The actuating unit 30a of the first type redirects the input force provided by the SMA wire 34 by approximately 90 degrees so as to apply the actuating force to the movable part 90.

[0203] The two actuating units 30b of the second type are arranged to apply actuating forces in two opposite directions along a second axis (the vertical axis in Figure 19) that is perpendicular to the first axis. The two actuating units 30b of the second type are arranged with two-fold rotational symmetry about the primary axis P. The actuating units 30b of the second type comprise an SMA wire 34 and a coupling flexure 33 that are parallel, or close to parallel, to each other. The SMA wire 34 and the coupling flexure 33 may be at an angle of about 0 degrees to each other, for example at an angle in the range from 0 to 10 degrees. The actuating unit 30a of the first type substantially maintains the direction of the input force so as to apply the actuating force to the movable part 20. Each type of actuating unit 30a, 30b may achieve the same amount of stroke or force amplification. So, the forces applied by the actuating units 30a, 30b may be balanced for an equal amount of actuation of the SMA wires 34. In the depicted embodiment, the amount of actuation of the SMA wire 34 is amplified to a relatively greater amount of movement of the movable part 20 by each type of actuating unit 30. The amplification factor is approximately three in the depicted actuating units.

[0204] One actuating unit 30a of the first type and one actuating unit 30b of the second type are arranged on a first side of the actuator assembly 2. The other actuating unit 30a of the first type and the other actuating unit 30b of the second type are arranged on a second side of the actuator assembly 2, where the second side is opposite to the first side. The SMA wires 34 of the different types of actuating units 30a, 30b arranged on the same side are substantially parallel, for example be angled by less than 10 degrees relative to each other. The coupling flexures 33 of the different types of actuating units 30a, 30b arranged on the same side are substantially perpendicular, for example be angled at 80 to 100 degrees relative to each other.

[0205] By providing the actuating units 30a, 30b on two opposing sides, the actuating units 30 may be arranged in an asymmetric space envelope. The limited space along arrow A in Figure 18 is effectively used by arranging only a coupling flexure of the actuating unit 30a of the first type. Other components of the actuating unit 30 may be arranged outside the limited space. The actuating units 30 are designed, despite their asymmetric arrangement, to apply balanced forces to the movable part 20 along the two orthogonal axes. As such, motion of the movable part along the two orthogonal axes and around the primary axis P may be accurately controlled.

[0206] Figures 20A and 20B show another actuator assembly 2 with an arrangement of actuating units 30 in an asymmetric space envelope. Figure 20A shows a perspective view of the arrangement of actuating units 30, and Figure 20B shows a view along the primary axis P of the arrangement of actuating units in combination with the movable part 20 and support structure 10.

[0207] The arrangement of actuating units 30 is similar to that described in relation to Figure 19, except that the actuating units 30b of the second type are not provided in the same plane as the actuating units 30a of the first type. Instead, the actuating units 30b of the second type extend along the primary axis P. As such, the footprint of the actuator assembly 2 orthogonal to the primary axis P is reduced, at the expense of an increased height of the actuator assembly 2 along the primary axis P. Such an increased height of the actuator assembly 2 may typically be acceptable and less than the height of other elements of a (periscope) camera assembly, such as a prism or lens. The actuating units 30a of the first type and the actuating units 30b of the second type may otherwise be as described in relation to Figure 19.

[0208] SMA

[0209] 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.

[0210] Although the embodiments have been described with SMA elements acting as an actuator component, in general other types of actuator components may be used to effect actuation of the actuation units. So, in general, the actuating units may comprise an actuator component arranged to apply the input force to the body portion. The actuator component may be the SMA element described herein, or may be a voice coil motor or piezo-electric actuating element.

Claims

Claims1. An actuator assembly comprising: first and second parts that are movable and / or tiltable relative to each other along and / or about two orthogonal axes that are perpendicular to a primary axis; and a total of four actuating units each configured, on actuation, to apply a respective actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein the four actuating units are arranged such that none of the four actuating forces are colinear and are capable of moving and / or tilting the first and second parts relative each other to any position within a range of movement along and / or about the two orthogonal axes; wherein each actuating unit comprises: a body portion; a shape memory alloy, SMA, element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts, and configured to modify the input force so as to give rise to the actuating force; wherein the SMA element is connected by connection elements between the body portion and the other of the first and second parts, wherein the length of the SMA element between the connection elements is less than half of the extent of the actuator assembly in a direction parallel to the SMA element, and wherein the four actuating units do not overlap when viewed along the primary axis.

2. An actuator assembly according to claim 1, wherein the length of the SMA element between the connection elements is less than 5mm, preferably less than 4mm, further preferably less than 3mm.

3. An actuator assembly according to claim 1 or 2, wherein the length of the SMA element between the connection elements is less than a third of the extent of the actuator assembly in a direction parallel to the SMA element.

4. An actuator assembly according to any one of claims 1 to 3, wherein none of the actuating units overlap when viewed along the primary axis.

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

6. An actuator assembly according to any preceding claim, wherein imaginary lines along the actuating force, along the input force, and along a force exerted by the force-modifying element on the body portion are concurrent.

7. An actuator assembly according to any one of the preceding claims, wherein each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

8. An actuator assembly according to claim 7, wherein the coupling link comprises a coupling flexure.

9. An actuator assembly according to claim 7 or 8, wherein the force-modifying element is arranged between the SMA element and the coupling link when viewed parallel to the primary axis.

10. An actuator assembly according to any one of claims 7 to 9, wherein actuating units are arranged on four sides of the actuator assembly, wherein two actuating units on opposite sides are arranged such that the SMA wires of the two actuating units face each other when viewed along the primary axis, and the other two actuating units are arranged such that the coupling flexures of the other two actuating units face each other when viewed along the primary axis.

11. An actuator assembly according to any one of the preceding claims, wherein the actuating units are arranged, when viewed along the primary axis, not to be mirror symmetric about an axis perpendicular to the primary axis.

12. An actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein at least one of the actuating units comprises: a body portion;an SM A element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element arranged to guide rotation of the body portion about an effective pivot axis relative to the other of the first and second parts to thereby modify the input force so as to give rise to the actuating force; wherein, when viewed along the effective pivot axis, the input force and the actuating force are on the same side of the effective pivot axis; and wherein imaginary lines extending along the input force, along the actuating force and along a force exerted by the force-modifying element on the body portion are concurrent lines or parallel lines.

13. An actuator assembly according to claim 12, wherein the body portion acts as a third-class lever so as to amplify the amount of actuation of the SMA element to a relatively greater amount of relative movement between first and second parts.

14. An actuator assembly according to claim 12 or 13, wherein the force-modifying element comprises a force-modifying flexure arranged to flex so as to guide the rotation of the body portion about the effective pivot axis, and wherein the force exerted by the force-modifying element on the body portion is in a direction along the length of the force-modifying flexure.

15. An actuator assembly according to any one of claims 12 to 14, wherein the SMA element is connected to the body portion at a connection point that is located, relative to a line that intersects the pivot axis and is perpendicular to the input force, in a direction opposite to the direction of the input force.

16. An actuator assembly according to any one of claims 12 to 15, wherein each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

17. An actuator assembly according to claim 16, wherein the coupling link comprises a coupling flexure.

18. An actuator assembly according to claim 16 or 17, wherein the coupling link is connected to the body portion at a connection point that is located, relative to a line that intersects the pivot axis and is perpendicular to the actuating force, in a direction along the direction of the actuating force.

19. An actuator assembly according to any one of claims 12 to 18, wherein the imaginary lines are angled relative to each other so as to intersect at a point located, relative to the body portion, in a direction along the input force.

20. An actuator assembly according to any one of claims 12 to 18, wherein the imaginary lines are angled relative to each other so as to intersect at a point located, relative to the body portion, in a direction opposite to a direction of the input force.

21. An actuator assembly according to any one of claims 12 to 20, wherein the one or more actuating units comprises two actuating units, wherein a first of the two actuating units is arranged to apply a respective actuating force in a first direction and a second of the two actuating units is arranged to apply a respective actuating force in a second direction that is at an angle to the first direction.

22. An actuator assembly according to claim 21, wherein the force-modifying elements of the two actuating units are connected to a common element on the other of the first and second parts.

23. An actuator assembly according to claim 21 or 22, wherein the force-modifying elements of the two actuating units are integrally formed.

24. An actuator assembly according to any one of claims 21 to 23 when dependent on claim 16, wherein the coupling links of the two actuating units are connected to a common element on the one of the first and second parts.

25. An actuator assembly according to claim 24, wherein the coupling links of the two actuating units are integrally formed.

26. An actuator assembly according to any one of claims 12 to 25, wherein the one or more actuating units comprises a total of four actuating units arranged such that none of the four actuating forces are colinear and such that the four actuating forces are capable of moving and / or tilting the first and second parts relative to each other to any position within a range of movement along and / or about two orthogonal axes that are perpendicular to a primary axis.U. An actuator assembly according to claim 26, wherein none of the actuating units overlap when viewed along the primary axis.

28. An actuator assembly according to claim 26 or 27, wherein the actuating units are each arranged to be planar within a plane that is perpendicular to the primary axis.

29. An actuator assembly according to any one of claims 12 to 25, wherein the one or more actuating units comprises a total of eight actuating units arranged to apply actuating forces capable of moving the first and second parts relative to each other along three orthogonal axes and / or tilting the first and second parts relative to each other about three orthogonal axes.

30. An actuator assembly comprising: first and second parts that are movable and / or tiltable relative to each other along and / or about two orthogonal axes that are perpendicular to a primary axis; and a total of four actuating units each configured, on actuation, to apply a respective actuating force to one of the first and second parts capable of moving the first and second parts relative to each other, wherein the four actuating units are arranged such that none of the four actuating forces are colinear and are capable of moving and / or tilting the first and second parts relative to each other to any position within a range of movement along and / or about the two orthogonal axes; wherein each actuating unit comprises: a body portion; shape memory alloy, SMA, element connected between the body portion and the other of the first and second parts, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the other of the first and second parts, and configured to modify the input force so as to give rise to the actuating force; wherein the actuator assembly comprises four sides extending in a loop around the primary axis, wherein the four sides meet at four corners, and wherein the body portion and the force-modifying element of each of the four actuating units is arranged in a different one of the four corners and each actuating unit is arranged to apply an actuating force at an angle to the four sides.

31. An actuator assembly according to claim 30, wherein the angle between each actuating force and the four sides is in the range from 30 to 60 degrees, preferably about 45 degrees.

32. An actuator assembly according to claim 30 or 31, wherein the SMA elements of the four actuating units extend along at least two of the four sides.

33. An actuator assembly according to any one of claims 30 to 32, wherein each actuating unit further comprises a coupling link connected between the body portion and the one of the first and second parts, wherein the coupling link is configured to transmit the actuating force from the body portion to the one of the first and second parts, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

34. An actuator assembly according to claim 33, wherein the coupling link of each actuating unit comprises a coupling flexure.

35. An actuator assembly according to claim 33 or 34, wherein the coupling link of each of the four actuating units is arranged in a respective one of the four corners.

36. An actuator assembly according to any one of claims 33 to 35, wherein the coupling link of each of the four actuating units is arranged between the primary axis and the body portion when viewed along the primary axis.

37. An actuator assembly according to any one of claims 30 to 36, wherein the force-modifying element comprises a force-modifying flexure arranged to flex so as to guide rotation of the body portion relative to the other of the first and second parts.

38. An actuator assembly according to any one of claims 30 to 37, wherein the force-modifying element comprises a bearing arranged to guide rotation of the body portion relative to the other of the first and second parts.

39. An actuator assembly according to any one of claims 30 to 38, wherein the body portion is arranged so as to rotate about an effective pivot point on actuation of the SMA element, wherein, when viewed along the effective pivot axis, the input force and the actuating force are opposite sides of the effective pivot axis.

40. An actuator assembly according to any one of claims 30 to 38, wherein the body portion is arranged so as to rotate about an effective pivot point on actuation of the SMA element, wherein, whenviewed along the effective pivot axis, the input force and the actuating force are on the same side of the effective pivot axis.

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