Field

The present application relates to an actuator assembly with one or more actuating units, each of which includes a shape memory alloy (SMA) element.

Background

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

For example, WO 2013/175197 Al describes a camera in which four SMA wires are arranged to move a lens element relative to an image sensor in a plane that is perpendicular to the optical axis of the lens element, thereby effecting optical image stabilization (OIS). WO 2010/029316 Al describes SMA actuator wires used to provide OIS in a camera by tilting a camera module. WO 2011/104518 Al describes an actuator assembly having eight SMA wires capable of effecting positional control of a movable element with multiple degrees of freedom.

Typically, the range of movement (also known as "stroke") of such SMA actuator assemblies is limited by the maximum contraction of the SMA wires, and the actuating force is limited by the maximum force that can generated by the SMA wires. To increase the movement range or the actuating force, longer or thicker SMA actuator 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 amplify the movement range of the movable part, to amplify the actuating force acting on the movable part, or to re-direct the force applied by the SMA wire.

Summary

According to an aspect of the present invention, there is provided an actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; an SMA element connected between the body portion and the first part, and arranged, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part and configured to modify the input force so as to give rise to the actuating force, wherein the force-modifying element guides movement of the body portion along a path in an actuating plane on actuation of the SMA element, and a component configured to increase the effective stiffness of the force-modifying element in a direction orthogonal to the actuating plane.

In some embodiments, the force-modifying element comprises a first portion and a second portion, wherein the second portion is offset and/or spaced apart from the first portion in a direction orthogonal to the actuating plane, thereby forming the component configured to increase the effective stiffness of the force-modifying element in a direction orthogonal to the actuating plane.

In some embodiments, a gap is formed between the first and second portions when viewed in a direction along the actuating plane, wherein the extent of the gap in the direction orthogonal to the actuating plane may be at least half of, preferably at least equal to or at least twice, the extent of the thinner of the first and second portions.

In some embodiments, the SMA element and the first and second portions each extend parallel to the actuating plane, and the position of the SMA element along an axis orthogonal to the actuating plane is between, preferably substantially midway between, the positions of the first and second portions along the axis orthogonal to the actuating plane.

In some embodiments, each actuating unit further comprises a foot portion via which the forcemodifying flexure is connected to the first part, wherein the foot portion, the body portion and the force-modifying flexure each comprise a first portion and a second portion which are spaced apart in a direction along the primary axis.

In some embodiments, the first portions are integrally formed with each other and the second portions are integrally formed with each other.

In some embodiments, the body portion and the foot portion each further comprise a third portion which is located between, and attached to each of, the respective first and second portions.

In some embodiments, the SMA element is connected to the body portion via a connection element, wherein the connection element is integrally formed with the third portion of the body portion.

In some embodiments, the first and second portions comprise sheets of material, optionally wherein the third portion comprises a sheet of material. In some embodiments, the component comprises a compliant material arranged between a part of the actuating unit and at least one of the first and second parts.

In some embodiments, the compliant material comprises a gel.

In some embodiments, the compliant material is further configured to dampen oscillations of the actuating unit and/or of the second part relative to the first part.

In some embodiments, the component comprises a first magnet on the actuating unit, wherein the first magnet repels a second magnet that is spaced from the first magnet in one direction orthogonal to the actuating plane, and the first magnet repels a third magnet that is spaced from the first magnet in the other direction orthogonal to the actuating plane.

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 the second part capable of moving the second part relative to the first part, wherein each actuating unit comprises: a body portion; an SMA element connected between the body portion and the first part, and arranged, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part and configured to modify the input force so as to give rise to the actuating force, wherein the force-modifying element guides movement of the body portion along a path in an actuating plane on actuation of the SMA element, wherein at least one endstop is arranged between the actuating unit and the first or second part, the endstop being arranged to limit deformation of the actuating unit in a direction orthogonal to the actuating plane.

In some embodiments, at least one endstop is configured to engage a part of the actuating unit when the part of the actuating unit moves in a first direction orthogonal to the actuating plane, and at least one further endstop is arranged between the actuating unit and the first or second part and configured to engage a part of the actuating unit when the part of the actuating unit moves in a first direction orthogonal to the actuating plane, wherein the second direction is opposite to the first direction.

In some embodiments, each endstop comprises a first endstop surface on the actuating unit and a second endstop surface on the first or second part, wherein the first and second endstop surfaces are spaced apart, in particular by a constant distance, during normal operation of the actuating unit.

In some embodiments, wherein the first and second endstop are parallel to the actuating plane. In some embodiments, the first endstop surface is formed on a protrusion protruding from the actuating unit and/or the second endstop surface is formed on a protrusion protruding from the first or second part.

In some embodiments, the endstop is formed on the body portion of the actuating unit.

In some embodiments, the endstop is formed on the coupling link of the actuating unit.

In some embodiments, the clearance of the endstop during normal operation is in the range from 0 to 25% of the length of the force-modifying element, preferably in the range from 5% to 15% of the length of the force-modifying element. In general, the clearance may alternatively be greater than 1%, 2%, 3%, 7%, 12% or 15% of the length of the force-modifying element. The clearance may be less than 20%, 12%, 10%, 8%, 6% or 4% of the length of the force-modifying element.

In some embodiments, the clearance of the endstop during normal operation is in the range from 0 to 500um, preferably in the range from 100 to 300um. In general, the clearance may alternatively be greater than lOum, 20um, 40um, 60um, 80um or 150um. The clearance may be less than 1mm, 700um, 500um, 300um, 250um, 200um or 150um.

In some embodiments, the force-modifying element comprises a force-modifying flexure.

In some embodiments, the force-modifying element is arranged to be in tension on actuation of the SMA element.

In some embodiments, the force-modifying element is arranged at an angle relative to the SMA wire, preferably at an angle in the range from 13 to 77 degrees, optionally from 13 to 40 degrees or from 77 to 50 degrees.

In some embodiments, each actuating unit is configured so as to amplify an amount of actuation of the SMA element to a relatively greater amount of movement of the second part relative to the first part, optionally by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3.

In some embodiments, each actuating unit is configured so as to amplify the input force such that the actuation force is greater than the input force, optionally by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3. In some embodiments, each actuating unit further comprises a coupling link connected between the body portion and the second part, wherein the coupling link is configured to transmit the actuating force from the body portion to the second part, and wherein the coupling link is compliant in a direction perpendicular to the direction of the actuating force.

In some embodiments, the coupling link comprises a coupling flexure.

In some embodiments, the coupling link is arranged to be in tension on actuation of the SMA element.

In some embodiments, the angle between the coupling link and the SMA wire is in the range from 70 to 110 degrees.

In some embodiments, each actuating unit extends substantially in the actuating plane.

In some embodiments, the body portion and the force-modifying flexure are integrally formed from the same material, optionally wherein the coupling link is further formed from the same material.

Some embodiments comprise a total of four actuating units arranged to apply actuating forces such that none of the actuating forces are non-collinear.

In some embodiments, the four actuating units are arranged such that a first pair of actuating units applies actuating forces in opposite directions parallel to a first axis in a plane and a second pair of actuating units applies actuating forces in opposite directions parallel to a second axis in the plane, wherein the first and second axes are non-parallel.

In some embodiments, the first pair of actuating units is arranged to apply a torque to the second part relative to the first part in a first sense, and the second pair of actuating units is arranged to apply a torque to the second part relative to the first part in a second sense, wherein the second sense is opposite to the first sense.

Some embodiments comprise an image sensor and/or a lens assembly, wherein the image sensor or the lens assembly is fixed relative to the second part and/or the lens assembly or the image sensor is fixed relative to the first part. According to another aspect of the present invention, there is provided an actuator assembly comprising: first and second parts which are movable relative to each other; and one or more actuating units, each of which comprises: a body portion; a force-modifying mechanism connected between the body portion and the first part; a coupling link connected between the body portion and the second part; and an SMA wire connected between the first part and the body portion for applying an input force on the body portion thereby causing the body portion to apply an output force on the coupling link and causing the coupling link to apply an actuating force on the second part; wherein the actuating force has at least a major component in a plane perpendicular to a primary axis, and the coupling link is compliant in directions perpendicular to the actuating force; and wherein the actuator assembly further comprises one or more limiting arrangements, each of which is configured to limit movement along the primary axis of at least a part of at least one of the actuating units.

The one or more limiting arrangements may be the component for increasing the stiffness in a direction orthogonal to the actuating plane, or may be the endstop.

Thus, the limiting arrangement can limit (e.g. prevent or reduce) movement of the actuating unit along the primary axis which may occur due to unstable/unbalanced forces in the actuating unit and which may adversely affect performance or reliability of the actuator assembly.

The actuating force having at least a major component in a plane perpendicular to the primary axis means, for example, that the actuating force is directed at an angle of less than 45° to the plane. The angle is typically substantially less than this (e.g. less than 5°) and the angle may be approximately zero, that is to say that the actuating force is in the plane.

The coupling link may correspond to a coupling flexure and the force-modifying mechanism may correspond to a force-modifying flexure.

Alternatively, the coupling link and/or the force-modifying mechanism may correspond to any of the non-flexure examples provided in WO2022/084699, which is incorporated by reference

At least one of the limiting arrangements may comprise an endstop configured to engage a part of the actuating unit when the part of the actuating unit moves in one direction along the primary axis.

The at least one of the limiting arrangements may comprises a further endstop configured to engage a part of the actuating unit when the part of the actuating unit moves in the other direction along the primary axis. The endstop may be comprised in the first part or the second part. The further endstop may be comprised in the first part or the second part.

At least one of the limiting arrangements may comprise a bearing between a part of the actuating unit and another part of the actuator assembly.

The other part may be comprised in the first part or the second part.

The actuator assembly may be configured to generate a biasing force to bias the part of the actuating unit against the other part of the actuator assembly.

The biasing force may be generated by way of a pre-stress in the force-modifying flexure.

The biasing force may be generated by the SMA wire when the SMA wire is in tension. To provide for this, the SMA wire and/or the force-modifying flexure may extend at a non-zero angle to the plane perpendicular to the primary axis.

The bearing may be a plain bearing or a rolling (e.g. ball) bearing.

The other part of the actuator assembly may comprise a planar surface that is perpendicular to the primary axis.

At least one of the limiting arrangements may comprise a first magnet on the actuating unit. The first magnet may repel a second magnet that is spaced from the first magnet in one direction along the primary axis, and the first magnet may repel a third magnet that is spaced from the first magnet in the other direction along the primary axis.

At least one of the limiting arrangements may comprise compliant material arranged between a part of the actuating unit and at least one of the first and second parts.

The compliant material may remain in contact with the part of the actuating unit during operation of the actuator assembly. The compliant material may be a gel.

At least one of the limiting arrangements may be configured to limit movement of at least part of the body portion of an actuating unit. When viewed along the primary axis, the body portion may be wider than the coupling flexure and/or the force-modifying flexure.

At least one of the limiting arrangements may be configured to limit movement of a plurality of parts of an actuating unit, and the plurality of parts are spaced from each other when viewed along the primary axis.

In at least one of the actuating units, the force-modifying flexure may comprise a first portion and a second portion which is offset and/or spaced from the first portion in a direction along the primary axis, thereby forming a limiting arrangement.

In the at least one of the actuating units, the SMA wire and the first and second portions may each extend perpendicularly to the primary axis, and the position of the wire along the primary axis may be substantially midway between the positions of the first and second portions along the primary axis.

The at least one of the actuating units may comprises a foot portion via which the force-modifying flexure is connected to the first part.

The body portion, the force-modifying flexure, and the foot portion may be configured such that the force-modifying flexure is in tension when the SMA wire is in tension.

In the at least one of the actuating units, the foot portion, the body portion and the force-modifying flexure may each comprise a first portion and a second portion which is spaced from the first portion in a direction along the primary axis. The first portions may be integrally formed with each other, and the second portions may be integrally formed with each other. The body portion and the foot portion may each further comprise a third portion which is located between, and attached to each of, the first and second portions.

The first, second and third portions may be formed from metal sheet.

In the at least one of the actuating units, the SMA wire may be connected to the body portion via a crimp. The crimp may be integrally formed with the third portion of the body portion. The crimp may be integrally formed with the first portion or the second portion of the body portion. The coupling flexure may be integrally formed with the first portion, second portion or third portion of the body portion.

The actuator assembly may comprise at least two actuating units arranged to apply actuating forces on the second part in perpendicular directions such that the coupling link of each of the two actuating units is compliant in the direction of the actuating force of the other of the two actuating units.

The first and second parts may be movable relative to each other in any direction in a plane perpendicular to the primary axis.

The actuator assembly may comprise four actuating units arranged so as to be capable of moving the second part relative to the first part in any direction in a plane perpendicular to the primary axis without applying any net torque to the second part about the primary axis.

The actuating units may be arranged so as to be capable of rotating the second part relative to the first part about any axis perpendicular to and intersecting the primary axis.

The actuator assembly may include a suitable bearing arrangement to allow such movements.

There may be provided a camera assembly comprising the actuator assembly, wherein the second part comprises an image sensor having an imaging axis parallel to the primary axis, and wherein the actuator assembly is for providing sensor-shift optical image stabilisation.

However, the actuator assembly may be used in any system or device, e.g. a head-mounted display.

Brief description of the drawings

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

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

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

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;

Figure 4 is a schematic plan view of an arrangement of four actuating units; Figures 5 is a schematic perspective view of an arrangement of eight actuating units;

Figures 6a and 6b are examples of an actuator assembly with an actuating unit in a central position and in two possible non-central positions;

Figures 7a-e show a two-layer actuating unit forming a component for increasing the stiffness of a forcemodifying element in directions orthogonal to the actuating plane;

Figures 8a and b show ways of forming the two-layer actuating unit;

Figures 9a-c show further components for increasing the stiffness of a force-modifying element in directions orthogonal to the actuating plan;

Figure 10 schematically shows endstops to limit out-of-plane deformation of the actuating unit; and Figures 11 to 13 show particular embodiments of the schematic endstops of Figure lOis a perspective view of an example of the actuator assembly of Figure 10.

Detailed description

Camera module

Figures 1A-E schematically shows different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera module 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.

The movable part 20 may be supported (i.e. suspended) on the support structure 10 exclusively by the actuating units 30. Alternatively, the actuator assembly 2 may include a bearing arrangement 40 that supports the movable part 20 on the support structure 10. The actuating units 30 and the bearing arrangement 40 may together support the movable part 20 on the support structure 10. The bearing arrangement 40 may have any suitable form for allowing movement of the movable part 20 with respect to the support structure 10 with one or more degrees of freedom (DOFs). The actuating units 30 and/or the bearing arrangement 40 may constrain, i.e. reduce or prevent, other DOFs of movement of the movable part 20 relative to the support structure 10. For this purpose, the bearing arrangement 40 may, for example, include one or more of the following bearings: a rolling bearing (such as a ball bearing), a flexure bearing (i.e. an arrangement of flexures or other resilient elements that guide movement), or a plain (i.e. sliding contact) bearing.

A primary axis P can be defined with reference to the actuator assembly 2 and/or the support structure 10. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2. In some examples, the actuator assembly 2, the support structure 10 and/or the movable part 20 extends predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 2, the support structure 10 and/or the movable part 20 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. 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:

• 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.

• Rx and Ry: Rotational movement (or simply rotation or tilting) about the x and y axes. In other words, the movable part 20 may be rotated about any line perpendicular to the primary axis P. The movable part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement. Instead of such two-axis rotation, the movable part 20 may be rotatable about a single axis, e.g. about the x or y axis. Tz: Translational movement along the z axis. The movable part 20 may be movable to any translational position along the z axis within a range of movement.

• Rz: Rotational movement (or simply rotation) about the z axis. The movable part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement.

In some examples, the movable part 20 may be supported, e.g. by the bearing arrangement 40, so as to allow translational movement in the x-y plane (Tx, Ty) and/or rotational movement about the z axis (Rz). Translational movement along the z axis (Tz) and rotational movement about the x and y axes (Rx, Ry) may be constrained. Such support may be provided, for example, with a bearing arrangement 40 with a suitable arrangement of ball bearings or plain bearings which produce bearing forces in the +z direction and a biasing arrangement which produces a biasing force in the -z direction. Examples of actuator assemblies with such a bearing arrangement are disclosed in WO 2013/175197 Al and WO 2017/072525 Al, each of which is herein incorporated by reference.

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.

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.

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, Tx, 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.

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.

The bearing arrangement 40 may cause the movable part 20 to move in directions which differ from the directions of the actuating forces F. In simple examples of this, one component of each actuating force F causes the movement of the movable part 20, and another component of each actuating force F acts against the bearing forces produced by the bearing arrangement 40.

The camera module 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 module 1 may be a compact camera module in which each lens has a diameter of 20mm or less, for example of 12mm or less.

In the ("sensor-shift") variation of the camera module 1 shown in Figure 1A, the movable part 20 includes the image sensor 4. The lens assembly 3 may be fixed relative to the support structure 10, or may be movable relative to the support structure 10 along the optical axis O, as described below.

In the ("lens-shift") variation shown in Figure IB, the image sensor 4 is fixed relative to the support structure 10 and the movable part 20 includes the lens assembly 3. The lens assembly 3 may be movable relative to the movable part 20 along the optical axis O, as described below.

In both of these variations, the actuator assembly 2 is configured to move the lens assembly 3 relative to the image sensor 4 in any direction in the plane perpendicular to the primary axis P and hence the optical axis O. Such movement has the effect of moving the image on the image sensor 4 and enables optical image stabilisation (OIS) to be implemented in the camera module 1. In the sensor-shift variation, the movable part 20 may also be rotatable about the primary axis P so as to also enable compensation for roll.

In the ("module-tilt") variation shown in Figure 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 module 1.

In the ("autofocus") 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 primary axis P and hence the optical axis O. Such movement has the effect of adjusting the focus of the image on the image sensor 4. So, auto-focus (AF) or zoom functionality can be implemented in the camera module 1.

In some examples (not shown), the camera module 1 may include a first actuator assembly for providing OIS as illustrated in Figures 1A-C, and a second actuator assembly for providing AF as illustrated in Figure ID. One or both of the first and second actuator assemblies may correspond to actuator assemblies 2 as described herein. One of the first and second actuator assemblies may be another type of SMA actuator assembly or may be a non-SMA actuator assembly, e.g. a voice-coil motor (VCM) actuator assembly. As will be appreciated, in the lens-shift and module-tilt variations, the support structure 10 of the second actuator assembly 2 is fixed to (or corresponds to) the movable part 20 of the first actuator assembly 2.

In the ("AF+OIS") variation shown in Figure IE, the movable part 20 includes the lens assembly 3 and the actuator assembly 2 produces three-dimensional translational movement of the movable part 20 relative to the support structure 10, enabling both AF and OIS to be implemented using one actuator assembly 2.

Other variations are also possible. For example, in the autofocus variation or the AF+OIS variation, the movable part 20 may include the image sensor 4 rather than the lens assembly 3. The camera module 1 may include combinations of the above-described features, e.g. (a) lens shift and sensor shift, (b) module tilt and lens shift or sensor shift and autofocus, or (c) module tilt and AF+OIS.

The camera module 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 move the movable part 20. The drive signals are chosen to drive 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/zoom by adjusting the focus of the image sensed by the image sensor 4. The controller 8 supplies the generated drive signals to the SMA wires 34.

Optionally, the camera module 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 module 1, which can be processed so as to produce signals representative of the required movement of the movable part 20 to compensate for such shake. The controller 8 receives such signals and can generate the drive signals for the SMA wires 34 to achieve OIS.

Although the actuator assembly 2 is described in connection with a camera module 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

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.

A single actuating unit 30 is shown in Figures 3A and 3B, but it will be appreciated that the actuator assembly 2 generally has multiple actuating units 30, each of which may include the same components described with reference to Figures 3A and 3B.

The actuating unit 30 includes a body portion 31 to which several other components of the actuating unit 30 are connected as described below. Typically, the body portion 31 is relatively rigid compared to the other components of the actuating unit, and does not deform significantly on actuation of the actuating unit 30. 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. 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. In the depicted design, the force-modifying flexure is formed integrally with the foot portion 36 and with the body portion 31, for example from a single sheet of material (such as metal). The force-modifying flexure 32 allows the body portion 31 to pivot relative to the support structure 10 about an effective pivot point P. Although the effective pivot point P is shown in Figure 3B as being positioned in the middle of force-modifying flexure 32, the effective pivot point P may have a different position and also need not lie on the force-modifying flexure 32. Such pivotal movement of the body portion 31 relative to the support structure 10 is initially in a direction that is substantially perpendicular to the force-modifying flexure 32.

The actuating unit 30 also includes an SMA element 34. In this example, the SMA element 34 is an SMA wire 34. The SMA wire 34 is connected between the body portion 31 and the support structure 10. One end of the SMA wire 34 is connected to the support structure 10, e.g. by a crimp 15. The other end of the SMA wire 34 is connected to the body portion 31, e.g. by a crimp 35.

The actuating unit 30 also includes a coupling link 33. In this example, the coupling link 33 is a coupling flexure 33. The coupling flexure 33 is connected between the body portion 31 and the movable part 20. One end of the coupling flexure 33 is connected to the body portion 31. The other end of the coupling flexure 33 is connected to the movable part 20. The coupling link 33 transfers or transmits an actuating force F from the body portion 31 to the movable part 20. The coupling link 33 is compliant (i.e. deformable) in a direction (or in multiple directions) perpendicular to the actuating force F. This allows the movable part 20 to move in directions other than the direction of the coupling flexure 33 and actuating force F. This can be needed, for example, where different actuating units 30 cause the movable part 20 to move in different directions.

The SMA wire 34 is arranged, on contraction, to apply an input force Fi on the body portion 31. The input force Fi acts parallel to the length of the SMA wire 34. The force-modifying flexure 32 and the body portion 31 are arranged to modify the input force Fi so as to give rise to the actuating force F, which is transmitted from the body portion 31 to the movable part 20 by the coupling flexure 33. In particular, the input force Fi deforms the force-modifying flexure 32, thereby causing the body portion 31 to pivot about the effective pivot point P. In simple terms, the force-modifying flexure 32 and the body portion 31 act like a lever. The force-modifying flexure 32 and the body portion 31 may modify the direction and/or the magnitude of the input force Fi so as to give rise to the actuating force F. In the example illustrated in Figures 3A and 3B, the coupling flexure 33 is at an angle of -90° relative to the SMA wire 34. Also, in this example, the force-modifying flexure 32 is arranged at an angle a of -30° relative to the SMA wire 34, and the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. Hence, on contraction of the SMA wire 34 and on resulting deformation of the forcemodifying flexure 32, the body portion 31 initially moves at an angle of -60° (90°-a) relative to the length of the SMA wire 34. Thus, it will be appreciated that, in this example, the force is de-amplified and the stroke is amplified, while the direction of the forces/movements is changed by an angle of -90°.

More generally, the change in direction of the force depends on the angle between the SMA wire 34 and the coupling flexure 33. Also more generally, the change in magnitude of the force is dependent on the ratio of i) the distance Ds from the effective pivot point P to the line on which the SMA wire 34 lies and ii) the distance De from the effective pivot point P to the line on which the coupling flexure 33 lies. In particular, F/Fi is proportional to Ds/Dc. If the SMA wire 34 lies on a line that is closer to the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is de-amplified. At the same time, the movement of the movable part 20 is amplified, i.e. increased relative to a change in length of the SMA wire 34. Alternatively, if the SMA wire 34 lies on a line that is further away from the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is amplified. At the same time, the movement of the movable part 20 is de-amplified, i.e. decreased relative to a change in length of the SMA wire 34. The actuating unit 30 can thus be configured to amplify movement or to amplify force due to contraction of the SMA wire 34. The actuating unit 30 can also be configured to change the direction of the input force Fi. In some examples, the actuating unit 30 is configured to change the direction of the input force Fi without changing the magnitude of the force or movement.

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 Ds could be increased by connecting the coupling flexure 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: adjusting the angle of SMA wire 34 (and thus the input force Fi);

• adjusting the location of the connection point between the SMA wire 34 and the body portion 31 (and thus the location at which the input force Fi acts on the body portion 31);

• adjusting the angle of the coupling flexure 33 (and thus the actuating force F); and/or

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

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.

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.

For instance, in the actuating unit 30 illustrated in Figure 3C, the coupling flexure 33 is substantially perpendicular to the SMA wire 34.

In the above-described examples, the actuating unit 30 is arranged in a plane. In particular, the SMA wire 34, the coupling flexure 33 and the 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. 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 and making the actuator assembly 2 more reliable. However, the forcemodifying flexure 32 could instead be arranged so as to be placed under compression on contraction of the SMA wire 34. 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.

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. units

Figure 4 schematically shows a plan view of an example of the actuator assembly 2, showing an arrangement of actuating units 30. In this example, the actuator assembly 2 includes a total of four actuating units 30. The four actuating units 30 may apply actuating forces F between the movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10. The arrangement of actuating units 30 of Figure 4 may be used, for example, in examples in which the movable part 20 is movable relative to the support structure 10 in a movement plane. So, Tx, Ty and optionally Rz movement of the movable part 20 may be allowed.

The four actuating units 30 of Figure 4 are in an arrangement capable of applying actuating forces F so as to move the movable part 20 relative to the support structure 10 to any position within a range of movement. The range of movement may be within a movement plane that is perpendicular to the primary axis P.

In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a first axis (e.g. the x axis). The other two of 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. 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.

In some examples, none of the actuating forces F are collinear. This allows the arrangement of actuating units 30 to translationally move the movable part 20 without applying any net torque to the movable part 20. So, the movable part 20 can be moved translationally in the movement plane without rotating the movable part 20 in the movement plane. In general, the arrangement of actuating units 30 is capable of accurately controlling a torque or moment of the movable part 20 about the primary axis P. So, the actuating units 30 are capable of rotating (or not rotating) the movable part 20 relative to the support structure about the primary axis P.

In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a first sense (e.g. clockwise) around the primary axis P. The other two actuating units 30 (e.g. the left and right actuating units 30 in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a second, opposite sense (e.g. anti-clockwise) around the primary axis P. This allows the movable part 20 to be rotated by simultaneously increasing or decreasing the tension of SMA wires in any of the two actuating units 30. As shown, two actuating units 30 may be arranged to apply actuating forces F in a corner of the actuator assembly 2. The other two actuating units 30 may be arranged to apply actuating forces F in another, opposite corner of the actuator assembly 2. The actuator assembly 2, and in particular the movable part 20 and/or the support structure 10, may have a square or rectangular footprint. Each actuating unit 30 may be provided on one of the four sides of the actuator assembly 2. In particular, each actuating unit 30 may bend around a corner of the movable part 20 such that the SMA wire 34 and the coupling flexure 33 of each actuating unit 30 extend along adjacent edges of the movable part 20. So, the actuating unit 30 may be as configured in Figures 3A and 3B, for example. The four SMA wires 32 of the four actuating units 32 may extend along the four different edges of the movable part 20.

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.

In this example, the actuating forces F are perpendicular to the primary axis P, and may be parallel to the movement plane. However, in general the actuating forces F may be angled relative to the movement plane. The actuating forces F may thus have a component along the primary axis P. This component along the primary axis P may be resisted by the bearing arrangement 40, for example, to provide movement of the movable part 20 in degrees of freedom allowed by the bearing arrangement 40. In some examples, it may even be desirable for actuating forces F to have a component in parallel to the primary axis P, for example so as to load plain or rolling bearings arranged between the movable part 20 and the support structure 10.

Although, for illustrative purposes, the arrangement of actuating units 30 was described as moving the movable part 20 in the movement plane (e.g. translationally along the x and y axis, or rotationally about the primary axis P), in other examples the movable part 20 may be moved differently. For example, the same arrangement of actuating forces F may be used to tilt the movable part 20 relative to the support structure 10 about axes perpendicular to the primary axis P, due to appropriate movement constraints provided by the bearing arrangement 40. For example, the bearing arrangement 40 may include a plurality of flexures for guiding tilting of the movable part 20 about the axes perpendicular to the primary axis P. Examples of such bearing arrangement 40 are described in WO2022/029441 Al, which is herein incorporated by reference.

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

Figures 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.

The arrangement of actuating units 30 of Figures 5A and 5B 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).

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.

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 with respect to each other, as 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, 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 actuating forces F are parallel to the outer faces of the square envelope of the moveable part 6 but this is not essential.

Four actuating forces F, including one force on each of the sides, form a 'first' group that have a component in one direction ('upwards' or +z) and the other four actuating forces F form a 'second' group that have a component in the opposite direction ('downwards' or -z). Herein, 'up' and 'down' refer to opposite directions along the primary axis P. The actuating forces F have a symmetrical arrangement in which their magnitudes and inclination angles are the same, so that both the first group of actuating forces F and the second group of actuating forces F are each arranged with two-fold rotational symmetry about the primary axis P.

As a result of this symmetrical arrangement, different combinations of the actuating forces F are capable of driving movement of the moveable 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 equally, drive downwards (-z) movement.

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.

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.

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 maybe 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).

Movement of actuating units along the primary axis

Referring in particular to Figures 6a and 6b, the issue of movement of actuating units along the primary axis will now be explained with reference to a comparative example of an actuator assembly without any bearing arrangement 50.

When an actuating unit 30 is subject to a relatively low force, as illustrated in Figure 6a, the actuating unit 30 (including the body portion 31, the force-modifying flexure 32, and the coupling link 33) extends parallel to the actuating plane. The size of the gap between the actuating unit 30 and the support structure 10 and/or movable part 20 may be substantially constant. However, when an actuating unit 30 is subject to a relatively large force, the actuating unit 30 may be susceptible to bending out of the actuating plane so that at least part of it is displaced along the primary axis P. Such undesired out-of-plane deformation may also arise when the SMA wire 34 and coupling link 33 are not in plane with the force-modifying element 32 (e.g. due to assembly misalignments), and so forces on the body portion 31 may create a moment that acts to rotate the body portion out of plane, rotating around the effective pivot of the force-modifying element 34. In extreme cases (high force or large misalignment) the moving crimp 35 may lift so far that the actuating unit 30 becomes unstable and folds over on itself.

This is schematically illustrated in Figure 6b. Relatively large forces may be, for example, due to the tension in the SMA wire 34 of the actuating unit 30 and/or due to the other actuating units 30. As will be appreciated, this may be due to unstable or unbalanced input and output forces on the body portion 31. Furthermore, impulses acting on the actuator assembly 2, for example due to drops or other impacts, may result in deformation of the actuating unit 30 out of the actuating plane. Deformation out of the actuating plane may be only by a small amount or may continue until part of the actuating unit 30 contacts the support structure 10 and/or movable part 20. In any case, the accuracy of actuation of the actuating unit may be reduced, and/or the actuating unit 30 is at risk of damage due to such undesirable deformation. So, the performance and/or reliability of the actuator assembly 2 may be adversely affected.

Managing out-of-plane deformation of the actuating unit

The inventors have identified this issue of possible undesirable out-of-plane deformation of the actuating unit 30. According to an aspect of the present invention, a component for increasing the effective stiffness of the actuating unit, in particular of the force-modifying element 34, in a direction orthogonal to the actuating plane is provided. This may reduce the extent and/or risk of undesirable out-of-plane deformation. According to another aspect of the invention, endstop components that engage on out-of- plane deformation of the actuating unit 30 are provided. This reduces the risk and/or extent of damage to the actuating unit 30 due to such out-of-plane deformation. The present invention is thus concerned with improving the reliability and/or performance of the actuating unit 30. Component for increasing effective out-of-plane stiffness

According to aspects of the present invention, a component 50 is provided to increase the effective stiffness of the force-modifying element 34 in a direction orthogonal to the actuating plane. The effective stiffness of the force-modifying element 34 may be increased compared to a situation in which the component 50 is not provided. The component 50 may thus help resist out-of-plane deformation of the actuating unit 30, making the actuating unit 50 more reliable and reducing the risk of damage thereto.

Double-decker flexure arrangement

Figures 7a-7d schematically show embodiment of the actuator assembly 30 in which the component 50 forms part of the force-modifying element 32. In particular, the component 50 is embodied as a second portion 32b of the force-modifying element 32.

Referring in particular to Figure 7a, the force-modifying flexure 32 comprises a first portion 32a and a second portion 32b. The second portion 32b is offset and/or spaced apart from the first portion 32a in a direction orthogonal to the actuating plane. .

This increases the effective stiffness of the force-modifying flexure 32 and reduce the likelihood of out- of-plane bending of the force-modifying flexure 32.

In the examples of Figures 7a and 7b, the first and second portions 32a, 32b are spaced apart from each other. In particular, a gap is formed between the two portions 32a, 32b. The extent of the gap in the direction orthogonal to the actuating plane may be at least half of, preferably at least equal to or at least twice, the extent of the thinner of the first and second portions 32a, 32b. This leads to an increase the relevant effective stiffness of the force-modifying flexure 32, without increasing the stiffness in the actuating plane of the force-modifying mechanism (beyond the initial increase associated with providing the two portions 32a, 32b).

Furthermore, in the examples of Figures 7a and 7b, the SMA wire 34 (in particular the portion of the SMA wire 34 connected to the body portion 31, i.e. the moving crimp 35) is positioned midway between the two portions 32a, 32b of the force-modifying flexure 32. This is preferable because it may improve the stability of the system. In general, the SMA wire 34 may be positioned between the two portions

32a, 32b.

In other embodiments, the two portions 32a, 32b of the force-modifying flexure 32 may be in contact with each other, but offset in a direction orthogonal to the actuating plane. This is shown, for example, in Figure 7c.

The two portions 32a, 32b may be different sheets of material. Each portion 32a, 32b may be formed from sheet metal, for example.

The two portions 32a, 32b may be connected to each other at least by the connection to the body portion 31 and by the connection to the support structure 10. So, each of the two portions 32a, 32b may be connected at one end to the support structure 10 and at the other end to the body portion 31. The two portions 32a, 32b may extend substantially parallel to each other when viewed along the actuating plane. Between the connections, the two portions 32a, 32b may coincide when viewed orthogonally to the actuating plane, i.e. the two portions 32a, 32b may have substantially the same shape, i.e. the same footprint or profile when viewed orthogonally to the actuating plane.

The two portions 32a, 32b are thus connected to each other at the body portion 31 and at the foot portion 36. This may be achieved in different manners.

In particular, as depicted in Figure 7b, the foot portion 36, the body portion 31 and the force-modifying flexure 32 may each comprise a first portion (labelled a) and a second portion (labelled b) which is spaced from the first portion in a direction orthogonal to the actuating plane. In the depicted embodiments, the first portions 36a, 32a, 31a are integrally formed with each other and the second portions 36b, 32b, 31b are integrally formed with each other. However, in general, the first and second portions may be separate parts that are connected to each other.

The body portion 31 and the foot portion 36 may each further comprise a third portion (labelled c) which is located between, and attached to each of, the first and second portions. The third portion 36c of the foot portion 36 is provided between the first and second portions 36a, 36b of the foot portion, in particular when viewed along the actuating plane. The third portion 36c of the foot portion 36 is provided between the first and second portions 36a, 36b of the foot portion, in particular when viewed along the actuating plane. A third portion is not provided for the force-modifying flexure 32, because a gap is instead formed between the first and second portions 32a, 32b of the force-modifying flexure 32. Figure 7d depicts an alternative embodiment in which the third portion 36c is provided as a plurality of smaller spacers between the first and second portions of the foot portion 36 and of the body portion 31, instead of as a separate sheet or layer. In particular, the third portion is formed as a plurality of spacers 31c, 36c used to space the first and second portions apart. The spacers 31c, 36c need not be provided entirely between the two portions, but may be provided only in a relatively small proportion of the space between the two portions. Although not shows, such spacers may also be provided between the two portions 32a, 32b of the force-modifying flexure 32.

In some embodiments, the gap between the portions 32a, 32b of the force-modifying flexure 32 may be filled with air or another atmosphere. So, the gap may be considered empty. Alternatively, a relatively low stiffness material (such as a gel or foam) may be provided in the gap.

In the depicted embodiments, the first, second and third portions are formed from a sheet material. The portions may be formed from sheet metal, for example, by etching.

The moving crimps 35 (or other connection element 35) may be integrally formed with the third portion 31c of the body portion 31c. This allows the connection element 35 to have a 'midway' location as described above. Alternatively, (especially when no third portion is provided) the moving crimp 35 may be integrally formed with the first portion 31a or the second 32b portion of the body portion, e.g. as in the embodiment of Figure 7c. Similarly, the coupling flexure 33 may be integrally formed with the first portion 31a, second portion 31b or third portion 31c of the body portion.

Instead of using a third portion of the body portion 31 and/or the foot portion 36 to connect to the two portions 32a, 32b of the force-modifying flexure 32 and serve as 'spacers' as described above, the actuating unit 30 may include a 'jog' 37. This is schematically illustrated in Figure 7e, for example. A jog 37 may be provided on the side of the foot portion 36 and/or on the side of the body portion 31. The jog 37 provides the space between the different portions 32a, 32b of the force-modifying flexure 32.

Figures 8a and 8b schematically show how the first and second portions of the force-modifying flexure 32, body portion 31 and foot portion 36 may be formed from a single sheet of material. So, in some embodiments, the first and second portions are formed from a folded sheet of material, such as sheet metal. The actuating unit 30 may comprise a fold between the two portions of the body portion 31, or between the two portions of the foot portion 36.

Figure 8b schematically depicts a variety of ways to create the first and second portions. The first and second portions may be formed: A. From a sheet material that is folded at one end with the two portions in contact (i.e. back to back). There may be no spacing between the two portions (note could be 2 separate parts, could be more that 2 layers)

B. From a sheet material that is folded at one end with a jog at the other to create the gap/spacing

C. From a sheet material that is folded at one end, with a third portion or spacer at the other to create spacing

D. From separate sheets (i.e. not connected by a fold), one having a jog at both ends to create the gap/spacing.

E. From a sheet material that is folded into wedge shape (no jog needed), and spaced at one end.

F. From a sheet material that is folded into wedge shape that has been bent downwards such that the nominal line of the SMA wire force is acting long the middle of the wedge, increasing stability.

Component separate from flexure arrangement

Figures 9a-c schematically show embodiments of the component 50 when it is not provided as part of the force-modifying flexure 32. In particular, the component 50 is formed separately from the forcemodifying flexure 32, and does not serve for force or stroke amplification. It will be appreciated that the component 50 described in relation to Figures 9a-c may be provided in addition to the component 50 described in relation to Figures 7 and 8, thereby further contributing to the increase in effective stiffness.

Referring in particular to Figure 9a, the component 50 is embodied by a compliant material 54.

The compliant material 54 may consist of a gel 54, such as a damping gel, for example. In general, the compliant material 54 may be any material with relatively lower shear modulus (thereby allowing compliance in a direction along the actuating plane) and relatively higher elastic modulus in the direction orthogonal to the actuating plane. The compliant material 54 may be a liquid material and/or a viscous material, for example.

The compliant material 54 is arranged between a part of the actuating unit 30, e.g. part of the body portion 31, and the support structure 10. In this example, the compliant material 54 is attached to and/or remains in contact with both the actuating unit 30 (in particular the body portion 31) and the support structure 30 during operation of the actuator assembly 2. Although not shown, pockets or depressions may be formed in the support structure 10 and/or body portion 31 (e.g. a partial etch in the body portion). The compliant material 54 may be arranged in the pockets or depressions, improving retainment of the compliant material 54 in position. The compliant material 54 is applied such that the body portion 31 is suspended on or within the compliant material 54and so as to allow a full range of motion of the body portion 31 in the actuating plane, while increasing the stiffness in directions orthogonal to the actuating plane.

The compliant material 54 may also have the additional benefit of damping oscillations and resonant behaviour of the actuator assembly 2.

The compliant material 54 may alternatively be attached to a part of the actuator assembly 2 other than the support structure 10, for example to the movable part 20 or to the body portion 31 of another actuating unit 30.

Figure 9b schematically shows a component 50 embodied by a magnetic arrangement 55.

The magnetic arrangement 55 includes a first magnet 55a on the actuating unit 30, e.g. on the body portion 31. The first magnet 55a repels a second magnet 55b that is spaced from the first magnet 55a in one direction ('downwards') along the primary axis P. The first magnet 55a also repels a third magnet 55c that is spaced from the first magnet 55a in the other direction ('upwards') along the primary axis P.

Such a magnetic arrangement 55has the advantages of not giving rise to undesirable friction, and providing very low lateral biasing forces that act in the actuating plane

Instead of a compliant material 54 or magnetic arrangement 55, the component 50 may be embodied by other materials or elements that increase the stiffness of the force-modifying flexure 32 in directions orthogonal to the actuating plane. For example, the component 50 may comprise a resilient element, such as a spring (e.g. a coil spring or other flexure that is separate from the force-modifying flexure).

The location of the component 50 relative to the actuating unit 30 is described herein with reference to Figure 9c. In the embodiments of Figures 9a and 9b, the component 50 is schematically shown as being located on or near (and directly limit the movement of) the body portion 31 of the actuating unit 30.

The component 50 may be located on an end of the body portion 31 that is distal to the connection of the body portion 31 to the force-modifying flexure 32. However, in general, the component may be located at any portion on the body portion 31, as illustrated in Figure 9c.

In other examples, the component 50 may be differently located. For example, the component 50 may be located on or near (and directly limit the movement of) a plurality of parts of the actuating unit 30 (which are spaced from each other when viewed orthogonally to the actuating plane). This is because, in practice, the actuating unit 30 could be damaged by excessive deflection at various points and as such may require multiple points of protection. So, the component 50 is not necessarily provided on one location on the actuating unit 30, but may be distributed over a plurality of separate locations.

Out-of-plane endstops

Figure 10 schematically shows to an embodiment of the actuator assembly 2 with an endstop 51 to the actuating unit 30. The endstop 51 is arranged to limit deformation of the actuating unit 30 (in particular of the portion of the actuating unit 30 on which the endstop is provided) in a direction orthogonal to the actuating plane. The endstop 51 may be provided in combination with or separately from the component 50 described above.

In Figure 10, the endstop 51 is arranged between the actuating unit 30 and the support structure 10. However, in general, the endstop may be provided between the actuating unit 30 and the movable part 20. In embodiments in which multiple actuating units 30 are provided, the endstop may be provided between adjacent actuating units 30.

In the embodiment of Figure 10, two endstops 51a, 51b are provided, in particular a 'lower' endstop 51a and an 'upper' endstop 51b. The lower endstop 51a is configured to engage when the actuating unit 30 moves in a 'downwards' direction in Figure 10, i.e. in a first direction orthogonal to the actuating plane. The upper endstop 51b is configured to engage when the actuating unit 30 moves in an 'upwards' direction in Figure 10, i.e. in a second direction orthogonal to the actuating plane. The second direction is opposite to the first direction.

In this way, only limited movement of the actuating unit 30 orthogonal to the actuating plane is allowed. During normal operation, the actuating unit 30 (in particular the body portion 31 thereof) moves only in the actuating plane. So, the endstop 51 is configured not to engage during normal operation of the actuating unit 30, or during normal operation of the actuator assembly 2 as a whole (e.g. due to actuation of other actuating units 30). However, the actuating unit 30 may move orthogonally to the actuating plane when abnormal loads act on the actuating unit 30, for example due to impact events such as drops. The endstop 31 limits such out-of-plane movement, thus reducing the risk of damage to the SMA element 34 and other parts of the actuating unit 30.

Each endstop 51 comprises a first endstop surface on the actuating unit 30, and further a second endstop surface on a different part. Preferably, the second endstop surface is provided on the support structure 10 or on the movable part 20. The endstop 51 engages when the first and second endstop surfaces engage, i.e. contact each other. During normal operation (i.e. due to actuation of the one or more actuating units 30 of the actuator assembly 2), the first and second endstop surfaces remain spaced apart.

The distance between the first and second endstop surfaces may remain substantially constant during normal operation, ensuring a more reliable and predictable engagement of the endstop. The first and second endstop surfaces may be substantially parallel to each other, and parallel to the actuating plane.

An endstop may be formed on the body portion 31 of the actuating unit 30. So, the first endstop surface may be provided on the body portion 31. The second endstop surface is preferably provided on the part connected to the force-modifying flexure, e.g. the support structure 10. This is particularly desirable because the body portion 31 may be the heaviest part of the actuating unit 30, and so undesirable movement of the body portion 31 is to be avoided.

Alternatively or additionally, an endstop may be formed on the coupling flexure 33 or other coupling link 33 of the actuating unit 30. So, the first endstop surface may be provided on the coupling flexure 33. The second endstop surface is preferably provided on the part connected to the coupling flexure 33, e.g. the movable part 20. An endstop to the coupling flexure 33 is desirable because the coupling flexure 33 may be relatively long, and so at risk of damage from excessive buckling. The endstop to the coupling flexure 33 is preferably provided at a mid portion of the coupling flexure, e.g. within the middle 50% of the length of the coupling flexure 33 between the body portion 31 and the movable part 20.

In general, an endstop may be formed on any one or on multiple parts of the actuating unit 30. For example, two endstops may be provided on the body portion 31 (to limit movement thereof in two opposite directions) and two endstops may be provided on the coupling flexure 33 (to limit movement thereof in two opposite directions)

In the schematic view of Figure 10, the lower endstop 51a comprises a separate piece that is attached to a base of the support structure 10, and the upper endstop 51b comprises a separate piece that is attached to a cover 11 of the support structure 10. However, in general, the endstops 51a, 51b may be formed on any other components of the actuator assembly 2. The endstops 51a, 51b may be integrally formed with the support structure 10, the cover 11 or other components of the actuator assembly 2. Figures 11a and lib show particular examples of the upper and lower endstops 51a, 51b that are schematically depicted in Figure 10.

Figure 11a shows an example of the upper endstop 51a. The upper endstop 51a is formed between the support structure 10 (in particular a cover of the support structure 10) and the body portion 31 of the actuating unit 30. In particular, the height of the support structure 10 above the actuating unit 30 is locally reduced to provide the endstop 51a. So, the second endstop surface may be considered to be formed on a protrusion of the support structure 10.

Figure lib shows an example of the lower endstop 51a. The lower endstop 51a is formed between the support structure 10 (in particular a base of the support structure 10) and the body portion 31 of the actuating unit 30. In particular, the space below the actuating unit 30 is locally reduced to provide the endstop 51b, in particular by providing a spacer as shown in Figure lib. So, the second endstop surface may be considered to be formed on a protrusion of the support structure 10.

The first endstop surfaces, i.e. the endstop surfaces on the body portion 31 of the actuating unit, are formed on a flat surface of the body portion 31 in the embodiment of Figures 11a and lib. In some embodiments, protrusions may be provided on the actuating unit 30, e.g. on the body portion 31, to provide the first endstop surfaces. Figure 12 shows an example in which dimples are formed in the sheet material of the body portion 31. In particular, one dimple (pointing towards the upper endstop 51a) is formed in an uppermost portion (e.g. a first portion 31a) of the body portion 31. Another dimple (pointing towards the lower endstop 51b) is formed in an uppermost portion (e.g. a first portion 31a) of the body portion 31. So, protrusions are effectively provided on the body portion 31 to form the first endstop surfaces.

Figure 13 shows another embodiment of an upper endstop 51a between the coupling flexure 33 and the movable part 20, and a lower endstop 51b between the coupling flexure 33 and the support structure 10. As shown, distance between the movable part 20 and the coupling flexure 33 is locally reduced (by a protrusion on the movable part 20), thereby providing an upper endstop 51a. The coupling flexure 33 is arranged close to the support structure 10, thereby providing a lower endstop 51b.

SMA element

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 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.