GB2630392A - Actuator assembly - Google Patents

Abstract

An actuator assembly comprises first and second relatively moveable parts and one or more actuating units 31-36 configured to apply an actuating force to the second part. Each actuating unit comprises a body portion 31, an SMA element 34 connected between the body portion and the first part, and a force-modifying element 32 connected between the body portion 31 and the first part, and configured to modify the input force so as to give rise to the actuating force using a coupling link 32. A damping material (50, figures 6-7) is arranged between the actuating unit and the first or second part, to dampen vibrations. The damping material may be arranged at various locations on the body portion 31d, 31p.

Description

ACTUATOR ASSEMBLY

Field

The present application relates to an actuator assembly with one or more actuating units, each of which includes a shape memory alloy (SMA) element.

Background

SMA actuator assemblies may be used in a variety of applications for moving a movable part relative to a support structure.

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 (015). WO 2010/029316 Al describes SMA actuator wires used to provide 015 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.

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.

WO 2022/084699 Al discloses an actuator assembly comprising at least one actuating unit (incorporating an SMA wire) that, on actuation, moves a movable part relative to the support structure. The actuating unit may be configured to amplify the movement range of the movable part, to amplify the actuating force acting on the movable part, or to re-direct the force applied by the SMA wire.

Summary

According to the present invention, there is provided an actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part, wherein each 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; and further comprising a damping material arranged between the one or more actuating units and the first or second part, wherein the damping material is configured to dampen vibrations of the second part relative to the first part.

In some embodiments, the damping material is provided between the body portion of the actuating unit and the first part.

In some embodiments, the body portion is configured to pivot about an effective pivot point on actuation of the SMA element, and wherein the damping material is provided within the half of the extent of the body portion that is located away from the effective pivot point.

In some embodiments, the damping material is located adjacent to the connection point between the body portion and the SMA element.

In some embodiments, the first part comprises a depression within which the damping material is located.

In some embodiments, the flexure body comprises first and second surfaces that are angled relative to each other, wherein the damping material contacts both of the first and second surfaces.

In some embodiments, the first and second surfaces are substantially perpendicular to each other.

In some embodiments, the flexure body comprises a sheet material, and wherein the first and second surfaces are adjacent to a fold in the sheet material.

In some embodiments, the body portion is arranged to move in a plane on actuation of the SMA element, and wherein the damping material is arranged so as to undergo shear deformation on movement of the body portion in the plane.

In some embodiments, the damping material is a viscous material, in particular a viscoelastic material.

In some embodiments, the damping material comprises a silicone gel or a damping oil.

In some embodiments, each 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.

Some embodiment comprise a plurality of actuating units in an arrangement capable of moving the second part relative to the first part along three orthogonal axes.

In some embodiments, the plurality of actuating units comprises eight actuating units.

Brief description of the drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1A-E are schematic cross-sectional views of different variations of a camera module incorporating an actuator assembly; Figure 2 is a schematic perspective view of the actuator assembly; 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; Figure 4 is a schematic plan view of an arrangement of four actuating units; Figures 5 is a schematic perspective view of an arrangement of eight actuating units; Figure 6 is a schematic side view of part of an actuator assembly comprising damping material according to the present invention; Figure 7 is a schematic side view of part of an actuator assembly comprising damping material according to the present invention; and Figure 8 is a schematic side view of positions on the body portion of the actuating unit on which the damping material may be provided.

Detailed description

Camera module Figures 1A-E schematically show different variations of an apparatus 1 incorporating an actuator assembly 2. The apparatus 1 is, for example, a camera module 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.

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

The movable part 20 may be supported (i.e. suspended) on the support structure 10 exclusively by the actuating units 30. Alternatively, the actuator assembly 2 may include a bearing arrangement 40 that supports the movable part 20 on the support structure 10. The actuating units 30 and the bearing arrangement 40 may together support the movable part 20 on the support structure 10. The bearing arrangement 40 may have any suitable form for allowing movement of the movable part 20 with respect to the support structure 10 with one or more degrees of freedom (DOFs). The actuating units 30 and/or the bearing arrangement 40 may constrain, i.e. reduce or prevent, other DOFs of movement of the movable part 20 relative to the support structure 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.

A primary axis P can be defined with reference to the actuator assembly 2 and/or the support structure 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 support structure 10 and/or the movable part 20 extends predominantly in a direction perpendicular to the primary axis P. In other words, the extent of the actuator assembly 2, the support structure 10 and/or the movable part 20 along the primary axis P is less than the extent thereof along any direction perpendicular to the primary axis P. Alternatively or additionally, the support structure 10 and/or movable 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 3) with an optical axis, or an imaging element (such as an imager sensor 4) 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 movable part 20 is in a central position or orientation (for example, see Figure 1A).

In general, the movable part 20 may be movable relative to the support structure 10 with up to six degrees of freedom (DOFs). In the context of describing the DOFs of 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 movable part 20 may be movable relative to the support structure 10 in all or in any subset (including only one) of the following DOFs: - Tx and Ty: Translational movement in the x-y plane. In other words, the movable part 20 may be independently movable along the x and y axes. The movable part 20 may be movable to any position in the x-y plane within a range of movement. Instead of such planar movement, the movable part 20 may be movable linearly, e.g. along the x or y axis.

- Rx and Ry: Rotational movement (or simply rotation or tilting) about the x and y axes. In other words, the movable part 20 may be rotated about any line perpendicular to the primary axis P. The movable 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 movable part 20 may be rotatable about a single axis, e.g. about the x or y axis.

- Tz: Translational movement along the z axis. The movable part 20 may be movable to any translational position along the z axis within a range of movement.

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

In some examples, the movable part 20 may be supported, e.g. by the bearing arrangement 40, so as to allow translational movement in the x-y plane (Tx, Ty) and/or rotational movement about the z axis (Rz).

Translational movement along the z axis (Tz) and rotational movement about the x and y axes (Rx, Ry) may be constrained. Such support may be provided, for example, with a bearing arrangement 40 with a suitable arrangement of ball bearings or plain bearings which produce bearing forces in the +z direction and a biasing arrangement which produces a biasing force in the -z direction. Examples of actuator assemblies with such a bearing arrangement are disclosed in WO 2013/175197 Al and WO 2017/072525 Al, each of which is herein incorporated by reference.

In some examples, the movable part 20 may be supported so as to allow tilting about the x and y axes (Rx, Ry) and optionally rotation about the z axis (Rz). The other DOFs of movement (i.e. Tx, Ty, Tz, Rz, or Tx, Ty, Tz) may be constrained. Such support may be provided by the bearing arrangement 40, for example in the form of a gimbal. Examples of such a bearing arrangement 40 are disclosed in WO 2021/209770 Al, which is herein incorporated by reference. Alternatively, such support may be provided exclusively by the actuating units 30, similarly to WO 2011/104518 Al which discloses an actuator assembly with 8 SMA wires connected between the support structure 10 and the movable part 20. WO 2011/104518 Al is herein incorporated by reference.

In some examples, the movable part 20 may be supported so as to allow three-dimensional translational movement (Tx, Ty, Tz), while rotational movement (Rx, Ry, Rz) may be constrained. Such support may be provided by the bearing arrangement 40, for example in the form of nested linear bearings. Examples of such a bearing arrangement 40 are disclosed in WO 2021/209769 Al, which is herein incorporated by reference. Alternatively, such support may be provided exclusively by the actuating units 30, similarly to WO 2011/104518 Al.

The movable part 20 may, alternatively or additionally, move in other DOFs. The movable part 20 may move in DOFs that are a combination of any two or more of Tx, Ty, Tx, Rx, Ry and Rz. For example, the movable part 20 may move along a helical path (i.e. move helically) 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.

The actuating units 30 are connected between the support structure 10 and the movable part 20. The actuating units 30 are arranged to apply actuating forces F (see e.g. Figs. 4 and 5) between the movable part 20 and the support structure 10. Selectively varying the actuating forces F may cause the movable part 20 to move relative to the support structure 10, for example within the DOFs allowed by the bearing arrangement 40. The actuating units 30 are thus capable of driving movement of the movable part 20 relative to the support structure 10.

The bearing arrangement 40 may cause the movable 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 movable part 20, and another component of each actuating force F acts against the bearing forces produced by the bearing arrangement 40.

The camera module 1 also includes a lens assembly 3 and an image sensor 4. The lens assembly 3 includes one or more lenses configured to focus an image on the image sensor 4. The lens assembly 3 defines an optical axis 0. The lens assembly 3 may include a lens carrier, for example in the form of a cylindrical body, supporting the one or more lenses. The image sensor 4 captures an image and may be of any suitable type, for example a charge coupled device (CCD) or a complementary metal-oxidesemiconductor (CMOS) device. The camera module 1 may be a compact camera module in which each lens has a diameter of 20mm or less, for example of 12mm or less.

In the ("sensor-shift") variation of the camera module 1 shown in Figure 1A, the movable part 20 includes the image sensor 4. The lens assembly 3 may be fixed relative to the support structure 10, or may be movable relative to the support structure 10 along the optical axis 0, as described below.

In the ("lens-shift") variation shown in Figure 1B, the image sensor 4 is fixed relative to the support structure 10 and the movable part 20 includes the lens assembly 3. The lens assembly 3 may be movable relative to the movable part 20 along the optical axis 0, as described below.

In both of these variations, the actuator assembly 2 is configured to move the lens assembly 3 relative to the image sensor 4 in any direction in the plane perpendicular to the primary axis P and hence the optical axis 0. Such movement has the effect of moving the image on the image sensor 4 and enables optical image stabilisation (015) to be implemented in the camera module 1. In the sensor-shift variation, the movable part 20 may also be rotatable about the primary axis P so as to also enable compensation for roll.

In the ("module-tilt") variation shown in Figure 1C, the movable part 20 includes both the lens assembly 3 and the image sensor 4. Again, the lens assembly 3 may be movable relative to the movable part 20 along the optical axis 0, as described below. The actuator assembly 2 is configured to tilt the movable part 20 about two axes perpendicular to the primary axis P and to each other, and optionally rotate the movable part 20 about the primary axis P, enabling 015 to be implemented in the camera module 1.

In the ("autofocus") variation shown in Figure 1D, the movable part 20 includes the lens assembly 3, and the actuator assembly 2 moves the movable part 20 relative to the support structure 10 along the primary axis P and hence the optical axis 0. Such movement has the effect of adjusting the focus of the image on the image sensor 4. So, auto-focus (AF) or zoom functionality can be implemented in the camera module 1.

In some examples (not shown), the camera module 1 may include a first actuator assembly for providing 015 as illustrated in Figures 1A-C, and a second actuator assembly for providing AF as illustrated in Figure 1D. One or both of the first and second actuator assemblies may correspond to actuator assemblies 2 as described herein. One of the first and second actuator assemblies may be another type of SMA actuator assembly or may be a non-SMA actuator assembly, e.g. a voice-coil motor (VCM) actuator assembly. As will be appreciated, in the lens-shift and module-tilt variations, the support structure 10 of the second actuator assembly 2 is fixed to (or corresponds to) the movable part 20 of the first actuator assembly 2.

In the ("AF+0IS") variation shown in Figure 1E, the movable part 20 includes the lens assembly 3, and the actuator assembly 2 produces three-dimensional translational movement of the movable part 20 relative to the support structure 10, enabling both AF and OIS to be implemented using one actuator assembly 2.

Other variations are also possible. For example, in the autofocus variation or the AF+OIS variation, the movable part 20 may include the image sensor 4 rather than the lens assembly 3. The camera module 1 may include combinations of the above-described features, e.g. (a) lens shift and sensor shift, (b) module tilt and lens shift or sensor shift and autofocus, or (c) module tilt and AF+01S.

The camera module 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 move the movable part 20. The drive signals are chosen to drive movement of the movable 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.

Optionally, the camera module 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 1, which can be processed so as to produce signals representative of the required movement of the movable 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 015.

Although the actuator assembly 2 is described in connection with a camera module 1, it will be appreciated that the actuator assembly 2 may be used in any device in which movement of a movable part 20 relative to a support structure 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.

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.

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

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.

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 support structure 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 support structure 10, e.g. via a foot portion 36. The foot portion 36 is fixed relative to the support structure 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 support structure 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 force-modifying 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 support structure 10 is initially in a direction that is substantially perpendicular to the force-modifying flexure 32.

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 support structure 10. One end of the SMA wire 34 is connected to the support structure 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.

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 movable 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 movable part 20. The coupling link 33 transfers or transmits an actuating force F from the body portion 31 to the movable 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 movable 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 movable part 20 to move in different directions.

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 movable 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. 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 force-modifying 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°.

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 Dc 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 movable 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 movable 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.

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 Ds 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 de-amplifies 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).

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.

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 movable 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.

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.

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.

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.

In the above-described examples, the force-modifying flexure 32 and the SMA wire 34 connect at one end to the support structure 10, and the coupling flexure 33 connects at one end to the movable 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 movable part 20, and the coupling flexure 33 connecting at one end to the support structure 10.

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 movable part 20 in directions perpendicular to the actuating force F. 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 movable 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 movable part 20 while allowing movement of the movable 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.

Arrangement of four actuating units 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 movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10.

The arrangement of actuating units 30 of Figure 4 may be used, for example, in examples in which the movable part 20 is movable relative to the support structure 10 in a movement plane. So, Tx, Ty and optionally Rz movement of the movable part 20 may be allowed.

The four actuating units 30 of Figure 4 are in an arrangement capable of applying actuating forces F so as to move the movable part 20 relative to the support structure 10 to any position within a range of movement. The range of movement may be within a movement plane that is perpendicular to the primary axis P. 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). 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. By appropriately varying the difference in actuation amount between the opposing actuating units 30, the movable part 20 may thus be moved independently along the first and second axes. The opposing actuating forces F are not colinear, but offset from each other in a direction perpendicular to the actuating forces F. Providing opposing actuating units 30 allows the tension in the SMA wires 30 of the respective actuating units 30 to be controlled, allowing for more accurate and reliable positioning of the movable part 20 compared to a situation in which actuating units 30 do not oppose each other.

In some examples, none of the actuating forces F are collinear. This allows the arrangement of actuating units 30 to translationally move the movable part 20 without applying any net torque to the movable part 20. So, the movable part 20 can be moved translationally in the movement plane without rotating the movable part 20 in the movement plane. In general, the arrangement of actuating units 30 is capable of accurately controlling a torque or moment of the movable part 20 about the primary axis P. So, the actuating units 30 are capable of rotating (or not rotating) the movable part 20 relative to the support structure about the primary axis P. In particular, two actuating units 30 (e.g. the top and bottom actuating units in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a first sense (e.g. clockwise) around the primary axis P. The other two actuating units 30 (e.g. the left and right actuating units 30 in Figure 4) are arranged to apply actuating forces F so as to generate a torque or moment between the movable part 20 and the support structure 2 in a second, opposite sense (e.g. anti-clockwise) around the primary axis P. This allows the movable part 20 to be rotated by simultaneously increasing or decreasing the tension of SMA wires in any of the two actuating units 30.

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 movable part 20 and/or the support structure 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 movable part 20 such that the SMA wire 34 and the coupling flexure 33 of each actuating unit 30 extend along adjacent edges of the movable 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 movable part 20.

The arrangement of actuating forces F applied between movable part 20 and support structure 10 corresponds to the arrangement of SMA wires 30 described in W02013/175197 Al, which is herein incorporated by reference.

In this example, the actuating forces F are perpendicular to the primary axis P, and may be parallel to the movement plane. However, in general the actuating forces F may be angled relative to the movement 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, for example, to provide movement of the movable part 20 in degrees of freedom allowed 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 movable part 20 and the support structure 10.

Although, for illustrative purposes, the arrangement of actuating units 30 was described as moving the movable part 20 in the movement plane (e.g. translationally along the x and y axis, or rotationally about the primary axis P), in other examples the movable part 20 may be moved differently. For example, the same arrangement of actuating forces F may be used to tilt the movable part 20 relative to the support structure 10 about axes 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 movable part 20 about the axes perpendicular to the primary axis P. Examples of such bearing arrangement 40 are described in W02022/029441 Al, which is herein incorporated by reference.

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. For 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 movable 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.

Arrangement of eight actuating units Figure 5 schematically shows a perspective view of an actuator assembly 2 with a total of eight actuating units 30. The eight actuating units 30 may apply actuating forces F between the movable part 20 and the support structure 10. The actuating forces F are applied to the movable part 20 relative to the support structure 10.

The arrangement of actuating units 30 of Figure 5 may be used, for example, in examples in which the movable part 20 is movable relative to the support structure 10 in three translational degrees of freedom (Tx, Ty, Tz) (see Figure 1E) or in two or three rotational degrees of freedom (Rx, Ry or Rx, Ry, Rz) (see Figure 1C).

The eight actuating units 30 may be arranged such that their actuating forces F are oriented or arranged in a manner equivalent to the orientation or arrangement of the forces applied by the eight SMA wires in the actuator assemblies disclosed in WO 2011/104518 Al.

More specifically, the actuating forces F (e.g. when visualised as vectors at particular positions in space) are arranged on each of four sides (i.e. a first side, a second side, a third side and then a fourth side) around the primary axis P. The two actuating forces F on each side are inclined in opposite senses relative to a plane perpendicular to the primary axis P, when viewed perpendicular from the primary axis P. The four sides on which the actuating forces F are arranged extend in a loop around the primary axis P. In this example, adjacent sides are perpendicular to each other, and the sides form a square when viewed along the primary axis P, but alternatively the sides could take a different e.g. quadrilateral shape. In this example, the actuating forces F are parallel to the outer faces of the square envelope of the movable part 20 but this is not essential.

Four actuating forces F, including one actuating force F on each of the sides, form a 'first' group that have a component in one direction ('upwards' or +z) and the other four actuating forces F form a 'second' group that have a component in the opposite direction ('downwards' or -z). Herein, 'up' and 'down' refer to opposite directions along the primary axis P. The actuating forces F have a symmetrical arrangement in which their magnitudes and inclination angles are the same, so that both the first group of actuating forces F and the second group of actuating forces F are each arranged with two-fold rotational symmetry about the primary axis P. As a result of this symmetrical arrangement, different combinations of the actuating forces F are capable of driving movement of the movable part 20 with multiple degrees of freedom, as follows.

The first group of actuating forces F, when generated together, drive upwards (+z) movement, and the second group of actuating forces F, when generated together, drive downwards (-z) movement.

Within each group, adjacent pairs of actuating forces F, when differentially generated, drive tilting about a lateral axis perpendicular to the primary axis P (Rx or Ry). Tilting in any arbitrary direction may be achieved as a linear combination of tilts about the two lateral axes.

Sets of four actuating forces F, including two actuating forces F from each group, when generated together, drive movement along a lateral axis perpendicular to the primary axis P (Tx or Ty). Movement in any arbitrary direction perpendicular to the primary axis z may be achieved as a linear combination of movements along the two lateral axes.

The actuator assembly 2 may have other specific arrangements of actuating units 30 to those shown in Figure 5. For example, strict symmetry is not required. Furthermore, instead of there being an up-pulling actuating unit 30 and a down-pulling actuating unit 30 on each side, there maybe two up-pulling actuating units 30 on each of two opposite sides (e.g. the first and third sides) and two down-pulling actuating units 30 on the other two sides (e.g. the second and fourth sides).

Damping material Damping gel may be applied to actuator assemblies to reduce the impact of resonant behaviour.

Conventional SMA actuator assemblies may comprise a damping material between the movable part 20 and the support structure 10. The purpose of such a damping material is to dampen undesired vibration or movement of the movable part 20 relative to the support structure 10. However, the inventors have realized that providing damping material between the movable part 20 and support structure 10 may have drawbacks. In particular, the damping material may undesirably limit the range of movement of the movable part 20 relative to the support structure 10, which is particularly undesirable in actuator assemblies comprising stroke amplification mechanisms. Furthermore, in some actuator assemblies damping material provided between the movable part 20 and the support structure 10 may undergo tension and compression (rather than primarily shearing), which can lead to damage and reduce the lifetime of the damping material. This issue is particularly pronounced in actuator assemblies enabling movement of the movable part 20 in three or more degrees of freedom, such as in the actuator assembly having the arrangement of eight actuating units 30 described above.

The inventors have realized that applying damping material directly between the actuating unit 30 and one of the support structure 10 and movable part 30 gives rise to surprising technical advantages.

Firstly, the damping material may be applied between parts that move less relative to each other than the movable part 20 and support structure 10, thus reducing the need for the damping material to deform. As such, stiffer damping material may be used and/or the lifetime of the damping material may be increased. Furthermore, different portions of the actuating unit 30 move by different amounts for a given amount of contraction of the SMA wire 34, allowing the location at which the damping material is applied to be tailored to the material properties (e.g. stiffness) of a particular type of damping material. More flexibility in designing the damping capability of the damping material is thus achieved. Finally, the damping material may be provided between parts that move primarily, or even solely, in a single degree of freedom or a single plane relative to each other. The damping material may thus primarily or solely undergo shear deformation, even in actuator assemblies achieving movement in three or more degrees of freedom. The lifetime of the damping material is thus further improved.

Figures 6 and 7 schematically shows a side view of an actuator assembly 2 with damping material 50 according to the present invention. Figure 8 schematically shows possible positions of the damping material 50 on the body portion 31.

The actuator assembly 2 comprises the support structure 10, the movable part 20 (not shown) and the actuating unit 30 (partly shown). The actuator assembly 2 further comprises a damping material 50. In Figures 6 and 7, the damping material 50 is arranged between the actuating unit 30 and the support structure 10, although in general the damping material 50 may also be arranged between the actuating unit 30 and the movable part 20. The damping material 50 is preferably provided on the part to which the force-modifying flexure 32 is connected. So, the damping material 50 is in direct contact with the actuating unit 30, as well as in direct contact with one of the support structure 10 and movable part 20.

The damping material 50 is configured to dampen vibrations of the movable part 20 relative to the support structure 10. The damping material 50 provides mechanical damping in the actuator assembly 2, thereby reducing undesirable motion of the movable part 20 relative to the support structure 10. , The accuracy of positional control of the actuator assembly 2may thus be improved and non-linear oscillations may be reduced.

As shown in Figure 6, the damping material 50 may be arranged on the body portion 31 of the actuating unit 30. The body portion 31 may be wider than other parts of the actuating unit 30, and so may be particularly suitable for the provision of damping material 50. The body portion 31 may also be relatively rigid, thus making it more suitable for provision of the damping material 50. However, in general, damping material 50 may be provided on any portion of the actuating unit 50 that is movable relative to the support structure 10, for example on the force-modifying flexure 32 or on the coupling link 33.

The body portion 31 may be arranged to move in an actuating plane on actuation of the SMA element 34. In particular, the body portion 31 may move in the actuating plane along a curved path around the effective pivot point P. In Figures 3B and 8, the actuating plane may be the plane of the figure. In Figures 6 and 7, the actuating plane may be parallel to the horizontal.

The damping material 50 is arranged so as to undergo shear deformation on movement of the body portion 31 in the actuating plane. As schematically depicted in Figures 6 and 7, the body portion 31 may comprise a surface that is parallel to the actuating plane. The support structure 10 (or where applicable the movable part 20) may comprise a surface that is parallel to the actuating plane. The damping material 50 may be provided between these surfaces. As such, the damping material is arranged to go primarily or exclusively shear deformation during use of the actuator assembly, improving the lifetime and damping quality of the damping material 50.

In general, the damping material 50 may be provided on any part of the body portion 31. Figure 8 schematically depicts locations on the body portion 31 on which the damping material 50 is preferably provided.

In some embodiments, the damping material 50 may be provided on a distal portion 31d of the body portion 31. The distal portion 31d is arranged distally from the effective pivot point P. The body portion 31 may have a maximum extent 41 away from the effective pivot point, and the damping material 50 may be provided on the body portion, when viewed from the effective pivot point P, at a distance from 50% to 100% of the maximum extent. The damping material 50 may be provided within the half of the extent of the body portion 31 that is located away from the effective pivot point P. For example, the damping material 50 may be located adjacent to the connection point between the body portion 31 and the SMA element, i.e. adjacent to the crimp 35 that is fixed relative to the body portion 31.

In some embodiments, the damping material 50 may be provided on a proximal portion 31p of the body portion 31. The damping material 50 may be provided on the body portion 31, when viewed from the effective pivot point P, at a distance from 0% to 50% of the maximum extent. The damping material 50 may be provided within the half of the extent of the body portion 31 that is located proximate to the effective pivot point P. An advantage of providing the damping material 50 on the proximate portion 31p is that shear deformation of the damping material 50 on the proximate portion is reduced. A relatively stiffer damping material 50 may be provided on the proximate portion 31p.

The exact position of the damping material 50 on the body portion 31 may be tuned for optimal damping performance. The optimal position may depend on the properties of the damping material 50.

The body portion 31 moves by an increasing amount with increasing distance from the effective pivot point P. As such, for example, a relatively stiffer damping material 50 may be provided on the proximal portion 31p. A relatively less stiff damping material may be provided on the distal portion 31d. In some embodiments, damping materials of different stiffnesses may be provided on different positions on the body portion 31.

The position of the damping material 50 may further be selected to allow access for UV curing of the damping material 50. The actuator assembly 2 may thus comprise an opening configured to allow access to the damping material 50.

Migration of the damping material 50 may be a problem in some actuator assemblies 2. It is desirable to retain the damping material 50 in position, to ensure reliable damping of the actuator assembly 2 and to reduce the risk of damping material 50 affecting other components of the actuator assembly 2. As such, the actuator assembly 2 may be provided with means for retaining the damping material in position.

Figure 6 schematically depicts a local depression or well in the support structure 10. The damping material 50 is provided in the depression. The damping material 50 may thus be better contained. A further advantage of the depression is that the extent of the damping material 50 in a direction orthogonal to the actuating plane is increased, ensuring that the damping material 50 shears less for a given amount of movement of the body portion 31. A local depression as depicted in Figure 6 may similarly be provided on the movable part 20 or on the body portion 31 (for example in the form of a partial etch).

Figure 7 schematically depicts a tap 31v of the body portion 31. The tap 31v may be formed by folding part of the body portion 31 out of the actuating plane, and so may also be referred to as a folded part 31v. The body portion 31 may comprise a first surface that is parallel to the actuating plane and a second surface that is angled, preferably substantially perpendicular to the actuating plane. The second surface may be formed by the tap 31v of the body portion. The first and second surfaces may be adjacent to a fold in a body portion 31 formed from sheet material.

The tap 31v may be in contact with the damping material 50. The tap 31v may thus aid in containing the damping material 50. As shown in Figure 7, only one side of the tap 31v may be in contact with the damping material 50. Alternatively, the tap 31v is surrounded by the damping material 50, i.e. the tap 31v may be provided in the center of the damping material.

The tap 31v further provides a surface that is orthogonal to the actuating surface. The damping material 50 on the tap 31v may thus dampen motion of the body portion 31 that is perpendicular to the actuating plane, so as to dampen undesired out-of-plane vibrations. Such out-of-plane vibrations may occur in some actuator assemblies 30 during impact events or, to a limited degree, due to actuation of other actuating units 30. The surface of the tap 31v that is orthogonal to the actuating plane is preferably arranged to be tangential to a path along which the body portion 31 moves on actuation of the SMA element 34. The surface of the tap 31v that is orthogonal to the actuating plane is preferably tangential to a circle around the effective pivot point P. The damping material 50 may be viscous material, in particular a viscoelastic material. The damping material 50 is preferably a damping gel. For example, the damping material 50 may comprise a silicone gel or a damping oil.

The damping material 50 may be applied to actuating units 30 in any of the arrangement described with reference to Figures 1, 2, 4 and 5. Particular advantageous may be application of damping material 50 to actuating units 30 in an arrangement as described in relation to Figure 5, i.e. in an arrangement in which the movable part 20 is movable along three orthogonal axes by the actuating units 30. Providing damping material 50 between the movable part 20 and the support structure 10 in such an actuator assembly 2 would require the damping material 50 to undergo tension and compression during operation, reducing the lifetime and damping capabilities of the damping material 50. The actuating units 30 move primarily in the actuating plane, and so the inventors have found that the actuating units 30 provide a particularly advantageous location for the damping material 50 in such an actuator assembly 2.

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

For example, instead of a force-modifying flexure, the actuator assembly may include another type of force-modifying element configured to enable the above-described movement of the body portion 31 relative to the support structure 10. Such a force-modifying element may include, for instance, a rigid member with one end connected to the support structure 10 via a suitable pivoting connection (e.g. a pin joint) and the other end connected to the body portion 31.

SMA

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

Claims (14)

1. Claims 1. An actuator assembly comprising: a first part; a second part that is movable relative to the first part; and one or more actuating units each configured to apply an actuating force to the second part capable of moving the second part relative to the first part, wherein each 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; and further comprising a damping material arranged between the one or more actuating units and the first or second part, wherein the damping material is configured to dampen vibrations of the second part relative to the first part.
2. 2. An actuator assembly according to claim 1, wherein the damping material is provided between the body portion of the actuating unit and the first part.
3. 3. An actuator assembly according to claim 1 or 2, wherein the body portion is configured to pivot about an effective pivot point on actuation of the SMA element, and wherein the damping material is provided within the half of the extent of the body portion that is located away from the effective pivot point.
4. 4. An actuator assembly according to any one of the preceding claims, wherein the damping material is located adjacent to the connection point between the body portion and the SMA element.
5. 5. An actuator assembly according to any one of the preceding claims, wherein the first part comprises a depression within which the damping material is located.
6. 6. An actuator assembly according to any one of the preceding claims, wherein the flexure body comprises first and second surfaces that are angled relative to each other, wherein the damping material contacts both of the first and second surfaces.
7. 7. An actuator assembly according to claim 6, wherein the first and second surfaces are substantially perpendicular to each other.
8. 8. An actuator assembly according to claim 6 or 7, wherein the flexure body comprises a sheet material, and wherein the first and second surfaces are adjacent to a fold in the sheet material.
9. 9. An actuator assembly according to any one of the preceding claims, wherein the body portion is arranged to move in a plane on actuation of the SMA element, and wherein the damping material is arranged so as to undergo shear deformation on movement of the body portion in the plane.
10. 10. The actuator assembly according to any preceding claim, wherein the damping material is a viscous material, in particular a viscoelastic material.
11. 11. The actuator assembly according to any preceding claim, wherein the damping material comprises a silicone gel or a damping oil.
12. 12. The actuator assembly according to any preceding claim, wherein each 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.
13. 13. An actuator assembly according to any preceding claim, comprising a plurality of actuating units in an arrangement capable of moving the second part relative to the first part along three orthogonal axes.
14. 14. An actuator assembly according to claim 12, wherein the plurality of actuating units comprises eight actuating units.