GB2613572A

GB2613572A - Actuator assembly

Info

Publication number: GB2613572A
Application number: GB2117572.4A
Authority: GB
Inventors: matthew bunting Stephen; Ooi David
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2021-12-06
Filing date: 2021-12-06
Publication date: 2023-06-14
Anticipated expiration: 2041-12-06
Also published as: GB202117572D0; GB2613572B; WO2023105213A1

Abstract

A shape memory alloy (SMA) actuator assembly 38 includes a first part 39, and a second part 40 mechanically coupled by a first bearing arrangement 41 which allows the second part 40 to be rotated relative to the first part 39 about an axis 46 parallel to a first direction. The second part 40 is driven by a first drive arrangement 42 which may include four lengths of SMA wire 471-474. A third part 43 is mechanically coupled to the second part by a second bearing arrangement 44 which allows helical or linear movement of the third part in the first direction. A second drive arrangement 45 may include four lengths of SMA wire 481-484. The arrangement is such that a torque applied about the axis parallel to the first direction 46 by the first drive arrangement 42 and/or the second drive arrangement 45 causes the third part 43 to move towards or away from the first part 39 along the first direction 46.

Description

ACTUATOR ASSEMBLY

Field

The present application relates to an actuator assembly, particularly an actuator assembly comprising a plurality of lengths of shape-memory alloy (SMA) wire.

Background

Such an actuator assembly may be used, for example, in a camera module (also referred to as simply a camera) to move a lens assembly in directions perpendicular to the optical axis so as to provide optical image stabilization (OIS). Where such a camera module is a compact camera module to be incorporated into a portable electronic device such as a mobile telephone, miniaturization can be important.

WO 2013/175197 Al describes an SMA actuation apparatus which moves a movable element relative to a support structure in two orthogonal directions using a total of four SMA actuator wires each connected at its ends between the movable element and the support structure and extending perpendicular to a primary axis. None of the SMA actuator wires are collinear, but the SMA actuator wires have an arrangement in which they are capable of being selectively driven to move the movable element relative to the support structure to any position in said range of movement without applying any net torque to the movable element in the plane of the two orthogonal directions around the primary axis.

WO 2019/243849 Al describes a shape memory alloy actuation apparatus which comprises a support structure and a movable element. A helical bearing arrangement supported on the movable element on the support structure guides helical movement of the movable element with respect to the support structure around a helical axis. At least one shape memory alloy actuator wire is connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, so as to drive rotation of the movable element around the helical axis which the helical bearing arrangement converts into said helical movement.

WO 2019/086855 Al describes a camera with an actuator assembly including a support platform, a moving platform that supports a lens assembly, SMA wires connected to the support platform and the moving platform, bearings to bear the moving platform on the support platform, and two arms extending between the support platform and the moving platform.

Summary

According to a first aspect of the present invention, there is provided an actuator assembly including a first part, a second part, and a first bearing arrangement mechanically coupling the first part to the second part. The actuator assembly also includes a first drive arrangement which includes four lengths of shape memory alloy wire. The first bearing arrangement and the first drive arrangement are configured such that the second part is rotatable relative to the first part about an axis parallel to a first direction. The actuator assembly also includes a third part, and a second bearing arrangement mechanically coupling the second part to the third part. The actuator assembly also includes a second drive arrangement which includes four lengths of shape memory alloy wire. The second bearing arrangement, the first drive arrangement and the second drive arrangement are configured such that in response to a torque applied about an axis parallel to the first direction by the first drive arrangement and/or the second drive arrangement, the third part moves towards or away from the first part along the first direction.

Thus, both the first and second drive arrangements may act on the second bearing arrangement and actuate in concert. This may be used to increase movement (i.e., stroke) along the first direction.

The first part may include, or take the form of, a static part. The static part may be a chassis section. The second part may include, or take the form of, an intermediate moving part. The intermediate part may be an autofocus chassis section. The third part may include, or take the form of, a moving part. The moving part may be a lens carriage supporting one or more lenses for a camera.

Each of the lengths of SMA wire in the first drive arrangement may be non-collinear with the other lengths of SMA wire in the first drive arrangement. Each of the lengths of SMA wire in the second drive arrangement may be non-collinear with the other lengths of SMA wire in the second drive arrangement.

The lengths of SMA wire in the first drive arrangement may be arranged so as to be capable of applying a torque about an axis parallel to the first direction and/or a force in a direction substantially perpendicular to the first direction between the first and second parts. The lengths of SMA wire in the second drive arrangement may be arranged so as to be capable of applying a torque about an axis parallel to the first direction and/or a force in a direction substantially perpendicular to the first direction between the first and third parts.

Each length of shape memory alloy wire of the first drive arrangement may be connected between the first part and the second part, either directly or via one or more intermediate structures. Each length of shape memory alloy wire of the second drive arrangement may be connected between the first part and the third part, either directly or via one or more intermediate structures.

The first bearing arrangement and the first drive arrangement may be configured such that the second part is movable relative to the first part perpendicular to the first direction. The second bearing arrangement and the second drive arrangement may be configured such that the third part is movable relative to the first part perpendicular to the first direction.

The actuator assembly may be configured such that the second and third parts are movable relative to the first part perpendicular to the first direction whilst maintaining a position of the third part relative to the second part.

The actuator assembly may be configured such that the second and third parts are differently movable perpendicular to the first direction, so as to tilt the third part relative to the first and second parts about an axis perpendicular to the first direction.

The first bearing arrangement may be configured to resist movement of the second part towards or away from the first part along the first direction.

Configured to resist may mean to discourage, or even to prevent. The first bearing arrangement may include one or more flexures connecting between the first and second parts. The flexures may be configured to resist movement of the second part towards and/or away from the first part along the first direction.

The first bearing arrangement may be configured to permit movement of the second part relative to the first part in a plane perpendicular to the first direction.

The first bearing arrangement may include, or take the form of, a planar bearing. The planar bearing may include first and second plates which face each other, and at least three protrusions (or "projections"). Each protrusion may respectively extend away from one of the first and second plates towards, and be in slideable contact with, the other of the first and second plates.

The at least three protrusions may extend away from the same plate, e.g. the first plate. However, in some embodiments, one or more, but not all protrusions may extend from one plate (e.g., the first plate) and the rest of the protrusions may extend from the other plate (e.g., the second plate).

The planar bearing may include first and second plates which face each other, and at least three ball bearings interposed between the first and second plates The first and plate and the second plate may include first and second apertures, respectively. The first and second apertures may preferably be circular. The first and second apertures may preferably be co-axial. The first and second apertures may preferably be co-axial in a resting or neutral configuration of the actuator assembly, and may cease to be co-axial when the actuator assembly is actuated away from the resting or neutral configuration.

The four lengths of shape memory alloy wire in the first drive arrangement may be substantially co-planar.

The second part may include a central portion and resilient arms extending from the central portion and connected to the first part to provide a force for biasing the second part towards the first part and/or for biasing the second part towards a central position through which an axis parallel to the first directionpasses.

The four lengths of shape memory alloy wire in the second drive arrangement may be substantially co-planar.

The four lengths of shape memory alloy wire may each extend at an angle to a plane normal to the first direction. The angle may be small. The angle may be less than 20 degrees, in some instances less than 10 degrees, and in further instances the angle may be less than 5 degrees. The angle may change at least as the position of the third part along the first direction changes. The angle may be zero when the third part is at a central position along the first direction.

The four lengths of shape memory alloy wire in the first drive arrangement may be substantially co-planar lying in a first plane. The four lengths of shape memory alloy wire in the second drive arrangement may be substantially co-planar lying in a second plane. The first and second planes may be parallel.

The first and second planes may be offset from each other along the first direction. The first and second planes may be substantially co-planar.

The first and second planes may be substantially co-planar if they are separated by a distance along the first direction which is less than or equal to 10 times a thickness of one of the lengths of shape memory alloy wire. The first and second planes may be substantially co-planar if the respective SMA wires of the first and second drive arrangements all span a length parallel to the first direction which is less than or equal to 500 microns, less than or equal to 750 microns, or less than or equal to 1 mm.

The four lengths of shape memory alloy wire in the first drive arrangement may span a first length parallel to the first direction. The four lengths of shape memory alloy wire in the second drive arrangement may span a second length parallel to the first direction. The first and second lengths may at least partly overlap.

The four lengths of shape memory alloy in the first and second drive arrangements may each be connected to the first part via a connection portion. The connection portions may lie in a plane normal to the first direction.

The actuator assembly may include four shape memory alloy wires, each shape memory alloy wire providing one of the four lengths of shape memory alloy in the first drive arrangement and one of the four lengths of shape memory alloy in the second drive arrangement. Each shape memory alloy wire may be connected to the first part via a common connection portion at (or near to) a midpoint of the shape memory alloy wire. The common connection portion may be connected to a system ground or common mode voltage, and may be used as a common current return. In this way, the drive currents applied to either side of the common connection portion may be independently varied. The common connection portions may take the form of crimps.

The second bearing arrangement may include, or take the form of, a helical bearing. The helical bearing may be configured to convert relative rotations between the second and third parts about an axis parallel to the first direction (caused by the first and/or second drive arrangements) to relative movements of the second and third parts parallel to the first direction. The helical bearing may include, or take the form of, a screw thread.

The second bearing arrangement may include, or take the form of, a helical rolling-element bearing. The helical rolling-element bearing may include a number of helical bearing parts arranged in a loop about an axis parallel to the first direction. Each helical bearing part may include a first bearing surface, a second bearing surface and at least one rolling element arranged to be guided by the first and second bearing surfaces along a helical path. Each helical bearing part may include a flexible ramp. The flexible ramps may be pre-stressed in an equilibrium or neutral configuration of the first bearing.

The helical bearing may include or take the form of a sliding surface configured to mate with a bearing surface and to be guided by the bearing surface.

The second bearing arrangement may include, or take the form of, a helical flexure. The helical flexure may include, or take the form of, at least three flexure arms extending in a direction parallel to an first direction and around an axis parallel to the first direction in the same sense. The helical flexure may include, or consist of, four, five or more flexure arms. The helical flexure may include a ring. The at least three flexures (e.g. five or more flexures) may extend from the ring. The flexure arms may be positioned at equally-spaced angles around a centroid of the ring. The centroid of the ring may coincide with an axis parallel to the first direction. The centroid of the ring may coincide with an axis parallel to the first direction in the resting or neutral configuration of the actuator assembly, and may cease to coincide when the actuator assembly is actuated away from the resting or neutral configuration. The ring and flexure arms may be formed as a single-piece.

The actuator may also include an annular ring connected to the third part and interposed between the third part and the second part.

The second part may include a first annulus. The first annulus may be substantially co-planar with the third part at a closest position of the third part relative to the second part along the first direction. This may help reduce the height of actuator assembly parallel to the first direction.

The third part may include, or take the form of, a second annulus. The first annulus and the second annulus may be substantially co-axial at a central lateral position of the third part relative to the second part. The second annulus may lie inside the first annulus. The second annulus may lie inside the first annulus. The second part may include a first pair of arms extending radially away from the first annulus. The third part may include a second pair of arms extending radially away from the axis parallel to the first direction. When the third part takes the form of the second annulus, the second pair of arms may extend radially away from the second annulus.

A camera module may include the actuator assembly, an image sensor supported by one of the first part and the third part, and a lens supported by the other of the first part and the third part.

The camera module may also include a controller configured to control the actuator assembly to implement an auto-focus function using the movement of the third part towards or away from the second part along the first direction.

According to a second aspect of the invention, there is provided a method including causing the actuator assembly of the first aspect, or the camera module including the actuator assembly of the first aspect, to implement an automatic focussing function and/or optical image stabilization function of a camera.

The method may include actuating the first drive arrangement and/or the second drive arrangement so as to apply a torque to the second bearing arrangement about an axis parallel to the first direction. In response to the torque, the third part may move towards or away from the first part along the first direction.

The method may include actuating the first drive arrangement so as to rotate the second part in a first sense about an axis parallel to the first direction, whilst rotating the third part in a second, opposite sense about that axis. In this way, the maximum displacement of the third part relative to the first part parallel to the first direction may be approximately double that obtainable if the first drive arrangement and second part were omitted and the second bearing coupled the first and third parts.

The method may include actuating the first and second drive arrangements so as to displace the second and third parts relative to the first part by a distance perpendicular to the first direction, whilst maintaining a position of the third part relative to the second part.

The method may include actuating the first and second drive arrangements so as to displace the second part relative to the first part by a first distance in a second direction and to displace the third part relative to the first part by a second distance in a third direction. The second and third directions may both be perpendicular to the first direction, so as to tilt the third part relative to the first and second parts about an axis perpendicular to the first direction.

The first distance may be equal to the second distance provided the second and third directions are different. The second and third directions may be the same provided that the first and second distances are different.

The method may include displacing the second and third parts together by the same amount (a "shift"), followed (or preceded) by displacing the second and third parts by different amounts and/or in different directions (a "tilt"). The method may include displacing the second and third parts using a combination of a shift and a tilt.

According to a third aspect of the invention, there is provided a computer program stored on a non-transitory machine readable medium. When executed by a processor of a device including the actuator assembly of the first aspect or the camera module including the actuator assembly of the first aspect, the computer program causes the actuator assembly or camera module to carry out the method of the second aspect.

According to a fourth aspect of the invention, there is provided an actuator assembly including a first part, a second part, and a first bearing arrangement mechanically coupling the first part to the second part. The actuator also includes a first drive arrangement which includes one or more lengths of shape memory alloy wire. The first bearing arrangement and the first drive arrangement are configured such that the second part is rotatable relative to the first part about an axis parallel to the first direction. The actuator assembly also includes a third part and a second bearing arrangement mechanically coupling the second part to the third part. The actuator assembly also includes a second drive arrangement which includes one or more lengths of shape memory alloy wire. The second bearing arrangement, the first drive arrangement and the second drive arrangement are configured such that in response to a torque applied about an axis parallel to the first direction by the first drive arrangement and/or the second drive arrangement, the third part moves towards or away from the first part along the first direction.

The actuator assembly of the fourth aspect may include features corresponding to any features of the actuator of the first aspect. Definitions applicable to the actuator of the first aspect may be equally applicable to the actuator of the fourth aspect.

The first drive arrangement may include a first length of shape memory alloy wire configured to apply a torque clockwise about an axis parallel to the first direction and a second length of shape memory alloy wire configured to apply a torque anti-clockwise about that axis parallel to the first direction. The first drive arrangement may only include the first and second lengths of shape memory alloy wire, and no further lengths of shape memory alloy wire.

The second drive arrangement may include a third length of shape memory alloy wire configured to apply a torque clockwise about an axis parallel to the first direction and a fourth length of shape memory alloy wire configured to apply a torque anti-clockwise about that axis parallel to the first direction. The second drive arrangement may only include the third and fourth lengths of shape memory alloy wire, and no further lengths of shape memory alloy wire.

The actuator assembly may also include one or more first springs coupling the first part to the second part. Each first spring may be configured to oppose contraction of at least one length of shape memory alloy wire of the first drive arrangement. Each first spring may be directly connected to the first and/or second parts, or may be connected to the first and/or second parts via one or more intermediate components.

The actuator assembly may also include one or more second springs coupling the second part to the third part. Each second spring may be configured to oppose contraction of at least one length of shape memory alloy wire of the second drive arrangement. Each second spring may be directly connected to the second and/or third parts, or may be connected to the second and/or third parts via one or more intermediate components.

Herein, the term annulus may encompass any ring or loop shape, including circular, elliptical, square, rectangular, or any other regular or irregular shape.

An annulus may have an outer perimeter with a first shape and an inner perimeter with a second, different shape.

Herein, any or all of the axes parallel to the first direction may correspond to the same axis defined relative to any one of the first, second and third parts, and movable with the respective part as the SMA wires are actuated.

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 1 is a schematic diagram of a camera incorporating a shape memory alloy (SMA) actuator assembly; Figure 2 schematically illustrates possible degrees of freedom which may be provided by an SMA actuator assembly; Figure 3 is a schematic plan view of a drive arrangement which may be used in an SMA actuator assembly; Figure 4 is a schematic perspective view of a flat SMA actuator assembly employing the drive arrangement shown in Figure 3; Figure 5A is a schematic side view of a planar (three-point) bearing; Figure 5B is a schematic exploded projection view of the planar bearing shown in Figure 5A; Figure 6 is a schematic perspective view of a helical flexure bearing; Figure 7A is a schematic exploded projection of a helical plain bearing; Figure 73 is a schematic projection of the helical plain bearing shown in Figure 7A; Figure 8A is a plan view of a rotary bearing; Figure 8B is a cross-section along the line labelled A-A' in Figure 8A Figure 9 is a schematic exploded projection of a first actuator assembly; Figure 10 is a schematic projection of the first actuator assembly shown in Figure 9; Figure 11 is schematic block diagram of the first actuator assembly shown in Figure 9; Figure 12 is a schematic plan view of a second actuator assembly; Figure 13A is a cross-section of the second actuator assembly along the line labelled B-B' in Figure 12; Figure 13B is a cross-section of the second actuator assembly along the line labelled C-C' in Figure 12; Figure 14 is schematic exploded projection of a third actuator assembly; Figure 15 is schematic projection of the third actuator assembly shown in Figure 14; Figure 16 is schematic plan view of a first two SMA-wire actuator; and Figure 17 is schematic plan view of a second two SMA-wire actuator.

Detailed Description

Camera Referring to Figure 1, a camera 1 incorporating an SMA actuator assembly 2 (herein also referred to as an "SMA actuator" or simply an "actuator") is shown.

The camera 1 includes first and second parts 3, 4.

The first part 3 of the camera takes the form of a support structure and includes a base 5. The second part 4 of the camera takes the form a lens assembly suspended on the first part 3 of the camera 1 by the SMA actuator assembly 2.

An image sensor 6 is disposed in front of a front side of the base 5, i.e., the image sensor 6 is interposed between the lens assembly 4 and the base 5.

The SMA actuator assembly 2 supports the lens assembly 4 and the image sensor 6 in a manner allowing one or more degrees-of-freedom of the lens assembly 4 relative to the support structure 3. The lens assembly 4 has an optical axis 0.

The camera 1 includes an integrated circuit (IC) 7, which implements a control circuit, and also a gyroscope sensor (not shown). The support structure 3 also includes a can 8 (or "screening can") which protrudes forwardly from the base 5 to encase and protect the other components of the camera 1.

The lens assembly 4 includes a lens carriage 9 in the form of a cylindrical body supporting two lenses 10 arranged along the optical axis 0. In general, any number of lenses 10 may be included, for example only one lens 10 or three or more lenses 10. Preferably, each lens 10 has a diameter of up to about 20 mm. The camera 1 can therefore be referred to as a miniature camera.

The lens assembly 4 is arranged to focus an image onto the image sensor 6. The image sensor 6 captures the image and may be of any suitable type, for example, a charge-coupled device (CCD) or a complementary metal-oxidesemiconductor (CMOS) device.

The lenses 10 are supported on the lens carriage 9 and the lens carriage 9 is supported by the SMA actuator assembly 2 such that the lens assembly 4 is movable along the optical axis 0 relative to the support structure 3, for example to provide focussing or zoom. Although all the lenses 10 are fixed to the lens carriage 9 in this example, in general, one or more of the lenses 10 may be mounted to a component other than the lens carriage 9, and may be fixed in place relative to the image sensor 6, leaving at least one of the lenses 10 attached to the lens carriage and movable along the optical axis 0 relative to the image sensor 6.

In general, the lens assembly 4 may be moved orthogonally to the optical axis 0 in use, relative to the image sensor 6, with the effect that the image on the image sensor 6 is moved. For example, if a set of right-handed orthogonal axes x, y, z is aligned so that a third axis z is oriented substantially parallel to the optical axis 0, then the lens assembly 4 may be moveable in a direction parallel to the first x axis and/or in a direction parallel to the second y axis. This is used to provide optical image stabilization (OIS), compensating for movement of the camera 1, which may be caused by hand shake etc. The movement providing OIS need not be constrained to the x-y plane. Additionally or alternatively, OIS functionality may be provided by tilting the lens assembly 4, or both the lens assembly 4 and the image sensor 6, about an axis parallel to the first x axis and/or about an axis parallel to the second y axes. Additionally, the lens assembly 4, or at least one lens 10 thereof, may be moved parallel to the optical axis 0 (parallel to the third axis z) to provide focussing of an image formed on the image sensor 6, for example as part of an automatic focussing (AF) function.

This specification is primarily concerned with examples of SMA actuator assemblies 2 which provide a combination of automatic focussing (AF) and optical image stabilisation (OIS) based on moving the lens assembly 4 relative to the support structure 3.

Degrees of freedom Referring also to Figure 2, possible types of movement (or degrees of freedom) which may be provided by an SMA actuator assembly 2 are illustrated.

A first degree-of-freedom (DOF) Tx corresponds to movement parallel to the first axis x. A second DOF Ty corresponds to movement parallel to the second axis y. A third DOF Tz corresponds to movement parallel to the third axis z, which is oriented substantially parallel to the optical axis 0. The third DOF Tz corresponds to movement of the lens assembly 3 towards or away from the image sensor 6.

The first, second and third axes x, y, z form a right-handed Cartesian coordinate system. A fourth DOF Rx corresponds to rotation about an axis parallel to the first axis x. A fifth DOF Ry corresponds to rotation about an axis parallel to the second axis y. A sixth DOF Rz corresponds to rotation about an axis parallel to the third axis z. In some examples, one or more of the axes may be attached to (and move and/or rotate/tilt with) a first part, a second part, or any other elements of an SMA actuator assembly 2 or camera 1. For example, an origin may be an element of the camera 1 such as the image sensor 6 or a lens 10 of the lens assembly 4.

Motions of the lens assembly 4 relative to the support structure 3 may be broken down into components of any or all of the first to sixth DOF (movements) Tx, Ty, Tz, Rx, Ry, Rz. Although described as degrees-of-freedom, in some cases translations and rotations may be linked. For example, a given translation Tz along the third axis z may be tied to a corresponding rotation Rz so that motion of the lens assembly 4 is helical. Such linked motions may be referred to using a pair enclosed in square brackets to avoid confusion with more independent motions, for example [Tz, Rz] will denote a helical motion as described hereinafter. Helical motion [Tz, Rz] may be provided by helical bearings such as, for example, helical roller bearings or helical flexures.

This specification primarily concerns SMA actuator assemblies 2 which provide the motions corresponding to first and second DOF Tx, Ty to provide OIS functionality herein, whilst the motion [Tz, Rz] parallel to the third axis z provides AF functionality. Other certain motions are constrained by the SMA actuator assemblies 2 described herein. Some examples of SMA actuator assemblies 2 according to the present specification may additionally or alternatively tilt a lens 10 to provide OIS functionality, corresponding to the fifth and sixth DOF Rx, Ry.

Shape-memory alloy drive assemblies Referring also to Figure 3, a drive arrangement 11 included in SMA actuator assemblies 2 is shown schematically.

The first drive arrangement 11 includes a first structure 12 and a second structure 13. The second structure 13 may be supported within a boundary defined by the first structure 12 (as shown in Figure 3), for example using one or more bearings as described hereinafter. The second structure 12 generally need not provide a complete or uninterrupted boundary. The first and second structures 12, 13 may take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, and may be coated with an electrically-insulating dielectric material.

Four SMA wires 141, 142, 143, 144 (shown in chain to aid visibility) form a loop around the second structure 13. First 141 and third 143 SMA wires extend substantially parallel to the first axis x and are spaced apart in a direction parallel to the second axis y. Contraction of the first SMA wire 141 will exert a force on the second structure 13 in the negative -x direction, whereas contraction of the third SMA wire 143 will exert a force on the second structure 13 in the positive +x direction. Second 142 and fourth 144 SMA wires extend substantially parallel to the second axis y and are spaced apart in a direction parallel to the first axis x. Contraction of the second SMA wire 142 will exert a force on the second structure 13 in the negative -y direction, whereas contraction of the fourth SMA wire 144 will exert a force on the second structure 13 in the positive +y direction.

Other example configurations may be used, and further details are provided in WO 2017/055788 Al and WO 2019/086855 Al, which are both incorporated herein in their entirety by this reference.

The position of the second structure 13 relative to the first structure 12 perpendicular to the optical axis 0 (aligned with the z axis as illustrated) is controlled by selectively varying the temperatures of the SMA wires 141, 142, 143, 144. This is achieved by passing selective drive signals through the SMA wires 141, 142, 143, 144 that provide resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the SMA wires 141, 142, 143, 144 to cool by conduction, convection and radiation to its surroundings.

In operation, the SMA wires 141, 142, 143, 144 are selectively driven to move the second structure 13 relative to the first structure 12 (or vice versa) in any lateral direction (i.e., a direction within a plane parallel to first and second axes x, y and perpendicular to the optical axis 0 and third axis z).

Further details are also provided in WO 2013/175197 Al, which is incorporated herein by this reference.

Taking the example of the set of four SMA wires 141, 142, 143, 144, the SMA wires 141, 142, 143, 144 have an arrangement in a loop at different angular positions around the optical axis 0 (corresponding here to the third axis z) to provide two pairs of opposed SMA wires 141 & 143, 142 & 144 that are substantially perpendicular to each other. Thus, each pair of opposed SMA wires 141 & 143, 142 & 144 is capable on selective driving of moving the second structure 13 in one of two perpendicular directions orthogonal to the optical axis 0. As a result, the SMA wires 141, 142, 143, 144 are capable of being selectively driven to move the second structure 13 relative to the first structure 12 to any position in a range of movement in a plane orthogonal to the optical axis 0. Another way to view this movement is that contraction of any pair of adjacent SMA wires (e.g. SMA wires 143, 144) will move the second structure 13 in a direction bisecting the pair of SMA actuator wires (diagonally in Fig. 3). The magnitude of the range of movement depends on the geometry and the range of contraction of the SMA wires 141, 142, 143, 144 within their normal operating parameters. Rotation of the second structure 13 relative to the first structure 12 is possible by driving a single pair of opposed SMA wires, for example 141 and 143, whilst allowing the other SMA wires 142, 144 to be extended.

In general, the four SMA wires 141, 142, 143, 144 may be driven so as to cause a movement of the second structure 13 relative to the first structure 12 which is a combination of DOF Tx, Ty and Rz.

On heating of one of the SMA wires 141, 142, 143, 144, the stress in the SMA wire 141, 142, 143, 144 increases and it contracts, causing movement of the second structure 13 relative to the first structure 12. A range of movement occurs as the temperature of the SMA increases over a range of temperature in which there occurs the transition of the SMA material from the Martensitic phase to the Austenitic phase. Conversely, on cooling of one of the SMA wires 141, 142, 143, 144 so that the stress in the SMA wire 141, 142, 143, 144 decreases, it expands under the force from opposing ones of the SMA wires 141, 142, 143, 144(and in some examples also biasing forces from one or more biasing means such as springs, armatures and so forth). This allows the second structure 13 to move in the opposite direction relative to the first structure 12.

The SMA wires 141, 142, 143, 144 may be made of any suitable SMA material, for example Nitinol or another titanium-alloy SMA material.

The drive signals for the SMA wires 141, 142, 143, 144 are generated and supplied by the control circuit implemented in the IC 7. For example, if the first structure 12 is fixed to (or part of) the support structure 3 and the second structure 13 is fixed to (or part or) the lens assembly 4, then the drive signals are generated by the control circuit in response to output signals of the gyroscope sensor (not shown) so as to drive movement of the lens assembly 4 to stabilise an image focused by the lens assembly 4 on the image sensor 6, thereby providing OIS. The drive signals may be generated using a resistance feedback control technique for example as described in WO 2014/076463 Al, which is incorporated herein by this reference.

Referring also to Figure 4, an example of a "flat" SMA actuator assembly 15 implementing the drive arrangement 11 is shown.

In the flat actuator assembly 15 the first structure 12 takes the form of a flat, annular plate 16 having a rectangular outer perimeter (or "outer edge") and a circular inner perimeter (or "inner edge"), whilst the second structure 13 takes the form of a flat, thin annular sheet 17 with a rectangular outer perimeter and a circular inner perimeter. The first structure 12 in the form of the plate 16 is supported on a base 5 (not shown in Figure 4 -see Figure 1) in the form of a rectangular plate. The four SMA wires 141, 142, 143, 144are each attached at one end to respective first crimps 181, 182, 183, 184 (also referred to as "static" crimps) which are fixedly attached to (or formed as part of) the first structure 12, 16. The other end of each SMA wire 141, 142, 143, 144 is attached to a respective second crimp 191, 192, 193, 194 (also referred to as "moving" crimps) which is fixedly attached to (or formed as part of) the second structure 13, 17.

The plate 16 and the sheet 17 may each take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, and may be coated with an electrically-insulating dielectric material. The plate 16 and the sheet 17 are each provided with a respective central aperture aligned with the optical axis 0 allowing the passage of light from a lens assembly 4 mounted to the sheet 17 to an image sensor 6 supported on the base 5 (not shown in Figure 4 -see Figure 1).

The four SMA wires 141, 142, 143, 144 may be perpendicular to the optical axis 0 or inclined at a small angle to a plane perpendicular to the optical axis 0. A "small angle" may in general mean less than 20 degrees, in some instances less than 10 degrees, or even less than 5 degrees. Generally, in a set, the four SMA wires 141, 142, 143, 144 are non-collinear. The four SMA wires 141, 142, 143, 144 are preferably co-planar.

The flat actuator assembly 15 includes a number of plain bearings (not shown in Figure 4) spaced around the optical axis 0 to bear the second structure 13, 17 on the first structure 12, 16. Preferably, at least three bearings are used in order to assist in providing stable support, although in general, a different number of bearings may be used. The plain bearings (not shown in Figure 4) may take the form of a bearing member in the form of cylinder, and may be attached to, or formed as part of, the first structure 12. Bearings (not shown in Figure 4) may be made from a suitable metal or alloy such as phosphor bronze or stainless steel with a diamond-like carbon coating. The plain bearings (not shown in Figure 4) may be made from, or may include an upper layer coating of, a polymer, such as Polyoxymethylene (POM, Acetal), Polytetrafluoroethylene (PTFE) or PTFE-impregnated POM.

The flat actuator assembly 15 will generally also include biasing means (not shown) such as one or more springs or flexure arms arranged and configured to maintain the first and second structures 12, 13 in contact (via the plain bearings and/or to urge the first and second structures 12, 13 towards a neutral (for example central) relative position when the SMA wires 141, 142, 143, 144 are not powered.

Details relevant to manufacturing actuator assemblies similar to the flat actuator assembly 15 can be found in WO 2016/189314 Al which is incorporated herein in its entirety this reference.

Although not shown in Figure 4, the flat actuator assembly 15 may be provided with end stops to provide limits on lateral movement of the second structure 13 relative to the first structure 12. In this way, the SMA wires 141, 142, 143, 144 can be protected from overextension resulting from, for example, impacts to which a device (not shown) incorporating the flat actuator assembly 15 may be subjected (for example being dropped).

The drive arrangement 11 can drive translations Tx, Ty along the first and/or second axes x, y and rotations Rz about an axis parallel to the third axis z (which is substantially parallel to the optical axis 0). However, in order to provide translation Tz parallel to the third axis z, the first drive arrangement 11 must be combined with at least one bearing capable of converting torque applied about the optical axis 0 into a combination of a rotation Rz and translation Tz (a helical movement).

One of more of the motions driven by the drive arrangement 11 may be fully or partly constrained by coupling one or more further bearings between the first and second structures 12, 13.

Bearings Most SMA actuators 2 according to this specification include at least a pair of drive arrangements 11 and also an arrangement of one or more mechanical bearings (also referred to as a "bearing arrangement") serving to support, constrain and/or convert the movements generated by the drive arrangements 11.

-Planar bearing -Referring also to Figures 5A and 5B, a planar bearing 20 (also referred to as a three-point bearing) is shown.

Figure 5A is a side view and Figure 5B is an exploded projection view.

The planar bearing 20 includes a first plate 21 which slides in contact with a second plate 22. The first plate 21 supports at least three cylindrical protrusions 23 including at least first 231, second 232 and third 233 cylindrical protrusions which are not co-linear, for example arranged at the points of a triangle. The second plate 22 is urged into contact with the flat surfaces of the cylindrical protrusions 23 by biasing means (not shown in Figures 5A and 5B), and is free to slide in a plane parallel to the first and second axes x, y, and to rotate about an axis parallel to the third axis z. In this way, the relative motions between the first plate 21 and the second plate 22 correspond to Tx, Ty and/or Rz. Unless a biasing force urging the plates 21, 22 together is overcome, Tz, Rx and Ry movements are constrained.

In the example shown in Figures 5A and 5B, both plates 21, 22 take the form of an annulus having a rectangular outer perimeter and a circular inner perimeter defining a central aperture 24. However, the shape of the plates 21, 22 is not relevant to the function of the planar bearing 20, and any shapes of plate may be used instead. Although three cylindrical protrusions 231, 232, 233 are shown in Figures 5A and 5B, in general any number of cylindrical protrusions greater than or equal to three may be used.

An alternative planar bearing (not shown) is the same as the planar bearing 20, except that the three or more cylindrical protrusions 23 are replaced by three or more ball bearings (not shown). Either or both plates 21, 22 may include recesses (not shown) to define runs for receiving corresponding ball bearings (not shown). The alternative planar bearing is a rolling bearing instead of a plain bearing.

-Helical flexure bearing -Referring also to Figure 6, an example of a helical bearing in the form of a helical flexure bearing 25 is shown.

The helical flexure bearing 25 includes a circular annulus 26 having a central aperture 24 and connected to three, four or more, preferably five or more, helical beam portions 27. In the example shown in Figure 6, there are four helical beam portions 271., 272, 273, 274. At the end not connected to the circular annulus 26, each helical beam portion 271, 272, 273, 274 is connected to a pad 281, 282, 283, 284, for example for connection to a layer or structure below (in relation to the third axis z as drawn) the circular annulus 26.

Each helical beam portion 271, 272, 273, 274 is approximately tangential to the circular annulus 26 (in the same sense) and its span includes both a first component parallel to the plane containing the first and second axes x, y and a second component parallel to the third axis z. If the pads 281, 282, 283, 284 are clamped and a force is exerted upwards (positive z direction) on the circular annulus 26, then in response the helical beam portions 271, 272, 273, 274 will deflect in the direction of that force. However, in doing so, the ends connected to the circular annulus 26 are also deflected closer the respective pad 281, 282, 283, 284, causing the circular annulus 26 to rotate clockwise about an axis parallel to the third axis z. Conversely, a force exerted downwards (negative z direction) on the circular annulus 26 will result in both a downwards movement of the circular annulus 26 and also an anti-clockwise (counter-clockwise) rotation of the circular annulus 26.

In this way, the helical flexure bearing 26 acts to convert a rotation about the third axis z into a relative displacement parallel to the third axis and vice versa. However, the movements are not independent of one another, and relative to clamped pads 281, 282, 283, 284 the circular annulus 26 is constrained to move along an approximately helical path. Since this does not reflect independent degrees of freedom, the motion will be denoted as [Tz, Rz] to highlight the relationship between translation Tz parallel to the third axis z and rotation Rz about the third axis z for this bearing type.

Although the helical beam portions 271, 272, 273, 274 shown in Figure 6 are curved, in other examples of helical flexure bearings 25 the helical beam portions 27 may be straight. Further examples of helical flexure bearings 25 are described in WO 2019/243849 Al, the contents of which are incorporated herein by reference in their entirety. Figures 19 to 22 of WO 2019/243849 Al and the accompanying description on page 22, line 23 to page 23, line 24, are particularly relevant to helical flexure bearings 25. Additional examples of implementing helical flexure bearings 25 are also shown and described hereinafter.

-Helical plain bearing -Referring also to Figures 7A and 73, an example of a helical bearing in the form of a helical plain bearing 29 is shown.

Figure 7A is an exploded projection view and Figure 73 is a projection of the assembled helical plain bearing 29. Occluded features are shown using dashed lines in Figure 7A.

The helical plain bearing 29 includes a first structure 30 and a second structure 31 configured to fit together for sliding motion between helical surfaces 321, 322 of the first structure 30 and helical surfaces 331, 332 of the second structure 31. Biasing means (not shown) urge the first and second structures 30, 31 together to maintain the pairs of helical surfaces 321 and 331, 322, 332 in contact. In this way, the relative motions between the first and second structures 30, 31 are constrained to a helical path [Tz, Rz].

The example shown in Figures 7A and 7B prioritises visual clarity of the functioning of a helical bearing over practicality of implementation, and specific embodiments described hereinafter include additional examples more suited to incorporation into a device such as a camera 1. In particular, although the helical surfaces 32, 33 may be curved to follow a helical path as shown in Figures 7A and 73, in other examples the helical surfaces 32, 33 may be substantially planar, for example ramps. In a practical example, the first structure 30 may also include a central aperture 24 to permit light to reach an underlying image sensor 6.

Although the helical bearing shown in Figures 7A and 73 is a helical plain bearing, other helical bearings in the form of rolling bearings are also possible (see Figures 14 and 15). Further examples of helical bearings may be found in WO 2019/243849 Al (already incorporated by reference). In particular, see Figures 1 to 18 of WO 2019/243849 Al and the corresponding description on page 7, line 10 to page 22, line 21.

-Rotary bearing -Referring also to Figures 8A and 83, a rotary bearing 34 is shown.

Figure 8A is a plan view of the rotary bearing 34, and Figure 83 is a cross-section along the line labelled A-A' in Figure 8A.

The rotary bearing 34 includes a first plate 35 having a rectangular outer perimeter and a circular inner perimeter defining a central aperture 24. A cylindrical portion 36 projects upwards (positive z direction as illustrated) from the circular inner perimeter of the first plate 35.

In the example shown in Figures 8A and 83, the cylindrical portion 36 is formed as a single piece with the first plate 35. However, the cylindrical portion 36 may instead be a separate piece which is received through the central aperture 24 of the first plate 35. In this case, the outer diameter of the cylindrical portion 36 should be just smaller than the diameter of the central aperture 24 of the first plate 35, so that lateral (x-y plane) movements of the cylindrical portion 36 are constrained by the first plate 35. When not formed as a single piece with the first plate 35, the cylindrical portion 36 may be secured or attached to the first plate 35, but does not need to be and could be free to rotate within the central aperture 24.

The rotary bearing 34 also includes a second plate 37 having a rectangular outer perimeter and a circular inner perimeter defining a central aperture 24. The second plate 37 is received over the cylindrical portion 36. The first plate 35 supports at least three cylindrical protrusions 23. The example shown in Figures 8A and 8B includes first 231, second 232, third 233 and fourth 234 cylindrical protrusions which are arranged at the points of a square arranged substantially concentrically with the cylindrical portion 36. In general, any three cylindrical protrusions 23 which are not co-linear may be used, according to any configuration suitable for the plain bearing 20. In other examples the cylindrical protrusions 23 may be supported by the second plate 37, or by a combination of the first and second plates 35, 37. In some examples, the cylindrical protrusions 23 may be replaced with ball bearings (not shown).

Similarly to the plain bearing 20, the second plate 37 of the rotary bearing 34 is able to rotate about an axis parallel to the third axis z relative to the first plate 35. However, unlike the plain bearing 20, the second plate 37 of the rotary bearing 34 is constrained from sliding in a plane parallel to the first and second axes x, y by the cylindrical portion 36.

The second plate 37 may be urged into contact with the flat surfaces of the cylindrical protrusions 23 by biasing means (not shown in Figures 8A and 8B). If biasing means are included, then a resulting biasing force urging the plates 35, 37 together must be overcome before movement Tz parallel to the z axis may occur. In some examples, the cylindrical portion 36 may include a lip arranged to retain the second plate 37.

Although illustrated and described in particular orientations with respect to a set of right-handed Cartesian axes x, y, z for reference, any of the bearings described hereinbefore may be oriented at an arbitrary angle.

The bearings described hereinbefore may be formed of any suitable materials and using any suitable fabrication methods. For example, plate-or sheet-like components may be fabricated from metal sheets, for example stainless steel, with patterning provided by chemical or laser etching. Milling or stamping could be used provided that this does not introduce unacceptable residual strains causing distortion of parts. After patterning, such parts may be bent or pre-deformed as needed. Complex three-dimensional parts may be built up by attaching parts to plates, sheets or other parts, for example using adhesives, welding, brazing, soldering and so forth. Alternatively, complex three-dimensional parts may be formed by, for example, sintering or die-casting of metals, or by injection moulding of polymers. Any bearing surfaces may be formed from a polymer such as POM (Acetal), PTFE or PTFE-impregnated POM.

First actuator assembly Referring also to Figures 9, 10, and 1, a first actuator assembly 38 is schematically shown.

The first actuator assembly 38 takes the form of an eight-SMA wire actuator. The first actuator assembly 38 can be seen as being two planar four-SMA wire actuators connected by a bearing arrangement which converts torque applied about an axis parallel to a first direction (the first direction is parallel to the z-axis as illustrated) into movement along the first direction z. Thus, the two planar four-SMA wire actuators can act in concert to increase movement along the first direction.

The first actuator assembly 38 comprises a first part 39, a second part 40, a first bearing arrangement 41, a first four-wire drive arrangement 42, a third part 43, a second bearing arrangement 44 and a second four-wire drive arrangement 45.

The first bearing arrangement 41 mechanically couples the first part 39 to the second part 40. The second part 40 is movable relative to the first part perpendicular to the optical axis 46 (or "primary axis" -which is parallel to the first direction z) passing through the actuator assembly 38, and is rotatable relative to the first part 39 about the primary axis 46 (lying parallel to the first direction z).

The first drive arrangement 42 comprises a total of four shape memory alloy wires 471, 472, 473, 474 (herein also referred to as "lengths"). The four shape memory alloy wires 471, 472, 473, 474 mechanically connect (or "couple") the second part 40 to the first part 39 of the actuator assembly. The shape memory alloy wires 471, 472, 473, 474 are formed from copper-aluminium-nickel alloy, nickel-titanium alloy or other suitable shape memory alloy.

The second bearing arrangement 44 mechanically couples the second part 40 to the third part 43. The third part 43 is movable relative to the second part 40 and to the first part 39 along the primary axis 46 (lying parallel to the first direction z).

The second drive arrangement 45 comprises a total of four shape memory alloy wires 481, 482, 483, 484. The four shape memory alloy wires 481, 482, 483, 484 mechanically connect the third part 43 to the first part 32 of the actuator assembly 38. The shape memory alloy wires 481, 482, 483, 484 are formed from copper-aluminium-nickel alloy, nickel-titanium alloy or other suitable shape memory alloy.

-First four-SMA wire actuator 49 -Referring in particular to Figure 9, the actuator assembly 38 includes a first flat four-SMA wire actuator 49 substantially as hereinbefore described with respect to Figure 4 (see drive arrangement 11).

The first part 39 of the actuator assembly 38 provides the first structure 12 of the first four-SMA wire actuator 49 and takes the form of a flat, annular plate having a rectangular outer perimeter (or "outer edge") and a circular inner perimeter (or "inner edge").

The second part 40 of the actuator assembly 38 provides the second structure 13 of the first four-SMA wire actuator 49 and takes the form of a flat, thin annular sheet with a rectangular outer perimeter and a circular inner perimeter. The first part 39 is supported on a base (not shown in Figure 10) in the form of a rectangular plate.

The four SMA wires 471, 472, 473, 474 are each attached at one end to respective first crimps 501, 502, 503, 504 (or "static crimps") which are fixedly attached to (or formed as part of) the first part 39. The other end of each SMA wire 471, 472, 473, 474 is attached to a respective second crimp 511, 512, 513, 514 (or "moving crimps") which is fixedly attached to (or formed as part of) the second part 40.

As explained hereinbefore, the first part 39, the second part 40 and the third part 43 may each take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, and may be coated with an electrically-insulating dielectric material. The first, second and third parts 39, 40, 43 are each provided with a respective central aperture aligned with the optical (primary) axis 46 allowing the passage of light from a lens assembly (not shown in Figure 10) mounted to the third part 43 to an image sensor (not shown) supported on the base (not shown in Figure 9).

The four SMA wires 471, 472, 473, 474 may be arranged perpendicular to the optical (primary) axis 46 (lying parallel to the first direction z), or may be inclined at a small angle to a plane perpendicular to the optical axis 46. A "small angle" may in general mean less than 20 degrees, in some instances less than degrees, or even less than 5 degrees. Generally, in a set, the four SMA wires 471, 472, 473, 474 are non-collinear.

The flat four-SMA wire actuator 49 includes two arms 52 connected between the first and second parts 39, 40. The arms 52 are resilient and are configured to provide a suitable retaining force along the optical axis 46 (lying parallel to the first direction z), and also to permit lateral movement with a suitable lateral biasing force.

In the assembled state of the actuator assembly, the arms 52 are deflected from their relaxed state in such a way that the arms 52 provide a force (i.e., the retaining force) which biases the first and second parts 39, 40 together to maintain the contact in the first bearing arrangement, 41, which is this example takes the form of plain bearings 20. At the same time, the arms 52 can be laterally deflected to permit the movement of the second part 40 relative to the first part 39 in directions perpendicular to the optical axis 46 (lying parallel to the first direction).

The arms 52 provide a force (i.e. the lateral biasing force) that biases the second part 40 towards a central position from any direction around the central position, wherein the central position corresponds to the optical axis 46 of the lens assembly (not shown) being substantially aligned with the centre of the light-sensitive region of the image sensor (not shown).

Each arm 52 is generally l'-shaped and extends around the optical axis 46. The angular extent of each arm 52 is preferably at least 90° as measured between the endpoints of the arm 52.

In this example, the arms 52 are formed integrally with the second part 40 at one end thereof and are connected to the first part 39 at the other end thereof.

Alternatively, the arms 52 may be formed integrally with the first part 39 and connected to the second part 40, or the arms 52 may be separate parts connected to both first and second parts 39, 40. The arms 52 may be connected to the plate(s) 39, 40 by welding, which provides both mechanical and electrical connections.

The arms 52 are made of a suitable material that provides the desired mechanical properties and is electrically conductive. Typically, the material is a metal having a relatively high yield, for example steel such as stainless steel.

The first flat actuator assembly 49 includes a number of plain bearings (not shown in Figure 9) spaced around the optical axis 46 (lying parallel to the first direction z) to bear the second part 40 on the first part 39. Preferably, at least three bearings are used in order to assist in providing stable support, although in general, a different number of bearings may be used. The plain bearings (not shown in Figure 9) may take the form of a bearing member in the form of cylinder, and may be attached to, or formed as part of, the first part 39. Bearings (not shown in Figure 9) may be made from a suitable metal or alloy such as phosphor bronze or stainless steel with a diamond-like carbon coating.

The plain bearings (not shown in Figure 9) may be made from, or may include, an upper layer coating of a polymer, such as Polyoxymethylene (POM, Acetal), Polytetrafluoroethylene (PTFE) or PTFE-impregnated POM. The plain bearings (not shown in Figure 9) may be the same or similar to the cylindrical protrusions 23 of the plain bearing 20 (see Figures 5A and 5B).

-Second four-SMA wire actuator 53 -Referring still to Figure 9, the actuator assembly 38 includes a second flat fourSMA wire actuator 53.

The first part 39 of the actuator assembly 38 provides the first structure 12 of the second four-SMA wire actuator 53. The third part 43 of the actuator assembly 38 provides the second structure 13 of the second four-SMA wire actuator 53 and takes the form of a flat, thin annular sheet with a rectangular outer perimeter and a circular inner perimeter.

The four SMA wires 481, 482, 483, 484 are each attached at one end to respective first crimps 541, 542, 543, 544 (or "static crimps") which are fixedly attached to (or formed as part of) the first part 39. The other end of each SMA wire 481, 482, 483, 484 is attached to a respective second crimp 551, 552, 553, 554 (or "moving crimps") which is fixedly attached to (or formed as part of) the third part 43.

The static crimps 541, 542, 543, 544 are arranged with the first and fourth static crimps 541, 544 disposed in a first corner 561 (corresponding to the first and fourth SMA wires 481, 484) and the second and third static crimps 542, 543 disposed in a diagonally opposite third corner 563 (corresponding to the second and third SMA wires 482, 483). Similarly, the first and second moving crimps 551, 552 are disposed at a second corner 562 (corresponding to the first and second SMA wires 481, 482), whilst the third and fourth moving crimps 553, 554 are disposed in a diagonally opposite fourth corner (corresponding to the third and fourth SMA wires 481, 482).

The second flat four-SMA wire actuator 53 is elevated by two pairs of walls 571, 572, 573, 574 (or "panels" or "pillars") upstanding from the first part 39 of the actuator assembly 38 in the two diagonally opposite corners 561, 563. The walls 571, 572, 573, 574 in each pair are perpendicular, lying on different sides of the plate-like first part 39. Each wall 572, 572, 573, 574 has a respective shelf portion (or "tab") extending inwardly to which the static crimps 541, 542, 543, 544 are attached (by welding, adhesive, or other suitable attachment methods).

-Second bearing arrangement 44 -Referring still to Figure 9, the actuator assembly 38 includes a second bearing arrangement 44 in the form of a helical flexure bearing 25 substantially as hereinbefore described with respect to Figure 6.

The second bearing arrangement 44 includes a circular annulus 58 having a central aperture 24 and connected to three, four or more, preferably five or more, helical beam portions 59. In the example shown in Figure 9, there are four helical beam portions 592, 592, 593, 594. The helical beam portions 59 are substantially the same as the helical beam portions 27 of the helical flexure bearing 25 shown in Figure 6. At the end not connected to the circular annulus 58, each helical beam portion 591, 592, 593, 594 is connected to a respective pad 6th, 602, 603, 604, for example for connection to the second part 40.

Each helical beam portion 592, 592, 593, 594 is approximately tangential to the circular annulus 58 (in the same sense) and its' span includes both a first component parallel to the plane containing the first and second axes x, y and a second component parallel to the third axis/first direction z (parallel to the primary or optical axis 46). If the pads 6th, 602, 603, 604 are clamped or otherwise secured and a force is exerted upwards (positive z direction) on the circular annulus 58, then in response the helical beam portions 591, 592, 593, 594 will deflect in the direction of that force. However, in doing so, the ends connected to the circular annulus are also deflected closer to the respective pads 60t, 602, 603, 604, causing the circular annulus 58 to rotate clockwise about an axis parallel to the third axis/first direction z. Conversely, a force exerted downwards (negative z direction) on the circular annulus 58 will result in both a downwards movement of the circular annulus 58 and also an anti-clockwise (counter-clockwise) rotation of the circular annulus 58.

The pads 6W, 602, 603, 604 of the second bearing arrangement 44 in the form of the helical flexure bearing are attached to the second part 40, for example by welding, adhesives, or other suitable attachment methods.

A hollow cylinder 61 having a central aperture is fixed to the circular annulus 58 of the second bearing arrangement 44 in the form of the helical flexure. The hollow cylinder 61 provides a lens carriage for mounting one of more lenses (not shown in Figure 9). The hollow cylinder 61 is mounted to a lower surface 62 (relative to the first direction z) of the circular annulus 58 and depends below (relative to the first direction z) the circular annulus 58 of the second bearing arrangement 44. The length of the hollow cylinder 61 along the optical axis 46 (i.e. length along the first direction z) leaves the bottom of the hollow cylinder 61 clear of the base (not shown in Figure 9) and of an image sensor (not shown in Figure 9) mounted thereon.

An upper surface 63 (relative to the first direction z) of the circular annulus 58 is fixed to the third part 43, which in this case takes the form of an annular rigid frame. In the example shown in Figures 9 and 10, the third part 43 has a generally rectangular outer perimeter and an inner perimeter defining a central aperture.

A can 64 (also referred to as a "screening can") is fitted over the actuator assembly 38 to protect and contain the parts. The can 64 is omitted in the assembled view of Figure 10 for clarity.

Second actuator assembly Referring also to Figures 12, 13A, and 1313, a second actuator assembly 65 is schematically shown.

Figure 12 is a schematic plan view of the second actuator assembly 65. Figure 13A is a schematic cross-section along a diagonal line B-B' shown in Figure 12. Figure 136 is a schematic cross-section along the line C-C' shown in Figure 12.

The second actuator assembly 65 takes the form of an eight-SMA wire actuator. 35 The second actuator assembly 65 is similar to the first actuator assembly 38, except that the shapes and configurations of some parts have been modified to reduce the height of the second actuator assembly 65 along the optical (primary) axis 46 (again parallel to a first direction aligned with the third axis z as shown). In particular, the block diagram shown in Figure 11 is equally applicable to the second actuator assembly 65 as to the first actuator assembly 38.

-First four-SMA wire actuator 66 -Referring in particular to Figure 12, the second actuator assembly 65 includes a first flat four-SMA wire actuator 66.

The first part 39 of the second actuator assembly 65 provides the first structure 12 of the first four-SMA wire actuator 66 and takes the form of a flat, annular plate having a rectangular outer perimeter (or "outer edge") and a circular inner perimeter (or "inner edge").

The second part 40 of the second actuator assembly 65 provides the second structure 13 of the first four-SMA wire actuator 66 and takes the form of a flat, thin annular sheet with a lozenge-shaped outer perimeter and a circular inner perimeter. The first structure 39 is supported on a base (not shown in Figures 12 to 133) in the form of a rectangular plate.

The four SMA wires 471, 472, 473, 474 are each attached at one end to respective first crimps 501, 502, 503, 504 (or "static crimps") which are fixedly attached to (or formed as part of) the first part 39. The other end of each SMA wire 471, 472, 473, 474 is attached to a respective second crimp 511, 512, 513, 514 (or "moving crimps") which is fixedly attached to (or formed as part of) the second part 40. The moving crimps 511, 514 are disposed in one corner of the second actuator assembly 65, with the other moving crimps 512, 513 are disposed in a diagonally opposite corner. Compared to the first actuator assembly 38, the four SMA wires 471, 472, 473, 474 have a reduced length along the directions x, y perpendicular to the optical (primary) axis 46 (lying parallel to the first direction).

As explained hereinbefore, the first and second parts 39, 40 may each take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, and may be coated with an electrically-insulating dielectric material. The first and second parts 39, 40 are each provided with a respective central aperture aligned with the optical (primary) axis 46 (lying parallel to the first direction) allowing the passage of light from a lens assembly (not shown in Figures 12 to 135) mounted to the third part 43 to an image sensor (not shown) supported on the base (not shown in Figures 12 to 135).

The four SMA wires 471, 472, 473, 474 may be perpendicular to the optical axis 46 (lying parallel to the first direction z), or inclined at a small angle to a plane perpendicular to the optical axis 46. A "small angle" may in general mean less than 20 degrees, in some instances less than 10 degrees, or even less than 5 degrees. Generally, in a set, the four SMA wires 471, 472, 473, 474 are non-collinear.

Similarly to the arms 52 of the first actuator assembly 38, the first four-SMA wire actuator 66 of the second actuator assembly 65 includes two or more arms (not shown in Figures 12 to 135) connected between the first and second parts 39, 40. The arms (not shown) are resilient and are configured to provide a suitable retaining force along the optical axis 46 (lying parallel to the first direction z), and also to permit lateral movement with a suitable lateral biasing force.

In the assembled state of the actuator assembly, the arms (not shown in Figures 12 to 135), are deflected from their relaxed state in such a way that the arms (not shown in Figures 12 to 135) provide a force (i.e., the retaining force) which biases the first and second parts 39, 40 together and maintains the contact in plain bearings (not shown in Figures 12 to 133) which provide the first bearing arrangement 41 of the second actuator assembly 65. At the same time, the arms (not shown in Figures 12 to 135) can be laterally deflected to permit the movement of the second part 40 relative to the first part 39 in directions perpendicular to the optical axis 46 (lying parallel to the first direction z).

The arms (not shown in Figures 12 to 133) provide a force (i.e., the lateral biasing force) that biases the second part 40 towards a central position from any direction around the central position, wherein the central position corresponds to the optical axis 46 of the lens assembly (not shown in Figures 12 to 136) being substantially aligned with the centre of the light-sensitive region of the image sensor (not shown in Figures 12 to 133).

Each arm (not shown in Figures 12 to 136) may be generally 'L-shaped and extends around the optical axis 46 (lying parallel to the first direction z). The angular extent of each arm (not shown in Figures 12 to 136) is preferably at least 900 as measured between the endpoints of the arm (not shown in Figures 12 to 136).

In this example, the arms (not shown in Figures 12 to 136) are formed integrally with the second part 40 at one end thereof and are connected to the first part 39 at the other end thereof. Alternatively, the arms (not shown in Figures 12 to 133) may be formed integrally with the first part 39 and connected to the second part 40 or the arms (not shown in Figures 12 to 133) may be separate parts connected to both first and second parts 39, 40. The arms (not shown in Figures 12 to 133) may be connected to the first and/or second parts 39, 40 by welding, which may provide both mechanical and electrical connections.

The arms (not shown in Figures 12 to 133) are made of a suitable material that provides the desired mechanical properties and is electrically conductive. Typically, the material is a metal having a relatively high yield, for example steel such as stainless steel.

The first four-SMA wire actuator 66 includes a number of plain bearings (not shown in Figures 12 to 136) spaced around the optical axis 46 (lying parallel to the first direction z) to bear the second structure 40 on the first structure 39. Preferably, at least three bearings are used in order to assist in providing stable support, although in general, a different number of bearings may be used. The plain bearings (not shown in Figures 12 to 133) may take the form of a bearing member in the form of cylinder, and may be attached to, or formed as part of, the first part 39, for example, the same as, or similar to, the cylindrical protrusions 23 of the plain bearing 20 (see Figures 5A and 56). Plain bearings (not shown in Figures 12 to 133) may be made from a suitable metal or alloy such as phosphor bronze or stainless steel with a diamond-like carbon coating.

The plain bearings (not shown in Figures 12 to 13B) may be made from, or may include an upper layer coating of, a polymer, such as Polyoxymethylene (POM, Acetal), Polytetrafluoroethylene (PTFE) or PTFE-impregnated POM.

-Second four-SMA wire actuator 67 -Referring still in particular to Figure 12, the second actuator assembly 65 includes a second flat four-SMA wire actuator 67.

The first part 39 of the second actuator assembly 65 provides the first structure 12 of the second four-SMA wire actuator 67. The third part 43 of the second actuator assembly 43 provides the second structure 13 of the second four-SMA wire actuator 67 and takes the form of a flat, thin annular sheet with a circular outer perimeter and a circular inner perimeter.

The four SMA wires 481, 482, 483, 484 are each attached at one end to respective the static crimps 541, 542, 543, 544 (or "static crimps") which are fixedly attached to (or formed as part of) the first part 39. The other end of each SMA wire 481, 482, 483, 484 is attached to a respective second crimp 551, 552, 553, 554 (or "moving crimps") which is fixedly attached to (or formed as part of) the third part 43. The moving crimps 551, 552 are disposed in one corner of the second actuator assembly 65, with the other moving crimps 553, 554 disposed in a diagonally opposite corner. Compared to the first actuator assembly 38, the four SMA wires 4th, 482, 483, 484 have a reduced length along the directions x, y perpendicular to the optical (primary) axis 46 (lying parallel to the first direction z).

The third part 43 comprises an annulus 68 which generally sits inside the central aperture in the second part 40. First and second diagonally-opposite arms 691, 692 (or "wings") extend outwardly and over the second part 40 so that the moving crimps 551, 552, 553, 554 of the second four-SMA actuator 67 lie outside the outer perimeter of the second part 40.

Each of the arms (or wings) 691, 692 includes a first portion 701, 702 and a second portion 711, 712 (see in particular Figure 13A), connected by a respective transition portion 721, 722. The first portions 701, 702 are co-planar with the annulus 68, and each extends to beyond the perimeter of the second part 40. The second portion 711 supports the pair of moving crimps 551, 552 and the second portion 712 supports the other pair of moving crimps 553, 554. The second portions 711, 712 are offset below (relative to the first direction z) the annulus 68 and the first portions 701, 702, such that the four SMA wires 481, 482, 483, 484 of the second four-SMA wire actuator 67 are generally co-planar with the four SMA wires 471, 472, 473, 474 of the first four-SMA wire actuator 66 (at least when the second actuator assembly 65 is unpowered and at rest in the central position). The transition portions 721, 722 run parallel to the optical axis 46 (lying parallel to the first direction) in the example shown in Figure 13A. In general, a transition portion 72 may have any shape which provides the required offset between the first and second portions 70, 71, and may be angled relative to the optical axis 46 and/or curved. The first, second and transition portions 70, 71, 72 may be formed from an initially planar arm (wing) 69, for example by bending or stamping. The first, second and transition portions 70, 71, 72 need not be separated by a discontinuities, and may be take the form of regions of a continuously profiled arm (wing) 69.

The second actuator assembly 65 includes first, second, third and fourth walls 731, 732, 733, 734 which run along the perimeter of the first part 39 and extend upwardly (relative to the first direction z). The walls 731, 732, 733, 744 may be formed as a single piece with the first part 39, or may be a separate part or parts joined to the plate of the first part 39. First, second, third and fourth tabs 741, 742, 743, 744 extend inwardly from the middle of each wall 731, 732, 733, 734 which support the static crimps 50, 54.

-Second bearing arrangement 44 -Referring still in particular to Figure 12, the second actuator assembly 65 includes second bearing arrangement 44 in the form of a helical flexure bearing substantially as hereinbefore described with respect to the first actuator assembly 38 and/or the helical flexure bearing 29 shown in Figure 6.

The second bearing arrangement 44 includes a circular annulus 58 (seen in cross-section in Figures 13A and 13B) having a central aperture and connected to three, four or more, preferably five or more, helical beam portions 59. In the example shown in Figures 12 to 13B, there are four helical beam portions 591, 592, 593, 594. At the end not connected to the circular annulus 58, each helical beam portion 591, 592, 593, 594 is connected to a pad 601, 602, 603, 604. Compared to the second bearing arrangement 44 of the first actuator assembly 38, the second bearing arrangement 44 of the second actuator assembly 65 may have the same or reduced height along the optical (primary) axis 46 (lying parallel to the first direction z), and is otherwise the same.

The pads 6th, 602, 603, 604 of the second bearing arrangement 44 in the form of a helical flexure bearing are attached to the second part 40, for example by welding, adhesives, or other suitable attachment methods.

A hollow cylinder 61 (visible in Figures 13A and 13B) having a central aperture is fixed to the circular annulus 58 of the second bearing arrangement 44. The hollow cylinder 61 provides a lens carriage for mounting one of more lenses (not shown in Figures 12 to 13B). The hollow cylinder 61 is mounted to a lower surface (relative to the first direction z) of the circular annulus 58 and depends below (relative to the first direction z) the circular annulus 58 of the second bearing arrangement. The length of the hollow cylinder 61 along the optical (primary) axis 46 (lying parallel to the first direction z as indicated) leaves the bottom of the hollow cylinder 61 clear of the base and the image sensor (not shown in Figures 12 to 13B) mounted on the base (not shown in Figures 12 to 13B).

An upper surface (relative to the first direction z) of the circular annulus 58 is fixed to an underside of the third part 43.

A can (not shown in Figures 12 to 13B) (also referred to as a "screening can") is fitted over the second actuator assembly 65 to protect and contain the parts.

In a modification (not shown) of the second actuator assembly 65, each pair of static crimps 50, 54 supported on a respective tab 74 may be replaced by a single, common crimp (not shown), and the corresponding pair of SMA wires 47, 48 may be replaced by a single length of SMA wire secured at either end to moving crimps 51, 55, and in the middle by the (static) common crimp (not shown). The driving currents in each half of the single length of SMA wire may be independently controlled by using the common crimp (not shown) as a common current sink (for example corresponding to system ground). Independent electrical connections to the moving crimps 51, 55 may be provided by respective flexures (not shown).

Third actuator assembly Referring to Figures 14 and 15, a third actuator assembly 75 is schematically shown.

The third actuator assembly 75 takes the form of an eight-SMA wire actuator. The third actuator assembly 75 is similar to the first actuator assembly 38, except that instead of a helical flexure bearing, the second bearing arrangement 44 takes the form of a helical roller bearing. In particular, the block diagram shown in Figure 11 is equally applicable to the third actuator assembly 65 as to the first actuator assembly 38.

-First four-SMA wire actuator 76 -Referring in particular to Figure 14, the third actuator assembly 75 includes a first flat four-SMA wire actuator 76 which is substantially the same as the flat SMA actuator assembly 15 as hereinbefore described with respect to Figure 4.

The first part 39 of the third actuator assembly 75 provides the first structure 12 of the first four-SMA wire actuator 76 and takes the form of a flat, annular plate having a rectangular outer perimeter (or "outer edge") and a circular inner perimeter (or "inner edge").

The second part 40 of the third actuator assembly 75 provides the second structure 13 of the first four-SMA wire actuator 76 and takes the form of a flat, thin annular sheet with a rectangular outer perimeter and a circular inner perimeter. The first part 39 is supported on a base (not shown in Figures 14 and 15) in the form of a rectangular plate.

The four SMA wires 471, 472, 473, 474 are each attached at one end to respective first crimps 501, 502, 503, 504 (or "static crimps") which are fixedly attached to (or formed as part of) the first part 39. The other end of each SMA wire 471, 472, 473, 47 is attached to a respective second crimp 511, 512, 513, 514 (or "moving crimps") which is fixedly attached to (or formed as part of) the second part 40.

As explained hereinbefore, the first and second parts 39, 40 may each take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, and may be coated with an electrically-insulating dielectric material. The first and second parts 39, 40 are each provided with a respective central aperture aligned with the optical (primary) axis 46 (lying parallel to the first direction z) allowing the passage of light from a lens assembly (not shown in Figures 14 and 15) mounted to the third part 43 to an image sensor 6 supported on the base (not shown in Figures 14 and 15).

The flat four-SMA wire actuator 76 includes two arms 52 connected between the first and second parts 39, 40, and configured the same as the arms 52 of the first four-wire drive arrangement 42 of the first actuator assembly 38.

The first four-SMA wire actuator 76 includes a number of plain bearings (not shown in Figures 14 and 15) spaced around the optical (primary) axis 46 (lying parallel to the first direction z) to bear the second structure 40 on the first structure 39. The plain bearings (not shown in Figures 14 and 15) are the same as plain bearings described hereinbefore for the first four-wire drive arrangement 42 of the first actuator assembly 38.

-Second four-SMA wire actuator 77 -Referring still in particular to Figure 14, the third actuator assembly 75 includes a second four-SMA wire actuator 77.

The third part 43 of the third actuator assembly 75 provides the second structure 13 of the second four-SMA wire actuator 77 and takes the form of a flat, thin annular sheet with a rectangular outer perimeter and a circular inner perimeter. The first structure 12 of the second four-SMA wire actuator 77 of the third actuator assembly 75 is provided by an extension plate 78 of the first part 39 in the form of a flat, thin annular sheet with a rectangular outer perimeter and a circular inner perimeter.

The extension plate 78 is rigidly connected to the first part 39. In this example, when the can 64 (also referred to as a "screening can") is fitted over the third actuator assembly 75 to protect and contain the parts, both the first part 39 and the extension plate 78 are attached to the can 64 (for example by welding). The can 8 is omitted in Figure 15 for clarity.

The four SMA wires 481, 482, 483, 484 are each attached at one end to respective first crimps 541, 542, 543, 544 (or "static crimps") which are fixedly attached to (or formed as part of) the extension plate 78. The other end of each SMA wire 481, 482, 483, 484 is attached to a respective second crimp 551, 552, 553, 554 (or "moving crimps") which is fixedly attached to (or formed as part of) the third part 43.

In contrast to the first four-SMA wire actuator 76, the second four-SMA wire actuator 77 does not include any plain bearings or flexure arms 52. Consequently, the third part 43 is not held in contact with the extension plate 78, either directly or via bearings. The height of the extension plate 78 above (relative to the first direction z) the first part 39 should be set according to a desired distance of travel of the third part 43 along the optical axis 46 (lying parallel to the first direction z). Advantageously, the extension plate 78 may also serve as an end-stop which may help prevent excessive travel of the third part 43 in response to a shock or drop.

-Second bearing arrangement 44 -Referring still to Figure 14, in contrast to the first and second actuator assemblies 38, 65 which employ helical flexure bearings, the third actuator assembly 75 includes a second bearing arrangement 44 in the form of a helical roller bearing 79 The second bearing arrangement 4 in the form of the helical roller bearing 79 includes a first portion in the form of a lens carriage 80 which performs the function of supporting a lens or lenses (not shown in Figures 14 and 15) of a lens assembly (not shown in Figures 14 and 15). The helical roller bearing 79 includes an annulus 81 having a circular inner perimeter defining a central aperture, and an outer perimeter which alternates between rectangular and circular outlines. The annulus 81 supports four ramps 821, 822, 823, 824 equispaced in a loop about the central aperture of the annulus 81. Each ramp 821, 822, 823, 824 takes the form of a rectangular frame having an elongated aperture 831, 832, 833, 834 extending along a length of the respective ramp 821, 822, 823, 824. The ramps 821, 822, 823, 824 all make substantially equal angles to the annulus 81 (which lies in a plane parallel to first and second axes x, y).

When assembled, each elongated aperture 831, 832, 833, 834 receives a corresponding ball bearing 841, 842, 843, 844.

The lens carriage 80 is generally cylindrical about a central aperture for mounting of one or more lenses (no shown). The lens carriage 80 also includes four protrusions 851, 852, 853, 854 extending radially outwards from the generally cylindrical lens carriage 80. The first protrusion 851 defines a first bearing surface 861 in the form of a 'V-shaped channel. The first bearing surface 861 is oriented generally upwards (normals to the first bearing surface 861 have components generally in the positive +z direction along the first direction). The second protrusion 852 defines a corresponding bearing surface 862 in the form of a 1V'-shaped channel oriented generally downwards (normals to the second bearing surface 862 have components generally in the negative -z direction along the first direction z). The third and fourth protrusions 853, 854 define third and fourth bearing surfaces 863, 863, respectively, each in the form of an angled planar surface oriented generally upwards (normals to the third and fourth bearing surfaces 863, 864 have components generally in the positive +z direction along the first direction z).

When assembled, each bearing surface 861, 862, 863, 864 is in rolling contact with the corresponding ramp 821, 822, 823, 824 via the respective ball bearing 841, 842, 843, 844. However, the first and third bearing surfaces 861, 863 will lie below (relative to the first direction z) the corresponding ramps 821, 823, whereas the second and fourth bearing surfaces 862, 864 will lie above the corresponding ramps 822, 824.

The annulus 81 is fixed to the 40 for example by welding, adhesive, or other suitable attachment methods. An upper surface (relative to the first direction z) of the lens carriage 80 is fixed to the third part 43.

In use, when the first drive arrangement 42 in the form of the first four-SMA wire actuator 76 and/or the second drive arrangement 45 in the form of the second four-SMA wire actuator 77 applies a torque about an axis parallel to the first direction z), the relative rotation between the second and third parts 40, 43 causes the ball bearings 841, 842, 843, 844 to roll between the ramps 821, 822, 823, 824 and bearing surfaces 861, 862, 863, 864, displacing the lens carriage 80 up or down (relative to the first direction z) depending on the direction of the torque and corresponding rotation Rz. Whilst the second part 40 is retained in bearing contact with the first part 39 by arms 52, the third part 43 and attached lens carriage 80 are moved towards or away from the extension plate 78.

Besides facilitating up or down movement of the lens carriage 80, the underover-under-over configuration of the ramps 821, 822, 823, 824 and bearing surfaces 861, 862, 863, 864 means that, when the actuator assembly is assembled the ramps 821, 822, 823, 824 are flexed, providing a loading force biasing the lens carriage 80 towards an equilibrium position along the optical axis 46 (lying parallel to the first direction z).

In addition to movements along the optical axis 46 (lying parallel to the first direction z), the first and second actuators 76, 77 may additionally or alternatively be actuated to displace the second and third parts 40, 43 perpendicularly to the first direction. This will displace a rotation axis of the helical roller bearing 79 from the optical axis 46, however the axes will remain parallel to the first direction z. Such lateral displacements of the lens carriage 80 may be controlled independently (within a range of motion) of the rotations to control travel of the lens carriage 80 along the optical axis 46 (parallel to the first direction z), and the two movements may be combined.

The extension plate 78 is not intended to support or to constrain movements of the third part 43, and primarily serves to support the static crimps 54 above (relative the first direction z) the third part 43. Accordingly, the extension plate 78 connected via the can 64 may be exchanged for any other structure which serves to support the static crimps 54 above (relative to the first direction z) the third part 43. For example, the extension plate 78 could instead be provided as an integral extension of the first part 39 which is folded back over on itself. Alternatively, the extension plate 78 could be omitted and the static crimps 55 of the second four-SAM wire actuator 77 could be supported on walls 57 as for the first actuator assembly 38 (essentially the first actuator assembly 38 with the helical flexure bearing exchanged for the helical roller bearing).

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

For example, the image sensor may be mounted on the third, movable part instead of (or possibly in addition to) the lens assembly.

More generally, the actuator assembly can be suitably used for moving any 25 component of any device.

Different SMA drive assemblies and different bearings can be suitably used in the actuator assemblies hereinbefore described.

In the description hereinbefore, parts have been described as rectangular, and this should be interpreted as encompassing square shapes. In the description hereinbefore, parts have been described as circular, and this should be interpreted as encompassing elliptical shapes.

First to fourth SMA wires have been described and shown as directly connecting the first and second parts and/or first and third part. However, in some examples the first to fourth SMA wires may indirectly connect the first and second/third parts, for example via one or more intermediate structures (not shown). Intermediate structures (not shown) may be configured to help extend the stroke of one or more SMA wires.

The first 38 and second 65 actuator assemblies include second bearing arrangements 44 in the form of helical flexure bearings, and the third 75 actuator includes a second bearing arrangement 44 in the form of a helical roller bearing. Alternatively, any of the first to third actuator assemblies 38, 65, 75 may be modified to use a second bearing arrangement 44 in the form of a helical plain bearing similar to the helical plain bearing 29 described in relation to Figures 7A and 7B.

The first to third actuator assemblies 38, 65, 75 have been described as including first bearing arrangements 41 in the form of planar (e.g. three-point) plain bearings (such as the three-point bearing 20 shown in Figures 5A and 5B). However, any of the actuator assemblies 38, 65, 75 may be modified to replace the first bearing arrangement 41 with a planar roller bearing or equivalent planar bearing.

Four-wire actuator assemblies The first to third actuator assemblies 38, 65, 75 and modifications thereof all use pairs of four-SMA wire actuators to provide lateral displacements (perpendicular) relative to the optical axis 46 (lying parallel to the first direction z) and/or rotations which are converted by the second bearing arrangement 44 into translations along (parallel to) the optical axis 46. When used as an SMA actuator assembly 2 for a camera 1, the lateral displacements may provide an ()IS function whilst the translations along the optical axis 46 provide an autofocus or zoom function.

However, in some applications, only translations parallel to the optical (primary) axis 46 may be required (i.e. translations parallel to the first direction z). For example, a camera 1 including an autofocus or zoom function and either omitting OIS, or using a separate actuator for OIS.

Constraint of displacements perpendicular to the optical (primary) axis 46 (lying parallel to the first direction z) of an actuator assembly 38, 65, 75 may be achieved by replacement the first bearing arrangement 41 with a rotary bearing, for example the rotary bearing 34 shown in Figures 8A and 8B. Alternatively, any other bearing which permits rotation about the optical axis 46 whilst resisting (or even preventing) displacements perpendicular to the optical axis 46.

With such additional constraint, eight SMA wires are not needed, and it is possible to simplify the first and second drive arrangements 42, 45 by using two SMA-wire actuators instead of four SMA-wire actuators. All that is needed is one SMA wire applying a torque in a clockwise sense about the optical (primary) axis 46 (lying parallel to the first direction z), and an opposed SMA wire applying a torque in an anti-clockwise sense about the optical axis 46. This may be done by simply omitting two SMA wires from each of the first and second drive arrangements 42, 45 Alternatively, referring also to Figure 16, a first two SMA-wire actuator 87 is shown.

The first two SMA-wire actuator 87 includes a first structure 88 and a second structure 89, coupled by a rotary bearing (not shown). A pair of pillars 901, 902 are upstanding from both corners along a single side of the first structure 88. A first SMA wire 911 connects the top-right (as illustrated) corner of the second structure to the first pillar 9th disposed in the top-left (as illustrated) corner of the first structure 88. A second SMA wire 912 connects the bottom-right (as illustrated) corner of the second structure to the second pillar 902 disposed in the bottom-left (as illustrated) corner of the first structure 88.

Upon contraction of the first SMA wire 911 a torque is applied anti-clockwise on the second structure 89. Upon contraction of the second SMA wire 912, a torque is applied anti-clockwise on the second structure 89. Neither torque is balanced, and a force in the -x direction as illustrated is also applied in either case. However, the lateral force is resisted by the constraint of the rotary bearing (not shown) which couples the first and second structures 88, 89.

A two-up, two-down, four-SMA wire actuator assembly may be formed by coupling a helical bearing between a pair of the first two SMA-wire actuator 87, so that rotations generated by applied torques may be converted into translations parallel to the optical (primary) axis 46 (lying parallel to the first direction z as illustrated).

Referring also to Figure 17, a second two SMA-wire actuator 92 is shown.

The second two-SMA wire actuator 92 is the same as the first two-SMA wire actuator 87, except that the second pillar 902 is omitted, and the second SMA wire 912 connects the bottom-left (as illustrated) corner of the second structure to the first pillar 901.

Two-wire actuator assemblies Even further simplification is possible if one of the SMA wires 911, 912 of a two-SMA wire actuator 87, 92 is replaced by a spring. In such examples, a torque in one sense (clockwise or anticlockwise) is provided by contraction of an SMA wire which is opposed by the spring instead an opposed SMA wire. A torque in the opposite sense is applied by ceasing driving of the SMA wire to allow it to cool and expand, driven by the spring.

Although examples have been described with respective first directions aligned parallel to the z-axis of a Cartesian coordinate system, this is purely for the same of explanatory clarity.

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

Claims

Claims 1. An actuator assembly comprising: a first part; a second part; a first bearing arrangement mechanically coupling the first part to the second part; a first drive arrangement comprising four lengths of shape memory alloy wire; wherein the first bearing arrangement and first drive arrangement are configured such that the second part is rotatable relative to the first part about an axis parallel to a first direction; a third part; a second bearing arrangement mechanically coupling the second part to the third part; and a second drive arrangement comprising four lengths of shape memory alloy wire; wherein the second bearing arrangement, the first drive arrangement and the second drive arrangement are configured such that in response to a torque applied about an axis parallel to the first direction by the first drive arrangement and/or the second drive arrangement, the third part moves towards or away from the first part along the first direction.
2. The actuator assembly of claim 1, wherein: the first bearing arrangement and the first drive arrangement are configured such that the second part is movable relative to the first part perpendicular to the first direction; and the second bearing arrangement and the second drive arrangement are configured such that the third part is movable relative to the first part perpendicular to the first direction.
3. The actuator assembly of claim 2, configured such that the second and third parts are movable relative to the first part perpendicular to the first direction whilst maintaining a position of the third part relative to the second 35 part.
4. The actuator assembly of claim 2 or 3, configured such that the second and third parts are differently movable perpendicular to the first direction, so as to tilt the third part relative to the first and second parts about an axis perpendicular to the first direction.
5. The actuator assembly of any one of claims 1 to 4, wherein the first bearing arrangement is configured to resist movement of the second part towards or away from the first part along the first direction.
6. The actuator assembly of any one of claims 1 to 5, wherein the first bearing arrangement is configured to permit movement of the second part relative to the first part in a plane perpendicular to the first direction.
7. The actuator assembly of any one of claims 1 to 6, wherein the first bearing arrangement comprises: a planar bearing.
8. The actuator assembly of any one or claims 1 to 7, wherein the four lengths of shape memory alloy wire in the first drive arrangement are substantially co-planar.
9. The actuator assembly of any one or claims 1 to 8, wherein the four lengths of shape memory alloy wire in the second drive arrangement are substantially co-planar.
10. The actuator assembly of any one or claims 1 to 9, wherein: the four lengths of shape memory alloy wire in the first drive arrangement are substantially co-planar lying in a first plane; and the four lengths of shape memory alloy wire in the second drive arrangement are substantially co-planar lying in a second plane; wherein the first and second planes are parallel.
11. The actuator assembly of claim 10, wherein the first and second planes are offset from each other along the first direction.
12. The actuator assembly of claim 10, wherein the first and second planes are substantially co-planar.
13. The actuator assembly of any one or claims 1 to 8, wherein the four lengths of shape memory alloy wire in the first drive arrangement span a first length parallel to the first direction, the four lengths of shape memory alloy wire in the second drive arrangement span a second length parallel to the first direction, and the first and second lengths at least partly overlap.
14. The actuator assembly of claim 12 or 13, wherein the four lengths of shape memory alloy in the first and second drive arrangements are each connected to the first part via a connection portion, and the connection portions lie in a plane normal to the first direction.
15. The actuator assembly of claim 14, comprising four shape memory alloy wires, each shape memory alloy wire providing one of the four lengths of shape memory alloy in the first drive arrangement and one of the four lengths of shape memory alloy in the second drive arrangement, wherein each shape memory alloy wire is connected to the first part via a common connection portion at (or near to) a midpoint of the shape memory alloy wire.
16. The actuator assembly of any preceding claim, wherein the second bearing arrangement comprises a helical bearing.
17. The actuator assembly of any one of claims 1 to 16, wherein the second bearing arrangement comprises a helical rolling-element bearing.
18. The actuator assembly of claim 17, wherein the helical rolling-element bearing comprises: a plurality of helical bearing parts arranged in a loop about an axis parallel to the first direction.
19. The actuator assembly of claim 18, wherein each helical bearing part 35 comprises: a first bearing surface, a second bearing surface and at least one rolling element arranged to be guided by the first and second bearing surfaces along a helical path.
20. The actuator assembly of claim 18, wherein each helical bearing part cornprises: a flexible ramp, wherein the flexible ramps are pre-stressed in an equilibrium or neutral configuration of the first bearing.
21. The actuator assembly of any one of claims 1 to 15, wherein the second bearing arrangement comprises a helical flexure.
22. The actuator assembly of claim 21, wherein the helical flexure comprises at least three flexure arms extending in a direction parallel to the first direction and around an axis parallel to the first direction in the same sense.
23. The actuator assembly of claim 21 or 22, further comprising: an annular ring connected to the third part and interposed between the third part and the second part.
24. The actuator assembly of any one of claims 1 to 23, wherein: the second part includes a first annulus; wherein the first annulus is substantially co-planar with the third part at a closest position of the third part relative to the second part along the first direction.
25. The actuator assembly of claim 24, wherein: the second part includes a first pair of arms extending radially away from the first annulus; and the third part includes a second pair of arms extending radially away from an axis parallel to the first direction.
26. A camera module comprising: an actuator assembly according to any one of claims 1 to 25; an image sensor supported by one of the first part and the third part; a lens supported by the other of the first part and the third part.
27. A camera module according to claim 26, further comprising: a controller configured to control the actuator assembly to implement an 5 auto-focus function using the movement of the third part towards or away from the second part along the first direction.
28. A method comprising: causing the actuator assembly of any one of claims 1 to 25 or the camera module of claim 26 or 27 to implement an automatic focussing function and/or optical image stabilization function of a camera.
29. A method according to claim 28, comprising: actuating the first drive arrangement and/or the second drive arrangement so as to apply a torque to the second bearing arrangement about an axis parallel to the first direction; wherein in response to the torque, the third part moves towards or away from the first part along the first direction.
30. A method according to claim 28 or claim 29, comprising: actuating the first and second drive arrangements so as to displace the second and third parts relative to the first part by a distance perpendicular to the first direction, whilst maintaining a position of the third part relative to the second part.
31. A method according to any one of claims 28 to 30, comprising: actuating the first and second drive arrangements so as to displace the second part relative to the first part by a first distance in a second direction and to displace the third part relative to the first part by a second distance in a third direction, wherein the second and third directions are both perpendicular to the first direction, so as to tilt the third part relative to the first and second parts about an axis perpendicular to the first direction.
32. A computer program stored on a non-transitory machine readable 35 medium, wherein when executed by a processor of a device comprising the actuator assembly according to any one of claims 1 to 25 or the camera module of claim 26 or 27, to cause the actuator assembly or camera module to carry out the method according to any one of claims 28 to 31.
33. An actuator assembly comprising: a first part; a second part; a first bearing arrangement mechanically coupling the first part to the second part; a first drive arrangement comprising one or more lengths of shape memory alloy wire; wherein the first bearing arrangement and the first drive arrangement are configured such that the second part is rotatable relative to the first part about an axis parallel to a first direction; a third part; a second bearing arrangement mechanically coupling the second part to the third part; and a second drive arrangement comprising one or more lengths of shape memory alloy wire; wherein the second bearing arrangement, the first drive arrangement and the second drive arrangement are configured such that in response to a torque applied about an axis parallel to the first direction by the first drive arrangement and/or the second drive arrangement, the third part moves towards or away from the first part along the first direction.
34. An actuator assembly according to claim 33, wherein the first drive arrangement comprises a first length of shape memory alloy wire configured to apply a torque clockwise about an axis parallel to the first direction and a second length of shape memory alloy wire configured to apply a torque anti-clockwise about that axis parallel to the first direction.
35. An actuator assembly according to claim 33 or claim 34, wherein the second drive arrangement comprises a third length of shape memory alloy wire configured to apply a torque clockwise about an axis parallel to the first direction and a fourth length of shape memory alloy wire configured to apply a torque anti-clockwise about that axis parallel to the first direction.
36. An actuator assembly according to any one of claims 33 to 35, further comprising one or more first springs coupling the first part to the second part, each first spring configured to oppose contraction of at least one length of shape memory alloy wire of the first drive arrangement.
37. An actuator assembly according to any one of claims 33 to 36, further comprising one or more second springs coupling the first part to the third part, each second spring configured to oppose contraction of at least one length of shape memory alloy wire of the second drive arrangement.