Field

This application relates to an actuator, particularly an actuator comprising eight SMA (shape memory alloy) wires that provide positional control of a movable element.

Background

WO 2011/104518 Al describes an SMA actuator that uses SMA wires to move a movable element relative to a support structure, for example to provide autofocus and optical image stabilization. Eight SMA wires are arranged inclined with respect to a notional primary axis, with a pair of SMA wires on each of four sides around the primary axis. The SMA wires are connected so that on contraction two groups of four SMA wires provide a force with a component in opposite directions along the primary axis, so that the groups are capable of providing movement along the primary axis. The SMA wires of each group have twofold rotational symmetry about the primary axis, and there are SMA wires opposing each other that are capable of providing lateral movement or tilting.

Summary

According to a first aspect of the presently-claimed invention, there is provided an actuator comprising: a support structure; a movable element; and eight SMA wires connected between the support structure and the movable element so as to enable the movable element to be moved relative to the support structure with at least three degrees of freedom; wherein two of the SMA wires are located on each of four sides, the four sides extending in a loop around a primary axis, wherein the two SMA wires on each side include an inner SMA wire and an outer SMA wire, wherein the outer SMA wire is, on average, further from the primary axis than the inner SMA wire; and wherein, on contraction, a first group of four of the SMA wires each provide a force on the movable element with a component in a first direction along the primary axis, and a second group of the other four of the SMA wires each provide a force on the movable element with a component in a second, opposite direction along the primary axis; characterised in that the first and second groups each include two inner SMA wires and two outer SMA wires.

The inner SMA wires may each have substantially the same thermal environment, and the outer SMA wires may each have substantially the same thermal environment that is different from the thermal environment of the inner SMA wires. SMA wires having substantially the same thermal environment may have substantially the same rate of heat transfer to/from their surroundings. This may be affected by proximity to other objects which may function as heat sinks, e.g. the movable element and/or the support structure.

SMA wires in different thermal environments may behave differently, for example when their temperatures (and hence lengths) are being controlled by varying electrical currents being passed through them. In particular, such SMA wires may have different nonlinearities in connection with such a control system.

Thus, because the first (e.g. upwards-pulling) and second (e.g. downwards-pulling) groups each have two inner SMA wires and two outer SMA wires, these two groups behave similarly to each other and can be more effectively controlled, particularly in relation to movement of the movable element along the primary axis.

In contrast, in e.g. the actuator described in WO 2011/104518 Al, one of the groups (e.g. the upwards-pulling group) consists of inner SMA wires, while the other group (e.g. the downwards- pulling group) consists of outer SMA wires, and this imbalance can lead to potential control problems (e.g. errors).

In most such actuators, due e g. to space constraints, the two SMA wires on each side cross such that, typically, one of the SMA wires must, on average, be further from the primary axis than the other SMA wire.

The primary axis may be an axis that passes through a centre of the movable element.

Wires that are, on average, further from the primary axis may (when taut) have a midpoint that is further from the primary axis.

On each side, the two SMA wires may cross when viewed along a direction perpendicular to the primary axis, wherein the outer SMA wire may be further from the primary axis than the inner SMA wire at the point at which the two SMA wires cross.

The SMA wires may be located in two different planes that are parallel to each other and to the primary axis, with the SMA wire that is, on average, further from the primary axis located in the plane that is further from the primary axis. References herein to positions in the actuator may apply at least when the movable element is at the centre of its range of operation positions.

Moving the movable element relative to the support structure with at least three degrees of freedom may involve moving the movable element along the primary axis and along two further axes that are perpendicular to each other and to the primary axis. Moving the movable element relative to the support structure with at least three degrees of freedom may involve rotating the movable element about at least one of the primary axis and the two further axes (or, in other words, tilting).

Two opposite sides may each have an inner SMA wire in the first group and an outer SMA wire in the second group, and the other two opposite sides may each have an inner SMA wire in the second group and an outer SMA wire in the first group. This will sometimes be referred to as the ‘DB’ configuration.

The DB configuration can have the advantage of not only making the first (e.g. upwards-pulling) and second (e.g. downwards-pulling) groups balanced in terms of numbers of inner and outer SMA wires, but also making the groups that tilt the movable element similarly balanced. This can avoid potential control problems in relation to tilt.

Alternatively, two adjacent sides may each have an inner SMA wire in the first group and an outer SMA wire in the second group, and the other two adjacent sides may each have an inner SMA wire in the second group and an outer SMA wire in the first group.

The actuator may comprise, on each side, an arrangement of four connectors via which the two SMA wires are connected to the support structure and the movable element.

For the DB configuration, each arrangement of connectors may include connectors with substantially the same relative positions.

In other words, each arrangement of connectors may be the same, albeit oriented differently within the actuator.

Relative to the arrangement on an adjacent side, each arrangement of connectors may be rotated about the primary axis (e.g. by 90°) and may be rotated by about 180° about an axis that is perpendicular to the primary axis. This will sometimes be referred to as the DB1 ’ configuration.

In simple terms, in the DB 1 configuration, each arrangement of connectors is an upside-down version of the arrangement on an adjacent side. Relative to the arrangement on an adjacent side, each arrangement of connectors is rotated about the primary axis (e.g. by 90°) and is rotated by about 180° about an axis that is parallel to the primary axis. This will sometimes be referred to as the ‘DB2’ configuration.

In simple terms, in the DB2 configuration, each arrangement of connectors is an inside-out version of the arrangement on an adjacent side.

Each connector may be connected to one of the support structure and the movable element via a support portion. Each connector may be connected to the support portion via an intermediate portion.

The connectors may be crimp portions. The crimp portions, intermediate portions and support portions on each side may be collectively referred to as a crimp component.

On each side, the support portions that are connected to the movable element may be interconnected.

The support portions, intermediate portions and the connectors may each form part of an electrical path used to pass an electrical current through the SMA wires. The ends of the SMA wires that are connected to the movable element may be electrically connected to a common, e.g. ground.

On each side, the support portions may each be generally planar and he in the same plane.

In the DB1 configuration, on each side, the two connectors for the outer SMA wire may be offset from the plane of the support portions in a direction at least partly away from the primary axis.

In the DB2 configuration: on each of two opposite sides, the two connectors for the outer SMA wire may be offset from the plane of the support portions in a direction at least partly away from the primary axis; and on each of the other two opposite sides, the two connectors for the inner SMA wire may be offset from the plane of the support portions in a direction towards the primary axis.

Connectors that are offset from the support portions may be connected to the support portions by angled intermediate portions.

On each of the other two opposite sides, the support structure and/or the movable element may comprise spaces to accommodate at least the two connectors for the inner SMA wire. Interconnected support portions, intermediate portions and connectors may be integrally formed. The integrally-formed support portions, intermediate portions and connectors may be formed from a sheet of metal.

The SMA wires in each of the first and second groups may be arranged with twofold rotational symmetry about the primary axis.

There may be provided a camera apparatus comprising the actuator, wherein the movable element comprises at least one lens and the support structure comprises an image sensor, wherein the primary axis is parallel to the optical axis of the lens or is a normal to the image sensor, and wherein the movement of the movable element relative to the support structure enables optical image stabilisation and/or autofocus.

Alternatively, there may be provided a camera apparatus comprising the actuator, wherein the movable element comprises a module with at least one lens and an image sensor, and wherein the movement of the movable element relative to the support structure enables module-tilt optical image stabilisation.

According to a second aspect of the presently-claimed invention, there is provided a method of producing the actuator wherein each arrangement of connectors includes connectors with substantially the same relative positions. The method comprises: providing the movable element and the support structure; providing four subassemblies, each subassembly comprising the four connectors via which two of the SMA wires are connected to the movable element and the support structure on each of the sides, wherein each subassembly comprises four connectors with substantially the same relative positions; and for each of the sides, suitably orienting a subassembly and attaching the connectors to the movable element and the support structure; wherein the SMA wires are attached to the connectors before or after attaching the connectors to the movable element and the support structure.

The connectors may be crimp portions, and providing each subassembly may comprise: providing a strut element shaped to comprise a sacrificial strut body and four crimp tabs held apart by the sacrificial strut body; laying each of the two SMA wires across two of the crimp tabs; and folding and pressing the two crimp tabs over each of the two SMA wires to form crimp portions holding the SMA wires therebetween; and the method may comprise removing the sacrificial strut body after attaching the crimp portions to the movable element and the support structure.

Thus, the same or a similar subassembly can be used for each of the sides, therefore potentially reducing the bill of materials, simplifying the tooling used to form the crimp portions and/or making the formation of the crimp portions more consistent.

Brief Description of the Drawings

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

Figures 1 A and 2B are top and side views, respectively, of certain elements of a known SMA actuator;

Figure 1C includes schematic views of the crimp component on each side of the known SMA actuator;

Figure 2 is a schematic cross-sectional view of certain elements of a camera module comprising the known SMA actuator;

Figures 3A and 3B are top and side views, respectively, of certain elements of a first SMA actuator; Figure 3C includes schematic views of the crimp component on each side of the first SMA actuator; Figures 4A and 4B are top and side views, respectively, of certain elements of a second SMA actuator;

Figure 4C includes schematic views of the crimp component on each side of the second SMA actuator;

Figures 5A and 5B are top and side views, respectively, of certain elements of a third SMA actuator;

Figure 5C includes schematic views of each of the crimp component on each side of the third SMA actuator, and also includes side views of certain elements; and

Figure 6 illustrates certain elements of a process that can be used to manufacture the second or third SMA actuator.

Detailed description

Known SMA actuator

Referring to Figures 1A and IB, a known SMA actuator 10 (also referred to simply as the known actuator) will now be described.

The known actuator 10 includes a movable element 11 supported on a support structure 12 by eight SMA wires w ₀ -w ₇ .

The movable element 11 may in general be any type of element As viewed along a primary axis z, the movable element 11 has the shape of a square with two diagonally-opposite comers that are rounded. However, more generally, the movable element 11 could have any shape. The support structure 12 has a square base 12a with two parts 12b (also referred to as support posts) that extend from this base 12a into the space left by the rounded comers of the movable element 11. However, in general, the support structure 12 could be any type of element suitable for supporting the movable element 11. The support structure 12 supports the movable element 11 in a manner allowing movement of the movable element 11 relative to the support stmcture 12. In this example, the movable element 11 is supported on the support stmcture 12 solely by the SMA wires wo-w ₇ but the SMA actuator 10 may comprise a suspension system additionally supporting the movable element 11 on the support stmcture 12.

Each SMA wire w comprises a piece of SMA wire connected at each end via a connector 5 to a respective one of the movable element 11 and the support stmcture 12. As will be described in more detail below, the connectors 5 are crimp portions (and will be generally referred to as such).

However, more generally, any suitable means that provides mechanical connection may be used. In addition, electrical connections are made to the SMA wires w, for example via the crimp portions 5.

Each SMA wire w extends along a side s of the primary axis z perpendicular to a notional line radial of the primary axis z and inclined with respect to the primary axis. Each SMA wire w is held in tension, thereby applying a component of force in a direction along the primary axis z and a component of force in a lateral direction perpendicular to the primary axis z.

SMA material has the property that on heating it undergoes a solid-state phase change which causes the SMA material to contract. At low temperatures, the SMA material enters the Martensite phase. At high temperatures the SMA enters the Austenite phase which induces a deformation causing the SMA material to contract. The phase change occurs over a range of temperature due to the statistical spread of transition temperature in the SMA crystal stmcture. Thus heating of the SMA wires w causes them to decrease in length. The SMA wires w may be made of any suitable SMA material, for example Nitinol or another titanium-alloy SMA material. Advantageously, the material composition and pre-treatment of the SMA wires w is chosen to provide phase change over a range of temperature that is above the expected ambient temperature during normal operation and as wide as possible to maximise the degree of positional control.

On heating of one of the SMA wires w, the stress therein increases and it contracts. This causes movement of the movable element 11. A range of movement occurs as the temperature of the SMA increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA wires w so that the stress therein decreases, and it expands under the force from opposing ones of the SMA wires w. This allows the movable element 11 to move in the opposite direction.

The position of the movable element 11 relative to the support structure 12 along the primary axis z is controlled by varying the temperature of the SMA wires w. This is achieved by passing through SMA wires w a drive current that provides resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the movable element 11 to cool by conduction to its surroundings.

Two of the SMA wires w are arranged on each of four sides s (i.e. a first side si, a second side sy, a third side S3 and then a fourth side S4) around the primary axis z. The two of the SMA wires w on each side s, for example SMA wires w<, and wy, are inclined in opposite senses with respect to each other, as viewed perpendicular from the primary axis z, and cross each other. The four sides si, sy, S3, S4 on which the SMA wires w are arranged extend in a loop around the primary axis z. In this example, the sides si, sy, S3, 54 are perpendicular and so form a square as viewed along the primary axis z, but alternatively the sides si, sy, S3, .v 4 could take a different e.g. quadrilateral shape. In this example, the SMA wires it’o-u’7 are parallel to the outer faces of the square envelope of the movable element 11 which conveniently packages the SMA actuator 10 but is not essential.

One of the SMA wires w on each side s provides a force on the movable element 11 in the same direction along the primary axis z. In particular, the SMA wires wo, W3, wt, wy form a ‘first’ group that provide a force in one direction (‘upwards’) and the other SMA wires wi, wy, W5, W6 form a ‘second’ group that provide a force in the opposite direction (‘downwards’). Herein, ‘up’ and ‘down’ generally refer to opposite directions along the primary axis z, wherein movement of the movable element 11 away from the base 12a ofthe support structure 12 is ‘up’.

The SMA wires wo-wy have a symmetrical arrangement in which lengths and inclination angles are the same, so that both the first group of SMA wires wo, wy, MM, wy and the second group of SMA wires wi, MM, ws, MM are each arranged with twofold rotational symmetry about the primary axis z (i.e. bisecting the angle between SMA wires w on adjacent sides s and across the diagonals of the square envelope of the movable element 11).

As a result of this symmetrical arrangement, different combinations of the SMA wires wo-w?, when selectively actuated are capable of driving movement of the movable element 11 with multiple degrees of freedom, as follows.

The first group of SMA wires w ₀ , w ₃ , w ₄ , w ₇ and the second group of SMA wires Wi, w ₂ , w _s , w ₆ when commonly actuated drive movement in different directions along the primary axis z.

Within each group, adjacent pairs of the SMA wires (for example on one hand SMA wires wi, w& and on the other hand SMA wires wi, ws) when differentially actuated drive tilting about a lateral axis perpendicular to the primary axis z. Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes.

Sets of four SMA wires, including two SMA wires from each group, (for example on one hand SMA wires w ₄ , ws, we, wy and on the other hand SMA wires wo, wi, wy, w ₃ ) when commonly actuated drive movement along a lateral axis (e.g. the line y=~x) perpendicular to the primary axis z. Movement in any arbitrary direction perpendicular to the primary axis z may be achieved as a linear combination of movements along the two lateral axes.

A control circuit can be electrically connected to the SMA wires for supplying drive currents thereto to drive these movements, e g. as described in WO 2011/104518 Al (which is incorporated by reference to the maximum extent permissible by law).

Use in a camera module

Although the actuator 10 may be used to provide positional control of a wide range of types of movable element 11, a non-limitative example in which the actuator 10 is used in a camera module will now be described with reference to Figure 2.

In this example, the actuator 10 is used in a camera module arranged to perform autofocus (AF) and optical image stabilisation (OIS). The camera module 100 is to be incorporated in a portable electronic device such as a mobile telephone. Thus, miniaturisation is an important design criterion.

The support structure 12 is a camera support supporting an image sensor 40 on which there is an IC (integrated circuit) chip 42 in which the control circuit 20 is implemented. The movable element 11 comprises a camera lens element 41 arranged to focus an image onto the image sensor 40. The image sensor 40 captures the image and may be of any suitable type for example a CCD (charge- coupled device) or a CMOS (complementary metal-oxide-semiconductor) device. The camera module is a miniature (or ‘compact’) camera module in which the camera lens element 41 has one or more lenses with a diameter of e.g. at most 12 mm.

In this example, OIS is provided by moving the camera lens element 41 laterally of the primary axis z, which is parallel to the optical axis of the camera lens element 41 (and may be collinear with the optical axis when the camera lens element 41 is in a central position). In addition, the camera lens element 41 may be moved along the primary axis z to provide AF. Thus, the AF and OIS functions are combined in the actuator 10.

The control circuit 20 may be configured as described in WO 2011/104518 Alin order to provide this functionality.

Arrangement of SMA wires and configuration of crimp components in the known SMA actuator Referring in particular to Figures IB and 1C, the arrangement of SMA wires wo-w7 and the configuration of the crimp components c in the known actuator 10 will now be described.

On each side s (e.g. the fourth side .s4 illustrated in Fig. IB), there are two SMA wires w (e.g. wires w6, w7) that cross e.g. when viewed along a direction to normal to that side s.

Each of the two SMA wires w on each side s is connected to the movable element 11 via a crimp portion 5 (also referred to as moving crimp portion) and is connected to a support post 12b via a crimp portion 5 (also referred to as a static crimp portion). Each crimp portion 5 is connected to the movable element 11 or to a support post 12b via a support portion 7, which is attached (in any suitable way) to the support post 12b or to the movable element 11. An intermediate portion 6 connects each crimp portion 5 to a support portion 7.

In this example, the support portions 7 that are connected to the movable element 11 are interconnected.

On each side s, the support portions 7 are each generally planar and lie in the same plane (also referred to as the support plane S (see Fig. 5C)), wherein the support plane S is parallel to the primary axis z. The same applies to the regions of the movable element 11 and the support post 12b to which the support portions 7 are attached.

The interconnected crimp portions 5, intermediate portions 6 and support portions 7 are integrally formed, e.g. from sheet metal. The two SMA wires w on each side s include an ‘inner’ wire w (e.g. wy) and an ‘outer’ wire w (e.g. w6.) that is, on average, further from the primary axis z than the inner wire w. The inner wire w is located on a first plane that corresponds to, or is parallel to, the support plane S, and the outer wire w is located on a second plane that is parallel to the first plane and is further from the primary axis z than the first plane.

Accordingly, on each side s, the crimp portions 5 for the outer wire w (e.g. w ₆ ) are offset from the support plane S in a direction away from the primary axis z. This may be achieved by angling the relevant intermediate portions 6, e g. with a fold between the support portion 7 and the intermediate portion 6 and an opposite fold between the intermediate portion 6 and crimp portion 5 so that the crimp portion 5 is substantially parallel to the support portion 7 (see Fig. 5C, particularly the side view of the movable part of the crimp component C3).

The crimp portions 5 for the inner wire w (e.g. w7) may be similarly offset from the support portions 7, albeit to a lesser degree, or they may lie in substantially the same plane as the support portions 7.

Herein, the crimp portions 5, intermediate portions 6 and support portions 7 on a side s are collectively referred to as a crimp component c.

The above-described crimp component C4 on the fourth side .s4 is illustrated schematically in the upper-right of Figure 1C, with the crimp portions 5 labelled with the index (e.g. 6) of the wire w (e.g. w6 ) to which they are connected. The three other crimp components c1, cy, Cy are similarly illustrated.

In Figure 1C (and Figures 3C, 4C and 5C), crimp components c in the same column are on opposite sides .s' of the actuator 10, and crimp components c in the same row are on adjacent sides .s' of the actuator 10.

The crimp components c1, cy on two opposite sides s (i.e., the first and third sides s1, s3) have the same configuration A as each other when viewed along a direction normal to the relevant side .s .

The crimp components cy, c4 on the other two opposite sides (i.e., the second and fourth sides sy, s4) each have the same configuration B as each other when viewed along a direction normal to the relevant side .s.

Accordingly, adjacent sides 5 (e.g. s1, s2) have crimp components c (e.g. c1, cy) with different configurations A, B. Relative to the crimp component c (e.g. c1) on an adjacent side 5 (e.g. 5i), the crimp component c (e g. C2) on each side s (e.g. ^2) has a configuration A, B that is the mirror image about a plane that contains the primary axis z and is perpendicular to e.g. the support plane S of the crimp component c. (Of course, each crimp component c is also rotated about the primary axis z by e.g. 90° relative to the crimp component c on an adjacent side.)

As can be seen from Fig. 1C (and Fig. 1A), the first group of four wires w ₀ , w ₃ , w ₄ , w- that pull upwards on the movable element 11 are all inner wires, and the second group of four wires w1, W2, ws, ws that pull downwards on the movable element 11 are all outer wires. Such an arrangement can lead to potential control problems, as explained above.

Example SMA actuators

Several SMA actuators 10', 10", 10"' (also referred to simply as actuators) will be described below. Each of these actuators 10', 10", 10'" is the same as the known actuator 10 except that some of the SMA wires w that were inner wires in the known actuator 10 are outer wires in the actuator 10', 10", some of the SMA wires w that were outer wires in the known actuator 10 are inner wires in the actuator 10', 10" 10'", and there are related changes to the crimp components c (and, in the case of the third actuator 10'", there are also related changes to the movable element 11 and the support structure 12). This is summarised in table 1, below.

In the first, second and third actuators 10', 10", 10'", the first (upwards-pulling) group of SMA wires wo, W3, w4, w7 and the second (downwards-pulling) group of SMA wires w1, W2, w5, w6 each have two inner wires and two outer wires. Thus, as explained above, these two groups behave similarly to each other and can be more effectively controlled in relation to movement of the movable element 11 along the primary axis z.

First SMA actuator

Referring to Figures 3A-C, the first actuator 10' will now be described in more detail. On the first and second sides s1, s2 (which are adjacent to each other), the first actuator 10' has the same arrangement of SMA wires w0-w4 as the known SMA actuator 10.

On the third and fourth sides S3, .s4 (which are adjacent to each other), the SMA wires W4, wy that were inner wires in the known actuator 10 are outer wires in the first actuator 10', and the SMA wires w5, w6 that were outer wires in the known actuator 10 are inner wires in the first actuator 10'.

Therefore, in the first actuator 10', two adjacent sides s1, S3 each have an inner SMA wire w0, w3 in the first (upwards-pulling) group and an outer wire w1, w2 in the second (downwards-pulling) group, and the other two adjacent sides S3, S4 each have an inner SMA wire w5, w6 in the second (downwards-pulling) group and an outer wire W4, wy in the first (upwards-pulling) group.

As explained above, as the first (e.g. upwards-pulling) and second (e.g. downwards-pulling) groups are balanced in terms of numbers of inner and outer wires, this can avoid potential control problems in relation to movement of the movable element 11 along the primary axis z.

However, the first actuator 10' has adjacent SMA wires w in the same group (i.e. in the first (‘up’) group or the second (‘down’) group) and that are both inner wires (wires wo, w3 and wires wg, wg) or outer wires (wires wi, w> and wires W4, wy) and so those groups of SMA wires w that tilt the movable element 11 are not (all) so balanced and there may be potential control problems in relation to tilt.

The crimp components c1, c2 on the first and second sides s1, s ₂ of the first actuator 10' have the same configurations A, B as the known actuator 10.

The crimp component c3' on the third side s3 of the first actuator 10' has a configuration C that, relative to the crimp component c ₂ on the second side s2, is rotated by 180° about an axis that is perpendicular to the primary axis z and perpendicular to e.g. the support plane S of the crimp component c. The crimp component C4' on the fourth side .s4 of the first actuator 10' has a configuration D that, relative to the crimp component c1 on the first side s1, is rotated by 180° about an axis that is perpendicular to the primary axis z and perpendicular to e.g. the support plane S of the crimp component c. (Of course, each crimp component c is also rotated about the primary axis z by e.g. 90° relative to the crimp component c on an adjacent side.)

Thus, like the known actuator 10, the first actuator 10' has more than one different type of crimp component (e.g. A and B) and so cannot be made using an advantageous manufacturing process that will be described below. Second SMA actuator (DB2)

Referring to Figures 4A-C, the second actuator 10" will now be described in more detail.

On the first and third sides s1, S3 (which are opposite each other), the second actuator 10" has the same arrangement of SMA wires w0, w1, W4, as the known actuator 10.

On the second and fourth sides s2, ,s4 (which are opposite each other), the SMA wires w3, w7 that were inner wires in the known actuator 10 are outer wires in the second actuator 10", and the SMA wires w6 that were outer wires in the known actuator 10 are inner wires in the first actuator 10'.

Therefore, in the second actuator 10", two opposite sides s1, s3 each have an inner wire wo, w4 in the first (upwards-pulling) group and an outer wire w1, w5 in the second (downwards-pulling) group, and the other two opposite sides s2, s4 each have an inner wire w3, w6, in the second (downwards-pulling) group and an outer wire w3, w7 in the first (upwards-pulling) group.

As explained above, such an arrangement of SMA wires w can avoid potential control problems in relation to movement of the movable element 11 along the primary axis z. Moreover, adjacent SMA wires w in the same group (i.e. in the first (‘up’) group or the second (‘down’) group) consist of one inner wire and one outer wire and so those groups of SMA wires that tilt the movable element 11 are also balanced in terms of numbers of inner and outer wires. Thus, the second actuator 10" can also avoid potential control problems in relation to tilt.

The crimp components c1, c3 on the first and third sides si, S3 of the second actuator 10" have the same configuration A as the known actuator 10.

The crimp components c2", 4i" on the second and fourth sides s2, S4 each have a different configuration A* that, relative to a crimp component c1 , c3 on an adjacent side S3, is rotated by 180° about an axis that is perpendicular to the primary axis z and perpendicular to e.g. the support plane S of the crimp component c. (Of course, each crimp component c is also rotated about the primary axis z by e.g. 90° relative to the crimp component c on an adjacent side.)

In simple terms, when viewed along a direction normal to the relevant side s, each crimp assembly c is an upside-down version of the crimp assembly c on an adjacent side .s\

Hence, the crimp components c of the second actuator 10" are themselves each the same, i.e. each have the same relative positions of the individual crimp portions 5, the intermediate portions 6 and the supporting portions 7. Accordingly, the second actuator 10" can be made using the advantageous manufacturing process described below. Furthermore, in the second actuator 10", the first (upwards-pulling) group of SMA wires w has the same number of crimp portions 5 that are offset from the support plane S as the second (downwards-pulling) group of SMA wires w. Compared to the third actuator 10"' (described below), this has the potential advantage of balancing any differences between the offset and non-offset crimp portions 5 that arise due to the manufacturing process.

Third SMA actuator (DB1)

Referring to Figures 5A-C, the third actuator 10"' will now be described in more detail.

The third actuator 10"' has the same arrangement of SMA wires w as the second actuator 10" in terms of which of the SMA wires w are inner wires and which of the SMA wires w are outer wires.

Therefore, the third actuator 10'" can have the same control-related advantages as the second actuator 10".

The crimp components c1, c3 on the first and third sides si, S3 of the third actuator 10'" have the same configuration A as the second actuator 10" (and the known actuator 10).

The crimp components c2", c4 on the second and fourth sides s2, s4 of the third actuator 10'" each have a different configuration A' that, relative to a crimp component c1, ca on an adjacent side s1, S3, is rotated by 180° about an axis that is parallel to the primary axis and passes through e.g. the support plane S of the crimp component c. (Of course, each crimp component c is also rotated about the primary axis z by e.g. 90° relative to the crimp component c on an adjacent side.)

In simple terms, when viewed along a direction normal to the relevant side .s. each crimp assembly c is an inside-out version of the crimp assembly c on an adjacent side v

Hence, like the second actuator 10", the crimp components c of the third actuator 10'" are themselves each the same and so the third actuator 10'" can also be made using the process described below.

However, as will be appreciated, the crimp components cz , c " on the second and fourth sides sz, S3 of the third actuator 10'" have crimp portions 5 for the inner wire w (e.g. w6) that are offset from the support plane S in a direction towards the primary axis z. Therefore, the movable element 11 and the support structure 12 have to be configured, e.g. provided with recesses 12c, to accommodate the relevant crimp portions 5, intermediate portions 6 and SMA wire w. This is illustrated in Figure 5c in the side view of the static part of the crimp component c ". Moreover, the configuration of the movable element 11 and the support structure 12 should be such that all of the inner SMA wires (i.e. wires w2, W6 and wires w0, W4) have substantially the same thermal environment, and all of the outer SMA wires (i.e. wires W3, W7 and wires wi, w5) also have substantially the same thermal environment. For example, the proximity of each wire w to the movable element 11 and/or the support structure 12 along the length of the wire w may be suitably selected.

Manufacturing process

Referring to Figure 6, a process that can be used to manufacture the second or third actuator 10", 10"' will now be described.

At a first step S 1, the movable element 11 and the support structure 12 are provided. The movable element 11 and the support structure 12 can be made of any suitable material and in any suitable way, e.g. moulded plastic.

At a second step S2, four subassemblies are provided, wherein each subassembly comprises a crimp component c. As explained above, the crimp components c are themselves each the same. The subassemblies and the crimp components c can be made, for example, by cutting (etching) and forming sheet metal.

In this example, the SMA wires w are attached to the crimp portions 5 before the crimp components c are attached to the movable element 11 and the support structure 12. This may be performed using a process as described in WO 2016/189314 Al (which is incorporated by reference to the maximum extent permissible by law). In brief, the process may involve: a. providing a strut element shaped to compnse a sacrificial strut body and four crimp tabs held apart by the sacrificial strut body; b. laying each of two SMA wires w across two of the crimp tabs; and c. folding and pressing the two crimp tabs over each of the two SMA wires w to form crimp portions 5 holding the SMA wires w therebetween.

As will be appreciated, some of these steps, including step c (crimping), may be carried out using specific tooling (e.g. crimp tooling). As mentioned above, compared to e.g. a process for manufacturing the known actuator 10 which has more than one different crimp component c, this process has the advantages of simplified crimp tooling and/or a more consistent formation of the crimp portions 5. At a third step S3, for each of the four sides of the actuator 10", 10"', the subassembly is suitably oriented and is attached to the movable element 11 and the support structure 12, by adhering the support portions 7 thereto or in any other suitable way. The sacrificial stmt body is then removed from the subassembly, forming the crimp component c.

In other examples, the crimp components c are attached to the movable element 11 and the support structure 12 before the SMA wires w are attached to the crimp portions 5 and/or the sacrificial stmt body may not be used.

Other variations

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

For example, crimp components c may have different positions on different sides .s.

The relative positions of the individual crimp portions 5, intermediate portions 6 and/or supporting portions 7 may differ on different sides s.

Further features of the crimp component c, e.g. electrical connection portions, may differ on different sides .s.

Instead of the above-described specific rotations (or other transformations) describing the relative orientations of elements of the actuator 10', 10", 10"', there may be equivalent rotations or transformations that provide equivalent functionality.

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