WO2024170864A1

WO2024170864A1 - Actuator assembly

Info

Publication number: WO2024170864A1
Application number: PCT/GB2024/000007
Authority: WO
Inventors: Robin Eddington; Samuel ARMSTRONG; Andrew Benjamin Simpson Brown; Oliver HART; Alexander Johnson; Robert LANGHORNE
Original assignee: Cambridge Mechatronics Limited
Priority date: 2023-02-17
Filing date: 2024-02-19
Publication date: 2024-08-22

Abstract

An actuator assembly (10) comprises: a first part (5); a second part (6) arranged to be movable relative to the first part; eight actuating units (80) arranged, on actuation, to move the second part relative to the first part, wherein each actuating unit comprises: a body portion (82); a force-modifying flexure (84) connected between the body portion and the first part; a coupling flexure (83) connected between the body portion and the second part; an SMA element (2) arranged, on actuation, to exert an input force on the body portion, thereby causing the force-modifying flexure to deform so as to modify the input force and cause the coupling flexure to apply an actuating force (Fa) on the second part; wherein the eight actuating units (80) are in an arrangement such that, on selective actuation, the eight actuating units (80) apply non-colinear forces on the second part relative to the first part capable of moving the second part relative to the first part in up to six degrees of freedom.

Description

ACTUATOR ASSEMBLY

Field

The present application relates to an actuator assembly, in particular a shape memory alloy (SMA) actuator assembly.

Background

SMA actuator assemblies may be used in miniature cameras to effect optical image stabilization and/or auto-focus (AF). WO 2011/104518 Al, for example, discloses an SMA actuation apparatus that uses a particular arrangement of eight SMA wires to move a movable element so as to effect OIS and/or AF.

Typically, the range of movement (also known as "stroke") of such SMA actuator assemblies is limited by the maximum contraction of the SMA wires, and the actuating force is limited by the maximum force that can be generated by the SMA wires. To increase the movement range or the actuating force, longer or thicker SMA wires can be used, but this may be at the expense of increased cost, size and/or power, which may not be practical in miniature applications.

WO 2022/084699 Al discloses an actuator assembly comprising at least one actuating unit incorporating an SMA wire that, on actuation, moves a movable part relative to the support structure. The actuating unit may be configured to increase the stroke or the actuating force and/or to re-direct the force applied by the SMA wire.

Summary

According to an aspect of the present invention, there is provided an actuator assembly comprising a first part; a second part arranged to be movable relative to the first part; eight actuating units arranged, on actuation, to move the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; an SMA element arranged, on actuation, to exert an input force on body portion, thereby causing the force-modifying flexure to deform so as to modify the input force and cause the coupling link to apply an actuating force on the second part; wherein the eight actuating units are in an arrangement such that, on selective actuation, the eight actuating units apply non-colinear forces on the second part relative to the first part capable of moving the second part relative to the first part in up to six degrees of freedom.

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 to the maximum extent permissible by law).

In some embodiments, the actuating units are actuated so as to cause rotation of the second part relative to the first part (in both senses) about any axis substantially perpendicular to the primary axis and optionally about the primary axis. Such embodiments may enable 2-axis or 3-axis module-tilt OIS. In such embodiments, the actuator assembly may comprise a bearing arrangement between the first and second parts. The bearing arrangement may be configured to allow rotation of the second part relative to the first part about any axis substantially perpendicular to the primary axis and optionally about the primary axis. Such a bearing arrangement may restrict other types of movement such as translational movement of the second part relative to the first part, and therefore may help improve performance of the actuator assembly. The bearing arrangement may include, for example, one or more gimbals.

The non-collinear forces may be capable of moving the second part relative to the first part in two or more rotational degrees of freedom or three translational degrees of freedom.

In each actuating unit, the SMA element may be connected between the body portion and the first part.

The eight actuating units may be arranged in four pairs of actuating units, wherein each pair of actuating units is arranged on a different side of the second part.

The actuator assembly may comprise a primary axis and wherein each of the sides are arranged around the primary axis, optionally wherein adjacent sides are substantially perpendicular such that the four sides form a quadrilateral shape when viewed along the primary axis.

The coupling flexure of at least one of the actuating units may be inclined at an angle of 30 to 60 degrees, optionally 35 to 55 degrees, preferably 40 to 50 degrees, with respect to a plane that is substantially perpendicular to the primary axis.

The arrangement of any pair of actuating units along any side of the actuator assembly may have 180 degree rotational symmetry about the primary axis with the arrangement of actuating units on the opposing side of the actuator assembly. The arrangement of any pair of actuating units along any given side of the actuator assembly may have mirror symmetry with the arrangement of actuating units along an adjacent side of the actuator assembly about a plane intersecting the two sides and containing the primary axis.

Each pair of actuating units may comprise a respective first actuating unit and a respective second actuating unit, wherein for at least one pair, the arrangement of the second actuating unit corresponds to a reflection of the first actuating unit in a plane containing the primary axis.

Each pair of actuating units may comprise a respective first actuating unit and a respective second actuating unit, wherein for at least one pair, the arrangement of the second actuating unit corresponds to a reflection of the first actuating unit in both a plane containing the primary axis and a plane substantially perpendicular to the primary axis.

Each pair of actuating units may be arranged such that the actuating units have 180 degree rotational symmetry about an axis normal to the side on which the pair of actuating units is arranged.

For at least one pair of actuating units, the respective coupling flexures may be substantially parallel.

The respective force-modifying flexures of at least one of the pairs of actuating units may be substantially parallel.

For at least one pair of actuating units, the coupling flexure of one actuating unit may be connected to a side of the second part at or near one longitudinal end of the side, and the coupling flexure of the other actuating unit in the pair may be connected to the side of the second part at or near the other longitudinal end of the side.

For at least one pair of actuating units, the force-modifying flexure of each actuating unit in the pair may be connected to a central portion of a side of the of first part, optionally wherein the force-modifying flexures are connected to the side at a point which is greater than 25% and less than 75% of the distance along the side.

For at least one pair of actuating units, the body portions of each actuating unit in the pair may be located at a central region of a side of the first part, optionally wherein the body portions are located along the side in a region which is greater than 25% and less than 75% of the distance along the side. For at least one pair of actuating units, the force-modifying elements of each actuating unit in the pair may be arranged to be placed under compression by the respective body portions when the respective SMA elements exert an input force on the respective body portions.

The actuating units may be arranged such that when the SMA elements exert an input force on the respective body portions, the body portions exert a compressive force on the respective force modifying flexures in a direction that is at least partly towards the point at which the respective force-modifying flexure is connected to the first part. The compressive force may be in a direction that is at least partly towards a centre of the side on which the pair of actuating units is arranged. The connection between the force-modifying flexure and the first part may be located closer to a centre of the side relative to the connection between the force-modifying flexure and the body portion.

The coupling flexure, SMA element and the force-modifying flexure may each extend from the body portion in a direction that is at least partly towards the same longitudinal end of the side.

In each actuating unit, the coupling flexure may be connected to a central portion of a side of the second part, optionally wherein the coupling flexure is connected to the side at a point which is greater than 25% and less than 75% of the distance along the side.

In each pair of actuating units, the force-modifying flexure of one actuating unit is connected to a side of the first part at or near one longitudinal end of the side, and the force-modifying flexure of the other actuating unit may be connected to the side at or near the other longitudinal end of the side.

In each pair of actuating units, the coupling link of one actuating unit may extend from the body portion to the second part in a direction that is at least partly towards one longitudinal end of a side, and the coupling link of the other actuating unit may extend from the body portion to the second part in a direction that is at least partly towards the other longitudinal end of the side.

The connection point between the coupling link of each actuating unit and the second part may be located closer to the opposite longitudinal end of the side than the longitudinal end of the side at which the respective body portion is arranged.

In each actuating unit, the coupling link may extend from the body portion to the second part in a direction that is at least partly towards a longitudinal end of a side, and the SMA element may extend from the body portion to the first part in a direction that is at least partly towards the same longitudinal end of the side. The SMA elements of each pair of actuating units may cross over when viewed perpendicularly to the side on which they are arranged.

The SMA elements of each pair of actuating units may not cross over when viewed perpendicularly to the side on which they are arranged, optionally wherein the SMA elements of each pair of actuating units are parallel.

The body portion, force modifying flexure and coupling flexure of each pair of actuating units may be integrally formed.

The body portion of each actuating unit may comprise a first arm extending between the connection point to the force-modifying flexure and the connection point to the SMA wire, and/or a second arm extending between the connection point to the force-modifying flexure and the connection point to the coupling flexure. The first arm may extend away from the end of the SMA wire connected to the first part and/or the second arm may extend away from the end of the coupling flexure connected to the second part. In each actuating unit, the first arm and/or the second arm may extend away from the connection point to the force-modifying flexure in a direction that is at least partly towards the other longitudinal end of the side. In each actuating unit, the first arm and/or second arm may extends away from the connection point to the force modifying flexure in a direction that is at least party towards the same longitudinal end of the side.

Each actuating unit may be configured such that the force-modifying flexure amplifies an amount of actuation of the SMA wire to a relatively greater amount of movement of the second part relative to the first part.

There may be provided a camera assembly comprising: the actuator assembly; one or more lenses comprised in one of the first and second parts of the actuator assembly; and an image sensor comprised in the other of the first and second parts of the actuator assembly; wherein the actuator assembly is configured to move the one or more lenses and the image sensor relative to each other in three translational degrees of freedom.

There may be provided a camera assembly comprising: the actuator assembly; a support structure comprising one of the first and second parts of the actuator assembly; a module comprised in the other of the first and second parts of the actuator assembly, wherein the module comprises one or more lenses and an image sensor; wherein the actuator assembly is configured to rotate the module relative to the support structure in two or more rotational degrees of freedom.

In another aspect, the actuator assembly may be as specified above except that one or more of the actuating units may be connected in the opposite sense between the first and second parts, i.e. one or more of the actuating units may have a force-modifying flexure connected between the body portion and the second part, a coupling flexure connected between the body portion and the first part, and an SMA element which may be connected between the body portion and the second part.

Brief description of the drawings

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

Figure 1A depicts an example of an SMA actuator assembly comprising eight SMA wires;

Figure IB depicts an actuator assembly;

Figures 2A and 2B each depict a pair of actuating units;

Figure 3 depicts an SMA actuator assembly comprising an arrangement of eight actuating units;

Figures 4A and 4B each depict a pair of actuating units;

Figures 5A and 5B each depict a pair of actuating units;

Figure 6 depicts an SMA actuator assembly comprising an arrangement of eight actuating units;

Figure 7 depicts a pair of actuating units;

Figure 8 depicts a pair of actuating units;

Figure 9 depicts a pair of actuating units;

Figure 10 depicts a pair of actuating units;

Figure 11 depicts an SMA actuator assembly comprising an arrangement of eight actuating units.

Detailed description

Conventional eight wire actuator assembly

Figure 1 shows an exploded view of a known shape memory alloy (SMA) actuator wire arrangement 10 in a miniature camera. The SMA actuator arrangement 10 includes a support structure 5 (also a "first part 5" or "static part 5" herein) that comprises a base 11 that is an integrated chassis and sensor bracket for mounting an image sensor (not shown), and a screening can 12 attached to the support structure 11. The SMA actuator arrangement 10 includes a moveable part 6 (also a "second part 6" or "moving part 6" herein), which is a lens assembly comprising a lens carriage 13 carrying at least one lens (not shown) configured to focus an image on the image sensor. In some other embodiments, the support structure 11 may comprise a lens assembly comprising a lens carriage 13 carrying at least one lens (not shown), wherein the moveable part 13 may comprise a sensor bracket for mounting an image sensor, and wherein the at least one lens is configured to focus an image on the image sensor. That is, in these alternative embodiments, the image sensor is moveable relative to (fixed or moveable) lenses.

In some other embodiments, the movable part 6 may include both the image sensor and the lens assembly configured to focus an image on the image sensor.

The lens assembly defines an optical axis. The image sensor 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. Each lens may have a diameter of 20mm or less, for example of 12mm or less.

In this example, the actuator 10 includes eight SMA wires 2 each attached between the static part 5 and the moving part 6. A pair of SMA wires 2 that cross each other are provided on each of four sides of the SMA actuator arrangement 10 as viewed along an optical axis, along a first direction. The SMA wires 2 are attached to the static part 5 and the moving part 6 in such a configuration that upon heating, they contract and thereby apply an actuating force Fa so as to provide relative movement of the moving part 5 with multiple degrees of freedom e.g. for providing both autofocus (AF) and optical image stabilisation (OIS).

Thus, in respect of each pair of SMA wires 2, the SMA wires 2 are attached at one end to two static mount portions 15, which are themselves mounted to the static part 5 for attaching the SMA wires 2 to the static part 5. The static mount portions 15 are adjacent to one another but are separated to allow them to be at different electrical potentials.

Similarly, in respect of each pair of SMA wires 2, the SMA wires 2 are attached at one end to a moving mount portion 16 which is itself mounted to the moving part 6 for attaching the SMA wires 2 to the moving part 6. The moving part 6 further comprises a conductive ring 17 connected to each of the moving mount portions 16 for electrically connecting the SMA wires 2 together at the moving part 6.

The static mount portions 15 and the moving mount portions 16 comprise crimp tabs 23 which may be formed into crimps and used to hold the SMA wires 2. The moving mount portions 16 may comprise electrical connection tabs 31 for providing electrical connection to the conductive ring 17. Thus, in the example shown in Figure 1, the crimp tabs 23 that are formed into crimps are integral parts of the static and moving portions 15, 16 of the actuator arrangement 10. Methods for forming the crimps and trapping the SMA wires within the crimp tabs 23 are described in International Patent Publication No. WO2016/189314.

Figure IB schematically shows the actuator assembly 10. As mentioned above, the movable part 6 is movable relative to the support structure 5. When the actuator assembly 10 is included e.g. in an apparatus (which may be a portable electronic device such as a smartphone), the support structure 5 may be fixed relative to the main body of the apparatus. However, in general, the support structure 5 need not be stationary and may be movable relative to or within the apparatus. Each SMA wire 2 is configured to apply an actuating force Fa capable of moving the movable part 6 relative to the support structure 5.

The SMA wires 2 may be arranged such that the movable part 6 may be supported (i.e. suspended) on the support structure 5 exclusively by the SMA wires 2. In other words, the SMA wires 2 may be arranged such that the movable part 6 is capable of being positioned in a suspended position relative to the support structure 5 (e.g. a position in which the movable part 6 is not in contact with the support structure 5) exclusively by the SMA wires 2 as shown in Figure IB.

A primary axis P can be defined with reference to the actuator assembly 10 and/or the support structure 5. The primary axis P extends through the actuator assembly 10, e.g. through the centre of the actuator assembly 10. The actuator assembly 10, the support structure 5 and the movable part 6 extend predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 10, the support structure 5 and the movable part 6 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. The primary axis P is the longitudinal axis of the actuator assembly 10 and the support structure 5. The primary axis P may be parallel to, and/or may coincide or be collinear with, the optical axis of the lens assembly and/or an imaging axis of the image sensor e.g. when the movable part 6 is in a central position or orientation (as shown in, for example, Figure IB).

The movable part 6 is movable relative to the support structure 5 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 6 may be movable relative to the support structure 5 in all of the following DOFs: Tx and Ty: Translational movement in the x-y plane. In other words, the movable part 6 is independently movable along the x and y axes. The movable part 6 is movable to any position in the x-y plane within a range of movement.

Rx and Ry: Rotational movement (or simply rotation or tilting) about the x and y axes. In other words, the movable part 6 may be rotated about any axis perpendicular to the primary axis P. The movable part 6 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement.

Tz: Translational movement along the z axis. The movable part 6 is movable to any translational position along the z axis within a range of movement.

Rz: Rotational movement (or simply rotation) about the z axis. The movable part 6 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement.

As mentioned above, the SMA wires 2 are connected between the support structure 5 and the movable part 6. The SMA wires 2 are arranged to apply actuating forces Fa between the movable part 6 and the support structure 5. Selectively varying the actuating forces Fa causes the movable part 6 to move relative to the support structure 5 within the DOFs mentioned above. The SMA wires 2 are thus capable of driving movement of the movable part 6 relative to the support structure 5.

The SMA wires 2 are connected so that on contraction two groups of four SMA wires 2 provide a force with a component in opposite directions along the primary axis P to effect movement along the primary axis P. The SMA wires 2 of each group have 2-fold rotational symmetry about the primary axis P so that SMA wires 2 are opposing each other to effect lateral movement, i.e. movement in directions perpendicular to the primary axis P.

The assembly 10 also includes a controller (not shown). The controller (herein also referred to as a control circuit) may be implemented in an integrated circuit (IC) chip. The controller generates drive signals for the SMA wires 2. 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 2, thereby heating the SMA wires 2 by causing an electric current to flow, will cause the SMA wires 2 to contract and thus drive relative movement of the movable part 6. The drive signals are chosen to drive relative movement of the movable part 6 in a desired manner, for example so as to achieve OIS by stabilizing the image sensed by the image sensor or to achieve AF by adjusting the focus of the image sensed by the image sensor. The controller supplies the generated drive signals to the SMA wires 2. Optionally, the assembly 10 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 assembly 1, which can be processed so as to produce signals representative of the required movement of the movable part 6 to compensate for such shake. The controller receives such signals and can generate the drive signals for the SMA wires 2 to achieve OIS.

Although the actuator assembly 10 is described in connection with a miniature camera, it will be appreciated that the actuator assembly 10 may be used in any device in which movement of a movable part 6 relative to a support structure 5 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.

As shown in Figure 1, a pair of the SMA wires 2 are provided on each of four sides around and extend at an angle to, the primary axis P. There is a 'minimum wire angle' that the actuator needs to prevent uncontrolled resonance in the SMA wires 2 along the primary axis P. Therefore, to maintain such a wire arrangement and to prevent the said uncontrolled resonance, the height of the actuator typically increases during scale-up. Therefore, such a known design may be unfavourable for larger lenses if the height (or thickness) of the actuator assembly 10 is at a premium.

In practice, when the SMA wires 2 are unenergized, i.e. when the SMA actuator 10 is powered off and the SMA wires 2 have sufficiently cooled down, they may no longer be under tension. Thus, in most cases, a degree of slack may be observed in the unenergized SMA wires 2. This may cause free movement in the SMA wires 2, as well as in the lens carriage. Since the SMA wires 2 are crossed as viewed from the side, such free movement may cause the SMA wires 2 to contact and rub over each other, leading to extensive abrasion and wear of the wires 2.

To help with these issues, the SMA wires 2 of the actuator assembly 10 of Figures 1A may be replaced with the SMA actuating units 80 described below. First example of an actuator assembly

In a first example actuator assembly 10, the eight SMA wires 2 of the actuator assembly 10 of Figure 1A are replaced with the actuating units 80 of Figure 2A, as shown in Figure 3.

Each actuating unit 80 of Figure 2A comprises a body portion 82 to which several components are connected. The body portion 82 is configured not to deform during use (i.e. during contraction or actuation of the SMA wires 2). The body portion 82 is thus relatively rigid.

Each actuating unit 80 of Figure 2A further comprises a force-modifying flexure 84. The force-modifying flexure 84 is connected between the body portion 82 and the support structure 5. One end 84m of the force-modifying flexure 84 is connected to the body portion 82. The other end 84s of the forcemodifying flexure 84 is connected to the support structure 5. The force-modifying flexure 84 may, on flexing, allow the body portion 82 to move relative to the support structure 5 in a direction that is substantially orthogonal to the force-modifying flexure 84. The force-modifying flexure 84 effectively allows the body portion 82 to pivot relative to the support structure 5. The force-modifying flexure 84 is configured to provide an effective pivot point V about which the body portion 82 is allowed to pivot relative to the support structure 5.

Each actuating unit 80 of Figure 2A further comprises an SMA wire 2. The SMA wire 2 is connected between the body portion 82 and the support structure 5. One end of the SMA wire 2 is connected to the support structure 5, in particular by a crimp 35s. The other end of the SMA wire 70 is connected to the body portion 82, in particular by a crimp 35m.

Each actuating unit 80 of Figure 2A further comprises a coupling flexure 83. The coupling flexure 83 is connected between the body portion 82 and the movable part 6. One end of the coupling flexure 83 is connected to the body portion 82. The other end of the coupling flexure 83 is connected to the movable part 6, e.g. via a moving mount portion 86.

Within each actuating unit 80 of Figure 2A, the SMA wire 2 is arranged, on contraction, to apply an input force Fi on the body portion 82. The input force acts parallel to the length of the SMA wire 2. The forcemodifying flexure 84 is arranged to modify the input force Fi so as to cause the coupling flexure 83 to apply an actuating force Fa to the movable part 6, which is transmitted from the body portion 82 to the movable part 6 by the coupling flexure 83. In particular, in the depicted embodiment the forcemodifying flexure 84 is placed in tension on contraction of the SMA wire 2. The force-modifying flexure 84 is arranged at an angle and/or offset relative to the SMA wire 2. As a result, the force-modifying flexure 84 is arranged to deform on contraction of the SMA wire 2. The body portion 82 pivots about the effective pivot point V provided by the force-modifying flexure 84. The force-modifying flexure 84 thus converts the input force Fi, in particular the magnitude and direction thereof, into the actuating force Fa. In other words, the force-modifying flexure 84 and the body portion 82 modify the direction and the magnitude of the input force Fi so as to give rise to the actuating force Fa.

Each actuating unit 80 of Figure 2A can be configured to amplify movement or to amplify force due to contraction of the SMA wire 2. In the depicted embodiment, the distance between the input force Fi applied by each SMA wire 2 and the effective pivot point V is smaller than the distance between the actuating force Fa and the effective pivot point V. Each actuating unit 80 effectively acts as a lever to amplify the movement of contraction of the SMA wire 2.

In some embodiments, at least one actuating unit 80, preferably each actuating unit 80, is configured such that the force-modifying flexure 84 amplifies an amount of contraction of the SMA wire 2 to a relatively greater amount of movement of the movable part 6 relative to the support structure 5. Such amplification, for example, may be by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3. This may be achieved, for example, by appropriate selection of the distance between the SMA wire 2 and the effective pivot point V, for example by modifying the angle between SMA wire 2 and force-modifying flexure 84 or by altering the extent of the body portion 82. The angle between SMA wire 2 and force-modifying flexure 84 may be in the range from 0 to 45 degrees, preferably from 13 to 40 degrees.

Each coupling flexure 83 of Figure 2A is compliant in a direction perpendicular to the actuating force Fa. This allows the movable part 6 to move in a directions perpendicular to the actuating forces Fa of the actuating units 80, and in a directions perpendicular to the coupling flexures 83.

As discussed, each force-modifying flexure 84 of Figure 2A is placed in tension on contraction of the corresponding SMA wire 2. This can reduce the risk of buckling of the force-modifying flexure 84. However, in general, the force-modifying flexure 84 could also be arranged so as to be placed under compression on contraction of the SMA wire 2.

Further details and alternative examples of actuating units are described in WO 2022/084699 Al, which is herein incorporated by reference to the maximum extent permissible by law.

As discussed, each force-modifying flexure 84 and SMA wire 2 of Figure 2A connect at one end to the support structure 5, and each coupling flexure 83 of Figure 2A connects at one end to the movable part 6. In general, this arrangement may also be reversed, with the force-modifying flexure 84 and the SMA wire 2 connecting at one end to the movable part 6, and the coupling flexure 83 connecting at one end to the support structure 5.

Figures 2A shows a pair of actuating units 80 that are integrally formed. In particular, the body portions 82, force-modifying flexures 84, coupling flexures 83 and moving mount portions 86 of the pair of actuating units 80 may be integrally formed, i.e. formed from the same material. The body portions 82, force-modifying flexures 84 , coupling flexures 83 and moving mount portions 86 of the pair of actuating units 80 may be formed from a single metal sheet, for example by etching. The pair of actuating units 80 may connect at the movable part 6 (e.g. the moving mount portion 86) when assembled in an actuator assembly. The pair of actuating units 80 may extend substantially in a common plane.

The body portion 82 of each actuating unit 80 of Figure 2A comprises two arms extending from the connection point 84m to the force-modifying flexure 84 back towards the effective pivot point V. The two arms extend towards the force-modifying flexure 84. The two arms extend away from the SMA wire 2 and/or coupling flexure 83. This allows the SMA wire 2 and/or coupling flexure 83 to have an increased length compared to a situation in which the arms do not extend back. A longer SMA wire 2 may extend the stroke capabilities of the actuating units 80. A longer coupling flexure 83 may reduce the lateral stiffness of the coupling flexure 83.

As shown in Figure 3, the first example actuator assembly 10 comprises eight such actuating units 80 surrounding the movable part 6, instead of the eight SMA wires 2 of Figure 1A. The actuating units 80 are arranged between the support structure 5 and the movable part 6 so as to, on selective actuation, drive movement of the movable part 6 relative to the support structure 5.

The eight actuating units 80 of the actuator assembly 10 of Figure 3 are arranged such that they are capable of moving the movable part 6 relative to the support structure 5 in three translational degrees of freedom (Tx, Ty, Tz) and in two or three rotational degrees of freedom (Rx, Ry or Rx, Ry, Rz), as with the eight SMA wires 2 in the prior art actuator described in relation to Figure 1A.

As discussed, the actuating units 80 are arranged to apply actuating forces Fa to the movable part 6. The actuating forces Fa (e.g. when visualised as vectors at particular positions in space) are arranged on each of four sides of the actuator assembly 10 (i.e. a first side, a second side, a third side and then a fourth side) around the primary axis P. Two actuating forces Fa are provided on each of the four sides. The two actuating forces Fa on each side are inclined in the same direction along the primary axis P. The four sides extend in a loop around the primary axis P. In this example, the sides are perpendicular and so form a square as viewed along the primary axis P, but alternatively the sides could take a different e.g. quadrilateral shape. In this example, the forces are parallel to the outer faces of the square envelope of the moveable part 6 but this is not essential.

A first, second, third, and fourth pair of actuating units 80 are arranged along the first, second, third and fourth sides of the actuator assembly 10 respectively, wherein the first and second sides are opposite sides through which the first axis x (herein also referred to as the x axis) extends and the third and fourth sides are opposite sides through which the second axis y (herein also referred to as y axis) extends.

Each actuating unit 80 of the first and second pairs of actuating units 80 are arranged to apply actuating forces Fa with a component in a first (e.g. upwards) direction along the primary axis P. Each actuating unit 80 of the third and fourth pairs of actuating units 80 are arranged to apply actuating forces Fa with a component in a second, opposite (e.g. downwards) direction along the primary axis P. The first and second pairs of actuating units 80 may be considered as upside-down flipped versions of the third and fourth pairs of actuating units 80.

Four actuating forces Fa form a 'first' group that have a force component in one direction ('upwards' or '+z' direction) along the primary axis P, and the other four actuating forces Fa form a 'second' group that have a component in the opposite direction ('downwards' or '-z' direction) along the primary axis P. Herein, 'up' and 'down' generally refer to opposite directions along the primary axis P.

The first and second pairs of actuating units 80 each comprise a first actuating unit 80 configured to apply an actuating force Fa with a force component in a first direction along the y axis, and a second actuating unit 80 configured to apply an actuating force Fa with a force component in a second, opposite direction along the y axis. The third and fourth pairs of actuating units 80 each comprise a third actuating unit 80 configured to apply an actuating force Fa with a force component in a first direction along the x axis, and a fourth actuating unit 80 configured to apply an actuating force Fa with a force component in a second, opposite direction along the x axis.

Both the first group of actuating forces Fa and the second group of actuating forces Fa are each arranged with two-fold rotational symmetry about the primary axis P. In other words, the eight actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P. The first and second pairs of actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P. The third and fourth pairs of actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P. As a result of this symmetrical arrangement, different combinations of the actuating forces Fa are capable of driving movement of the moveable part 6 with multiple degrees of freedom, as follows.

The first group of actuating forces Fa, when generated together, drive upwards movement, and the second group of actuating forces Fa, when generated together, drive downwards movement.

When the actuating forces Fa of the first pair of actuating units 80 and the actuating forces Fa of the second pair of actuating units 80 are differentially generated, tilting about y axis (i.e. Ry movement) can be driven. When the actuating forces Fa of the third pair of actuating units 80 and the actuating forces Fa of the fourth pair of actuating units 80 are differentially generated, tilting about x axis (i.e. Rx movement) can be driven. Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes x, y.

When the actuating forces Fa of the first actuating units 80 and the actuating forces Fa of the second actuating units 80 are differentially generated, movement along the y axis (i.e. Ty movement) can be driven. When the actuating forces Fa of the third actuating units 80 and the actuating forces Fa of the fourth actuating units 80 are differentially generated, movement along the x axis (i.e. Ty movement) can be driven. Movement in any arbitrary direction perpendicular to the primary axis P, z may be achieved as a linear combination of movements along the two lateral axes x, y. In some arrangements, sets of four forces, including two forces from each group, when generated together, drive movement along a lateral axis perpendicular to the primary axis z.

A first set of four actuating units 80, comprising one actuating unit 80 from each of the first, second, third and fourth pair of actuating units 80, are configured drive rotation of the movable part 6 relative to the support structure 5 in a first sense around the primary axis P (e.g. drive +Rz movement) when actuated together. A second set of four actuating units 80 (i.e. the remaining four actuating units 80), comprising one actuating unit 80 from each of the first, second, third and fourth pair of actuating units 80, are configured to drive rotation of the movable part 6 relative to the support structure 5 in a second, opposite sense around the primary axis P (e.g. drive -Rz movement) when actuated together.

As discussed above in relation to the actuator assembly 10 of Figure 1A, a control circuit can be electrically connected to the SMA wires 2 for supplying drive currents thereto to drive these movements, e.g. as described in WO 2011/104518 Al (which is herein incorporated by reference to the maximum extent permissible by law). The SMA wires 2 of the pair of actuating units 80 of Figure 2A cross over when viewed in a direction perpendicular to the SMA wires 2 and/or coupling flexures 83. However, as shown in Figure 2B, the SMA wires 2 of the pair of actuating units may instead be arranged to be parallel, or at least substantially parallel, to each other.

Second example of an actuator assembly

In a second example actuator assembly 10, the first and second pairs of actuating units 80 of Figure 3 are replaced with first and second pairs of actuating units 80 each corresponding to the pair shown in Figure 4A, and the third and fourth pairs of actuating units 80 of Figure 3 are replaced with third and fourth pairs of actuating units 80 each corresponding to the pair shown in Figure 4B (which is merely an upside-down flipped version of the pair of actuating units of Figure 4A).

The second example actuator assembly 10 is identical to the first example actuator assembly 10 except for the following differences.

The coupling flexures 83 are connected to corners of the movable part 6, rather than to a central portion of the movable part 6. In other words, the actuating units 80 are each configured to apply actuating forces Fa to corners of the movable part 6 (via moving mount portions 86), instead of configured to apply actuating forces Fa to central portions of the movable part 6 (via moving mount portions 86).

The ends 84s of the force-modifying flexures 84 are connected to central portions of the support structure 5, rather than to locations adjacent to the edges of the support structure 5.

Each of the first, second, third and fourth pair of actuating units 80 are configured to apply actuating forces Fa in directions towards each other, rather than in directions away from each other.

The body portions 82 of the second example actuator assembly 10 do not comprise the two arms of the body portions 82 of the first example actuator assembly 10.

Each pair of actuating units 80 are discrete units (i.e. are separate from each other), rather than integrally formed pairs of actuating units 80.

The second example actuator assembly 10 drives movement of the movable part 6 relative to the support structure 5 in the same way as the first example actuator assembly 10. Third example of an actuator assembly

In a third example actuator assembly 10, the eight SMA wires 2 of the actuator assembly 10 of Figure 1A are replaced with the actuating units 80 of Figure 5A on two sides and with the actuating units 80 of Figure 5B (which is merely an upside-down flipped version of the pair of actuating units of Figure 5A) on a different two sides of the actuator assembly 10, as shown in Figure 6.

The pair of actuating units 80 of Figure 5A is identical to the pair of actuating units 80 of Figure 2A except that one actuating unit 80 (the actuating unit 80 on the left) is flipped upside-down. As mentioned above, the pair of actuating units 80 of Figure 5B is merely an upside-down flipped version of the pair of actuating units of Figure 5A. As a result, each pair of actuating units 80 of this third example is configured to apply actuating forces Fa that are offset from each other along the primary axis P. Moreover, as a result, within each pair, the SMA wires 2 are parallel (or at least substantially parallel) to each other, and the coupling flexures are also parallel (or at least substantially parallel) to each other. Also, within each pair, the coupling flexures 83 connect to top and bottom locations (offset along the primary axis P) of the central moving mount portion 86 (or the movable part 6), rather than to the same Z-height (i.e. the same height/position along the primary axis P) as shown in Figure 2A.

As shown in Figure 6, the third example actuator assembly 10 comprises eight such actuating units 80 surrounding the movable part 6, instead of the eight SMA wires 2 of Figure 1A. The actuating units 80 are arranged between the support structure 5 and the movable part 6 so as to, on selective actuation, drive movement of the movable part 6 relative to the support structure 5.

The eight actuating units 80 of the actuator assembly 10 of Figure 6 are arranged such that they are capable of moving the movable part 6 relative to the support structure 5 in three translational degrees of freedom (Tx, Ty, Tz) and in two or three rotational degrees of freedom (Rx, Ry or Rx, Ry, Rz), as with the eight SMA wires 2 in the prior art actuator described in relation to Figure 1A.

As discussed, the actuating units 80 are arranged to apply actuating forces Fa to the movable part 6. The actuating forces Fa are arranged on each of four sides of the actuator assembly 10 (i.e. a first side, a second side, a third side and then a fourth side) around the primary axis P. Two actuating forces Fa are provided on each of the four sides. The two actuating forces Fa on each side are inclined in opposite directions along the primary axis P. The four sides extend in a loop around the primary axis P. In this example, the sides are perpendicular and so form a square as viewed along the primary axis P, but alternatively the sides could take a different e.g. quadrilateral shape. In this example, the forces are parallel to the outer faces of the square envelope of the moveable part 6 but this is not essential. A first, second, third, and fourth pair of actuating units 80 are arranged along the first, second, third and fourth sides of the actuator assembly 10 respectively, wherein the first and second sides are opposite sides through which the first axis x (herein also referred to as the x axis) extends and the third and fourth sides are opposite sides through which the second axis y (herein also referred to as y axis) extends.

The first, second, third, and fourth pairs of actuating units 80 each comprise an actuating unit 80 configured to apply an actuating force Fa with a force component in a first (e.g. upwards) direction along the primary axis P and an actuating unit 80 configured to apply an actuating force Fa with a force component in a second, opposite (e.g. downwards) direction along the primary axis P.

In other words, four actuating forces Fa, including one actuating force Fa on each of the sides, form a 'first' group that have a force component in one direction ('upwards' or '+z' direction) along the primary axis P, and the other four actuating forces Fa form a 'second' group that have a component in the opposite direction ('downwards' or '-z' direction) along the primary axis P. Herein, 'up' and 'down' generally refer to opposite directions along the primary axis P.

Both the first group of actuating forces Fa and the second group of actuating forces Fa are each arranged with two-fold rotational symmetry about the primary axis P. The eight actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P. The first and second pairs of actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P. The third and fourth pairs of actuating units 80 are arranged with two-fold rotational symmetry about the primary axis P.

As a result of this symmetrical arrangement, different combinations of the actuating forces Fa are capable of driving movement of the moveable part 6 with multiple degrees of freedom, as follows.

The first pair of the actuating units 80, when actuated together, are configured to apply a torque to the movable part 6 to drive rotation/tilting of the movable part 6 relative to the support structure 5 in a first sense about the first axis x. The second pair of the actuating units 80, when actuated together, are configured to apply a torque to the movable part 6 to drive rotation/tilting of the movable part 6 relative to the support structure 5 in a second, opposite, sense about the first axis x. The third pair of the actuating units 80 are configured to apply a torque to the movable part 6 to drive rotation/tilting of the movable part 6 relative to the support structure 5 in a first sense about the second axis y. The fourth pair of the actuating units 80 are configured to apply a torque to the movable part 6 to drive rotation/tilting of the movable part 6 relative to the support structure 5 in a second, opposite, sense about the second axis y. Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes x, y.

When the actuating forces Fa of the first actuating units 80 and the actuating forces Fa of the second actuating units 80 are differentially generated, movement along the y axis (i.e. Ty movement) can be driven. When the actuating forces Fa of the third actuating units 80 and the actuating forces Fa of the fourth actuating units 80 are differentially generated, movement along the x axis (i.e. Ty movement) can be driven. Movement in any arbitrary direction perpendicular to the primary axis P, z may be achieved as a linear combination of movements along the two lateral axes x, y.

A first set of four actuating units 80, comprising one actuating force Fa from each of the first, second, third and fourth pair of actuating units 80, are configured drive rotation of the movable part 6 relative to the support structure 5 in a first sense around the primary axis P (e.g. drive +Rz movement) when actuated together. A second set of four actuating units 80 (i.e. the remaining four actuating units 80), comprising one actuating force Fa from each of the first, second, third and fourth pair of actuating units 80, are configured to drive rotation of the movable part 6 relative to the support structure 5 in a second, opposite sense around the primary axis P (e.g. drive -Rz movement) when actuated together.

As discussed above in relation to the actuator assembly 10 of Figure 1A, a control circuit can be electrically connected to the SMA wires 2 for supplying drive currents thereto to drive these movements, e.g. as described in WO 2011/104518 Al.

As shown in Figure 7, one or more (or all) of the force-modifying flexures 84 of the third example could be arranged so as to be placed under compression on contraction of the corresponding SMA wires 2, instead of arranged so as to be placed in tension on contraction of the corresponding SMA wires 2. As shown in Figure 8, the coupling flexures 83 of each pair of actuating units 80 (i.e. the coupling flexures 83 of the first, second, third and/or fourth pair of actuating units 80) may cross the primary axis P when viewed along the first axis x or the second axis y. This may help reduce the XY footprint of the actuator assembly 10. Alternatively, this may allow the coupling flexures 83 to be longer in length without impacting the XY footprint of the actuator assembly 10 to gain extra stroke amplification for a given flexure design and wire length. This may also bring the parallel coupling flexures 83 and wires 2 closer together which may help reduce any secondary torque generated by the flexure system.

Fourth example of an actuator assembly

In a fourth example actuator assembly 10, the first and second pairs of actuating units 80 of Figure 6 are replaced with first and second pairs of actuating units 80 each corresponding to the pair shown in Figure 9, and the third and fourth pairs of actuating units 80 of Figure 6 are replaced with third and fourth pairs of actuating units 80 each corresponding to an upside-down flipped version (i.e. vertically flipped version) of the pair of actuating units 80 of Figure 9.

The fourth example actuator assembly 10 is identical to the fourth example actuator assembly 10 except for the following differences.

The ends 84s of the force-modifying flexures 84 are connected to central portions of the support structure 5, rather than at locations adjacent to the edges of the support structure 5.

Each of the first, second, third and fourth pair of actuating units 80 are configured to apply input forces Fi in directions away each other, rather than in directions towards each other. The coupling flexures 83 of each pair of actuating units 80 are not parallel to each other, but instead are substantially parallel to each other. It will, however, be appreciated that they may be parallel to each other.

Each pair of actuating units 80 are connected to each other via the ends 84s for connecting to the support structure 5, instead of being connected to each other via the moving mount portion 86. In other words, each of the first, second, third and fourth pair of actuating units 80 share a common end 84s for connecting to the support structure 5, instead of sharing a common moving mount portion 86.

The fourth example actuator assembly 10 drives movement of the movable part 6 relative to the support structure 5 in the same way as the third example actuator assembly 10.

Fifth example of an actuator assembly

In a fifth example actuator assembly 10, shown in Figure 11, the first and second pairs of actuating units 80 of Figure 6 are replaced with first and second pairs of actuating units 80 each corresponding to the pair shown in Figure 10, and the third and fourth pairs of actuating units 80 of Figure 6 are replaced with third and fourth pairs of actuating units 80 each corresponding to an upside-down flipped version (i.e. vertically flipped version) of the pair of actuating units 80 of Figure 10.

The fifth example actuator assembly 10 is identical to the fourth example actuator assembly 10 except for the following differences.

The SMA wires 2 of the actuating units 80 are arranged to extend perpendicular to the primary axis P, instead of being inclined in directions along the primary axis P.

The actuating units 80 of each pair are not integrally formed. In other words, each pair of actuating units 80 are not connected to each other. More specifically, the ends 84s of the force-modifying flexures 84 of each pair are not integrally formed. Instead, the actuating units 80 of each pair of actuating units 80 (i.e. each of the first, second, third, and fourth pair of actuating units 80) are separate from each other, i.e. are discrete units.

The actuating units 80 (e.g. the body portion 82 and/or the force-modifying flexure 84) cross the primary axis P when viewed along the first axis x or the second axis y.

The body portions 82 do not comprise the two arms of the body portions 82 of the fourth example actuator assembly 10. Each of the first, second, third and fourth pair of actuating units 80 are configured to apply input forces Fi in directions towards each other, rather than in directions away from each other.

The coupling flexures 83 of each pair of actuating units 80 are parallel to each other. It will, however, be appreciated that they may not be parallel to each other (e.g. may instead be substantially parallel to each other).

The fifth example actuator assembly 10 drives movement of the movable part 6 relative to the support structure 5 in the same way as the third example actuator assembly 10.

Further details

The SMA wires 2 of the actuating units 80 of Figures 2B, 5A, 5B, 6, 7, 8, 9, 10 and 11 do not cross/overlap each other when viewed along the x axis or the y axis. This may help reduce issues with SMA wires 2 contacting and rubbing over each other, leading to abrasion and wear of the wires 2. Moreover, the SMA wires 2 of the actuating units 80 of Figures 2B, 8, 9, 10 and 11 additionally do not cross/overlap with any other part of the actuating unit 80 (e.g. with the coupling flexure 83) when viewed along the x axis or the y axis. This may help reduce issues with SMA wires 2 contacting and rubbing with other parts of the actuating unit 80, leading to abrasion and wear of the wires 2.

The actuating units 80 of Figures 4A, 4B, 10, and 11 may be easily side mounted during assembly of the actuating assembly 10.

The actuating units 80 of Figures 4A and 4B may have SMA wires 2 that are longer in length compared to the actuating units 80 of Figures 10 and 11 for a given XY footprint.

One or more of the coupling flexures 83 of the actuating units 80 discussed herein may be inclined at an angle of 30 to 60 degrees, or more preferably 35 to 55 degrees, or most preferably 40 to 50 degrees relative to a plane perpendicular to the primary axis P. This may help ensure that the tilt that can be achieved after Rz movement is similar to the tilt that can be achieved in Rx and Ry.

The third, fourth and fifth examples of actuator assemblies 10 may provide better Rx, Ry and/or Rz performance compared to the first and second examples of actuator assemblies 10. The first and second examples of actuator assemblies 10 may provide better Tx and Ty performance compared to the third, fourth and fifth examples of actuator assemblies 10. In the third, fourth and fifth examples of actuator assemblies 10, the x axis may pass through the centre of the first and second pairs of actuating units 80 and the y axis may pass through the centre of the third and fourth pairs of actuating units 80.

Bearing arrangement

The embodiments described above can be used, amongst other things, to enable 2-axis or 3-axis module-tilt OIS. In such embodiments, the actuating units 80 are actuated so as to cause rotation of the movable part 6 relative to the support structure 5 about any axis substantially perpendicular to the primary axis P (i.e. so as to cause Rx and Ry movement of the movable part 6 relative to the support structure 5) and optionally about the primary axis P (i.e. Rz movement of the movable part 6 relative to the support structure 5). In such embodiments, the movable part 6 may be supported (e.g. suspended) on the support structure 5 exclusively by the actuating units 80. However, such embodiments may also have a bearing arrangement between the support structure 5 and the movable part 6. The bearing arrangement may be configured to allow rotation of the movable part 6 relative to the support structure 5 about any axis substantially perpendicular to the primary axis P and optionally about the primary axis P. The bearing arrangement may restrict other types of movement such as translational movement of the movable part 6 relative to the support structure 5, and therefore may help improve performance of the actuator assembly 10. The bearing arrangement may include, for example, one or more gimbals. The bearing arrangement may include, for example, bearing arrangements equivalent to those described in WO 2021/209770 Al (which is herein incorporated by reference to the maximum extent permissible by law) with reference to e.g. Figures 16 or 17 thereof.

Other variations

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

Although the actuating units 80 of Figures 2A, 2B, 3, 5A, 5B, 6, 7, 8 and 9 are integrally formed, this may not be the case. The actuating units 80 within each of pair may instead be discrete units. For example, the actuating units 80 of Figures 2A, 2B, 3, 5A, 5B, 6, 7 and 8 may not share a common moving mount portion 86, but may instead comprise separate moving mount portions 86. For example, the actuating units 80 of Figure 9 may not share a common end 84s for connecting to the support structure 5, but may instead comprise separate ends 84s for connecting to the support structure 5 (as e.g. shown in Figure 10).

Although the actuating units 80 of Figures 4A, 4B, 10 and 11 are not integrally formed, this may not be the case. The actuating units 80 within each of pair may instead be integrally formed. For example, the ends 84s for connecting to the support structure 5 of the actuating units 80 of Figures 4A, 4B, 10 and 11 may be integrally formed, as e.g. shown in Figure 9.

The actuator assembly 10 may comprise a biasing arrangement configured to bias the moveable part 6 and the support structure 5 towards each other e.g. such that, when the actuating units 80 are unpowered, the moveable part 6 is biased into engagement with one or more end stops of the support structure 5. The actuator assembly 10 may comprise a biasing arrangement configured, when the actuating units 80 are unpowered, to bias the moveable part 6 towards a pre-determined ('parking') position and/or orientation relative to the support structure 5. Examples of biasing arrangements that may be used with the actuator assembly 10 are described in WO 2021/005351 Al which is herein incorporated by reference to the maximum extent permissible by law.

The actuator assembly 10 may comprise a further ('AF' or 'auto-focus') actuator assembly configured to move one or more lenses of the lens assembly relative to the image sensor along an axis parallel to the optical axis (e.g. along the optical axis itself) of the one or more lenses. The 'AF' actuator assembly 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.

Although eight actuating units 80 are provided in the examples shown, it will be appreciated that a different number of actuating units 80 may instead be provided.

As mentioned above, although the actuator assembly 10 is described in connection with a camera, it will be appreciated that the actuator assembly 10 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 an emitter or a display in an augmented reality (AR) or virtual reality (VR) device.

SMA

The above-described actuating units 80 comprise at least one SMA wire, which more generally may be referred to as an SMA element. The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. 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 and/or other forming process(es). The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field.

Claims

1. An actuator assembly comprising a first part; a second part arranged to be movable relative to the first part; eight actuating units arranged, on actuation, to move the second part relative to the first part, wherein each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; an SMA element arranged, on actuation, to exert an input force on the body portion, thereby causing the force-modifying flexure to deform so as to modify the input force and cause the coupling link to apply an actuating force on the second part; wherein the eight actuating units are in an arrangement such that, on selective actuation, the eight actuating units apply non-colinear forces on the second part relative to the first part capable of moving the second part relative to the first part in up to six degrees of freedom.

2. An actuator assembly according to claim 1, wherein the non-collinear forces are capable of moving the second part relative to the first part in two or more rotational degrees of freedom or three translational degrees of freedom.

3. An actuator assembly according to any claim 1 or 2, wherein, in each actuating unit, the SMA element is connected between the body portion and the first part.

4. An actuator assembly according to any preceding claim, wherein the eight actuating units are arranged in four pairs of actuating units, wherein each pair of actuating units is arranged on a different side of the second part.

5. An actuator assembly according to claim 4, wherein each pair of actuating units comprises a respective first actuating unit and a respective second actuating unit, wherein for at least one pair, the arrangement of the second actuating unit corresponds to a reflection of the first actuating unit in a plane containing the primary axis.

6. An actuator assembly according to claim 4 or 5 wherein each pair of actuating units comprises a respective first actuating unit and a respective second actuating unit, wherein for at least one pair, the arrangement of the second actuating unit corresponds to a reflection of the first actuating unit in both a plane containing the primary axis and a plane substantially perpendicular to the primary axis.

7. An actuator assembly according to any one of claims 4 to 6, wherein, for at least one pair of actuating units, the coupling flexure of one actuating unit is connected to a side of the second part at or near one longitudinal end of the side, and the coupling flexure of the other actuating unit in the pair is connected to the side of the second part at or near the other longitudinal end of the side.

8. An actuator assembly according to any one of claims 4 to 7, wherein, for at least one pair of actuating units, the force-modifying flexure of each actuating unit in the pair is connected to a central portion of a side of the of first part, optionally wherein the force-modifying flexures are connected to the side at a point which is greater than 25% and less than 75% of the distance along the side.

9. An actuator assembly according to any one of claims 4 to 8, wherein for at least one pair of actuating units, the force-modifying elements of each actuating unit in the pair are arranged to be placed under compression by the respective body portions when the respective SMA elements exert an input force on the respective body portions.

10. An actuator assembly according to any preceding claim, wherein the coupling flexure, SMA element and the force-modifying flexure each extend from the body portion in a direction that is at least partly towards the same longitudinal end of the side.

11. An actuator assembly according to claim 4, wherein, in each actuating unit, the coupling flexure is connected to a central portion of a side of the second part, optionally wherein the coupling flexure is connected to the side at a point which is greater than 25% and less than 75% of the distance along the side.

12. An actuator assembly according to claim 4 or 5, wherein, in each pair of actuating units, the force-modifying flexure of one actuating unit is connected to a side of the first part at or near one longitudinal end of the side, and the force-modifying flexure of the other actuating unit is connected to the side at or near the other longitudinal end of the side.

13. An actuator assembly according to any one of claims 4 to 6, wherein, in each pair of actuating units, the coupling link of one actuating unit extends from the body portion to the second part in a direction that is at least partly towards one longitudinal end of a side, and the coupling link of the other actuating unit extends from the body portion to the second part in a direction that is at least partly towards the other longitudinal end of the side.

14. An actuator assembly according to claim 13, when the connection point between the coupling link of each actuating unit and the second part is located closer to the opposite longitudinal end of the side than the longitudinal end of the side at which the respective body portion is arranged.

15. An actuator assembly according to claim 4, 11, 12 or 13 when dependent on claim 3, wherein, in each actuating unit, the coupling link extends from the body portion to the second part in a direction that is at least partly towards a longitudinal end of a side, and the SMA element extends from the body portion to the first part in a direction that is at least partly towards the same longitudinal end of the side.

16. An actuator assembly according to any one of claims 4 to 15, wherein the SMA elements of each pair of actuating units cross over when viewed perpendicularly to the side on which they are arranged.

17. An actuator assembly according to any one of claims 4 to 16, wherein the SMA elements of each pair of actuating units do not cross over when viewed perpendicularly to the side on which they are arranged, optionally wherein the SMA elements of each pair of actuating units are parallel.

18. An actuator assembly according to any preceding claim, wherein the body portion, force modifying flexure and coupling flexure of each pair of actuating units are integrally formed.

19. An actuator assembly according to claim 3 or any one of claims 4 to 18 when dependent on claim 3, wherein the body portion of each actuating unit comprises a first arm extending between the connection point to the force-modifying flexure and the connection point to the SMA wire, and/or a second arm extending between the connection point to the force-modifying flexure and the connection point to the coupling flexure.

20. An actuator assembly according to claim 19, wherein the first arm extends away from the end of the SMA wire connected to the first part and/or wherein the second arm extends away from the end of the coupling flexure connected to the second part.

21. An actuator assembly according to claim 19 or 20 when dependent on claim 15, wherein, in each actuating unit, the first arm and/or the second arm extends away from the connection point to the force-modifying flexure in a direction that is at least partly towards the other longitudinal end of the side.

22. An actuator assembly according to claim 19 or 20 when dependent on claim 15, wherein, in each actuating unit, the first arm and/or second arm extends away from the connection point to the force modifying flexure in a direction that is at least party towards the same longitudinal end of the side.

23. An actuator assembly according to any preceding claim, wherein each actuating unit is configured such that the force-modifying flexure amplifies an amount of actuation of the SMA wire to a relatively greater amount of movement of the second part relative to the first part.

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

25. A camera assembly comprising: an actuator assembly according to any one of claims 1 to 23; and a support structure comprising one of the first and second parts of the actuator assembly; a module comprised in the other of the first and second parts of the actuator assembly, wherein the module comprises one or more lenses and an image sensor; wherein the actuator assembly is configured to rotate the module relative to the support structure in two or more rotational degrees of freedom.