Field

The present application relates to a shape memory alloy (SMA) actuator assembly, in particular an SMA actuator assembly for rotating a movable part about a primary axis relative to a support structure.

Background

WO 2011/104518 Al discloses an SMA actuation apparatus that uses SMA actuator wires to move a movable element (for example, a camera module comprising an image sensor and a lens assembly) relative to a support structure to provide, for example, optical image stabilization (OIS) by lateral movement or tilting of the movable element relative to the support structure.

It is desirable to enhance OIS, for example by increasing the amount of rotational control of the camera module. More generally, it is desirable to provide an improved SMA actuator assembly for providing rotational movement control of a movable part.

Summary

According to an aspect of the present invention, there is provided an SMA actuator assembly comprising: a support structure; a movable part that is movable relative to the support structure; a first plurality of SMA elements, electrically connected together (e.g. in series or parallel), arranged to apply a torque to the movable part for rotating the movable part relative to the support structure about a primary axis in a first sense; a second plurality of SMA elements, electrically connected together (e.g. in series or parallel), arranged to apply a torque to the movable part for rotating the movable part relative to the support structure about the primary axis in a second sense, wherein the second sense is opposite to the first sense.

The SMA actuator assembly allows the rotational position of the movable part to be controlled by selective actuation of the SMA elements. Electrically connecting SMA elements of each plurality together reduces the number of electrical connections and the number of control channels required to control the rotational position of the movable part relative to the support structure compared to a situation in which the SMA elements are not electrically connected together.

Optionally, the distance (e.g. minimum distance) between the SMA elements of the first plurality of SMA elements is less than the length of the SMA elements of the first plurality of SMA elements and/or the distance (e.g. minimum distance) between the SMA elements of the second plurality of SMA elements is less than the length of the SMA elements of the second plurality of SMA elements. Optionally, the ratio of the distance (e.g. minimum distance) between the SMA elements of the first plurality of SMA elements to the length of the SMA elements is in the range from 0.1 to 1, preferably 0.25 to 0.6.

Optionally, the ratio of the distance (e.g. minimum distance) between the SMA elements of the second plurality of SMA elements to the length of the SMA elements is in the range from 0.1 to 1, preferably 0.25 to 0.6.

Optionally, the SMA elements of the first plurality of SMA elements overlap with the SMA elements of the second plurality of SMA elements when viewed along the primary axis.

Optionally, the SMA elements of the first plurality of SMA elements are connected together in electrical series and/or the SMA elements of the second plurality of SMA elements are connected together in electrical series.

Optionally, the SMA elements of the first plurality of SMA elements are electrically connected together at the movable part and/or the SMA elements of the second plurality of SMA elements are electrically connected together at the movable part.

Optionally, the SMA actuator assembly further comprises a flexible electrical connection between the movable part and the support structure, wherein the flexible electrical connection is deformable so as to allow movement of the movable part relative to the support structure, and wherein the flexible electrical connection is configured to provide a common electrical connection to the movable part.

Optionally, the SMA actuator assembly comprises a bearing arrangement between the support structure and the movable part, wherein the bearing arrangement allows movement of the movable part relative to the support structure in a plane that is orthogonal to the primary axis.

Optionally, the SMA actuator assembly comprises a bearing arrangement between the support structure and the movable part, wherein the bearing arrangement constrains movement of the movable part relative to the support structure to rotation about the primary axis.

Optionally, the movable part comprises two sheets of material that are stacked along the primary axis, wherein a first of the two sheets of material comprises connection elements that are mechanically and electrically connected to the first plurality of SMA elements and a second of the two sheets of material comprises connection elements that are mechanically and electrically connected to the second plurality of SMA elements.

Optionally, the first and second sheets of material are similar.

Optionally, the SMA elements of the first plurality of SMA elements are (at least substantially) parallel to each other and/or the SMA elements of the second plurality of SMA elements are (at least substantially) parallel to each other, e.g. at least as viewed along the primary axis.

Optionally, the SMA elements of the first plurality of SMA elements and/or the SMA elements of the second plurality of SMA elements extend in a plane that is orthogonal to the primary axis.

Optionally, the SMA elements of the first plurality of SMA elements and/or the SMA elements of the second plurality of SMA elements are angled relative to a plane that is orthogonal to the primary axis so as to urge the movable part along the primary axis towards the support structure.

Optionally, the SMA actuator assembly comprises a bearing arrangement configured to support the relative rotation of the movable part about the primary axis.

Optionally, the bearing arrangement comprises: a first bearing surface of the support structure extending in a direction parallel to the primary axis, and a second bearing surface of the movable part extending in a direction parallel to the primary axis.

Optionally, the first and second bearing surfaces are configured to slide relative to each other so as to allow rotation of the movable part relative to the support structure.

Optionally, the bearing arrangement comprises one or more rolling bearings provided between the first and second bearing surfaces so as to allow rotation of the movable part relative to the support structure about the primary axis.

Optionally, the movable part is configured to rotate relative to the support structure in a plane perpendicular to the primary axis.

Optionally, the first plurality of SMA elements are configured to apply forces to different locations of the movable part, and/or the second plurality of SMA elements are configured to apply forces to different locations of the movable part. Optionally, the first plurality of SMA elements cross with the second plurality of SMA elements when viewed along the primary axis.

Optionally, the first and second plurality of SMA elements are arranged in a loop at different angular positions around the primary axis.

Optionally, successive SMA elements around the primary axis are configured to apply a force to the movable element in alternate senses around the primary axis.

Optionally, the first plurality of SMA elements comprises a first pair of SMA elements, and/or the second plurality of SMA elements comprises a second pair of SMA elements. The first plurality of SMA elements may comprise only two SMA elements. The second plurality of SMA elements may comprise only two SMA elements.

Optionally, the first pair of SMA elements are arranged to apply a couple to the movable part for rotating the movable part relative to the support structure about the primary axis in the first sense, and/or the second pair of SMA elements are arranged to apply a couple to the movable part for rotating the movable part relative to the support structure about the primary axis in the second sense.

Optionally, the first plurality of SMA elements comprises three SMA elements, and the second plurality of SMA elements comprises three SMA elements. The first plurality of SMA elements may comprise only three SMA elements. The second plurality of SMA elements may comprise only three SMA elements.

It will be appreciated that the first plurality of SMA elements may comprise more than two or three SMA elements. It will be appreciated that the second plurality of SMA elements may comprise more than two or three SMA elements.

According to another aspect of the present invention, there is provided an actuator apparatus comprising: the SMA actuator assembly mentioned above, and a second actuator assembly arranged in mechanical series with the SMA actuator assembly, the second actuator assembly comprising: a second support structure, a second movable part and a plurality of actuator components arranged, on actuation, to tilt the second movable part relative to the second support structure about one or more tilt axes that are orthogonal/perpendicular to the primary axis. The one or more tilt axes may be nonparallel to each other. Optionally, the plurality of actuator components are arranged, on actuation, further to rotate the second movable part relative to the second support structure about the primary axis.

Optionally, the support structure of the SMA actuator assembly is fixed relative or formed integrally with the movable part of the second actuator assembly (i.e. the second movable part) or wherein the support structure of the second actuator assembly (i.e. the second support structure) is fixed relative or formed integrally with the movable part of the SMA actuator assembly.

Optionally, the second actuator assembly is a second SMA actuator assembly, and wherein the plurality of actuator components comprises a second set of SMA elements. The second set of SMA elements may be configured to, on actuation, tilt the second movable part relative to the second support structure about one or more tilt axes that are orthogonal/perpendicular to the primary axis. The one or more tilt axes may be non-parallel to each other.

Optionally, the second actuator assembly comprises eight SMA elements that are inclined relative to the primary axis, with two SMA elements on each of four sides around the primary axis, the SMA elements being connected between the second movable part and the second support structure so that on contraction two groups of four SMA elements provide a force on the movable element with a component in opposite directions along the primary axis, the SMA elements of each group being arranged with two-fold rotational symmetry about the primary axis.

According to another aspect of the present invention, there is provided a camera apparatus comprising: the SMA actuator assembly mentioned above, or the actuator apparatus mentioned above; and a camera module comprising an image sensor and a lens assembly arranged to focus an image on the image sensor, wherein the camera module is arranged such that the optical axis of the lens assembly can be aligned with the primary axis, and wherein the image sensor or the camera module is rotatable about the primary axis by the SMA actuator assembly or the actuator apparatus, and/or wherein camera module is tiltable about one or more tilt axes that are orthogonal/perpendicular to the primary axis by the actuator apparatus. The one or more tilt axes may be non-parallel to each other.

According to another aspect of the present invention, there is provided a variable aperture apparatus comprising: the SMA actuator assembly mentioned above, and a variable aperture assembly arranged between the support structure and the movable part such that rotation of the movable part relative to the support structure adjusts a variable aperture defined by the variable aperture assembly. The variable aperture apparatus may be configured to be mounted on a lens assembly comprising one or more lenses e.g. arranged to focus an image on an image sensor. The variable aperture may be configured to be mounted on an auto-focus (AF) actuator assembly e.g. comprising one or more SMA elements configured to move at least one lens element relative to an image sensor along the optical axis of the lens element.

Other aspects of the present invention are set out in the claims and in the detailed description.

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 is a schematic view of a camera apparatus including a tilt actuator assembly;

Figure 2 schematically illustrates possible degrees of freedom which may be provided by the tilt actuator assembly of Figure 1;

Figure 3 is a schematic diagram of an embodiment of the tilt actuator assembly;

Figures 4A and 4B schematically show an SMA actuator assembly for rotating a movable part about a primary axis;

Figures 5A-C are schematic views of camera apparatuses incorporating a combination of the SMA actuator assembly of Figures 4A-B and a tilt actuator assembly;

Figure 6 is a schematic perspective view of an SMA actuator assembly for rotating a movable part about a primary axis; and

Figure 7 is a schematic perspective view of an SMA actuator assembly for rotating a movable part about a primary axis.

Detailed description

Figure 1 is a schematic diagram of a SMA actuation apparatus 1. The SMA actuation apparatus 1 includes a movable part 100 and a support structure 3. The support structure 3 includes a base 5. The movable part 100 may be a camera module 100 comprising a lens assembly 4 and an image sensor 6. When comprising the camera module 100, the SMA actuation apparatus 1 may also be referred to as a camera apparatus 1.

The movable part 100 may be suspended on the support structure 3 by an actuator apparatus 2 comprising SMA elements, for example in the form of SMA wires. The image sensor 6 is disposed in front of a front side of the base 5, i.e., the image sensor 6 is interposed between the lens assembly 4 and the base 5. The lens assembly 4 is positioned above the image sensor 6 with respect to a primary axis P of the camera assembly 1. The primary axis P is defined with reference to the support structure 3. The primary axis P may be perpendicular to the major surfaces of the base 5 and may pass through the centre of the support structure 3, the centre of an aperture of the can 8 and/or the centre of the SMA actuation apparatus 1.

The term support structure is used herein as the combination of components that remain fixed relative to one another, whereas the term movable part is used herein as the combination of components that is moved by the actuator apparatus 2 relative to the support structure 3. So, the support structure 3 and the movable part 100 may be formed from multiple components that are connected to each other, or alternatively may be integrally formed of a single part. The actuator apparatus 2 may be considered to comprise the support structure 3 or part of the support structure 3, as well as the movable part 100 or part of the movable part 100.

The actuator apparatus 2 supports the movable part 100 in a manner allowing one or more degrees-of- freedom of movement of the movable part 100 relative to the support structure 3. The lens assembly 4 has an optical axis O. As shown in Fig. 1, the optical axis O is aligned with the primary axis P when the movable part 100 is in its neutral position in which the image sensor 6 is substantially parallel to the base 5 (i.e. when the movable part 100 is in the untilted position with respect to the support structure 3) and the movable part 100 is laterally centered between the actuator apparatus 2.

The SMA actuation apparatus 1 includes a controller 7, for example in the form of an integrated circuit (IC) 7, which implements a control circuit, and also a gyroscope sensor (not shown). The support structure 3 also includes a can 8 which protrudes forwardly from the base 5 to encase and protect the other components of the SMA actuation apparatus 1.

The lens assembly 4 includes a lens carriage 9 in the form of a cylindrical body supporting two lenses 10 arranged along the optical axis O. In general, any number of one or more lenses 10 may be included. Each lens 10 may have a diameter of up to about 20 mm. The SMA actuation apparatus 1 may be comprised in a camera, which may be referred to as a miniature camera. The lens assembly 4 is arranged to focus an image onto the image sensor 6. The image sensor 6 captures the image and may be of any suitable type, for example, a charge-coupled device (CCD) or a complementary metal-oxide- semiconductor (CMOS) device.

Although all the lenses 10 are fixed to the lens carriage 9 in this example, the lens carriage 9 may include an actuator assembly (not shown) configured to move at least one of the lenses 10 along the optical axis 0 relative to the image sensor 6, for example to provide auto-focus (AF) or zoom functionality. Such an actuator is also referred to as an AF actuator and may be an SMA actuator assembly comprising SMA elements, a voice coil motor (VCM) actuator, or any other suitable type of actuator.

In general, one or more SMA wires are arranged, on selective contraction, to tilt the movable part 100 relative to the support structure 3 about axes (e.g. two orthogonal axes) that are perpendicular about the primary axis P of the SMA actuation apparatus 1. For example, if a set of right-handed orthogonal axes x, y, z is aligned so that a third axis z is aligned with the primary axis P, the one or more SMA wires are arranged, on contraction, to tilt the movable part 100 relative to the support structure 3 about axes parallel to the x and y axes.

OIS functionality may be provided by tilting the lens assembly 4 and the image sensor 6 about an axis parallel to the first axis x and/or about an axis parallel to the second y axis. This is used to provide OIS, compensating for movement of the SMA actuation apparatus 1, which may be caused by hand shake etc. Additionally, as discussed above, the lens assembly 4, or at least one lens 10 thereof, may be moved parallel to the optical axis O (parallel to the third axis z) to provide focussing of an image formed on the image sensor 6, for example as part of an automatic focussing (AF) function.

This specification is concerned with examples of SMA actuation apparatuses 1 which provide OIS that is based on tilting the lens assembly 4 and the image sensor 6 relative to the support structure 3. AF may be provided by an additional system which may or may not use SMA wires.

Referring also to Figure 2, possible types of movement (or degrees of freedom) which may be provided in an SMA actuation apparatus 1 are illustrated.

A first degree-of-freedom (DOF) Tx corresponds to movement parallel to the first axis x. A second DOF Ty corresponds to movement parallel to the second axis y. A third DOF Tz corresponds to movement parallel to the third axis z, which is aligned with the primary axis P. The third DOF Tz corresponds to movement of the lens assembly 4 and the image sensor 6 towards or away from the base 5. The first, second and third axes x, y, z form a right-handed Cartesian coordinate system. A fourth DOF Rx corresponds to rotation about an axis parallel to the first axis x. A fifth DOF Ry corresponds to rotation about an axis parallel to the second axis y. A sixth DOF Rz corresponds to rotation about an axis parallel to the third axis z.

Motions of the movable part 100 relative to the support structure 3 may be broken down into components of any or all of the first to sixth DOF (movements) Tx, Ty, Tz, Rx, Ry, Rz. Although described as degrees-of-freedom, in some cases translations and rotations may be linked. For example, a given translation Tz along the third axis z may be tied to a corresponding rotation Rz so that motion of the lens assembly 4 is helical.

The actuator apparatus 2 may provide the motions corresponding to at least the fourth and fifth DOF Rx, Ry. The fourth and fifth DOF Rx, Ry provide the OIS functionality herein. The actuator apparatus 2 may further provide the motion corresponding to the sixth DOF Rz, for improved OIS functionality. Other motions may be constrained by the SMA actuation apparatuses 1.

The plurality of SMA wires of the actuator apparatus 2 are arranged, on contraction, to tilt the movable part 100 relative to the support structure 3 about axes, e.g. the x and y axes, that are perpendicular to a primary axis P of the SMA actuation apparatus 1. In some embodiments, the plurality of SMA wires of the actuator assembly 2 may further be arranged, on contraction, to rotate the movable part 100 relative to the support structure 3 about the primary axis P, i.e. the z axis.

The type of drive arrangement which may be included in the actuator assembly 2 may comprise, for example, four SMA wires or eight SMA wires. For example, when eight SMA wires are provided (as shown in Figure 3), two of the SMA wires are arranged on each of four sides around the z axis. The two SMA wires on each side are inclined in opposite senses with respect to each other, as viewed perpendicular from the z axis, and cross each other. The four sides on which the SMA wires are arranged extend in a loop around the z axis. In one example, the sides are perpendicular and so form a square as viewed along the z axis, but alternatively the sides could take a different quadrilateral shape. In one example, the SMA wires are parallel to the outer faces of the movable part 100 which conveniently packages the SMA actuation apparatus 1 but is not essential. Examples of such a drive arrangement are described in WO 2011/104518 Al. The description of these drive arrangements, particularly those depicted in Figure 1, Figure 2 and Figure 4 of that document, is incorporated herein by reference. Optionally, the two SMA wires on each side are connected to the movable part 100 and the support structure 3 to provide forces on the movable part 100 with components in opposite directions along the z axis.

Alternatively, the two SMA wires on each side are connected to the movable part 100 and the support structure 3 to provide a force on the movable part 100 with a component in the same direction along the z axis, this alternating on successive sides. Thus the four SMA wires on opposite sides form a group that provide a force in one direction and the four SMA wires on the other opposite sides form a group that provide a force in the opposite direction.

The actuation apparatus 1 comprises a controller 7 electrically connected to the SMA wires for supplying drive signals to the SMA wires. The forces exerted by the SMA wires are controlled by selectively varying the temperatures of the SMA wires. This is achieved by passing selective drive signals through the SMA wires that provide resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the SMA wires to cool by conduction, convection and radiation to its surroundings. Further details are also provided in WO 2013/175197 Al, which is incorporated herein by this reference.

In general, the SMA wires are arranged, on contraction, to tilt the movable part 100 relative to the support structure 3 about at least one axis, and preferably two orthogonal axes, perpendicular to the primary axis P of the SMA actuation apparatus 1. The primary axis P is perpendicular to the major surfaces of the movable part 100 (e.g. the light-sensitive surface of the image sensor 6) when the movable part 100 is in its neutral or untilted position with respect to the support structure 3.

8-wire tilt actuator assembly

Figure 3 is a schematic diagram of an actuator assembly 80 comprising eight SMA wires 71-78. The arrangement shown in Figure 3 is described to help with understanding of how a movable part may be tilted relative to a support structure about two orthogonal axes. The actuator assembly 80 may form part of the actuator apparatus 2.

The arrangement shown in Figure 3 includes SMA wires 71-78 arranged on each of four perpendicular sides of the primary axis P and connected to the movable element 81 and the support structure 82. Thus, one of the SMA wires 71-78 on each side provides a force on the movable element 81 in the same direction along the primary axis P. In particular, the SMA wires 71, 73, 75, 77 form a group that provide a force in one direction (upwards in Figure 3) and the other SMA wires 72, 74, 76, 78 form a group that provide a force in the opposite direction (downwards in Figure 3). The SMA wires 71-78 have a symmetrical arrangement in which lengths and inclination angles are the same, so that both the group of SMA wires 71, 73, 75, 77 and the group of SMA wires 72, 74, 76, 78 are each arranged with two-fold rotational symmetry about the primary axis P (i.e. bisecting the angle between SMA wires 71-78 on adjacent sides and across the diagonals of the square shape of the movable element). As a result of this symmetrical arrangement, different combinations of the SMA wires 71-78, when selectively actuated are capable of driving movement of the movable element 81 with multiple degrees of freedom, as follows. In general, the SMA wires 71-78 are arranged, on contraction, to tilt the movable element 81 relative to the support structure 82 about two orthogonal axes, perpendicular to the primary axis P.

The group of SMA wires 71, 73, 75, 77 and the group of SMA wires 72, 74, 76, 78 when commonly actuated drive movement along the primary axis P.

Within each group, adjacent pairs of the SMA wires (for example on one hand SMA wires 71, 77 and on the other hand SMA wires 73, 75) when differentially actuated drive tilting about a lateral axis perpendicular to the primary axis P. Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes.

Sets of four SMA wires, including two SMA wires from each group, (for example on one hand SMA wires 71, 72, 77, 78 and on the other hand SMA wires 73-76) when commonly actuated drive movement along a lateral axis perpendicular to the primary axis P. Movement in any arbitrary direction perpendicular to the primary axis P may be achieved as a linear combination of movements along the two lateral axes. Hence the arrangement shown in Figure 3 can perform tilting movement or translational movement. The control circuit of the present invention is also capable of performing tilting movement or translational movement. The control circuit of the present invention is further configured to generate drive signals that combine the tilting and the translational movement so as to cause the movable element 100 to tilt about at least one second axis that is perpendicular to the primary axis P and spaced from the first axis.

The actuator assembly 2 is capable of moving the movable part 100 to have both rotational and translation motion. By adding translation to rotation it is possible to produce rotation about different heights (i.e. the position along the z axis of the axis of rotation can be controlled). For example adding translation in the x direction to rotation about the y axis results in rotation about a vector in the y direction that has a negative (or alternatively positive) position in the z direction. This allows the axis of tilt to be controlled to be at a position where there is less resistance to the tilting motion from other parts of the SMA actuation apparatus 1.

Rz actuator assembly

In some situations, it may be desirable to increase rotation of the movable part 100 relative to the support structure 3 about the primary axis P, for example compared to the rotation about the primary axis P achievable using the actuator assembly 80 already described. In general, it may be desirable to provide a dedicated actuator assembly 2 for rotation of a movable part 100 about a primary axis P.

Figure 4A schematically depicts, in plan (viewed along the primary axis P), an SMA actuator assembly 50. The SMA actuator assembly 50 comprises a support structure 52 and a movable part 51. The movable part 51 is movable relative to the support structure 52.

As shown in Figures 6 and 7, the support structure 52 and the movable part 51 may be rotatably fitted together.

The SMA actuator assembly 50 further comprises a first pair of SMA elements 55a. The SMA elements of the first pair of SMA elements 55a are electrically connected together. So, the SMA elements are not independently controllable. A single channel is used to control the first pair of SMA elements 55a. The first pair of SMA elements 55a is arranged to apply a torque to the movable part 51 for rotating the movable part 51 about the primary axis P in a first sense. In the depicted example, the first pair of SMA elements 55a is arranged, on actuation, to apply a clockwise torque.

The SMA actuator assembly 50 further comprises a second pair of SMA elements 55b. The SMA elements of the second pair of SMA elements 55b are electrically connected together. So, the SMA elements are not independently controllable. A single channel is used to control the second pair of SMA elements 55b. The second pair of SMA elements 55b is arranged to apply a torque to the movable part 51 for rotating the movable part 51 about the primary axis P in a second sense. The second sense it opposite to the first sense. In the depicted example, the second pair of SMA elements 55b is arranged, on actuation, to apply an anti-clockwise torque.

Thus, by selective actuation of the first and second pairs of SMA elements 55a, 55b, the rotational position of the movable part 51 relative to the support structure 52 may be adjusted. The movable part 51 may be rotated relative to the support structure 52 and about the primary axis P within a range of rotations. The first and/or second pairs of SMA elements 55a, 55b may be arranged with two-fold rotational symmetry about the primary axis P. This allows the torques applied by the first and/or second pairs of SMA elements 55a, 55b to be centered specifically about the primary axis P, reducing and indeed avoiding off-axis forces on the movable part 51. Motion of the movable part 51 may thus be purely rotational upon actuation of the first and/or second pairs of SMA elements 55a, 55b.

In other words, the first pair of SMA elements 55a may be arranged to apply a couple (i.e. a pair of equal and opposite forces with lines of action that do not coincide) to the movable part 51 for rotating the movable part 51 relative to the support structure 52 about the primary axis P in the first sense, and the second pair of SMA elements 55b are arranged to apply a couple to the movable part 51 for rotating the movable part 51 relative to the support structure 52 about the primary axis P in the second sense.

It will be appreciated that, instead of only two SMA elements 55a, the first plurality of SMA elements 55a arranged to rotate the movable part 51 relative to the support structure 52 about the primary axis P in the first sense may comprise three SMA elements 55a (as shown in Figure 7) or more. Moreover, instead of only two SMA elements 55b, the second plurality of SMA elements 55b arranged to rotate the movable part 51 relative to the support structure 52 about the primary axis P in the second sense may comprise three SMA elements 55b (as shown in Figure 7) or more.

As shown in Figures 4A, 6 and 7, the first plurality of SMA elements 55a are configured to apply forces to different locations of the movable part 51, and the second plurality of SMA elements 55b are configured to apply forces to different locations of the movable part 51.

As shown in Figures 4A, 6 and 7, the SMA elements 55a, 55b are arranged in a loop at different angular positions around the primary axis P. Successive SMA elements 55a, 55b around the primary axis P are configured to apply a force to the movable element 51 in alternate senses around the primary axis P.

The distance between SMA elements of the first and/or second plurality (e.g. pair) of SMA elements 55a, 55b affects the rotation of the movable part for a given amount of actuation (e.g. change in length) of the SMA elements. For example, when the SMA elements are relatively close to each other, and so relatively close to the primary axis P, the movable part 51 will rotate by a relatively large angle for a given amount of actuation of the SMA elements. When the SMA elements are relatively far away from each other, and so relatively far away from the primary axis P, the movable part 51 will rotate by a relatively small angle for a given amount of actuation of the SMA elements. In some embodiments, and as shown in Figure 4A, it may thus be desirable that the distance between the SMA elements of the first plurality (e.g. pair) of SMA elements 55a is less than the length of the SMA elements of the first plurality (e.g. pair) of SMA elements 55a. Similarly, it may be desirable that the distance between the SMA elements of the second plurality (e.g. pair) of SMA elements 55b is less than the length of the SMA elements of the second plurality (e.g. pair) of SMA elements 55b. So, the ratio of the distance between the SMA elements of the first and/or second plurality (e.g. pair) of SMA elements 55a, 55b to the length of the SMA elements may be less than 1. Preferably, this ratio is less than 0.6. A smaller ratio increases the amount of rotation of the movable part 51 for a given amount of actuation of the SMA elements.

A lower limit for the ratio may be 0.1, preferably 0.25. This ensures that rotation of the movable part 51 remains reliably and accurately controllable using the SMA elements. A very small distance between SMA elements may make accurate rotational positioning of the movable part difficult.

In general, however, the ratio of distance between SMA elements to length may have any value. In some situations, it may be desirable to gear down actuation of the SMA elements to rotation of the movable part, and so the ratio may be greater than 1. In some other situations, accurate position control of the movable part 51 may not be required, and so the ratio may be less than 0.1.

As shown in Figures 4A, 6 and 7, the SMA elements of the first plurality (e.g. pair) of SMA elements 55a may overlap with the SMA elements of the second pair of SMA elements 55b when viewed along the primary axis P. In other words, as shown in Figures 4A, 6 and 7, the first plurality of SMA elements 55a cross with the second plurality of SMA elements 55b when viewed along the primary axis P. Direct contact between the SMA elements (which can lead to rubbing and damage to the SMA elements) may be avoided by spacing the first and second plurality (e.g. pairs) of SMA elements 55a, 55b along the primary axis P. The SMA elements 55a, 55b may be coated to avoid shorting from direct contact between the SMA elements. Glue and/or gel (e.g. made of non-conductive material) may be provided between the overlapping SMA elements 55a, 55b e.g. to avoid shorting and/or avoid damage from the SMA elements rubbing against each other. So, the first and second plurality (e.g. pairs) of SMA elements 55a, 55b may effectively be stacked along the primary axis P.

As shown in Figures 4A, 4B and 6, the SMA elements of the first pair of SMA elements 55a may be parallel to each other. Similarly, the SMA elements of the second pair of SMA elements 55b may be parallel to each other. The SMA elements of the first pair of SMA elements 55a may be at angle, for example perpendicular to, the SMA elements of the second pair of SMA elements 55b. In some embodiments, the SMA elements of the first plurality (e.g. pair) of SMA elements 55a and/or the SMA elements of the second plurality (e.g. pair) of SMA elements 55b extend in a plane that is orthogonal to the primary axis P. So, the SMA elements may extend in the plane of Figure 4A, for example. Alternatively, the SMA elements of the first plurality (e.g. pair) of SMA elements 55a and/or the SMA elements of the second plurality (e.g. pair) of SMA elements 55b are angled relative to a plane that is orthogonal to the primary axis P. This allows the SMA elements, when in tension, to urge the movable part 51 along the primary axis P towards the support structure 52. A bearing arrangement between the movable part 51 and the support structure 52 may thus be loaded by the SMA elements.

The SMA elements of the first plurality (e.g. pair) of SMA elements 55a and the SMA elements of the second pair of SMA elements 55b are electrically connected together. Preferably, the SMA elements of each plurality (e.g. pair) 55a, 55b are connected together in electrical series. So, a first SMA element of each pair may be electrically connected to a respective control terminal 51a, 51b at one end and to the second SMA element of the pair at the other end. The second SMA element of each pair may be electrically connected to the first SMA element at one end and to a common ground terminal 51g at the other end. A control signal applied at the control terminal 51a, 51b thus is applied to both SMA elements of each pair 55a, 55b.

Preferably, the SMA elements of each plurality (e.g. pair) 55a, 55b are electrically connected together at the movable part 51, as e.g. shown in Figure 4A. As such, an electrical connection to the movable part 51 is not required. Electrical terminals need only be provided at the support structure 52, thus making manufacture of the SMA actuator assembly 50 simpler, as well as reducing the risk of electrical connections to the movable part affecting movement of the movable part due to inadvertent biasing forces on the movable part by such electrical connections.

However, in an alternative, a flexible electrical connection (not shown) may be provided between the moveable part 51 and the support structure 52. The flexible electrical connection may be deformable so as to allow movement of the movable part relative to the support structure. The flexible electrical connection may be embodied by a flexure arm or other spring arm, by a flexible printed circuit, or by any other deformable element capable of carrying electrical current. The flexible electrical connection may provide a common electrical connection to the movable part 51. The SMA elements of each plurality (e.g. pair) 55a, 55b may connect at one end to the common electrical connection at the movable part 51, and at the other end to a control terminal that is shared between SMA elements within each plurality (e.g. pair) 55a, 55b. So, the SMA elements within each plurality (e.g. pair) 55a, 55b may be electrically connected in parallel. The SMA actuator assembly 50 may comprise a bearing arrangement between the support structure 52 and the movable part 51. The bearing arrangement may constrain the degrees of freedom of movement of the movable part 51 relatively to the support structure 52. The bearing arrangement may be a rolling bearing arrangement (so may comprise roller bearings or ball bearings) or a plain bearing arrangement (so may comprise plain bearings or sliding bearings). The bearing arrangement may also be a flexure arrangement, i.e. comprise one or more flexures that guide movement of the movable part relative to the support structure.

In some embodiments, the bearing arrangement allows movement of the movable part 51 relative to the support structure 52 in a plane that is orthogonal to the primary axis P. So, the bearing arrangement may, in essence, comprise a planar surface on the movable part 51 and a planar surface on the support structure 52, where the planar surfaces either bear directly against each other (so as to form a plain bearing) or wherein a ball or other rolling element is provided between the planar surfaces (so as to form a rolling bearing). The bearing arrangement may constrain translational movement of the movable part 51 relative to the support structure 52 along the primary axis P (so Tz) and tilt of the movable part 51 relative to the support structure 52 about axes orthogonal to the primary axis (so Rx, Ry). The arrangement of SMA elements may ensure that, even though Tx and Ty are not constrained by the bearing arrangement, pure rotation about the primary axis is achieved on actuation of the SMA elements.

In some other embodiments, the bearing arrangement constrains movement of the movable part 51 relative to the support structure 52 to rotation about the primary axis. So, movement of the movable part 52 in other degrees of freedom (i.e. Tx, Ty, Tz, Rx, Ry) may be constrained or prevented.

In some other embodiments, the bearing arrangement constrains movement of the movable part 51 relative to the support structure 52 to helical movement about the primary axis P. So, the bearing arrangement may be a helical bearing arrangement that couples rotation about the primary axis P to translation along the primary axis P. Such helical movement corresponds to one degree of freedom. Rotation of the movable part 52, driven by the SMA elements 55, may be converted by the bearing arrangement into helical movement (i.e. Rz+Tz movement).

In some other embodiments, as shown in Figures 6 and 7, the bearing arrangement comprises: a first bearing surface of the support structure extending (generally) in a direction parallel to the primary axis P, and a second bearing surface of the movable part extending (generally) in a direction parallel to the primary axis P. In the illustrated embodiments, the first and second bearing surfaces, are configured to slide relative to each other so as to allow rotation of the movable part 51 relative to the support structure 52. However, it will be appreciated that the bearing arrangement may comprise one or more rolling bearings (e.g. ball bearings) provided between the first and second bearing surfaces so as to allow rotation of the movable part 51 relative to the support structure 52 about the primary axis P.

As shown in Figures 4A and 4B, the movable part 51 may comprise two sheets of material 51a, 51b that are stacked along the primary axis P. The movable part 51 may be formed from or consist of the two sheets of material 51a, 51b. Each sheet of material may be formed from sheet metal, for example stainless steel. Each sheet of material may comprise connection elements, for example in the form of crimps. The connection elements are mechanically and electrically connected to the plurality (e.g. pairs) of SMA elements 55a, 55b. The first and second sheets of material may be similar, in particular geometrically similar. So, the first and second sheets of material may be identical or may be mirror images of one another. This allows the first and second sheets of material to be connected to the first and second plurality (e.g. pairs) of SMA element 55a, 55b in line, as for example depicted in Figure 4B, making manufacture of the SMA actuator assembly simpler.

As with the embodiment illustrated in Figures 6 and 7, the first plurality of SMA elements 55a may be electrically connected together via electrical connections that are fixed to (e.g. insert moulded within) the movable part 51 and the support structure 52.

As shown in Figures 6 and 7, the movable part 51 may comprise a hole (e.g. optical opening) extending through the movable part 51 along the primary axis P.

As shown in Figures 6 and 7, the support structure 52 comprises a hole (e.g. optical opening) extending through the support structure 52 along the primary axis P.

As shown in Figure 6, the SMA actuator assembly 50 may be for driving a variable aperture assembly comprising a plurality of blades 56 (of which only two are shown in Figure 6 so that other parts of the actuator assembly 50 can be seen) configured to define a variable aperture with a central axis which coincides with the primary axis P; wherein the plurality of blades 56 are connected to the support structure 52 via a first plurality of pins and connected to the movable part 51 via a second plurality of pins, and configured to rotate about the first or second pins when the movable part 51 is rotated relative to the support structure 52; and wherein the plurality of blades 56 are configured such that rotation of the plurality of blades 56 about the first or second pins changes the size of the variable aperture. Combination of Rz actuator assembly with tilt actuator assembly

As already mentioned, the SMA actuator assembly described in relation to Figures 4A, 6 and 7 may be combined with the tilt actuator assembly described in relation to Figures 2 and 3.

So, there may be provided an actuator apparatus that comprises the SMA actuator assembly 50 and a second actuator assembly 80. The SMA actuator assembly 50 may be provided in mechanical series with the second actuator assembly 80. The second actuator assembly 80 may comprise a second support structure 82, a second movable part 81 and a plurality of actuator components arranged, on actuation, to tilt the second movable part relative to the second support structure about tilt axes that are orthogonal to the primary axis P. The plurality of actuator components may be arranged, on actuation, further to rotate the second movable part 81 relative to the second support structure 82 about the primary axis P. This rotation about the primary axis P by the second actuator assembly 80 may be extended by the SMA actuator assembly 50. The actuator components of the second actuator assembly 50 may be SMA wires, as in Figure 3, or may more generally be any other actuator component capable of tilting the second movable part 81 relative to the second support structure 82, such as a voice coil motor (VCM) or piezoelectric actuator.

The second actuator assembly 80 may correspond to the actuator assembly 80 already described in relation to Figure 3. So, the second actuator assembly 80 may comprise eight SMA elements that are inclined relative to the primary axis P, with two SMA elements on each of four sides around the primary axis, the SMA elements being connected between the second movable part and the second support structure so that on contraction two groups of four SMA elements provide a force on the movable element with a component in opposite directions along the primary axis, the SMA elements of each group being arranged with 2-fold rotational symmetry about the primary axis.

Figures 5A to 5C schematically show three different arrangements of an actuator apparatus in which the SMA actuator assembly 50 is arranged in mechanical series with the second actuator assembly 80. In Figures 5A to 5C, the actuator apparatus is a camera apparatus 1 in which OIS is enabled due to the provision of a camera module 100, but it will be appreciated that the same arrangement may be used without camera module 100 to provide an actuator apparatus for other purposes.

In Figure 5A, the support structure 52 of the SMA actuator assembly 50 is fixed relative to the movable part 81 of the second actuator assembly 80. In general, the support structure 52 of the SMA actuator assembly 50 may also be formed integrally with the movable part 81 of the second actuator assembly 80. The support structure 82 of the second actuator assembly 80 is fixed relative to the base 3 of the camera apparatus 1. The camera module 100 is fixed relative to the movable part 51 of the SMA actuator assembly 50. Movement of the camera module 100 is thus a superposition of i) movement (in particular Rx, Ry and optionally Rz movement) of the second movable part 81 relative to the second support structure 82 of the second actuator assembly 80 and ii) movement (in particular Rz movement) of the movable part 51 relative to the support structure 52 of the SMA actuator assembly 50.

The SMA actuator assembly 50 may be provided on a side of the camera module 100 along the primary axis P that is away from the image sensor 6 of the camera module 100. This can reduce the risk of electromagnetic interference due to driving the SMA elements in the image sensor 6.

In Figure 5B, the support structure 82 of the second actuator assembly 80 formed integrally with the movable part 51 of the SMA actuator assembly 50. In general, the support structure 82 of the second actuator assembly 80 may also be formed separately and fixed relative to the movable part 51 of the SMA actuator assembly 50. The support structure 52 of the SMA actuator assembly 50 is fixed relative to the base 3 of the camera apparatus 1. The camera module 100 is fixed relative to the movable part 81 of the second actuator assembly 80. Movement of the camera module 100 is thus a superposition of i) movement (in particular Rz movement) of the movable part 51 relative to the support structure 52 of the SMA actuator assembly 50 and ii) movement (in particular Rx, Ry and optionally Rz movement) of the second movable part 81 relative to the second support structure 82 of the second actuator assembly 80.

In Figure 5C, the SMA actuator assembly 50 is provided within the camera module 100 so as to rotate the image sensor 6 of the camera module 100 about the primary axis P and relative to the lenses of the camera module 100. This may provide OIS in essentially the same manner as the arrangement in Figure 5A, because whether or not the lenses of the camera module 100 are rotated about the primary axis P need not significantly affect OIS performance due to the lenses' symmetry about the primary axis P. One advantage of providing the SMA actuator assembly 50 within the camera module 100 is that less force is required to rotate the relatively lighter image sensor 6 compared to a situation in which the entire camera module 100 is rotated.

Variable aperture apparatus

The SMA actuator assembly 50 is not required to be combined with the second actuator assembly 80. Provision of the SMA actuator assembly 50 in isolation from the second actuator assembly 80 may be useful in any apparatus in which it is desired to rotate a movable part relative to a support structure about a single axis. One such apparatus is a variable aperture apparatus, or iris apparatus. Known examples of such a variable aperture apparatus rely on the relative rotation of two parts to open or close a variable aperture assembly or iris. So, the variable aperture assembly may be arranged between the support structure 52 and the movable part 51 of the SMA actuator assembly 50. Rotation of the moveable part 51 relative to the support structure 52 may adjust the opening or aperture of the variable aperture assembly. Preferably, the movable part 51 may be rotated relative to the support structure 51 within a continuum of rotational positions, so as to vary the aperture of the variable aperture assembly within a continuous range of opening diameters.

SMA

The above-described SMA actuator assemblies comprise at least one SMA element. The term 'shape memory alloy (SMA)element' may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and/or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and/or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling, deposition and/or other forming process(es). The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field.