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 to move a lens assembly in directions perpendicular to the optical axis so as to provide optical image stabilization (OIS). Where such a camera is to be incorporated into a portable electronic device such as a mobile telephone, miniaturization can be important.

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 and a second part constrained to move along a first path in a first plane relative to the first part. The actuator assembly also includes a first set of one or more shape memory alloy wires configured to move the second part along the first path. The first set of shape memory alloy wires is arranged such that movements of the second part are amplified relative to corresponding length changes of the first set of shape memory alloy wires. The actuator assembly also includes a third part constrained to move along a second path in a second plane relative to the second part. The second plane is parallel to, or coplanar with, the first plane. The second path is non-parallel with the first path. The actuator assembly also includes a second set of one or more shape memory alloy wires configured to move the third part along the second path. The second set of shape memory alloy wires are arranged such that movements of the third part are amplified relative to corresponding length changes of the second set of shape memory alloy wires. So, movement of the third part in the second plane with respect to the first part is a combination of movement of the second part relative to the first part, and movement of the third part relative to the second part.

The first path may be a straight, or at least substantially straight, line. The second path may be a straight, or at least substantially straight, line. The first and second paths may be orthogonal axes. However, in general, the first path may be curved and/or he second path may be curved.

Each shape memory alloy wire of the first set may be fixed between the second part and the first part. Each shape memory alloy wire of the first set may be fixed to the second part at one end and fixed to the first part at the other end. Alternative, each shape memory alloy wire of the first set may be fixed to the second part at one or more points along its length, and to the first part at both its ends. Similarly, each shape memory alloy wire of the first set may be fixed to the first part at one or more points along its length, and to the second part at both its ends.

Each shape memory alloy wire of the second set may be fixed between the third part and the second part. Each shape memory alloy wire of the second set may be fixed to the third part at one end and fixed to the second part at the other end. Alternatively, each shape memory alloy wire of the second set may be fixed to the third part at one or more points along its length, and to the second part at both its ends. Each shape memory alloy wire of the second set may be fixed to the second part at one or more points along its length, and to the third part at both its ends.

The second part may have one degree of freedom, i.e. move in one degree of freedom, with respect to the first part. The third part may have one degree of freedom, i.e. move in one degree of freedom other than the degree of freedom in which the second part moves relative to the first part, with respect to the second part. Thus, the third part may have two independent degrees of freedom, i.e. move in two degrees of freedom, with respect to the first part. Each shape memory alloy wire of the first set may have a span length between attachment points (or fixed/contact points) which is at least 80% of a side length of the second part. Additionally or alternatively, each shape memory alloy wire of the second set may have a span length between attachment points (or fixed/contact points) which is at least 80% of a side length of the third part.

Each shape memory alloy wire of the first set may include a single span. Additionally or alternatively, each shape memory alloy wire of the second set may include a single span. So, the shape memory alloy wires may extend in a single straight line between the parts they are connected to.

So, none of the shape memory alloy wires of the first set are configured in a V- shape when viewed perpendicular to the first plane. None of the shape memory alloy wires of the second set are configured in a V-shape when viewed perpendicular to the second plane. In other words, no shape memory alloy wire of the first or second sets is fixed at first and second ends, and hooked over (without fixing) a retaining feature which is non-collinear with the first and second ends.

The first set of shape memory alloy wires may be configured to apply net moment between the first part and the second part. Although the first set of shape memory alloy wires may apply net moment between the first part and the second part, rotation of the second part relative to the first part may be constrained, for example by one or more bearings, flexures and so forth. The constraint against rotation may be provided by the same features which constrain the first part to move along the first path.

The second set of shape memory alloy wires may be configured to apply net moment between the second part and the third part. Although the second set of shape memory alloy wires may apply net moment between the second part and the third part, rotation of third part relative to the second part may be constrained, for example by one or more bearings, flexures and so forth. The constraint against rotation may be provided by the same features which constrain the third part to move along the second path. The first set of shape memory alloy wires may consist of two shape memory alloy wires, and each shape memory alloy wire of the first set may include a single straight span. Additionally or alternatively, the second set of shape memory alloy wires may consist of two shape memory alloy wires, and each shape memory alloy wire of the second set may include a single straight span.

The first path may be substantially parallel (which includes parallel) to a first axis. The second path may be substantially parallel (which includes parallel) to a second axis. The first and second axes may make an angle between 10° and 90° to one another. In some embodiments, the first and second axes are substantially perpendicular to each other.

The actuator assembly may include a first bearing arrangement coupling the first part and the second part. The first bearing arrangement may be configured to constrain movement of the second part relative to the first part to the first plane and/or to the first path. The actuator assembly may include a second bearing arrangement coupling the third part and the second part. Alternatively, the actuator assembly may include a second bearing arrangement coupling the third part and the first part. In either case, the second bearing arrangement may be configured to constrain movement of the third part relative to the second part to the second plane and/or to the second path.

Movements of a second/third part may be amplified relative to corresponding length changes of a shape memory alloy wire of the first/second set by constraining the second/third part such that it cannot move directly in a contraction direction of that shape memory alloy wire. In other words, the shape memory alloy wires of the first set are not parallel to the first path, and the shape memory alloy wires of the second set are not parallel to the second path. Constraint leading to amplification may be provided by one or more resilient elements, which may be comprised by the first and/or second bearing arrangements. Resilient elements may include, or take the form of, springs. Resilient elements may include, or take the form of, flexures. Constraint leading to amplification may be provided by one or more other types of bearings (comprised by the first and/or second bearing arrangements), such as roller bearings, plain bearings, sliding bearings and so forth. Constraint leading to amplification may be provided by a combination of two or more of: other shape memory alloy wires of the respective first/second set, one or more resilient elements, one or more springs, one or more flexures, and one or more bearings.

Movements of the second part may be amplified relative to corresponding length changes of a shape memory alloy wire of the first set because that shape memory alloy wire makes an angle relative to the first path of less than 90° and more than 0°. Movements of the third part may be amplified relative to corresponding length changes of a shape memory alloy wire of the second set because that shape memory alloy wire makes an angle relative to the second path of less than 90° and more than 0°.

Each shape memory alloy wire of the first set may make an angle with the first path between 20° and 80°, inclusive of endpoints. Preferably, each shape memory alloy wire of the first set may make an angle with the first path between 45° and 77°, inclusive of end-points. A lower limit on the angle ensures that sufficient stroke amplification is achieved. An upper limit on the angle ensures that movement of the second part may be controlled accurately and reliably.

Similarly, each shape memory alloy wire of the second set may make an angle with the second path between 20° and 80°, inclusive of endpoints. Each shape memory alloy wire of the second set may make an angle with the second path between 45° and 77°, inclusive of end-points.

When the first path is not straight, a shape memory alloy wire of the first set may be considered to make an angle with the first path within a range between 0min to Qmax if all points along the first path (and within a range of motion of the second part relative to the first part) make an angle with that shape memory alloy wire within the range dmin to 9max. When the second path is not straight, a shape memory alloy wire of the second set may be considered to make an angle with the second path within a range between 9min to 9max if all points along the second path (and within a range of motion of the third part relative to the second part) make an angle with that shape memory alloy wire within the range 9 min tO 9 max. The constraint of the second part to the first path may include, or take the form of, one or more first flexures. Additionally or alternatively, the constraint of the third part to the second path may include, or take the form of, one or more second flexures. The first and/or second flexures may respectively be comprised by the first and/or second bearing arrangements.

Each first flexure may be axially loaded in response to actuation of the first set of shape memory alloy wires. Additionally or alternatively, each second flexure may be axially loaded in response to actuation of the second set of shape memory alloy wires. The axial load of the first and/or second flexure may be at least 5%, preferably at least 20% or at least 50%, of the tension in the SMA wires corresponding to the flexure.

So, each first flexure may be axially loaded in tension in response to actuation of a corresponding shape memory alloy wire of the first set. Each first flexure may be axially loaded in compression in response to actuation of a corresponding shape memory alloy wire of the first set. Each second flexure may be axially loaded in tension in response to actuation of a shape memory alloy wire of the second set. Each second flexure may be axially loaded in compression in response to actuation of a shape memory alloy wire of the second set. Preferably, the first and/or second flexures are placed in tension, thereby reducing the risk of buckling of the flexures compared to a situation in which the flexures are placed under compression.

Each first flexure may connect a corresponding side of the second part to the first part. Each first flexure may make an angle between 0° and 45° to the corresponding side of the second part. Each shape memory alloy wire of the first set may connect a corresponding side of the second part to the first part. Each shape memory alloy wire of the first set may make an angle between 0° and 45° to the corresponding side of the second part. A first flexure and a shape memory alloy wire of the first set connected to the same side of the second part may make an angle between 13° and 45° to one another. The first flexure may make an angle of substantially 90° relative to the first path. Each second flexure may connect a corresponding side of the third part to the second part. Each second flexure may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the third part. A lower angle reduces the extent of the actuator assembly in a direction orthogonal to the sides of the actuator assembly, thus reducing the footprint of the actuator assembly. Each shape memory alloy wire of the second set may connect a corresponding side of the third part to the second part. Each shape memory alloy wire of the second set may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the third part. A second flexure and a shape memory alloy wire of the second set connected to the same side of the third part may make an angle between 13° and 45° to one another. The second flexure may make an angle of substantially 90° relative to the second path.

References to angles made by shape memory alloy wires of the first and/or second sets may refer to an equilibrium state of the actuator assembly. For example, when none of the shape memory alloy wires are actuated or when the parts are in a central position.

The actuator assembly may also include a controller configured to control selective contraction of the shape memory alloy wires of the first set so as to move the second part relative to the first part along the first path. Control of the second part may be implemented by controlling drive signals (e.g. drive currents or drive voltages) supplied to the first set of shape memory alloy wires. The controller may also be configured to control selective contraction of the shape memory alloy wires of the second set so as to move the third part relative to the second part along the second path. Control of the third part may be implemented by controlling drive signals (e.g. drive currents or drive voltages) supplied to the second set of shape memory alloy wires.

The constraint of the second part to the first path may include, or take the form of, one or more first rolling bearings. Additionally or alternatively, the constraint of the third part to the second path may include, or take the form of, one or more second rolling bearings. The first and/or second rolling bearings may be comprised by the first and/or second bearing arrangements.

A first rolling bearing may include, or take the form of, a first ball bearing race formed between the second part and the first part and retaining one or more ball bearings. The first ball bearing race may define, at least in part, the first path. The first ball bearing race may be aligned with the first path. A second rolling bearing may include, or take the form of, a second ball bearing race formed between the third part and the second part and retaining one or more ball bearings. The second ball bearing race may define, at least in part, the second path. The second ball bearing race may be aligned with the second path. Alternatively, the rolling bearings may comprise a roller (e.g. cylindrical rolling element) between two bearing surfaces.

Contraction of each shape memory alloy wire of the first set may be opposed by one or more other shape memory alloy wires of the first set. Additionally or alternatively, contraction of each shape memory alloy wire of the second set may be opposed by one or more other shape memory alloy wires of the second set. Providing opposed shape memory alloy wires allows the tension in the shape memory alloy wires to be controller, allowing for more accurate and reliable movement control.

So, the first set of shape memory alloy wires may include first and second shape memory alloy wires, and may be configured such that, relative to the first part:

• Actuation of the first shape memory alloy wire urges the second part along the first path in a first direction;

• Actuation of the second shape memory alloy wire urges the second part along the first path opposite to the first direction.

The second set of shape memory alloy wires may include third and fourth shape memory alloy wires, and may be configured such that, relative to the second part:

• Actuation of the third shape memory alloy wire urges the third part along the second path in a second direction; • Actuation of the fourth shape memory alloy wire urges the third part along the second path opposite to the second direction.

Alternatively, contraction of each shape memory alloy wire of the first set may be opposed by one or more springs coupling the first part to the second part. Contraction of each shape memory alloy wire of the second set may be opposed by one or more springs coupling the second part to the third part. A spring (opposing an SMA wire of either the first or second set) may take the form of a coil spring, a flat spring, a leaf spring, a flexure, an element formed of elastomeric material, and so forth.

The first and second planes may be co-planar. The second part may surround the third part. The third part may surround the second part. Alternatively, the first and second planes may be parallel. Any or all of the first part, the second part and the third part may be stacked in order along a vertical direction perpendicular to the first and second planes.

The third part may include a central aperture, and no shape memory alloy wires may cross the central aperture. So, no shape memory alloy wires belonging to the first set may cross the central aperture. No shape memory alloy wires belonging to the second set may cross the central aperture.

The third part may have first and second surfaces, the second surface opposing the first part across a gap. Shape memory alloy wires belonging to the first set may be routed through the gap. In other words, shape memory alloy wires belonging to the first set may be routed through a space formed between the first and third parts. Additionally or alternatively, shape memory alloy wires belonging to the second set may be routed through the gap. In other words, shape memory alloy wires belonging to the second set may be routed through a space formed between the first and third parts. The shape memory alloy wires of the first and/or second set may be arranged diagonally in the gap, so extend between corner portions of the first, second and/or third parts. This allows the shape memory alloy wires to be made longer compared to a situation in which the shape memory alloy wires are not arranged diagonally. The third part may have first and second surfaces, the second surface opposing the first part across a gap. At least one first flexure may be routed through the gap. Additionally or alternatively, at least one second flexure may be routed through the gap.

The actuator assembly may include further parts, for example a fourth part, a fifth part and so forth. Further parts may be constrained to move along further paths, under the control of further sets of shape memory alloy wires. Further parts may be configured and/or constrained in any way described herein in relation to the first, second and/or third parts.

According to a second aspect of the invention there is provided a method of controlling the shape memory alloy actuator according to the first aspect. The method includes controlling the second part to move along the first path in the first plane relative to the first part. The method also includes controlling the third part to move along the second path in the second plane relative to the second part.

The method according to the second aspect may include features corresponding to any features of the shape memory alloy actuator of the first aspect. Definitions applicable to the shape memory alloy actuator of the first aspect may be equally applicable to the method according to the second aspect.

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 illustrates a camera;

Figure 2 is a plan view of a first actuator assembly;

Figures 3A and 3B illustrate a stroke amplification mechanism using shape memory alloy wires;

Figures 4A to 4D are plan views of a second actuator assembly. Figure 4D shows a plan view of second actuator assembly, and Figures 4A to 4C show plan views of the second actuator assembly with selected parts omitted for visual clarity;

Figure 5A is a plan view of a third actuator assembly; Figure 5B shows a cross section along the line labelled A-A* in Figure 5A; and Figure 5C shows a cross-section along the line labelled B-B* in Figure 5A.

Detailed Description

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

The camera 1 includes a lens assembly 3 suspended on a first part 4 (or "support structure") by an actuator assembly 2 that supports the lens assembly 3 in a manner allowing movement of the lens assembly 3 relative to the first part 4 in directions perpendicular to the optical axis 0 (on a first plane).

The first part 4 includes a base 5. An image sensor 6 is mounted on a front side of the base 5. On a rear side of the base 5, there is mounted a controller 7. For example, the controller 7 may take the form of an integrated circuit (IC) in which a control circuit is implemented. Optionally, for example when the camera 1 is configured with an optical image stabilisation (OIS) function, a gyroscope sensor 8 may be mounted on the rear side of the base 5 and coupled to the controller 7. The precise locations of mounting the controller 7 (and optionally the gyroscope sensor 8 if present) relative to the actuator assembly 2 are not crucial, though it is preferred the arrangement be compact.

The first part 4 also includes a screening can (or "can") 9 which protrudes forwardly from the base 5 to encase and protect the other components of the camera 1.

The lens assembly 3 includes a lens carriage 10 in the form of a cylindrical body supporting two lenses 11 arranged along an optical axis O (parallel to the z-axis as illustrated). In general, any number of one or more lenses 11 may be included. Preferably, each lens 11 has a diameter of up to about 20 mm. The camera 1 can therefore be referred to as a miniature camera.

The lens assembly 3 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-oxide- semiconductor (CMOS) device.

The lenses 11 are supported on the lens carriage 10 such that the lenses 11 are movable along the optical axis O relative to the lens carriage 10, for example to provide focussing or zoom. In particular, the lenses 11 are fixed to a lens holder 12 which is movable along the optical axis O relative to the lens carriage 10. Although all the lenses 11 are fixed to the lens holder 12 in this example, in general, one or more of the lenses 11 may be fixed to the lens carriage 10 and may not be movable along the optical axis O relative to the lens carriage 10, leaving at least one of the lenses 11 fixed to the lens holder 12.

An axial actuator assembly 13 provided between the lens carriage 10 and the lens holder 12 is arranged to drive movement of the lens holder 10 and the lenses 11 along the optical axis O relative to the lens carriage 10. The axial actuator arrangement 13 may be of any suitable type, for example, a voice coil motor (VCM) or an arrangement of SMA wires.

In operation, the lens assembly 3 is moved orthogonally to the optical axis O by the actuator assembly 2, relative to the image sensor 6, with the effect that the image on the image sensor 6 is moved. This is used to provide optical image stabilization (OIS), compensating for movement of the camera 1, which may be caused by hand shake etc.

First actuator assembly

Referring also to Figure 2, a first exemplary actuator assembly 14 is shown (hereinafter "first actuator assembly").

The first actuator assembly 14 may provide the actuator assembly 2 of a camera 1, but is not restricted to use in cameras 1. The first actuator assembly 14 includes a first part 4 (also referred to as a "support structure"), a second part 15 (also referred to as an "intermediate part") constrained to move along a first path 16 in a first plane 17 relative to the first part, and a third part 18 (also referred to as a "moving part") constrained to move along a second path 19 in a second plane 20 relative to the second part 15. The second plane 20 is coplanar with the first plane 17 in the first actuator assembly 14. However, in modifications of the first actuator assembly 14 the first and second planes 17, 20 need not be co-planar, and may be parallel to one another at different heights along a vertical direction (z-axis as illustrated).

The first actuator assembly 14 includes a first set of shape memory alloy (SMA) wires 21 configured to move the second part 15 along the first path 16 relative to the first part 4. The first actuator assembly 14 has first to fourth sides 22i, 222, 223, 224 (moving clockwise about the perimeter), and the first set of shape memory alloy wires 21 includes first and second SMA wires 21i, 212 arranged respectively along the first and third sides 22i, 22s of the first actuator assembly 14. In general, the first set may include more or fewer SMA wires 21, though the minimum number is one (contraction of which should be opposed by a spring as described hereinafter). In the first actuator assembly 14, each SMA wire 21 of the first set is fixed to the first part 4 by a first crimp 23 at one end, and at the other end is fixed to the second part 15 by a second crimp 34. The SMA wires 21 of the first set need not be attached between the first 4 and second 15 parts by crimping, and may be fixed between the first 4 and second 15 parts in any suitable way.

The first actuator assembly 14 also includes a second set of shape memory alloy wires 25 configured to move the third part 18 along the second path 19 relative to the second part 15. In the first actuator assembly 14, the second set of shape memory alloy wires 25 includes first and second SMA wires 25i, 25z, arranged respectively along the fourth and second sides 224, 222 of the first actuator assembly 14. In general, the second set may include more or fewer SMA wires 25, though the minimum number is one (contraction of which should be opposed by a spring as described hereinafter). Each SMA wire 25 of the second set is fixed to the second part 15 by a respective third crimp 26 at one end, and at the other end is fixed to the third part 18 by a respective fourth crimp 27. The SMA wires 25 of the first set need not be attached between the second 15 and third 18 parts by crimping, and may be fixed between the second 15 and third 18 parts in any suitable way In this way, the second part 15 is coupled to the first part 4 via the first set of shape memory alloy wires 21, and the third part 18 is coupled to the second part 15 via the second set of shape memory alloy wires 25. Consequently, movement of the third part 18 relative to the first part 4 is a combination of movement of the second part 15 along the first path 16 relative to the first part 4 and movement of the third part 18 along the second path 19 relative to the second part 15.

In the first actuator assembly 14, the constraint of the second part 15 to move relative to the first part 4 along the first path 16 is provided by a pair of first flexures 28i, 282 connecting the second part 15 to the first part 4 along the first 22i and third 22s sides. Each first flexure 28i, 282 is connected to the first part 4 at a first end 29i, 292, and to the second part 15 at a second, opposite end 30i, 302. The first flexures 28i, 282 are parallel to one another, but directed oppositely between the respective first ends 29i, 292 and the second part 15. The first flexures 28i, 282 have relatively high compliance to transverse deflections in the first plane 17, and relatively low, preferably negligible compliance along the length of each flexure 28i, 282. The parallel first flexures 28i, 282 arranged on opposite sides 22i, 223 of the second part 15 constrain the motion of the second part 15 relative to the first part 4 to follow the first path 16. For visualisation, first and second lines I61, I62 are drawn in Figure 2 to indicate the motions of the second ends 30i, 302 of the first flexures 28i, 282 as the second part 15 is deflected along the first path 16.

Similarly, in the first actuator assembly, the constraint of the third part 18 to move relative to the second part 15 along the second path 19 is provided by a pair of second flexures 31i, 312 connecting the third part 18 to the second part 15 along the fourth 224 and second 222 sides. Each second flexure 31i, 312 is connected to the second part 15 at a first end 32i, 322, and to the third part 18 at a second, opposite end 33i, 332. The second flexures 31i, 312 are parallel to one another, but directed oppositely between the respective first ends 32i, 322 and the third part 18. Similarly to the first flexures 28i, 282, the second flexures 31i, 312 have relatively high compliance to transverse deflections in the second plane 20, and relatively low, preferably negligible compliance along the length of each flexure 31i, 312. The parallel second flexures 31i, 312 arranged on opposite sides 222, 224 of the third part 18 constrain the motion of the third part 18 relative to the second part 15 to follow the second path 19. For visualisation, first and second lines 19i, 192 are drawn in Figure 2 to indicate the motions of the second ends 33i, 332 of the second flexures 31i, 312 as the third part 18 is deflected along the second path 19.

Another way to describe the constraints is that the second part 15 has one degree of freedom with respect to the first part 4 (along the first path 16), whilst the third part 18 has one degree of freedom with respect to the second part 15 (along the second path). However, because the first and second degrees of freedom (paths 16, 19) are not parallel, the third part 18 overall has two independent degrees of freedom relative to the first part 4.

The first and second paths 16, 19 will be substantially linear for small deflections of the respective parts 15, 18, and have been drawn as linear in Figure 2 because SMA actuator assemblies 2, 14 are generally intended for relatively small, precise movements. It will be appreciated that the first and second paths 16, 19, will start to curve the further from equilibrium the respective parts 15, 18 are deflected by the SMA wires 21, 25.

The SMA wires 21 of the first set and the SMA wires 25 of the second set may be caused to contract by resistive heating provided by electrical currents. Electrical connections between the first part 4 and the second part 15 may be supported on (or provided by) the first flexures 28i, 282 connecting the first part 4 and the second part 15. Each first flexure 28i, 282 may support one, two, or more separate electrical connections, for example insulated from one another.

Alternatively, additional flexures (not shown) may connect between the first part 4 and the second part 15 to support electrical connections. Such additional flexures (not shown) should be highly compliant to as to avoid, or at least minimise, interference with the motion of the second part 15 relative to the first part 4 along the first path 16. Similarly, electrical connections between the first part 4 and the third part 18 may be routed via a combination of a second flexure 31i, 312 and a first flexure 28i, 282. For example, each second flexure 31i, 312 may support one, two, or more separate electrical connections, for example insulated from one another. Alternatively, additional flexures (not shown) may connect between the third part 18 to the second part 15, or directly to the first part 4, to support electrical connections. Such additional flexures (not shown) should be highly compliant to as to avoid, or at least minimise, interference with the motion of the third part 18 relative to the second part 15 along the second path 19. Alternative options for implementing electrical connections may include sliding sprung contacts, conductive ball-bearings, and so forth.

On heating of one of the SMA wires 21, 25, the stress in the SMA wire 21, 25 increases and it contracts, providing a force urging the parts 4, 15, 18 that SMA wire 21, 25 connects between to be pulled toward one another (and to move if there is net force along an unconstrained direction such as the first or second paths 16, 19). A range of movement occurs as the temperature of the SMA material increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA wires 21, 25 so that the stress in the SMA wire 21, 25 decreases, it may extend under the force from opposing ones of the SMA wires 21, 25 and/or the restoring forces arising from deflection of the flexures 28i, 282, 31i, 312. The SMA wires 21, 25 may be made of any suitable SMA material, for example Nitinol or another titanium-alloy SMA material.

The drive signals for the SMA wires 21, 25 are generated and supplied by a controller 7, for example a control circuit implemented in an IC as described hereinbefore. For example, the drive signals may be generated by the controller 7 in response to output signals of the gyroscope sensor 8, so as to drive movement of the lens assembly 3 to stabilise an image focused by the lens assembly 3 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. An example of operation of the controller 7 to control the first actuator assembly 14 is described hereinafter

In operation, the SMA wires 21, 25 are selectively driven to move the third part 18 relative to the first part 4 in any lateral direction (i.e., a direction perpendicular to the vertical direction z), via a combination of a first displacement of the second part 15 along the first path 16 and a second displacement of the third part 18 along the second path 19. Background details of methods of driving SMA wires 21, 25 to are also provided in WO 2013/175197 Al, which is incorporated herein by this reference.

The first actuator 14 is square with first to fourth sides 22i, 222, 223, 224. The first and third sides 22i, 223 are parallel to one another and the x-axis as illustrated. The second and fourth sides 222, 224 are parallel to one another and the y-axis as illustrated, perpendicular to the x-axis. In the first actuator 14, the sides 22 of the actuator 14 coincide with edges of the first part 4, which takes the form of a square plate. The first part 4 may provide the base 5 if used in a camera 1. Each of the second 15 and third 18 parts takes the form of a flat, thin annulus having square outer and inner edges, defining an aperture 34. When used in a camera 1, the aperture 34 allows passage of light focused by lenses 11 onto the image sensor 6 (for example mounted on the first part 4). For this reason, none of the SMA wires 21, 25 intersects the aperture 34 of the third part 18. The third part 18 is smaller than the second part 15, and is received within the aperture 34 of the second part 15 so that the second 15 and third 18 parts are substantially co-planar and the first and second planes 17, 20 coincide. The first 4, second 15 and third 18 parts are each generally perpendicular to a vertical axis (z-axis as illustrated). When used in a camera, the vertical axis z will lie parallel to the optic axis O.

The first part 4, second part 15 and third part 18 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. The dielectric material layer may include one or more windows (not shown) to allow electrical connections.

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

The second part 15 is constrained to move along the first path 16 by the first flexures 28i, 282. In some examples, the first flexures 28i, 282 may additionally constrain the second part 15 to move within the first plane 17, for example the first flexures 28i, 282 may be configured with relatively low compliance for deflection perpendicular to the first plane 17 (i.e. in the vertical direction z). Additionally or alternatively, the second part 15 may be constrained within the first plane 17, at least in part, using a first bearing arrangement (not shown) coupling the second part 15 to the first part 4. The first part 15 may be retained in contact with the first bearing arrangement (not shown) by the first flexures 28i, 282, one or more additional flexures (not shown), springs (not shown) or similar devices providing force along the vertical axis z urging the second part 15 towards the first part 4.

Similarly, the third part 18 is constrained to move along the second path 19 by the second flexures 31i, 312. In some examples, the second flexures 31i, 312 may additionally constrain the third part 18 to move within the second plane 20, for example the second flexures 31i, 312 may be configured with relatively low compliance for deflection perpendicular to the second plane 20 (i.e. in the vertical direction z). Additionally or alternatively, the third part 18 may be constrained within the second plane 20, at least in part, using a second bearing arrangement (not shown) coupling the third part 18 to the second part 15. The second 15 and third 18 parts may be retained in contact with the second bearing arrangement (not shown) by the second flexures 31i, 312, one or more additional flexures (not shown), springs (not shown) or similar devices providing force along the vertical axis z to urge the second 15 and third 18 parts towards one another. Alternatively, the second bearing arrangement (not shown) may couple the third part 18 directly to the first part 4.

The first and/or second bearing arrangement (not shown) may take the form or three or more plain bearings, three or more roller bearings, further sets of flexures (not shown), and so forth.

SMA wire arrangement of the first actuator assembly

The first set of SMA wires 21 are arranged in a loop about the aperture 34, with the first SMA wire 21i of the first set opposing the first of the first flexures 281 along the first side 22i (in terms of contraction), and the second SMA wire 212 of the first set opposing the second of the first flexures 282 along the third side 22s. The first set of SMA wires 21i, 212 are parallel to one another. The arrangement of the second SMA wire 212 of the first set and corresponding first flexure 28 is rotated 180° relative to the first SMA wire 21i of the first set and corresponding first flexure 28i. Both SMA wires 21i, 212 of the first set make substantially the same angles to the x- and y-axes. The first set of SMA wires 21 make a smaller angle to the y-axis y than to the x-axis.

Actuation of the first SMA wire 21i of the first set to contract urges the second part 15 along the first path 16 towards the left hand side of the illustration relative to the first part 4 (in the negative x-direction, but not parallel thereto). To urge the second part 15 in the opposite direction along the first path 16 (in the positive x-direction, but not parallel thereto), the second SMA wire 212 of the first set is instead actuated to contract. When neither SMA wire 21 of the first set is actuated, the first flexures 28i, 282 urge the second part 15 back to an equilibrium position relative to the first part 4.

Clockwise moment on the second part 15 relative to the first part 4 is applied by actuating either SMA wire 21i, 212 of the first set. However, the second part 15 does not rotate due to the constraint of the first flexures 28i, 282.

Consequently, each first flexure 28i, 282 is axially loaded (in tension) in response to actuation of the first set of shape memory alloy wires 21.

The second set of SMA wires 25 are also arranged in a loop about the aperture 34, with the first SMA wire 25i of the second set opposing the first of the second flexures 31i (in terms of contraction) along the fourth side 224, and second SMA wire 252 of the second set opposing the second of the second flexures 312 along the second side 222. The arrangement of the second SMA wire 252 of the second set and corresponding second flexure 312 is rotated 180° relative to the first SMA wire 25i of the second set and corresponding second flexure 31i. Both SMA wires 25i, 252 of the second set make substantially the same angles to the x- and y-axes. The second set of SMA wires 25 make a smaller angle to the x-axis than to the y-axis.

Clockwise moment on the third part 18 relative to the second part 15 is applied by actuating either SMA wire 25i, 252 of the second set. However, the third part 18 does not rotate due to the constraint of the second flexures 31i, 312. Consequently, each second flexure 31i, 312 is axially loaded (in tension) in response to actuation of the second set of shape memory alloy wires 25.

The total movement of the third part 18 relative to the first part 4 is the sum of the movement of the second part 15 relative to the first part 4 along the first path 16 (from actuation of the first set of SMA wires 21), and the movement of the third part 18 relative to the second part 15 along the second path 19 (from actuation of the second set of SMA wires 25). Although slightly angled relative to the sides 22 of the actuator assembly (and x- and y-axes as illustrated), the first 16 and second 19 paths permit two degrees of freedom for lateral movements of the third part 18 relative to the first part 4 (perpendicular to the vertical direction z). The first path 16 may correspond to a first axis, and the second path 19 to a second axis.

The first set of shape memory alloy wires 21 are arranged such that movements of the second part 15 relative to the first part 4 along the first path 16 are amplified compared to corresponding length changes of the first set of shape memory alloy wires 21. Similarly, the second set of shape memory alloy wires 25 are arranged such that movements of the third part 18 relative to the second part 15 along the second path 19 are amplified compared to corresponding length changes of the second set of shape memory alloy wires 25.

SMA wire amplification

Referring also to Figures 3A and 3B, the SMA wire 21, 25 amplification mechanism is illustrated.

Referring in particular to Figure 3A, an angled SMA wire 35 makes an angle 9 to the x-axis and an angle 90-9 to the y-axis. In the example shown in Figure 3A, the angle is 0 = 45°.

The SMA wire 35 has an initial length L, having a component xo along the x-axis and a component yo along the y-axis. A first end 36 of the SMA wire 35 is fixed to the origin of the axes x-y drawn in Figure 3A. The SMA wire 35 is then actuated (by resistive heating using a drive current) and caused to contract by an amount 5L to a new length L-5L. The locus of points which a second end 37 of the SMA wire 35 can reach is a circle 38 of radius L-6L drawn for reference in Figure 3A. If the second end 37 of the SMA wire 35 is unconstrained, or constrained to move along the direction that the SMA wire 35 is lying (0 = 45°), then the total displacement of the second end 37 relative to the first end will simply be 3L to the point labelled Pl. This represents the unamplified displacement, and many SMA actuators operate in this way, directly pulling part of actuator along the length of an SMA wire 35. However, this limits the stroke of such actuator to the maximum length change 6L.

However, if the second end 37 is constrained to move along a path which is not parallel to the initial orientation of the SMA wire 35, for example the first 16 or second path 19, amplification may be obtained. For example, if the second end 37 is constrained to move parallel to the y-axis, then the second end 37 is forced to the point P2 on the circle 38 intersecting the original component xo along the x-axis. The total displacement is then 1y = yo-yi > 5L. Alternatively, if the second end 37 is constrained to move parallel to the x-axis, then the second end 37 is forced to the point P3 on the circle 38 intersecting the original component yo along the y-axis. The total displacement is then Ax = xo-xi > 3L.

For the geometry shown in Figure 3A, with 0 = 45°, the amplification is the same when constrained to the x-axis or the y-axis, i.e. Ax = Ay, and the gain is Ax/6L « 1.5.

The gain may be increased for movements parallel to one axis x, y, at the expense of reduced gain for movements parallel to the other axis y, x, by changing the initial orientation angle 9.

Referring also to Figure 3B shows a configuration identical to Figure 3A, except that the angle is 9 = 60° instead of 9 = 45°. In the configuration of Figure 3B, when the second end 37 is constrained to move parallel to the x-axis to point P3, the gain is increased to Ax/5l_ « 2.4. However, the when the second end 37 is constrained to move parallel to the y-axis to point P2, the gain is reduced (compared to 6 = 45°) to Ay/5L 1.2.

Since the shortest displacement corresponding to a length change 6L (zero amplification) will always be directly along the initial orientation of the SMA wire 35, constraining the second end 37 to any other path which is not parallel with 9 will lead to amplification. In other words, amplification does not require strict constraint to either the x-axis x or the y-axis.

Referring again to Figure 2, the SMA wires 21 of the first set are angled relative to the first path 16, such that relative to the first part 4, movements of the second part 15 along the first path 16 are amplified (the constraint arising from the first flexures 28i, 282). Similarly, the SMA wires 25 of the second set are angled relative to the second path 19, such that relative to the second part 15, movements of the third part 18 along the second path are amplified (the constraint arising from the second flexures 28i, 282)..

In general, to optimise amplification (gain) against the net component of force in the desired direction, each SMA wire 21 of the first set preferably makes an angle with the first path 16 between (and including) 45° and 77°. In the first actuator assembly 14, the first path 16 is approximately perpendicular to the first flexures 28. Similarly, each SMA wire 25 of the second set preferably makes an angle with the second path 19 between (and including) 45° and 77°.

In the first actuator assembly 14, the second path 19 is approximately perpendicular to the second flexures 31.

Alternatively, each SMA wire 21 of the first set may make an angle with the first path 16 between (including end points) 10° and 80°, and each SMA wire 25 of the second set may make an angle with the second path 19 between (including end points) 10° and 80°.

The controller 7 is configured to control selective contraction of the SMA wires 21 of the first set so as to move the second part 15 relative to the first part 4 along the first path 16 by an amount Ai, and to control selective contraction of the SMA wires 25 of the second set so as to move the third part 18 relative to the second part 15 along the second path 19 by an amount 2. In this way, movements may be controlled relative to first and second axes aligned along the first 16 and second 19 paths respectively. Alternatively, the controller 7 may be configured to control selective contraction of the shape memory alloy wires 21, 25 of the first and second sets so as to cause a desired overall movement of the third part 18 relative to the first part 4 by a first component Ax parallel to the x-axis x and a second component Zly parallel to the y-axis. Each component Ax, 1y will include a combination of movements along the first 16 and second 19 paths.

The controller 7 controls contraction of the SMA wires 21 of the first set and the SMA wires 25 of the second set by controlling drive signals supplied to the shape memory alloy wires 21, 25. Drive signals may be current controlled or voltage controlled. The drive signals may be generated using a resistance feedback control technique, for example, as described in WO 2014/076463 Al

Since movements (by A and A) of the third part 18 relative to the first part 4 are essentially isolated along the first 16 and second 19 paths, this may simplify the drive signals required to control the first and second sets of SMA wires 21, 25. Primarily, this may help to reduce cross-talk between intended movements parallel to the first 16 and second 19 paths. In other words, cross-talk is reduced between the two degrees of freedom of the third part 18 relative to the first part 4.

Incorporation into a camera

The first actuator assembly 14 may be incorporated into a camera in a number of different ways.

For example, the first actuator assembly 14 may be incorporated into the camera 1 shown in Figure 1, with the image sensor 6 supported on the first part 4 and the lens carriage 10 supported on the third part 18. The first part 4 is connected to the can 9, and functions as the fixed reference point relative to the camera 1. However, the first actuator 14 may be incorporated into a camera in other ways. For example, another camera (not shown) may be similar to the camera 1, except that the second part 15 is fixed relative to the camera (not shown), e.g. to the can 9. In this way, the image sensor 6 supported on the first part 4 and the lens carriage 10 supported on the third part 18 may be moved independently relative to the optic axis O (parallel to the vertical axis z as illustrated).

In general, for incorporation into a camera, any one of the first part 4, the second part 15 or the third part 18 may support the image sensor 6, whilst one of the remaining pair of parts 4, 15, 18 supports at least one lens 11. In general, any one of the first part 4, the second part 15 or the third part 18 may be fixed relative to the camera. Fixed relative to the camera mean that the part 4, 15, 18 in question is mechanically fixed, and has no degrees of freedom relative to the rest of the camera. For example, whichever of the parts 4, 15, 18 is fixed may be rigidly attached to (or be integrally formed with) a can 9, a case (not shown), a frame (not shown) or a package of the camera.

Whilst the first actuator assembly 14 has been described with the shape memory alloy wires 21 of the first set being parallel, this is not essential. In other examples, one or more SMA wires 21 of the first set may be arranged to be nonparallel with one, some or all of the other SMA wires 21 of the first set.

Similarly, one or more SMA wires 25 of the second set may be arranged to be non-parallel with one, some or all of the other SMA wires 25 of the second set.

The first actuator assembly 14 has been described in which the first set of SMA wires 21 apply a net moment (torque) about the vertical axis z (countered by the first flexures 28i, 282), and in which the second set of SMA wires 25 also apply a net moment about the vertical axis z (countered by the second flexures 31i, 3I2). However, in other examples the first and/or second sets of SMA wires 21, 25 may be arranged such that a net moment is not provided and/or may be small (for example by including additional SMA wires 21, 25).

The first actuator assembly 14 has been described in which the first set of SMA wires 21 and the first flexures 28 possess two-fold rotational symmetry, and the second set of SMA wires 25 and the second flexures 31 also possess two-fold rotational symmetry. However, this is not essential, and in other examples, the first and/or second sets of SMA wires 21, 25 and corresponding flexures 28, 32 may be configured to have no rotational symmetry.

The first actuator assembly 14 has been described relative to x- and y-axes which are orthogonal (or relative to first and second orthogonal axes aligned along the first 16 and second 19 paths). However, this is not essential, and in other examples the sides 22 and/or paths 16, 19 may be parallel to first and second axes arranged at any non-parallel angle to one another, for example, any angle between 10° and 90°. The first actuator assembly 14 has been described relative to first 16 and 19 paths which are substantially straight and orthogonal. However, this is not essential, and in other examples the first 16 and second 19 paths may be arranged at any non-parallel angle to one another, for example, any angle between 10° and 90°.

It is not essential that the first 16 and/or second paths 19 be straight, and in other examples either or both paths 16, 19 may be curved (even for small displacements). When the first path 16 is not straight, a SMA wire 21 of the first set may be considered to make an angle with the first path 16 within a range 6min to Qmax if all points along the first path 16 make an angle with the SMA wire 21 within the range 9mm to 9 ax (within the range of movement of the second part 15 relative to the first part 4). Similarly, when the second path 19 is not straight, a SMA wire 25 of the second set may be considered to make an angle with the second path 19 within a range 9min to 9 max if all points along the second path 19 make an angle with the SMA wires 25 within the range 9min to 9max (within the range of movement of the third part 18 relative to the second part 15).

The first actuator assembly 14 has been described with the constraint of the second 15 and third 18 parts to the respective paths 16, 19 provided by opposing flexures 28, 31. Since the paths 16, 19 are not parallel to the SMA wires 21, 25, amplification is provided. However, in other examples, constraint of SMA wires 21, 25 leading to amplification and/or constraint of motions along the paths 16, 19 may be provided by one or more alternative resilient elements such as, for example, springs and so forth. Alternatively, constraint may be provided by one or more bearings (for example roller bearings as in Figure 5). In further examples, constraint leading to amplification and/or confinement of movements to the paths 16, 19 may be provided by a combination of two or more elements selected from opposing shape memory alloy wires of the respective first/second set, one or more resilient elements, one or more springs, one or more flexures, and one or more bearings.

The sides 22 of the first actuator assembly 14 form a square shape, however, this is not essential. In other examples, the sides of an actuator assembly may form other shapes such as, for example, rectangular, diamond, kite, or any other regular or irregular quadrilateral. In still other examples, an actuator assembly may have more or fewer than four sides, for example three, five, six or eight sides.

In the first actuator assembly 14, the third part 18 is substantially coplanar with, and received within, the second part 15. However, in other examples, the third part 18 may be stacked above (along the vertical axis z), and substantially coextensive with, the second part 15 (see for example Figure 4).

In the first actuator assembly 14, each SMA wire 21 of the first set is fixed to the second part 15 at one end and fixed to the first part 4 at the other end, whilst each SMA wire 25 of the second set is fixed to the third part 18 at one end and to the second part 15 at the other end. However, in other implementations, each SMA wire 21 of the first set may be fixed to the second part 15 at one or more points along its length, and be fixed to the first part 2 at one or more points along its length, whilst each SMA wire 25 of the second set is fixed to the third part 18 at one or more points along its length and to the second part 15 at one or more points along its length.

Each SMA wire 21 of the first set preferably has a span length between attachment points (or fixed/end points) which is at least 80% of a side length of the second part 15. Additionally or alternatively, each SMA wire 25 of the second set preferably has a span length between attachment points (or fixed/end points) which is at least 80% of a side length of the third part 18. Preferably, each SMA wire 21, 25 comprises a single span. In other words, it is preferable that no SMA wire 21, 25 is hooked or looped over any elements to cause a change in direction between the fixed ends/points. For example, none of the SMA wires 21, 25 are configured in a V-shape when viewed perpendicular to the first/second plane 17, 20.

In the first actuator assembly 14, the first set of SMA wires 21 consists of two SMA wires 21i, 212, each having a single, straight span. Similarly, the second set of SMA wires 25 consists of two SMA wires 251, 252, each having a single straight span. However, in other example, either or both of the first and second sets may include more than two SMA wires 21, 25, each SMA wire 21, 25 having a single, straight span.

In the first actuator assembly 14, each first flexure 28 connects a corresponding side of the second part 15 to the first part 4. In general, each first flexure 28 may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the second part 15. In the first actuator assembly 14, each SMA wire 21 of the first set connects a corresponding side of the second part 15 to the first part 4. In general, each SMA wire 21 of the first set may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the second part 15. A first flexure 28 and a SMA wire 21 of the first set connected to the same side of the second part 15 (for example SMA wire 21i and first flexure 28i in Figure 2) may make an angle between 13° and 45° to one another.

In the first actuator assembly 14, each second flexure 31 connects a corresponding side of the third part 18 to the second part 15. In general, each second flexure 31 may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the third part 18. In the first actuator assembly 14, each SMA wire 25 of the second set connects a corresponding side of the third part 18 to the second part 15. Each SMA wire 25 of the second set may make an angle between 0° and 45°, preferably between 0° and 20°, further preferably between 0° and 10°, to the corresponding side of the third part 18. A second flexure 31 and a SMA wire 25 of the second set connected to the same side of the third part 18 (for example SMA wire 312 and second flexure 312) may make an angle between 13° and 45° to one another.

In the first actuator assembly 14, the first flexures 28 are axially loaded in tension in response to actuation of the first set of SMA wires 21, and similarly the second flexures 31 are axially loaded in tension in response to actuation of the second set of SMA wires 25. In other example, some, or all, of either the first 28 or second flexures 31 may be arranged to be axially loaded in compression in response to actuation of the respective set of SMA wires 21, 25. When flexures 28, 31 are to be loaded in compression, the design of the flexure should take account of the need to prevent buckling.

In the first actuator assembly 14, the first 17 and second 20 planes are coplanar, and the second part 15 surrounds the third part 18. In other examples, the third part 18 may instead surround the second part 15. In still other examples, the first 17 and second 20 planes may instead be parallel, but offset from one another along the vertical direction z. For example, any or all of the first part, the second part and the third part may be stacked in order along the vertical direction z perpendicular to the first 17 and second 20 planes.

Second exemplary actuator assembly

Referring also to Figures 4A to 4D, a second exemplary actuator assembly 39 is shown (hereinafter "second actuator assembly").

Each of Figures 4A to 4D shows all or a portion of the second actuator assembly 39 viewed from below (along the vertical axis z). Figure 4A shows the third part 18, second flexures 31 and second set of SMA wires. Figure 4B shows everything in Figure 4A, plus the second part 15. Figure 4C shows everything in Figure 4B, and adds the first flexures 28 and first set of SMA wires 21. Figure 4D shows everything in Figure 4C, and adds the first part 4.

The second actuator assembly 39 is the same as the first actuator assembly 14, except that the first 4, second 15 and third 18 parts are configured differently, as are the flexures 28, 31 and SMA wires 21, 25 connecting between them. Only those parts of the second actuator assembly 39 differing from the first actuator assembly 14 are described in detail hereinafter.

Referring in particular to Figure 4A, the third part 18 takes the form of a thin, flat, rectangular plate having sides aligned with x- and y-axes. Second flexures 31i, 312 are fixed to the underside (relative to the vertical direction z) of the third part 14, and are oriented substantially diagonally to maximise the length of each second flexure 31i, 312. Each second flexure 31i, 312 extends between a first attachment tab 40i, 402 fixed to (or formed as part of) the third part 18, and a second attachment tab 41i, 412 for fixing to the second part 15. In addition to their lateral extent, each second flexure 31i, 312 also depends slightly downwards from the underside of the third part 18, such that when unstressed the second attachment tabs 41i, 412 sit below the first attachment tabs 40i, 402. The SMA wires 25i, 252 of the second set are fixed (for example crimped) to the first attachment tabs 40i, 402, and extend in the same direction, but at an angle to, the respective second flexures 31i, 312. Consequently, the second flexures 31i, 312 are compressively loaded when an SMA wires 25i, 252 of the second set is actuated.

Referring in particular to Figure 4B, the second part 15 takes the form of a thin, flat and generally "H" shaped plate including first 42 and second 43 members extending generally along the short sides of the rectangular footprint of the third part 18, connected by a rigid connecting bar 44. The first 42 and second 43 members and the rigid connecting bar 44 are preferably formed as a single piece (for example, stamped from a sheet of metal), but alternatively may be formed as individual components and attached together (for example welded).

The first attachment tab 40i corresponding to the first SMA wire 25i of the second set is attached to an upper surface of the first member 42, proximate to the connection to the connecting bar 44, whilst the first SMA wire 25i of the second set is fixed (for example crimped) to an upper surface of the first member 42 at (or close to) the maximum extent of the first member 42 in the negative direction along the y-axis. The first attachment tab 402 corresponding to the second SMA wire 252 of the second set is attached to an upper surface of the second member 43, proximate to the connection to the connecting bar 44, whilst the second SMA wire 25i of the second set is fixed (for example crimped) to an upper surface of the first member 42 at (or close to) the maximum extent of the first member 42 in the positive direction along the y-axis.

Referring in particular to Figures 4C and 4D, the first part 4 takes the form of a thin, flat annulus having rectangular inner and outer edges. The first flexures 28i, 282 and the first set of SMA wires 21i, 212 are connected to the underside of the second part 15. Each first flexure 28i, 282 has a respective attachment tab 45i, 452 fixed to, or integrally formed with, the second part 15, and the opposite ends are directly fixed to (or integrally formed with) the first part 4 (for example an upper surface, or the inner edge thereof). Each of the SMA wires 21i, 212 of the first set is fixed (for example crimped) at one end to a respective one of the attachment tabs 45i, 452 of the first flexures 28i, 282, and is fixed at the opposite end to the first part 4.

The attachment tab 45i corresponding to the first SMA wire 21i of the first set is fixed to the opposite end of the first member 42 to the first SMA wire 25i of the second set. Similarly, the attachment tab 452 corresponding to the second SMA wire 212 of the first set is fixed to the opposite end of the second member 43 to the second SMA wire 252 of the second set.

The first flexures 28i, 282 are generally parallel to one another, and perpendicular to the second flexures 31i, 312 (which are also generally parallel to one another). The first set of SMA wires 21i, 212 are generally parallel to one another, and perpendicular to the second set of SMA wires 25i, 252 (which are also generally parallel to one another).

The first flexures 28i, 282 may be oriented downwards in an un-stressed state, such that the first 4 and second parts 15 are offset from one another along the vertical direction z at equilibrium. Alternatively, the first flexures 28i, 282 need not be directed downwards, and the second part 15 may be substantially coplanar with the first part 4 and disposed within the aperture of the first part 4. When the first 4 and second parts 15 are offset from one another along the vertical direction z, the first part 4 may alternatively take the form a flat, thin rectangular plate (i.e. the aperture may be omitted). Another way of looking at the second actuator assembly 39 is that the third part 18 has first (upper) and second (lower) surfaces, the second (lower) surface opposing the first part 4 across a gap in the vertical direction z, and that SMA wires 21, 25 belonging to the first and second sets are routed through the gap. In the second actuator assembly 39, the first 28 and second 31 flexures are also routed through the gap in the vertical direction z between the first part 4 and the second (lower) surface of the third part 18.

In this way, by routing SMA wires 21, 25 and constraining flexures 28, 31 behind the third part 18 (through the space formed between the first 4 and third 18 parts), the length of the SMA wires 21, 25, and hence maximum stroke of the second actuator assembly 39, may be increased without increasing the lateral (x-y plane) footprint of the second actuator assembly 39.

The rectangular shape of the second actuator assembly 39 may be particularly suited to a camera using a periscope configuration. However, the overall shape of the second actuator assembly 39 may be modified to any shape described in relation to the first actuator assembly 14, for example, square. In general, absent a technical incompatibility, any features or functions described in relation to the first actuator assembly 14 are equally applicable to (e.g. combinable with) the second actuator assembly 39.

When incorporated into a camera, for example camera 1, the lens assembly 3 may be fixed relative to the first part 4 (or coupled via an actuator providing relative motion along the vertical direction z), whilst the image sensor 6 is mounted to the upper surface of the third part 18. This allows lateral motions between the image sensor 6 and lens(es) 11 for OIS functionality

Third exemplary actuator assembly

Referring also to Figures 5A to 5C, a third exemplary actuator assembly 46 is shown (hereinafter "third actuator assembly"). Figure 5A shows a plan view of the third actuator assembly 46. Figure 5B shows a cross-section along the line labelled A-A* in Figure 5A. Figure 5C shows a cross-section along the line labelled B-B* in Figure 5A.

The second actuator assembly 39 is the same as the first actuator assembly 14, except that the constraint of the second part 15 to move relative to the first part 4 along the first path 16, and of the third part 18 to move relative to the second part 15 along the second path 19 are provided by respective roller bearings instead of flexures 28, 31. Only those parts of the third actuator assembly 46 differing from the first actuator assembly 14 are described in detail hereinafter.

First roller bearings 47i, 472 couple the second part 15 to the first part 4 and constrain relative movements to the first path 16. Second roller bearings 48i, 482 couple the third part 18 to the second part 15 and constrain relative movements to the second path 19.

Referring in particular to Figure 5B, each of the first roller bearings 47i, 472 includes a ball bearing 49 retained in a ball-bearing race formed between a groove 50i, 502 formed in an upper (relative to the vertical direction z) surface of the first part 4 and a slot 51i, 512 formed in the second part 15. The ball bearing races so formed extend parallel to, and at least partly define, the first path 16. Protrusions 52i, 522 which locally expand the width of the second part 15 around the slots 51i, 512 may be included to enable extending the lengths of the ball bearing races of the first roller bearings 47i, 472.

The second roller bearings 48i, 482 have a different structure to the first roller bearings 47i, 472, because the intention is to constrain and guide movements relative to the second part 15 rather than the first part. Referring in particular to Figure 5C, each of the second roller bearings 48i, 482 includes a ball bearing 49 retained in a ball-bearing race formed between a slot 53i, 532 formed in the third part 18 and a slot 54i, 542 formed in an overhanging extension portion 55i, 552 of the second part 15. The ball bearing races so formed extend parallel to, and in fact define, the second path 19. Each overhanging extension portion 55i, 552 extends inwards from an inner edge of the second part 15, and is offset above the third part 18 by an angled connecting portion 56i, 562. In the vicinity of the second roller bearings 48i, 482, the second part 15 may be offset outwards away from the third part 18 by respective kinked sections 57i, 572. Overhanging extension portions 55i, 552 may extend inwards from inner edges of respective kinked portions 57i, 572, as is the case shown in Figures 5A to 5C. The third part 18 may include protrusions 58i, 582 which expand into the spaces provided by the kinked portions 57i, 572 to enable extending the length of the corresponding ball-bearing races.

Other variations

It will be appreciated that there may be many other variations of the abovedescribed embodiments.

The first 14 to third 46 actuator assemblies include two SMA wires 21, 25 in each of the first and second sets. However, more or fewer SMA wires 21, 25 may be used in one or both of the first and second sets.

For example, contraction of each SMA wire 21 of the first set may be opposed by one or more springs coupling the first part 4 to the second part 15. For example, in the first 14 or second 39 actuator assemblies, the second SMA wire 212 of the first set may be omitted. One extreme of the range of motion along the first path 16 will then be the equilibrium position of the flexures, and the other extreme will correspond to the maximum amplified stroke of the first SMA wire 21i along the first path 16. In the third actuator assembly 46, the second SMA wire 212 of the first set may be replaced with a spring (of any form, including a flexure). In analogous ways, contraction of each SMA wire 25 of the second set may be opposed by one or more springs coupling the second part 15 to the third part 18. At a minimum, the first set of SMA wires 21 may include a single SMA wire 21, and the second set of SMA wires 25 may include a single SMA wire 25, each opposed by one or more corresponding springs, flexures and so forth. A spring (opposing any SMA wire 21, 25) may take the form of a coil spring, a flat spring, a leaf spring, a flexure, an element formed of elastomeric material, and so forth. One or more of the first plane 17 and the second plane 20 need not be parallel to one or both other planes. One or more of the first plane 17 and the second plane 20 need not be perpendicular to the vertical axis z.

The actuator assemblies 2, 14, 39, 46, or parts 4, 15, 18 thereof, need not be configured to support a lens assembly and, for example, may be configured to support another type of optical element, an image sensor, etc. The parts 4, 15, 18, may, or may not, include apertures 34. The actuator assemblies 2, 14, 39, 46 need not be used in a camera.

The vertical axis z need not correspond to an optical axis O. The vertical axis z may correspond to a line that is perpendicular to a plane defined by planar surfaces of the first 4, second 15 and/or third 18 parts. The vertical axis z may correspond to a line that is perpendicular to a plane defined by the directions of movement of the second 15 and/or third 18 parts along respective path 16, 19.

The actuator assembly may include further parts, for example a fourth part, a fifth part and so forth (not shown). Such further parts may be constrained to move along further paths (third, fourth etc), under the control of further sets of SMA wires (not shown). Further parts may be configured and/or constrained in any way described herein in relation to the first 4, second 15 and/or third 18 parts. Further paths may be aligned with the first 16 and/or second 19 paths, or may be defined so as to not coincide with either of the first 16 and second 19 paths.

The actuator assemblies 2, 14, 39, 46 may be, or may be provided in, any one of the following devices: a smartphone, a protective cover or case for a smartphone, a functional cover or case for a smartphone or electronic device, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, a camera with folded optics, an image capture device, an array camera, a 3D sensing device or system, a servomotor, a consumer electronic device, a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader, a computing accessory or computing peripheral device, an audio device, a security system, a gaming system, a gaming accessory, a robot or robotics device, a medical device, an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device, a drone, an aircraft, a spacecraft, a submersible vessel, a vehicle, and an autonomous vehicle, a tool, a surgical tool, a remote controller, clothing, a switch, dial or button, a display screen, a touchscreen, a flexible surface, and a wireless communication device. It will be understood that this is a non-exhaustive list of example devices.