GB2620798A

GB2620798A - Actuator assembly

Info

Publication number: GB2620798A
Application number: GB2210793.2A
Authority: GB
Inventors: Eddington Robin; Langhorne Robert; Klopfenstein Reto
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2022-07-22
Filing date: 2022-07-22
Publication date: 2024-01-24
Anticipated expiration: 2042-07-22
Also published as: GB202210793D0; GB2620798B

Abstract

An actuator assembly, such as for a camera lens, comprises first and second parts 10, (20, figure 2A) movable and/or tiltable relative to each other along and/or about two orthogonal axes that are, or in a plane that is, perpendicular to a primary axis. At least one pair of actuating units (30, figure 2A) is connected, and applies an actuating force, between the parts. Each actuating unit comprises a body portion 31, a force-modifying flexure 32 between the body portion and one of the parts, a coupling flexure 33 between the body portion and the other part and a shape memory alloy (SMA) wire 34 between the body portion and the one part. The SMA wire contracts to apply an input force on the body portion which the force modifying flexure modifies and causes the coupling flexure to apply the actuating force between the parts. The coupling flexure may be compliant perpendicular to the actuating force, and the coupling flexures of each pair of actuating units overlap when viewed along the primary axis. The actuating units of each pair may apply actuating forces parallel to respective non-parallel axes in a plane spanned by the two orthogonal axes.

Description

ACTUATOR ASSEMBLY

Field

The present application relates to an actuator assembly, in particular an actuator assembly comprising multiple actuator units for moving two parts relative to each other.

Background

SMA actuator assemblies have various applications and, for example, can be used to provide optical image stabilisation (015) in compact cameras for smartphones and other electronic devices. For instance, WO 2013/175197A1 describes an actuator assembly with four SMA wires for moving the movable part in any direction perpendicular to a primary axis.

Summary

According to an aspect of the present invention, there is provided an actuator assembly comprising: first and second parts that are movable and/or tiltable relative to each other along and/or about two orthogonal axes that are perpendicular to a primary axis; and at least one pair of actuating units, each actuating unit connected between the first and second parts and arranged to apply a respective actuating force between the first and second parts. Each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and one of the first and second part; a coupling flexure connected between the body portion and the other of the first and second part; and an SMA wire connected between the body portion and the one of the first and second part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts; wherein the coupling flexure is compliant in a direction perpendicular to the direction of the actuating force. The coupling flexures of each pair of actuating units overlap when viewed along the primary axis, wherein one actuating unit of each pair of actuating units is configured to apply a respective actuating force parallel to a first axis in a plane spanned by the two orthogonal axes and the other actuating unit of each pair of actuating units is configured to apply a respective actuating force parallel to a second axis in the plane spanned by the two orthogonal axes, wherein the second axis is non-parallel to the first axis.

In some embodiments, at least one coupling flexures of one actuating unit of each pair of actuating units comprises a kinked portion in the region of overlap with the coupling flexure of the other actuating unit of each pair of actuating units, thereby avoiding contact between the coupling flexures.

In some embodiments, the coupling flexures of each pair of actuating units are arranged offset along the primary axis relative to one another, thereby avoiding contact between the coupling flexures.

In some embodiments, the actuating units are substantially identical.

In some embodiments, each actuating unit comprising a first surface parallel to the plane spanned by the two orthogonal axes and a second surface parallel to the plane spanned by the two orthogonal axes, wherein the first and second surfaces are provided on opposite sides of the actuating unit, wherein for each pair of actuating units the first surface of one actuating unit and the second surface of the other actuating unit face in the same direction along the primary axis.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the SMA wire extends, viewed orthogonally to the SMA wire, past a point at which the coupling flexure connects to the body portion.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that, viewed along the primary axis, the SMA wire is arranged on the same side of the body portion as a point at which the force-modifying flexure connects to the first or second part.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure is in tension on contraction of the SMA wire.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure amplifies an amount of contraction of the SMA wire to a relatively greater amount of movement between first and second parts.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the angle between force-modifying flexure and SMA wire is in the range from 0 to 45 degrees, preferably from 13 to 40 degrees.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure is formed integrally with at least part of the body portion.

In some embodiments, at least one actuating unit, preferably each actuating unit, is configured such that the coupling flexure is formed integrally with at least part of the body portion.

In some embodiments, the actuator assembly comprises a total of four actuating units, wherein the four actuating units consist of two pairs of actuating units.

In some embodiments, none of the actuating forces applied by the four actuating units are colinear.

In some embodiments, the four actuating units are in an arrangement capable of applying actuating forces between first and second parts so as to move the first and second parts relative to each other to any positions within a range of movement within a movement plane spanned by the two orthogonal axes without applying any net torque between the first and second parts.

In some embodiments, two of the four actuating units are arranged to apply actuating forces so as to generate a torque between the first and second parts in a first sense around the primary axis and the other two of the four actuating units are arranged to apply actuating forces so as to generate a moment between the first and second parts in a second, opposite sense around the primary axis.

In some embodiments, two of the four actuating units are arranged to apply actuating forces in a corner of the actuator assembly, and the other two of the four actuating units are arranged to apply actuating forces in another, opposite corner of the actuator assembly.

In some embodiments, two of the four actuating units are arranged to apply actuating forces so as to move the first and second parts relative to each other in opposite directions parallel to the first axis, and the other two of the four actuating units are arranged to apply actuating forces so as to move the first and second parts relative to each other in opposite directions parallel to the second axis.

In some embodiments, each actuating unit extends parallel to the two orthogonal axes.

In some embodiments, the actuator assembly further comprises a bearing arrangement between first and second parts and arranged to allow the relative movement between first and second parts.

According to the present invention, there is also provided an actuator assembly comprising: first and second parts that are movable relative to each other in a movement plane that is perpendicular to a primary axis; and at least one pair of actuating units, each actuating unit connected between the first and second parts and arranged to apply a respective actuating force between the first and second parts. One of each pair of actuating units comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; and an SMA wire connected between the body portion and the first part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts. The other of each pair of actuating units comprises: a body portion; a force-modifying flexure connected between the body portion and the second part; a coupling flexure connected between the body portion and the first part; and an SMA wire connected between the body portion and the second part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts; In some embodiments, none of the actuating units overlap when viewed along the primary axis.

In some embodiments, the four actuating units are in an arrangement capable of applying actuating forces between first and second parts so as to move the first and second parts relative to each other to any positions within a range of movement within the movement plane without applying any net torque between the first and second parts.

According to the present invention, there is also provided a camera apparatus, comprising the actuator assembly; an image sensor coupled to one of the first and second part of the actuator assembly; and a lens assembly coupled to the other of the first and second part of the actuator assembly, wherein an optical axis defined by the lens assembly aligns with the primary axis of the actuator assembly.

Further aspects of the present invention are set out in the detailed description.

Brief description of the drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1A is a schematic view of a camera apparatus according to the present invention; Figure 1B is a schematic plan view of an actuator assembly according to the present invention; Figures 2A-2C schematically depicts an embodiment of an actuator assembly including actuating units; Figures 3A-3B schematically depict an actuator assembly including actuating units; Figure 4 schematically depicts an actuating unit for use in the actuator assembly; Figure 5 schematically depicts an embodiment of an actuator assembly including actuating units; Figures 6A and 6B schematically depict an embodiment of an actuator assembly including actuating units; Figures 7A and 7B schematically depict another actuator assembly according to the present invention; and Figures 8A-8C schematically depict structural details of the actuator assembly.

Detailed description

Camera apparatus Figure 1A schematically shows an apparatus 1 incorporating an actuator assembly 2 in accordance with an embodiment of the present invention. Figure 1B schematically shows a plan view of the actuator assembly 2. The apparatus 1 is, for example, a camera apparatus 1. The apparatus 1 is to be incorporated in a portable electronic device such as a mobile telephone, or tablet computer. Thus, miniaturisation is an important design criterion.

The apparatus 1 comprises an actuator assembly 2 or may itself be considered an example of an actuator assembly 2. The actuator assembly 2 comprises a support structure 10 (an example of a first part 10) and a movable part 20 (an example of a second part 20). The movable part 20 is supported on the support structure 10. The movable part 20 is movable relative to the support structure 10. For example, the movable part 20 may be supported in a manner allowing movement of the movable part 20 relative to the support structure 10 in a plane orthogonal to a primary axis P. Movement along the primary axis P may be constrained or prevented. Alternatively, the movable part 20 may be supported in a manner allowing tilting of the movable part 20 relative to the support structure 10 about any axes orthogonal to the primary axis P. Movement other than such tilting may be constrained or prevented.

The support structure 10 is used as a reference point to describe movement of the movable part 20.

When the actuator assembly 2 is included in an apparatus or device, such as a camera, smartphone, a drone, the support structure 10 may be fixed relative to a main body of the apparatus or device. However, in general the support structure 10 need not necessarily be stationary and may be movable relative to or within such a device. In some embodiments, the movable part 20 may be fixed relative to a main body of the device. Furthermore, although the support structure 10 is schematically depicted as one part in Figure 1A, in practice the support structure 10 may be formed from a plurality of layers, parts and components that are fixed relative to one another. Similarly, the movable part 20 may be formed from a plurality of layers, parts and components that are fixed relative to one another.

The actuator assembly 2 comprises actuating units 30. 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 between the movable part 20 and the support structure 10. Selectively applying and varying the actuating forces F may move the movable part 20 relative to the support structure 10. The actuating units 30 are thus capable, on selective actuation, of driving movement of the movable part 20 relative to the support structure 10.

The actuator assembly 2 extends primarily in a direction orthogonal to a primary axis P. The extent of the actuator assembly 2 along the primary axis is less than the extent of the actuator assembly 2 along axes orthogonal to the primary axis P. The movable part 20 may be supported (so suspended) on the support structure 10 exclusively by the actuating units 30. However, preferably, the actuator assembly 2 comprises a bearing arrangement 40 that supports 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. According to embodiments, the bearing arrangement 40 may guide movement of the movable part 20 relative to the support structure 10 in a plane, also referred to as a movement plane. In alternative embodiments, the bearing arrangement 40 guides movement of the movable part 20 relative to the support structure 10 such that the movable part 20 tilts about axes orthogonal to the primary axis P. The bearing arrangement 40 may constrain movement of the movable part relative to the support structure in other degrees of freedom. For this purpose, the bearing arrangement 40 may, for example, comprise a rolling bearing (such as a roller bearing or ball bearing), a flexure bearing (i.e. an arrangement of flexures or other resilient elements guiding movement), or a plain bearing or sliding bearing.

The camera apparatus 1 further comprises a lens assembly 3 and an image sensor 4. The lens assembly 3 comprises one or more lenses configured to focus an image on the image sensor 4. The lens assembly 3 defines an optical axis 0, which is aligned with the primary axis Pin Figure 1A. The image sensor 4 captures an image and may be of any suitable type, for example a charge coupled device (CCD) or a CMOS device. The lens assembly 3 comprises a lens carrier, for example in the form of a cylindrical body, supporting the one or more lenses. The one or more lenses may be fixed in the lens carrier, or may be supported in the lens carrier in a manner in which at least one lens is movable along the optical axis 0, for example to provide zoom or focus, such as auto-focus (AF). The lens carrier itself may be movable along the optical axis 0. The lenses or the lens carrier may be moved by a voice coil motor (VCM) or an arrangement of SMA wires (not shown), for example. The apparatus 1 may be a miniature camera apparatus in which the or each lens of the lens assembly 3 has a diameter of 20mm or less, for example of 12mm or less.

In the embodiment shown in Figure 1, the movable part 20 may be considered to comprise the image sensor 4. The lens assembly 3 may be fixed relative to the support structure 10, i.e. mounted on the support structure 10. In other embodiments (not shown), the image sensor 4 may be fixed relative to the support structure 10 and the movable part 20 may comprise the lens assembly 3. In either embodiment, in operation the lens assembly 3 is moved relative to the image sensor 4. This has the effect that the image on the image sensor 4 is moved. So, optical image stabilization (015) may be implemented in the apparatus 1.

The camera apparatus 1 further comprises 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 allowing 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.

The controller 8 supplies the generated drive signals to the SMA wires 34.

Optionally, the camera apparatus comprises an inertial measurement unit 6. The inertial measurement unit 6 may comprise one or more vibration sensors, such as gyroscopes, accelerometers or magnetometers, although in general other types of sensors could be used. The inertial measurement unit 6 detects changes in the orientation of and/or the forces on the camera apparatus 1 and generates sensor signals representative of the orientation of and/or forces on the camera apparatus 1. The controller 8 receives the sensor signals and generates the drive signals for the SMA wires 34 in response to the sensor signals, for example so as to counteract the changes in orientation and/or forces represented by the output signals. The controller 8 may thus control the SMA wires 34 to achieve 015.

Arrangement of actuating units Figure 1B schematically shows the arrangement of actuating units 30 in the actuator assembly 2. As shown, the actuator assembly 2 may comprise 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 may be applied to the movable part 20 relative to the support structure 10.

In the depicted embodiment, 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 embodiment 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.

In the depicted embodiment, the four actuating units 30 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 positions 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 1B) are arranged to apply actuating forces F in opposite directions parallel to a first axis (e.g. the x axis in Figure 1B). The other two of actuating units (e.g. the left and right actuating units in Figure 1B) are arranged to apply actuating forces F opposite directions parallel to a second axis (e.g. the y axis in Figure 1B), orthogonal 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. 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 embodiments, 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 1B) 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 1B) 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 in a corner of the actuator assembly 2. The other two actuating units 30 may be arranged to apply actuating forces 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.

The arrangement of 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.

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 embodiments 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 orthogonal to the primary axis, due to appropriate movement constraints provided by the bearing arrangement 40. For example, the bearing arrangement 40 may comprise a plurality of flexures for guiding tilting of the movable part 20 about the axes orthogonal 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 comprise fewer actuating units 30. For example, the actuator assembly 2 may comprise two actuating units 30, e.g. the two actuating units 30 depicted in the top left of Figure 1B. 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 1B, 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.

Actuating units Figure 2A shows, in plan, an embodiment of the actuator assembly 2 in further detail, including the components of the actuating units 30. Figure 2B depicts an enlarged version cut-out A of Figure 2A.

Figure 2C shows a side view of Figure 2B.

One actuating unit 30 is provided with reference numerals in Figure 2B, but it will be appreciated that the other actuating units 30 may comprise the same components described with reference to that actuating unit 30. The actuating units 30 may be substantially identical, i.e. the structure and components of the actuating units 30 may be the same, but the actuating units' arrangement relative to the support structure 10 and/or movable part 20 may differ.

The actuating unit 30 comprises a body portion 31. The body portion 31 is a substantially rigid part and is designed not to deform on actuation of the actuating unit 30.

The actuating unit 30 further comprises 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, in particular 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 is formed integrally with the foot portion 36 and with part of the body portion 31, for example from a single sheet of material (such as metal). The force-modifying flexure 32 may, on flexing, allow the body portion 31 to move relative to the support structure 10 in a direction that is substantially orthogonal to the force-modifying flexure 32. The force-modifying flexure 32 effectively allows the body portion 31 to pivot relative to the support structure 10, with the pivot point P provided in a region along the force-modifying flexure 32. The force-modifying flexure 32 thus effectively provides the pivot point P. Although the pivot point P is depicted in the middle of force-modifying flexure 32 in Figure 2B, in practice the pivot point P may be virtual and need not lie on the force-modifying flexure 32.

The actuating unit 30 further comprises 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, in particular by a respective crimp 15. The other end of the SMA wire 34 is connected to the body portion 31, in particular by a respective crimp 35.

The actuating unit 30 further comprises 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 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 is arranged to modify the input force Fi so as to cause the coupling flexure 33 to apply the actuating force F to the movable part 20. In particular, in the depicted embodiment the force-modifying flexure 32 is placed in tension on contraction of the SMA wire 34. The force-modifying flexure 32 is arranged at an angle a relative to the SMA wire 34. As a result, the body portion 31 is arranged, on SMA wire contraction, to move at an angle (of about 90 degrees minus a) relative to the length of the SMA wire 34. The force-modifying flexure 32 thus converts the input force H, in particular the magnitude and direction thereof, into the actuating force F In the depicted embodiment, the change in magnitude of the force is dependent on (and indeed proportional to) the ratio of i) the (shortest) distance Ds of the SMA wire 34 from the pivot point P and ii) the (shortest) distance Dc of the coupling flexure 33 from the pivot point P. So, F/Fi is proportional to Ds/Dc. It will be appreciated that the ratio Ds/Dc is dependent, at least in part, on the angle a between SMA wire 34 and force-modifying flexure 32.

So, if the SMA wire 34 is relatively closer to the (virtual) pivot point P than the coupling flexure 33, then the input force Fi applied on contraction of the SMA wire 32 is de-amplified. At the same time, the movement of the movable part 20 is amplified relative to a change in length of the SMA wire 32.

Alternatively, if the SMA wire 34 is relatively further away from the (virtual) pivot point P compared to the coupling flexure 33, then the input force Fi applied on contraction of the SMA wire 32 is amplified. At the same time, the movement of the movable part 20 is de-amplified relative to a change in length of the SMA wire 32. The actuating unit 30 can thus be configured to amplify movement or to amplify force due to contraction of the SMA wire 34.

In some embodiments, at least one actuating unit 30, preferably each actuating unit 30, is configured such that the force-modifying flexure 32 amplifies an amount of contraction of the SMA wire 34 to a relatively greater amount of movement of the movable part 20 relative to the support structure 10. Such amplification, for example, may be by a factor greater than 1.5, preferably greater than 2, further preferably greater than 3. This may be achieved, for example, by appropriate selection of the angle a between the force-modifying flexure 32 and the SMA wire 34. The angle a may be in the range from 0 to 45 degrees, preferably from 13 to 40 degrees.

The coupling flexure may be at an angle of substantially 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.

However, in general, the angle between coupling flexure 33 and SMA wire 34 may be any angle other than 90 degrees.

The coupling flexure 33 is compliant in a direction perpendicular to the actuating force F. This allows the movable part 20 to move in a direction perpendicular to the actuating force F, and in a direction perpendicular to the coupling flexure 33, for example due to actuation of a different actuation unit 30.

In the above-described embodiments, 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. However, in general, the force-modifying flexure 32 could also be arranged so as to be placed under compression on contraction of the SMA wire 34.

In the above-described embodiments, 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.

Overlapping coupling flexures for reduced height According to some embodiments, the coupling flexures 33 of two different actuating units 30 (in particular of adjacent actuator units 30) overlap when viewed along the primary axis P. The two different actuating units 30 are also referred to as a pair of actuating units 30 herein. In particular, only the coupling flexures 33 of the two actuator units 30 overlap. The body portions 31 and amplifying flexures of adjacent actuator units 30 do not overlap when viewed along the primary axis P. This is apparent from Figure 2B, for example. One of the two different actuating units 30 applies a respective actuating force F parallel along the x axis, and the other of the two different actuating units 30 applies a respective actuating force F parallel to the y axis. The coupling flexures 33 of the two actuating units 30 not shown in the cut-out of Figure 2B also overlap when viewed along the primary axis P. In particular, the coupling flexures 33 of the two different actuating units 30 cross over or intersect when viewed along the primary axis. The coupling flexures 33 of the two different actuating units 30 may for an angle of about 90 degrees therebetween.

Providing such overlap between coupling flexures 33 allows the height of the actuator assembly 2 to be reduced while maintaining a comparably compact footprint, compared to a situation in which the coupling flexures 33 do not overlap. This is apparent, for example, from a comparison with the actuator assembly 2 depicted in Figures 3A and 3B. In the actuator assembly 2 of Figures 3A and 3B, the coupling flexures 33 do not overlap. Instead, overlap is provided between the body portions 31 of two adjacent actuating units 30. As a result, the height of the actuator assembly 2 of Figures 3A and 3B is greater than that of the actuator assembly 2 of Figures 2A-C. Furthermore, a hypothetical example in which neither the coupling flexures 33 nor other parts of the actuating units 30 of adjacent actuator assemblies 2 overlap would have a much greater footprint (in the x-y plane) than the actuator assembly 2 of Figures 2A-C. Allowing the coupling flexures 33 of adjacent actuator units 30 to overlap thus provides a generally compact actuator assembly 2.

Put another way, the body portion 31, the force-modifying flexure 32 and the foot portion 36 of one actuating unit 30 are located between the SMA wire of the one actuating unit 30 and the coupling flexure 33 of the other actuating unit 30 of the two adjacent actuating units 33. The distance between the SMA wire 34 of one actuating unit 30 and the coupling flexure 33 of the other actuating unit 30 is increased compared to the Figure 3 actuator assembly 2.

Despite the overlap when viewed along the primary axis P, the coupling flexures 33 may be configured not to be in direct contact with each other upon movement of the movable part 20, in particular over the entire movement range of the movable part 20 relative to the support structure 10.

This may be achieved, for example, by providing at least one coupling flexure 33 (optionally both coupling flexures 33) with a kinked portion (not shown) in the region of overlap. This kinked portion may also be referred to as a jog or as an offset, along the primary axis, formed in the coupling flexure 33. A major portion of both of the coupling flexures 33 may thus extend in the same plane, with only the kinked portion offset from the plane to avoid clashes between the coupling flexures 33.

Alternatively, the coupling flexures 33 of the two actuating units 33 may be arranged to be offset along the primary axis P, thereby avoiding direct contact. Figure 4, for example, depicts an embodiment of an actuating units 30 in a multi-layer arrangement. In particular, the body portion 31 comprises at least two layers, stacked along the primary axis P. In the depicted embodiment, the force-modifying flexure 34 and the foot portion 36 also comprise two layers stacked along the primary axis P, but in general only one layer may also be provided. The coupling flexure 33 is a single flexure, with a height along the primary axis P that is less (in particular half) of the height of the body portion 31.

So, in general, the coupling flexure 33 may have an extent along the primary axis P that is less than that of the body portion 31, in particular less than half of the extent of the body portion 31 along the primary axis P. This allows one of the two adjacent actuating units 30 to be arranged with one side up, and the other of two adjacent actuating units 30 to be arranged with the other side up. The two actuating units 30 may thus be identical in structure, but arranged on the actuator assembly 2 with different sides facing in a given direction along the primary axis P. Clashing of the coupling flexures 33 can thus be avoided. Figure 6B shows an embodiment with such an arrangement of actuator units 30.

In particular, the each actuating unit 30 may comprise a first surface parallel to a plane orthogonal to the primary axis P and a second surface parallel to the plane. The first and second surfaces are provided on opposite sides of the actuating unit 30. The two adjacent actuating units 30 may be arranged on the actuator assembly 2 with the first surface of one and the second surface of the other facing in the same direction along the primary axis P. As depicted in the embodiments of Figures 2, sand 6, the SMA wire 34 extends, viewed orthogonally to the SMA wire, past a point at which the coupling flexure 33 connects to the body portion 31. In Figure 2B, for example, the SMA wire 34 extends further to the left than the connection point between coupling flexure 33 and body portion 31. As a result, the length of the SMA wire 34 is greater compared to a situation in which the SMA wire 34 stops at a point where the coupling flexure 33 connects to the body portion 31 (as in Figure 3B, for example). A longer SMA wire 34 allows for increased stroke and/or more accurate positioning control of the movable part 20.

Figure 5 shows another embodiment of an actuating unit 30. Compared to the actuating unit 30 of Figures 2 and 3, the SMA wire 34 is arranged on the same side of the body portion 31 as a point at which the force-modifying flexure 32 connects to support structure 10. In particular, the foot portion 36 is provided on the same side of the body portion 31 as the SMA wire 34. This reduces the extent of the actuating unit in a lateral direction, i.e. in a direction along the actuating force F. The footprint of the actuator assembly 2 may thus be reduced.

Figure 6A and 6B show further embodiments of an actuating unit 30. Compared to the actuating unit 30 of Figures 2 and 3, the SMA wire 34 is arranged so as to overlap with the body portion 31 when viewed along the primary axis P. This allows the extent of the actuating unit 30 in a lateral direction, i.e. in a direction along the actuating force F to be reduced. The footprint of the actuator assembly 2 may thus be reduced.

Connecting actuating units to different parts As already discussed above, the coupling flexures 33 may connect to either one of the support structure 10 and movable part 20, and the SMA wires 34 and force-amplifying flexures may respectively connect to either of the movable part 20 and support structure 10.

Figures 7A and 7B show embodiments of the actuator assembly 2 in which some actuating units 30 are arranged such that their coupling flexures 33 connect to the movable part 20 and some other actuating units 30 are arranged such that their coupling flexures connect to the support structure 10. Figure 7A shows this conceptionally, whereas Figure 7B shows further details of the arrangement of actuator units 30.

In particular, the actuating units 30 applying actuating forces F along the y axis are referred to herein as static actuating units 30s. These actuating units 30s are connected between the movable part 20 and the support structure 10 with the force-modifying flexure 32s and the SMA wire 34s connecting to the support structure 10, and the coupling flexure 33s connecting to the movable part 20. The actuating units 30 applying actuating forces F along the x axis are referred to herein as movable actuating units 30m. These actuating units 30m are connected between the movable part 20 and the support structure 10 with the force-modifying flexure 32m and the SMA wire 34m connecting to the movable part 20, and the coupling flexure 33m connecting to the support structure 10. Of course, in other arrangements, the static actuating units 30s may apply actuating forces F along the x axis and the movable actuating units 30m may apply actuating forces F along the y axis.

In some other embodiments, one static actuating unit 30s may apply an actuating force F along the x axis and the other static actuating unit may apply an actuating force F along the y axis. Similarly, one movable actuating unit 30m may apply an actuating force F along the x axis (opposing the actuating force F of the corresponding static actuating unit 30s) and the other movable actuating unit 30m may apply an actuating force F along the y axis (opposing the actuating force F of the corresponding static actuating unit 30s).

Providing both static actuating units 30s and movable actuating units 30m in combination may reduce the amount of overlap, when viewed along the primary axis, of the actuating units 30m. Indeed, as shown in Figures 7A and 7B, overlap may be avoided entirely. The height of the actuator assembly 2 may thus be reduced. This is achieved without increasing the footprint of the actuator assembly 2 significantly.

Further details of actuator assembly Figures 8A and 8B show further details of the actuator assembly 2. In particular, Figure 8A shows an example of the static crimp 15 mounted to the support structure 10. Figure 8B shows an example of the foot portion 36 of the actuating unit 30 mounted to the support structure 10.

As shown in Figure 8A, the static crimp 15 may be elevated or offset from a surface of the support structure 10. In particular, kinks or bends may be provided in a portion connected to or integrally formed with the static crimp 15 so as to elevate the static crimp.

Similarly, as shown in Figure 8B, the foot portion 36 may include a kink or bend. This allows the body portion 31, as well as the crimp 35 connected to the body portion 31 and the force-modifying flexure 32 to be elevated or offset from a surface of the support structure 10. Both crimps 15, 35 connecting to the SMA wire 34 may thus be elevated above the surface of the support structure 10, allowing alignment of the two crimps 15, 35 in a common plane. The SMA wire 34 may extend parallel to the surface of the support structure 10 and/or parallel to the actuating forces F and/or parallel to the movement plane.

The force-modifying flexures 32 and/or body portions 31 of different actuating units 30 may also be provided at different offsets along the primary axis P in this manner, thus avoiding clashes between actuating units 30 even when there is overlap when viewed along the primary axis P. Figure 8C shows a raised feature 20r on the moving part 20. The coupling flexure 33 of an actuating unit 30 may connect to this raised feature 20r. The height of this raised feature 20r may be designed so as to allow the coupling flexure 33 to extend substantially parallel to the surface of the support structure 10 and/or parallel to the actuating forces F and/or parallel to the movement plane.

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

Claims

Claims 1. An actuator assembly comprising: first and second parts that are movable and/or tiltable relative to each other along and/or about two orthogonal axes that are perpendicular to a primary axis; and at least one pair of actuating units, each actuating unit connected between the first and second parts and arranged to apply a respective actuating force between the first and second parts, wherein each actuating unit comprises: a body portion; a force-modifying flexure connected between the body portion and one of the first and second part; a coupling flexure connected between the body portion and the other of the first and second part; and an SMA wire connected between the body portion and the one of the first and second part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts; wherein the coupling flexure is compliant in a direction perpendicular to the direction of the actuating force; and wherein the coupling flexures of each pair of actuating units overlap when viewed along the primary axis, wherein one actuating unit of each pair of actuating units is configured to apply a respective actuating force parallel to a first axis in a plane spanned by the two orthogonal axes and the other actuating unit of each pair of actuating units is configured to apply a respective actuating force parallel to a second axis in the plane spanned by the two orthogonal axes, wherein the second axis is nonparallel to the first axis.
2. An actuator assembly according to claim 1, wherein at least one coupling flexures of one actuating unit of each pair of actuating units comprises a kinked portion in the region of overlap with the coupling flexure of the other actuating unit of each pair of actuating units, thereby avoiding contact between the coupling flexures.
3. An actuator assembly according to claim 1, wherein the coupling flexures of each pair of actuating units are arranged offset along the primary axis relative to one another, thereby avoiding contact between the coupling flexures.
4. An actuator assembly according to any preceding claim, wherein the actuating units are substantially identical.
5. An actuator assembly according to claim 4, wherein each actuating unit comprising a first surface parallel to the plane spanned by the two orthogonal axes and a second surface parallel to the plane spanned by the two orthogonal axes, wherein the first and second surfaces are provided on opposite sides of the actuating unit, wherein for each pair of actuating units the first surface of one actuating unit and the second surface of the other actuating unit face in the same direction along the primary axis.
6. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the SMA wire extends, viewed orthogonally to the SMA wire, past a point at which the coupling flexure connects to the body portion.
7. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that, viewed along the primary axis, the SMA wire is arranged on the same side of the body portion as a point at which the force-modifying flexure connects to the first or second part.
8. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure is in tension on contraction of the SMA wire.
9. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure amplifies an amount of contraction of the SMA wire to a relatively greater amount of movement between first and second parts.
10. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the angle between force-modifying flexure and SMA wire is in the range from 0 to 45 degrees, preferably from 13 to 40 degrees.
11. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the force-modifying flexure is formed integrally with at least part of the body portion.
12. An actuator assembly according to any preceding claim, wherein at least one actuating unit, preferably each actuating unit, is configured such that the coupling flexure is formed integrally with at least part of the body portion.
13. An actuator assembly according to any preceding claim, comprising a total of four actuating units, wherein the four actuating units consist of two pairs of actuating units.
14. An actuator assembly according to claim 13, wherein none of the actuating forces applied by the four actuating units are colinear.
15. An actuator assembly according to claim 13 or 14, wherein the four actuating units are in an arrangement capable of applying actuating forces between first and second parts so as to move the first and second parts relative to each other to any positions within a range of movement within a movement plane spanned by the two orthogonal axes without applying any net torque between the first and second parts.
16. An actuator assembly according to any one of claims 13 to 15, wherein two of the four actuating units are arranged to apply actuating forces so as to generate a torque between the first and second parts in a first sense around the primary axis and the other two of the four actuating units are arranged to apply actuating forces so as to generate a moment between the first and second parts in a second, opposite sense around the primary axis.
17. An actuator assembly according to any one of claims 13 to 16, wherein two of the four actuating units are arranged to apply actuating forces in a corner of the actuator assembly, and the other two of the four actuating units are arranged to apply actuating forces in another, opposite corner of the actuator assembly.
18. An actuator assembly according to any one of claims 13 to 16, wherein two of the four actuating units are arranged to apply actuating forces so as to move the first and second parts relative to each other in opposite directions parallel to the first axis, and the other two of the four actuating units are arranged to apply actuating forces so as to move the first and second parts relative to each other in opposite directions parallel to the second axis.
19. An actuator assembly according to any one of claims 13 to 16, wherein each actuating unit extends parallel to the two orthogonal axes.
20. An actuator assembly according to any preceding claim, further comprising a bearing arrangement between first and second parts and arranged to allow the relative movement between first and second parts.
21. An actuator assembly comprising: first and second parts that are movable relative to each other in a movement plane that is perpendicular to a primary axis; and at least one pair of actuating units, each actuating unit connected between the first and second parts and arranged to apply a respective actuating force between the first and second parts, wherein one of each pair of actuating units comprises: a body portion; a force-modifying flexure connected between the body portion and the first part; a coupling flexure connected between the body portion and the second part; and an SMA wire connected between the body portion and the first part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts; and wherein the other of each pair of actuating units comprises: a body portion; a force-modifying flexure connected between the body portion and the second part; a coupling flexure connected between the body portion and the first part; and an SMA wire connected between the body portion and the second part, wherein the SMA wire is arranged, on contraction, to apply an input force on the body portion, wherein the force-modifying flexure is arranged to modify the input force so as to cause the coupling flexure to apply the actuating force between the first and second parts;
22. An actuator assembly according to claim 21, wherein none of the actuating units overlap when viewed along the primary axis.
23. An actuator assembly according to claim 21 or 22, comprising a total of four actuating units, wherein the four actuating units consist of two pairs of actuating units.
24. An actuator assembly according to any one of claims 21 to 24, wherein the four actuating units are in an arrangement capable of applying actuating forces between first and second parts so as to move the first and second parts relative to each other to any positions within a range of movement within the movement plane without applying any net torque between the first and second parts.
25. A camera apparatus, comprising the actuator assembly of any preceding claim; an image sensor coupled to one of the first and second part of the actuator assembly; and a lens assembly coupled to the other of the first and second part of the actuator assembly, wherein an optical axis defined by the lens assembly aligns with the primary axis of the actuator assembly.