SMA actuator assembly

Abstract

A shape memory alloy (SMA) actuator assembly, particularly for use in a camera assembly, assembly having a primary axis and comprising a support structure, and a movable part that is movable relative to the support structure across a range of movement in a plane. Four SMA elements are arranged as a first pair of SMA elements and a second pair of SMA element, each SMA element which are configured to move the movable part relative to the support structure to any position in the range of movement. The pairs of SMA elements are arranged on adjacent sides of the actuator assembly, and an anti-rotation mechanism configured to constrain rotation of the movable part relative to the support structure about the primary axis. The actuator assembly of this construction has a reduced assembly footprint.

Description

[0001] SMA ACTUATOR ASSEMBLY

[0002] Field

[0003] The present invention relates to the use of shape memory alloy (SMA) elements to provide positional control of a movable part supported on a support structure.

[0004] Background

[0005] There are a variety of types of actuator assembly in which it is desired to provide positional control of a movable part. SMA wire is advantageous as an actuator, in particular due to its high energy density which means that the SMA wire required to apply a given force is of relatively small size.

[0006] One type of actuator assembly in which SMA elements are known for use as an actuator is a camera, particularly a miniature camera. The actuator assembly may, for example, be used to provide optical image stabilization (OIS) in such a camera. WO 2013 / 175197 Al discloses a SMA actuator assembly in which a total of four SMA wires are used to provide OIS, by moving a movable lens element relative to an image sensor on a support structure to any position across a range of movement in two orthogonal directions, without applying any net torque to the movable part. WO 2017 / 072535 Al discloses an SMA actuator assembly in which SMA wires are used to provide OIS by moving a movable image sensor relative to a lens element.

[0007] The present invention is concerned with providing an alternative SMA actuator assembly for moving a movable part relative to a support structure in a plane, for example for the purpose of providing OIS.

[0008] Summary

[0009] According to the present invention, there is provided a shape memory alloy (SMA) actuator assembly having a primary axis and comprising: a support structure; a movable part that is movable relative to the support structure across a range of movement in a first plane; four SMA elements arranged as a first pair of SMA elements and a second pair of SMA element, each SMA element being configured to move the movable part relative to the support structure to any position in the range of movement, and wherein the first pair of SMA elements and the second pair of SMA elements are arranged on adjacent sides of the actuator assembly, and the actuator assembly further comprises an anti-rotation mechanism configured to constrain rotation of the movable part relative to the support structure about the primary axis.

[0010] Provision of the anti-rotation mechanism in combination with the four SMA elements arranged allows for control of movement of the movable part along the x-axis, and along the y-axis, and tension in the SMA elements. The anti-rotation mechanism constrains rotation of the movable part, such that any torque applied to the movable part by the SMA elements is converted into translational movement and / or tension in the SMA elements. The SMA actuator assembly is thuscapable of accurately and controllably moving the movable part within a plane of movement, for example for the purposes of providing OIS.

[0011] The anti -rotation mechanism may be configured to allow translation in the x-y plane.

[0012] The movable element may have a primary axis and the actuator assembly is configured such that the primary axis of the movable element and the primary axis of the actuator assembly are laterally offset from each other.

[0013] Thus, the movable element may be arranged so as to be closer to one or more of the sides of the actuator assembly.

[0014] The first pair of SMA elements may be arranged on one side of a second plane, whilst the second pair of the SMA elements is arranged on the opposite side of the second plane such that each of the first pair of SMA elements and the second pair of S MA elements are configured to generate a torque in opposite directions around the primary axis of the lens assembly.

[0015] The anti-rotation mechanism may be a bearing arrangement comprising first bearing portion and a second bearing portion, each bearing portion being connected in mechanical series and allowing movement in one of the first axis and the second axis and constraining movement in the other of the first and second axis.

[0016] The bearing mechanism may comprise rolling bearings allowing movement in one of the first axis and the second axis. Alternatively, the bearing mechanism may be a plain bearing.

[0017] Alternatively, the bearing arrangement may comprise two pairs of flexure arms connected between the support structure and the movable part and arranged in series to allow movement in one of the first axis and the second axis.

[0018] The anti-rotation mechanism may have an asymmetric configuration so as to define a recess for accommodating a component provided on the movable part.

[0019] The first pair of SMA elements may comprise first and third SMA elements and the second pair of SMA elements may comprises second and fourth SMA elements, the first SMA element being connected between the support structure and a first coupling point of the movable part, the second SMA element being connected between the support structure and a second coupling point of the movable part, the third SMA element being connected between the support structure and a third coupling point of the movable part, and the fourth SMA element being connected between the support structure and a fourth coupling point of the movable part.

[0020] The SMA element may be an SMA wire.

[0021] The second coupling point may be located diametrically opposite the first coupling point. The third and fourth coupling points may be arranged either side of a line bisecting a line extending between the first and second connection points.

[0022] The first pair of SMA elements and the second pair of SMA elements may be arranged in a plane substantially parallel to the first plane. As such, each pair of SMA elements may be arrangedwith each element of the pair in a side-by-side arrangement. In the side-by-side arrangement, the pitch between the elements is small.

[0023] The first pair of SMA elements and the second pair of SMA elements may be arranged in a stacked configuration. Each pair of elements is arranged in respective planes orthogonal to the first plane. If the first plane is the x-y plane, then the orthogonal planes are x-z and y-z planes.

[0024] The SMA actuator assembly may further comprise actuating units coupled between each SMA element of each pair of SMA elements and the moving part so as to provide stroke amplification.

[0025] The movable element may include a lens element. The primary axis of the movable element may include the optical axis of the lens.

[0026] According to the present invention, there is also provided a camera apparatus comprising the SMA actuator assembly and an image sensor that is fixed relative to the support structure. The movable part comprises a lens assembly comprising one or more lenses configured to focus an image on the image sensor. The SMA actuator assembly may be used to provide OIS in the camera apparatus by moving the lens assembly laterally of the optical axis. The overall size of the camera apparatus may be reduced compared to a camera in which OIS is provided by tilting of the camera unit or of the image sensor, where the camera apparatus requires additional clearance in the z direction to allow for such tilting.

[0027] There may also be provided an electronic device comprising the camera apparatus.

[0028] Brief description of the drawings

[0029] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

[0030] Fig. 1 is a schematic side view of a camera apparatus incorporating an SMA actuator assembly;

[0031] Fig. 2A is a schematic plan view of an SMA actuator assembly in accordance with an embodiment of the present invention showing the location of the lens assembly in relation to the actuator assembly footprint;

[0032] Fig. 2B is a schematic plan view of a conventional SMA actuator assembly showing the location of the lens assembly in relation to the actuator assembly footprint for comparison with Figure 2A;

[0033] Fig. 3 is a further schematic plan view of an SMA actuator assembly in accordance with an embodiment of the present invention;

[0034] Fig. 4 is a schematic plan view of a flexure bearing arrangement and anti -rotation mechanism in an SMA actuator assembly in accordance with an embodiment of the invention;Figs. 5 A and 5B is a schematic exploded view of another bearing arrangement and antirotation mechanism in an SMA actuator assembly in accordance with an embodiment of the invention;

[0035] Fig. 6A is a schematic plan view of an SMA actuator assembly in accordance with a second embodiment of the present invention;

[0036] Fig. 6B is a schematic side view of an SMA actuator assembly of Fig. 5A and in the direction of the arrow V’ in Figure 5A;

[0037] Fig. 6C is a schematic side view of an SMA actuator assembly of Fig. 5A and in the direction of the arrow V” in Figure 5 A;

[0038] Fig. 6D is a schematic perspective view of an SMA actuator assembly of Figures 5A to 5C; Fig. 7A is a schematic plan view of an SMA actuator assembly in accordance with a third embodiment of the present invention; and

[0039] Fig. 7B is a schematic side view of an SMA actuator assembly of Fig. 6A and in the direction of the arrow VI in Figure 6A.

[0040] Detailed description

[0041] In the following description, the present invention will be described with reference to a camera in which OIS is desired. However, this is one non-limiting example use of the present invention and it will be understood that the present invention may be used in any optical system or non-optical system and for any purpose. For example, the present invention may be used to improve the performance of a system used to perform 3D sensing (i.e. generate a 3D representation of a scene) or in haptics applications.

[0042] Fig. 1 schematically shows a camera apparatus 1 that incorporates an SMA actuator assembly 2 in accordance with the present invention. The camera apparatus 1 is to be incorporated in a portable electronic device such as a mobile telephone, or tablet computer. Thus, miniaturisation is an important design criterion.

[0043] The SMA actuator assembly 2 comprises a support structure 10 and a movable part 20. The movable part 20 is supported on the support structure 10. The movable part 20 is movable relative to the support structure 10 across a range of movement in a plane A of the actuator assembly i.e. in the x-y plane.

[0044] Movement in a direction perpendicular to the plane A, i.e. along the z-axis, may be constrained or prevented.

[0045] The actuator assembly 2 has a primary axis P defined with reference to the actuator assembly 2 and, in particular the support structure 10. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2

[0046] The SMA actuator assembly 2 comprises plural SMA elements in the form of SMA wires 30. The SMA wires 30 may be connected in tension between the support structure 10 and the movablepart 20. The SMA wires 30 may be connected at their ends to the support structure 10 and / or to the movable part 20 using connection elements 35, for example crimp connections. The crimp connections may crimp the SMA wires to hold them mechanically, as well as providing electrical connections to the SMA wires 30. The SMA wires 30 are connected to the movable part 20 at coupling points 33. Any other suitable connections may alternatively be used. The SMA wires 30 are capable, on selective contraction, of driving movement of the movable part 20 with respect to the support structure 10 in translational movement with two degrees of freedom (i.e. along the x and y axes).

[0047] The movable part 20 may be supported (and so suspended) on the support structure 10 exclusively by the SMA wires 30. However, the SMA actuator assembly 2 may comprise a bearing arrangement 40 that supports the movable part on the support structure 10. The bearing arrangement 40 may have any suitable form for allowing movement of the movable part 20 with respect to the support structure 10 in the x-y plane. For this purpose, the bearing arrangement 40 may, for example, comprise a rolling bearing, a flexure bearing or a plain bearing. The bearing arrangement 40 may constrain or prevent movement of the movable part 20 relative to the support structure 10 in the z-direction. The bearing arrangement 40 may also constrain movement in the x-y plane within a particular range of movement. An alternative mechanism can be provided to constrain movement within the x-y plane rather than using the bearing arrangement 40.

[0048] The camera apparatus 1 further comprises a lens assembly 3 and an image sensor 4. The lens assembly 3 comprises one or more lenses configured to focus an image on the image sensor 4. The image sensor 4 captures an image and may be of any suitable type, for example a charge coupled device (CCD) or a CMOS device. The lens assembly 3 comprises a lens carrier, for example in the form of a cylindrical body, supporting the one or more lenses. The one or more lenses may be fixed in the lens carrier or may be supported in the lens carrier in a manner in which at least one lens is movable along an optical axis O defined by reference to the lens assembly, for example to provide zoom or focus, such as auto-focus (AF). The camera apparatus 1 may be a miniature camera apparatus in which the (or each lens) of the lens assembly 3 has a diameter of 20mm or less, preferably of 17mm or less. For ease of reference, the z axis is taken to be the optical axis O of the lens assembly 3 and the x and y axes are perpendicular thereto. In the desired orientation of the lens assembly 3, the optical axis O is perpendicular to a light-sensitive region of the image sensor 4 and the x and y axes are parallel to the light-sensitive region of image sensor 20.

[0049] In the embodiment shown in Fig. 1, the movable part 20 comprises the lens assembly 3. The image sensor 4 may be fixed relative to the support structure 10, i.e. mounted on the support structure 10. In other embodiments (not shown), the lens assembly 3 may be fixed (in the x-y plane) relative to the support structure 10 and the movable part 20 may comprise the image sensor 4. In either embodiment, in operation the lens assembly 3 is moved relative to the image sensor 4 orthogonally to the optical axis O in the x-y plane. This has the effect that the image on the image sensor 4 is moved.This is used to provide OIS, compensating for image movement of the camera apparatus 1, caused for example by a user’s handshake. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2

[0050] The camera apparatus 1 comprises a vibration sensor 6 and a control circuit 8. The vibration sensor 6 may be a gyroscope sensor, for example, although in general other types of vibration sensor 6 could be used. The vibration sensor 6 detects vibrations that the camera apparatus 1 is experiencing and generates output signals representative of the vibration of the camera apparatus 1. The control circuit 8 may be implemented in an integrated circuit (IC) chip. The control circuit 8 generates drive signals for the SMA wires 30 in response to the output signals of the vibration sensor 6. SMA material has the property that on heating it undergoes a solid-state phase change that causes the SMA material to contract. Thus, applying drive signals to the SMA wires 30, thereby heating the SMA wires 30 by allowing an electric current to flow, will cause the SMA wires 30 to contract and move the movable part 20. The drive signals are chosen to drive movement of the movable part 20 in a manner that stabilizes the image sensed by the image sensor 4. The control circuit 8 supplies the generated drive signals to the SMA wires 30, thereby providing OIS.

[0051] In an example of the present disclosure, the actuator assembly 2 comprises four SMA wires 30a, 30b, 30c, 30d (shown in Figure 3). Generally, four SMA wires in an actuation assembly allows control of the movable part 20 with respect to the support structure 10 in four degrees of freedom, in particular control of: movement along the x-axis, movement along the y-axis, rotation about the z-axis, and tension in the SMA wires. However, in the present invention, rotation about the z-axis is constrained by a bearing system as will be described in further detail below, whilst still allowing translation within the x-y plane.

[0052] Lens assembly arrangement

[0053] Fig. 2 A schematically depicts a plan view of an embodiment of the actuator assembly 2. The moveable part 20 is arranged relative to the support part 10, such that the primary axis O of the lens assembly 3 is laterally displaced or offset from the primary axis P of the actuator assembly 2. The lens assembly primary axis O and the actuator assembly primary axis P are substantially parallel to each other and to the z axis, but laterally offset or displaced from each other in a first plane B. The first plane B is orthogonal to the x-y plane and subtends acute angles to the x-z and y-z plane such that the primary axis O of the lens assembly and the primary axis P of the actuator assembly 2 are laterally offset along a line C extending obliquely across the actuator assembly 2. In the example illustrated in Figures 2A and 2B, the line C is a diagonal line extending between opposite comers of the rectangular footprint 9 of the actuator assembly 2.

[0054] By offsetting the lens assembly axis O (i.e. the optical axis) from the primary axis P of the actuator assembly 2, so that the two are not colinear, the lens assembly 3 is offset from the centre of the actuator assembly footprint 9 i.e. from the actuator assembly primary axis P, thereby minimisingthe distance from the centre of the lens assembly 3 to the outside of the actuator assembly 2 on one and / or two sides 5c 5d of the actuator assembly footprint 9. The image sensor 4 will also be offset in relation to the actuator assembly footprint to ensure that the image sensor is able to detect an image as formed by the lens assembly 3.

[0055] A conventional actuator footprint in which the lens assembly primary axis i.e. the optical axis and the primary axis of the actuator assembly are colinear is illustrated in Figure 2B for comparison.

[0056] Wire configuration

[0057] Figure 3 schematically illustrates an SMA wire arrangement for an embodiment of the actuator assembly of the present disclosure. The four SMA wires 30 are arranged as two pairs of SMA wires 30a, 30b; 30c, 30d. A first pair 30a, 30b and a second pair 30c, 30d are arranged on respective adjacent sides 5a, 5b of the actuator assembly 2. Thus, the first pair 30a, 30b of the SMA wires 30 are arranged on one side of the first plane B, whilst the second pair 30c, 30d of the SMA wires is arranged on the opposite side of the first plane B.

[0058] As mentioned above, each of the SMA wires 30 are coupled between the movable part 20 and the support part 10 by means of connection elements 35, such as crimp connections as described above.

[0059] On heating of one of the SMA wires 30, the stress therein increases and it contracts. This causes movement of the lens assembly 3 . A range of movement occurs as the temperature of the SMA 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 30 so that the stress therein decreases, it extends under the force from opposing ones of the SMA wires 30. This allows the lens assembly 3 to move in the opposite direction.

[0060] As a result, the SMA wires 30 are capable of being selectively driven to move the lens assembly 3 relative to the support structure 10 to any position in a range of movement in two orthogonal directions, x and y, perpendicular to the optical axis O. The magnitude of the range of movement depends on the geometry and the range of contraction of the SMA wires 30 within their normal operating parameters. Each of the SMA wires 30 applies, upon contraction, a respective force to the movable part 20.

[0061] Selective driving of the SMA wires 30, enable the first pair of SMA wires 30a, 30b to move the lens assembly 3 relative to the support structure 10 in a first direction x in the x-y plane, and the second pair of SMA wires 30c, 30d are arranged to move the lens element 2 relative to the support structure 10 in a second direction y in the x-y plane and orthogonal to the first direction x. Movement in directions other than parallel to the SMA actuator wires 30a to 30d may be driven by a combination of actuation of these pairs of the SMA actuator wires 30a to 30d to provide a linear combination of movement in the transverse directions.Unlike known four-wire actuators, for example as described in WO2013175197A1 in which the four wires are arranged on four sides of the actuator assembly 2, the four SMA wires in the present disclosure are arranged on adjacent sides 5a, 5b of the actuator assembly 2 as already described.

[0062] Specifically, and as illustrated in Figure 3, the first pair of SMA wires comprises first SMA wire 30a and second SMA wire 30b, and the second pair of SMA wires comprises third SMA wire 30c and fourth SMA wire 30d. The first SMA wire 30a is connected between the support structure 10 and a first coupling point 33a of the movable part 20, the second SMA wire 30b is connected between the support structure 10 and a second coupling point 33b of the movable part 20, the third SMA wire 30c is connected between the support structure 10 and a third coupling point 33c of the movable part 20, and the fourth SMA 30d wire is connected between the support structure 10 and a fourth coupling point 33d of the movable part 20. In one example of the disclosure illustrated in Figure 3, the first and fourth coupling points 33a, 33d are connected to the movable part 20 at a mutual coupling point 33e.

[0063] Anti-rotation control

[0064] As can be seen in Figure 3, the pitch i.e. the distance between opposing wires (30c, 30d; 30a, 30b) is significantly less than known arrangements where the pairs of opposing SMA wires are located on opposite sides of the actuator assembly 2.

[0065] In this arrangement embodiments, because the wires are configured so that there is little or no separation between them, creation of a controlling torque in response to applied forces is more difficult. In this case the wires cannot create sufficient torque to resist other forces which might act on the system, such a gravity.

[0066] Due to the small pitch, this asymmetric wire configuration therefore gives rise to a sensitivity to large rotations of the movable part 20 around the Z axis.

[0067] To address this sensitivity to large rotations, the actuator assembly 2 includes an anti-rotation mechanism.

[0068] Figs. 4 and 5 schematically depict, in plan, bearing arrangements 40 that comprise or incorporate the anti -rotation mechanism 7. The bearing arrangements 40 of Figs. 4 and 5 constrain rotation of the movable part 20 relative to the support structure 10 about the z-axis. Each bearing arrangement 40 comprises in essence two bearing portions that are connected in mechanical series, each bearing portion allowing movement in a respective one of two non-colinear directions in the x-y plane but constraining in another of the two non-colinear directions in the x-y plane.

[0069] Fig. 4 shows a bearing arrangement 40 comprising an arrangement of flexure arms connected between the support structure 10 and the movable part 20 (not shown in Figure 4). The bearing arrangement 40 comprises two pairs of flexure arms 41a, 42a that are connected in mechanical series.A first pair of flexure arms 41a allows movement in one of two orthogonal directions in the x-y plane, for example in the y-direction as indicated by double-headed arrows 46 in Figure 4A. The first pair of flexure arms 41a constrains movement in any other direction, for example in the x direction - as indicated by the double-headed arrows 47 in Figure 4A.

[0070] A second pair of flexure arms 42a allows movement in the other of the two orthogonal directions in the x-y plane, for example in the x-direction. The second pair of flexure arms 42a constrains movement in any other direction, for example in the y-direction.

[0071] In combination, the two pairs of flexure arms 41a, 42a thus allow movement in the x-y plane and constrain rotation about the z-axis. The bearing arrangement 40 comprises a bearing element 43 comprising a first portion 43a and a second portion 43b. The first portion 43a includes the first pair of flexure arms 41a which are connected between the movable part 20 and the support structure 10, and the second portion 43b is connected to the first portion 43a by means of the second pair of flexure arms 42a. The bearing arrangement 40 may be a single piece, so all portions of the bearing arrangement may be integrally formed, for example from a sheet material such as a sheet metal. The bearing arrangement 40 may be rigidly connected to the movable part 20 and the support structure 10 or may be integrally formed with (part of) the support structure 10 and / or movable part 20.

[0072] The bearing element 43 can be configured to accommodate the lens assembly 2, for example by extending around an open region 44 into which the lens assembly 3 can be located so as to not obscure the lens assembly 3 and image sensor 4, and such that the lens assembly axis O extends though the open region 44.

[0073] Fig 5A and 5B show an alternative bearing arrangement 40 that comprises an arrangement of rolling bearings connected between the support structure 10 and the movable part 20 (not shown in Figures 5A and 5B). The rolling bearings may be ball bearings, roller bearings or rocker bearings, for example. The rolling bearings may comprise a rolling element (such as a ball, a roller or a rocker) that bears upon two bearing surfaces. The bearing arrangement 40 comprises two rolling bearings 45a, 45b that are arranged in mechanical series between the movable part 20 and the support structure 10.

[0074] The bearing arrangement 40 comprises three cooperating plates 40a, 40b, 40c which incorporate the rolling bearings 45a, 45b.

[0075] The first rolling bearing 45a allows movement in one of two orthogonal directions in the x-y plane, for example in the x-direction as indicated by the double-headed arrow 47 in Figure 5A. The first rolling bearing 45a constrains movement in another direction, for example in the y-direction as shown by the double-headed arrow 46 in Fig. 5A. The first rolling bearing 45a may comprise a pair of co-linear rolling elements 45a’ that bear upon corresponding bearing surfaces in the first plate 40c and second plate 40b. The movable part 20 may move in the x-direction with respect to the intermediary element. A third rolling element 45a”that bears upon corresponding bearing surfaces in the first plate 40c and second plate 40b, is provided to ensure that the rolling bearing 40 remains level and in contact with the bearing surfaces.The second rolling bearing 45b is similar to the first rolling bearing 45a but allows movement in the other of the two orthogonal directions in the x-y plane, for example in the y-direction as indicated by the double-headed arrow 46. The second rolling bearing 45b constrains movement in any other direction, for example the x-direction as indicated by the double-headed arrow 46. The second rolling bearing 45b may comprise rolling elements that bear upon a surface of the second plate 40b and third plate 40a. The second rolling bearing 45b may also comprise a pair of co-linear rolling elements. The movable part 20 may move in the y-direction. A third rolling element 45b” is provided to ensure that the rolling bearing 40 remains level and in contact with the bearing surfaces. In combination, the two rolling bearings 45a, 45b thus allow movement in the x-y plane and constrain rotation about the z-axis.

[0076] The three cooperating plates 40a, 40b, 40c also include pairs of cooperating retention members 48a, 48b. A first cooperating member 48a in the lower plate 40a is a magnet and the second cooperating member 48b in the upper plate 40c is magnetic steel, they are arranged to provide a biasing force to hold the cooperating plates 40a, 40b, 40c together

[0077] The bearing arrangement 40 can also be configured to accommodate the lens assembly 2, for example by extending around an open region 44 into which the lens assembly 3 can be arranged such that the lens assembly axis O extends though the open region 47 and can be located so as to not obscure the lens assembly 3 and image sensor 4, and such that the lens assembly axis O extends though the open region 44.

[0078] Although Figs. 4 and 5A and 5B show two examples of bearing arrangements 40 that incorporate the anti-rotation mechanism, it will be appreciated that the anti-rotation mechanism 7 may be separate from the bearing arrangement 40 or incorporated in a different bearing arrangement 40. In general, the anti-rotation mechanism 7 may comprise any mechanism that constrains rotation of the movable part 20 relative to the support structure 10. Further examples of such anti-rotation mechanisms 7 are disclosed in co-pending GB 2005570.3, which examples are incorporated by reference herein.

[0079] Alternative bearing arrangements such as plain bearings can also be used.

[0080] Stacked wire arrangement

[0081] Figures 6A to 6D schematically illustrate an alternative embodiment of an actuator assembly. In the embodiment described in relation to Figures 1 and 2, the SMA wires are arranged within the plane of the actuator assembly 2 i.e. parallel to the plane A shown in Figure 1. However, in the alternative embodiment described with reference to Figures 5A to 5D, the pairs of SMA wires 30a to 30d are stacked or arranged in adjacent planes C, D extending laterally of the actuator plane A and, in particular in a plane that is substantially orthogonal to the plane A. In the embodiment described herein, adjacent planes C and D are arranged substantially perpendicularly of each other and in planes extending in a direction parallel to the lens assembly axis O and actuator assembly primary axis P.The arrangement of the SMA wires 30a, 30b, 30c, 30d as connected between the movable part 20 and the support structure 10 are as described in relation to Figures 1 and 2 above. The movable part 20 is configured to mount the connection elements 33 such that the pairs SMA wires 30a to 30d are connected between movable part 20 and the support structure 10 in a respective plane extending substantially perpendicular to the plane of movement of the movable part 20 relative to the support structure 10.

[0082] The stacked wire arrangement of Figures 5A to 5B can be used to integrate stroke amplification mechanisms. Conventionally, stroke amplification mechanisms increase the actuation assembly footprint. However, using a stacked wire arrangement there is only a single layer of amplification flexures and connection elements which minimises the footprint increase.

[0083] Flexure amplification

[0084] Figures 7A and 7B illustrate actuating units 50 used with the stacked wire arrangement of Figures 6A to 6D.

[0085] It should be noted that, in this configuration there is no pitch between opposing wires as they are in a stacked arrangement.

[0086] Each actuating unit 50 includes a body portion 51 to which several other components of the actuating unit 50 are connected as described below. Typically, the body portion 51 is relatively rigid compared to the other components of the actuating unit 50 and does not deform significantly on actuation of the actuating unit 50. In some examples, the body portion 51 is not a distinct part of the actuating unit 50. For example, the body portion 51 may be defined as part of one of the other components of the actuating unit 50 or simply as a connection point between other components of the actuating unit 50.

[0087] The actuating unit 50 also includes a force-modifying flexure 52. The force-modifying flexure 52 is connected between the body portion 51 and the support structure 10. One end of the force-modifying flexure 52 is connected to the body portion 51. The other end of the force-modifying flexure 32 is connected to the support structure 10 and fixed relative to the support structure 10. The force-modifying flexure 52 allows the body portion 51 to pivot relative to the support structure 10 about an effective pivot point 53. . It will be understood that other pivoting arrangements and force modifying mechanisms are possible within the scope of the present invention.

[0088] The actuating unit 50 also includes a respective SMA wire 30a to 30d. The SMA wire 30a to 30d is connected between the body portion 51 and the support structure 10. One end of the SMA wire 30a to 30d is connected to the support structure 10 by a connection element 35. The other end of the SMA wire 30a to 30d is connected to the body portion 51 via connection elements 35.

[0089] The actuating unit 50 also includes a coupling link 54. In this example, the coupling link 54 is a coupling flexure 54. The coupling flexure 54 is connected between the body portion 51 and the movable part 20. One end of the coupling flexure 54 is connected to the body portion 51. The otherend of the coupling flexure 54 is connected to the movable part 20. The coupling link 54 transfers or transmits an actuating force F from the body portion 51 to the movable part 20. The coupling link 54 is compliant (i.e. deformable) in a direction (or in multiple directions) perpendicular to the actuating force F. This allows the movable part 20 to move in directions other than the direction of the coupling flexure 54 and actuating force. This can be needed, for example, where different actuating units 50 cause the movable part 20 to move in different directions.

[0090] In this example, the body portion 51, the force-modifying flexure 52, and the coupling flexure 54 are integrally formed, for example from a single sheet of material (such as metal). In other examples, one or more or these features, if present, may be formed from different parts or materials.

[0091] The SMA wire 30a to 30d is arranged, on contraction, to apply an input force on the body portion 31. The input force acts parallel to the length of the SMA wire 30 to 30d. The forcemodifying flexure 52 and the body portion 51 are arranged to modify the input force so as to give rise to the actuating force, which is transmitted from the body portion 51 to the movable part 20 by the coupling flexure 54. In particular, the input force deforms the force-modifying flexure 52, thereby causing the body portion 51 to pivot about the effective pivot point 53. In simple terms, the forcemodifying flexure 52 and the body portion 51 act like a lever. The force-modifying flexure 52 and the body portion 51 may modify the direction and / or the magnitude of the input force so as to give rise to the actuating force.

[0092] Figure 7B schematically shows a side view of an example of the actuator assembly 2, showing an arrangement of two actuating units 50 in each of the two adjacent sides of the actuator assembly 2 i.e. four actuating units 50 in total. The four actuating units 50 may apply actuating forces between the movable part 20 and the support structure 10. The actuating forces are applied to the movable part 20 relative to the support structure 10.

[0093] Although the schematic plan views of the figures described above show an example in which the movable part 20 has a square footprint in the x-y plane, it will be appreciated that the movable part 20 may generally have any other shape. For example, the movable part 20 may be substantially rounded and follow, for example, the outline of a cylindrical lens carrier. When reference is made to the SMA wires 30 extending along an edge or side of the movable part 20, it is thus not required that the SMA wires are parallel to such an edge or side. Rather, the intention is that the SMA wires 30 are arranged in a manner allowing the footprint of the SMA actuator assembly 2 in the x-y plane to be reduced compared to a situation in which the SMA wires 30 extend radially away from the optical axis O, while achieving a given amount of stroke (i.e. movement of the movable part 20). The SMA wires 30 may, in particular, extend in a manner similar to that depicted in the figures, regardless of the shape of the movable part 20 or support structure 10. As such, the term side should be understood to describe an outer section of the footprint of the actuator assembly.It will be appreciated that the direction in which any one of the above-described SMA wires 30 applies a force to the movable part 20 may change, to some degree, as the movable part 20 moves relative to the support structure 10.

[0094] 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.

[0095] Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and where appropriate other modes of performing the present disclosure, the present disclosure should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that the present invention has a broad range of applications, and that the embodiments may take a wide range of modifications without departing from scope of the claims.

Claims

Claims1. A shape memory alloy (SMA) actuator assembly having a primary axis and comprising: a support structure;a movable part that is movable relative to the support structure across a range of movement in a plane;four SMA elements arranged as a first pair of SMA elements and a second pair of SMA element, each SMA element being configured to move the movable part relative to the support structure to any position in the range of movement, and wherein the first pair of SMA elements and the second pair of SMA elements are arranged on adjacent sides of the actuator assembly; andan anti-rotation mechanism configured to constrain rotation of the movable part relative to the support structure about the primary axis.

2. The SMA actuator assembly of claim 1, wherein the anti -rotation mechanism is a bearing arrangement comprising first bearing portion and a second bearing portion, each bearing portion being connected in mechanical series and allowing movement in one of the first axis and the second axis and constraining movement in the other of the first and second axis.

3. The SMA actuator assembly of claim 2, wherein the bearing arrangement comprises rolling bearings allowing movement along one of the first axis and the second axis.

4. The SMA actuator assembly of claim 2, wherein the bearing arrangement is a flexure bearing.

5. The SMA actuator assembly of claim 3, comprising a first pair of flexure arms and a second pair of flexure arms, each connected between the support structure and the movable part and arranged in series such that the first pair of flexure arms allows movement along the first axis and constrains movement in the second axis, and the second pair of flexure arms allows movement along the second axis and constrains movement in the first axis.

6. The SMA actuator assembly of claim 2, wherein the bearing arrangement is a plain bearing7. The SMA actuator assembly of any of claims 1 to 6, wherein the anti -rotation mechanism has an asymmetric configuration so as to define a recess for accommodating a component provided on the movable part.

8. The SMA actuator assembly of any preceding claim, wherein the first pair of SMA elements comprises first and third SMA wires and the second pair of SMA wires comprises second and fourth SMA wires, the first SMA wire being connected between the support structure and a first coupling point of the movable part, the second SMA wire being connected between the support structure and a second coupling point of the movable part, the third SMA wire being connected between the support structure and a third coupling point of the movable part, and the fourth SMA wire being connected between the support structure and a fourth coupling point of the movable part.

9. The SMA actuator assembly of claim 6, wherein the second coupling point is located opposite the first coupling point, and wherein the third and fourth coupling points are arranged either side of a line bisecting a line extending between the first and second connection points.

10. The SMA actuator assembly of any of claims 1 to 9 wherein the first pair of SMA elements and the second pair of SMA elements are arranged in a plane parallel to the first plane.

11. The SMA actuator assembly of any of claims 1 to 9 wherein the first pair of SMA elements and the second pair of SMA elements are arranged in respective planes orthogonal to the first plane.

12. The SMA actuator assembly of any preceding claim, further comprising actuating units coupled between each SMA element of each pair of SMA elements and the moving part so as to provide stroke amplification.

13. The SMA actuator assembly of any preceding claim, wherein the movable element has a primary axis and the actuator assembly is configured such that the primary axis of the movable element and the primary axis of the actuator assembly are laterally offset from each other along a line extending obliquely across the actuator assembly.

14. The SMA actuator assembly of any of claims 1 to 13, wherein the movable element may include a lens element,15. The SMA actuator assembly of claim 14, wherein the movable element has a primary axis and the movable element includes a lens element, and wherein the primary axis of the movable element may include the optical axis of the lens element and the actuator assembly is configured such that the primary axis of the movable element and the primary axis of the actuator assembly are laterally offset from each other along a line extending obliquely across the actuator assembly.1616. A camera apparatus comprising the SMA actuator assembly of the preceding claims.

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