WO2021240165A1

WO2021240165A1 - Actuation apparatus

Info

Publication number: WO2021240165A1
Application number: PCT/GB2021/051298
Authority: WO
Inventors: Oliver HART; Robin Eddington; Peter VAN WYK; Andrew Benjamin Simpson Brown; Geoffrey Farmer
Original assignee: Cambridge Mechatronics Limited
Priority date: 2020-05-27
Filing date: 2021-05-27
Publication date: 2021-12-02
Also published as: GB202218399D0; GB2610971A; CN115461663A

Abstract

An actuation apparatus is disclosed. The actuation apparatus comprises a first part (2), a second part (10), and a bearing arrangement (20) supporting the second part on the first part. The bearing arrangement is arranged to guide movement of the second part with respect to the first part. The bearing arrangement comprises a bearing having a first bearing surface (31) located on the first part and a second bearing surface (32) located on the second part, and a rolling bearing (33, 38) configured to be disposed between the first and second bearing surfaces such that the first and second bearing surfaces are spaced by a gap. One of the first bearing surface and the second bearing surface is configured such that the bearing surface has a single contact point with the rolling bearing at any one time and the other of the first bearing surface and the second bearing surface is configured such that the bearing surface has two contact points with the rolling bearing at any one time. The two contact points of the first or second bearing surface are located closer to the axis of rotation of the rolling bearing than the single contact point of the other of the first or second bearing surface, such that the distance moved by the rolling bearing relative to the first part is different to the distance moved by the second part relative to the rolling bearing.

Description

ACTUATION APPARATUS

Field

The present application relates to an actuation apparatus, in particular a shape memory alloy (SMA) actuation apparatus.

Background

It is known to use SMA wires in an actuator to drive movement of a movable element with respect to a support structure. Such SMA actuators have particular advantages in miniature devices such as smartphones. An SMA actuator may be used, for example, in an optical device such as a compact camera module (also referred to as simply a camera module) for driving movement of a lens assembly along its optical axis to effect focussing (autofocus, AF) or zoom.

Miniaturisation is an important design criteria in many applications. For example, in a camera module in which an SMA actuator moves a lens assembly along the optical axis, it is desirable to minimise the size of the module along the optical axis (i.e. the movement direction). In smartphones, for example, reducing the height of such an SMA actuator can lead to a reduction in the height of the camera module and can therefore reduce or remove the 'camera bump'. Reduced camera module height may also facilitate front-facing cameras to be positioned under the screen.

Summary

According to a first aspect of the present invention, there is provided an actuation apparatus. The actuation apparatus comprises a first part, a second part, and a bearing arrangement supporting the second part on the first part.

The bearing arrangement is arranged to guide movement of the second part with respect to the first part. The bearing arrangement comprises a total of three or more bearings, each bearing comprising a first bearing surface located on the first part and a second bearing surface located on the second part, and a rolling bearing element configured to be disposed between the first and second bearing surfaces such that the first and second bearing surfaces are spaced by a gap. One of the first bearing surface and the second bearing surface is configured such that the bearing surface has at least one contact point with the rolling bearing at any one time and the other of the first bearing surface and the second bearing surface is configured such that the bearing surface has two contact points with the rolling bearing at any one time. The two contact points of the first or second bearing surface are located closer to the axis of rotation of the rolling bearing element than the at least one contact point of the other of the first or second bearing surface, such that the distance moved by the rolling bearing element relative to the first part is different to the distance moved by the second part relative to the rolling bearing element.

The actuation apparatus is preferably a shape memory alloy (SMA) actuator assembly and/or a miniature actuator assembly.

In some embodiments, the at least one contact point may be located on a first line which extends parallel to the axis of rotation and the two contact points may be located on a second line which extends parallel to the axis of rotation.

In some embodiments, the distance between the second line and the axis of rotation may be substantially in the range of 1% to 50% of the distance between the first line and the axis of rotation.

In some embodiments, the distance between the second line and the axis of rotation may be substantially in the range of 1% to 25% of the distance between the first line and the axis of rotation.

In some embodiments, the distance between the plane of two contact points and the axis of rotation may be substantially in the range of 1% to 90% of the distance between the single contact point and the axis of rotation of the bearing.

In some embodiments, the distance between the plane of two contact points and the axis of rotation may be substantially in the range of 1% to 75% of the distance between the single contact point and the axis of rotation of the bearing. In some embodiments, the bearing arrangement may be a helical bearing arrangement arranged to guide helical movement of the second part with respect to the first part around a helical axis, and each of the three or more bearings may be a helical bearing.

In some embodiments, the helical bearing arrangement may comprise a total of five helical bearings, wherein each helical bearing may comprise only one rolling bearing element, and wherein the one bearing surface of each helical bearing may have a single contact point with the rolling bearing element at any one time.

In some embodiments, at any point in the range of the helical movement of the second part relative to the first part, the one bearing surface of each helical bearing may extend in a plane that is different to, and non-parallel with, the plane in which the one bearing surface of each of the other helical extends, wherein the plane in which a helical bearing extends may be defined as the plane parallel to the helical axis and tangential to the one bearing surface at the contact point.

In some embodiments, the five helical bearings may together provide constraints corresponding to the five degrees of freedom in a helical coordinate system.

In some embodiments, the helical bearing arrangement may comprise a total of three helical bearings, wherein each helical bearing comprises only one rolling bearing element. The first and second bearing surfaces of two helical bearings each have two contact points with the respective rolling bearing element at any one time. One bearing surface of one helical bearing may have a single contact point and the other bearing surface of the one helical bearing may have two contact points with the rolling bearing element at any one time.

In some embodiments, the three helical bearings may together provide constraints corresponding to the five degrees of freedom in a helical coordinate system. In some embodiments, the helical bearings may be spaced about the helical axis.

In some embodiments, the rolling bearing element of each helical bearing may be located in the same plane normal to the helical axis at least at the extremes of the helical movement of the second part relative to the first part.

In some embodiments, at least one of the helical bearings may comprise a plurality of rolling bearing elements.

In some embodiments, the first bearing surface in the first part may be configured such that the first bearing surface comprises the two contact points with the rolling bearing element.

In some embodiments, the first bearing surface may comprise a groove in a surface of the first part.

In some embodiments, the groove may comprise a first surface and a second surface that is non-parallel with the first surface.

In some embodiments, the first surface of the groove may extend at an acute angle to the second surface of the groove.

In some embodiments, the angle formed between the surface of the first part and one of the surfaces of the groove may be greater than 90 and less than 180 degrees, preferably about 95 degrees.

In some embodiments, the first surface may form a first edge with the surface of the first part and the second surface may form a second edge with the surface of the first part.

In some embodiments, the angle formed between the surface of the first part and the first surface of the groove may be the same as the angle formed between the inner surface of the first part and the second surface of the groove, such that the cross-section of the groove is symmetrical.

In some embodiments, the groove may have a substantially isosceles trapezium cross-section.

In some embodiments, the distance between the first and second edges may be larger than the diameter of the rolling bearing and one of the two contact points may be located on the first surface of the groove and the other of the two contacts points may be located on the second surface of the groove.

In some embodiments, the distance between the first and second edges may be smaller than the diameter of the rolling bearing and the two contact points may be located on the first and second edges of the groove.

In some embodiments, the second bearing surface in the second part may be configured such that the second bearing surface comprises the at least one contact point with the rolling bearing element, wherein the at least one contact point may be a single contact point.

In some embodiments, the second bearing surface may comprise a smooth surface.

According to a second aspect of the present invention there is provided an actuation apparatus. The actuation apparatus comprises a first part, a second, and a helical bearing arrangement supporting the second part on the first part. The helical bearing is arranged to guide helical movement of the second part with respect to the first part around a helical axis. The bearing arrangement comprises a plurality of bearings. Each bearing comprises a race configured to determine the range of motion of the second part relative to the first part. Each race comprises a first end wall at one extremity and a second end wall at the other extremity. At least one of the plurality of bearings is offset relative to at least one of the other of the plurality of bearings such that the first end wall of one of the plurality of bearings is offset in the direction of the helical axis from the first end wall of at least one of the other of the plurality of bearings. In some embodiments, the at least one bearing may be offset relative to the at least one other bearing such that the second end wall of the at least one bearing may be offset in the direction of the helical axis from the second end wall of the at least one other bearing.

In some embodiments, each of the plurality of bearings may comprise a bearing surface on the second part with a normal thereto and the bearing may be of a first type if the normal generally has a component in a first direction along the helical axis and the bearing may be of a second type if the normal generally has a component in a second, opposite direction along the helical axis; and the at least one bearing may be a bearing of the first type and the at least one other bearing may be a bearing of the second type and the at least one bearing may be offset relative to the at least one other bearing such that the first and/or second end wall is offset in the first direction if on the first part and in the second direction if on the second part.

In some embodiments, for each bearing with a first and/or second end wall comprised in the first part, when the second part is at one extremity of its range of movement, the gap between the second part and the end wall at the other extremity of the race may be smaller than the diameter of a bearing element of the bearing; and for each bearing with a first and/or second end wall comprised in the second part, when the second part is at one extremity of its range of movement, the gap between the first part and the end wall at the same extremity of the race may be smaller than the diameter of a bearing element of the bearing.

In some embodiments, for each bearing and each extremity of its range of movement, the gap may be smaller than 2rcos(0/2), where Q is the angle between the end wall and the one of the first and second parts that moves relative to the end wall and r is the radius of the bearing element.

In some embodiments, for the at least one bearing and/or the at least one other bearing, the gap at one extremity of its range of movement may be substantially the same as the gap at the other extremity of its range of movement. According to a third aspect of the present invention there is provided an actuation apparatus. The actuation apparatus comprises a first part, a second part configured to be moved with respect to the first part around a helical axis and at least one length of shape memory alloy, SMA, wire. The at least one length of shape memory alloy wire is connected between a static connector on the first part and a movable connector on the second part. When the second part is in its mid-position, the movable connector is offset from the static connector (along the helical axis) such that at least one length of shape memory alloy wire extends at an acute angle to a plane normal to the helical axis. The second part may be configured to be moved with respect to the first part within a range of movement between two extreme positions along the helical axis. The mid position of the second part may be substantially half-way between the two extreme positions along the helical axis.

In some embodiments, the static connector and the movable connector may be positioned towards first ends of the first and second parts, respectively, that define a maximum extent of the first and second parts in a first direction along the helical axis and, when the second part is in its mid-position, the movable connector may be offset from the static connector in a second, opposite direction along the helical axis.

In some embodiments, the at least one length of SMA wire may comprise first and second lengths of SMA wire; the static connector and the movable connector of the first length of SMA wire may be positioned towards the first ends of the first and second parts, respectively, and, when the second part is in its mid position, the movable connector of the first length of SMA wire may be offset from the static connector of the first length of SMA wire in the second direction; and the static connector and the movable connector of the second length of SMA wire may be positioned towards second ends of the first and second parts, respectively, that define a maximum extent of the first and second parts in the second direction along the helical axis and, when the second part is in its mid position, the movable connector of the second length of SMA wire may be offset from the static connector of the second length of SMA wire in the first direction. In some embodiments, the movable connector may be offset such that when the second part is moved to an extremity of its range of movement, the movable connector is not moved along the helical axis substantially beyond the static connector on the first part.

In some embodiments, the second part may comprise an end surface having a depressed section, the movable connector being attached to the depressed section of the second part such that when the second part is in its mid-position the movable connector may be offset from the static connector in the direction of the helical axis.

In some embodiments, the actuation apparatus may further comprise at least one spring arm, the spring arm being attached at one end to the second part and at the other end to the first part and extending around the helical axis between its ends, wherein the second part may comprise a helical surface configured to allow for a range of movement of the second part relative to the first part without the spring arm contacting the second part.

In some embodiments, the spring arm may be connected to the movable connector via a connected section connected to an end of the second part and via a kinked section configured such that the movable connector is offset relative to the static connector.

According to a fourth aspect of the present invention there is provided an actuation apparatus. The actuation apparatus comprises a first part, and a second part. A first length of SMA wire is connected to the first part via a first static connector in a first corner of the actuation apparatus and to the second part via a first moving connector in a second corner of the actuation apparatus.

A second length of SMA wire connected to the first part via a second static connector in the second corner of the actuation apparatus and to the second part via a second moving connector in the first corner of the actuation apparatus. The actuation apparatus further comprises a helical bearing arrangement supporting the second part on the first part. The helical bearing arrangement is arranged to guide helical movement of the second part with respect to the first part around a helical axis. The second length of SMA wire is spaced from the first length of SMA wire in a first direction along the helical axis. The first part or the second part or each of the first and second parts comprises a side portion between the first and second corners that generally extends in a plane orientated at an acute angle to a plane normal to the helical axis.

In some embodiments, the plane may extend in the first direction from the first corner to the second corner of the actuation apparatus.

In some embodiments, for each of the first and second lengths of SMA wire, the side portion may comprise a generally planar surface that is parallel to the length of SMA wire when the second part is at one extremity of its range of movement.

In some embodiments, the actuation apparatus may a shape memory alloy actuator.

According to a fifth aspect of the invention, there is provided a camera system comprising: an actuation apparatus an image sensor, and a lens system, wherein the lens system is mounted to one of the first part and the second part, and wherein the lens system is mounted to the other one of the first part and second part.

Brief Description of the Drawings

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

Figure 1 shows a schematic view of a shape memory alloy (SMA) actuation apparatus that is a camera;

Figure 2 shows a schematic perspective view of a bearing arrangement;

Figure 3 shows a schematic top-down cross-sectional view of a bearing arrangement;

Figures 4a to 4c show schematic top views of a known bearing arrangement at various stages in its range of movement;

Figures 5a to 5c show schematic top views of a bearing arrangement at various stages in its range of movement; Figure 6 shows a schematic top-down cross-sectional view of a shape memory alloy actuation apparatus;

Figures 7a to 7c show schematic cross-sectional side views of helical bearings located at different points of a shape memory alloy actuation apparatus;

Figures 8a to 8c show schematic side views of a shape memory alloy actuation apparatus at various positions in its range of movement, with the first part omitted for clarity; and

Figure 9 shows a schematic cross-sectional side views of a shape memory alloy actuation apparatus.

Detailed Description

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

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

An actuation apparatus 1 that is a camera is shown schematically in Fig. 1. In the present embodiment, the actuation apparatus 1 is a shape memory alloy (SMA) actuation apparatus. The SMA actuation apparatus 1 described herein is an auto-focus actuator. It will be understood by a person skilled in the art that the auto-focus SMA actuation apparatus 1 may be placed on top of an optical image stabilisation (OIS) actuator.

The SMA actuation apparatus 1 comprises a first part 2 that has an image sensor 3 mounted thereon. The first part 2 is also referred to herein as a support structure 2. The first part 2, or support structure 2, may take any suitable form, typically including a base 4 to which the image sensor 3 is fixed. The first part 2, or support structure 2, may also support an IC chip 5, described in more detail hereinafter.

The SMA actuation apparatus 1 also comprises a second part 10. The second part 10 is also referred to herein as a movable element 10. In this example, the second part 10, or movable element 10, is a lens element. The lens element 10 may comprise a lens 11, although it may alternatively comprise a plurality of lenses. The lens 11, movable 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 is a miniature device. In some examples of a miniature device, the movable element 10, lens or plurality of lenses, when provided, may have a diameter of at most 20mm, preferably at most 15mm, and more preferably at most 10mm.

Although the SMA actuation apparatus 1 in this example is a camera, that is not in general essential. It will be understood by a person skilled in the art that in some examples, the SMA actuation apparatus 1 may be an optical device in which the movable element 10 is a lens element but there is no image sensor. In other examples, the SMA actuation apparatus 1 may be a type of apparatus that is not an optical device, and in which the movable element 10 is not a lens element and there is no image sensor. Examples include apparatuses for depth mapping, face recognition, games consoles, projectors, and security scanners.

The SMA actuation apparatus 1 also comprises a bearing arrangement 20 (shown schematically in Figure 1) that supports the movable element 10 on the support structure 2. In the present embodiment, the bearing arrangement 20 is a helical bearing arrangement, although it will be understood that the bearing arrangement does not have to be helical.

The helical bearing arrangement 20 is arranged to guide helical movement of the movable element 10 with respect to the support structure 2 around a helical axis H. In the present embodiment, the helical axis H is coincident with the optical axis O. The helical movement of the movable element 10 is shown in Fig. 1 by the arrow M. Preferably, the helical motion is along a circular helix.

That is, the helical motion is along a helix with a constant radius. However, in general, any helix is possible. The pitch of the helix may be constant or vary along the helical motion. Preferably, the helical movement is generally only a small portion (less than one quarter) of a full turn of the helix.

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

Referring now to Fig. 2, the bearing arrangement 20 will now be described in more detail. The bearing arrangement 20 may be a helical bearing arrangement. The bearing arrangement 20 comprises a plurality of bearings 30. Each bearing 30 may be a helical bearing 30. Each bearing 30 comprises a pair of bearing surfaces. The pair of bearing surfaces comprises a first bearing surface 31 and a second bearing surface 32. The first bearing surface 31 is located on the support structure 2. The second bearing surface 32 is located on the movable element 10.

Each bearing 30 further comprises a rolling bearing element 33 configured to be disposed between the first bearing surface 31 and the second bearing surface 32. The rolling bearing element 33 is configured to be disposed between the first and second bearing surfaces 31, 32 such that the first and second bearing surfaces 31, 32 are separated by a gap 34, as will be described in more detail hereinafter.

Each helical bearing 30 guides the helical movement of the movable element 10 with respect to the support structure 2, as shown by the arrow M. This may be achieved by the first and second bearing surfaces 31, 32 extending helically around the helical axis H, i.e. following a path that is helical. In practical embodiments, the length of the first and second bearing surfaces 31, 32 may be short compared to the distance of the first and second bearing surfaces 31, 32 from the helical axis H, such that their shape is close to straight or even each being straight, provided that the helical bearings 30 of the helical bearing arrangement 20 guide helical movement of the movable element 10 with respect to the support structure 2.

The plural helical bearings 30 are located at different angular positions around the helical axis H, and the helical bearings 30 have different orientations so that they cooperate and maintain adequate constraints to guide the helical movement of the movable element 10 with respect to the support structure 2.

Referring to Figure 3, one of the first bearing surface 31 and the second bearing surface 32 is configured such that the bearing surface 31, 32 has a single contact point XI with the rolling bearing element 33 at any one time. The other of the first bearing surface 31 and the second bearing surface 32 is configured such that the bearings surface 31, 32 has two contact points Yl, Y2 with the rolling bearing element 33, at any one time.

The two contact points Yl, Y2 of the first bearing surface 31 or second bearing surface 32 are located closer to an axis of rotation R of the rolling bearing element 33 than the single contact point XI of the other of the first or second bearing surface 31, 32. Therefore, the distance moved by the rolling bearing element 33 relative to the support structure 2 is different to the distance moved by the movable element 10 relative to the rolling bearing element 33. In the present embodiment, the first bearing surface 31 in the support structure 2 is configured such that the first bearing surface 31 comprises two contact points Yl, Y2 with the rolling bearing element 33. Furthermore, the second bearing surface 32 in the movable element 10 is configured such that second bearing surface 32 comprises one contact point XI with the rolling bearing element 33.

Therefore, the distance moved by the rolling bearing element 33 relative to the support structure 2 is less than the distance moved by the movable element 10 relative to rolling bearing element 33, as will be explained in more detail hereinafter.

Preferably, the two contact points Yl, Y2 are located in a plane which extends parallel to the axis of rotation R of the rolling bearing 33, as will be explained in more detail hereinafter. Furthermore, the plane Y extends perpendicularly to a diametric line extending from the single contact point XI.

It will be understood that in an alternative embodiment, the first bearing surface 31 may be configured such that the support structure 2 comprises a single contact point XI with the rolling bearing element 33 and the second bearing surface 32 may be configured such that the movable element 10 comprises two contact points Yl, Y2 with the rolling bearing element 33. In such an embodiment, the distance moved by the rolling bearing element 33 relative to the support structure would be more than the distance moved by the movable element 10 relative to the rolling bearing element 33.

In a further alternative embodiment (not pictured), both the first bearing surface 31 and the second bearing surface 32 may be configured such that the support structure 2 and movable element 10 each comprises a pair of contact points with the rolling bearing element 33. The distance between one pair of contact points and the axis of rotation R may be larger than the distance between the other pair of contact points and the axis of rotation R. In such an embodiment, the distance moved by the rolling bearing element 33 relative to the one pair of contact points would be more than the distance moved by the rolling bearing element 33 relative to the other pair of contact points. Referring to Figures 2 and 3, the first bearing surface 31 on the support structure 2 comprises a groove 35. The rolling bearing element 33 is seated in the groove 35 of the first bearing surface 31. In the present embodiment, the movable element 10 is located inside the support structure 2. That is, the support structure 2 is further from the helical axis H than the movable element 10. Therefore, in the present embodiment, the groove 35 is located in an inner surface of the support structure 2.

The second bearing surface 32 on the movable element 10 comprises a smooth surface 36. The smooth surface 36 is smooth in the sense that it is a surface which is an even and regular surface. The smooth surface 36 may be free from perceptible projections, lumps, and/or indentations. The smooth surface 36 is a surface which is not a groove and one which provides only a single point of contact with the rolling bearing element 33. In other words, the second bearing surface 32 is effectively smooth across a scale of the width of the rolling bearing element 33, although being helical at a larger scale.

For example, as pictured, the smooth surface 36 is helical, being a line in cross-section which twists helically along the movement direction M, maintaining a single point of contact with the ball at any time. Alternatively and as mentioned above, in practical embodiments the length of the first and second bearing surfaces 31, 32 may be short, in which case the second bearing surface 32 may be helical or planar or close to planar or essentially planar, provided that the helical bearings 30 of the helical bearing arrangement 20 guide helical movement of the movable element 10 with respect to the support structure 2.

Referring to Figure 2, each helical bearing 30 comprises a single rolling bearing element 33. However, in alternative embodiments, at least one helical bearing 30 may comprise a plurality of rolling bearing elements 33.

In some examples, each helical bearing 30 may include a single rolling bearing element 33. In that case, each helical bearing 30 by itself does not constrain the rotational movement of the movable element 10 with respect to the support structure 2 about the single rolling bearing element 33, i.e. 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 travel of the rolling bearing element 33 to allow for the required movement between the first and second bearing surfaces 31, 32.

In other examples, at least one helical bearing 30 may include a plurality of rolling bearing elements 33. In that case, the helical bearing 30 constrains the rotation movement of the movable 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 the 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 20 may in general comprise any suitable number of helical bearings 30 with a configuration chosen to guide the helical movement of the movable element 10 with respect to the support structure 2 while constraining the movement of the movable element 10 with respect to the support structure 2 in other degrees of freedom.

Referring to Figure 3, it can be seen that there is a single contact point XI between the planar surface 32 of the second bearing surface 32 and the rolling bearing element 33. The rolling bearing element 33 rolls about its centre of rotation, which is the centre of the rolling bearing, i.e. the centre of the sphere. The distance between the single contact point XI and the centre of rotation of the rolling bearing element 33 is the radius of the rolling bearing element 33.

The groove 35 comprises a first surface 41. The first surface 41 of the groove 35 may be helical. When viewed in cross-section, perpendicular to the helical axis H, the first surface 41 of the groove 35 forms a smooth surface which may be planar, i.e. a line, as shown in Figure 3. The first surface 41 of the groove 35 twists helically along the movement direction M. The first surface 41 of the groove 35 extends at an angle to the surface of the support structure 2 into which the first bearing surface 31 is formed. Therefore, the first surface 41 of the groove 35 extends at an angle to the second bearing surface 32, 36 of the movable element 10. More specifically, the first surface 41 of the groove 35 extends at an angle to a tangent plane T to the rolling bearing element 33 at the single contact point XI.

The groove 35 further comprises a second surface 42. The second surface 42 of the groove 35 may be helical. When viewed in cross-section, perpendicular to the helical axis H, the second surface 42 of the groove 35 forms a planar surface, i.e. a line, as shown in Figure 3. The second surface 42 of the groove 35 twists helically along the movement direction M. The second surface 42 of the groove 35 extends at an angle to the surface of the support structure 2 into which the first bearing surface 31 is formed. Therefore, the second surface 42 of the groove 35 extends at an angle to the second bearing surface 32, 36 of the movable element 10. More specifically, the second surface 42 of the groove 35 extends at an angle to the tangent plane T to the rolling bearing element 33 at the single contact point XI.

The first surface 41 of the groove 35 extends at an acute angle to the second surface 42 of the groove 35. That is, the first and second surfaces 41, 42 of the groove 35 do not extend parallel to one another. Referring to Figure 3, the first and second surfaces 41, 42 converge as they extend away from the surface of the support structure 2. That is, the further a point on the first or second surface 41, 42 of the groove 35 is from the tangent plane T to the rolling bearing element 33 at the single contact point XI, the closer the point on the first or second surface 41, 42 is to the other of the first or second surface 41, 42 of the groove 35.

The groove 35 further comprises a third surface 43. The third surface 43 of the groove 35 may be helical. When viewed in cross-section, perpendicular to the helical axis H, the third surface 43 of the groove 35 forms a planar surface, i.e. a line, as shown in Figure 3. The third surface 43 of the groove 35 twists helically along the movement direction M.

The third surface 43 of the groove 35 forms the base of the groove 35.

The third surface 43 extends between the first surface 41 and the second surface 42. Preferably, the third surface 43 extends parallel to the tangent plane to the rolling bearing element 33 at the single contact point XI. Therefore, the groove 35 has a quadrilateral shaped cross-section. The third surface 43 of the groove 35 is configured such that it is spaced from the rolling bearing element 33. That is, there is no contact between the third surface 43 and the rolling bearing element 33.

As mentioned above, one end of the first surface 41 of the groove 35 meets the third surface 43 of the groove 35. At the other end of the first surface

41 of the groove 35 is a first edge 45 of the groove 35. The first edge 45 of the groove 35 is formed where the first surface 41 of the groove 35 and the inner surface of the support structure 2 meet. Similarly, one end of the second surface

42 of the groove 35 meets the third surface of the groove 35. At the other end of the second surface 42 of the groove 35 is a second edge 46. The second edge 46 of the groove 35 is formed where the second surface 42 of the groove 35 and the inner surface of the support structure 2 meet.

The angle formed between the first surface 41 or the second surface 42 of the groove 35 and the inner surface of the support structure 2 is obtuse. Therefore, the first and second surfaces 41, 42 of the groove 35 can converge.

In the present embodiment, the angle of the first edge 45 formed between the inner surface of the support structure 2 and the first surface 41 of the groove 35 is the same as the angle of the second edge 46 formed between the inner surface of the support structure 2 an the second surface 4 of the groove 35. The angle formed between the inner surface of the support structure 2 and the first surface 41 of the groove 35 may be in the range of 90 to 180 degrees. Preferably, the angle is in the range of more than 90 degrees to less than 180 degrees. The angle formed between the inner surface of the support structure 2 and the second surface 42 of the groove 35 may be in the range of 90 to 180 degrees. Preferably, the angle is in the range of more than 90 degrees to less than 180 degrees.

More preferably, the range for the angles mentioned above is in the range of 95 degrees to 175 degrees. This range of angles helps to prevent the rolling bearing element 33 becoming unconstrained as may occur outside the range due to manufacturing tolerances. The closer the angles are to 90 or 95 degrees (and hence the closer the angle between the first and second surfaces 41, 42 of the groove 35 is to 0 or 5 degrees), the smaller the range of travel of the rolling bearing element 33 along the support structure 2.

Therefore, the cross-section of the groove 35 is symmetrical.

Furthermore, the cross-section of the groove 35 is an isosceles trapezium. However, it will be understood that in alternative embodiments, the cross- section of the groove 35 may take another form. For example, in embodiments where the third surface 43 of the groove 35 is omitted, the cross-section of the groove 35 may be triangular.

The distance between the first edge 45 of the groove 35 and the second edge 46 of the groove 35 is larger than the diameter of the rolling bearing element 33. Therefore, the two contact points Yl, Y2 of the rolling bearing element 33 with the groove 35 of the first bearing surface 31 are located on the first and second surfaces 41, 42 of the groove 35. That is, the first contact point Yl of the rolling bearing element 33 with the first bearing surface 31 is on the first surface 41 of the groove 35, and the second contact point Y2 of the rolling bearing element 33 with the first bearing surface 31 is on the second surface 42 of the groove 35. For a right helical bearing 30 the above is true at any point along the range of movement of the movable element 10.

The embodiment in which the distance between the first edge 45 of the groove 35 and the second edge 46 of the groove 35 is larger than the diameter of the rolling bearing element 33 is advantageous because it reduces the distance that the rolling bearing element 33 protrudes out of the grove 35. Therefore, the overall size of the SMA actuation apparatus 1 can be reduced.

In an alternative embodiment, which is not shown in the drawings, the distance between the first edge 45 of the groove 35 and the second edge 46 of the groove 35 may be smaller than the diameter of the rolling bearing element 33. In such an embodiment, the two contact points Yl, Y2 of the rolling bearing element 33 with the groove 35 of the first bearing surface 31 are located on the first and second edges 45, 46 of the groove 35. That is, the first contact point Yl of the rolling bearing element 33 with the first bearing surface 31 is on the first edge 45 of the groove 35, and the second contact point Y2 of the rolling bearing element 33 with the first bearing surface 31 is on the second edge 46 of the groove 35. For a right helical bearing 30 the above is true at any point along the range of movement of the movable element 10.

In alternative embodiments in which both the first bearing surface 31 and the second bearing surface 32 are configured such that the support structure 2 and movable element 10 each comprises a pair of contact points with the rolling bearing element 33, both first and second bearing surfaces 31, 32 may comprise a groove as described in relation to the first bearing surface 31 above. The angle formed between the first and second surfaces 41, 42 of the groove comprised by one of the first and second bearing surfaces 31, 32 is larger than the angle formed between the first and second surfaces 41, 42 of the groove comprised by the other of the first and second bearing surfaces 31, 32.

Referring briefly to Figures 5a to 5c, which show schematic top views of a bearing arrangement 30, it can be seen that in either scenario described above, the plane or line Y in which two contact points Yl, Y2 between the rolling bearing element 33 and the first bearing surface 31 on the support structure 2 lie is closer to the centre of rotation R of the rolling bearing element 33 than the tangential plane or line T at the single contact point XI of the rolling bearing element 33 with the second bearing surface 32 of the movable element 10.

By way of comparison, Figures 4a to 4c show schematic top views of a known bearing arrangement 30 in which the rolling bearing element 33 has a single contact point with the first bearing surface 31 of the support structure 2 and a single contact point with the second bearing surface 32 of the movable element 10. In the known arrangement, each contact point of the rolling bearing element 33 is spaced from the centre of rotation R of the rolling bearing element 33 by a distance equal to the radius r of the rolling bearing element 33, as shown in Figure 4a. Therefore, as can be seen in Figures 4b and 4c, the movement of the movable element 10 relative to the rolling bearing element 33 is the same as the movement of rolling bearing element 33 relative to the support structure 2. More specifically, referring to Figure. 4b it can be seen that when the SMA actuation device 1, shown in Figure 1, is actuated, the movable element 10 is moved relative to the support structure 2. When the movable element 10 is moved by a distance equal to a quarter of the circumference of the rolling bearing element 33, shown on the drawings by an arrow labelled rrr/2, the rolling bearing element 33 is rotated about its centre of rotation R by a quarter turn due to friction at the single contact point between the rolling bearing element 33 and the second bearing surface 32 of the movable element 10.

Due to friction between the rolling bearing element 33 and the first bearing surface 31 of the support structure 2, as the rolling bearing element 33 is rotated about its centre of rotation R, the rolling bearing element 33 rolls along the first bearing surface 31 of the support structure 2 by a distance equal to a quarter of the circumference of the rolling bearing element 33, as shown by an arrow labelled nr/2.

Therefore, when the movable element 10 is moved a distance equal to a quarter of the circumference of the rolling bearing element 33, the total distance moved by the movable element 10 relative to the support structure 2 is half of the circumference of the rolling bearing element 33. Therefore, to achieve the required range of the movable element 10, the track or race formed by the first bearing surface 31 on the support structure 2 must be at least half of the required range. This necessary track length of the first bearing surface 31 on the support structure limits the minimum size of the support structure 2 and thus the overall size of the SMA actuation device 1, shown in Figure 1.

Referring briefly to Figure 4c, for completeness, it can be seen that the movable element 10 has been moved by a further distance equal to a quarter of the circumference nr/2 of the rolling bearing element 33. Furthermore, the rolling bearing element 33 has rolled along the support structure 2 by a further distance equal to a quarter of the circumference nr/2 of the rolling bearing element 33. Thus, the movable element 10 has moved by a distance equal to a half of the circumference nr of the rolling bearing element 33 relative to the rolling bearing element 33, and the rolling bearing element 33 has moved by a distance of half of the circumference nr of the rolling bearing element 33 relative to the support structure 2. Therefore, overall the movable element 10 has moved by a distance equal to the circumference of the rolling bearing element 33 relative to the support structure 2.

The effect illustrated in Figures 4a to 4c (i.e. the distance moved by the movable element relative to the rolling bearing element being equal to the distance moved by the rolling bearing element relative to the support structure) is also provided by a bearing arrangement in which the rolling bearing element sits in two similar grooves, i.e. a first groove in a first bearing surface and a second groove in a second bearing surface with the same shape as the first groove. Such grooves can be considered as reducing the 'effective radius' of the rolling bearing element (wherein the effective radius of a rolling bearing element with respect to a particular groove can be defined as the distance between the axis of rotation of the rolling bearing element and a line parallel to the axis rotation that includes the contact points between the groove and the rolling bearing element).

Referring back to Figures 5a to 5c, the bearing arrangement is shown. The first bearing surface 31 of the support structure 2 is shown by a straight line 49 for clarity, although in practice the line may be helical. The line 49 shown represents the contact points Yl, Y2 between the first bearing surface 3 of the support structure 2 and the rolling bearing element 33, as the rolling bearing element 33 is moved along the support structure 2. The line 49 may be the contact points Yl, Y2 on the first and second surfaces 41, 42 of the groove 35 of the first bearing surface 31, or alternatively, the line 49 may be the contact points Yl, Y2 along the first and second edges 45, 46 of the groove 35.

Referring to Figure 5a, the single contact point XI between the rolling bearing element 33 and the movable element 10 is located at a distance of the radius r of the rolling element 33 away from the centre of rotation R of the rolling bearing element 33. However, the plane Y in which the two contact points Yl, Y2 of the rolling bearing element 33 with the first bearing surface 31 of the support structure 2 is located at a distance of half the radius r/2 of the rolling elements 33 away from the centre of rotation R of the rolling bearing element 33.

The two different sets of contact points on the rolling bearing element 33 are shown in Figures 5a to 5c by concentric circles. The outer, or larger, circle represents the circumference of the rolling bearing element 33 and therefore the single contact points with the second bearing surface 32 of the movable element 10. The inner, or smaller, circle represents the two contact points of the rolling bearing element 33 with the first bearing surface 31 of the support structure 2, i.e. the first surface 41 or first edge 45 of the groove 35 and the second surface 42 or second edge 46 of the groove 35.

As illustrated in Figure 5a, the tangent plane in which the single contact point XI is located is double the distance than the plane in which the two contact points Yl, Y2 is located. Furthermore, as each point of the rolling bearing element 33 rotates with the same angular velocity, when the initial single contact point XI is rotated through 90 degrees, the two contact points Yl, Y2 are also only rotated through 90 degrees. However, as the radial distance between the plane Y in which the two contact points Yl, Y2 are located in and the centre of rotation R is less than the radial distance between the single contact point XI and the centre of rotation R, the movable element 10 moves more relative to the rolling bearing element 33 than the rolling bearing element 33 moves relative to the support structure 2, as I shown in Fig. 5c and will be described in more detail hereinafter.

Referring to Figure 5b, it can be seen that when the SMA actuation device 1, shown in Figure 1, is actuated, the movable element 10 is moved relative to the support structure 2. When the movable element 10 is moved by a distance equal to a quarter of the circumference of the rolling bearing element 33, shown on the drawings by an arrow labelled rrr/2, the rolling bearing element 33 is rotated about its centre of rotation R by a quarter turn due to friction at the single contact point between the rolling bearing element 33 and the second bearing surface 32 of the movable element 10. Due to friction between the rolling bearing element 33 and the first bearing surface 31 of the support structure 2, as the rolling bearing element 33 is rotated about its centre of rotation R. In the present invention, the rolling bearing element 33 rolls along the first bearing surface 31 of the support structure 2 by a distance equal to an eighth of the circumference of the rolling bearing element 33, as shown by an arrow labelled rrr/4. The rolling bearing element 33 moves less relative to the support structure 2 because the smaller radius between the centre of rotation R and the two contact points creates a shorter arc of curvature. Thus, the rolling bearing element 33 moves along the shorter arc of curvature, compared to the circumference. Therefore, the rolling bearing element 33 moves a smaller distance along the support structure 2 than the movable element 10 moves relative to the rolling element 33.

Therefore, when the movable element 10 is moved a distance equal to a quarter of the circumference of the rolling bearing element 33, the total distance moved by the movable element 10 relative to the support structure 2 is three eights of the circumference of the rolling bearing element 33. Therefore, to achieve the required range of the movable element 10, the track or race formed by the first bearing surface 31 on the support structure 2 only needs to be a third of the required range of motion of the movable element 10. This necessary track length of the first bearing surface 31 on the support structure limits the minimum size of the support structure 2 and thus the overall size of the SMA actuation device 1, shown in Figure 1. However, the length of the track required is less than the length of the track required in known bearing arrangements. Therefore, the present invention allows the support structure 2, and therefore device 1, to be reduced in height.

The height of the SMA actuator apparatus 1 is typically limited by the height of the moveable element 10 and the stroke length of the moveable element 10. Thus, for a given stroke, it is the height of the moveable element 10 that determines the minimum height of the SMA actuator apparatus 1. However, as will be explained in more detail below with reference to Figures 7a to 7c, there should also be sufficient overlap between the movable element 10 and the support structure 2 when the movable element 10 is at an extremity of its range of motion to minimise the risk of the rolling bearing element 33 escaping from the bearing 30 in certain scenarios such as an impact.

In this example, in which the support structure 2 defines (i.e. includes) the end walls 61, 62 (see Figures 7a to 7c) of the bearing 30, by reducing the length of the track required on the support structure 2, the height of the support structure 2 and hence the height of the SMA actuator apparatus 1 can be reduced. Alternatively, or additionally, the overlap described in the previous paragraph can be increased.

In other examples, e.g. those in which the moveable element 10 includes one or both of the end walls of the bearing 30, the height of the SMA actuator apparatus 1 can be reduced and/or the overlap can be increased by instead reducing the length of the track required on the moveable element 10.

Generally speaking, the 'gearing' described herein provides a way of adjusting the track lengths of the (helical) bearings and, thus, enabling the properties of a particular SMA actuator apparatus 1 to be advantageously adjusted.

Referring briefly to Figure 5c, for completeness, it can be seen that the movable element 10 has been moved another by a further distance equal to a quarter of the circumference rrr/2 of the rolling bearing element 33.

Furthermore, the rolling bearing element 33 has rolled along the support structure 2 by a further distance equal to an eighth of the circumference rrr/4 of the rolling bearing element 33. Thus, the movable element 10 has moved by a distance equal to a half of the circumference nr of the rolling bearing element 33 relative to the rolling bearing element 33, and the rolling bearing element 33 has moved by a distance of a quarter of the circumference rrr/2 of the rolling bearing element 33 relative to the support structure 2. Therefore, overall the movable element 10 has moved by a distance equal to one and a half circumferences of the rolling bearing element 33 relative to the support structure 2.

The exemplary embodiment described above has reduced the required size of the track or race formed by the first bearing surface 31 of the support structure 2 by 25%. However, it will be understood that by moving the plane in which the two contact points Yl, Y2 are located closer to the centre of rotation R of the rolling bearing element 33 will further reduce the required size of the track and thus support structure 2, and thus overall device 1, without compromising on the range of motion of the movable element 10.

In some embodiments, the distance between the plane Y in which the two contact points Yl, Y2 are located and the centre of rotation R is substantially in the range of 1% to 75% of the distance between the single contact point XI and the centre of rotation R of the rolling bearing element 33. That is, the plane Y in which the two contact points Yl, Y2 are located is at a distance of less than 75% of the radius from the centre of rotation R.

In some embodiments, the distance between the plane Y in which the two contact points Yl, Y2 are located and the centre of rotation R is substantially in the range of 1% to 50% of the distance between the single contact point XI and the centre of rotation R of the rolling bearing element 33. That is, the plane Y in which the two contact points Yl, Y2 are located is at a distance of less than 50% of the radius from the centre of rotation R.

In some embodiments, the distance between the plane Y in which the two contact points Yl, Y2 are located and the centre of rotation R is substantially in the range of 1% to 25% of the distance between the single contact point XI and the centre of rotation R of the rolling bearing element 33. That is, the plane Y in which the two contact points Yl, Y2 are located is at a distance of less than 25% of the radius from the centre of rotation R.

The effect illustrated in Figures 5a to 5c (e.g. the distance moved by the movable element 10 relative to the rolling bearing element 33 being greater than the distance moved by the rolling bearing element 33 relative to the support structure 2) is also provided by a bearing arrangement 30 in which the rolling bearing element 33 sits in two dissimilar grooves 35, e.g. a first groove in a first bearing surface and a second groove in a second bearing surface that is shallower than the first groove. As explained above, the effective radius of a rolling bearing element 33 with respect to a particular groove can be defined as the distance between the axis of rotation of the rolling bearing element 33 and a line parallel to the axis rotation that includes the contact points between the groove and the rolling bearing element). In such a bearing arrangement, the effective radius of the rolling bearing element with respect to the second groove is reduced by a greater amount than the effective radius of the rolling bearing element for the second groove, thereby still providing gearing as illustrated in Figures 5a to 5c. As will be appreciated, in such a bearing arrangement, each of the first and second bearing surfaces have two contact points with the rolling bearing element.

Referring now Figure 6, a schematic top-down cross-sectional view of a shape memory alloy actuation apparatus 50 is shown. The shape memory alloy actuation apparatus 50 is generally the same as the shape memory alloy actuation apparatus 1 described above and therefore, a detailed description thereof will be omitted. Likewise, features of the shape memory alloy actuation apparatus 50 similar to features of the shape memory actuation apparatus 1 described above will retain their terminology and reference numbers.

The shape memory alloy actuation apparatus 50 comprises a support structure 2 and a movable element 10. The shape memory alloy actuation apparatus 50 further comprises a helical bearing arrangement 20 supporting the movable element 10 on the support structure 2 and arranged to guide helical movement of the movable element 10 with respect to the support structure 2 around a helical axis H.

Referring to Figure 6, the helical bearing arrangement 20 comprises a plurality of helical bearings 30 (i-v). The helical bearings 30 are preferably the same as the helical bearings 30 described above in relation to Figures 2 to 5c. However, they may be another type of helical bearing 30.

Similarly to the helical bearings 30 described above, the helical bearings 30i of the present embodiment comprises a first bearing surface 31 on one of the support structure 2 and the movable element, and a second bearing surface 32 on the other of the support structure 2 and the movable element 10. The first and second bearing surfaces 31, 32 extend around the helical axis H in a helical fashion. That is, the first and second bearing surfaces 31, 32 form a race 39 which extends helically about the helical axis H. The angle at which the race 39 extends relative to the helical axis H is the helical angle a of the race 39, best shown in Fig. 2. Therefore, the race 39 extends in a helical bearing plane h. In addition, each helical bearing 30i comprises one rolling bearing element 33 disposed between the bearing surfaces 31, 32. Throughout its range of movement the at least one rolling bearing element 33 moves helically along the helical bearing plane h, i.e. the helical path around the helical axis H, the helical bearing plane being most clearly illustrated in Fig. 2. Thus, the centre of rotation R of the rolling bearing element 33 traces the helical bearing plane h.

In the present embodiment, the support structure 2 comprises the first bearing surface 31. The first bearing surface 31 of the support structure 2 preferably comprises a groove 35, as described above in relation to Figures 1 to 5c. Furthermore, in the present embodiment, the movable element 10 comprises the second bearing surface 32. Preferably, the sec ond bearing surface 32 of the movable element 10 is smooth.

It will be appreciated that in alternative embodiments, the first bearing surface 31 of the support structure 2 may be smooth, and/or the second bearing surface 32 of the movable element 10 may comprise a groove 35, as described above. Alternatively, the first bearing surface 31 comprises a groove 35 may be on the movable element 10, and/or the second bearing surface 32 which is smooth may be on the support structure 2.

Referring to Figure 6, the second bearing surface 32 of at least one of the helical bearings 30i extends in a first plane A. Furthermore, the second surface 32 of at least one other helical bearing 30M extends in a second plane B. The second plane B extends at an angle to the first plane A. That is, the first plane A and second plane B do not extend parallel to one another.

In some embodiments, the plane A in which a helical bearing 30i extends at any cross-sectional point along the helical axis H is parallel to the helical axis H. That is, the plane A is defined by a tangential line extending from the contact point XI between the at least one bearing element 33 and the second bearing surface 32 on the movable element 10. That is, the helical bearing 30i extends in a tangential plane to the contact point XI between the rolling bearing element 33 and the movable element 10.

More specifically, the plane in which a helical bearing 30 extends at any point along the helical axis H is defined by the tangential plane (A-E) in which the contact point XI between the rolling bearing element 33 and the moveable element 10 is located. That is, the plane in which the second bearing surface 32 of the helical bearing 30 extends at any point along the helical axis H is defined by the tangential plane extending from the contact point XI between the at least one bearing element 33 and the second bearing surface 32 on one of the support structure 2 or the movable element 10. Therefore, the tangential plane A in which the helical bearing 30 extends will vary as the position of the rolling bearing element 33 changes along the helical axis H, due to the rolling bearing element 33 moving in a helical manner, i.e. vertically and circumferentially as the movable element 10 is actuated.

Each of the plurality of helical bearings 30 in the helical bearing arrangement 20 extends helically around the helical axis H. Furthermore, as mentioned above, each of the plurality of helical bearings 30 comprises a race 39 which extends in a helical bearing plane h with a helical angle a. The helical angle a is the angle between the helical bearing plane h in which the race 39 extends and the helical axis H. In the embodiments described thus far, each of the plurality of helical bearings 30 extends in a helical bearing plane h having the same helical angle a.

Therefore, the first plane A and second plane B do not extend parallel to one another at any point along the helical axis H, i.e., in any plane perpendicular to the helical axis H. That is, the first plane A and second plane B extend at an angle to one another at each point along the helical axis H in any given plane which is perpendicular to the helical axis H.

Preferably, the plane of the second bearing surface 32 in each of the helical bearings 30 extends at an angle to the plane of the second bearing surface 32 of each of the other helical bearings 30. Therefore, none of the second bearing surfaces 32 of the helical bearings 30 of the helical bearing arrangement 20 extend parallel to one another.

The helical bearings 30 of the helical bearing arrangement 20 may be evenly spaced about the helical axis H. Alternatively, the helical bearings 30 of the helical bearing arrangement 20 may be unevenly spaced about the helical axis H. The helical bearing arrangement 20 preferably comprises five helical bearings 30i, 30M, 30iii, 30iv, 30v. Having five helical bearings 30 arranged such that not two bearings extend parallel to one another allows for motion of the movable element 10 to be constraint to helical motion about the helical axis H only. However, it will be appreciated that the bearing arrangement 20 may comprise a different number of helical bearings 30.

In some embodiments, the rolling bearing element 33 of each helical bearing 30 is located in the same plane normal to the helical axis H, as shown in Figure 6. However, it will be appreciated that in an alternative embodiment, the rolling bearing element 33 of at least one of the helical bearings 30 is located in a plane normal to the helical axis H which is offset in the direction of the helical axis H from the plane in which the rolling bearing element 33 of at least one of the other helical bearings 30 is located.

In some embodiments, at least one of the helical bearings 30 may comprises a plurality of bearing elements 33. Furthermore, at least one of the rolling bearing elements 33 of at least one of the helical bearings 33 may comprise a rolling bearing 33.

Referring now Figure 7a to 7c, a schematic cross-sectional side views of an actuation apparatus 60 is shown. In the present embodiment, the actuation apparatus 60 is a shape memory alloy (SMA) actuation apparatus. The shape memory alloy actuation apparatus 60 is generally the same as the shape memory alloy actuation apparatuses 1, 50 described above and therefore, a detailed description thereof will be omitted. Likewise, features of the shape memory alloy actuation apparatus 60 similar to features of the shape memory actuation apparatuses 1, 50 described above will retain their terminology and reference numbers. The shape memory alloy actuation apparatus 60 comprises a support structure 2 and a movable element 10. The shape memory alloy actuation apparatus 60 further comprises a helical bearing arrangement 20 supporting the movable element 10 on the support structure 2 and arranged to guide helical movement of the movable element 10 with respect to the support structure 2 around a helical axis H.

The bearing arrangement 20 comprises a plurality of bearings 30a, 30b, 30c, as shown in Figures 7a to 7c. The bearing arrangement illustrated by Figures 7a to 7c comprises three helical bearings 30. The bearings 30 are spaced in three of the four corners of the apparatus 1. However, it will be understood that in alternative embodiments the number of bearings 30 and the spacing between each of them may differ.

Each bearing 30 comprises a race 39. The race 39 of a bearing 30 is configured to determine the range of motion of the movable element 10 relative to the support structure 2.

The race 39 comprises a first bearing surface 31 on one of the support structure 2 and the movable element 10, and a second bearing surface 32 on the other of the support structure 2 and the movable element 10. In the present embodiment, the first bearing surface 31 is on the support structure 2 and the second bearing surface 32 is on the movable element 10. The first and second bearing surfaces 31, 32 may be as described above.

Each bearing 30 comprises a bearing element 33. The rolling bearing element 33 contacts the first bearing surface 31 on the support structure 2 and the second bearing surface 32 on the movable element 10.

Each race 39 comprises a first end wall 61. The first end wall 61 is located at one extremity of the race 39. In the present example, the first end wall 61 is located at the top end 63 of the race 39. Furthermore, the first end wall 61 is located on the support structure 2. The first end wall 61 may be integrally formed with the support structure 2. Each race 39 may further comprise a second end wall 62. The second end wall 62 is located at the other extremity of the race 39. The second end wall 62 is located at the bottom end 64 of the race 39. Furthermore, the second end wall 62 is located on the support structure 2. The second end wall 62 may be integrally formed with the support structure 2.

It will be appreciated that in an alternative embodiment, first and second end walls 61, 62 may alternatively or additionally be located on the moveable element 10.

The rolling bearing element 33 spaces the movable element 10 from the support structure 2 and, in particular, the first end wall 61 and the second end wall 62. Therefore, a gap exists between the second bearing surface 32 of the movable element 10 and the end walls 61, 62 of the support structure 2.

The first and second end walls 61, 62 act as rolling bearing element stops to prevent the rolling bearing element 33 from popping out of the bearing 30 in an impact scenario. The height of the SMA actuator apparatus 1, as explained above, is typically limited by the height of the moveable element 10 and the stroke of the moveable element 10. Thus, as the moveable element 10 moves to an extremity of its range of motion, the moveable element 10 extends beyond the support structure 2.

However, the moveable element 10 must be large enough such that the gap between the end of the moveable element 10 overlapped by the support structure 2, i.e. not extending from the support structure 2, and the end of the race 39 on the support structure 2 is small enough to retain the rolling bearing element 33 in an impact scenario.

At least one of the plurality of bearings 30 is offset relative to at least one of the other of the plurality of bearings such that the first end wall 61 of one of the plurality of bearings is offset in the direction of the helical axis from the first end wall of at least one of the other of the plurality of bearings. Each of the plurality of bearings 30 comprises a bearing surface 32 on the second part 10 with a normal extending thereto. The bearing 30 is of a first type if the normal generally has a component that extends in a first direction along, or parallel to, the helical axis H (e.g. upwards). The bearing 30 is of a second type if the normal generally has a component extending in a second direction, opposite the first direction, along, or parallel to, the helical axis H (e.g. downwards).

The at least one bearing 30 may be a bearing of the first type, and the at least one other bearing 30 may be a bearing of the second type. Furthermore, the at least one bearing 30 may be offset relative to the at least one other bearing 30 such that the first and/or second end wall 61, 62 is offset in the first direction if on the first part and in the second direction if on the second part.

Referring to Figures 7a and 7c, it can be seen that in the first race 39a and the third race 39c, the movable element 10, or second part 10, is above the support structure 2 in the direction of the helical axis H. Therefore, the normal component to the bearing surface 32 on the moveable element 10 is in the second direction, downwards along the helical axis H. Thus, the first and third bearings 30a, 30c are of a second type. As a result, purely downward vertical movement of the movable element 10 relative to the support structure 2 is prevented. Referring to Figure 7b, it can be seen that in the second race 39b, the support structure 2 is above the movable element 10 in the direction of the helical axis H, i.e. the opposite to the first and third races 39a, 39c. Therefore, the normal component to the bearing surface 32 on the moveable element 10 is in the first direction, upwards along the helical axis H. Thus, the second bearing 30b is of the first type. As a result, purely upward vertical movement of the moveable element relative to the support structure 2 is prevented.

The races 39a, 39b, 39c extend at an angle to the helical axis H known as the helical bearing angle Q. Known races usually extend parallel to the helical axis H to allow movement between the movable element 10 and the support structure 2. An advantage of having the first race 39a and third race 39c extend at an angle such that the movable element 10 is above the support structure 2 is that the gap between the first end wall 61 of the support structure 2 and the end of the movable element 10 when the movable element is at the bottom of its range of motion is smaller than the same condition in a vertical race arrangement.

However, as a result of this angling of the first and third races 39a, 39c, the gap between the second end wall 62 of the support structure 2 and the end of the movable element 10 when the movable element 10 is at the top of its range of motion is larger than the same condition in a vertical race.

The converse is true for the second race 39b. An advantage of having the second race 39b extend at an angle such that the support structure 2 is above the movable element 10 the gap between the second end wall 62 of the support structure 2 and the end of the movable element 10 when the movable element is at the bottom of its range of motion is smaller than the same condition in a vertical race arrangement.

However, as a result of this angling of the second 39b, the gap between the first end wall 61 of the support structure 2 and the end of the movable element 10 when the movable element 10 is at the top of its range of motion is larger than the same condition in a vertical race.

As shown in Figures. 7a to 7c, at least one of the plurality of bearings 30b is offset relative to at least one of the other plurality of bearings 30a, 30c such that the first end wall 61b of one of the plurality of bearings 30b extends in a plane spaced in the direction of the helical axis H from the plane in which the first end wall 61a, 61c of at least one of the other of the plurality of bearings 30a, 30c extends.

Furthermore, at least one of the plurality of bearings 30b is offset relative to at least one of the other bearings 30a, 30c such that the second end wall 62b of the at least one of the plurality of bearings 30b extends in a plane spaced in the direction of the helical axis H from the plane in which the second end wall 62a, 62c of at least one of the other of the plurality of bearings 30a, 30c extends.

That is, each of the end walls 61, 62 may be generally planar. The first and/or second end wall 61, 62 of the at least one bearing 30 may extend in a plane that is spaced in the direction of the helical axis from the plane in which the first and/or second end wall 61, 62 of the at least one other bearing extends.

One of the parts (e.g. the first part 2) may comprise each of the first and second end walls 61, 62. For each of the plurality of bearings 30, the other of the parts (e.g. the second part 10) may comprise a bearing surface whose extent along the helical axis H corresponds to the extent of the part 10 along the helical axis H.

By offsetting at least one of the helical bearings 30b relative to at least one of the other helical bearings 30a, 30c, the gap 65 between the movable element 10 and the first end wall 61 or second end wall 62 can be reduced. Furthermore, offsetting the bearings 30 mean that the overall height of the movable element 10 does not need to be increased and thus, the overall size of the apparatus 1 can be reduced.

As shown in Figures 7a and 7c, the race 39a, 39c on the support structure 2 is moved downwards in the direction of the helical axis H, and as shown in Figure 7b, the race 39b on the support structure 2 is moved upwards in the direction of the helical axis H. as will be explained in more detail hereinafter. Therefore, the likelihood the rolling bearing element 33 escaping from the race 39 through the gap 65 during an impact is reduced. Furthermore, by offsetting the races 39, the gaps 65 created at either extremity of the races 39 can be made the same size. Therefore, the likelihood of a bearing element 33 escaping one race 39 is not larger than the other. Consequently, it is preferred that each race 39 is offset either up or down by the same amount compared to the vertical arrangement in order to achieve equal gap sizes at both ends of each race 39 when the movable element 10 is at the top or bottom of its range of motion. For a bearing 30 with a first part 2, or support structure, comprising a first end wall 61 and/or a second end wall 62, when the second part 10, or movable element, is at one extremity of its range of movement, the gap 65 between the movable element 10 and the end wall 61, 62 at the other extremity of the race 39 is smaller than the diameter of a bearing element 33 of the bearing 30.

Furthermore, a bearing 30 with a second part 10, or movable element, comprising a first end wall 61 and/or a second end wall 62, when the movable element 10 is at one extremity of its range of movement, the gap 65 between the first part 2, or support structure, and the end all 61, 62 at the same extremity of the race 39 is smaller than the diameter of a bearing element 33 of the bearing 30.

That is, the race 39 is configured such that when the movable element 10 is at one extremity of its range of movement, the gap 65 between the movable element and one of the end walls 61, 62 of the race 69 at the opposite end of the race 39 to the movable element 10 is smaller than the diameter of the rolling bearing element 33. Furthermore, the gap 65 between the movable element 10 when it is at one extremity of its range of movement and the end wall 61, 62 at the other extremity of the race 39 should be substantially smaller than the diameter of the rolling bearing element 33 in order to maintain contact between the movable element 10 and the rolling bearing element 33. Preferably, for each bearing 30, and each extremity of its range of movement, the gap is smaller than 2rcos(0/2), where Q is the angle between the end wall and the one of the support structure or movable element that moves relative to the end wall 61, 62, and r is the radius of the rolling bearing element.

As previously mentioned, for the at least one bearing 30 and/or the at least one other bearing 30, the gap 65 at one extremity of its range of movement is substantially the same as the gap 65 at the other extremity of its range of movement.

Contact between the movable element 10 and the rolling bearing element 33 is desirable because if there is a case where there is no contact then the movable element 10 is no longer constrained by the bearing 30 and can tilt. Tilt of the movable element 10 can cause other issues in the SMA actuator apparatus 1 such as clashing of delicate parts of the apparatus 1 during impact scenarios.

The schematic illustrations in Figures 7a to 7c show the moveable element 10 at the lower extremity of its range. However, the rolling bearing element 33 is shown at the top of the race 39 to illustrate that the rolling bearing element 33 is too large to fit through the gap between the movable element 10 and the first end wall 61 (or second end wall 62).

Referring now Figures 8a to 8c, schematic side views of an actuation apparatus 70 is shown. In the present embodiment, the actuation apparatus 70 is a shape memory alloy actuation apparatus. The shape memory alloy actuation apparatus 70 is generally the same as the shape memory alloy actuation apparatuses 1, 50, 60 described above and, therefore, a detailed description thereof will be omitted. Likewise, features of the shape memory alloy actuation apparatus 70 similar to features of the shape memory actuation apparatuses 1, 50, 60 described above will retain their terminology and reference numbers.

The shape memory alloy actuation apparatus 70 comprises a support structure 2, shown in Figure 1, a movable element 10 configured to be moved helically with respect to the support structure 2 around a helical axis H.

The shape memory alloy actuation apparatus 70 further comprises at least one length of shape memory alloy wire 71. The at least one length of shape memory alloy wire 71 is connected between a static connector 72 on the support structure 2 and a movable connector 73 on the movable element 10.

As illustrated in Figure 8a, when the movable element 10 is in its mid position, the movable connector 73 is offset from the static connector 72 such that the at least one length of shape memory alloy wire 71 extends at an acute angle to a plane normal to the helical axis H. The movable connector 73 is located closer to the centre of the support structure 2 in the direction of the helical axis H than the static connector 72. That is, the movable connector 73 is offset towards the centre of the support structure 2 in the direction of the helical axis H. Therefore, when the movable element 10 is in its mid-position, the movable connector 73 is located below the static connector 72 along the helical axis H.

That is, the static connector 72 and the movable connector 73 are positioned towards first ends of the support structure 2 and movable element 10, respectively. The first (e.g. upper) ends of the support structure 2 and the movable element 10 define a maximum extent of the support structure 2 and movable element 10 in a first direction along the helical axis H. When the movable element 10 is in its mid-position, the movable connector 73 is offset from the static connector 72 is a second, opposite direction along the helical axis H.

The movable element 10 further comprises an end surface 75. The end surface 75 comprises a depressed section 76. The movable connector 73 is attached to the depressed section 76 of the movable element 10. Therefore, when the movable element 10 is in its mid-position, the movable connector 73 is offset from the static connector 72 in the direction of the helical axis H.

Furthermore, the movable connector 73 is offset such that when the movable element 10 is moved to an extremity of its range of movement, the movable connector 73 is not moved along the helical axis substantially beyond the static connector 72 on the support structure 2.

The shape memory alloy actuation apparatus 70 comprises at least one spring arm 77. The spring arm 77 is attached at one end 81 to the movable element 10. The spring arm 77 is attached at the other end 82 to the support structure 2. The spring arm 77 extends around the helical axis H between its ends. The spring arm 77 may extend in an arc around the helical axis H.

In addition, the spring arm 77 is connected to the movable connector 73 via a connected section connected to an end of the movable part 10. Furthermore, the spring arm 77 comprises a kinked section 78. Preferably, the kinked section 78 of the spring arm 77 is located proximate to the movable element end 81 of the spring arm 77. The spring arm 7 is connected to the movable connector 73 via the connected section and the kinked section to the end of the movable element 10.

The kinked section 78 is configured such that the movable connector 73 is offset relative to the static connector 72. That is, the spring arm 77 kinks towards the centre of the support structure 2 in the direction of the helical axis H. Therefore, kinked section 78 offsets the movable connector 73 relative to the static connector 72.

The spring arm 77, the connected section, and the kinked section 78 may be integral. Preferably, each connector 72, 73 is a crimp.

The kinked section 78 of the spring arm 77 is configured such that when the movable element 10 is moved to an extremity of its range of movement, as shown in Figures 8b and 8c, the movable connector 73 is not moved substantially beyond the static connector 72 on the support structure 2. That is, the movable connector 73 does not move completely past the static connector 72 when the movable element 10 is moved to the extremities of its range.

The description of the shape memory alloy actuation apparatus 70 has referred to a single length of SMA wire 71a connected between a single static connector 72a and a single movable connector 73a which is arranged on one side, for example upper side, of the apparatus 70. That is, one static connector 72a on an upper surface of the support structure 2 and one movable connector 73a on an upper surface of the movable element 10. However, the arrangement on one side of the apparatus 70 may by itself only be able to move the movable element 10 away from its mid-position in one direction.

Therefore, a second arrangement of an SMA wire 71b connected between a static connector 72b and a movable connector 73b on the opposite side, for example lower side, of the apparatus 70.

That is, the at least one length of SMA wire 71 comprises a first length 71a of SMA wire 71 and a second length 72a of SMA wire. The static connector 72 and the moveable connector 73 of the first length of SMA wire 71 are positioned towards the first (e.g. upper) ends of the support structure 2 and the movable element 10, respectively. When the movable element 10 is in its mid position, the movable connector 73 of the first length 71a of SMA wire 71 is offset from the static connector 72 of the first length 71a of SMA wire 71 in the second direction.

The static connector 72 and the movable connector 73 of the second length 71b of SMA wire 71 are positioned towards second (e.g. lower) ends of the support structure 2 and the movable element 10, respectively. The second ends of the support structure 2 and the movable element 10 define a maximum extent of the support structure 2 and the movable element 10 in the second direction about the helical axis H. When the movable element 10 is in its mid position, the movable connector 73 of the second length 71b of SMA wire 71 is offset from the static connector 72 of the second length 71b of SMA wire 71 in the first direction.

It will be appreciated that the first and second lengths 71a, 71b of SMA wires 71 can be spaced from each other along the helical axis. The first and second lengths 71a, 71b of SMA wires 71 may be configured to apply torques to the movable element 10 in opposite senses about the helical axis H.

Referring briefly to Figure 8b, the movable element 10 is shown moved to the lowest extremity of its range. In this position, the upper movable connector 73a is moved downwards away from the upper static connector 72a, and the lower movable connector 73b is moved downwards towards the lower static connector 72b. When the movable element 10 is in its lowest position, the lower movable connecter 73b is in the same plane which extends perpendicularly to the helical axis H as the lower static connector 72b.

Referring briefly to Figure 8c, the movable element 10 is shown moved to the highest extremity of its range. In this position, the upper movable connector 73a is moved upwards towards from the upper static connector 72a, and the lower movable connector 73b is moved upwards away from the lower static connector 72b. When the movable element 10 is in its highest position, the upper movable connector 73b is in the same plane which extends perpendicularly to the helical axis H as the upper static connector 72b.

Therefore, as the range of movement of the movable connectors 73 does not extend beyond the static connector 72 located on the upper surface of the structure support 2, the height required by the apparatus 70 is reduced because the movable connector 73 does not move further away from the centre of the support structure 2 than the static connector 72 in the direction of the helical axis H.

The movable element 10 further comprises a helical surface 86. The helical surface 86 is configured to allow for movement of the movable element 10 relative to the support structure 2 without the spring arm 77 contacting the movable element 10 throughout the stroke length.

The at least one spring arm 77 may comprise a first spring arm 77a and a second spring arm 77b. The movable element 10 may comprise corresponding first and second helical surfaces 86a, 86b. The first helical surface 86a and second helical surface 86b may form part of the first and second ends of the movable element 10. The first end may define a maximum extent of the movable element 10 in a first direction along the helical axis and the second end may define a maximum extent of the movable element 10 is a second, opposite direction along the helical axis H.

That is, the upper helical surface 86a may be configured such that it extends parallel to the spring arm 77a when the movable element 10 is in its highest position. The lower helical surface 86b may be configured such that it extends parallel to the spring arm 77b when the movable element 10 is in its lowest position. In some embodiments, the spring arm 77 may contact the helical surface 86 when the movable element 10 is at one extremity of its range of motion.

The helical surfaces 86 may extend to an inner perimeter of the movable element 10. Therefore, the area on the inner surface of the movable element 10 can be maximised, which is advantageous e.g. for adhering the lenses thereto. In addition, the movable connector 73 is attached to the movable element 10 such that the movable connector 73 is as close to the static connector 72 when the movable element 10 is in its mid-position without passing the static connector 72 when the movable element 10 is at one of its extremities. Therefore, the movable connector 73 sweeps through the smallest area possible such that a larger area of the movable element 10 can be used to attached a device, such as a lens, to the movable element 10.

Referring now to Figure 9, a schematic cross-sectional side views of an actuation apparatus 90 is shown. In the present embodiment, the actuation apparatus 90 is a shape memory alloy actuation apparatus. The shape memory alloy actuation apparatus 90 is generally the same as the shape memory alloy actuation apparatuses 1, 50, 60, 70 described above and therefore, a detailed description thereof will be omitted. Likewise, features of the shape memory alloy actuation apparatus 90 similar to features of the shape memory actuation apparatuses 1, 50, 60, 70 described above will retain their terminology and reference numbers.

The shape memory alloy actuation apparatus 90 comprises a support structure 2, a movable element 10, shown in Figure 1, and a helical bearing arrangement 20 supporting the movable element 10 on the support structure 2 and arranged to guide helical movement of the moveable element 10 with respect to the support structure 2 around a helical axis H.

The shape memory alloy actuation apparatus 90 further comprises a first length 71a of SMA wire 71 connected to the support structure 2 via a first static connector 72a in a first corner of the actuation apparatus 90 (e.g. on the left in the drawing). The first length 71a of SMA wire 71 is also connected to the movable element 10 via a first movable connector 73a in a second corner of the actuation apparatus 90 (e.g. on the right in the drawing).

The shape memory alloy actuation apparatus 90 further comprises a second length 71b of SMA wire 71 connected to the support structure via a second static connector 72b in the second corner of the actuation apparatus 90 and to the movable element 10 via a second moving connector 73b in the first corner of the actuation apparatus 90. The second length 71b of SMA wire 71 is spaced from the first length 71a of SMA wire 71 in a first direction along the helical axis H (e.g. downwards in this instance).

The first length 71a of SMA wire 71 may drive rotation of the movable element 10 relative to the support structure 2 in a first sense (e.g. clockwise) about the helical axis H, and the second length 71b of SMA wire 71 may drive rotation of the movable element 10 relative to the support structure 2 in a second, opposite sense (e.g. anti-clockwise) about the helical axis H.

The support structure 2 or movable element 10, or each of the support structure 2 and the movable element 10, comprises a side portion between the first and second corners that generally extends in a plane oriented at an acute angle to a plane normal to the helical axis H.

The side portion may be arranged between the first and second lengths 71a, 71b of SMA wire 71 at least at an extreme of the range of movement of the movable element 10. This allows the x-y footprint of the actuator assembly to be reduced. The angled structure of the support structure 2 and/or movable element 10 may ensure that movement of the first and second lengths 71a, 71b of SMA wire 71 is not impeded at the extreme of the range of movement of the movable element 10.

The angled support structure 2 allows for more material to be used which in turn makes the support structure 2 stiffer and more reliable. Furthermore, by having the support structure 2 on an angle, the most can be made of the space between the static connectors 72a, 72b without impeding the movement of the movable connectors 73a, 73b. For example, when the movable part 10 moves upwards in figure 9 (e.g. upon contraction of the first length 71a), the support structure 2 does not impede movement of the movable connector 73b. When the movable part 10 moves downward in figure 9 (e.g. upon contraction of the second length 71b), the support structure 2 does not impede movement of the movable connector 73a. The plane extending at an acute angle to a plane normal to the helical axis H may extend in the first direction from the first corner to the second corner of the actuation apparatus 90 (e.g. downwards from left to right).

The side portion comprises a generally planar surface that extends parallel to the length of SMA wire 71, whether it is the first length 71a or second length 71b of SMA wire 71, when the movable element 10 is at one extremity of its range of movement.

Preferably, as mentioned throughout the description, the actuation apparatus is a shape memory alloy actuator apparatus, although this disclosure is not limited thereto.

In all of the examples above, the SMA actuator wires 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 and supplies the drive signals to the SMA actuator wires. The control circuit receives an input signal representing a desired position for the movable element 10 along the optical axis O and generates drive signals selected to drive the movable element 10 to the desired position. The drive signals may be generated using a resistance feedback control technique, in which case the control circuit measures the resistance of the lengths of SMA actuator wires and uses the measured resistance as a feedback signal to control the power of the drive signals.

Such a resistance feedback control technique may be implemented as disclosed in any of WO 2013/175197, WO 2014/076463, WO 2012/066285, WO 2012/020212, WO 2011/104518, WO 2012/038703, Wo 2010/089529, or WO 2010/029316, each of which is incorporated herein by reference.

As an alternative, the control circuit may include a sensor which senses the position of the movable element 10, for example a Hall sensor which senses the position of a magnet fixed to the movable element 10. In this case, drive signals use the sensed position as a feedback signal to control the power of the drive signals. 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 the 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.

The actuation apparatus may be any type of actuator that comprises a first part and a second part movable with respect to the first part.

The actuation apparatus need not be an SMA actuation apparatus and may be a voice coil motor (VCM) actuation apparatus or any other type of actuation apparatus.

The actuation apparatus may be, or may be provided in, any one of the following devices: a smartphone, a protective cover or case for a smartphone, a functional cover or case for a smartphone or electronic device, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, a camera with folded optics, an image capture device, an array camera, a 3D sensing device or system, a servomotor, a consumer electronic device (including domestic appliances such as vacuum cleaners, washing machines and lawnmowers), a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader (also known as an e-book device), a computing accessory or computing peripheral device (e.g. mouse, keyboard, headphones, earphones, etc.), an audio device (E.g. headphones, headset, earphones, etc.), a security system, a gaming system, a gaming accessory (e.g. controller, headset, a wearable controller, joystick, etc.), a robot or robotics device, a medical device (e.g. an endoscope), an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device (e.g. a watch, a smartwatch, a fitness tracker, etc.), a drone (aerial, water, underwater, etc.), an aircraft, a spacecraft, a submersible vessel, a vehicle, and an autonomous vehicle (e.g. a driverless car), a tool, a surgical tool, a remote controller (e.g. for a drone or consumer electronic device), clothing (e.g. a garment, shoes, etc.), a switch, dial or button (e.g. a light switch, a thermostat dial, etc.), a display screen, a touchscreen, a flexible surface, and a wireless communication device (e.g. near-field communication (NFC) device). It will be understood that this is a non-exhaustive list of example devices.

The actuation apparatus described herein may be used in devices/systems suitable for image capture, 3D sensing, depth mapping, aerial surveying, terrestrial surveying, surveying in or form space, hydrographic surveying, underwater surveying, scene detection, collision warning, security, facial recognition, augmented and/or virtual reality, advanced driver-assistance systems in vehicles, autonomous vehicles, gaming, gesture control/recognition, robotic devices, robotic device control, touchless technology, home automation, medical devices, and haptics.

Claims

1. An actuation apparatus comprising: a first part; a second part; and a bearing arrangement supporting the second part on the first part and arranged to guide movement of the second part with respect to the first part; the bearing arrangement comprising a total of three or more bearings, each bearing comprising a first bearing surface located on the first part and a second bearing surface located on the second part, and a rolling bearing element configured to be disposed between the first and second bearing surfaces such that the first and second bearing surfaces are spaced by a gap; wherein one of the first bearing surface and the second bearing surface is configured such that the bearing surface has at least one contact point with the rolling bearing element at any one time and the other of the first bearing surface and the second bearing surface is configured such that the bearing surface has two contact points with the rolling bearing element at any one time; the two contact points of the first or second bearing surface being located closer to the axis of rotation of the rolling bearing element than the at least one contact point of the other of the first or second bearing surface, such that the distance moved by the rolling bearing element relative to the first part is different to the distance moved by the second part relative to the rolling bearing element.

2. The actuation apparatus according to claim 1, wherein the at least one contact point is located on a first line which extends parallel to the axis of rotation and the two contact points are located on a second line which extends parallel to the axis of rotation.

3. The actuation apparatus according to claim 2, wherein the distance between the second line and the axis of rotation is substantially in the range of 1% to 50% of the distance between the first line and the axis of rotation.

4. The actuation apparatus according to claim 3, wherein the distance between the second line and the axis of rotation is substantially in the range of 1% to 25% of the distance between the first line and the axis of rotation.

5. The actuation apparatus according to any preceding claim, wherein the bearing arrangement is a helical bearing arrangement arranged to guide helical movement of the second part with respect to the first part around a helical axis, and each of the three or more bearings is a helical bearing.

6. The actuation apparatus according to claim 5, wherein the helical bearing arrangement comprises a total of five helical bearings, wherein each helical bearing comprises only one rolling bearing element, and wherein the one bearing surface of each helical bearing has a single contact point with the rolling bearing element at any one time.

7. The actuation apparatus according to claim 6, wherein, at any point in the range of the helical movement of the second part relative to the first part, the one bearing surface of each helical bearing extends in a plane that is different to, and non-parallel with, the plane in which the one bearing surface of each of the other helical extends, wherein the plane in which a helical bearing extends is defined as the plane parallel to the helical axis and tangential to the one bearing surface at the contact point.

8. The actuator apparatus according to any one of claim 5 to claim 7, wherein the helical bearings are spaced about the helical axis.

9. The actuator apparatus according to any one of claim 5 to claim 8, wherein the rolling bearing element of each helical bearing is located in the same plane normal to the helical axis at least at the extremes of the helical movement of the second part relative to the first part.

10. The actuator apparatus according to claim 5, wherein at least one of the helical bearings comprises a plurality of rolling bearing elements.

11. The actuation apparatus according to any one of the preceding claims, wherein the first bearing surface in the first part is configured such that the first bearing surface comprises the two contact points with the rolling bearing element.

12. The actuation apparatus according to claim 11, wherein the first bearing surface comprises a groove in a surface of the first part.

13. The actuation apparatus according to claim 12, wherein the groove comprises a first surface and a second surface that is non-parallel with the first surface.

14. The actuation apparatus according to claim 13, wherein the first surface of the groove extends at an acute angle to the second surface of the groove.

15. The actuation apparatus according to claim 13 or claim 14, wherein the first surface forms a first edge with the surface of the first part and the second surface forms a second edge with the surface of the first part.

16. The actuation apparatus according to claim 15, wherein the angle formed between the surface of the first part and the first surface of the groove is the same as the angle formed between the inner surface of the first part and the second surface of the groove, such that the cross-section of the groove is symmetrical.

17. The actuation apparatus according to claim 16, wherein the groove has a substantially isosceles trapezium cross-section.

18. The actuation apparatus according to any one of claim 15 to claim 17, wherein the distance between the first and second edges is larger than the diameter of the rolling bearing and one of the two contact points is located on the first surface of the groove and the other of the two contacts points is located on the second surface of the groove.

19. The actuation apparatus according to any one of claim 15 to claim 17, wherein the distance between the first and second edges is smaller than the diameter of the rolling bearing and the two contact points are located on the first and second edges of the groove.

20. The actuation apparatus according any one of the preceding claims, wherein the second bearing surface in the second part is configured such that the second bearing surface comprises the at least one contact point with the rolling bearing element, wherein the at least one contact point is a single contact point.

21. The actuation apparatus according to claim 20, wherein the second bearing surface comprises a smooth surface.

22. An actuation apparatus comprising: a first part; a second part; and a helical bearing arrangement supporting the second part on the first part and arranged to guide helical movement of the second part with respect to the first part around a helical axis; the bearing arrangement comprising a plurality of bearings, each bearing comprising a race configured to determine the range of motion of the second part relative to the first part; the race comprising a first end wall at one extremity and a second end wall at the other extremity; wherein at least one of the plurality of bearings is offset relative to at least one of the other of the plurality of bearings such that the first end wall of one of the plurality of bearings is offset in the direction of the helical axis from the first end wall of at least one of the other of the plurality of bearings.

23. The actuation apparatus according to claim 22, wherein the at least one bearing is offset relative to the at least one other bearing such that the second end wall of the at least one bearing is offset in the direction of the helical axis from the second end wall of the at least one other bearing.

24. The actuation apparatus according to claim 22 or 23, wherein: each of the plurality of bearings comprises a bearing surface on the second part with a normal thereto and the bearing is of a first type if the normal generally has a component in a first direction along the helical axis and the bearing is of a second type if the normal generally has a component in a second, opposite direction along the helical axis; and the at least one bearing is a bearing of the first type and the at least one other bearing is a bearing of the second type and the at least one bearing is offset relative to the at least one other bearing such that the first and/or second end wall is offset in the first direction if on the first part and in the second direction if on the second part.

25. The actuation apparatus according to any one of claims 22 to claim 24, wherein: for each bearing with a first and/or second end wall comprised in the first part, when the second part is at one extremity of its range of movement, the gap between the second part and the end wall at the other extremity of the race is smaller than the diameter of a bearing element of the bearing; and for each bearing with a first and/or second end wall comprised in the second part, when the second part is at one extremity of its range of movement, the gap between the first part and the end wall at the same extremity of the race is smaller than the diameter of a bearing element of the bearing.

26. The actuation apparatus according to claim 25, wherein, for each bearing and each extremity of its range of movement, the gap is smaller than 2rcos(0/2), where Q is the angle between the end wall and the one of the first and second parts that moves relative to the end wall and r is the radius of the bearing element.

27. The actuation apparatus according to claim 24 or 25, wherein, for the at least one bearing and/or the at least one other bearing, the gap at one extremity of its range of movement is substantially the same as the gap at the other extremity of its range of movement.

28. An actuation apparatus comprising: a first part; a second part configured to be moved with respect to the first part around a helical axis; and at least one length of shape memory alloy, SMA, wire connected between a static connector on the first part and a movable connector on the second part; wherein when the second part is in its mid-position the movable connector is offset from the static connector such that the at least one length of SMA wire extends at an acute angle to a plane normal to the helical axis.

29. The actuation apparatus according to claim 28, wherein the static connector and the movable connector are positioned towards first ends of the first and second parts, respectively, that define a maximum extent of the first and second parts in a first direction along the helical axis and, when the second part is in its mid-position, the movable connector is offset from the static connector in a second, opposite direction along the helical axis.

30. The actuation apparatus according to claim 29, wherein: the at least one length of SMA wire comprises first and second lengths of SMA wire; the static connector and the movable connector of the first length of SMA wire are positioned towards the first ends of the first and second parts, respectively, and, when the second part is in its mid-position, the movable connector of the first length of SMA wire is offset from the static connector of the first length of SMA wire in the second direction; and the static connector and the movable connector of the second length of SMA wire are positioned towards second ends of the first and second parts, respectively, that define a maximum extent of the first and second parts in the second direction along the helical axis and, when the second part is in its mid position, the movable connector of the second length of SMA wire is offset from the static connector of the second length of SMA wire in the first direction.

31. The actuation apparatus according to any one of claims 28 to 30, wherein the movable connector is offset such that when the second part is moved to an extremity of its range of movement, the movable connector is not moved along the helical axis substantially beyond the static connector on the first part.

32. The actuation apparatus according to any one of claims 28 to 31, wherein the second part comprises an end surface having a depressed section, the movable connector being attached to the depressed section of the second part such that when the second part is in its mid-position the movable connector is offset from the static connector in the direction of the helical axis.

33. The actuation apparatus according to any one of claims 28 to 32, further comprising at least one spring arm, the spring arm being attached at one end to the second part and at the other end to the first part and extending around the helical axis between its ends, wherein the second part comprises a helical surface configured to allow for a range of movement of the second part relative to the first part without the spring arm contacting the second part.

34. The actuation apparatus according to claim 33, wherein the spring arm is connected to the movable connector via a connected section connected to an end of the second part and via a kinked section configured such that the movable connector is offset relative to the static connector.

35. An actuation apparatus comprising: a first part; a second part; a first length of SMA wire connected to the first part via a first static connector in a first corner of the actuation apparatus and to the second part via a first moving connector in a second corner of the actuation apparatus; a second length of SMA wire connected to the first part via a second static connector in the second corner of the actuation apparatus and to the second part via a second moving connector in the first corner of the actuation apparatus; and a helical bearing arrangement supporting the second part on the first part and arranged to guide helical movement of the second part with respect to the first part around a helical axis; wherein the second length of SMA wire is spaced from the first length of SMA wire in a first direction along the helical axis; and wherein the first part or the second part or each of the first and second parts comprises a side portion between the first and second corners that generally extends in a plane oriented at an acute angle to a plane normal to the helical axis.

36. The actuation apparatus according to claim 35, wherein the plane extends in the first direction from the first corner to the second corner of the actuation apparatus.

37. The actuation apparatus according to claim 35 or 36, wherein, for each of the first and second lengths of SMA wire, the side portion comprises a generally planar surface that is parallel to the length of SMA wire when the second part is at one extremity of its range of movement.

38. An actuation apparatus according to any preceding claim, wherein the actuation apparatus is a shape memory alloy actuator.

39. A camera system comprising: the actuation apparatus according to any one of the preceding claims, an image sensor, and a lens system, wherein the lens system is mounted to one of the first part and the second part, and wherein the image sensor is mounted to the other one of the first part and second part.