The present invention generally relates to an actuator assembly in which at least one actuator component drives movement of a movable part with respect to a support structure to produce helical movement and particularly, but not exclusively, to shape memory alloy (SMA) actuator assemblies. The present invention also relates to a method of manufacturing such an actuator assembly.

Actuator assemblies may be used to drive translational movement of a movable part with respect to a support structure. Such actuator assemblies may be used for example in an optical device such as a camera for driving translational movement of a camera lens element along its optical axis, for example to effect focussing (autofocus, AF) or zoom. Some examples of an actuator assembly of this type are disclosed in WO 2007/113478. Herein, the movable part is a camera lens element supported on a support structure, and an SMA wire is connected at its ends to the support structure and hooked over a hook on the camera lens element for driving the translational movement.

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

WO 2019/243849 Al discloses an exemplary actuator assembly comprising a helical bearing arrangement which guides helical movement of the movable part with respect to the support structure. Such helical movement involves rotation around a helical axis together with an overall translation along the helical axis. SMA wire is connected between the support structure and the movable part so as to drive rotation of the movable part around the helical axis. The rotation driven by contraction of the SMA wire is converted by the helical bearing arrangement into helical movement of the movable part. Thus, translational movement of the movable part is achieved along the helical axis as part of the helical movement.

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

An object of the present invention is to provide an alternative actuator assembly that provides helical movement. A further object of the present invention is to provide an actuation assembly which has reduced friction between movable part and support structure and/or reduces tilt of the movable part. Another object of the invention is to provide an actuator assembly with a bearing arrangement that is simpler to fabricate.

A first aspect of the present invention provides an actuator assembly comprising: a support structure; a movable part movable relative to the support structure; a bearing arrangement supporting the movable part on the support structure and arranged to guide helical movement of the movable part with respect to the support structure about a helical axis; and at least one actuator component connected between the support structure and the movable part and arranged to drive rotation of the movable part around the helical axis, said rotation being converted into helical movement around the helical axis by the bearing arrangement, wherein the bearing arrangement includes at least two flexures connected between the support structure and the movable part and arranged to flex to cause said guiding, the flexures each having a central portion between two outer portions, wherein the central portion is stiffer in at least one direction than each of the outer portions.

Using the at least two flexures in the bearing arrangement may reduce friction compared to a bearing arrangement that comprises, for example, a plain bearing or a roller bearing. By virtue of the central portion of each flexure being stiffer in at least one direction (e.g. in a direction parallel to the helical axis) than each of the outer portions, when subjected to a force in that direction, the flexure will bend preferentially at the outer portions rather than the central portion. This may reduce tilt of the movable part in normal operation.

In normal operation, the flexures may be arranged to flex only by flexing of the outer portions. It will be understood that, when subject to a force, all parts of the flexure will flex in reaction to this force. Thus flexing “only” by flexing of the outer portions will be understood to mean that substantially all of the flexing occurs in the outer portions even though inevitably the central portion will flex very slightly. For example, the central portion may be significantly stiffer than each of the outer portions in the direction(s) in question. Thus substantially all of the flexing of the flexure will occur at the outer portions and the central portion will not bend or stretch at all under normal loads.

Thus the flexure may behave substantially as if it is pin-jointed at either end, without the complexity of using pin-jointed attachment(s).

The central portion may be stiffer than each of the outer portions in only one direction, but may also be stiffer in more directions, including in all directions. For example, the central portion may be stiffer in directions perpendicular to the direction between the outer portions (i.e. the direction of the extent of the central portion). This latter configuration enables bending of the flexure, which is likely to be more relevant in the operation of the flexure as part of the bearing arrangement, whilst both the outer portions and the central portion have similar stiffness in the direction along the flexure and therefore are equally responsive to stretching or compressing forces along the length of the flexure.

In certain configurations the difference in stiffness can be provided by the outer portions having a smaller cross section in at least one direction than the central portion. For example, the cross-section when viewed along the extent of the flexure may be small for the outer portions, either by being thinner in the vertical direction (i.e. along the helical axis), or thinner in the horizontal direction (i.e. along a direction perpendicular to the helical axis), or both.

In certain configurations the difference in stiffness can be provided by the central portion having a reinforcing portion. For example, if the central portion extends in a longitudinal direction between the outer portions, the flexure can have a reinforcing portion extending from the central portion in a direction perpendicular to said longitudinal extent.

The reinforcing portion may be formed integrally with the central portion, which may make the manufacture of the flexure simpler. For example, the reinforcing portion and the central portion may be formed of a sheet material, with the reinforcing portion being formed by folding or bending at a connection point to the central portion. In certain arrangements there is at least one gap or slit between the central portion and the reinforcing portion. Provision of such a gap may make forming of the reinforcing portion, e.g. by folding or bending, easier.

Clearly the differences in cross section and the provision of a reinforcing portion can be combined.

In certain arrangements of the bearing arrangement, each flexure extends in an arc around the helical axis. This allows the flexure to follow a generally circular path and follow the outer profile of the movable part which may be substantially circular around the helical axis.

In certain embodiments, each flexure is pre-deflected along the helical axis. So, the flexure extends at an angle relative to a plane orthogonal to the helical axis.

The flexures may extend along the helical axis and may be inclined with respect to a plane perpendicular to the helical axis with rotational symmetry around the helical axis. This enables the flexures to at least partially follow the helical path guided by the bearing arrangement.

The bearing arrangement may further comprise a support plate mounted on the support structure and a movable plate mounted on the movable part, the at least one flexure being integrally formed with the support plate and/or the movable plate. Integral formation of the flexure may be substantially beneficial for manufacturing of the flexure and bearing arrangement, particularly for miniature assemblies where connecting components can be difficult. The support plate and/or the movable plate, and the at least one flexure may be formed of a sheet material, such as sheet metal.

Preferably the bearing arrangement comprises five flexures. Generally, a pin-jointed connection is known to remove a single degree of freedom from the movement of the assembly and so the provision of five flexures operating substantially as pin-joined connectors will leave a single degree of freedom, which is the desired helical motion.

In a number of embodiments, the actuator component may be formed from an SMA wire, but other actuator components may also be used. Using an SMA wire as the actuator component has particular advantages in miniature devices, due to its small size and high actuation forces, and may be applied in a variety of devices including handheld devices, such as cameras and mobile phones.

The movable part may have a maximum lateral extent of at most 20mm, preferably at most 15mm, further preferably at most 10 mm. This allows the actuator assembly to be used in miniature devices, such as miniature cameras.

The actuator assembly may include any combination of some, all or none of the abovedescribed preferred and optional features.

According to the present invention, there is also provided a camera apparatus comprising the actuator assembly. An image sensor is fixed relative to the support structure of the actuator assembly. The movable part comprises a lens assembly having one or more lenses that is configured to focus an image onto the image sensor.

The camera apparatus may further include a controller arranged to control the position of the lens assembly relative to the support structure by controlling the actuator component. The controller may thus effect focussing (autofocus, AF) or zoom in the camera apparatus.

According to the present invention, there is also provided an actuator assembly comprising a support structure; a movable part movable relative to the support structure; and a bearing arrangement configured to guide helical movement of the movable part with respect to the support structure about a helical axis. The bearing arrangement comprises a support plate connected to the support structure; a movable plate connected to the movable part; and at least two flexures connected between the support plate and the movable plate so as to guide helical movement of the movable plate with respect to a support plate about the helical axis. The bearing arrangement is integrally formed from sheet material, for example sheet metal. At least one actuator component is connected between the support structure and the movable part and arranged to drive rotation of the movable part around the helical axis, said rotation being converted into helical movement around the helical axis by the bearing arrangement.

Integrally forming the bearing arrangement from sheet material may make fabrication of the bearing arrangement simpler. A single movable plate and/or a single support plate may be connected to each of the at least two flexures. The single movable plate and/or single support plate may thus fix the relative position of the flexures, which may be useful when assembling the actuator assembly.

Each flexure may have a central portion between two outer portions, wherein the central portion is stiffer in at least one direction than each of the outer portions, and wherein the central portion and the two outer portions are formed from the sheet material. The central portion may extend in a plane, and each flexure may have a reinforcing portion connected to the central portion and extending in a plane that is angled relative to the plane of the central portion, wherein the reinforcing portion is formed from the sheet material. Each flexure may thus resemble a pin-jointed arm, which can reduce tilt of the actuator assembly.

According to the present invention, there is also provided a method of manufacturing the actuator assembly. The method comprises providing a bearing arrangement comprising a support plate, a movable plate, and at least two flexures connected between the support plate and the movable plate so as to guide helical movement of the movable plate with respect to a support plate about the helical axis, by providing a piece of sheet material, and selectively removing portions of the piece of sheet material so as to provide the bearing arrangement. The method further comprises mounting a movable part on the movable plate of the bearing arrangement and mounting a support structure on the support plate, such that the bearing arrangement is configured to guide helical movement of the movable part with respect to the support structure about the helical axis; and connecting at least one actuator component between the support structure and the movable part in an arrangement such that the at least one actuator component drives rotation of the movable part around the helical axis, said rotation being converted into helical movement around the helical axis by the bearing arrangement.

Providing the bearing arrangement may comprise partially etching outer portions of the flexures such that the outer portions have a smaller cross section than a central portion of the flexures. After selectively removing portions of the piece of sheet material, the sheet material may be bent so as to form a reinforcing portion for each flexure, the reinforcing portion extending in a plane that is angled relative to other portions of the flexure. The bearing arrangement may be provided with a single movable plate and/or a single support plate that connects the flexures. After mounting the movable part on the movable plate and/or after mounting the support structure on the support plate, portions of the single movable plate and/or of the single support plate may be removed to form a plurality of movable plates and/or support plates.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. l is a schematic view of an actuator assembly according to an embodiment of the present invention;

Fig. 2 is a plan view of the bearing arrangement of the actuator assembly shown in Fig. 1;

Figs. 3 A and 3B show, respectively, plan and side views of a flexure used in the bearing arrangement of embodiments of the present invention;

Figs. 4A and 4B show part of a bearing arrangement which forms part of an actuator assembly according to an embodiment of the present invention;

Fig. 5 shows an arrangement of an actuator assembly according to an embodiment of the present invention; and

Figs. 6A and 6B show a bearing arrangement formed from sheet material, according to an embodiment of the present invention.

An actuator assembly 1 that is incorporated in a camera apparatus is shown schematically in Fig. 1. The actuator assembly 1 comprises a support structure 2 that has an image sensor 3 mounted thereon. The support structure 2 may take any suitable form, typically including a base 4 to which the image sensor 3 is fixed. The support structure 2 may also support a controller 5. The controller 5 may be an integrated circuit (IC) chip 5.

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

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

Although the actuator assembly 1 in this example is incorporated in a camera apparatus, that is not essential. In some examples, the actuator assembly 1 may be incorporated in an optical device in which the movable part 10 comprises a lens assembly but there is no image sensor. In other examples, the actuator assembly 1 may be incorporated in an apparatus of a type that is not an optical device, and in which the movable part 10 does not comprise a lens assembly and there is no image sensor. Examples include apparatuses for depth mapping, face recognition, game consoles, projectors and security scanners, or haptics.

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

The helical motion of the movable part 10 guided by the bearing arrangement 20 includes a component of translational movement along the helical axis H and rotational movement around the helical axis H. The translational movement along the helical axis H is the desired movement of the movable part 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 when incorporated into a camera apparatus. 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 lens assembly comprised by the movable part 10 does not change the focus of the image on the image sensor 3. Fig. 2 shows a plan view, i.e. viewed along the axis O, H of the actuator assembly 1 shown in Fig. 1, of the bearing arrangement 20 according to an embodiment of the present invention. For simplicity, only the movable part 10 and the bearing arrangement 20 are shown in Fig. 2.

The bearing arrangement 20 includes five arms 22 which are arranged equidistantly around the circumference of the movable part 10 such that the bearing arrangement exhibits five-fold rotational symmetry around the helical axis H. The arms 22 are generally arc-shaped so that they extend around part of a circle of slightly larger diameter than the exterior of the movable part 10 and are each attached at a first end 24 to the movable part 10 and at a second end 26 to the support structure 2 (not shown in Fig. 2).

The arms 22 are flexures 22 which translate horizontal force applied to the movable part 10 by one or more SMA actuator wires (not shown) into a helical motion about the central axis O, H.

The bearing arrangement 20 further includes a movable plate 32. The movable part 10 is mounted on the movable plate 32, so the movable part 10 is fixed relative to the movable plate 32. The movable plate in Fig. 2 connects to each of the flexures 22. The bearing arrangement 20 further includes five support plates 34. Each support plate 34 is connected to a respective flexure 22. The support structure 2 is mounted to the support plates 34, so the support structure 2 is fixed relative to the support plates 34. Although a single, common movable plate 32 and individual support plates 34 are shown in Fig. 2, in some embodiments there may be multiple individual movable plates 32 (e.g. one per flexure 22). In some embodiments, there may be a single, common support plate 34.

Figures 3A and 3B show, respectively, plan and side views of one of the flexures 22. For simplicity, the flexure 22 shown in Figures 3 A and 3B is straight rather than arcuate like those shown in Figure 2. It will be appreciated that both straight and arcuate flexures can be used in embodiments of the present invention.

The flexure 22 has a central portion 25 which is located between two outer portions 23, 27.

In the embodiment shown, the outer portions 23, 27 correspond to necked portions 23, 27. A first of the necked portions 23 is proximal to the first end 24 of the flexure 22, while a second of the necked portions 27 is proximal to the second end 26 of the flexure. These necked portions 23, 27 are thinner than the central portion 25 in both plan and side cross-sections. The necked portions 23, 27 may be formed by partial etching of the flexure during manufacture or by other known production techniques.

The flexure 22 has a reinforcing portion 28 connected to the central portion 25, which increases the flexure’s cross-section in at least one direction relative to the overall dimensions of the flexure 22. In the embodiment shown in Figures 3 A and 3B, the reinforcing portion 28 extends the width of the flexure adjacent to the central portion 25 (as seen in Figure 3 A) whilst the flexure’s height (as seen in Figure 3B) is the same as the central portion 25. Alternative reinforcing portions may extend the dimensions of the flexure 22 in different directions.

The reinforcing portion 28 may be integrally formed with the central portion 25 as shown in Figure 3 A, or may be a separate component (e.g. of a different material) which is attached to the flexure 22. The reinforcing portion may be connected to the central portion 25 at all points along its length. Alternatively, the flexure may have one or more cut-outs 29 (so gaps) between the central portion 25 and the reinforcing portion 28.

It will be appreciated that the necked portions 23, 27 and the reinforcing portion 28 both have the effect of causing the central portion 25 of the flexure 22 to be stiffer than the portions proximal to the first and second ends 24, 26, in particular the necked portions 23, 27. This means that, at least under low to moderate stresses, the flexure 22 will preferentially flex by bending at the necked portions 23, 27, rather than in the central portion (or more generally along its length). The flexure 22 will also react to applied forces by bending at the necked portions 23, 27 rather than by stretching or compressing.

Such configuration of the flexure 22 causes it to act, at least over small movements, in the same manner as a rigid arm which is pin-jointed at either end (to the movable part and to the support structure, respectively). However, the flexure 22 does not require the complex connection arrangement that a true pin-jointed arm would require and therefore can be made much more simply and accurately, particularly when manufactured on a microscopic scale. For example, the flexure 22 may be connected at the first end 24 and the second end 26 to the movable part and the support structure by heat stakes as known in existing miniature assemblies.

Connection by a true pin-jointed arm constrains or removes one degree of freedom from the relative motion of the parts joined. Accordingly, by providing five flexures 22 of the kind described in relation to Figures 3 A and 3B, for example as in the arrangement shown in Figure 2, five degrees of freedom of the relative motion of the movable part 10 relative to the support structure 2 can be removed, leaving a single degree of freedom, which is motion along the desired helical path. Accordingly, actuator assemblies according to embodiments of the present invention preferably have at least five flexures.

For the purposes of manufacturing an actuator assembly, arrangements with even numbers of components may be preferable due to symmetry of manufacture. Therefore, actuator assemblies according to some embodiments of the present invention may have, for example, four, six or eight flexures which may be arranged with rotational symmetry around the helical axis H. An arrangement with four flexures 22 may be advantageous in actuator assemblies 1 with a square footprint, as in some camera apparatuses.

Flexures in accordance with embodiments of the present invention may have one or other of the necked portions or the reinforcing portion, or both. Further, other approaches which lead to the stiffening of the central portion 25 relative to the outer portions are also possible, for example by manufacturing the flexure from different materials, or from treating the material of the flexure to adjust its properties along its length.

Figures 4A and 4B show part of a bearing arrangement 20 which forms part of an actuator assembly 1 according to an embodiment of the present invention. For clarity, only a single flexure 22a is shown in these figures, whilst the full bearing arrangement 20 would incorporate several such flexures (for example, four or five, as shown in Figure 2). Similarly, many of the other features of the actuator assembly 1 as a whole (such as the actuator components) are also omitted from these figures. Figure 4B shows a close-up of the flexure 22a in the arrangement shown in Figure 4 A. The flexure 22a in the arrangement shown in Figures 4A and 4B is a straight flexure like that shown in Figures 3 A and 3B and shows how a flexure such as that shown in Figures 3 A and 3B can be connected as part of the bearing arrangement 20.

The flexure 22a has necked portions 23a, 27a either side of the central portion 25a. These necked portions are formed by a reduced dimension of the flexure 22a in the vertical direction (i.e. direction parallel to the helical axis) only. The central portion 25a has a reinforcing portion 28a which is formed integrally with the central portion as an extension to the side of the central portion and has a cut-out (or gap) 29a etched along most of the length between the central portion and the reinforcing portion such that the reinforcing portion is connected to the central portion at either end. During the manufacture and/or assembly of the bearing arrangement 20 or actuator assembly the reinforcing portion 28a is bent downwards such that it is formed at a right angle to the central portion 25a.

It will be understood that the reinforcing portion 28a increases the stiffness of the central portion 25a compared to the necked portions 23a, 27a. This causes the flexure 22a to act in a manner akin to that of a rigid arm which is pin-jointed at either end, whilst being attached to the movable part 10 and the support structure 2 by standard heat stakes 21 which are much simpler to form than a true pin-joint.

By using flexures such as those described above, a bearing arrangement 20 can be formed in which the flexures 22 are less prone to stretching or buckling, thus leading to changes in length when subject to compression or extension forces along the length of the flexure. Thus the flexures 22 can maintain a constant distance between the connection points (e.g. heat stakes 21). This can improve the accuracy of the bearing arrangement 20 in following the desired helical motion with reduced or eliminated tilt of the movable part 10 during the helical motion.

As described above, in certain arrangements, flexures 22 used in embodiments of the present invention are configured so as to operate in a similar manner to a rigid arm which is pin- jointed at either end. Such flexures 22 are less likely to change (or likely to experience relatively smaller changes) in length when subject to compression or tension forces along the longitudinal direction of the flexure 22. Figure 5 shows an arrangement of an actuator assembly 1 according to an embodiment of the present invention. The flexures 22 of the bearing arrangement 20 of the actuator assembly 1 may be those described above, but detail of the flexures 22 is omitted from Figure 5 in order to show the configuration and attachment of SMA wires 40 which drive the motion of the movable part 10 in more detail.

The flexures 22 in the embodiment shown in Figure 5 are similar to those described in relation to Figures 3 and 4 above. The flexures 22 in this embodiment are arcuate and follow the form of the outer circumference of the movable part 10.

Four SMA wires 40 are arranged in a square pattern around the movable part 10. In order to give the greatest amount of stroke in the available space, the SMA actuator wires 40 run substantially along the length of, and close to the edges of, the support structure 2. Each SMA wire 40 is connected between a static crimp 41 which is attached to or forms part of the support structure 2 and a moving crimp 42 which is attached to or forms part of the movable part 10. For ease of manufacture, the movable crimps 42 are formed as pairs so that two SMA wires 40 are connected so that they extend in substantially perpendicular directions from each movable crimp.

In operation, a controller 5, which may be included in the IC 5 mounted on the support structure 2 controls the supply of power to the SMA wires 40, for example to control an autofocus function of a miniature camera. In the configuration shown, the controller will typically supply power to the SMA wires 40 in pairs, such that SMA wires 40 on opposing sides of the movable part 10 are powered at the same time. When power is supplied to the SMA wires 40, it causes them to heat and thus contract, which exerts a force on the moving crimps 42 and thus on the movable part 10.

The force exerted on the movable part 10 by contraction of a pair of SMA wires 40 is, due to the configuration of the SMA wires in this embodiment, a torsional force acting about the central axis H (which may also be, for example, the optical axis of a lens assembly mounted on the movable part 10). This force is then converted by the bearing arrangement comprising the flexures 22c into helical motion so that the movable part 10 not only rotates about the central axis H, but also translates along that axis (in a direction into or out of the plane of Figure 5). Thus, torsional forces on the movable part 10 are converted into lateral motion. The configuration of the actuator assembly 1 in the embodiment shown in Figure 5 allows for an actuator assembly 1 that provides good control and range of movement along the axis H by virtue of the length of the SMA wires 40 that can be used, but also provides an actuator assembly whose form factor in the direction along the axis H is minimised as the SMA wires 40 are all arranged around the movable part, rather than parallel to the axis.

Although four SMA wires 40 are shown in Fig. 4, the actuator assembly 1 may comprise any other number and arrangement of SMA wires 40.

As described above, the bearing arrangement 20 is for guiding helical movement of the movable part 10 with respect to the support structure 2 about a helical axis and comprises flexures 22. The bearing arrangement 20 may be integrally formed from sheet material. So, all parts of the bearing arrangement 20 may be formed from the sheet material. This may reduce the complexity of fabricating the bearing arrangement 20, especially when the bearing arrangement 20 is a miniature bearing arrangement 20 for use in miniature apparatuses, such as miniature cameras.

There is thus provided a bearing arrangement 20 comprising at least one flexure 22. Preferably, the bearing arrangement 20 comprises at least two flexures 22, for example four flexures 22. The bearing arrangement may comprise any of the features of the bearing arrangement 20 described in relation to Figs. 2 to 5. The flexures 22 of the bearing arrangement 20 may or may not comprise a central portion 25 that is stiffer than respective outer portions 23, 27.

Such a bearing arrangement 20 is shown in plan view (along the helical axis H) in Fig. 6A and in perspective view in Fig. 6B. The bearing arrangement 20 comprises a movable plate 32 that may be connected to the movable part 10, and a support plate 34 that may be connected to the support structure 2. The bearing arrangement 20 guides helical movement of the movable plate 32 with respect to the support plate 34 about the helical axis H (and thus guide helical movement of the movable part 10 with respect to the support structure 2 about the helical axis H). The bearing arrangement 20 is integrally formed from sheet material. Thus, the flexures 22, the movable plate 32 and the support plate 34 may be integrally formed from the sheet material. The sheet material may be sheet metal, for example a sheet of stainless steel or other metal. The sheet material may have a thickness in the range from 5 to 500pm, preferably from 10 to 200pm, further preferably from 20 to 80pm, most preferably from 30 to 50pm. The bearing arrangement 20 may have a lateral extent (i.e. perpendicular to the helical axis) in the range from 1 to 16mm, preferably from 2 to 10mm, further preferably from 3 to 7mm.

The sheet material may be electrically conductive. This allows current to be directed to from the support structure to the movable part via the bearing arrangement 20. The sheet material may be coated with an electrically-insulating dielectric material. The dielectric coating or other type of dielectric layer may include one or more windows allowing electrical connections therethrough.

As shown in Figs. 6A and 6B, the bearing arrangement 20 may comprise a single movable plate 32 that is common to the flexures 22 of the bearing arrangement 20. So, all flexures 22 of the bearing arrangement 20 may be connected by the movable plate. This fixes the relative position of the flexures 22, which may be useful when assembling the actuator assembly 1. The movable plate 32 may be ring-shaped, i.e. shaped as a circular annulus having a central aperture, for example. Additionally, the bearing arrangement 20 of Fig. 6 A and 6B comprises a single support plate 34 that is common to the flexures 22 of the bearing arrangement 32. The support plate 34 connects to all flexures 22 of the bearing arrangement 32. The support plate 34 may be ring-shaped, i.e. shaped as a circular annulus having a central aperture, for example

Alternatively, a plurality of movable plates 32 and/or support plates 34 may be provided. For example, the bearing arrangement may comprise individual movable plates 32 and/or support plates 34 for each flexure 22.

Each flexure 22 may have a central portion 25 between two outer portions 23, 27. The central portion 25 may be stiffer in at least one direction, e.g. in a direction parallel to the helical axis H, than each of the outer portions 23, 27. Optionally, each flexure 22 may have a reinforcing portion 29. The bearing arrangement 20 may thus correspond to the bearing arrangement 20 described in relation to Figs. 2-5. The central portion 25, the two outer portions 23, 27, and optionally the reinforcing portion 29 may integrally be formed from the sheet material.

The central portion 25 may extend substantially in a plane. The reinforcing portion 29 may be formed from the sheet material and extends in a plane that is angled relative to the plane of the central portion 25. The central and reinforcing portions may be formed, for example, by bending or folding the sheet material.

The bearing arrangement 20 may be incorporated into an actuator assembly 1, such as the actuator assembly 1 described in relation to Figs. 1 or 5.

A method of manufacturing the bearing arrangement 20 comprises providing a piece of sheet material and selectively removing portions of the piece of sheet material so as to provide the bearing arrangement 20. The piece of sheet material may be a piece of sheet metal.

Selectively removing portions of the piece of sheet material may comprise selectively etching the sheet material, for example through a photomask or other mask. Such etching may be especially suitable for miniature devices and high-throughput manufacturing. Alternatively, portions of the piece of sheet material may be removed by any other suitable techniques, such as laser ablation or other laser processes, or cutting or stamping out the portions of the piece of sheet material.

Outer portions 23, 27 of the flexures 22 may be partially etched, so that the outer portions 23, 27 have a smaller cross section than a central portion 25 of the flexures 22. Alternatively or additionally, after selective removal of portions of the sheet material, the sheet material may be bent so as to form the reinforcing portion 29 for each flexure 22. Each flexure 22 may thus be formed to have a central portion 25 that is stiffer than the two outer portions 23, 27, and so resemble a pin-jointed arm as explained above.

Manufacturing the bearing arrangement 20 may further comprise moving the movable plate 32 relative to the support plate 34 in a direction perpendicular to the plane of the sheet material. The flexures 22 may thus be pre-deflected and are angled relative to the plane of the piece of sheet material. The bearing arrangement 20 may then be incorporated into the actuator assembly 1, for example the actuator assembly 1 described in relation to Figs. 1 and 5. A method of manufacturing the actuator assembly 1 comprises connecting the movable plate 32 of the bearing arrangement 20 to the movable part 10 of the actuator assembly 1 and connecting the support plate 34 of the bearing arrangement 20 to the support structure 2 of the actuator assembly 1. The bearing arrangement 20 may be connected to the movable part 10 and/or support structure 1 by any suitable techniques, for example by heat-staking or gluing using an adhesive. An actuator component 40, for example an SMA wire 40, may be connected between the support structure 2 and the movable part 10 in an arrangement such that, on actuation or contraction, the actuator component 40 drives rotation of the movable part 10 around the helical axis H. The rotation is converted into helical movement around the helical axis H by the bearing arrangement 20. The actuator component 40 is connected to the support structure 2 and to the movable part 10 by any suitable techniques, for example by crimping.

The bearing arrangement 20 may initially be provided with a single movable plate 32 and/or a single support plate 34 that connects the flexures 22, as shown in Figs. 6A and 6B. The single movable plate 32 and/or the single support plate 34 fixes the relative position of the flexures 22. After connection to the movable part 10 and/or support structure 2, portions of the movable plate 32 and/or of the support plate 34 may be selectively removed. Multiple movable plates 32 and/or multiple support plates 34 may be formed, for example an individual movable plate 32 and/or an individual support plate 34 for each flexure 22. This may make space for other components of the actuator assembly 1, or make the actuator assembly 1 lighter and more compact. The flexures 22 may be held in place due to their connection to the movable part 10 and/or to the support structure 2.

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

Whilst the embodiments above have described actuator assemblies which use SMA wires, the skilled person will appreciate that the features of the bearing arrangements and the flexures described can be readily used with other forms of actuator components. For example, each actuator component may be a voice coil motor (VCM) actuator, but other types of actuator are possible, for example a piezoelectric actuator, a radial motor or others.

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 the present disclosure, the present disclosure 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 invention has 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.