EP4081710A1

EP4081710A1 - Shape memory alloy actuation apparatus

Info

Publication number: EP4081710A1
Application number: EP20838280.4A
Authority: EP
Inventors: James Howarth; Oliver HART; Daniel John BURBRIDGE; David OOI; Stephen Matthew BUNTING; Andrew Benjamin Simpson Brown; Peter VAN WYK
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2019-12-26
Filing date: 2020-12-29
Publication date: 2022-11-02
Also published as: WO2021130506A1; GB201919340D0; CN115103959A; WO2021130506A8; CN115103959B; CN115103959A8

Abstract

An SMA actuation apparatus comprising: a support structure; a movable element; a helical bearing arrangement supporting the movable element on the support structure and arranged to guide helical movement of the movable element with respect to the support structure around a helical axis; and a set of four SMA actuator wires, each wire connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, the set of wires comprising a first pair of wires arranged, on contraction, to drive rotation of the movable element in a first sense around the helical axis and a second pair of wires arranged, on contraction, to drive rotation of the movable element in a second, opposite sense around the helical axis, wherein the helical bearing arrangement converts the rotation into the helical movement.

Description

Shape Memory Alloy Actuation Apparatus

The present disclosure relates to a shape memory alloy (SMA) actuation apparatus in which at least one SMA actuator wire drives movement of a movable element with respect to a support structure.

It is known to use an SMA wire as an actuator to drive translational movement of a movable element with respect to a support structure. SMA actuator wires have particular advantages in miniature devices and may be applied in a variety of devices including handheld devices, such as cameras and mobile phones. Such SMA actuator wires may be used for example in an optical device such as a camera for driving translational movement of a camera lens element along its optical axis, for example to effect focussing (autofocus, AF) or zoom.

Some examples of an SMA actuation apparatuses which are cameras of this type are disclosed in WO-2007/113478. Herein, the movable element is a camera lens element supported on a support structure by a helical bearing arrangement comprising flexures that guide translational movement along the optical axis. In one example described herein, the SMA actuator wire is a piece of SMA wire connected at its ends to a support structure and hooked over a hook on a camera lens element for driving the translational movement. The straight SMA actuator wires formed by the portions of the piece of SMA wire on either side of the hook extend at an acute angle of greater than 0 degrees to the movement direction parallel to the optical axis. Angling the SMA actuator wires in this way increases the amount of movement compared to an SMA actuator wire extending along the movement direction and also reduces the extent of the actuator in the movement direction.

Miniaturisation is an important design criteria in many types of SMA actuation apparatus. In many applications, it is desirable to minimise the size of the SMA actuation apparatus in the movement direction. For example, where the SMA actuation apparatus comprises a lens element that is moved along the optical axis, it is desirable to minimise the size along the optical axis.

In an SMA actuation apparatus in which SMA actuator wires extend at an acute angle to the movement direction, as in the camera disclosed in WO-2007/113478 for example, the SMA actuator wires themselves necessarily have an extent projected along the movement direction. This places a minimum size on the SMA actuation apparatus along the movement direction, even if other components may be made smaller in that direction. In particular, the extent of the SMA actuator wires projected along the movement direction is determined by the required degree of translational movement required, because the maximum change in length of the SMA actuator wires is a given percentage of the overall length of the SMA actuator wires, this resulting from the electromechanical properties of the SMA material.

According to a first aspect of the presently claimed invention, there is provided a shape memory alloy, SMA, actuation apparatus comprising: a support structure; a movable element; a helical bearing arrangement supporting the movable element on the support structure and arranged to guide helical movement of the movable element with respect to the support structure around a helical axis; and a set of four SMA actuator wires, each wire connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, the set of wires comprising a first pair of wires arranged, on contraction, to drive rotation of the movable element in a first sense around the helical axis and a second pair of wires arranged, on contraction, to drive rotation of the movable element in a second, opposite sense around the helical axis, wherein the helical bearing arrangement converts the rotation into the helical movement.

The four SMA actuator wires can provide an alternative and advantageous way of moving the movable element.

Further (optional) features are specified in the dependent claims and further advantages are described below.

In some embodiments, the helical bearing arrangement comprises at least one flexure arm extending between the support structure and the movable element. For example, the helical bearing arrangement may comprise two flexure arms, preferably four flexure arms.

In some embodiments, the maximum extent of the flexure arms and the SMA wires along a first axis is substantially less than the maximum extent of the flexure arms and the four SMA wires along a second axis; wherein the first axis is perpendicular to the helical axis, and the second axis is perpendicular to the helical axis and perpendicular to the first axis. For example, the maximum extent of the flexure arms and the SMA wires along the first axis may be less than 90%, preferably less than 80%, of the maximum extent of the flexure arms and the four SMA wires along the second axis.

The SMA actuation apparatus may comprise a first side and a second side, wherein the first side comprises at least one flexure arm and a first pair of the four SMA wires, and the second side comprises at least one flexure arm and a second pair of the four SMA wires. The first side and the second side are on opposite sides of the helical axis. The first and second sides may be separate, non-overlapping and contiguous.

The helical bearing arrangement may comprise four flexure arms. The four flexure arms may be substantially equally spaced around the perimeter of the movable element. The flexure arms may protrude from the outer perimeter of the main body of the movable element from four locations that are generally offset from each other by 90°.

The four SMA wires may be substantially aligned with the first axis. For example, the angle between each of the four SMA wires and the axis may be less than 20°, preferably less than 10°, further preferably less than 5°.

The four SMA wires may occupy substantially the maximum extent of the flexure arms and the SMA wires along the first axis. For example, the four SMA wires may occupy more than 80%, preferably more than 90%, further preferably more than 95%, of the maximum extent of the flexure arms and the SMA wires along the first axis.

In some embodiments, the movable element comprises four movable connection portions and the support structure comprises four static connection portions. Each of the four SMA wires may be connected between each of the four movable portions and each of the four static connection portions. The four movable connection portions may extend from locations substantially equally spaced around the perimeter of the main body of the movable element. The locations may be generally offset from each other by about 90°.

The flexure arms and the movable connection portions may be unitary. For example, the flexure arms and the movable connection portions may be made from a single sheet, e.g. a sheet of metal. Alternatively, the flexure arms and the movable connection portions may not be unitary, and e.g. comprise different thicknesses and/or materials.

Particular advantage is achieved when applied to an SMA actuation apparatus in which the movable element is a lens element comprising at least one lens, for example where the helical axis is the optical axis of the lens element. There are many applications where it is desirable to minimise the size along the direction of translational movement of such a lens element. For example, the SMA actuation apparatus may be a camera wherein the support structure has an image sensor mounted thereon and the lens element is arranged to focus an image on the image sensor. The advantages of size reduction achieved by the present techniques are particularly valuable in a handheld device where space is at a premium and in a miniature device, for example wherein the at least one lens has a diameter of at most 30mm, preferably at most 20mm, preferably at most 15mm, preferably at most 10mm.

However, the present techniques may in general be applied to any type of device that comprises a static part and a moveable part which is moveable with respect to the static part. By way of non-limitative example, the actuator assembly may be, or may be provided in, any one of the following devices: a smartphone, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, an image capture device, a foldable 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, 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. It will be understood that this is a non-exhaustive list of example devices.

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

Fig. 1 is a schematic view of an actuator assembly that is a camera;

Figs. 2 and 3 are perspective views of two helical bearings;

Fig. 4 is a schematic cross-sectional view of the actuator assembly with different helical bearing arrangements;

Figs. 5 and 6 are perspective views of an example of the actuator assembly as shown in Fig. 4; Fig. 7 is a plan view of the actuator assembly shown in Figs. 5 and 6;

Figs. 8 to 10 are schematic cross-sectional views of the actuator assembly with different helical bearing arrangements;

Fig. 11 is a perspective view of the helical bearing arrangement of the actuator assembly of Fig. 9;

Fig. 12 is a perspective view of a first example of the actuator assembly of

Fig. 9;

Fig. 13 is a side view of the actuator assembly shown in Fig. 12;

Fig. 14 is a plan view of the actuator assembly shown in Fig. 12;

Fig. 15 is a perspective views of a second example of the actuator assembly of Fig. 9;

Fig. 16 is a plan view of the actuator assembly shown in Fig. 15; and

Fig. 17 is a perspective view of the actuator assembly with another possible helical bearing arrangement;

Figs. 18 to 22 are side views of possible loading arrangements;

Fig. 22A is a schematic cross-sectional view of the actuator assembly with yet another possible helical bearing arrangement

Fig. 23 is a cross-sectional view of a first alternative bearing, the cross- section being taken perpendicular to the direction of movement of the bearing;

Fig. 24 is a side view of the first alternative bearing of Fig. 23;

Fig. 25 is a cross-sectional view of a second alternative bearing, the cross- section being taken perpendicular to the direction of movement of the bearing;

Fig. 26 is a side view of the alternative bearing of Fig. 25;

Fig. 27 is a side view of the actuator assembly with a helical bearing arrangement comprising plural flexures;

Figs. 28 and 29 are plan views of the helical bearing arrangement of Fig. 27 with different forms of flexures;

Fig. 29A is a perspective view of an alternative helical bearing arrangement comprising plural flexures;

Figs. 30 to 32 are perspective views of various arrangements of SMA actuator wires, helical bearings and, where present, biasing elements;

Fig. 33 is a perspective view of an alternative helical bearing arrangement;

Figs. 34A-B are perspective views of a first helical flexure assembly.

Fig. 35 is a plan view of a second helical flexure assembly; Fig. 36 is a plan view of a third helical flexure assembly;

Fig. 37 is a plan view of a fourth helical flexure assembly; and Fig. 38 is a plan view of a fifth helical flexure assembly.

Except where the context requires otherwise, the term "bearing" is used herein as follows. The term "bearing" is used herein to encompass the terms "sliding bearing", "plain bearing", "rolling bearing", "ball bearing", "roller bearing", an "air bearing" (where pressurised air floats the load) and "flexure". The term "bearing" is used herein to generally mean any element or combination of elements that functions to constrain motion to only the desired motion and reduce friction between moving parts. The term "sliding bearing" is used to mean a bearing in which a bearing element slides on a bearing surface, and includes a "plain bearing". The term "rolling bearing" is used to mean a bearing in which a rolling bearing element, for example a ball or roller, rolls on a bearing surface. Such a rolling bearing element may be a compliant element, for example a sac filled with gas. In embodiments, the bearing may be provided on, or may comprise, non-linear bearing surfaces.

In some embodiments of the present disclosure, more than one type of bearing element may be used in combination to provide the bearing functionality. Accordingly, the term "bearing" used herein includes any combination of, for example, plain bearings, ball bearings, roller bearings and flexures.

Actuator assembly

An actuator assembly 1 that is a camera is shown schematically in Fig. 1.

The actuator assembly 1 comprises a static part 2 that has an image sensor 3 mounted thereon. The static part 2 may take any suitable form, typically including a base 4 to which the image sensor is fixed. The static part 2 may also support an IC chip 5 described further below.

The actuator assembly 1 also comprises a lens element 10 that is the movable part in this example. The lens element 10 comprises a lens 11, although it may alternatively comprise plural lenses. The lens element 10 has an optical axis O aligned with the image sensor 3 and is arranged to focus an image on the image sensor 3.

The actuator assembly 1 is a miniature device. In some examples of a miniature device, the lens 11 (or plural lenses, when provided) may have a diameter of at most 30mm, preferably at most 20mm, preferably at most 15mm, preferably at most 10mm.

Although the actuator assembly 1 in this example is a camera, that is not in general essential. In some examples, the actuator assembly 1 may be an optical device in which the movable part is a lens element but there is no image sensor. In other examples, the actuator assembly 1 may be a type of apparatus that is not an optical device, and in which the movable part is not a lens element and there is no image sensor. Examples include apparatuses for depth mapping, face recognition, game consoles, projectors and security scanners.

Helical bearing arrangement

The actuator assembly 1 also comprises a helical bearing arrangement 20 (shown schematically in Fig. 1) that supports the lens element 10 on the static part 2. The helical bearing arrangement 20 is arranged to guide helical movement of the lens element 10 with respect to the static part 2 around a helical axis H. The helical axis H in this example is coincident with the optical axis O and the helical movement is shown in Fig. 1 by the arrow M. Preferably, the helical motion is along a right helix, that is, a helix with constant radius, but in general any helix is possible. The pitch of the helix may be constant or vary along the helical motion. Preferably, the helical movement is generally only a small portion (less than one quarter) of a full turn of the helix.

The helical motion of the lens element 10 guided by the helical bearing arrangement 20 includes a component of translational movement along the helical axis H and rotational movement around the helical axis H. The translational movement along the helical axis H is the desired movement of the lens element 10, for example to change the focus of the image on the image sensor 3 and/or to change the magnification (zoom) of the image on the image sensor 3. The rotational movement around the helical axis H is in this example not needed for optical purposes, but is in general acceptable as rotation of the lens element 10 does not change the focus of the image on the image sensor 3.

The helical bearing arrangement 20 may take a variety of forms.

One possibility is that the helical bearing arrangement 20 comprises one or more helical bearings 30 that are rolling bearings, examples of which are shown in Figs. 2 and 3. In each of Figs. 2 and 3, the helical bearing 30 comprises a pair of bearing surfaces 31 and 32 and plural rolling bearing elements 33, for example balls, disposed between the bearing surfaces 31 and 32. One of the bearing surfaces 31 and 32 is provided on the static part 2 and the other of the bearing surfaces 31 and 32 is provided on the lens element 10.

The helical bearing 30 guides the helical movement of the lens element 10 with respect to the static part 2 as shown by the arrow M. This may be achieved by the bearing surfaces 31 and 32 extending helically around the helical axis H that is following a line that is helical. That said, in practical embodiments, the length of the bearing surfaces 31 and 32 may be short compared to the distance of the bearing surfaces 31 and 32 from the helical axis H, such that their shape is close to straight or even each being straight, provided that the one or more helical bearings of the helical bearing arrangement 20 guide helical movement of the lens element 10 with respect to the support structure 2. Plural helical bearings 30 are typically present, located at different angular positions around the helical axis H, in which case the helical bearings 30 have different orientations so that they cooperate and maintain adequate constraints to guide the helical movement of the lens element 10 with respect to the static part 2 , even if the bearing surfaces 31 and 32 of an individual helical bearing 30 are straight.

In the example of Fig. 2, the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35 in which the rolling bearing elements 33 are seated. In this example, the grooves 34 and 35 constrain transverse translational movement of the lens element 10 with respect to the static part 2, that is transverse to the direction of movement shown by arrow M. The grooves shown in figure 2 are V-shaped in cross-section, but other cross-sections are possible, for example curved as in portions of a circle or an oval. In general, the grooves 34 and 35 provide two points of contact with the respective rolling bearing elements 33. The grooves 34 and 35 may extend helically. Alternatively, in practical embodiments, the length of the bearing surfaces 31 and 32 may be short compared to the distance of the bearing surfaces 31 and 32 from the helical axis H, in which case the grooves 34 and 35 may be straight or close to straight, provided that the one or more helical bearings 30 of the helical bearing arrangement 20 guide helical movement of the lens element 10 with respect to the support structure 2

In the example of Fig. 3, a first bearing surface 31 comprises a groove 36 in which the rolling bearing elements 33 are seated and a second bearing surface 32 wherein the bearing surface is 'planar'. The first bearing surface 31 comprising a groove 36 may be provided on either one of the static part 2 and the lens element 10, with the second bearing surface 32 being provided on the other one of the static part 2 and the lens element 10. In the example of Fig. 3, the helical bearing 30 does not constrain transverse translational movement of the lens element 10 with respect to the static part 2, that is transverse to the direction of movement shown by arrow M. The bearing surface 32 is 'planar' in the sense that it is a surface which is not a groove and one which provides only a single point of contact with the ball. In other words, the bearing surface 32 is effectively planar across a scale of the width of the rolling bearing element 33, although be helical at a larger scale. For example, as pictured, the 'planar' surface is helical, being a line in cross section which twists helically along the movement direction, maintaining a single point of contact with the ball at any time. Alternatively and as mentioned above, in practical embodiments the length of the bearing surfaces 31 and 32 may be short, in which case the bearing surface 32 may be planar or close to planar, provided that the one or more helical bearings 30 of the helical bearing arrangement 20 guide helical movement of the lens element 10 with respect to the support structure 2.

A single rolling bearing element 33 is shown in Figs. 2 and 3 by way of example, but in general may include any plural number of rolling bearing elements 33.

In some examples, the helical bearing 30 may include a single rolling bearing element 33. In that case, the helical bearing 30 by itself does not constrain the rotational movement of the lens element 10 with respect to the static part 2 about the single rolling bearing element 33, that is around an axis transverse to the direction of movement shown by arrow M. However, this minimises the overall size of the helical bearing 30, and in particular the height of the helical bearing 30 projected along the helical axis H as it is only needed to accommodate the size of the rolling bearing element 33 and the relative travel of the bearing surfaces 31 and 32.

In other examples, the helical bearing 30 may include plural rolling bearing element 33. In that case, the helical bearing 30 constrains the rotational movement of the lens element 10 with respect to the static part 2 about either one of the rolling bearing elements 33, that is around an axis transverse to the direction of movement shown by arrow M. However, compared to use of a single rolling bearing element 33, this increases the overall size of the helical bearing 30, and in particular the height of the helical bearing 30 projected along the helical axis H.

The helical bearing arrangement may in general comprise any number of helical bearings 30 with a configuration chosen to guide the helical movement of the lens element 10 with respect to the static part 2 while constraining the movement of the lens element 10 with respect to the static part 2 in other degrees of freedom. Many helical bearing arrangements may comprise plural helical bearings 30 and at least one which comprises plural rolling bearing elements 30.

Some specific examples of the actuator assembly 1 with different possible helical bearing arrangements are illustrated in Figs. 4, 8, 9 and 10 which are schematic plan views normal to the helical axis showing the static part 2, the lens element 10 and the helical bearings 30.

Fig. 4 illustrates a possible helical bearing arrangement that includes two helical bearings 37 and 38 only. The helical bearings 37 and 38 are arranged on opposite sides of the lens element 10.

The first helical bearing 37 is of the same type as the helical bearing 30 shown in Fig. 2 wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35. The first helical bearing 37 includes plural rolling bearing elements 33 to constrain the relative movement of the lens element 10 and the static part 2.

The second helical bearing 38 is of the same type as the helical bearing 30 shown in Fig. 3 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing elements 33 are seated and the second bearing surface 32 is planar. Fig. 4 illustrates the case that the first bearing surface 31 of the second helical bearing 38 is on the static part 2, but it could alternatively be on the lens element 10. The second helical bearing 38 may comprise a single rolling bearing element 33 or plural rolling elements 33 and principally adds a constraint against relative rotation of the lens element 10 and the static part 2 around the direction of movement (arrow M) of the first helical bearing 37.

The helical bearing arrangement of Fig. 4 includes a smaller number of helical bearings (i.e. two) than the other examples below, which simplifies the construction and reduces footprint of the actuator assembly 1.

Figs. 5 to 7 illustrate an example of the actuator assembly 1 shown in Fig.4, wherein the static part 2 and the lens element 10 are formed by moulded components. In Figs. 5 to 7, the detailed form of the static part 2, the lens element 10 and the helical bearings 37 and 38 can be seen. In addition, the actuator assembly 1 includes a resilient element 70 connected in compression between the support structure 2 and the lens element 10 and extending parallel to the helical axis H, so providing a force along the helical axis H. As a result, the resilient element 70 loads the one or more helical bearings. The resilient element 70 is in this example a spring, but in principle could be formed by any other element for example being a flexure or a piece of resilient material.

Fig. 8 illustrates a possible helical bearing arrangement that includes three helical bearings 39, 40 and 41 only. The three helical bearings 39, 40 and 41 are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

The first and second helical bearings 39 and 40 are of the same type as the helical bearing 30 shown in Fig. 2 wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35.

The third helical bearing 41 is of the same type as the helical bearing 30 shown in Fig. 3 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. Fig. 8 illustrates the case that the first bearing surface 31 of the third helical bearing 41 is on the lens element 10, but it could alternatively be on the static part 2.

Each of the three helical bearings 39, 40 and 41 may comprise a single rolling or plural bearing elements 33. This is possible because the constraints imposed by three helical bearings 39, 40 and 41, and in particular the grooves of the first and second helical bearings 39 and 40 sufficient to constrain the movement of the lens element 10 with respect to the static part 2 in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element 33 in each of the three helical bearings 39, 40, 41, the overall size of the three helical bearings 39, 40 and 41, and in particular the height of the three helical bearings 39, 40 and 41 projected along the helical axis H is reduced compared to the helical bearing arrangement of Fig. 4.

Fig. 10 illustrates a possible helical bearing arrangement that includes four helical bearings 42 to 45 only. The four helical bearings 42 to 45 are equally angularly spaced around the helical axis H.

The first helical bearing 42 is of the same type as the helical bearing 30 shown in Fig. 2 wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35.

The second, third and fourth helical bearings 43, 44 and 45 are each of the same type as the helical bearing 30 shown in Fig. 3 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. Fig. 10 illustrates the case that the first bearing surface 31 of the second, third and fourth helical bearings 43, 44 and 45 is on the lens element 10, but it could alternatively be on the static part 2.

Each of the second, third and fourth helical bearings 43, 44 and 45 may comprise a single rolling bearing element 33 while the first helical bearing 42 comprises two rolling bearing elements. This is possible because the constraints imposed by four helical bearings 42 to 45 are sufficient to constrain the movement of the lens element 10 with respect to the static part 2 in degrees of freedom other than the helical movement.

Fig. 9 illustrates another possible helical bearing arrangement that includes four helical bearings 46 to 49 only. The four helical bearings 46 to 49 are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

The first and second helical bearings 46 and 47 are of the same type as the helical bearing 30 shown in Fig. 2 wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35.

The third and fourth helical bearings 48 and 49 are of the same type as the helical bearing 30 shown in Fig. 3 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. Fig. 9 illustrates the case that the first bearing surface 31 of the third and fourth helical bearings 48 and 49 on the lens element 10, but it could alternatively be on the static part 2.

Each of the four helical bearings 46 to 49 may comprise a single rolling bearing element 33. This is possible because the constraints imposed by four helical bearings 46 to 49 are sufficient to constrain the movement of the lens element 10 with respect to the static part 2 in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element 33 in each of the four helical bearings 46 to 49, the overall size of the four helical bearings 46 to 49, and in particular the height of the four helical bearings 46 to 49 projected along the helical axis H is reduced compared to the helical bearing arrangement of Fig. 4.

Fig. 11 illustrates an example of the helical bearing arrangement 20 of the actuator assembly 1 shown in Fig. 9, wherein the static part 2 and the lens element 10 are formed by moulded components. In Fig. 11, the detailed form of the static part 2, the lens element 10 and the helical bearings 30 can be seen.

Figs. 12 to 14 illustrate a first example of the actuator assembly 1 shown in Fig. 9 including a helical bearing arrangement 20 as shown in Fig. 11. In addition, the actuator assembly 1 includes two resilient elements 70 connected in compression between the support structure 2 and the lens element 10 and extending at an acute angle to the helical axis H so that they provide a force with a component that loads the four helical bearings 46 to 49. The resilient element 70 is in this example a spring, but in principle could be formed by any other element for example being a flexure or a piece of resilient material.

Figs. 15 and 16 illustrate a second example of the actuator assembly 1 shown in Fig. 9 including a helical bearing arrangement 20 as shown in Fig. 11. In addition, the actuator assembly 1 includes two resilient elements 70 connected in compression between the support structure 2 and the lens element 10 and extending orthogonally to the helical axis H with rotational symmetry around the helical axis H, so that they provide a force with a component that loads the helical bearings 46 to 49.

In each of the helical bearing arrangements described above, the bearing surfaces 32 which are on the lens element 10 are each arranged on the same side of (all above or all below) the bearing surfaces 31 on the support structure 2. As the bearing surfaces 31 and 32 extend helically, this means that in the view of Fig. 8 which is a cross-section perpendicular to the helical axis H, all the bearing surfaces 32 which are on the lens element 10 are on the right of the bearing surfaces 31 on the support structure 2 as viewed outwardly of the helical axis H, and in the view of Figs. 9 and 10 all the bearing surfaces 32 which are on the lens element 10 are on the left of the bearing surfaces 31 on the support structure 2 as viewed outwardly of the helical axis H. As a result of this arrangement, the helical bearings all the bearing surfaces 31 on the support structure 2 face in the same direction as each other, which assists in manufacture of the bearing surfaces 31 by the same tool. Similarly, manufacturing advantages apply to the bearing surfaces 32 on the lens element 2 which also face in the same direction as each other. As a result of this arrangement, all the helical bearings 30 need to be loaded in the same helical sense. Thus loading of the helical bearings 30 may be provided by applying a loading force along the helical axis H, a loading force around the helical axis H, or a combination thereof. In the arrangements described in more detail below, this loading force may be applied by the resilient biasing element 70.

Fig. 17 illustrates another possible helical bearing arrangement that is a modification of the helical bearing arrangement of Fig. 7. Thus, the helical bearing arrangement includes four helical bearings 46 to 49 only, and the four helical bearings 46 to 49 are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

As in the helical bearing arrangement of Fig. 11, (a) the first and second helical bearings 46 and 47 are of the same type as the helical bearing 30 shown in Fig. 2 wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35, and (b) the third and fourth helical bearings 48 and 49 are of the same type as the helical bearing 30 shown in Fig. 3 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. Fig. 17 illustrates the case that the first bearing surface 31 of the third and fourth helical bearings 48 and 49 is on the lens element 10, but it could alternatively be on the support structure 2.

As in the helical bearing arrangement of Fig. 17, each of the four helical bearings 46 to 49 may comprise a single rolling bearing element 33. This is possible because the constraints imposed by four helical bearings 46 to 49 are sufficient to constrain the movement of the lens element 10 with respect to the support structure 2 in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element 33 in each of the four helical bearings 46 to 49, the overall size of the four helical bearings 46 to 49, and in particular the height of the four helical bearings 46 to 49 projected along the optical axis is reduced when each of the helical bearings has a single rolling element only.

However, the helical bearing arrangement of Fig. 17 is modified compared to that of Fig. 11 to change the arrangement of the bearing surfaces 31 and 32 in the individual bearings 46 to 49, as follows. In the first helical bearing 46, the bearing surfaces 32 on the lens element 10 are above the bearing surfaces 31 on the support structure 2 as viewed along the helical axis H, whereas in the second helical bearing 47, the bearing surfaces 32 on the lens element 10 are below the bearing surfaces 31 on the support structure 2 as viewed along the helical axis H. Similarly, in the third helical bearing 48, the bearing surfaces 32 on the lens element 10 are above the bearing surfaces 31 on the support structure 2 as viewed along the helical axis H, whereas in the fourth helical bearing 49, the bearing surfaces 31 on the lens element 10 are below the bearing surfaces 32 on the support structure 2 as viewed along the helical axis H.

This may be understood on the following basis with reference to a constraint of the bearings in the vertical plane, parallel to the helical axis. The first and third helical bearings 46 and 48 constrain the lens element 10 from moving down, and the second and fourth helical bearings 47 and 49 constrain the lens element 10 from moving up, or rotating around an axis between first and third helical bearings 46 and 48.

As a result of this arrangement, the helical bearings 46 to 49 do not all need to be loaded in the same helical sense around the helical axis H. This facilitates the loading of the helical bearings 46 to 49. For example, this arrangement allows for loading by a resilient loading arrangement as will now be described.

Optionally, an etching may be used to create resilient loading of any of the bearing surfaces on the lens element 10, in which case this same etching can be used to create a common connection between support structure 2 and the lens element 10.

Any of the types of helical bearing arrangement 20 may include a resilient loading arrangement that loads a bearing surface of at least one of the rolling bearings with respect to the support structure or the moveable element on which the bearing surface is provided, against the rolling bearing element. Figs. 18 to 22 show some examples of resilient loading arrangements of this type.

Each of the examples of Figs. 18 to 22 is applied to a rolling bearing 100 that comprises a first bearing surface 101, a second bearing surface 102 and a rolling bearing element 103 (for example a ball or a roller) disposed between the first and second bearing surfaces 101 and 102. The rolling bearing 100 may be applied as any one or more of the rolling bearings of the helical bearings in any SMA actuation apparatus 1 described herein. When so applied, the first bearing surface 101 is provided on one of the support structure 2 or the lens element 10, and the second bearing surface 102 is provided on the other of the support structure 2 or the lens element 10, either way around. In each case, the first bearing surface 101 is movable with respect to one of the support structure 2 or the lens element 10 on which it is provided. In contrast, the second bearing surface 102 is fixed with respect to the other of the support structure 2 or the lens element 10 on which it is provided.

In the example of Fig. 18, the first bearing surface 101 is formed on a flexure element 104 that is connected to the lens element 10 or the support structure 2. The flexure element 104 is made of a resilient material, typically metal such as steel, and is connected to the adjacent part of the lens element 10 or the support structure 2. Thus, the flexure element 104 is a resilient element which both allows the movement of the first bearing surface 101 with respect to the adjacent support structure 2 or lens element 10 and acts as a resilient loading arrangement that resiliently loads the first bearing surface 101 away from the adjacent part of the lens element 10 or the support structure 2, against the rolling bearing element 103.

In the example of Fig. 19, the first bearing surface 101 is formed on a body 105. The body 105 is connected to the lens element 10 or the support structure 2 by a bridge portion 106 formed integrally with the body 105 and the adjacent part of the lens element 10 or the support structure 2 which allows the movement of the first bearing surface 101 with respect to the adjacent support structure 2 or lens element 10. The bridge portion 106 is configured as a resilient element arranged between the body 105 and the adjacent part of the lens element 10 or the support structure 2. Thus, the bridge portion 106 acts as a resilient loading arrangement that resiliently loads the body 106 and hence the first bearing surface 101 away from the adjacent part of the lens element 10 or the support structure 2, against the rolling bearing element 103.

The example of Fig. 20 is the same as the example of Fig. 19, except that a flexure element 107 is connected to the bridge portion 106. In this case, the flexure element 107 and the bridge portion 106 together allow the movement of the first bearing surface 101 with respect to the adjacent support structure 2 or lens element 10, whereas the flexure element 107 is a resilient element which acts as a resilient loading arrangement that resiliently loads the body 106 and hence the first bearing surface 101 away from the adjacent part of the lens element 10 or the support structure 2, against the rolling bearing element 103. In contrast to the example of Fig. 19, the flexure element 107 may be designed to provide the dominant resilient effect. The bridge portion 106 may have resilience and thus contribute to the loading in combination with the flexure element 107, or may have substantially no resilience compared to the flexure element. As such, the bridge portion 106 may be relatively thin compared to the example of Fig. 10. Advantageously, this arrangement reduces the occurrence of stress relaxation.

The example of Fig. 21 is the same as the example of Fig. 20, except that the bridge portion 106 is omitted, so that the body portion 105 is a separate element from the adjacent part of the lens element 10 or the support structure 2, and is connected thereto by the flexure element 107. As a result, the flexure element 107 alone is a resilient element which acts as a resilient loading arrangement that resiliently loads the body 105 and hence the first bearing surface 101 away from the adjacent part of the lens element 10 or the support structure 2, against the rolling bearing element 103.

In the example of Fig. 22, the first bearing surface 101 is formed on a flexible arm 108 that is formed integrally with the adjacent part of the lens element 10 or the support structure 2. Thus, the flexible arm 108 allows the movement of the first bearing surface 101 with respect to the adjacent support structure 2 or lens element 10. In addition, a spring 109 (or other resilient element) is arranged between the arm 108 and the adjacent support structure 2 or lens element 10. The spring 109 is in compression. Thus, the spring 109 is a resilient element which acts as a resilient loading arrangement that resiliently loads the first bearing surface 101 away from the adjacent part of the lens element 10 or the support structure 2, against the rolling bearing element 103.

Another alternative for the resilient loading arrangement is that one of the bearing surfaces on either the support structure 2 or lens element 10 is replaced by an etching, a thin walled section of the support structure 2 or lens element 10. Considering a thin wall or twist in either support structure 2 or lens element 10, these tolerance accommodations could be fixed for each assembly by using glue. In the case that SMA actuation apparatus 1 is a camera, the thin wall section or twist in the lens element 10 could be fixed into position when the lens is glued into position, or the thin wall section or twist in the chassis could be fixed into position when a screening can is glued into position. Such thin walls or twists could be made to dynamically accommodate variations in bearing surface, in the same way as the examples of Figs. 18 to 22.

Fig. 22A shows an example of the actuator assembly 1 with a helical bearing arrangement which is similar to that of Fig. 10 but with some modifications as will now be described. The helical bearing arrangement includes four helical bearings 42 to 45 that are arranged in the same as in Fig. 10, as described above. The helical bearings 42 to 45 each include a single rolling bearing element 33, so that they provide a total of five constraints. The first helical bearing 42 is of the same type as the helical bearing 30 shown in Fig. 2, wherein the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35. The second, third and fourth helical bearings 43, 44 and 45 are each of the same type as the helical bearing 30 shown in Fig. 3, wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. As in Fig. 10, the first bearing surface 31 of the second, third and fourth helical bearings 43, 44 and 45 is illustrated as being on the lens element 10, but it could alternatively be on the support structure 2.

The bearing surfaces 32 which are on the lens element 10 are each arranged on the same side of (all above or all below) the bearing surfaces 31 on the support structure 2. As the bearing surfaces 31 and 32 extend helically, this means that in the view of Fig. 22A which is a cross-section perpendicular to the helical axis H, all the bearing surfaces 32 which are on the lens element 10 are on the left of the bearing surfaces 31 on the support structure 2 as viewed outwardly of the helical axis H. As a result of this arrangement, all the helical bearings 42 to 46 need to be loaded in the same helical sense, corresponding to a clockwise rotation of the lens element 10 in Fig. 22A.

To provide such loading, the helical bearing arrangement is modified compared to Fig. 10 to include two additional rolling bearings 110 that are helical bearings arranged as follows. The rolling bearings 110 comprise a first bearing surface 111, a second bearing surface 112 and a rolling bearing element 113 (for example a ball or a roller) disposed between the first and second bearing surfaces 111 and 112. The first bearing surface 111 is movable with respect to the support structure 2 and a resilient element 114 is arranged between the first bearing surface 111 and the support structure 2. The resilient element 114 loads the first bearing surface 111 away from the support structure 2, thereby acting as a resilient loading arrangement that resiliently loads the first bearing surface 111 against the rolling bearing element 113. As an alternative, the rolling bearing element 110 could be reversed so that the second bearing surface 112 is movable with respect to the lens element 10 and the resilient element 114 loads the second bearing surface 112 against the rolling bearing element 113. The additional rolling bearings 110 may have any suitable construction, including the construction of the rolling bearing 110 in any of the examples of Figs. 18 to 22.

The additional rolling bearings 110 are arranged the opposite way around relative to the helical bearings 42 to 46 so that they load the helical bearings 42 to 46 in the same helical sense, corresponding to a clockwise rotation of the lens element 10 in Fig. 22A. As a result, the helical bearing arrangement shown in Fig. 22A is highly balanced and the tolerances are reduced, which assists manufacture. Similarly to the helical bearing arrangement of Fig. 10, manufacture of the helical bearings 42 to 46 is assisted by all the bearing surfaces 31 on the support structure 2 facing in the same direction as each other, and all the bearing surfaces 32 on the lens element 10 facing in the same direction as each other.

Two additional rolling bearings 110 are shown here, arranged on opposite sides of the lens element 10. More generally, any number of one or more additional rolling bearings 110 may be provided, but plural additional rolling bearings 110 spaced around the lens element 10 are advantageous to assist balancing of forces.

In the above examples, the helical bearings 30 are rolling bearings, but in each case the helical bearings 30 may be replaced by a sliding bearing, two examples of which are shown in Figs. 23 to 26.

In the first example shown in Figs. 23 and 25, the plain bearing 81 comprises an elongate bearing surface 83 on one of the support structure 2 and the lens element 10. The plain bearing 81 also comprises protrusions 85 formed on the other of the support structure 2 and lens element 10, the ends of the protrusions 85 forming bearing surfaces 86 which bear on the elongate bearing surface 83. Although two protrusions 85 are shown in this example, in general any number of one or more protrusions 85 may be provided. The elongate bearing surface 83 and the bearing surfaces 86 are conformal, both being planar in this example, so as to permit relative movement of the lens element 10 with respect to the support structure 2. The elongate bearing surface 83 and the bearing surfaces 86 desirably have a coefficient of friction of 0.2 or less.

In the second example shown in Figs. 25 and 26, the plain bearing 91 comprises a channel 92 on one of the support structure 2 and the lens element 10, the inner surface of the channel 92 forming a bearing surface 93. The plain bearing 91 comprises protrusions 95 formed on the other of the support structure 2 and lens element 10, the ends of the protrusions 95 forming bearing surfaces 96 which bear on the bearing surface 93. Although two protrusions 95 are shown in this example, in general any number of one or more protrusions 95 may be provided. The elongate bearing surface 93 and the bearing surfaces 96 are conformal, both being planar in this example, so as to permit relative movement of the lens element 10 with respect to the support structure 2. The elongate bearing surface 93 and the bearing surfaces 96 desirably have a coefficient of friction of 0.2 or less.

In each of the plain bearings 81 and 91, the materials of the bearing surfaces 83, 86, 93, 96 are chosen to provide smooth movement and a long life. The bearing surfaces 83, 86, 93, 96 may be unitary with the underlying component or may be formed by a surface coating. Suitable materials include, for example PTFE or other polymeric bearing materials, or metal.

In each of the plain bearings 81 and 91, a lubricant may be provided on the bearing surfaces 83, 86, 93, 96. Such a lubricant may be a powder or a fluid, for example. Suitable lubricants include graphite; silicon paste or a low viscosity oil.

While the helical bearing arrangement 20 comprises helical bearings 30 that are rolling bearings in the above example, another possibility is that the helical bearing arrangement 20 comprises at least one flexure extending between the static part 2 and the lens element 10 as shown for example in Fig. 27 wherein the helical bearing arrangement 20 comprises two flexure elements 50 that each comprise four flexures 51 having a configuration as shown either in Fig. 28 or in Fig. 29. As shown in Fig. 27, the flexures 51 are each pre-deflected along the helical axis H, and as shown in Figs. 28 and 29, the flexures 51 each extend in an arc around the helical axis H. As a result of this configuration, the flexures 51 guide the helical movement of the lens element 10 with respect to the static part 2 around the helical axis H. The specific number and arrangement of flexures 51 in Figs. 27 to 29 is not essential and other configurations of flexures that are pre deflected along the helical axis H and extend in an arc around the helical axis H may be used to provide the same function.

Fig. 22 is a perspective view of an alternative helical bearing arrangement 20 comprising plural flexures 120, four flexures 120 being shown in Fig. 22 although in general any number of flexures 120 could be provided. In this example, the helical bearing arrangement also comprises a movable plate 121 mounted on lens element 10 and a support plate 122 mounted on the support structure 2. The movable plate 121 and the support plate 122 are spaced along the helical axis H and the flexures 120 extend along the helical axis H and are inclined with respect to a plane normal to the helical axis H helical axis with rotational symmetry around the helical axis H. With this arrangement, the flexures 120 guide the helical movement of the lens element 10 with respect to the support structure 2 around the helical axis H.

The flexures 120 are integrally formed with the movable plate 120 and the support plate 122. This form of connection is advantageous because it allows the helical bearing arrangement to be made as a single part, for example in a moulding, providing exact constrains. This solution therefore combines precision with a low manufacturing cost. That said, in principle the flexures 120 could be separate elements connected to the lens element 10 and the support structure 2 in any suitable way.

SMA actuator wires

Referring to Figures 30 to 32, the actuator assembly 1 includes a set of four SMA actuator wires 60 (also referred to as simply "wires") arranged to drive movement of the lens element 10 with respect to the static part 2 around the helical axis H.

The wires 60 are each connected between the support structure 2 and the lens element 10 and are arranged as described in WO 2013/175197 A1 which is incorporated herein by this reference.

In brief, the wires 60 include a first pair of wires 60 and a second pair of wires 60. The first pair of wires 60 is arranged, on contraction, to drive rotation of the lens element 10 in a first sense around the helical axis. The second pair of wires 60 is arranged, on contraction, to drive rotation of the lens element 10 in a second, opposite sense around the helical axis. The helical bearing arrangement 20 converts the rotation into the helical movement.

The wires 60 are arranged in a loop at different angular positions around the helical axis and successive wires 60 are connected between the support structure the lens element 10 so as to apply a torque in alternate senses around the helical axis. Within each pair, the wires 60 are arranged on opposite sides of the helical axis.

The lens element 10 includes a first pair of connection portions (e.g. crimps, also referred to herein as "moving crimps") located at a first angular position around the helical axis and a second pair of connection portions ("moving crimps") located at a second angular position around the helical axis. These first and second angular positions are offset from each other by 180°. A wire 60 of each of the first and second pairs of wires 60 is connected to the lens element 10 via the first pair of moving crimps and a wire of each of the first and second pairs of wires 60 is connected to the lens element 10 via the second pair of connection portions.

Referring in particular to Fig. 30, in some examples, the helical bearing arrangement 20 includes a set of three helical bearings, in particular two ("pinned") bearings 401 of the type illustrated in Fig. 2 and one ("slider") bearing 402 of the type illustrated in Fig. 3.

The three helical bearings are, in order, a first pinned bearing, a second slider bearing and a third pinned bearing. The second bearing is angularly spaced from the first bearing by about 90° around the helical axis and the third bearing is angularly spaced from the second bearing by about 90° around the helical axis.

In some examples, including the one illustrated in Fig. 30, the actuator assembly 1 comprising a biasing arrangement 90 configured to exert a biasing force on the lens element 10 in a direction that is at least substantially normal to a helical path along which the lens element 10 moves so as to at least partly load the helical bearing arrangement 20, i.e. the bearings 401, 402. The biasing arrangement 90 may have any suitable form. For example, the biasing arrangement 90 may include a resilient element connected between the support structure 2 and the lens element. The resilient element may be a flexure or another elastic element. The biasing arrangement 90 may a magnetic loading arrangement, e.g. comprising a permanent magnet on one of the support structure 2 and the lens element 10 and a magnetic material (e.g. steel) on the other one of the support structure 2 and the lens element 10. As illustrated in Fig. 30, the biasing arrangement 90 may be angularly spaced from the third bearing by about 90° around the helical axis.

In some examples, there may be no (separate) biasing arrangement and instead the four wires 60 may be arranged, e.g. at an acute angle to a plane normal to the helical axis, to apply a force to the lens element 10 in order to load the helical bearing arrangement 20, i.e. the bearings 401, 402.

One such example is illustrated in Fig. 31. This example is otherwise same as that illustrated in Fig. 30

Referring in particular to Fig. 32, in other such examples, the space made available by the omission of the (separate) biasing arrangement is made use to include a fourth helical bearing. In particular, in such an example, there is one ("pinned") bearings 401 of the type illustrated in Fig. 2 and three ("slider") bearings 402 of the type illustrated in Fig. 3. Together, these bearings 401, 402 provide the required constraints. Pairs of adjacent helical bearings 401, 402 are angularly spaced from each other by about 90° around the helical axis. This distribution of helical bearings 401, 402 provides a particularly stable arrangement, e.g. in relation to tilt, manufacturing tolerances, etc., while also being space (footprint) efficient.

As can be seen from Figs. 30 to 32 the lens element 10 includes portions 10a which extend at least partly outwards from the helical axis and which carry e.g. a part of a bearings 401, 402 and then a moving crimp. Preferably, the helical bearings 401, 402 are located within the square loop of the four wires 60. This makes efficient use of the available space (footprint), while maximising the length of the wires 60 and hence the maximum displacement (stroke).

The SMA actuator wires 60 are driven by the control circuit implemented in the IC chip 5. In particular, the control circuit generates drive signals for each of the SMA actuator wires 60 and supplies the drive signals to the SMA actuator wires 60. The control circuit receives an input signal representing a desired position for the lens element 10 along the optical axis O and generates drive signals selected to drive the lens element 10 to the desired position. The drive signals may be generated using a resistance feedback control technique, in which case the control circuit 20 measures the resistance of the lengths of SMA actuator wire 20 and uses the measured resistance as a feedback signal to control the power of the drive signals. Such a resistance feedback control technique may be implemented as disclosed in any of WO-2013/175197; WO-2014/076463; WO-2012/066285; WO- 2012/020212; WO-2011/104518; WO-2012/038703; WO-2010/089529 or WO- 2010029316, each of which is incorporated herein by reference. As an alternative, the control circuit may include a sensor which senses the position of the lens element 10, for example a Hall sensor which sense the position of a magnet fixed to the lens element 10. In this case, the drive signals use the sensed position as a feedback signal to control the power of the drive signals.

Alternative helical flexure bearing

Fig. 33 is a perspective view of an alternative helical bearing arrangement 20 (herein referred to as helical flexure bearing 1090) comprising plural flexures 1092 (herein also referred to as flexure arms) arranged to extend between the static part 2 and the lens element 10. Four flexure arms 1092i, 10922, 10923, 10924 are shown in this example, however in general any number of flexure arms 1092 could be provided.

The helical flexure bearing 1090 includes a circular annulus 1091 having a central aperture 1009. However, in general the central annulus 1091 need not comprise the central aperture 1009. The circular annulus 1091 is connected to the four flexure arms 1092i, 10922, 10923, 10924. Instead of the circular annulus 1091, any other shaped central portion may be connected commonly to the flexure arms 1092. At the end not connected to the circular annulus 1091, each flexure arms 1092i, 10922, 10923, 10924 is connected to a respective pad 1093i, 10932, 10933, 10934. The pad 1093 is for connection to the static part 2. The circular annulus 1091 is connected to the lens element 10. The central axis of the central aperture 1009 is coincident with the optical axis O of the lens element 10 and the helical axis H.

Each flexure arm 1092i, 10922, 10923, 10924 is approximately tangential to the circular annulus 1091 (in the same sense). Each flexure arm's span includes both a first component parallel to the plane containing the first and second axes x, y and a second component parallel to the primary axis z. The flexure arms are thus pre-deflected along the primary axis z. If the pads 1093i, 10932, 10933, 10934 are clamped and a force is exerted upwards (positive z direction) on the circular annulus 1091, then in response the flexure arms 1092i, 10922, 10923, 10924 will deflect in the direction of that force. In doing so, the ends connected to the circular annulus 1091 are deflected closer the respective pad 1093i, 10932, 10933, 10934 in the x-y plane, causing the circular annulus 1091 to rotate clockwise about an axis parallel to the primary axis z.

Conversely, a force exerted downwards (negative z direction) on the circular annulus 1091 will result in both a downwards movement of the circular annulus 1091 and also an anti-clockwise (counter-clockwise) rotation of the circular annulus 1091. It will be appreciated that the circular annulus 1091 may rotate anti-clockwise about an axis parallel to the primary axis z, with an arrangement of flexure arms 1092 that is mirror symmetric to the arrangement in Fig. 33.

In this way, the helical flexure bearing 1090 acts to convert a relative displacement parallel to the primary axis z into a rotation about the primary axis z and to convert a rotation about the primary axis z into a relative displacement parallel to the primary axis z. These movements are not independent of one another. The helical flexure bearing 1090 allows movement along one degree of freedom. Relative to clamped pads 1093i, 10932, 10933, 10934 the circular annulus 1091 is constrained to move along an approximately helical path.

Although the flexure arms 1092i, 10922, 10923, 10924 shown in Figure 33 are curved in the x-y plane, in other examples of helical flexure bearings 1090 the flexure arms 1092 may be straight in the x-y plane. Further examples of helical flexure bearings 1090 are described in WO 2019/243849 Al, the contents of which are incorporated herein by reference in their entirety.

Figures 19 to 22 of WO 2019/243849 Al and the accompanying description on page 22, line 23 to page 23, line 24 are particularly relevant to helical flexure bearings 1090. Additional examples of implementing helical flexure bearings 1090 are also shown and described hereinafter.

Helical flexure bearing assembly

Referring to Figs. 34A and 34B, an example of the actuator assembly 1 comprising the four SMA actuator wires 60 (described above in relation to Figs. 30 to 32) and the helical flexure bearing 1090 (described above in relation to Fig. 33) will now be described. This example of actuator assembly 1 will be hereinafter referred to as the "first helical flexure assembly" 1000.

Fig. 34A shows an exploded perspective view of the first helical flexure assembly 1000 and Fig. 34B shows a perspective view.

As described above, the SMA actuator wires 60, connected between the static part 2 and the lens element 10, include a first pair of SMA actuator wires 60 and a second pair of SMA actuator wires 60. The first pair of SMA actuator wires 60 is arranged, on contraction, to drive rotation of the lens element 10 in a first sense around the helical axis. The second pair of SMA actuator wires 60 is arranged, on contraction, to drive rotation of the lens element 10 in a second, opposite sense around the helical axis. The helical bearing arrangement 20 converts the rotation into the helical movement.

The SMA actuator wires 60 are arranged in a loop at different angular positions around the helical axis. Successive SMA actuator wires 60 are connected between the static part 2 (herein also referred to as the support structure 2) and the lens element 10 so as to apply a torque in alternate senses around the helical axis. Within each pair, the SMA actuator wires 60 are arranged on opposite sides of the helical axis. The lens element 10 includes a first pair of connection portions 19 (e.g. crimps, also referred to herein as "moving crimps") located at a first angular position around the helical axis and a second pair of connection portions 19 ("moving crimps") located at a second angular position around the helical axis. These first and second angular positions are offset from each other by 180° around the helical axis. An SMA actuator wire 60 of each of the first and second pairs of SMA actuator wires 60 is connected to the lens element 10 via the first pair of moving crimps 19 and the other SMA actuator wire of each of the first and second pairs of SMA actuator wires 60 is connected to the lens element 10 via the second pair of moving crimps 19.

The first helical flexure assembly 1000 includes a movable plate 24 which in this example can be considered to be part of the lens element 10 as it provides or supports the lens element 10, and is fixed to the lens element 10.

In the depicted embodiment, the movable plate 24 takes the form of an annular plate. The annular plate has an outer perimeter shaped as a rectangle. The annular plate has first and second diagonally opposite corners 151i, 1512 that are truncated. The annular plate has a circular inner perimeter defining a central aperture 1009 of the first helical flexure assembly 1000. However, in general, the movable plate 24 may have any other shape. Third and fourth diagonally opposite corners 1513, 1514 of the movable plate 24 support the first pair of moving crimps 19 and the second pair of moving crimps 19.

The static part 2 of the first helical flexure assembly 1000 includes a static plate 149. In the depicted embodiment, the static plate 149 is formed as an annular plate having a rectangular outer perimeter and a circular inner perimeter that defines the central aperture 1009. In general, however, the static plate 149 may have any other shape. The static part 2 also includes a first pair of connection portions 18 (e.g. crimps, also referred to herein as "static crimps") located at a first angular position around the helical axis and a second pair of connection portions 18 ("static crimps") located at a second angular position around the helical axis. These first and second angular positions are offset from each other by 180° and offset from the angular position of the moving crimps 19 by 90°. A SMA actuator wire 60 of each of the first and second pairs of SMA actuator wires 60 is connected to the static part 2 via the first pair of static crimps 18 and a SMA actuator wire of each of the first and second pairs of SMA actuator wires 60 is connected to the static part 2 via the second pair of static crimps 18.

A first end of each of the four SMA actuator wires 60 is connected to the static part 2 via the static crimps 18, and a second end of each of the four SMA actuator wires 60 is connected to the lens element 10 via the movable crimps 19.

In the depicted embodiment, the static crimps 18 are supported by first and second pillars 152i, 1522. The first and second pillars 152i, 1522 are attached (using welding, adhesive or other suitable attachment methods) to diagonally opposed corners of the static plate 149 to be substantially aligned with the truncated corners 151i, 1512 of the movable plate 24.

The lens element 10, via the movable plate 24, is coupled to the static part 2, via the static plate 149, by the helical flexure bearing 1090. The pads 1093 are fixed to the static plate 149 (herein also referred to as a "base" or "base plate"), for example by welding, adhesive or other suitable attachment methods. The circular annulus 1091 is fixed to the movable plate 24 in the same or a similar way. Alternatively, the circular annulus 1091 may be integrally formed with the movable plate 24.

Alternative helical flexure bearing assembly

Referring to Fig. 35, a further example of the actuator assembly 1 comprising four SMA actuator wires 60' and the helical bearing arrangement 20 (also referred to as helical flexure bearing 1090') having plural flexures 1092' will now be described. In the depicted examples, the helical flexure bearing 1090' comprises four flexure arms 1092i', 10922', 10923', 10924', although in general any number of flexure arms may be provided. This example of the actuator assembly 1 will be hereinafter referred to as the "second helical flexure assembly" 1000'.

The second helical flexure assembly 1000' comprises four SMA actuator wires 60'. The four SMA actuator wires 60' are arranged to drive movement of the lens element 10 with respect to the static part 2 around the helical axis H, for example in the manner described in relation to Figs. 30-32, 34A and 34B.

The four SMA actuator wires 60' comprise or consist of a first pair of SMA actuator wires 60i' and a second pair of SMA actuator wires 6O2'. The first pair of SMA actuator wires 6O1' is arranged, on contraction, to drive rotation of the lens element 10 in a first sense around the helical axis H. The second pair of SMA actuator wires 6O2' is arranged, on contraction, to drive rotation of the lens element 10 in a second, opposite sense around the helical axis H. The helical flexure bearing 1090' converts the rotation of the lens element 10 into helical movement around the helical axis H. The four SMA actuator wires 60' may drive movement of the lens element 10 in the manner described in relation to the previous embodiments.

As described in relation to the helical flexure bearing 1090 of Figs. 33- 34B, the depicted helical flexure bearing 1090' may include a circular annulus 1091' with a central aperture 1009'. The circular annulus 1091' is connected to an end of each of the four flexure arms 1092i', 10922', 10923', 10924'. At the end not connected to the circular annulus 1091', each flexure arm 1092i',

10922', 10923', 10924' is connected to a pad 1093i', 10932', 10933', 10934'. The pads 1093 are for connection to the static part 2. The circular annulus 1091' is connected to the lens element 10. The central axis of the central aperture 1009', the optical axis O of the lens element 10, the helical axis H, and the primary axis z are coincident. In general, the helical flexure bearing 1090' need not comprise the circular annulus 1091', and may instead comprise any central portion that is commonly connected to the flexure arms 1092.

In the depicted embodiment, each helical flexure arm 1092i', 10922', 10923', 10924' of the helical flexure bearing 1090' is approximately tangential to the circular annulus 1091'. The span of the helical flexure bearing 1090' includes both a first component parallel to the plane containing the x and y axes, and a second component parallel to the primary axis z. If the pads 1093i', 10932', 10933', 10934' are clamped and a force is exerted upwards (the positive z direction) on the circular annulus 1091', then in response the flexure arms 1092i', 10922', 10923', 10924' will deflect in the direction of that force. In doing so, the ends connected to the circular annulus are also deflected closer the respective pad 1093i', 10932', 10933', 10934' in the x-y plane, causing the circular annulus 1091' to rotate clockwise about an axis parallel to the primary axis z. Conversely, a force exerted downwards (negative z direction) on the circular annulus 1091' will result in both a downwards movement of the circular annulus 1091' and also an anti-clockwise (counter-clockwise) rotation of the circular annulus 1091'. It will be appreciated that the circular annulus 1091' may rotate anti-clockwise about an axis parallel to the primary axis z when displaced upwards, with an arrangement of flexure arms 1092' that is mirror symmetric to the arrangement in Fig. 35.

In this way, helical flexure bearing 1090' acts to convert a relative displacement parallel to the primary axis z into a rotation about the primary axis z and to convert a rotation about the primary axis z into a relative displacement parallel to the primary axis z. These movements are not independent of one another. Relative to clamped pads 1093i', 10932', 10933', 10934', the circular annulus 1091' is constrained to move along an approximately helical path.

The second helical flexure assembly 1000' is generally asymmetric. The maximum extent of the helical flexure assembly 1000' along a first axis (which in this example is parallel to the y-axis) is substantially less than the maximum extent of the helical flexure assembly 1000' along a second axis (which in this example is parallel to the x-axis). The first axis and the second axis are perpendicular to the helical axis H and are perpendicular to each other. In other words, generally, the maximum extent of the components of the helical flexure assembly 1000' (particularly the flexure arms 1092' and the SMA actuator wires 60') along the first axis is substantially less than the maximum extent of the components along the second axis. The maximum extent of the helical flexure assembly 1000' (and its components) along the first axis may be less than 95%, preferably less than 90%, further preferably less than 85%, particularly preferably less than 80%. The maximum extent of the helical flexure assembly 1000' (and its components) along the first axis may be less than that, for example less than 70% or less than 60% of the maximum extent of the helical flexure assembly 1000' (and its components) along the second axis.

Such an asymmetric design helps minimise or reduce the extent of the actuator assembly 1 along one axis (i.e. the y-axis in this example). This can be useful, for example, in smartphones with front-facing cameras, as the reduced extent along one axis can help reduce the gap between the screen and the front facing camera. The gap between the top edge of the smartphone and the front facing camera can also be reduced.

The asymmetric design is achieved by arranging the SMA actuator wires 60' on two opposite sides of the second helical flexure assembly 1000' (rather than four sides of the first helical flexure assembly 1000, as in Figs. 34A and 34B). In particular, an SMA actuator wire 60' of each of the first and second pairs of SMA actuator wires 60i', 6O2' is arranged entirely on a first side Si of the helical axis H (for ease of reference, these SMA actuator wires will be hereinafter referred to as the "SI pair of SMA actuator wires 6O3' ") The other SMA actuator wires 60' of the first and second pairs of SMA actuator wires 6O1', 6O2' are arranged entirely on a second and opposite side S2 of the helical axis H (for ease of reference, these SMA actuator wires will be hereinafter referred to as "S2 pair of SMA actuator wires 6O4' "). The first side Si corresponds to a first half of the actuator assembly 1 and the second side S2 corresponds to a second half of the actuator assembly 1. The first and second sides Si, S2 are separate, non overlapping and contiguous. The first and second sides Si, S2 are divided by a plane P parallel to the helical axis H (and parallel to the y-axis in Fig. 35). The SMA actuator wires 60' generally extend parallel to the plane P and thus are generally parallel to the first axis. The SMA actuator wires 60' on each side SI, S2 are connected between the static part 2 and the lens element 10 so as to apply a torque in alternate senses around the helical axis (as described above).

The helical flexure bearing 1090' includes a first pair of connection portions 19' (e.g. crimps, also referred to herein as "moving crimps") located on the first side Si, and a second pair of connection portions 19' ("moving crimps") located on the second side S2. The moving crimps 19' are each located at different angular positions around the helical axis H and are each located at respective corners C of the actuator assembly 1.

The moving crimps 19' are each provided at ends of respective crimp arms 119' of the helical flexure bearing 1090'. The crimp arms 119' may extend from the circular annulus 1091' at the same locations from which the flexure arms 1092i', 10922', 10923', 10924' extend from the circular annulus 1091'. These locations are generally equally spaced around the perimeter of the circular annulus 1091'. The flexure arms 1092' extend along the helical axis H (from the circular annulus 1091' towards the base 4) and substantially wrap around the perimeter of the circular annulus 1091'. The crimp arms 119' extend away from the helical axis H and generally towards the corners C of the actuator assembly 1 (from the circular annulus 1091'). The crimp arms 119' are generally flat and coplanar with the circular annulus 1091' (i.e. the crimp arms 119' and the circular annulus 1091' sit on a common plane perpendicular to the primary axis z).

The static part 2 may have four pillars (not shown but comparable to pillars 152i, 1522, 1523, 1524 in Fig. 34B), each upstanding (in the positive z direction) from a respective corner C of the base 4. Each pillar has a connection portion 18' (e.g. crimps, also referred to herein as "static crimps"). The four pillars may be integrally formed with the base 4 or attached to the base 4 using welding, adhesive or other suitable attachment methods.

A first pair of the four corners C and a first pair of the static crimps 18' are on the first side Si of the actuator assembly 1. A second pair of the four corners C and a second pair of the static crimps 18' are on the second side S2 of the actuator assembly 1. The SI pair of SMA actuator wires 6O3' is connected between the first pair of the static crimps 18' and the first pair of moving crimps 19'. The S2 pair of SMA actuator wires 6O4' is connected between the second pair of static crimps 18' and the second pair of moving crimps 19'. The SMA actuator wires 60' generally extend from corner to corner, in a direction generally parallel to plane P (i.e. the y-axis in this example). In other words, the SI pair of SMA actuator wires 6O3' extend from one corner of the first pair of corners C to the other corner of the first pair of corners C, and the S2 pair of SMA actuator wires 6O4' extend from one corner of the second pair of corners C to the other corner of the second pair of corners C. Thus, the SMA actuator wires 60' substantially extend along the entire length of the actuator assembly 1 along the first axis (in this example, the y-axis). The SMA actuator wires 60' generally have the same lengths between the moving crimps 19' and the static crimps 18'.

The flexure arms 1092', the movable crimps 19', the static crimps 18' and the SMA actuator wires 60' have a two-fold rotational symmetry around the helical axis H.

Like the flexure arms 1092 of the first helical flexure assembly 1000, the flexure arms 1092' have pads 1093i', 10932', 10933', 10934' at its lowermost end (i.e. the end closest to the base 4) for attaching the flexure arms 1092' to the base 4. The pads 1093i', 10932', 10933', 10934' extend in a direction perpendicular to plane P and, in this example, away from plane P. The extent of the pads 1093i', 10932', 10933', 10934' (and so the extent of the actuator assembly 1) in a direction parallel to plane P is thus reduced. A first pair of the four flexure arms 1092i', 10923' (and its corresponding pads 1093i', 10933') is on the first side Si of the actuator assembly 1, and a second pair of the four flexures 10922', 10924' (and its corresponding pads 10932', 10934') is on the second side S2 of the actuator assembly 1. To minimise the extent of the actuator assembly 1 along the first axis, the static crimps 18' (including the corresponding pillars), the helical flexure bearing 1090' (including the circular annulus 1091', the crimp arms 119', the moving crimps 19', the flexure arms 1092', the flexure pads 1093') and the SMA actuator wires 60' do not extend (or do not extend substantially) beyond the extremities of the main body of the lens element 10 in the first axis. So, the extent of the helical flexure bearing 1090' along the first axis is less or equal to the extent of the main body of the lens element 10 along the first axis.

The circular annulus 1091', the crimp arms 119', the flexure arms 1092' and the flexure pads 1093' may be formed of a single patterned sheet of metal, e.g. etched or machined stainless steel, and may be coated with an electrically- insulating dielectric material. The dielectric coating or other type of dielectric layer may include one or more windows allowing electrical connections therethrough.

As described above in relation to the first helical flexure assembly 1000, the lens element 10 is movably coupled to the static part 2 via the helical bearing arrangement 20 with plural flexures 1092' (i.e. the helical flexure 1090'). The pads 1093' are fixed to the base 4, for example, by welding, adhesive or other suitable attachment methods, whilst the circular annulus 1091' is fixed to the lens element 10 in the same or similar way.

Alternatively, as described in relation to the first helical flexure assembly 1000, the crimp arms 119' and the movable crimps 19' may be provided on a movable plate instead. The circular annulus 1091' may then be fixed to the movable plate by the attachment methods mentioned above, and the movable plate may be fixed to and/or form part of the lens element 10. Furthermore, the movable plate and the crimp arms 119' may be formed of a first single patterned sheet of metal, and the circular annulus 1091', the flexure arms 1092' and the flexure pads 1093' may be formed of a second single patterned sheet of metal. As shown in Figs. 36 and 37, such an arrangement would allow the crimp arms 119' and the flexure arms 1092' to be connected to the lens element 10 separately and overlap along the z-axis. This allows the flexure arms 1092' to be longer, thus potentially decreasing stress in the arms during AF actuation and increasing AF stroke. This would also allow the flexure arms 1092' and the crimp arms 119' to be made out of different materials and have different thicknesses. Other variations

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

Although the above examples only describe that a single SMA actuator wire is provided between each static crimp and each corresponding moving crimp, any number of SMA actuator wires (or lengths of SMA actuator wires) could be provided between the static crimps and moving crimps.

Although the above examples only describe that the pillars (supporting the static crimps) are integrally formed with the base 4 or attached to the base 4 using welding, adhesive or other suitable attachment methods, the pillars could be integrally formed with any other component that is part of the static part 2 of the actuator assembly 1 or attached to such a component by any suitable attachment method.

Although the above examples focus on helical flexure arrangements with four flexure arms, any number of flexure arms may be provided between the static part 2 and the lens element 10. For example, as shown in Fig. 38, two flexure arms could be provided, although this would likely require further component(s) to restrict undesired movement (e.g. tilting) of the lens element 10.

Claims

1. A shape memory alloy, SMA, actuation apparatus comprising: a support structure; a movable element; a helical bearing arrangement supporting the movable element on the support structure and arranged to guide helical movement of the movable element with respect to the support structure around a helical axis; and a set of four SMA actuator wires, each wire connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, the set of wires comprising a first pair of wires arranged, on contraction, to drive rotation of the movable element in a first sense around the helical axis and a second pair of wires arranged, on contraction, to drive rotation of the movable element in a second, opposite sense around the helical axis, wherein the helical bearing arrangement converts the rotation into the helical movement.

2. An SMA actuation apparatus according to claim 1, wherein the set of wires are arranged in a loop at different angular positions around the helical axis and successive wires are connected so as to apply a torque in alternate senses around the helical axis.

3. An SMA actuation apparatus according to claim 2, wherein, within each pair, the wires are arranged on opposite sides of the helical axis.

4. An SMA actuation apparatus according to claim 3, wherein the movable element comprises a first pair of connection portions located at a first angular position around the helical axis and a second pair of connection portions located at a second angular position around the helical axis, wherein the first and second angular positions are offset from each other by 180°, wherein a wire of each pair is connected to the movable element via the first pair of connection portions and a wire of each pair is connected to the movable element via the second pair of connection portions.

34

SUBSTITUTE SHEET (RULE 26}

5. An SMA actuation apparatus according to any preceding claim, wherein the helical bearing arrangement comprises a set of one or more helical bearings, each of which is a rolling bearing comprising bearing surfaces on the support structure and the moveable element and at least one rolling bearing element disposed between the bearing surfaces.

6. An SMA actuation apparatus according to claim 5, wherein the set of helical bearings comprises: at least one helical bearing of a first type wherein the bearing surfaces comprises grooves on each of the support structure and the movable element; and; at least one helical bearing of a second type wherein the bearing surfaces comprise a groove on one of the support structure and the movable element and a planar surface on the other of the support structure and the movable element.

7. An SMA actuation apparatus according to claim 6, wherein the set of helical bearings comprises two helical bearings of the first type and one helical bearing of the second type.

8. An SMA actuation apparatus according to claim 7, wherein the three helical bearings consist of a first bearing, a second bearing and a third bearing, and the second bearing is angularly spaced from the first bearing by about 90° around the helical axis and the third bearing is angularly spaced from the second bearing by about 90° around the helical axis.

9. An SMA actuation apparatus according to any preceding claim, comprising a biasing arrangement configured to exert a biasing force on the movable element in a direction that is at least substantially normal to a helical path along which the movable element moves so as to at least partly load the helical bearing arrangement.

10. An SMA actuation apparatus according to claim 9, wherein the biasing arrangement comprises a resilient element connected between the support structure and the movable element.

35

SUBSTITUTE SHEET (RULE 26}

11. An SMA actuation apparatus according to claim 10, wherein the resilient element is a flexure.

12. An SMA actuation apparatus according to claim 9, wherein the biasing arrangement is a magnetic loading arrangement.

13. An SMA actuation apparatus according to any one of claims 9 to 12 when dependent on claim 8 wherein at least part of the biasing arrangement is angularly spaced from the third bearing by about 90° around the helical axis.

14. An SMA actuation apparatus according to any one of claims 1 to 8, wherein the set of SMA actuator wires is arranged to apply a force to the movable element that loads the helical bearing arrangement.

15. An SMA actuation apparatus according to claim 14 when dependent on claim 6, wherein the set of helical bearings comprises one helical bearing of the first type and three helical bearings of the second type

16. An SMA actuation apparatus according to claim 15, wherein pairs of adjacent helical bearings are angularly spaced from each other by about 90° around the helical axis.

17. An SMA actuation apparatus according to claim 4 or a claim dependent thereon, wherein the helical bearing arrangement comprises at least first and second bearings and wherein the moveable element comprises first and second portions each extending at least partly outwards from the helical axis, wherein the first portion carries the first connection portion and a part of the first bearing and the second portion carries the second connection portion and a part of the second bearing.

18. An SMA actuation apparatus according to claim 2 or a claim dependent thereon, wherein the helical bearing arrangement is located within the loop of wires.

19. An SMA actuation apparatus according to any preceding claim, wherein the

36

SUBSTITUTE SHEET (RULE 26} helical bearing arrangement comprises at least one flexure arm extending between the support structure and the movable element.

20. An SMA actuation apparatus according to claim 19, wherein the maximum extent of the flexure arms and the SMA wires along a first axis is substantially less than the maximum extent of the flexure arms and the four SMA wires along a second axis; wherein the first axis is perpendicular to the helical axis, and the second axis is perpendicular to the helical axis and perpendicular to the first axis.

21. An SMA actuation apparatus according to claim 20, wherein the maximum extent of the flexure arms and the SMA wires along the first axis is less than 90% of the maximum extent of the flexure arms and the SMA wires along the second axis.

22. An SMA actuation apparatus according to claim 20 or 21, wherein the SMA actuation apparatus comprises a first side and a second side, and wherein: the first side comprises at least one flexure arm and a first pair of the four SMA wires, and the second side comprises at least one flexure arm and a second pair of the four SMA wires; and wherein the first side and the second side are on opposite sides of the helical axis.

23. An SMA actuation apparatus according to claim 22, wherein the first side corresponds to a first half of the SMA actuation apparatus, and the second side corresponds to a second half of the SMA actuation apparatus.

24. An SMA actuation apparatus according to any one of claims 20 to 23, wherein the helical bearing arrangement comprises four flexure arms extending between the support structure and the movable element.

25. An SMA actuation apparatus according to claim 24, wherein the four flexure arms are substantially equally spaced around the perimeter of the movable element.

37

SUBSTITUTE SHEET (RULE 26}

26. An SMA actuation apparatus according to any one of claims 20 to 25, wherein the four SMA wires are of equal length.

27. An SMA actuation apparatus according to any one of claims 20 to 26, wherein the four SMA wires are substantially aligned with the first axis.

28. An SMA actuation apparatus according to any one of claims 20 to 27, wherein the four SMA wires occupy substantially the maximum extent of the flexure arms and the SMA wires along the first axis.

29. An SMA actuation apparatus according to claim 22 or a claim dependent thereon, wherein the first pair of the four SMA wires and the second pair of the four SMA wires each comprise: a first SMA wire arranged to drive rotation of the movable element in a first sense around the helical axis, and a second SMA wire arranged to drive rotation of the movable element in a second, opposite sense around the helical axis.

30. An SMA actuation apparatus according to any one of claims 20 to 29, wherein the movable element comprises four movable connection portions and the support structure comprises four static connection portions, and wherein each of the four SMA wires are connected between each of the four movable portions and each of the four static connection portions.

31. An SMA actuation apparatus according to claim 30, wherein the four movable connection portions extend to four movable crimps and the four static connection portions comprise four static crimps, and wherein a first pair of the four movable crimps and a first pair of the four static crimps are positioned towards a first end of the maximum extent of the flexure arms and the SMA wires along the first axis, and a second pair of the four movable crimps and a first pair of the four static crimps are positioned towards a second, opposite end of the maximum extent of the flexure arms and the SMA wires along the first axis.

32. An SMA actuation apparatus according to any one of claims 31, wherein the

38

SUBSTITUTE SHEET (RULE 26} four movable connection portions extend from locations substantially equally spaced around the perimeter of the main body of the movable element.

33. An SMA actuation apparatus according to any one of claims 30 to 32, wherein the flexure arms and the movable connection portions are unitary.

34. An SMA actuation apparatus according to any one of claims 30 to 33, wherein the flexure arms and the movable connection portions have a common connection point to the main body of the movable element.

35. An SMA actuation apparatus according to any one of claims 20 to 34, wherein the flexure arms and/or the movable connection portions and/or the static connection portions and/or the SMA wires have a two-fold rotational symmetry around the helical axis.

36. An SMA actuation apparatus according to any preceding claim, wherein the at least one shape memory alloy actuator wire is arranged, on contraction, to drive rotation of the movable element around the helical axis by less than one quarter of a full turn.

37. An SMA actuation apparatus according to any preceding claim, wherein the movable element is a lens element comprising at least one lens, and the helical axis is the optical axis of the lens element.

38. An SMA actuation apparatus according to claim 37 wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

39. An SMA actuation apparatus according to claim 37 or 38, wherein the at least one lens has a diameter of at most 30 mm.

39

SUBSTITUTE SHEET (RULE 26}