Actuator assembly

Abstract

An actuator assembly comprising: a first part (10); a second part (20) that is movable relative to the first part; a bearing arrangement (40) configured to guide rotation of the second part relative to the first part about an axis of rotation (P); a first actuating unit (30a) configured to apply an actuating force (F) to the second part to drive rotation of the second part relative to the first part in a first sense about the axis of rotation; wherein the first actuating unit comprises: a body portion (31); an SMA element (34) connected between the body portion and the first part, and configured, on actuation, to apply an input force (Fi) to the body portion; and a force-modifying element (32a) connected between the body portion and the first part, and configured to modify the input force so as to give rise to the actuating force.

Description

[0001] ACTUATOR ASSEMBLY

[0002] Field

[0003] The present application relates to an actuator assembly with at least one actuating unit including a shape memory alloy (SMA) element.

[0004] Background

[0005] SMA actuator assemblies may be used in a variety of applications for moving a second part relative to a first part.

[0006] For example, WO 2013 / 175197 Al describes a camera in which four SMA wires are arranged to move a lens element relative to an image sensor in a plane that is perpendicular to the optical axis of the lens element, thereby effecting optical image stabilization (OIS). WO 2010 / 029316 A2 describes SMA wires used to provide OIS in a camera by tilting a camera module. WO 2011 / 104518 Al describes an actuator assembly having eight SMA wires capable of effecting positional control of a movable element with multiple degrees of freedom.

[0007] Typically, the range of movement (also known as "stroke") of such SMA actuator assemblies is limited by the maximum contraction of the SMA wires, and the actuating force is limited by the maximum force that can be generated by the SMA wires. To increase the movement range or the actuating force, longer or thicker SMA wires can be used, but this may be at the expense of increased cost, size and / or power, which may not be practical in miniature applications.

[0008] WO 2022 / 084699 Al discloses an actuator assembly comprising at least one actuating unit (incorporating an SMA wire) that, on actuation, moves a second part relative to the support structure. The actuating unit may be configured to increase the stroke or the actuating force and / or to re-direct the force applied by the SMA wire.

[0009] WO 2013 / 175197 Al, WO 2010 / 029316 A2, WO 2011 / 104518 Al and WO 2022 / 084699 Al are each incorporated herein by reference.

[0010] Summary

[0011] According to an aspect of the present invention, there is provided an actuator assembly comprising: a first part; a second part that is movable relative to the first part; a bearing arrangement configured to guide rotation of the second part relative to the first part about an axis of rotation; a first actuating unit configured to apply an actuating force to the second part to drive rotation of the second part relative to the first part in a first sense about the axis of rotation; wherein the first actuating unit comprises: a body portion; an SMA element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part, and configured to modify the input force so as to give rise to the actuating force.

[0012] Using an actuating unit to drive rotation in this way may provide an actuator assembly which enables significant rotation whilst reducing (or minimizing) power consumption and cost.

[0013] The bearing arrangement may constrain the second part to rotate about the axis of rotation and optionally may restrict or prevent movement of the second part in other degrees of freedom. The bearing arrangement may comprise a rolling bearing, a plain bearing or may comprise one or more flexures, for example. The bearing arrangement may comprise one or more bearing surfaces which guide rotation of the second part about the axis of rotation. One or more such bearing surfaces may be parallel to (or substantially parallel to) the axis of rotation.

[0014] The first actuating unit may further comprise a coupling link connected between the body portion and the second part. The coupling link may be configured to transmit the actuating force from the body portion to the second part. The coupling link may be compliant in a direction perpendicular to the actuating force. Thus, the coupling link can accommodate movement of the second part in directions other than the direction in which the actuating force is applied.

[0015] The coupling link may be elongate and may be stiff along its length and compliant in a direction perpendicular to its length. The coupling link may be or may comprise a coupling flexure. Such embodiments may be particularly preferable due to improved manufacturability and reduced cost.

[0016] In operation, the coupling link may be generally in tension. The force-modifying element may pull on the second part via the coupling link so as to apply the actuating force to the second part. This is particularly preferable, for example, when the coupling link comprises a flexure. Alternatively, the coupling link may be generally in compression. The force-modifying element may push on the second part via the coupling link so as to apply the actuating force to the second part. The force-modifying element may be or may comprise a force-modifying flexure. The force-modifying element may be elongate and may be stiff along its length and compliant in a direction perpendicular to its length.

[0017] The body portion, the coupling link and / or the force-modifying element may be integrally formed. Such embodiments may be particularly preferable due to improved manufacturability and reduced cost.

[0018] The actuator assembly may comprise a second actuating unit configured to apply an actuating force to the second part to drive rotation of the second part relative to the first part in a second sense, opposite to the first sense, about the axis of rotation. The second actuating unit may comprise: a body portion; an SMA element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part, and configured to modify the input force so as to give rise to the actuating force. In other words, the actuator assembly may also comprise a second actuating unit, which may be arranged in substantially the same way as the first actuating unit, and which is configured to drive rotation of the second part in a second sense, which is opposite to the first sense.

[0019] Alternatively, the actuator assembly may comprise a resilient element such as a spring to oppose the first actuating unit and cause rotation of the second part in the second sense.

[0020] Any of the features described herein with reference to the first actuating unit may be applied to the second actuating unit. For example, the second actuating unit may comprise a coupling link as described above with reference to the first actuating unit and that coupling link may have any of the features described herein with reference to a coupling link.

[0021] The SMA element of the first actuating unit may be substantially parallel to the SMA element of the second actuating unit when viewed along the axis of rotation. This arrangement may be particularly compact.

[0022] Alternatively, the SMA element of the first actuating unit may be substantially perpendicular to the SMA element of the second actuating unit when viewed along the axis of rotation. This may be advantageous in certain space envelopes. The actuator assembly may comprise four sides arranged in a loop. Such a loop may be in a plane perpendicular to the axis of rotation. In embodiments in which a first actuating unit and a second actuating unit are present, the actuating units may be arranged in a number of different ways, for example:

[0023] The first actuating unit may be disposed on a first side of the actuator assembly and the second actuating unit may be disposed on a second side of the actuator assembly, where the second side is adjacent to the first side.

[0024] The first actuating unit and the second actuating unit may be disposed on the same side of the actuator assembly.

[0025] The first actuating unit may disposed on a first side of the actuator assembly and the second actuating unit may be disposed on a second side of the actuator assembly, where the second side is opposite to the first side.

[0026] In some embodiments, the first actuating unit may be arranged along two sides of the actuator assembly. The first actuating unit may be arranged along two adjacent sides of the actuator assembly. In embodiments in which a second actuating unit is present, the second actuating unit may be arranged along two adjacent sides of the actuator assembly. When an actuating unit is arranged along two adjacent sides of the actuator assembly, the SMA element of the actuating unit may be arranged along a first side of the actuator assembly and a coupling link of the actuating unit may be arranged along a second side of the actuator assembly (the second side being adjacent to the first side).

[0027] The actuator assembly may comprise a total of two actuating units. In some embodiments the actuator assembly may comprise a different number of actuating units. For example, the actuator assembly may comprise two or more actuating units, three or more actuating units, four or more actuating units or any other number of actuating units. The actuator assembly may comprise a total of one actuating unit or a total of three actuating units or a total of four actuating units.

[0028] The second part may define a plane and the axis of rotation may be perpendicular to that plane. For example, the second part may be generally planar and the axis of rotation may be perpendicular to the plane of the second part. The axis of rotation may be parallel to a shorted dimension of the second part.

[0029] The actuator assembly can produce relative movement of the first and second parts. The first part may correspond to a support structure, and the second part may correspond to a movable part (which may comprise e.g. the relevant optical component). Alternatively, the first part may correspond the movable part, and the second part may correspond to the support structure. One of first and second parts may comprise an image sensor. The axis of rotation may be perpendicular to a light-sensitive region of the image sensor. One of the first and second parts further may comprise a lens. The lens may be arranged to focus an image onto the image sensor.

[0030] The actuator assembly may comprise a variable aperture mechanism defining a variable aperture. The actuator assembly may be configured such that rotation of one of the first and second parts relative to the other of the first and second parts changes the size of the variable aperture. In an example, the variable aperture mechanism comprises a plurality of blades which are configured to define a variable aperture. The plurality of blades may be connected to the first part via a first plurality of pins and connected to the second part via a second plurality of pins. The blades may be configured to rotate about the first or second pins when the second part is rotated relative to the first part. The plurality of blades may be configured such that rotation of the plurality of blades about the first or second pins changes the size of the variable aperture.

[0031] The actuator assembly may be configured such that on contraction of SMA element of the first actuating unit, the second part rotates about the axis of rotation by an amount which is greater than a change in length of the SMA element. In other words, the movement of the second part about the axis of rotation is amplified, i.e. there is an overall gearing-up of the motion about the axis of rotation.

[0032] In some embodiments the actuator assembly may be configured such that on contraction of the SMA element of the first actuating unit, the second part rotates about the axis of rotation by an amount which is less than a change in length of the SMA element. In other words, the movement of the second part about the axis of rotation is de-amplified, i.e. there is an overall gearing-down of the motion about the axis of rotation.

[0033] An amount by which the second part rotates about the axis of rotation may refer to a distance by which a point on the second part moves along a curved (e.g. circular path). The point may be on an outer edge (radially) of the second part.

[0034] In some embodiments the second actuating unit may be configured to gear-up or gear-down the motion of the second part, as described above with reference to the first actuating unit.

[0035] In summary, the first and / or second actuating units may be arranged to amplify or de-amplify the rotation of the second part.

[0036] According to an aspect of the present invention, there is provided a system comprising: an actuator assembly as disclosed herein (for example above); and a tilt assembly configured to tilt a moving part about two axes which are perpendicular to each other and to the axis of rotation, wherein the actuator assembly is arranged in mechanical series with the tilt assembly.

[0037] The moving part may comprise an image sensor and a lens assembly. The axis of rotation may be parallel to or colinear with an optical axis of the lens assembly. The axis of rotation may be perpendicular to a light-sensitive region of the image sensor.

[0038] The actuator assembly may be configured to drive rotation of the image sensor. In other words, the second part may comprise the image sensor (and optionally also the lens).

[0039] The SMA may be a nickel-titanium alloy. For example, the SMA may be nitinol.

[0040] Brief description of the drawings

[0041] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0042] Figures 1A-C are schematic cross-sectional views of different variations of a camera module assembly incorporating an actuator assembly;

[0043] Figure 2 is a schematic perspective view of the actuator assembly;

[0044] Figures 3A and 3B are perspective and plan views of an actuating unit forming part of the actuator assembly, and Figure 3C is a plan view of another such actuating unit;

[0045] Figure 4 is a schematic plan view of an arrangement of four actuating units;

[0046] Figure 5a is a schematic plan view of an actuator assembly comprising two actuating units;

[0047] Figure 5b is a schematic plan view of one of the actuating units shown in Figure 5a;

[0048] Figure 6 is a schematic plan view of an actuator assembly comprising two actuating units;

[0049] Figure 7 is a schematic plan view of an actuator assembly comprising two actuating units;

[0050] Figure 8 is a schematic view of an actuator assembly as part of a module tilt arrangement;

[0051] Figure 9 is a schematic view of an actuator assembly as part of another module tilt arrangement;

[0052] Figure 10A is a schematic view of an arrangement of actuating units;

[0053] Figure 10B is a schematic view of a further arrangement of actuating units;

[0054] Figure IOC is a schematic view of a further arrangement of actuating units; and

[0055] Figure 11 is a schematic perspective view of an SMA actuator assembly for rotating a movable part about a primary axis.

[0056] Detailed description Figures 1A-C schematically show different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera module assembly 1. Generally, the apparatus 1 is to be incorporated in a portable electronic device such as a smartphone. Thus, miniaturisation can be an important design criterion. However, the actuator assemblies disclosed herein may be used to move any component, whether optical or otherwise.

[0057] Figure 2 schematically shows an actuator assembly 2. The actuator assembly 2 includes a first part 10 and a second part 20. The second part 20 is movable relative to the first part 10. When the actuator assembly 2 is included in an apparatus 1, the first part 10 may be fixed relative to the main body of the apparatus. For example, the first part may be a support structure and may be fixed relative to a main body of the apparatus. However, in general, the first part 10 need not be stationary and may be movable relative to or within the apparatus. The actuator assembly 2 includes one or more actuating units 30. Each actuating unit 30 is configured to apply an actuating force to the second part 20 capable of moving the second part 20 relative to the first part 10.

[0058] The actuator assembly 2 further includes a bearing arrangement 40 that supports the second part 20 on the first part 10. The actuating units 30 and the bearing arrangement 40 may together support the second part 20 on the first part 10. The bearing arrangement 40 is configured to guide rotation of the second part relative to the first part about an axis of rotation P. The bearing arrangement 40 may have any suitable form for allowing movement of the second part 20 with respect to the first part 10 and for guiding rotation of the second part about the axis of rotation P. The actuating units 30 and / or the bearing arrangement 40 may constrain, i.e. reduce or prevent, other degrees of freedom of movement of the second part 20 relative to the first part 10. For this purpose, the bearing arrangement 40 may, for example, include one or more of the following bearings: a rolling bearing (such as a ball bearing), a flexure bearing (i.e. an arrangement of flexures or other resilient elements that guide movement), or a plain (i.e. sliding contact) bearing.

[0059] A primary axis P can be defined with reference to the actuator assembly 2 and / or the first part 10. The primary axis P may extend through the actuator assembly 2, e.g. through the centre of the actuator assembly 2. In some examples, the actuator assembly 2, the first part 10 and / or the second part 20 extend predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 2, the first part 10 and / or the second part 20 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. The primary axis P may be the longitudinal axis of the actuator assembly 2 and / or the first part 10. Alternatively or additionally, the first part 10 and / or second part 20 may include a planar component that extends perpendicularly to the primary axis P. Alternatively or additionally, in examples in which the apparatus 1 includes an optical element (such as a lens assembly) with an optical axis, or an imaging element (such as an image sensor) with an imaging axis, the primary axis P may be parallel to such an axis and / or may coincide with such an axis when the second part 20 is in a central position or orientation.

[0060] In general, as mentioned above, the second part 20 is movable relative to the first part 10. In particular, the second part is driven to rotate about an axis of rotation. In the context of describing the movement, the primary axis P may also be referred to as the z axis, and two further axes that are perpendicular to the primary axis P and to each other may be referred to as the x and y axes. The second part 20 may be movable relative to the first part 10 as follows:

[0061] Rx and / or Ry: Rotational movement (or simply rotation or tilting) about the x and / or y axes. In other words, the second part 20 may be rotated about any line perpendicular to the primary axis P. The second part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement. Instead of such two-axis rotation, the second part 20 may be rotatable about a single axis, e.g. about the x or y axis.

[0062] Rz: Rotational movement (or simply rotation) about the z axis. The second part 20 may be rotatable to any rotational position (i.e. to any orientation) within a range of movement.

[0063] The second part 20 may additionally move in other DOFs. The second part 20 may move in DOFs that are a combination of rotation about an axis and translation along that axis. In other words, the second part 20 may move along a helical path (i.e. move helically). For example, the second part 20 may move along a helical path about the z axis, and so concurrently move along the z axis and rotate about the z axis. In other words, Tz and Rz movement may be coupled. An example of such a helical actuator assembly is disclosed in WO 2019 / 243849 Al, which is herein incorporated by reference.

[0064] The assembly 2 may be configured such that rotation of the second part 20 about an axis may drive rotation of a third part along that axis. An example of such an actuator arrangement is disclosed in WO2021 / 209767A1, which is herein incorporated by reference.

[0065] The actuating units 30 are connected between the first part 10 and the second part 20. The actuating units 30 are arranged to apply actuating forces F (see e.g. Figure 4) between the second part 20 and the first part 10. Selectively varying the actuating forces F may cause the second part 20 to move relative to the first part 10 within the DOFs allowed by the bearing arrangement 40. The actuating units 30 are thus capable of driving movement of the second part 20 relative to the first part 10.

[0066] The bearing arrangement 40 may cause the second part 20 to move in directions which differ from the directions of the actuating forces F. In simple examples of this, one component of each actuating force F causes the movement of the second part 20, and another component of each actuating force F acts against the bearing forces produced by the bearing arrangement 40.

[0067] The actuator assembly 2 may be or comprise a camera module assembly. The actuator assembly 2 may include a lens assembly and an image sensor. The lens assembly includes one or more lenses configured to focus an image on the image sensor. The lens assembly defines an optical axis O. The lens assembly may include a lens carrier, for example in the form of a cylindrical body, supporting the one or more lenses. The image sensor captures an image and may be of any suitable type, for example a charge coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. The camera module camera assembly may be a compact camera module camera assembly in which each lens has a diameter of 20mm or less, for example of 12mm or less.

[0068] In the ("sensor-shift") variation of the camera module assembly 1 shown in Figure 1A, the second part 20 includes the image sensor 4. The image sensor is thus rotated (e.g. about the axis P) relative to the first part 10. The lens assembly 3 may be fixed relative to the first part 10, or may be movable relative to the first part 10 along the optical axis O, as described below.

[0069] In the ("lens-shift") variation shown in Figure IB, the image sensor 4 is fixed relative to the first part 10 and movement of the second part 20 drives movement of a lens assembly 3. For example, the lens assembly may be a third part which is driven to move as a result of movement of the second part 20. An example of such a system is disclosed in WO2021 / 209767A1, which is herein incorporated by reference. The lens assembly 3 may be movable relative to the first part 10 along the optical axis O, as described below.

[0070] In both of these variations, the actuator assembly 2 is configured to cause relative movement between the lens assembly 3 and the image sensor 4. Such movement has the effect of moving or otherwise varying the image on the image sensor 4 and may enable optical image stabilisation (OIS) and / or a change in focus of the image (e.g. autofocus) to be implemented in the camera module camera assembly 1. In the sensor-shift variation, the second part 20 is rotatable about the primary axis P so as to also enable compensation for roll.

[0071] In the ("module-tilt") variation shown in Figure 1C, the camera module assembly 1 comprises a module 6 comprising the lens assembly 3 and the image sensor 4. The module may be configured so as to be tilted (e.g. by a further actuator arrangement which may be referred to as a tilt assembly) about two axes perpendicular to the primary axis P and to each other, enabling OIS to be implemented in the camera module camera assembly 1. The actuator assembly 2 may be connected in mechanical series with such a further actuator arrangement ('tilt assembly'). In a first example, shown schematically in Figure 8, the actuator assembly 2 may be disposed on (e.g. within) the module itself and arranged to be tilted with the module about the X and Y axes. In such an example, the second part 20 may comprise the image sensor 4, for example. In a second example, shown schematically in Figure 9, the actuator assembly 2 may be arranged to drive rotation of the entire module 6, e.g. about the Z axis (when the module is in a neutral, untilted position). In this second example the second part 20 would comprise the module 6. Figures 8 and 9 both show a side view (i.e. viewed along a direction perpendicular to the primary axis P) of a module 6 and the actuator assembly 2

[0072] The camera module camera assembly 1 also includes a controller 8. The controller 8 may be implemented in an integrated circuit (IC) chip. The controller 8 generates drive signals for the actuating units 30, in particular for SMA wires 34 forming part of the actuating units 30. SMA material has the property that, on heating, it undergoes a solid-state phase change that causes the SMA material to contract. Thus, applying drive signals to the SMA wires 34, thereby heating the SMA wires 34 by causing an electric current to flow, will cause the SMA wires 34 to contract and thus actuate the actuating unit 30 so as to drive relative movement of the second part 20. The drive signals are chosen to drive relative movement of the second part 20 in a desired manner, for example so as to achieve OIS by stabilizing the image sensed by the image sensor 4 or to achieve AF / zoom by adjusting the focus of the image sensed by the image sensor 4. The controller 8 supplies the generated drive signals to the SMA wires 34.

[0073] Optionally, the camera module camera assembly 1 also includes a motion sensor (not shown), which may include a 3-axis gyroscope and a 3-axis accelerometer. The motion sensor can generate signals representative of the motion (specifically vibrations or "shake") of the camera module camera assembly 1, which can be processed so as to produce signals representative of the required movement of the second part 20 to compensate for such shake. The controller 8 receives such signals and can generate the drive signals for the SMA wires 34 to achieve OIS.

[0074] Although the actuator assembly 2 is described in connection with a camera module camera assembly 1, it will be appreciated that the actuator assembly 2 may be used in any device in which movement of a second part 20 relative to a first part 10 is desired, e.g. to provide haptic feedback in a haptic feedback device or to move a projector or display in an augmented reality (AR) or virtual reality (VR) device or in a variable aperture mechanism, to change the size of an aperture.

[0075] Actuating unit Figure 3A shows a perspective view of an example of the actuating unit 30. Figure 3B shows part of the actuating unit 30 in plan view.

[0076] A single actuating unit 30 is shown in Figures 3A and 3B, but it will be appreciated that the actuator assembly 2 may have multiple actuating units 30, each of which may include the same components described with reference to Figures 3A and 3B.

[0077] The actuating unit 30 includes a body portion 31 to which several other components of the actuating unit 30 are connected as described below. Typically, the body portion 31 is relatively rigid compared to the other components of the actuating unit, and does not deform significantly on actuation of the actuating unit 30. In some examples, the body portion 31 is not a distinct part of the actuating unit 30. For example, the body portion 31 may be defined as part of one of the other components of the actuating unit 30 or simply as a connection point between other components of the actuating unit 30.

[0078] The actuating unit 30 also includes a force-modifying flexure 32. The force-modifying flexure 32 is connected between the body portion 31 and the first part 10. One end of the force-modifying flexure 32 is connected to the body portion 31. The other end of the force-modifying flexure 32 is connected to the first part 10, e.g. via a foot portion 36. The foot portion 36 is fixed relative to the first part 10. In the depicted design, the force-modifying flexure 32 is formed integrally with the foot portion 36 and with the body portion 31, for example from a single sheet of material (such as metal). The force-modifying flexure 32 allows the body portion 31 to pivot relative to the first part 10 about an effective pivot point P. Although the effective pivot point P is shown in Figure 3B as being positioned in the middle of forcemodifying flexure 32, the effective pivot point P may have a different position and also need not lie on the force-modifying flexure 32. Such pivotal movement of the body portion 31 relative to the first part 10 is initially in a direction that is substantially perpendicular to the force-modifying flexure 32.

[0079] The actuating unit 30 also includes an SMA element 34. In this example, the SMA element 34 is an SMA wire 34. The SMA wire 34 is connected between the body portion 31 and the first part 10. One end of the SMA wire 34 is connected to the first part 10, e.g. by a crimp 15. The other end of the SMA wire 34 is connected to the body portion 31, e.g. by a crimp 35.

[0080] The actuating unit 30 also includes a coupling link 33. In this example, the coupling link 33 is a coupling flexure 33. The coupling flexure 33 is connected between the body portion 31 and the second part 20. One end of the coupling flexure 33 is connected to the body portion 31. The other end of the coupling flexure 33 is connected to the second part 20. The coupling link 33 transfers or transmits an actuating force F from the body portion 31 to the second part 20. The coupling link 33 is compliant (i.e. deformable) in a direction (or in multiple directions) perpendicular to the actuating force F. This allows the second part 20 to move in directions other than the direction of the coupling flexure 33 and actuating force F. This can be needed, for example, where different actuating units 30 cause the second part 20 to move in different directions or senses.

[0081] In this example, the body portion 31, the force-modifying flexure 32, the coupling flexure 33 and the foot portion 36 are integrally formed, for example from a single sheet of material (such as metal). In other examples, one or more or these features, if present, may be formed from different parts or materials.

[0082] The SMA wire 34 is arranged, on contraction, to apply an input force Fi on the body portion 31. The input force Fi acts parallel to the length of the SMA wire 34. The force-modifying flexure 32 and the body portion 31 are arranged to modify the input force Fi so as to give rise to the actuating force F, which is transmitted from the body portion 31 to the second part 20 by the coupling flexure 33. In particular, the input force Fi deforms the force-modifying flexure 32, thereby causing the body portion 31 to pivot about the effective pivot point P. In simple terms, the force-modifying flexure 32 and the body portion 31 act like a lever. The force-modifying flexure 32 and the body portion 31 may modify the direction and / or the magnitude of the input force Fi so as to give rise to the actuating force F.

[0083] In the example illustrated in Figures 3A and 3B, the coupling flexure 33 is at an angle of ~90° relative to the SMA wire 34. Also, in this example, the force-modifying flexure 32 is arranged at an angle a of ~30° relative to the SMA wire 34, and the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. Hence, on contraction of the SMA wire 34 and on resulting deformation of the forcemodifying flexure 32, the body portion 31 initially moves at an angle of ~60° (90°-a) relative to the length of the SMA wire 34. Thus, it will be appreciated that, in this example, the force is de-amplified and the stroke is amplified, while the direction of the forces / movements is changed by an angle of ~90°.

[0084] More generally, the change in direction of the force depends on the angle between the SMA wire 34 and the coupling flexure 33. Also more generally, the change in magnitude of the force is dependent on the ratio of i) the distance Ds from the effective pivot point P to the line on which the SMA wire 34 lies and ii) the distance De from the effective pivot point P to the line on which the coupling flexure 33 lies. In particular, F / Fi is proportional to Ds / Dc. If the SMA wire 34 lies on a line that is closer to the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is de-amplified. At the same time, the movement of the second part 20 is amplified, i.e. increased relative to a change in length of the SMA wire 34. Alternatively, if the SMA wire 34 lies on a line that is further away from the effective pivot point P than the line on which the coupling flexure 33 lies, then the input force Fi is amplified. At the same time, the movement of the second part 20 is de-amplified, i.e. decreased relative to a change in length of the SMA wire 34. The actuating unit 30 can thus be configured to amplify movement or to amplify force due to contraction of the SMA wire 34. The actuating unit 30 can also be configured to change the direction of the input force Fi. In some examples, the actuating unit 30 is configured to change the direction of the input force Fi without changing the magnitude of the force or movement.

[0085] The ratio Ds / Dc is dependent on the location of the end of the SMA wire 34 that is connected to the body portion 31, and on the location of the end of the coupling flexure 33 that is connected to the body portion 31. By way of example, the distance DsDc could be increased by connecting the coupling flexure 33 further to the left of body portion 31 shown in Figure 3B, thereby decreasing Ds / Dc and so increasing the amount of stroke amplification. The ratio Ds / Dc is also dependent on the orientation of the SMA wire 34, and on the orientation of the coupling flexure 33. Such orientations can be defined with reference to the force-modifying flexure 32 (as above) or any suitable reference line. By way of example, the distance Ds could be decreased by angling the SMA wire 34 shown in Figure 3B so that it passes closer to the effective pivot point P, thereby decreasing Ds / Dc and so increasing the amount of stroke amplification. In summary, the amount by which the force-modifying flexure 32 amplifies or deamplifies the force / stroke of the SMA wire 34 may be tailored by: adjusting the orientation of the SMA wire 34 (and thus of the input force Fi); adjusting the location of the connection point between the SMA wire 34 and the body portion 31 (and thus the location at which the input force Fi acts on the body portion 31); adjusting the orientation of the coupling flexure 33 (and thus of the actuating force F); and / or adjusting the location of the connection point between the coupling flexure 33 and the body portion 31 (and thus the location from which the body portion 31 applies the actuating force F).

[0086] In some examples, at least one actuating unit 30 (preferably each actuating unit 30) is configured such that the force-modifying flexure 32 and the body portion 31 amplifies an amount of contraction of the SMA wire 34. Such amplification, for example, may be by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3. For this purpose, in the example illustrated in Figures 3A and 3B, the angle a between the SMA wire 34 and the force-modifying flexure 32 may be in the range from 0 to 45 degrees, preferably from 13 to 40 degrees. However, in general, the angle a may have other values and the connection points of the SMA wire 34 and / or coupling flexure 33 to the body portion 31 may be adjusted to achieve a desired amount of amplification.

[0087] As described above, in the example illustrated in Figures 3A and 3B, the coupling flexure 33 is at an angle of about 90 degrees relative to the SMA wire 34. This allows the actuating unit 30 to fold around a corner of the second part 20 in a compact manner. The angle between the coupling flexure 33 and the SMA wire 34 may be in the range from 70 to 110 degrees, preferably from 80 to 100 degrees. However, in general, the angle between coupling flexure 33 and SMA wire 34 may be outside these ranges.

[0088] For instance, in the actuating unit 30 illustrated in Figure 3C, the force-modifying flexure 32, the coupling flexure 33 and the SMA wire 34 are substantially parallel to one another.

[0089] In the above-described examples, the actuating unit 30 is arranged in a plane. In particular, the SMA wire 34, the coupling flexure 33 and the force-modifying flexure 32 are arranged so as to substantially extend in a common plane, at least when the actuator assembly 2 is in an initial configuration. This allows for a compact configuration of the actuating unit 30. The body portion 31, when embodied by a plate, may further be arranged to extend in the plane. However, in general, the components of the actuating unit 30 need not be arranged in a common plane. The SMA wire 34 and / or the coupling flexure 33 may be angled relative to the plane, for example.

[0090] In the above-described examples, the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. This reduces the risk of buckling of the force-modifying flexure 32, reducing the risk of damage to the actuator assembly 2 and making the actuator assembly 2 more reliable. However, the force-modifying flexure 32 could instead be arranged so as to be placed under compression on contraction of the SMA wire 34. With reference to Figure 3B, for example, the force-modifying flexure 32 could extend to the bottom-right from the connection point between the body portion 31 and the force-modifying flexure 32, and so be placed under compression on contraction of the SMA wire 34. An arrangement in which the force-modifying flexure 32 is placed under compression is disclosed in WO 2022 / 084699 Al, which is herein incorporated by reference.

[0091] In the above-described examples, the force-modifying flexure 32 and the SMA wire 34 connect at one end to the first part 10, and the coupling flexure 33 connects at one end to the second part 20. In general, this arrangement may also be reversed, with the force-modifying flexure 32 and the SMA wire 34 connecting at one end to the second part 20, and the coupling flexure 33 connecting at one end to the first part 10.

[0092] In the above-described examples, the actuating unit 30 includes a coupling link 33 in the form of a coupling flexure 33. The purpose of the coupling link 33 is to allow movement of the second part 20 in directions perpendicular to the actuating force F, in particular movement of the point at which the actuating unit connects to the second part 20 in directions perpendicular to the actuating force. In general, however, the actuating unit 30 need not include a coupling link 33, e.g. in examples in which there is no movement of the second part 20 in directions perpendicular to the actuating force F. Furthermore, the coupling link 33 may be embodied by components other than the coupling flexure 33, for example by a ball bearing or plain bearing configured to transmit the actuating force F to the second part 20 while allowing movement of the second part 20 in directions perpendicular to the actuating force F. Such alternative examples of the coupling link 33 are disclosed in WO 2022 / 084699 Al, which is incorporated herein by reference. The coupling link 33 may (or may not) be formed by an SMA wire, which may (or may not) be integral with the SMA wire 34 and may (or may not) be driven together with the SMA wire 34.

[0093] Furthermore, instead of the force-modifying flexure 32, the actuator assembly may include a different type of force-modifying element configured to enable the above-described movement of the body portion 31 relative to the first part 10. Such a force-modifying element may include, for instance, a rigid member with one end connected to the first part 10 via a suitable pivoting connection (e.g. a pin joint) and the other end connected to the body portion 31.

[0094] Arrangement of four actuating units

[0095] Figure 4 schematically shows a plan view of an example of the actuator assembly 2, showing an arrangement of actuating units 30. In this example, the actuator assembly 2 includes a total of four actuating units 30. The four actuating units 30 may apply actuating forces F between the second part 20 and the first part 10. The actuating forces F are applied to the second part 20 relative to the first part 10.

[0096] The arrangement of actuating units 30 of Figure 4 may be used, for example, in examples in which the second part 20 is rotatable about the Z axis.

[0097] The four actuating units 30 of Figure 4 are in an arrangement capable of applying actuating forces F so as to move the second part 20 relative to the first part 10. In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a first axis (e.g. the x axis), thus driving rotation of the second part 20 in a first sense (clockwise, as seen in Figure 4). The other two actuating units (e.g. the left and right actuating units in Figure 4) are arranged to apply actuating forces F in opposite directions parallel to a second axis (e.g. the y axis), perpendicular to the first axis, thus driving rotation of the second part 20 in a second sense , opposite to the first sense (i.e. anti-clockwise, as seen in Figure 4). The opposing actuating forces F are not colinear, but offset from each other in a direction perpendicular to the actuating forces F, thus facilitating rotation of the second part 20. As shown, two actuating units 30 may be arranged to apply actuating forces F in a corner of the actuator assembly 2. The other two actuating units 30 may be arranged to apply actuating forces F in another, opposite corner of the actuator assembly 2. The actuator assembly 2, and in particular the second part 20 and / or the first part 10, may have a square or rectangular footprint. Each actuating unit 30 may be provided on one of the four sides of the actuator assembly 2. In particular, each actuating unit 30 may bend around a corner of the second part 20 such that the SMA wire 34 and the coupling flexure 33 of each actuating unit 30 extend along adjacent edges of the second part 20. So, the actuating unit 30 may be as configured in Figures 3A and 3B, for example. The four SMA wires 32 of the four actuating units 32 may extend along the four different edges of the second part 20.

[0098] The arrangement of actuating forces F applied between second part 20 and first part 10 corresponds to the arrangement of SMA wires 30 described in WO2013 / 175197 Al, which is herein incorporated by reference.

[0099] In this example, the actuating forces F are perpendicular to the primary axis P, and may be parallel to a plane perpendicular to the primary axis. However, in general the actuating forces F may be angled relative to the plane. The actuating forces F may thus have a component along the primary axis P. This component along the primary axis P may be resisted by the bearing arrangement 40. In some examples, it may even be desirable for actuating forces F to have a component in parallel to the primary axis P, for example so as to load plain or rolling bearings arranged between the second part 20 and the first part 10.

[0100] Although, for illustrative purposes, the arrangement of actuating units 30 was described as rotating the second part 20 about the primary axis P (i.e. the Z axis), in other examples the second part 20 may be rotated about a different axis, e.g. the X or the Y axis. For example, the same arrangement of actuating forces F may be used to tilt the second part 20 relative to the first part 10 about an axis perpendicular to the primary axis P, due to appropriate movement constraints provided by the bearing arrangement 40. For example, the bearing arrangement 40 may include a plurality of flexures for guiding tilting of the second part 20 about the axes perpendicular to the primary axis P. Examples of such bearing arrangement 40 are described in WO2022 / 029441 Al, which is herein incorporated by reference.

[0101] Although the actuator assembly 2 is described herein in the context of four actuating units 30, in general the actuator assembly 2 may include fewer actuating units 30. In a first example, the actuator assembly 2 may include two actuating units 30, e.g. the two actuating units 30 depicted in the top left of Figure 4. The forces applied to the second part 20 by the two actuating units 30 may be opposed by a biasing force of one or more resilient elements, such as springs. With reference to Figure 4, the two actuating units 30 in the bottom right corner may be replaced with springs applying biasing forces along the corresponding depicted arrows, for example. In a second example, the actuator assembly 2 may include only one actuating unit 30, e.g. the actuating unit on the left side of Figure 4, which would drive rotation of the second part 20 anti-clockwise (when viewed along the primary axis P). The force applied to the second part 20 by the actuating unit may be opposed by a biasing force of one or more resilient elements, such as springs.

[0102] With reference to Figure 5A, an example of an actuator assembly 2 is described. The actuator assembly 2 comprises a first part 10 and a second part 20 which is movable relative to the first part 10. The actuator assembly 2 comprises a first actuating unit 30a and a second actuating unit 30b. Movement of the second part 20 relative to the first part 10 is supported by and guided by a bearing arrangement 40. The bearing arrangement 40 is a rolling bearing and comprises a plurality of ball bearings disposed between a surface of the second part 20 and a surface of the first part 10. The bearing arrangement guides rotation of the second part 20 relative to the first part 10 about the primary axis P.

[0103] Each of the actuating units 30a and 30b is the same as that illustrated in and described with reference to Figure 3C and operates in the same way. In short, taking the first actuating unit 30a as an example and with reference to Figure 5B, the SMA element 34a is arranged, on contraction, to apply an input force on the body portion 31a. The input force acts parallel to the length of the SMA wire 34a. The forcemodifying flexure 32a and the body portion 31a are arranged to modify the input force so as to give rise to the actuating force, which is transmitted from the body portion 31a to the second part 20 by the coupling flexure 33a. The second actuating unit 30b acts on the second part 20 in the same way.

[0104] The first actuating unit 30a is arranged to drive rotation of the second part 20 in a first sense (anticlockwise as seen in Figure 5A) about the axis of rotation P. The second actuating unit 30b is arranged to drive rotation of the second part 20 in a second sense, opposite to the first sense, (i.e. clockwise as seen in Figure 5A) about the axis of rotation P. The rotation is guided by the bearing arrangement 40.

[0105] In the embodiment illustrated in Figure 5A, the first and second actuating units 30a and 30b are arranged on opposite sides of the actuator assembly 2. The actuator assembly 2 comprises four sides arranged in a loop around the axis P and the first and second actuating units 30a and 30b are arranged on opposite sides. Figures 6 and 7 illustrate further embodiments of an actuator assembly 2 in which the first and second actuating units 30a and 30b are arranged differently. The embodiments of figures 6 and 7 comprise the same components as the embodiment of Figure 5A and are operated in the same way and so description of the structure and operation of the embodiments of Figure 6 and 7 will not be repeated.

[0106] With reference to Figure 6, the first and second actuating units 30a and 30b are arranged on the same side of the actuator assembly 2. In particular, the actuator assembly 2 comprises four sides arranged in a loop around the primary axis P and the first and second actuating units 30a and 30b are arranged on the same side.

[0107] With reference to Figure 7, the first and second actuating units 30a and 30b are arranged on adjacent sides of the actuator assembly 2. In particular, the actuator assembly 2 comprises four sides arranged in a loop around the primary axis P and the first and second actuating units 30a and 30b are arranged on adjacent sides.

[0108] In the embodiments of Figures 5A, 6 and 7, each of the first and second actuating units is disposed on a single side of the actuator assembly 2. In other embodiments, one or both of the first and second actuating units may span adjacent sides of the actuator assembly 2. For example, one or both of the first and second actuating units may be arranged as illustrated in Figures 3A and 3B, i.e. around a corner of the actuator assembly 2. In an arrangement in which both of the first and second actuating units are each arranged around a corner, the first and second actuating units may completely or partially overlap, as shown schematically in Figure 10A, 10B and 10C.

[0109] In any of the embodiments described with reference to Figures 5A, 5B, 6, 7, 10A, 10B or 10C, the actuator assembly 2 may comprise only one actuating unit. One of the first and second actuating units 30a and 30b may be omitted and replaced by one or more resilient elements such as springs.

[0110] As shown in Figure 11, the SMA actuator assembly 2 may arranged to drive a variable aperture assembly comprising a plurality of blades 56 (of which only two are shown in Figure 11 so that other parts of the actuator assembly 2 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 first part 10 via a first plurality of pins and connected to the second part 20 via a second plurality of pins, and configured to rotate about the first or second pins when the second part 20 is rotated relative to the first part 10; 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. The actuator assembly 2 may comprise four actuating units 30a, 30b, 30c, 30d which may impart forces in the directions shown in Figure 4. Alternatively, two of the actuating units may be omitted such that only a single actuating unit is present for driving rotation of the second part 20 in each sense about the primary axis P. In another embodiment, the actuator assembly 2 may comprise only one actuating unit in total. That actuating unit may drive rotation of the second part 20 in a first sense about the primary axis P. The actuator assembly 2 may comprise a resilient element such as a spring to oppose the actuating unit and cause rotation of the second part 20 in a second sense, opposite to the first sense, about the primary axis.

[0111] It will be appreciated that a reference to a component being "connected between" two other components means, for example, that the component is directly or indirectly connected to each of the other components. Such an indirect connection may involve a connection via further component(s) (e.g. a connector) with fixed position(s) relative to one of the other components. Such an indirect connection may involve a connection via further component(s) which is / are movable relative to the other components. For example, an SMA element may be connected to the one of the first and second parts via a further flexure, e.g. as described in WO 2022 / 144541 (which is herein incorporated by reference).

[0112] SMA

[0113] 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, sintering or powder fusion. 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.

[0114] Other variations

[0115] It will be appreciated that there may be many other variations of the above-described examples.

Claims

Claims1. An actuator assembly comprising: a first part; a second part that is movable relative to the first part; a bearing arrangement configured to guide rotation of the second part relative to the first part about an axis of rotation; a first actuating unit configured to apply an actuating force to the second part to drive rotation of the second part relative to the first part in a first sense about the axis of rotation; wherein the first actuating unit comprises: a body portion; an SMA element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part, and configured to modify the input force so as to give rise to the actuating force.

2. An actuator assembly according to claim 1, wherein the first actuating unit further comprises a coupling link connected between the body portion and the second part, wherein the coupling link is configured to transmit the actuating force from the body portion to the second part, and wherein the coupling link is compliant in a direction perpendicular to the actuating force.

3. An actuator assembly according to any preceding claim wherein the force-modifying element is or comprises a force-modifying flexure.

4. An actuator assembly according to any preceding claim wherein the force-modifying element is elongate and is stiff along its length and compliant in a direction perpendicular to its length.

5. An actuator assembly according to any preceding claim wherein the coupling link is or comprises a coupling flexure.

6. An actuator assembly according to any preceding claim wherein the coupling link is elongate and is stiff along its length and compliant in a direction perpendicular to its length.

7. An actuator assembly according to any preceding claim wherein the body portion, the coupling link and / or the force-modifying element are integrally formed.

8. An actuator assembly according to any preceding claim comprising a second actuating unit configured to apply an actuating force to the second part to drive rotation of the second part relative to the first part in a second sense opposite to the first sense about the axis of rotation, wherein the second actuating unit comprises: a body portion; an SMA element connected between the body portion and the first part, and configured, on actuation, to apply an input force to the body portion; and a force-modifying element connected between the body portion and the first part, and configured to modify the input force so as to give rise to the actuating force.

9. An actuator assembly according to claim 8 wherein the SMA element of the first actuating unit is substantially parallel to the SMA element of the second actuating unit when viewed along the axis of rotation.

10. An actuator assembly according to claim 8, wherein the SMA element of the first actuating unit is substantially perpendicular to the SMA element of the second actuating unit when viewed along the axis of rotation.

11. An actuator assembly according to any of claims 8 to 10, wherein the actuator assembly comprises four sides arranged in a loop, wherein the first actuating unit is disposed on a first side of the actuator assembly and the second actuating unit is disposed on a second side of the actuator assembly, wherein the second side is adjacent to the first side.

12. An actuator assembly according to any of claims 8 to 10 wherein the actuator assembly comprises four sides arranged in a loop, wherein the first actuating unit and the second actuating unit are disposed on the same side of the actuator assembly.

13. An actuator assembly according to any of claims 8 to 10, wherein the actuator assembly comprises four sides arranged in a loop, wherein the first actuating unit is disposed on a first side of the actuator assembly and the second actuating unit is disposed on a second side of the actuator assembly, wherein the second side is opposite to the first side.

14. An actuator assembly according to any preceding claim, wherein the actuator assembly comprises four sides arranged in a loop and wherein the first actuating unit is arranged along two adjacent sides of the actuator assembly.

15. An actuator assembly according to any of claims 8 to 14, wherein the actuator assembly comprises four sides arranged in a loop and wherein the second actuating unit is arranged along two adjacent sides of the actuator assembly.

16. An actuator assembly according to any preceding claim, wherein the actuator assembly comprises a total of two actuating units.

17. An actuator assembly according to any preceding claim wherein the bearing arrangement comprises a rolling bearing.

18. An actuator assembly according to any preceding claim wherein the bearing arrangement comprises a plain bearing.

19. An actuator assembly according to any preceding claim, wherein the second part defines a plane and the axis of rotation is perpendicular to the plane.

20. An actuator assembly according to any preceding claim, wherein one of the first and second parts comprises an image sensor.

21. An actuator assembly according to claim 20, wherein the axis of rotation is perpendicular to a light-sensitive region of the image sensor.

22. An actuator assembly according to claim 20 or claim 21, wherein one of the first and second parts further comprises a lens.

23. An actuator assembly according to any preceding claim further comprising a variable aperture mechanism defining a variable aperture, wherein the actuator assembly is configured such that rotation of one of the first and second parts relative to the other of the first and second parts changes the size of the variable aperture.

24. A system comprising: an actuator assembly according to any preceding claim; and a tilt assembly configured to tilt a moving part about two axes which are perpendicular to each other and to the axis of rotation, wherein the actuator assembly is arranged in mechanical series with the tilt assembly.

25. A system according to claim 24, wherein the moving part comprises an image sensor and a lens assembly.

Images