GB2575026A

GB2575026A - Shape memory alloy actuation apparatus

Info

Publication number: GB2575026A
Application number: GB201810207A
Authority: GB
Inventors: matthew bunting Stephen; Scholz Marc-Sebastian; Benjamin Simpson Brown Andrew; Howarth James
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2018-06-21
Filing date: 2018-06-21
Publication date: 2020-01-01
Also published as: GB201810207D0

Abstract

A shape memory alloy actuation apparatus 1 e.g. for a miniature camera comprises a support structure 2 and a movable element 10. A suspension system 31-36 supports the movable element and guides helical movement of the movable element with respect to the support structure around a helical axis. At least one shape memory alloy actuator wire is connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, so as to drive rotation of the movable element around the helical axis which the suspension system converts into said helical movement. The suspension system may include rolling elements engaging with grooved and/or plane surfaces 31, 32, 35.

Description

Shape Memory Alloy Actuation Apparatus

The present techniques generally relate 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.

According to the present techniques, there is provided a shape memory alloy actuation apparatus comprising: a support structure; a movable element; a suspension system 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 at least one shape memory alloy actuator wire connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis and arranged, on contraction, to drive rotation of the movable element around the helical axis which the suspension system converts into said helical movement.

This type of SMA actuation apparatus makes use of a suspension system which guides helical movement of the movable element with respect to the support structure. Such helical movement involves rotation around a helical axis together with an overall translation along the helical axis. Thus, the SMA actuator wire is connected between the support structure and the movable element so as to drive rotation of the movable element around the helical axis. The rotation driven by contraction of the SMA actuator wire is converted by the suspension system into helical movement of the movable element. Thus, translational movement of the movable element is achieved along the helical axis as part of the helical movement.

As the SMA actuator wire has the primary purpose of driving rotation, the extent of the SMA actuator wire projected along the helical axis may be minimised, such that some other component of the SMA actuation apparatus determines the size of the actuator in the direction of the helical axis along which translational movement is achieved.

In some embodiments, the SMA actuator wire may extend in a plane normal to the helical axis. In that case, the SMA actuator wire has a minimum extent projected along the helical a”^

In other embodiments, the SMA actuator wire may extend at an acute angle to a plane normal to the helical axis. In that case, the SMA actuator wire has an extent projected along the helical axis, but this may be controlled by adjusting the acute angle to fit within the size constraint of some other component of the SMA actuation apparatus.

Various different types of suspension system may be used to guide the helical movement of the movable element with respect to the support structure. For example, the suspension system may comprise a helical bearing arrangement that comprises at least one helical bearing, or may comprise at least one flexure extending between the support structure and the movable element.

Similarly, various different configurations for the SMA actuator wires may be used to drive rotation of the movable element around the helical axis. For example, there may be a single SMA actuator wire or plural SMA actuator wires disposed at any positions around the helical axis.

A resilient biasing element may be connected between the support structure and the movable element and arranged to resiliently bias the at least one SMA actuator wire. In general terms, use of a resilient biasing element with an SMA actuator wire is known, the resilient biasing element applying a stress to the SMA actuator wire and driving movement in the opposite direction from contraction of the SMA actuator wire. Such a resilient biasing element may be employed with a single SMA actuator wire or plural SMA actuator wires.

Alternatively, a pair of SMA actuator wires may be arranged, on contraction, to drive rotation of the movable element in opposite senses around the helical axis. Whereas use of a pair of SMA actuator wires that apply opposed forces to an element in translation is known in general terms, here the SMA actuator wires apply opposed torques around the helical axis. However, in a similar manner to known uses of opposed SMA actuator wires, the SMA actuator wires apply a stress to each other and, on contraction, drive rotation of the lens element in the opposite directions around the helical axis.

The present techniques may in general be applied to a range of types of SMA actuation apparatus including a range of types of movable element.

However, 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 20mm, preferably at most 15mm, preferably at most 10mm.

Preferred features of the present techniques are set out in the appended dependent claims.

Implementations of the present techniques 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 SMA actuation apparatus that is a camera;

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

Figs. 4 to 7 are schematic cross-sectional views of the SMA actuation apparatus with different possible helical bearing arrangements;

Fig. 8 is a side view of the SMA actuation apparatus with a suspension system comprising plural flexures;

Figs. 9 and 10 are plan views of the suspension system of Fig. 8 with different forms of flexures;

Figs. 11 and 12 are schemata '--vs of the SMA actuator apparatus including an SMA actuator wire extending at two different angles;

Figs. 13 to 15 are schematic plan views of the SMA actuator apparatus with different arrangements of SMA actuator wire and a resilient biasing element;

Figs. 16 to 18 are schematic plan views of the SMA actuator apparatus with different arrangements of SMA actuator wire that are opposed in rotation;

Fig. 19 and 20 are perspective views of a further example of the SMA actuator apparatus;

Fig. 21 is a plan view of the SMA actuator apparatus shown in Figs. 19 and 20;

Fig. 22 is a perspective views of a yet further example of the SMA actuator apparatus;

Fig. 23 is a side view of the SMA actuator apparatus shown in Fig. 22;

Fig. 24 is a plan view of the SMA actuator apparatus shown in Fig. 22;

Fig. 25 is a perspective view of the suspension system of the SMA actuator apparatus shown in Fig. 22;

Fig. 26 is a perspective views of a yet further example of the SMA actuator apparatus;

Fig. 27 is a side view of the SMA actuator apparatus shown in Fig. 26;

Fig. 28 is a plan view of the SMA actuator apparatus shown in Fig. 26;

Fig. 29 is a perspective views of a yet further example of the SMA actuator apparatus;

Fig. 30 is a plan view of the Ε^ΚΛΛ ^^or apparatus shown in Fig. 29;

Fig. 31 is a perspective views of a yet further example of the SMA actuator apparatus;

Fig. 32 is a plan view of the SMA actuator apparatus shown in Fig. 31; and

Fig. 33 and 34 are plan views of further examples of the SMA actuator apparatus.

Broadly speaking, the present techniques provide 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. Specifically, the SMA actuation apparatus makes use of a suspension system which guides helical movement of the movable element with respect to the support structure. Such helical movement involves rotation around a helical axis together with an overall translation along the helical axis.

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 WO2007/113478. Herein, the movable element is a camera lens element supported on a support structure by a suspension system 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 greate- ⁿ agrees 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 WO2007/113478 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.

Thus, the SMA actuator wires in such an arrangement constrain the reduction in size along the movement direction and it would however be desirable to reduce this constraint.

An SMA actuation apparatus 1 that is a camera is shown schematically in Fig. 1.

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

The SMA actuation apparatus ⁱ ^mprises a lens element 10 that is the movable element 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 SMA actuation apparatus 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 20mm, preferably at most 15mm, preferably at most 10mm.

Although the SMA actuation apparatus 1 in this example is a camera, that is not in general essential. In some examples, the SMA actuation apparatus 1 may be an optical device in which the movable element is a lens element but there is no image sensor. In other examples, SMA actuation apparatus 1 may be a type of apparatus that is not an optical device, and in which the movable element 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.

The SMA actuation apparatus 1 also comprises a suspension system 20 (shown schematically in Fig. 1) that supports the lens element 10 on the support structure 2. The suspension system 20 is arranged to guide helical movement of the lens element 10 with respect to the support structure 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. 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 suspension system 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 _3S rotation of the lens element 10 does not change the focus of the image on the image sensor 3.

The suspension system 20 may take a variety of forms.

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

The helical bearing surfaces 31 and 32 extend helically around the helical axis H. Thus, the helical bearing 30 guides the helical movement of the lens element 10 with respect to the support structure 2 as shown by the arrow M. That said, in practical embodiments, the length of the helical bearing surfaces 31 and 32 may be short compared to the distance of the helical bearing surfaces 31 and 32 from the helical axis H, such that their shape is close to straight. 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 support structure 2.

In the example of Fig. 2, the helical 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 support structure 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 crosssections are possible, for example curved as in portions of a circle or an oval. In general, the groove provides two points of contact with the ball.

In the example of Fig. 3, a first helical bearing surface 31 comprises a groove 36 in which the rolling bea-ⁱ”'’ ''’''^nnts 33 are seated and a second helical bearing surface 32 wherein the bearing surface is 'planar'. The first helical bearing surface 31 comprising a groove 36 may be provided on either one of the support structure 2 and the lens element 10, with the second helical bearing surface being provided on the other one of the support structure 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 support structure 2, that is transverse to the direction of movement shown by arrow M. The 'planar' surface 32 is a surface which is not a groove and one which provides only a single point of contact with the ball. As pictured, the 'planar' surface is a line in cross section which line twists helically along the movement direction, maintaining a single point of contact with the ball at any time.

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 support structure 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 helical 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 support structure 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 support structure 2 while constraining the movement of the lens element 10 with respect to the support structure 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 SMA actuation apparatus 1 with different possible helical bearing arrangements are illustrated in Figs. 4 to 6 which are schematic plan views normal to the helical axis showing the support structure 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 2.

The first helical bearing 37 is of the same type as the helical bearing 30 shown in Fig. 2 wherein the helical 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 support structure 2.

The second helical bearing 38 is of the same type as the helical bearing 30 shown in Fig. 3 wherein the first helical bearing surface 31 comprises a groove 36 in which the rolling bearing elements 33 are seated and the second helical bearing surface 32 is planar. Fig. 4 illustrates the case that the first helical bearing surface 31 of the second helical bearing 38 is on the support structure 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 support structure 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 -—'mples below, which simplifies the construction and reduces footprint of the SMA actuation apparatus 1.

Fig. 5 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.

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 helical 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 helical bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second helical bearing surface 32 is planar. Fig. 5 illustrates the case that the first helical bearing surface 31 of the third helical bearing 41 is on the lens element 10, but it could alternatively be on the support structure 2.

Each of the three helical bearings 39, 40 and 41 may comprise a single rolling bearing element 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 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 three helical bearings 41, 42 and 43, 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. 6 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 helical bearing surfaces 31 and 32 each comprise respective grooves 34 and 35.

The second, third and fourth helical bearings 43, 44 and 45 is of the same type as the helical bearing 30 shown in Fig. 3 wherein the first helical bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second helical bearing surface 32 is planar. Fig. 6 illustrates the case that the first helical 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 support structure 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 support structure 2 in degrees of freedom other than the helical movement.

Fig. 7 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 helical 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 helical bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second helical bearing surface 32 is planar. Fig. 7 illustrates the case that the first helical 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.

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 sup—^-^ure 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.

Another possibility is that the suspension system 20 comprises at least one flexure extending between the support structure 2 and the lens element 10 as shown for example in Fig. 8 wherein the suspension system comprises two flexure elements 50 that each comprise four flexures 51 having a configuration as shown either in Fig. 9 or in Fig. 10. As shown in Fig. 8, the flexures 51 are each pre-deflected along the helical axis H, and as shown in Figs. 9 and 10, 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 support structure 2 around the helical axis H. The specific number and arrangement of flexures 51 in Figs. 8 to 10 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.

The use of SMA actuator wires to rotate the lens element 10 will now be described.

The SMA actuation apparatus 1 includes at least one SMA actuator wire 60 for the purpose of rotating the lens element 10. The or each SMA actuator wire 60 is connected between the support structure 2 and the lens element 10, for example as shown in Figs. 11 and 12. The SMA actuator wire 60 is connected to the support structure 2 and lens element 10 by crimp portions 61 which crimp the SMA actuator wire 60 to provide both mechanical and electrical connection. In the case of Fig. 11, the SMA actuator wire 60 extends in a plane normal to the helical axis H. In the case of Fig. 12, the SMA actuator wire 60 extends at an acute angle θ to a plane normal the helical axis H. The SMA actuator wire 60 is offset from the helical axis. Thus, in both the case Fig. 11 and Fig. 12, contraction of the SMA actuator wire 60 drives rotation of the lens element 10 around the helical axis H. Accordingly, either of the orientations of the SMA actuator wire 60 of Fig. 11 or Fig. ⁿ used in any of the arrangements described below.

As the suspension system 20 guides helical movement of the lens element 10 with respect to the support structure 2 and constrains movement in other degrees of freedom, the rotation driven by contraction of the SMA actuator wire 60 is converted by the suspension system 20 into helical movement of the lens element 10 with respect to the support structure 2. Thus, as well as the component of rotational movement, a component of translational movement of the lens element 10 with respect to the support structure 2 is achieved along the helical axis H. This changes the focus of the image on the image sensor 3 as described above.

As the SMA actuator wire 60 has the primary purpose of driving rotation of the lens element 10, the extent of the SMA actuator wire projected along the helical axis H may be minimised. As such, other components of the SMA actuation apparatus 1 constrain the reduction in size along the helical axis H. Typically, the height projected along the helical axis H becomes dependent on the suspension system 20, for example the helical bearing arrangement, which is illustrated schematically in Figs. 11 and 12.

In the case of Fig. 11, as the SMA actuator wire 60 extends in a plane normal to the helical axis H, the SMA actuator wire 60 has a minimum extent projected along the helical axis H being essentially the thickness of the SMA actuator wire 60, which is clearly less than the extent Eb of the suspension system 20 projected along the helical axis H. However, the SMA wire 60 is angled with respect to the flexures to allow the desired movement. Thus in Figure 11 the flexures of the suspension system need to be at an angle to the SMA wire 60.

In the case of Fig. 12, as the SMA actuator wire 60 extends at an acute angle to a plane normal to the helical axis H, the SMA actuator wire 60 has a greater extent Es projected along the helical axis H than in the case of Fig. 11, but this extent Es may be controlled by adjusting the acute angle to fit within any desired size constraint, typically being selected to be less than the extent Eb of the suspension system 20 projected along the helical axis H.

Various different arrangements of the at least one SMA actuator wire 60 may be used in the SMA actuation apparatus, provided that the at least one SMA actuator wire 60 drives rotation of the lens element 10 with respect to the support structure 2. Some examples of possible arrangements of the at least one SMA actuator wire 60 are as follows with reference to Figs. 13 to 19 which are each schematic drawings of the SMA actuation apparatus 1 including schematically illustrated connection portions 65 that are part of the lens element 10 and to which the SMA actuator wire 60 is connected.

In a first type of embodiment, the SMA actuation apparatus 1 further comprises a resilient biasing element 70 connected between the support structure 2 and the lens element 10, as in Fig 13. The resilient biasing element 70 is typically a spring, as in the examples below, but in principle could be formed by any other element for example being a flexure or a piece of resilient material.

Such a resilient biasing element 70 is arranged to resiliently bias the at least one SMA actuator wire 60. In general terms, use of a resilient biasing element 70 with an SMA actuator wire is known, the resilient biasing element 70 applying a stress to the SMA actuator wire 60 and driving movement in the opposite direction from contraction of the SMA actuator wire 60. Thus, such a resilient biasing element 70 may be employed with a single SMA actuator wire 60 or plural SMA actuator wires 60. In the specific case of the SMA actuation 1, the resilient biasing element 70 may be arranged in various ways, some examples of which are as follows.

Fig. 13 shows an example where the SMA actuation apparatus 1 comprises a single SMA actuator wire 60 only and the resilient biasing element 70 extends around the helical axis H and so provides a force around the helical axis H. In Fig. 13, the resilient biasing element operates in tension, but alternatively could operate in compression, for example being arranged alongside the SMA actuator wire 60. The use of a resilient biasing element 70 extends around the helical axis H minimises the extent of the resilient biasing element 70 projected along the helical axis H.

Fig. 14 shows an exampl :he SMA actuation apparatus 1 comprises a single SMA actuator wire 60 only and the resilient biasing element 70 extends parallel to the helical axis H and so provides a force along the helical axis H. In this case, the forces applied by the resilient biasing element 70 acts in a different direction from the SMA actuator wire 60, but resilient biasing is still provided due to the effect of the suspension system 20. In Fig. 14, a helical spring is the resilient biasing element 70, shown with its axis parallel to the optic axis. The spring axis could alternatively be at an angle to the optic axis, as depicted and described further below and in Figure 22.

The examples shown in Figs. 13 and 14 include a single SMA actuator wire 60, but may be modified to include plural SMA actuator wires 60 acting in parallel.

Fig. 15 shows an example of this which corresponds to the example of Fig. 13 but with the SMA actuator wire 60 and the resilient biasing element 70 being duplicated on opposite sides of the lens element 10. The SMA actuator wires 60 and the resilient biasing elements 70 have rotational symmetry around the helical axis, and so the SMA actuator wires 60 are complimentary and drive rotation of the lens element 10 with respect to the support structure 2 in parallel, that is in the same sense around the helical axis H, and so are actuated together. However, as the SMA actuator wires 60 are arranged on opposite sides of the helical axis H, the SMA actuator wires 60 also provide translational forces on the lens element 10 in opposite directions in a plane normal to the helical axis H (left and right in Fig. 15. Thus, the net translational force applied by the SMA actuator wires 60 is minimised, thereby reducing the force applied to the suspension system 20.

In a second type of embodiment, no resilient biasing element is provided, and instead the SMA actuation apparatus 1 comprises at least one pair of SMA actuator wires 60 that are arranged to drive rotation of the lens element 10 in opposite senses around the helical axis H. Similar to known uses of opposed SMA actuator wires to provide opposed forces in translation of an object that moves linearly, the or each pair of SMA actuator wires 60 apply opposed torques around the helical axis H. Thus, the SMA actuator wires 60 of the pair apply a stress to each other, which may act through the suspension system 20, and drive rotation of the lens element 10 —nosite directions around the helical axis Η.

In the case of the SMA actuation 1, the at least one pair of SMA actuator wires 60 may be arranged in various ways, some examples of which are as follows.

Fig. 17 shows an example where the SMA actuation apparatus 1 comprises a pair of SMA actuator wires 60 are arranged on opposite sides of the helical axis H. As a result, the pair of SMA actuator wires 60 apply lateral forces to the lens element 10 perpendicular to the helical axis in parallel (that is from left to right in Fig. 16). In this case, the combined lateral force is resisted by the suspension system 20. This is advantageous for the type of the suspension system 20 that needs to be loaded, as may be the case when the helical bearings 30 are used, as in the example in Fig. 4.

Fig. 16 shows an example where the SMA actuation apparatus 1 comprises a pair of SMA actuator wires 60 are arranged on the same side of the helical axis H. Although Fig. 16 shows the SMA actuator wires 60 as being alongside each other as viewed along the helical axis H, the SMA actuator wires 60 may alternatively overlie each other to reduce the footprint of the SMA actuation apparatus 1. As a result, the SMA actuator wires 60 apply lateral forces to the lens element 10 perpendicular to the helical axis H in opposite directions (that is, in Fig. 16, one SMA actuator wire 60 applying a force from left to right and the other SMA actuator wire 60 applying a force from right to left). Thus, the net translational force applied by the SMA actuator wires 60 to the suspension system 20 is minimised, thereby reducing the force applied to the suspension system 20. This may be advantageous for types of suspension system 20 where loading is disadvantageous, as may be the case when flexures 51 are used, as in the example in Fig. 8.

Fig. 18 shows an example where the SMA actuation apparatus 1 comprises a pair of SMA actuator wires 60 on two adjacent sides of the lens element 10 and having an angle therebetween of 90 degrees. More generally the orientation of the SMA actuator wires 60 may be changed so that the angle therebetween has any size less than 180 degrees, but preferably the angle is in the range from 70 to 110 degrees along the helical axis H. In this case, the net translational force applied by the SMA actuator wires 60 to the suspension system 20 is reduced compared to the example of Fig. 16. The reduction is by a factor of V2 in the example of Fig. 18 but this factor may be controlled by selection of the angle between the SMA actuator wires. This type of configuration is useful for controlling the loading applied to the suspension system 20. This is advantageous for type of the suspension system 20 that need to be loaded, as may be the case when the helical bearings 30 are used.

In general terms, any of the forms of the suspension system 20 described herein, including any helical bearing arrangement or the flexure arrangement, may be used with any of the arrangements of at least one SMA actuator wire 60 described herein.

By way of non-limitative example, Figs. 19 to 26 illustrate some different examples of the SMA actuation apparatus 1 employing specific forms of the suspension system 20 and specific configurations for the at least one SMA actuator wire 60, as follows. In each of Figs. 19 to 26, the support structure 2 and the lens element 10 are formed by moulded components.

In the example of Figs. 19 to 21, the suspension system 20 comprises a helical bearing arrangement of two helical bearings 37 and 38 with an arrangement of the type shown in Fig. 4 and described above. That is, the first helical bearing 37 comprises helical bearing surfaces 31 and 32 each comprising respective grooves 34 and 35, with plural rolling bearing elements 33, and the second helical bearing 38 comprises a first helical bearing surface 31 comprising a groove 36 and a second helical bearing surface 32 that is planar, with a single rolling bearing element 33.

Also, in the example of Figs. 19 to 21, the SMA actuation apparatus 1 comprises a single SMA actuator wire 60 only and a resilient biasing element 70 providing a resilient biasing force having an arrangement of the type shown in Fig. 14. That is, the resilient biasing element 70 extends parallel to the helical axis H and so provides a force along the helical axis H. The SMA actuator wire 60 extends at a slight angle with respect to the normal to the helical axis.

In the example of Figs. 22 tc uspension system 20 comprises a helical bearing arrangement of four helical bearings 46 to 49 with an arrangement of the type shown in Fig 7 and described above. The arrangement of the four helical bearings 46 to 49 is shown in greater detail in Fig. 25. That is, the first and second helical bearings 46 and 47 comprise helical bearing surfaces 31 and 32 each comprising respective grooves 34 and 35, with a single rolling bearing element 33, and the third and fourth helical bearings 48 and 49 comprise a first helical bearing surface 31 comprising a groove 36 and a second helical bearing surface 32 that is planar, with a single rolling bearing element 33. The particular arrangement of the bearings is shown in more detail in Fig.

21.

Also, in the example of Figs. 22 to 24, the SMA actuation apparatus 1 comprises pair of SMA actuator wires 60 having an arrangement of the type shown in Fig. 16. That is, SMA actuator wires 60 are arranged on the same side of the helical axis H but, on contraction, drive rotation of the lens element 10 in opposite senses around the helical axis H. The SMA actuator wire 60 extends at an angle with respect to a plane normal to the helical axis H.

In the example of Figs. 26 to 28, the suspension system 20 comprises a helical bearing arrangement of four helical bearings 46 to 49 with the same arrangement as shown in Fig. 25 and described above.

Also, in the example of Figs. 26 to 28, the SMA actuation apparatus 1 comprises two SMA actuator wires 60 only and a resilient biasing element 70 providing a resilient biasing force having an arrangement of the type similar to that shown in Fig. 14. One difference is that two SMA actuator wires 60 are provided, but these are arranged, on contraction, to drive rotation of the lens element 2 relative to the support structure in the same sense around the helical axis H, i.e. they provide torques in the same sense around the helical axis H. Thus, the SMA actuator wires 60 are complimentary and apply increased force compared to a single SMA actuator wire 60 but are not opposed in rotation, so that a resilient biasing element is still needed, two resilient biasing elements 70 being present. In this example, the resilient biasing elements 70 extend at an acute angle to the helical axis H and so provides a force with a component along the helical axis H and a component that loads the four helical bearings 46 to 49. The SMA actuator wire 60 extend'· ” ^^l:~ht angle with respect to a plane normal to the helical axis H.

Also in the example of Figs. 26 to 28, the angle of the resilient biasing elements 70 can be selected to provide a desired force holding the balls on to the bearing surface, while also providing a biasing force for the SMA wires 60, as described above. Such an angled resilient biasing element may also be used with a different type of bearing, such as a plain bearing, where high forces are undesirable.

In the example of Figs. 29 and 30, the suspension system 20 comprises a helical bearing arrangement of four helical bearings 46 to 49 with the same arrangement as shown in Fig. 25 and described above.

Also, in the example of Figs. 29 and 30, the SMA actuation apparatus 1 comprises two SMA actuator wires 60 and two resilient biasing elements 70 providing resilient biasing, having an arrangement of the type similar to that shown in Fig. 14. Similarly to the example of Figs. 26 to 28, a difference is that two SMA actuator wires 60 are provided, but these are arranged, on contraction, to drive rotation of the lens element 2 relative to the support structure in the same sense around the helical axis H, i.e. they provide torques in the same sense around the helical axis H. Thus, the SMA actuator wires 60 are complimentary and apply increased force compared to a single SMA actuator wire 60 but are not opposed in rotation, so that the resilient biasing element 70 is still needed. In this example, the resilient biasing elements 70 extend parallel to along the helical axis H and so provides a force along the helical axis H. The SMA actuator wire 60 extends at a slight angle to a plane normal to the helical axis H.

In the example of Figs. 29 and 30, the crimp portions 61 on the lens element 10 are formed integrally with a connection member 62 that provides for electrical connection between the crimp portions 61 across the lens element 10.

In the example of Figs. 31 and 32, the suspension system 20 comprises a helical bearing arrangement of four helical bearings 46 to 49 with the same arrangement as shown in Fig. 25 and described above.

Also, in the example of Figs. 31 and 32, the SMA actuation apparatus 1 comprises two SMA actuator wires 60 and two resilient biasing elements providing resilient biasing, having an arrangement of the type shown in Fig. 15. That is, the SMA actuator wires 60 and the resilient biasing elements 70 have rotational symmetry around the helical axis H, and the SMA actuator wires 60 are complimentary and drive rotation of the lens element 10 with respect to the support structure 2 in parallel, that is in the same sense around the helical axis H, and so are actuated together. In this example, the resilient biasing element 70 extends around the helical axis H and provides a force around the helical axis H. The SMA actuator wire 60 extends at a slight angle with respect to a plane normal to the helical axis H.

In the example of Figs. 31 and 32, the crimp portions 61 on the lens element 10 are formed integrally with a connection member 62 that provides for electrical connection between the crimp portions 61 across the lens element 10.

In the example of Fig. 33, the suspension system 20 comprises a helical bearing arrangement of two helical bearings 37 and 38 with an arrangement of the type shown in Fig. 4 and described above. That is, the first helical bearing 37 comprises helical bearing surfaces 31 and 32 each comprising respective grooves 34 and 35, with plural rolling bearing elements 33, and the second helical bearing 38 comprises a first helical bearing surface 31 comprising a groove 36 and a second helical bearing surface 32 that is planar, with a single rolling bearing element 33.

Also, in the example of Fig. 33, the SMA actuation apparatus 1 comprises a pair of SMA actuator wires 60 having an arrangement of the type shown in Fig. 18. No resilient biasing element is provided, and the pair of SMA actuator wires 60 drive rotation of the lens element 10 in opposite senses around the helical axis H. The pair of SMA actuator wires 60 are arranged on two adjacent sides of the lens element 10 with an angle therebetween of 90 degrees. The SMA actuation apparatus 1 includes an electrical connection element 80 is provided to make an electrical connection from the support structure 2 to the ends of the SMA wire 60 which are connected to the movable element 10. The electrical connection element 80 comprises plates 81 and 82 mounted on the lens element 10 and the suppoH 2, respectively, and a flexible connector 81 connecting the plates 81 and 82 across the gap between the lens element 10 and the support structure 2.

In the example of Fig. 34, the suspension system 20 comprises a helical bearing arrangement of two helical bearings 37 and 38 with the same arrangement as in Fig. 5 (although only partially illustrated in Fig. 34).

Also, in the example of Fig. 34, the SMA actuation apparatus 1 comprises a single SMA actuator wire 60 and a resilient biasing element 70 for providing resilient biasing, having an arrangement of the type shown in Fig. 13 with the resilient biasing element extending around the helical axis H to provide a force around the helical axis H. The SMA actuation apparatus 1 includes an electrical connection element 80 mounted on the lens element 20 and providing an electrical connection from the end of the SMA wire 60 which is connected to the lens element 10 to the support structure 2, in the same manner as the example of Fig. 33.In all of the examples above, 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 which may for example 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 in its entirety.

Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and where appropriate other modes of performing present techniques, the present techniques should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that present techniques have a broad range of applications, and that the embodiments may take a wide range of modifications without departing from any inventive concept as defined in the appended claims.

Claims

1. A shape memory alloy actuation apparatus comprising:

a support structure;

a movable element;

a suspension system 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 at least one shape memory alloy actuator wire connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis and arranged, on contraction, to drive rotation of the movable element around the helical axis which the suspension system converts into said helical movement.

2. The shape memory alloy actuation apparatus according to claim 1, wherein the suspension system comprises a helical bearing arrangement that comprises at least one helical bearing.

3. The shape memory alloy actuation apparatus according to claim 2, wherein the helical bearing arrangement comprises plural helical bearings.

4. The shape memory alloy actuation apparatus according to claim 2 or 3, wherein the at least one helical bearing comprises helical bearing surfaces on the support structure and the moveable element and at least one rolling bearing element disposed between the bearing surfaces.

5. The shape memory alloy actuation apparatus according to claim 4, wherein the helical bearing arrangement comprises plural helical bearings and at least one of the helical bearings comprises plural rolling bearing elements.

6. The shape memory alloy actuation apparatus according to claim 4 or 5, wherein the bearing arrangement comprises two helical bearings only.

7. The shape memory alloy actuation apparatus according to claim 5 or 6, wherein the bearing surfaces of the first helical bearing comprises grooves on each of the support structure and the movable element, and the bearing surfaces of the second helical bearing 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.

8. The shape memory alloy actuation apparatus according to claim 7, wherein the first helical bearing comprises plural rolling bearing elements.

9. The shape memory alloy actuation apparatus according to claim 4 or 5, wherein the bearing arrangement comprises three helical bearings only.

10. The shape memory alloy actuation apparatus according to claim 9, wherein the bearing surfaces of the first and second helical bearings each comprises grooves on each of the support structure and the movable element, and the bearing surfaces of the third helical bearing comprises 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.

11. The shape memory alloy actuation apparatus according to claim 10, wherein the first, second and third helical bearings each comprise a single rolling bearing element only.

12. The shape memory alloy actuation apparatus according to claim 4 or 5, wherein the bearing arrangement comprises four helical bearings only.

13. The shape memory alloy actuation apparatus according to claim 12, wherein the bearing surfaces of the first helical bearing each comprise grooves on each of the support structure and the movable element, and the bearing surfaces of the second, third and fourth helical bearings 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.

14. The shape memory alloy actuation apparatus according to claim 1, wherein the suspension system comprises at least one flexure extending between the support structure and the movable element.

15. The shape memory alloy actuation apparatus according to claim 14, wherein the flexures extend in an arc around the helical axis and are predeflected along the helical axis.

16. The shape memory alloy actuation apparatus according to any one of the preceding claims, wherein, projected along the helical axis, the extent of the shape memory alloy actuator wire is no greater than the extent of the bearing arrangement.

17. The shape memory alloy actuation apparatus according to any one of the preceding claims, wherein the at least one shape memory alloy actuator wire is perpendicular to the helical axis.

18. The shape memory alloy actuation apparatus according to any one of the preceding claims, 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.

19. The shape memory alloy actuation apparatus according to any one of the preceding claims, wherein the shape memory alloy actuation apparatus further comprises a resilient biasing element connected between the support structure and the movable element and arranged to resiliently bias the at least one shape memory alloy actuator wire.

20. The shape memory alloy actuation apparatus according to claim 19, wherein the resilient biasing element is arranged to provide a force around the helical axis.

21. The shape memory alloy actuation apparatus according to claim 19, wherein the resilient biasing element is arranged to provide a force along the helical axis.

22. The shape memory alloy actuation apparatus according to any one of claims 19 to 21, wherein the at least one shape memory alloy actuator wire comprises a single shape memory alloy actuator wire only.

23. The shape memory alloy actuation apparatus according to any one of claims 19 to 21, wherein the at least one shape memory alloy actuator wire comprises a pair of shape memory alloy actuator wires arranged on opposite sides of the helical axis so that they apply forces to the movable element perpendicular to the helical axis in opposite directions.

24. The shape memory alloy actuation apparatus according to any one of claims 1 to 18, wherein the at least one shape memory alloy actuator wire comprises at least one pair of shape memory alloy actuator wires arranged, on contraction, to drive rotation of the movable element in opposite senses around the helical axis.

25. The shape memory alloy actuation apparatus according to claim 24, wherein the pair of shape memory alloy actuator wires are arranged on opposite sides of the helical axis so that they apply forces to the movable element perpendicular to the helical axis in parallel.

26. The shape memory alloy actuation apparatus according to claim 24, wherein the pair of shape memory alloy actuator wires are arranged on the same side of the helical axis so that they apply forces to the movable element perpendicular to the helical axis in opposite directions.

27. The shape memory alloy actuation apparatus according to claim 24, wherein the pair of shape memory alloy actuator wires have an angle therebetween of less than 180 degrees as viewed along the helical axis.

28. The shape memory alloy actuation apparatus according to claim 27, wherein the pair of shape memory alloy actuator wires have an angle therebetween in the range from 70 to 110 degrees as viewed along the helical axis.

29. The shape memory alloy actuation apparatus according to any one of the preceding claims, wherein the movable element is a lens element comprising at least one lens.

30. The shape memory alloy actuation apparatus according to claim 29, wherein the helical axis is the optical axis of the lens element.

31. The shape memory alloy actuation apparatus according to claim 30, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

32. The shape memory alloy actuation apparatus according to any one of claims 29 to 31, wherein the at least one lens has a diameter of at most 20 mm.