Patent Publication Number: US-2022236583-A1

Title: Actuator assembly

Description:
FIELD 
     The present application relates to an actuator assembly, particularly an actuator assembly comprising a plurality of lengths of shape-memory alloy (SMA) wire. 
     BACKGROUND 
     Such an actuator assembly may be used, for example, in a camera to move a lens assembly in directions perpendicular to the optical axis so as to provide optical image stabilization (OIS). Where such a camera is to be incorporated into a portable electronic device such as a mobile telephone, miniaturization can be important. 
     WO 2019/086855 A1 describes a camera with an actuator assembly including a support platform, a moving platform that supports a lens assembly, SMA wires connected to the support platform and the moving platform, and bearings to bear the moving platform on the support platform. This actuator assembly also includes two arms extending between the support platform and the moving platform. The arms provide, amongst other things, a lateral biasing force that biases the lens assembly towards a central position. 
     SUMMARY 
     First Aspect 
     According to a first aspect of the present invention, there is provided an actuator assembly comprising:
         first and second parts, wherein a first axis is defined with reference to the second part;   shape-memory alloy wire connected between the first and second parts for moving the first part relative to the second part in any of a set of directions that are at least partly perpendicular to the first axis, wherein the set of directions includes first and second directions;   a set of arms, each of which is connected between the first and second parts and extends partly around the first axis, the set of arms configured to provide a biasing force that biases the first part towards a first position relative to the second part;   wherein the set of arms has a first stiffness when the first part is moved away from the first position in the first direction and a second, lower stiffness when the first part is moved away from the first position in the second direction; and   wherein at least one of the set of arms comprises a portion that is configured to decrease the first stiffness by a larger relative amount than the portion decreases the second stiffness.       

     Thus, the arms can provide a more symmetric (centring) biasing force, which, in turn, can enable the actuator assembly to be controlled more effectively, etc. 
     The ‘first part’ may also be referred to as a movable part and the second part may also be referred to as a static part. Additionally, each of the ‘arms’ which provide a bias force may also be referred to as a flexure. 
     Further (optional) features are specified in the dependent claims. 
     For instance, the portion may correspond to at least one hairpin-shaped portion of the arm. For ease of reference, such a portion is hereinafter sometimes referred to as a kink and such an arm as a kinked arm. 
     The above-described decreases in the first and second stiffness are compared, for example, to an equivalent arm without the portion (e.g. an arm that does not have a hairpin-shaped portion but is merely straight in the corresponding segment of the arm). The portion need not decrease the second stiffness. 
     Second and Third Aspects 
     According to a second aspect of the present invention there is provided an actuator assembly comprising:
         a static part on which a static crimp portion is mounted;   a movable part comprising a crimp support portion on which a moving crimp portion is mounted;   shape memory alloy wire connected between the static part and the moving part by being crimped by the static crimp portion and the moving crimp portion and arranged to drive relative movement of the movable part with respect to the static part in directions in a movement plane perpendicular to a primary axis; and   a bearing arrangement arranged to guide the relative movement of the movable part relative to the static part in directions in the movement plane and to resist relative movement of the movable part relative to the static part along the primary axis, the bearing arrangement comprising a flexure connected between the static part and moveable part, the flexure extending around the primary axis,   wherein the flexure is arranged such that it overlaps the crimp support portion as viewed along the primary axis.       

     Thus, in accordance with this second aspect of the invention, it is possible to include flexures which are arranged to overlap the crimp support portion and thus this arrangement may advantageously avoid increasing the footprint of the actuator assembly. In certain instances this may permit the inclusion of additional flexures on the actuator assembly which may have otherwise been avoided due to space constraints. This overlapping arrangement may be contrasted to an arrangement whereby the flexure is routed around the crimp support portion, which may increase the footprint of the actuator assembly. Keeping the footprint of the actuator assembly to a minimum is particularly important as such actuator assemblies are increasingly used in applications where the available space is limited. In accordance with this second aspect of the invention, the overlapping of the flexures with the moving crimp corners may allow an arrangement of flexures which provides a more uniform symmetry of stiffness in the movement plane. 
     In a set of embodiments the movable part further comprises a main body to which the crimp support portion is connected. In a further set of embodiments the crimp support portion is a separate portion from the main body. Equally, the crimp support portion may be integrally provided with the main body of the movable part. The main body of the movable support may have any suitable form. In a set of embodiments, the main body is formed as a sheet of material. 
     In prior art actuator assemblies, for example of the type seen in WO-2019/086855, the flexures typically extend around the corners which comprise static crimp portions and they simply avoid passing the corners with the moving crimp portions completely. As a result, this may limit the ability for such prior art actuator assemblies to achieve an arrangement of flexures which provides a more uniform stiffness in multiple directions in the movement plane. 
     In a set of embodiments, the flexure is separated from the crimp support portion. Arranging the flexure such that it is separated from the crimp support portion may advantageously help to avoid a short circuit forming between the flexure and the crimp support portion, one or both of which may be an electrically live component. 
     Of course the actuator assembly may comprise further flexures which don&#39;t overlap the crimp support portion. 
     It is often desirable to keep the depth of the actuator assembly in the primary axis to a minimum, due to the space constrains of the devices in which the actuator assemblies are typically used. A number of different means for separating the flexure and the crimp support portion whilst at the same time keeping the depth of the actuator assembly as small as possible are possible. 
     In a set of embodiments, the flexure comprises a first thinned section, having a reduced depth along the primary axis, that provides the separation between the flexure and the crimp support portion. A flexure which has a thinned section, which extends partially along its length, may be sufficient to provide the desired separation, whilst at the same time not impacting too significantly how the flexure responds to deformation. As will be appreciated by those skilled in the art, thinning the entire flexure in order to achieve the desired separation may necessitate a change in the material of the flexure in order to provide the desired characteristics, which may be not feasible. Therefore by only thinning a section of the flexure this may be avoided. 
     In a set of embodiments, the crimp support portion comprises a second thinned section, having a reduced depth along the primary axis, that provides the separation between the flexure and the crimp support portion. As with the flexure discussed above, it may not be desirable to thin the entire crimp support portion as it may no longer be capable of providing its supporting function, yet thinning a section of it may be sufficient to provide the separation. 
     The first thinned section or second thinned section may be created by any suitable means, for example etching. 
     In a set of embodiments, the crimp support portion comprises a cut-out section (i.e. a section in which the entire thickness is removed) that provides the separation between the flexure and the crimp support portion. 
     In a set of embodiments, the crimp support portion comprises a shoulder portion extending from a main body of the movable part along the primary axis which offsets the moving crimp portion along the primary axis to provide the separation between the flexure and the crimp support portion. This may provide a simple arrangement for forming the separation which does not require any thinning of sections of the flexure or crimp support portion. 
     In a set of embodiments the crimp support portion is connected to an upper or lower surface of a main body of the movable part to provide the separation between the flexure and the crimp support portion. As will be appreciated by those skilled in the art, arranging the crimp support portion in this manner effectively displaces the crimp support portion along the primary axis, when compared to an example whereby the crimp support portion extends directly from a main body of the movable part. This displacement may thus provide the separation. This particular arrangement, again, may be a relatively simple means for achieving the separation, but may impact the depth of the actuator assembly. 
     In another set of embodiments at least a portion of the flexure is arched to provide the separation between the flexure and the crimp support portion. Such an arching of the flexure to provide the separation may be easy to achieve during manufacture of the assembly. Arching the flexure to provide the separation may further be advantageous as it may provide a secondary function of preloading the flexure in the primary axis such that when arranged appropriately within the assembly, e.g. through connection between the moving part and static part, the arched flexure may resist movement of the movable part away from the static part along the primary axis. However, arching the flexure in this manner may increase the depth of the assembly along the primary axis which may be less desirable in some instances. The portion of the flexure may be arched such that it extends above or below the crimp support portion. 
     A set of embodiments may comprise at least one further flexure arranged such that it does not overlap the crimp support portion as viewed along the primary axis. In this set of embodiments, only the at least one further flexure may be preloaded so as to resist movement of the movable part away from the static part along the primary axis. This may help in providing the separation between the flexure and the crimp support portion (and/or not unduly increasing the depth of the assembly along the primary axis). 
     Of course, any of the embodiments described above in relation to providing the separation may be combined such that the assembly comprises any combination of different means for achieving the separation. For example the assembly may comprise a combination of a first thinned section on the flexure and a second thinned section on the crimp support portion. The specific means and its extent, e.g. the depth of the respective thinned sections, may be determined by the level of separation that is required. For example, in instances where a large separation is essential, it may be necessary, for example, to provide thinned sections on both the flexure and crimp support portion. 
     The prevention of a short circuit may also be achieved by alternative means. In a set of embodiments, an electrical insulation layer is arranged between the crimp support portion and the flexure. Depending on the particular properties of the electrical insulation layer, the inclusion of the electrical insulation layer without the separation discussed above may be sufficient to prevent to formation of a short circuit. However, this may not always be the case and the electrical insulation layer may be advantageously combined with the separation of the flexure and crimp support component to further reduce the risk of a short circuit occurring. 
     The electrical insulation layer may be arranged in any suitable position such that it provides an insulation layer between the flexure and the crimp support portion. In a set of embodiments the electrical insulation layer is arranged on a surface of the flexure which faces the crimp support portion. In a set of embodiments, the electrical insulation layer is arranged on a surface of the crimp support portion which faces the flexure. The position of the insulation layer may depend on the particular configuration of the flexure and the crimp support structure. For example, if the flexure passes above the crimp support structure, a surface of the crimp support structure and/or a surface of the flexure may be provided with the electrical insulation layer. 
     The electrical insulation layer may be formed as a coating on the flexure and/or the crimp support portion. The electrical insulation layer may be made from any material which provides appropriate insulation properties. The electrical insulation layer may comprise a ceramic layer. The ceramic layer may, for example, comprise at least one of: titanium carbide, silicon dioxide, diamond-like carbon (DLC), tungsten carbide/carbon (WC/C). 
     In a set of embodiments the moveable part comprises a further crimp support portion on which a further moving crimp portion is mounted, and wherein the bearing arrangement comprises a further flexure connected between the static part and movable part, wherein the further flexure extends around the primary axis, and wherein the further flexure is arranged such that it overlaps the further crimp support portion as viewed along the primary axis. The further crimp support portion and further flexure may comprise any of the features described above with respect to the crimp support portion and the flexure. 
     The static part may comprise a static crimp support portion on which the static crimp portion is mounted. 
     In another set of embodiments, the actuator assembly comprises an additional flexure connected between the static and movable part. In embodiments which comprise at least three flexures, it is possible to arrange the at least three flexures such that the symmetry of the stiffness of the movable part in numerous orthogonal axes in the movement plane can be significantly improved. 
     In fact, the inclusion of three flexures which improves the symmetry in this manner is novel and inventive in its own right and thus when viewed from a third aspect of the present invention there is provided an actuator assembly comprising:
         a static part;   a movable part;   at least one shape memory alloy wire connected between the static part and the moving part and arranged to drive relative movement of the movable part with respect to the static part in directions in a movement plane perpendicular to a primary axis; and   a bearing arrangement arranged to guide the relative movement of the movable part relative to the static part in directions in the movement plane and to resist relative movement of the movable part relative to the static part along the primary axis, the bearing arrangement comprising at least three flexures connected between the static part and moveable part, each of the at least three flexures extending around the primary axis,   wherein, for every pair of first and second orthogonal axes in the movement plane, defining a first stiffness as the combined lateral stiffness of the at least three flexures along the first axis and a second stiffness as the combined lateral stiffness of the at least three flexures along the second axis, the maximum ratio of the first and second stiffnesses is no more than 5.       

     As will readily be understood by those skilled in the art, for any set of two stiffness values which are not equal, there will be two ratios, one of which is greater than the other. It is this greater ratio, which will inherently form the maximum ratio, which much satisfy the ratio quoted above in relation to this third aspect of the invention. 
     Through the inclusion of at least three flexures extending around the primary axis appropriately positioned to provide a maximum stiffness ratio above, it will be appreciated that the stiffness along any pair of orthogonal axes will be significantly more symmetric, at least when compared to prior art actuator assemblies which comprise only two flexures, for example of the type described in WO-2019/086855. 
     Having an actuator assembly wherein the stiffness of the movable part in any pair of orthogonal axes is more symmetrical, to the degree referred, to above is advantageous as it may allow for simpler and more accurate control of the movable part. As will be appreciated, when compared to prior art assemblies in which the stiffness along a first axis may be, for example, ten times larger than the stiffness along its orthogonal axis, by minimising the difference in stiffness along each pair of orthogonal axes, the control algorithms which act to control the movable part may be less complicated. This improved symmetry may therefore mean that it is possible to achieve more accurate control of the shape memory alloy wire and thus more accurate control of the position of the movable part. 
     In a set of embodiments, the at least three flexures comprise a total of three flexures. 
     It may be possible to obtain further control over the symmetry of the stiffness of the movable part through the inclusion of further flexures. Therefore, in a set of embodiments, the at least three flexures comprise a total of four flexures connected between the static part and movable part. The use of four flexures extending around the primary axis in accordance with the third aspect of the present invention provides a further improvement in the symmetry of the stiffness of any pair of two orthogonal axes. 
     The at least four flexures may be arranged around the primary axis in any suitable manner. In a set of embodiments, however, the at least four flexures are arranged to have four-fold rotational symmetry about the primary axis. Such an arrangement may achieve the ratio quoted above. In another set of embodiments, the at least four flexures are arranged to have at least two-fold mirror symmetry around the primary axis. Similarly, such an arrangement of flexures may achieve the ratio quoted above. Of course there may be a large number of different arrangements of the at least four flexures which achieves the above quoted ratio and these are merely two examples. 
     In a set of embodiments at least two of the at least three flexures share a common connection point to the static or movable parts. 
     As will be appreciated by those skilled in the art, the stiffness along any axes will be the combined stiffness of each of the at least three flexures, as all of the at least three flexures will deform to some level in order to permit the movement along any axis. 
     In the second or third aspect of the present invention, the flexure or at least one of the flexures may be an arm configured in accordance with the first aspect of the present invention, for example by comprising at least one hairpin-shaped portion such that the arm is a kinked arm. 
     In a set of embodiments the static part comprises a static crimp portion and the moving part comprises a moving crimp portion, and wherein a shape memory alloy wire is connected between the one static crimp portion and the moving crimp portion. As will be appreciated by those skilled in the art, the inclusion of a shape memory alloy wire connected in this manner will provide a means for driving movement of the movable part. 
     In any of the aspects of the present invention, the movable part may be a lens assembly comprising at least one lens having an optical axis, the optical axis being the primary axis. In a further set of embodiments, the actuator assembly further comprises an image sensor arranged to capture an image focused by the lens assembly. In such a case, the actuator assembly may be used, for example, to perform optical image stabilisation. 
     Whilst the maximum ratio of the first and second stiffnesses, in relation to the third aspect is described above as no more than 5, depending on the particular application this may differ. For example, the maximum ratio of the first and second stiffnesses may instead be 3, 2, 1.5, 1.25 or ˜1. 
     Features of the second and/or third aspects of the present invention of the present invention may be combined with features of the first, second and/or third aspects of the present invention 
     Fourth Aspect 
     According to a fourth aspect of the present invention there is provided an actuator assembly suitable for connection to a further actuator assembly, the further actuator configured to actuate in directions parallel to a primary axis, the actuator assembly comprising:
         a static part;   a movable part;   at least two lengths of shape memory alloy (SMA) wire connected between the static part and the movable part and configured to drive movement of the movable part with respect to the static part in directions in a movement plane perpendicular to the primary axis; and   one or more flexible elements connecting the static part and the movable part;   wherein the static part, the one or more flexible elements and the movable part comprise one or more current paths electrically connectable to the further actuator assembly via the movable part.       

     The flexible elements may be a flexure arm connecting the static part and the movable part. 
     At least one of the flexible elements may provide a biasing force that biases the movable part and the static part towards each other. 
     At least one of the flexible elements may form part of a bearing arrangement configured to guide relative movement of the movable part relative to the static part in directions in the movement plane, and to resist movement of the movable part relative to the static part in directions parallel to the primary axis. 
     At least one of the flexible elements may be formed integrally with one of the static part and the movable part and may be mechanically and electrically connected to the other one of the static part and the moveable part. 
     The one or more current paths may comprise two current paths, three current paths or four current paths. 
     At least one of the current paths may be electrically connected to at least one of the lengths of SMA wire via the movable part. 
     The static part, the at least one flexible element and the movable part may comprise one or more further current paths electrically connected to at least one of the lengths of SMA wire. 
     The flexible elements may comprise one flexible element for each one of the current path(s) and the further current path(s). 
     The movable part may comprise one or more first conductive elements and the static part may comprise one or more second conductive elements, with one first conductive element and one second conductive element for each one of the current paths and the further current paths. 
     Each of the first conductive elements may have a terminal for connecting to the further actuator and/or each of the second conductive elements may have a terminal for connecting to external electronic circuitry. 
     Each of the first conductive elements may comprise one or more generally planar portions of the moving part. 
     The generally planar portions may be arranged in two or more layers and the portions in the same layer may be physically separated from one another and certain portions in different layers may be electrically interconnected. 
     The adjacent ones of the layers may be physically interconnected via a generally insulating layer so as to form an integral structure. 
     The actuator assembly may comprise one or more connectors, each of the connectors for electrically and physically interconnecting adjacent ones of the layers. 
     The generally planar portions may comprise at least one portion with an integral connecting portion for connecting to at least one of the lengths of SMA wire. 
     The generally planar portions may comprise at least one portion that is integral with at least one of the flexible elements. 
     One of the layers may be connected to the SMA wires and another one of the layers may be connected to the flexible elements. 
     The movable part and the static part of the actuator assembly may comprise patterned metallic sheets. 
     The one or more flexible elements may comprise:
         four flexures that extend in an arc around the primary axis without an outer perimeter of the static part and/or the movable part; and   one flexure that extends in an arc around the primary axis within an inner perimeter of the static part and/or the movable part.       

     The four flexures may substantially wrap around the outer perimeter of the static part and/or the movable part. The one flexure may substantially wrap around the inner perimeter of the static part and/or the movable part. 
     One or more of the current paths and/or the further current paths may comprise electrically conductive tracks. 
     There may be provided an apparatus comprising:
         the actuator assembly; and   the further actuator assembly, wherein the further actuator assembly is connected to the movable part so as to move with the movable part in the directions in the movement plane.       

     The further actuator assembly may comprise a further static part and a further movable part movable in the directions parallel to the primary axis relative to the further static part, and the further static part may be mechanically and electrically connected to the movable part. 
     Features of the fourth aspect of the present invention may be combined with features of the first, second and/or third aspects of the present invention. For instance, the flexures arms of the fourth aspect may have a ‘kink’ as in the first aspect and/or may be arranged as specified in the second and/or third aspects. 
    
    
     
       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: 
         FIG. 1  illustrates a schematic cross-sectional view of a camera incorporating a known SMA actuator assembly; 
         FIG. 2  illustrates an exploded perspective view of the SMA actuator assembly of  FIG. 1  (A) in a simplified, schematic form and (B) in more detail; 
         FIG. 3  illustrates a side view of the SMA actuator assembly of  FIG. 1  expanded along an optical axis O; 
         FIG. 4  illustrates a cross-sectional view of a plain bearing of the SMA actuator assembly of  FIG. 1 ; 
         FIG. 5  illustrates a top view of the moving platform and the arms of the SMA actuator assembly of  FIG. 1 ; 
         FIG. 6  illustrates top views of (A) the SMA actuator assembly of  FIG. 1 , (B) only the moving platform and arms thereof; 
         FIG. 7  illustrates top views of (A) an SMA actuator assembly of a similar type to that of  FIG. 1  but for use with a larger lens assembly and (B) only the moving platform and arms thereof; 
         FIG. 8  illustrates top views of (A) an example of an SMA actuator assembly with kinked arms and (B) only the moving platform and arms thereof; 
         FIG. 9  illustrates the bending moment on the arms of  FIG. 8  for displacement of the moving platform in (A) the strong diagonal and (B) the weak diagonal; 
         FIG. 10  illustrates (exaggerated) displacement of the moving platform and the arms of  FIG. 8  in (A) the strong diagonal and (B) the weak diagonal; 
         FIG. 11  illustrates top views of (A) a further example of an SMA actuator assembly with kinked arms and (B) only the moving platform and arms thereof; 
         FIG. 12  illustrates a top view of a further example of an SMA actuator assembly with kinked arms; 
         FIG. 13  illustrates top views of (A) a further example of an SMA actuator assembly with kinked arms and (B) only the moving platform and arms thereof; 
         FIG. 14  illustrates top views of (A) a further example of an SMA actuator assembly with kinked arms and (B) only the moving platform and arms thereof; 
         FIG. 15  illustrates a top view of a further example of an SMA actuator assembly with kinked arms; 
         FIG. 16  illustrates a top view of a further example of an SMA actuator assembly with kinked arms; 
         FIG. 17  illustrates a top view of a further example of an SMA actuator assembly with kinked arms and a damping substance; 
         FIG. 17A  illustrates a top view of a further example of an SMA actuator assembly with kinked arms and the SMA wires arranged off-centre; 
         FIG. 18  illustrates an exploded view of a four-arm SMA actuator assembly; 
         FIG. 19  illustrates a top view of the actuator assembly seen in  FIG. 18 ; 
         FIGS. 20A-20D  illustrate different arrangements for providing a separation between the flexures and the crimp support portions in the actuator assembly seen in  FIGS. 18 and 19 ; 
         FIG. 21  illustrates a top view of an alternative actuator assembly to the seen in  FIG. 18 , wherein the flexures overlap on top of the crimp support portions; 
         FIGS. 22A-22C  illustrate different arrangements for providing a separation between the flexures and the crimp support portions in the actuator assembly seen in  FIG. 21 ; 
         FIGS. 23A-23C  show different arrangements of an insulation layer arranged on the flexure, the crimp support portion and on both the flexure and crimp support portion; 
         FIGS. 24A-B  show two different embodiments of a movable part with two flexures; 
         FIG. 25  shows an embodiment of a movable part with two flexures which together encompass the entire movable part; 
         FIG. 26  shows an embodiment of a movable part with three flexures; 
         FIGS. 27A-C  show three different embodiments of a movable part with four flexures; 
         FIG. 28  shows another embodiment of a movable part with four flexures; 
         FIG. 29  shows another embodiment of a movable part with four flexures; 
         FIG. 30  shows another embodiment of a movable part which comprises four flexures; and 
         FIG. 31  shows an example of a movable part with two flexures which do not overlap moving crimp portions; and 
         FIG. 32  is a top view of the SMA actuator assembly of  FIG. 1 ; 
         FIG. 33  is an exploded perspective view of the SMA actuator assembly of  FIG. 1  showing current flow; 
         FIG. 34  is a perspective view of a VCM AF actuator assembly mounted on the SMA actuator assembly of  FIG. 1 ; 
         FIGS. 35-37  are top views of components of a further embodiment of an SMA actuator assembly; 
         FIG. 38  is a top view of the component of  FIG. 36  mounted on top of the component of  FIG. 37 ; 
         FIG. 39  is a top view of the component of  FIG. 35  mounted on top of the component of  FIG. 36 ; 
         FIG. 40  is a top view of the components shown in  FIGS. 35-37  mounted on top of each other; 
         FIG. 41  is an exploded top view of the actuator assembly of  FIGS. 35-37  showing current flow; 
         FIG. 42  is a schematic circuit diagram of the SMA actuator assembly of  FIG. 41 ; 
         FIG. 43-47  are schematic circuit diagram of other SMA actuator assemblies. 
     
    
    
     DETAILED DESCRIPTION 
     Camera 
     Referring to  FIG. 1 , a camera  1  incorporating a known SMA actuator assembly  40  will now be described. 
     The camera  1  includes a lens assembly  20  suspended on a support structure  4  by an SMA actuator assembly  40  that supports the lens assembly  20  in a manner allowing movement of the lens assembly  20  relative to the support structure  4  in directions perpendicular to the optical axis O. 
     The support structure  4  includes a base  5 . An image sensor  6  is mounted on a front side of the base  5 . On a rear side of the base  5 , there is mounted an integrated circuit (IC)  30  in which a control circuit is implemented, and also a gyroscope sensor  31 . The support structure  4  also includes a can  7  which protrudes forwardly from the base  5  to encase and protect the other components of the camera  1 . 
     The lens assembly  20  includes a lens carriage  21  in the form of a cylindrical body supporting two lenses  22  arranged along the optical axis O. In general, any number of one or more lenses  22  may be included. Preferably, each lens  22  has a diameter of up to about 20 mm. The camera  1  can therefore be referred to as a miniature camera. 
     The lens assembly  20  is arranged to focus an image onto the image sensor  6 . The image sensor  6  captures the image and may be of any suitable type, for example a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) device. 
     In this example, the lenses  22  are supported on the lens carriage  21  such that the lenses  22  are movable along the optical axis O relative to the lens carriage  21 , for example to provide focusing or zoom. In particular, the lenses  22  are fixed to a lens holder  23  which is movable along the optical axis O relative to the lens carriage  21 . Although all the lenses  22  are fixed to the lens holder  23  in this example, in general one or more of the lenses  22  may be fixed to the lens carriage  21  and so not movable along the optical axis O relative to the lens carriage  21 , leaving at least one of the lenses  22  fixed to the lens holder  23 . 
     An axial actuator arrangement  24  provided between the lens carriage  21  and the lens holder  23  is arranged to drive movement of the lens holder  21  and the lenses  22  along the optical axis O relative to the lens carriage  21 . The axial actuator arrangement  24  may be of any suitable type, for example a voice coil motor (VCM) or an arrangement of SMA wires. 
     In operation, the lens assembly  20  is moved orthogonally to the optical axis O, relative to the image sensor  6 , with the effect that the image on the image sensor  6  is moved. This is used to provide OIS, compensating for image movement of the camera  1 , which may be caused by hand shake etc. 
     Actuator Assembly 
     Referring in particular to  FIGS. 2 to 6  the actuator assembly  40  will now be described in more detail. 
     The actuator assembly  40  includes a sub-assembly  50  (hereinafter referred to as a ‘support platform’) and a further sub-assembly  60  (hereinafter referred to as a ‘moving platform’) (see in particular  FIG. 2A ). The moving platform  60  supports the lens assembly  20  and is connected to the lens carriage  21 . 
     In this example, the sub-assembly referred to as the support platform  50  is formed from two separate components, namely a support component  500  and a conductive component  501 , which are affixed to each another (see in particular  FIG. 2B ). The actuator assembly  40  has an additional component, namely a base component  400 , which is affixed to the support platform  50 , and to the base  5  of the camera  1 . As will be appreciated, other examples may have other configurations. Further details are provided in WO 2017/055788 A1 and WO 2019/086855 A1, which are incorporated herein by this reference. 
     The support platform  50 , the moving platform  60  and the base component  400  are each provided with a central aperture aligned with the optical axis O allowing the passage of light from the lens assembly  20  to the image sensor  6 . 
     Movement of the moving platform  60  (and hence the lens assembly  20 ) relative to the support platform  50  is driven by a lateral actuation arrangement comprising four SMA wires  80 . The support platform  50  is formed with crimps  51  (hereinafter referred to as ‘static crimps’) and the moving platform  60  is formed with crimps  61  (hereinafter referred to as ‘moving crimps’). The crimps  51 ,  61  crimp the four SMA wires  80  so as to connect them to the support platform  50  and the moving platform  60 . The SMA wires  80  may be perpendicular to the optical axis O or inclined at a small angle to the plane perpendicular to the optical axis O. 
     In operation, the SMA wires  80  are selectively driven to move the moving platform  60  relative to the support platform  50  in any lateral direction (i.e. direction perpendicular to the optical axis O), as will now be explained. 
     Further details are also provided in WO 2013/175197 A1, which is incorporated herein by this reference. 
     The SMA wires  80  have an arrangement in a loop at different angular positions around the optical axis O to provide two pairs of opposed SMA wires  80  that are perpendicular to each other. Thus, each pair of opposed SMA wires  80  is capable on selective driving to move the lens assembly  20  in one of two perpendicular directions orthogonal to the optical axis O. As a result, the SMA wires  80  are capable of being selectively driven to move the lens assembly  20  relative to the support structure  4  to any position in a range of movement in two directions orthogonal to the optical axis O. The magnitude of the range of movement depends on the geometry and the range of contraction of the SMA wires  80  within their normal operating parameters. 
     The position of the lens assembly  20  relative to the support structure  4  perpendicular to the optical axis O is controlled by selectively varying the temperature of the SMA wires  80 . This is achieved by passing through SMA wires  80  selective drive signals that provide resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the SMA wire  80  to cool by conduction, convection and radiation to its surroundings. 
     On heating of one of the SMA wires  80 , the stress in the SMA wire  80  increases and it contracts, causing movement of the lens assembly  20 . A range of movement occurs as the temperature of the SMA increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA wires  80  so that the stress in the SMA wire  80  decreases, it expands under the force from opposing ones of the SMA wires  80 . This allows the lens assembly  20  to move in the opposite direction. 
     The SMA wires  80  may be made of any suitable SMA material, for example Nitinol or another titanium-alloy SMA material. 
     The drive signals for the SMA wires  80  are generated and supplied by the control circuit implemented in the IC  30 . The drive signals are generated by the control circuit in response to output signals of the gyroscope sensor  31  so as to drive movement of the lens assembly  20  to stabilise an image focused by the lens assembly  20  on the image sensor  6 , thereby providing OIS. The drive signals may be generated using a resistance feedback control technique for example as described in WO 2014/076463 A1, which is incorporated herein by this reference. 
     In addition, the actuator assembly  40  includes four plain bearings  100  spaced around the optical axis O to bear the moving platform  60  on the support platform  50 . In general, a different number of bearings  100  may be used. Preferably, at least three bearings  100  are used in order to assist in providing stable support. 
     Referring in particular to  FIG. 4 , each plain bearing  100  includes a bearing member  101 . The bearing member  101  may be fixed to the support platform  50 , for example by adhesive. In this case, a surface  102  of the bearing member  101  on the opposite side from the support platform  50  and a surface  103  of the moving platform  60  are planar, conforming surfaces which contact one another. Alternatively, the bearing member  101  may be fixed to the moving platform  60 , for example by adhesive. In this case, a surface  104  of the bearing member  101  on the opposite side from the moving platform  60  and a surface  105  of the support platform  50  are planar, conforming surfaces which contact one another. 
     Thus, the contact between the conforming surfaces  102  and  103  or between the conforming surfaces  104  and  105  supports and bears the moving platform  60  on the support platform  50 , allowing relative motion parallel to their extent, i.e. perpendicular to the optical axis O. 
     The bearing  100  may be made from a suitable metal or alloy such as phosphor bronze. 
     The actuator assembly  40  also includes two arms  70  connected between the support platform  50  and the moving platform  60 . The arms  70  are resilient and are configured to provide a suitable retaining force along the optical axis O, and also to permit lateral movement with a suitable lateral biasing force. The arms  70  also provide electrical connections from the support structure  4  to the lens assembly  20 . 
     In the assembled state of the actuator assembly  40 , the arms  70  are deflected from their relaxed state in such a way that the arms  70  provide a force (i.e. the retaining force) which biases the platforms  50 ,  60  together and maintains the contact in the plain bearings  100 . At the same time, the arms  70  can be laterally deflected to permit the movement of the lens assembly  20  relative to the support structure  4  in directions perpendicular to the optical axis O. 
     The arms  70  provide a force (i.e. the lateral biasing force) that biases the lens assembly  20  towards a central position from any direction around the central position, wherein the central position corresponds to the optical axis O of the lens assembly being substantially aligned with the centre of the light-sensitive region of the image sensor  6 . As a result, in the absence of driving of the lateral movement of the lens assembly  20 , the lens assembly  20  will tend towards the central position from any direction around the central position. This ensures that the camera  1  remains functional to capture images, even in the absence of driving of the SMA wires  80 . The magnitude of the lateral biasing force is kept low enough so as not to hinder OIS whilst being high enough to centre the lens assembly  20  in the absence of driving. 
     Each arm  70  is approximately L-shaped and extends around the optical axis O. The angular extent of each arm  70  is preferably at least 90° as measured between the endpoints of the arm  70 . 
     In this example, the arms  70  are formed integrally with the moving platform  60  at one end thereof and are connected to the support platform  50  at the other end thereof. Alternatively, the arms  70  may be formed integrally with the support platform  50  and connected to the moving platform  60  or the arms  70  may be separate parts connected to both platforms  50 ,  60 . The arms  70  may be connected to the plate(s)  50 ,  60  by welding, which provides both mechanical and electrical connections. 
     The arms  70  are made of a suitable material that provides the desired mechanical properties and is electrically conductive. Typically, the material is a metal having a relatively high yield, for example steel such as stainless steel. 
     Space for the Actuator Assembly 
     Reference will be made herein to a cartesian coordinate system in which the Z-axis coextends with the optical axis O, the origin is at an arbitrary point on the optical axis O, and the positive Z-direction is e.g. the direction faced by the image sensor  6 . 
     The actuator assembly  40  is configured to fit within a cuboidal space S within the can  7 . The space S has two major faces which are square, perpendicular to the optical axis O (Z-axis), i.e. parallel to the XY-plane, and centred on the optical axis O (Z-axis). Hence the optical axis O (Z-axis) is hereinafter sometimes referred to as the centreline. The lowermost major face of the space S defines a footprint for the actuator assembly  40 . The space S has four minor faces (hereinafter referred to simply as ‘sides’) perpendicular to the X- or Y-axes. Generally, it is desirable to minimize the size, i.e. length and width (X- and Y-dimensions), of the footprint relative to the diameter of the lens, while also minimizing the height (i.e. Z-dimension) of the space S. 
     Asymmetric Lateral Biasing Force 
     The arrangement of arms  70  in the known actuator assembly  40  provides an asymmetric lateral biasing force, as will now be explained. 
     The support platform  50  and the moving platform  60  each have a flat, planar portion  50   a ,  60   a  (hereinafter generally referred to as a ‘body portion’). Each body portion  50   a ,  60   a  has a shape that can be approximated as an irregular octagon with four major side surfaces  50   b ,  60   b  and four minor side surfaces  50   c ,  60   c  (hereinafter referred to simply as ‘sides’). Each body portion  50   a ,  60   a  also has a central circular hole (i.e. the above-described aperture). The body portions  50   a ,  60   a  are each perpendicular to the optical axis O (Z-axis), i.e. parallel to the XY-plane. The body portions  50   a ,  60   a  are each centred on the optical axis (Z-axis) and have a similar size, shape and orientation to each other. The major sides  50   b ,  60   b  are parallel with the sides of the space S. 
     The support platform  50  and the moving platform  60  each have further portions,  50   d ,  60   d  supporting the crimps  51 ,  61  (these portions are hereinafter referred to as ‘crimp supports’ or ‘crimp support portions’). In this example, the support platform  50  has four crimp supports  50   d , each of which supports a static crimp  51 , and the moving platform  60  has two crimp supports  60   d , each of which supports two moving crimps  61 . The static crimp supports  50   d  are on diagonally-opposite minor sides  50   c  of the body portion  50   a  of the support platform  50 . The moving crimp supports  60   d  are on diagonally-opposite minor sides  60   c  of the body portion  60   a  of the moving platform  60 , on a different diagonal to the static crimp supports  50   d . Each crimp support  50   d ,  60   d  may be integral with a body portion  50   a ,  60   a  or may be a separate part which is connected to the body portion  50   a ,  60   a . In this example, the static crimp supports  50   d  are integral whereas the moving crimp supports  60   d  are not. 
     The static crimp supports  50   d  each extend generally outwards (i.e. away from the centreline (Z-axis)) and also upwards (in a positive Z-direction) to bring the static crimps  51  to a similar Z-height as the moving crimps  61 . 
     The regions of the actuator assembly  40  in which the static crimp supports  50   d  are located are hereinafter referred to as the ‘static crimp corners’, and those in which the moving crimp supports  60   d  are located are hereinafter referred as the ‘moving crimp corners’. 
     One of the arms  70   1  (hereinafter referred to as the ‘first arm’) starts on one of the major sides  60   b   1  of the moving platform  60 . The first arm  70   1  may start relatively close to one of the moving crimp corners or anywhere along the major side  60   b   1 . The first arm  70   1  then extends around a static crimp corner and towards the other moving crimp corner. Accordingly, the first arm  70   1  extends alongside three sides  60   b   1 ,  60   c   1 ,  60   b   2  of the body portion  60   a  of the moving platform  60  and also extends gradually downwards (i.e. in the negative Z-direction) to a foot  71   1  on the support platform  50  (or other element). Accordingly, the first arm  70   1  is made up of three substantially-straight segments, i.e. first, second and third segments  70   a   1 ,  70   b   1 ,  70   c   1  (see  FIG. 5 ). At the static crimp corner, the first arm  70   1  and, in particular, the second segment  70   b   1  passes over (i.e. at a greater Z-height) the static crimp supports  50   d   1 ,  50   d   2  in that corner. 
     The other one of the arms  70   2  (hereinafter referred to as the ‘second arm’) corresponds to the first arm  70   1  rotated by 180° about the Z-axis. Accordingly, compared to the first arm  70   1 , the second arm  70   2  starts on the opposite side  60   b   3  of the moving platform  60  and extends around the opposite corner, with the same sense of rotation about the Z-axis. As will be appreciated, both arms  70  may extend anticlockwise (as in the illustrated example) or clockwise. 
     The lateral biasing force provided by the arms  70  is asymmetric in that its magnitude varies with the angle of displacement of the moving platform  60  in the X-Y plane. In particular, for displacements of a given magnitude within an operating range, the lateral biasing force is a maximum for displacements along a line D 1  (hereinafter referred to as the ‘strong diagonal’) which, in this example, passes through the moving crimp corners, and a minimum for displacements along a line D 2  (hereinafter referred to as the ‘weak diagonal’) which, in this example, passes through the static crimp corners. In this example, the strong and weak diagonals D 1 , D 2  substantially correspond to the major diagonals of the space S, i.e. the lines Y=X and Y=−X, respectively. 
     In practice, a maximum ratio of the stiffness of the strong diagonal D 1  to the that of the weak diagonal D 2  may be specified in order to achieve sufficient performance of the actuator assembly  40  (this ratio is hereinafter referred to as the asymmetry ratio). Here, the stiffness of a diagonal corresponds e.g. to the force required to displace the moving platform  60  a unit distance in that diagonal. 
     Actuator Assemblies for Larger Lenses 
     Currently, cameras for portable electronic devices may have lenses with diameters of up to ˜8 mm and hence actuator assemblies (hereinafter referred to as ‘small lens actuator assemblies’) with footprints of up to ˜13×13 mm. However, there is a trend towards larger lenses and so cameras may in the future have lenses with diameters of say ˜13 mm and hence actuator assemblies (hereinafter referred to as a ‘large lens actuator assemblies’) with footprints of ˜17×17 mm or more. 
     At the same time, the distance by which an actuator assembly needs to move (in other words, the required stroke) in order to provide suitable OIS may remain substantially the same or may change by a relatively small amount. For actuator assemblies such as those described herein, the required stroke determines the minimum lengths of the SMA wires, which is generally preferred as most cost-efficient, and hence the crimp-to-crimp (C2C) distances. 
     Accordingly, each crimp  51 ,  61  is generally a distance d 3 ′ from the corner of the space S′ (and the can  7 ′) in the large lens actuator assembly  40 ′ that is greater than the equivalent distance d 3  in the small lens actuator assembly  40 . 
     As will be appreciated, if a small lens actuator assembly has a smaller stroke requirement, then it may also have crimps  51 ,  61  that are further from the corner of the space S. 
     First Example 
     Referring in particular to  FIG. 8 , a first example of an actuator assembly  140  with kinked arms  170  will now be described (the actuator assembly  140  is hereinafter referred to as the ‘first actuator assembly’). 
     The first actuator assembly  140  is the same as the above-described large lens actuator assembly  40 ′ except that the second segment  170   b  of each arm  170  includes a further feature  100  (hereinafter referred to as a kink). 
     The kink  100  is located around halfway along the second segment  170   b  and divides the second segment  170   b  into two parts, i.e. first and fourth subsegments  17   a ,  17   d.    
     At the kink  100 , the arm  170  has two substantially-straight subsegments, i.e. second and third subsegments  17   b ,  17   c , which are positioned alongside each other and which each extend diagonally outwards (e.g. in a direction substantially parallel with the line Y=−X). The inner ends of the second and third subsegments  17   b ,  17   c  are respectively connected to the first and fourth subsegments  17   a ,  17   d  via ˜90° turns, while the outer ends are connected to each other via a ˜180° turn. 
     Hence the kink  100  causes the arm  170  to extend between the static crimps  51  and their respective crimp supports  50   d ′ and into a region of the space S′ at the static crimp corner. 
     Referring in particular to  FIG. 9A , and considering projections onto the XY-plane, the kink  100  corresponds to a part of the arm  170  which is a greater distance from a line segment L between the endpoints  18 ,  19  of the arm  170  (which is substantially parallel to the strong diagonal D 1 ). Hence the force F 1  on the arm  170  associated with a displacement of the moving platform  60 ′ along the strong diagonal D 1  applies a greater bending moment to this part of the arm  170 , thereby reducing the stiffness of the strong diagonal D 1 . 
     Generally speaking, in the context of the actuator assemblies described herein, the stiffness of the strong diagonal is reduced by a change in shape of the arm that produces a greater length of arm  70 ′ at a greater distance from the centreline (Z-axis). 
     Referring in particular to  FIG. 9B , and again considering projections onto the XY-plane, the kink  100  is substantially parallel to the weak diagonal D 2 . The force F 2  on the arm  170  associated with a displacement of the moving platform  60 ′ along the weak diagonal D 2  is substantially parallel to the kink  100 . Hence the kink  100  does not significantly change the bending moment applied to the second segment  170   b  and so there is no significant change in the stiffness of the weak diagonal D 2 . 
     Referring in particular to  FIG. 10A , the relatively large bending moment produced at the kinks  100  by a displacement of the moving platform  60 ′ along the strong diagonal D 1  leads to relatively large deformations of the kinks  100 . 
     Referring in particular to  FIG. 10B , in contrast, a displacement of the moving platform  60 ′ along the weak diagonal D 2  leads to relatively small or insignificant deformations of the kinks  100 . 
     Accordingly, the kinks  100  have the effect of reducing the asymmetry of the lateral biasing force and, more specifically, reducing the above-described asymmetry ratio, i.e. the ratio of the stiffness of the strong diagonal D 1  to that of the weak diagonal D 2 . 
     The kinks  100  may reduce the asymmetry ratio by up to 50% or more. For instance, the kinks  100  may reduce the asymmetry ratio from being greater than 5 for a large lens actuator assembly (such as the above-described assembly  40 ′) to being below 5 or below 4 or below 3 or below 2 or below 1.5. 
     This reduced asymmetry can enable the first actuator assembly  140  to be controlled more effectively, for example because of increased linearity (e.g. linearity of the response to a driving signal unit), reduced hysteresis, reduced crosstalk (i.e. movement in a direction perpendicular to a driven direction), reduced stroke asymmetry, reduced slew rate asymmetry (wherein the slew rate is the rate at which the moving platform  60  returns to its central position), etc. 
     The reduced asymmetry can enable large lens actuator to be utilised in similar ways to small lens actuator assemblies. 
     Moreover, extending as it does between the static crimps  51 , the kink  100  can be at a greater distance from the centreline (Z-axis) than any part of an arm  70  of a small lens actuator assembly (compare  FIGS. 6A and 8A ). Accordingly, in some instances, the kinks  100  can even enable a large lens actuator assembly to have a lower asymmetry ratio than a corresponding small lens actuator assembly. 
     The reduced asymmetry also advantageously reduces the differences between the constrained and unconstrained stiffnesses in the X- and Y-directions. Here, a constrained stiffness is the stiffness when the moving platform  60 ′ is constrained by the SMA wires  80  to move in the X- or Y-direction, whereas an unconstrained stiffness is the stiffness when there are no forces applied to the moving platform  60 ′ by the SMA wires  80 . The reduced asymmetry reduces the tendency for the moving platform  60 ′ to move off the axis along which it is being moved and hence reduces the forces required for constrained movement, i.e. reduces the constrained stiffnesses such that they are closer to the unconstrained stiffnesses. This avoids there being such large constrained stiffnesses when large unconstrained stiffnesses are required, e.g. for more effective unpowered centring, counteracting the effect of gravity. 
     Further Examples 
     Various different forms of kinked arms can be provided which have advantages as described above. 
     Referring to  FIG. 11 , a second example of an actuator assembly  240  (hereinafter referred to as the ‘second actuator assembly’) will now be described. The second actuator assembly  240  is the same as the first actuator assembly  140  except that the second segments  270   b  of the arms  270  each have three kinks, i.e. first, second and third kinks  101 ,  102 ,  103 . The second kink  102  is substantially the same as the above-described kink  100 . The first and third kinks  101 ,  103  are positioned alongside, and on either side of, the second kink  102 . The first and third kinks  101 ,  103  are each similar to the second kink  102  but are shorter so as to fit within the space S′. In other examples, there may be different numbers of kinks and/or different lengths of kinks. 
     Referring to  FIG. 12 , a third example of an actuator assembly  340  (hereinafter referred to as the ‘third actuator assembly’) will now be described. The third actuator assembly  340  is the same as the second actuator assembly  240  except that the second kinks  102 ′ (and the subsegments of the arms  370  connected to the second kinks  102 ′) each extend further inwards, i.e. closer to the centreline (Z-axis). The body portions  50   a ′,  60   a ′ of the platforms  50 ′,  60 ′ have recesses  301  to accommodate the kinks  101 ′,  102 ′,  103 ′. 
     Referring to  FIG. 13 , a fourth example of an actuator assembly  440  (hereinafter referred to as the ‘fourth actuator assembly’) will now be described. The fourth actuator assembly  440  is the same as the first actuator assembly  140  except that the subsegments  17   b ′,  17   c ′ of the arms  470  at the kinks  100 ′ each have three kinks  200  therein (these kinks  200  are hereinafter referred to as ‘secondary kinks’). Each secondary kink  200  extends at an angle of ˜90° away from the kink  100 ′. In other examples, there may be different numbers of secondary kinks  200 , and the secondary kinks  200  may extend along different paths. 
     Referring to  FIG. 14 , a fifth example of an actuator assembly  540  (hereinafter referred to as the ‘fifth actuator assembly’) will now be described. The fifth actuator assembly  540  is the same as the first actuator assembly  140  except that the kinks  100 ″ each have a feature  150  (hereinafter referred to as a loop) at their outer ends. The loop corresponds to a part of the kink  100 ″ where the separation between the subsegments  17   b ″,  17   c ″ of the arm  570  increases and then decreases. Hence the loop  150  increases the radius of curvature at the outer end of kink  100 ″, thereby avoiding the high stress concentration regions that may occur with the kink  100  of the first actuator assembly  40 . Hence the loop  150  can be a useful additional, particularly as space limitations generally mean that the subsegments  17   b ″,  17   c ″ of the arm  570  generally need to be positioned alongside each other and so would otherwise have a small radius of curvature at the outer end and so more prone to failure. In the example illustrated in the figure, the loop  150  is rhombus-shaped. However, the loop  150  may have any suitable shape. For example, the loop  150  may be round, which may be beneficial in relation to radius of curvature. 
     Referring to  FIG. 15 , a sixth example of an actuator assembly  640  (hereinafter referred to as the ‘sixth actuator assembly’) will now be described. The sixth actuator assembly  640  is equivalent to the first actuator assembly  140  except that the first and third segments  70   a ″,  70   c ″ of the arms  670  each follow a more complex path that passes under an SMA wire  80  and around the outside of a static crimp  51  (i.e. at a greater distance from the centreline (Z-axis)) towards a corner of the space S′ at a static crimp corner. The first and third segments  70   a ″,  70   c ″ of an arm  670  are then connected via a kink  100 ′″ which is equivalent to the above-described kink  100  except that it extends inwards rather than outwards. As will be appreciated, notwithstanding these differences, the kink  100 ′″ has equivalent effects on the stiffnesses in the strong and weak diagonals D 1 , D 2  to those described above. 
     Referring to  FIG. 16 , a seventh example of an actuator assembly  740  (hereinafter referred to as the ‘seventh actuator assembly’) will now be described. The seventh actuator assembly  740  is equivalent to the first actuator assembly  140  except that the arms  770  each extend around a moving crimp corner rather than around a static crimp corner. Each arm  770  and, in particular, the second segment  770   b  of each arm passes under (i.e. at a lesser Z-height) the moving crimp support  60   d ′ in that corner. In this example, the kink  100  in the second segment  770  is the same as the above-described kink  100  of the first actuator assembly  100 . As will be appreciated, there may be greater design freedom in this instance due to the second segments  770   b  of the arms  770  occupying different vertical (Z-height) regions to the moving crimps  61 ′ and their supports  60   d ′. However, generally, such actuator assemblies may have a greater total Z-height than the other actuator assemblies described herein. 
     Eighth Example 
     Referring to  FIG. 17 , an eighth example of an actuator assembly  840  (hereinafter referred to as ‘the eighth actuator assembly’) will now be described. The eighth actuator assembly  840  is the same as the first actuator assembly  140  except for two regions  801  where a damping substance has been applied such that the damping substance connects a part of each arm  170  and a corresponding part of the support platform  50   a  (or other element). Each region  801  includes at least part of one of the kinks  100 . The damping substance acts to reduce vibrations of the moving platform  60 ′. The damping substance may be, for example, a damping gel or a soft glue. 
     In actuator assemblies without kinked arms, the damping substance may be applied between the moving crimp supports  60   d  and the support platform  50   a . However, it can be relatively difficult to apply the damping substance in this way. Furthermore, where the damping substance requires light curing, it can be relatively difficult to illuminate the damping substance applied in this way. 
     In contrast, the kinks  100  provide regions  801  to which it is generally much easier to apply the damping substance. For example, the damping substance can be applied between, and on either side of, the subsegments of the arm  70  at the kink  100 . It is also generally much easier to illuminate the damping substance in the regions  801  because they are more exposed. Furthermore, the surface area of the arms  170  in contact with, and hence damped by, the damping substance can be more easily controlled (e.g. increased), enabling more controlled (e.g. higher) damping. In addition, because the displacement of the arms  170  at the kinks  100  has a smaller magnitude than that of the moving platform  60   a ′, the regions  801  can be more suitable for the damping substance as the strain in the damping substance will be less and so the likelihood of the damping substance tearing is less. Hence reliability may be improved. 
     Ninth Example 
     Referring to  FIG. 17A , a ninth example of an actuator assembly  940  (hereinafter referred to as ‘the ninth actuator assembly’) will now be described. The ninth actuator assembly  940  is the same as the first actuator assembly  140  except that that each of the SMA wires  80 ′ extends further towards a moving crimp corner and each of the moving crimps  61 ′ is positioned closer to a moving crimp corner. This illustrates that the SMA wires  80 ′ may be non-centrally positioned in relation to e.g. the major sides  50   b ′,  60   b ′ of the platforms  50 ′,  60 ′. 
     Other Variations 
     It will be appreciated that there may be many other variations of the above-described embodiments. 
     For example, each arm may have fewer or more (sub)segments. One or more of the (sub)segments may extend in a different direction, along a differently-shaped path (e.g. a curved path when projected onto the X-Y plane) and/or may have a different shape (e.g. a cross-section that varies along its length). 
     Features of different examples may be combined. For example, the secondary kinks  200  of the fourth actuator assembly  440  and/or the loops  150  of the fifth actuator assembly  540  may be included in the kinks of any of the other actuator assemblies  140 ,  240 ,  340 ,  640 ,  740 . 
     Instead of an arm having parallel subsegments at the kink, the arm may have subsegments that are generally oriented at an acute angle to each other (e.g. when projected onto the XY-plane). Such a kink may be referred to as a V-shaped kink. The subsegments at the kink need not be positioned alongside each other. 
     Generally, the kinks may have any shape that produces a greater length of arm at a greater distance from the centreline in such a way as to reduce the stiffness of the strong diagonal while (if at all) only reducing the stiffness of the weak diagonal by a relatively small amount. This may be achieved in a practical way by arms that occupy a gap between SMA wires at the static (or moving) crimp corners. 
     The above-described principles also apply to actuator assemblies with different static and moving platforms, different footprints, different configurations of arms, etc. 
     For instance, the static and moving platforms may have any suitable shape. Since the arms are generally arranged around the platforms, this may, in turn, affect the shape of the arms. 
     The static and moving platforms (and the ‘first and second parts’ referred to in the claims) may be formed of any number of one or more components. 
     The footprint may allow the arms to use more space outside the SMA wires. For example, the arms may pass between, and then around the outside of, the static crimp corners. 
     In contrast to the above-described examples, each arm may have one endpoint that it is at a significantly different distance from the major diagonal of the cuboidal space than the other endpoint. In such a case, the strong diagonal D 1  may not be substantially parallel to the major diagonal of the cuboidal space. 
     The arms need not have two-fold rotational symmetry about the centreline (Z-axis). The arms may instead have mirror symmetry about the major diagonal of the space through the moving crimp corners (i.e. the line Y=X). In other words, both of the arms may start e.g. near one of the moving corners and one arm may extend clockwise and the other arm may extend anticlockwise towards the other moving crimp corners (cf.  FIG. 5 ). 
     There may be a different number of arms, e.g. three or four or more arms. In this case, there may be multiple stronger and weaker diagonals. 
     The moving platform need not move only in the X-Y plane. 
     The actuator assembly need not be configured to support a lens assembly and, for example, may be configured to support another type of optical element, an image sensor, etc. The platforms need not include apertures. 
     The actuator assembly need not be used in a camera. 
     The Z-axis (and the ‘first axis’ referred to in the claims) may not correspond to an optical axis. The Z-axis may correspond to a line that is perpendicular to a plane defined by planar surfaces of the moving and/or support platform. The Z-axis may correspond to a line that is perpendicular to a plane defined by the directions of movement of the moving platform. 
     The actuator assembly may be any type of assembly that comprises a first part and a second part movable with respect to the first part. The actuator assembly may be, or may be provided in, any one of the following devices: a smartphone, a protective cover or case for a smartphone, a functional cover or case for a smartphone or electronic device, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, a camera with folded optics, an image capture device, an array camera, a 3D sensing device or system, a servomotor, a consumer electronic device (including domestic appliances such as vacuum cleaners, washing machines and lawnmowers), a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader (also known as an e-book reader or e-book device), a computing accessory or computing peripheral device (e.g. mouse, keyboard, headphones, earphones, earbuds, etc.), an audio device (e.g. headphones, headset, earphones, etc.), a security system, a gaming system, a gaming accessory (e.g. controller, headset, a wearable controller, joystick, etc.), a robot or robotics device, a medical device (e.g. an endoscope), an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device (e.g. a watch, a smartwatch, a fitness tracker, etc.), a drone (aerial, water, underwater, etc.), an aircraft, a spacecraft, a submersible vessel, a vehicle, and an autonomous vehicle (e.g. a driverless car), a tool, a surgical tool, a remote controller (e.g. for a drone or a consumer electronics device), clothing (e.g. a garment, shoes, etc.), a switch, dial or button (e.g. a light switch, a thermostat dial, etc.), a display screen, a touchscreen, a flexible surface, and a wireless communication device (e.g. near-field communication (NFC) device). It will be understood that this is a non-exhaustive list of example devices. 
     The actuator assembly described herein may be used in devices/systems suitable for image capture, 3D sensing, depth mapping, aerial surveying, terrestrial surveying, surveying in or from space, hydrographic surveying, underwater surveying, scene detection, collision warning, security, facial recognition, augmented and/or virtual reality, advanced driver-assistance systems in vehicles, autonomous vehicles, gaming, gesture control/recognition, robotic devices, robotic device control, touchless technology, home automation, medical devices, and haptics. 
     Referring to  FIG. 18  an actuator assembly  1040  in accordance with an embodiment of the present invention will be described in detail. The actuator assembly  1040  includes a sub-assembly  1050  (hereinafter referred to as a ‘static part’) and a further sub-assembly  1060  (hereinafter referred to as a ‘moving part’). The moving part  1060  may support a variety of different components, for example a lens assembly  20  similar to that in embodiments described above. The actuator assembly  1040  is substantially the same as the actuator assembly  40  described above with reference to  FIGS. 2A and 2B  except that the actuator assembly  1040  comprises four flexures  1070   1 ,  1070   2 ,  1070   3 ,  1070   4  as opposed to the two arms, i.e. flexures, seen in  FIGS. 2A and 2B . In the embodiment shown, the four flexures  1070   1 ,  1070   2 ,  1070   3 ,  1070   4  are integrally formed with the moving part  1060 . However, one or more of the four flexures  1070   1 ,  1070   2 ,  1070   3 ,  1070   4  could instead be integrally formed with the static part  1050  or indeed be provided as independent parts. The actuator assembly  1040  has a primary axis which corresponds to the optical axis O seen in  FIG. 1 . 
     The sub-assembly referred to as the static part  1050  is essentially the same as the support platform  50  described above with reference to  FIGS. 2A and 2B . 
     Movement of the moving part  1060  relative to the static part  1050  is driven by a lateral actuation arrangement comprising four SMA wires  1080 . The static part  1050  is formed with crimps  1051  (hereinafter referred to as ‘static crimps’ and the moving platform is formed with crimps  1061  (hereinafter referred to as ‘moving crimps’). The crimps  1051 ,  1061  crimp the four SMA wires  1080  so as to connect them to the static part  1050  and the moving part  1060 . Similarly to earlier embodiments, the SMA wires  1080  may be perpendicular to the primary axis or included at a small angle to the plane perpendicular to the primary axis. 
     In operation, the SMA wires  1080  are selectively driven to move the moving part  1060  relative to the static part  1050  in any lateral direction (i.e. direction perpendicular to the primary axis), as will now be explained. 
     The moving part  1060  is driven in an identical manner to the arrangement described above with respect to  FIGS. 2A and 2B . 
     The actuator assembly  1040  may also include, for example, four plain (or ball) bearings  1100  which operate in a similar manner to the embodiment described above. 
     Each of the moving crimps  1061  is supported by a crimp support portion  1062  which extends from the moving part  1060 . The crimp support portion  1062  may be a separate component attached to the moving part  1060  by any suitable means, e.g. by welding or an adhesive, or alternative it may be integrally formed with the moving part  1060  thereby forming a unitary component. 
     Whilst the movable part  1060  is technically an eight-sided polygon, due to proportions of the shape the movable part  1060  may be considered to have a square shape with four corners. In the four wire SMA actuator assembly  1040  seen in  FIG. 18 , it is only necessary to have moving crimps  1061  arranged on two opposing corners of the moving part  1060  and for the static part  1050  to have static crimps  1051  on the other set of opposing corners. As will be appreciate by those skilled in the art, connecting the SMA wires  1080  between the moving crimps  1061  and static crimps  1051  in the arrangement shown in these Figures will result in an actuation arrangement which is capable of driving movement in a variety of different directions in a movement plane which is perpendicular to the primary axis. 
     With the arrangement of moving crimps  1061  described above, as will be appreciated from  FIG. 18 , two of the flexures  1070   1 ,  1070   3  extend around corners where there are no moving crimps  1061  and the other two flexures  1070   2 ,  1070   4  are routed via corners which comprise moving crimps  1061 , i.e. they overlap the moving crimps  1061  when viewed along the primary axis. In this embodiment according to the present invention, the flexures  1070   2 ,  1070   4  are arranged to pass under the moving crimps  1061 . This advantageously keeps the lateral extent of the actuator assembly  1040  to a minimum and keeps the depth of the actuator assembly  1040  in the primary axis to a minimum. 
       FIG. 19  shows a top view of an embodiment of the actuator assembly  1040  seen in  FIG. 18 . As can be seen in this Figure, the two flexures  1070   1 ,  1070   3  extend around the moving part  1060  and pass by the static crimps  1051 . The other two flexures  1070   2 ,  1070   4  pass under the crimp support portions  1062  such that when the actuator assembly  1040  is viewed along the primary axis, i.e. when viewed end on as shown in  FIG. 5 , the crimp support portions  1062  and flexures  1070   2 ,  1070   4  overlap. As will be appreciated, if the flexures  1070   2 ,  1070   4  were instead to be routed around the crimp support portions  1062 , this may increase the overall lateral size of the actuator assembly  1040 . Therefore, by overlapping the flexures  1070   2 ,  1070   4  and the moving crimps  1061  the footprint of the actuator assembly  1040  is kept to a minimum. 
     The flexures  1070   2 ,  1070   4  may be separated from the crimp support portions  1062  in a number of different ways. 
     In  FIG. 19 , this separation is achieved with a cut-out section or notch  1067  in each of the crimp support portions  1060  which is aligned with the overlapping one of the flexures  1070   2 ,  1070   4 . In particular, when viewed along the primary axis, each notch  1067  extends part way across the crimp support portion  1060  and is positioned on the side of the crimp support portion  1060  at which the flexure  1070   2 ,  1070   4  is highest, i.e. is closest to its connection to the moving part  1060 . 
       FIGS. 20A-20D  illustrate different sub-embodiments of how the separation between the flexures  1070   2 ,  1070   4  and the crimp support portions  1062  may be achieved. The features of each of these embodiments may be combined with the above-described notch  1067 . Each of  FIGS. 20A-D  show a sectional view through the line A-A seen in  FIG. 19 . 
     In the embodiment shown in  FIG. 19 , the flexures  1070   1 ,  1070   2 ,  1070   3 ,  1070   4  are mounted off centre with respect to the moving part  1060 . Two flexures  1070   1 ,  1070   4  extend from a first flexure connection section  1073   1  and the other two flexures  1070   2 ,  1070   3  extend from a second flexure connection section  1073   2 . As is apparent from  FIG. 19 , the first and second flexure connection sections  1073   1 ,  1073   2  are positioned off centre and located on the moving part  1060  closer to the static crimp portions  1051  than the moving crimp portions  1061 . 
       FIGS. 20A-20D  show cross sectional views through the line A 1 -A 2  seen in  FIG. 19 , focusing on the end of the line labelled A 1 , with various arrangements for providing a separation  1064 . The opposite end A 2  may have the same arrangement to that seen in at A 1  or an alternative arrangement with the flexure  1070   3  overlapping the crimp support portion  1062 . In the cross-sectional view shown in  FIG. 20A , it can be seen how the various components are arranged with respect to one another. Starting from the bottom up there is the base component  1400 , the static part  1500  and the conductive component  1501 . Then there is the moving part  1060  which comprises the spring arm  1070   2 . The crimp support portion  1062  extends from the moving part  1060 , and arranged at the end thereof is the moving crimp  1061 . In the embodiment shown in  FIG. 20A , an underside of the crimp support  1062  comprises a thinned section  1063  where the crimp support  1062  overlaps the spring arm  1070   2 . This thinned section  1063  creates a separation  1064  between the spring arm  1070   2  and the crimp support portion  1062 . As discussed previously this separation  1064  may help to prevent interference between them and prevent the formation of short circuits between the flexure  1070   2  and the crimp support portion  1062 . 
       FIGS. 20B to 20D  illustrate the same components as those shown in  FIG. 20A  and so only different features will be discussed. In the sub-embodiment shown in  FIG. 20B , instead of a thinned section on the crimp support portion  1062 , the flexure  1070   2  comprises a thinned section  1072 . This thinned section  1072  also forms a separation  1064  between the flexure  1070   2  and the crimp support portion  1062  which may help to avoid interference between them and help to avoid the formation of a short circuit. 
       FIG. 20C  shows a further sub-embodiment wherein the crimp support portion  1062  comprises a thinned section  1063  and the flexure  1070   2  also comprises a thinned section  1072 . These two thinned sections  1063 ,  1072  together form a separation  1064  which may be increased when compared to only having one thinned section as seen in  FIGS. 20A and 20B . Additionally, by having a thinned section in each of the crimp support portion  1062  and flexure  1070   2  it may be possible to have a shallower thinned section in each of the components thereby potentially reducing the impact the thinned section has on the ability for each component to perform its function. This may be particularly relevant for the flexure  1070   2  wherein creating a thinned section may impact how the flexure  1070   2  responds to deformations when the moving part  1060  is moved in use. 
       FIG. 20D  shows another embodiment wherein the crimp support portion  1062  is mounted to an upper surface  1065  of the movable part  1060 . This arrangement will serve to move the crimp support portion  1062  along the primary axis and therefore contribute to the separation  1064  between the crimp support portion  1062  and the flexure  1070   2 . As is also visible in this Figure, the crimp support portion  1062  also comprises a section  1066  which extends along the primary axis away from the movable part  1060 . This section  1066  also provides the separation  1064  between the crimp support portion  1062  and the flexure  1070   2 . In this embodiment the crimp support portion  1062  also comprises a thinned section  1063  as described in earlier Figures. 
     Referring back to  FIG. 19 , the flexures  1070   1 ,  1070   3  which do not overlap the crimp support portions  1062 , i.e. those which pass by the static crimp portions  1051  may be formed in order to provide a pre-loading along the primary axis so as to retain the moving part along the bearing surfaces. If the forming is applied to these flexures  1070   1 ,  1070   3 , it may not be necessary to apply any specific forming on the other flexures  1070   2 ,  1070   4  which overlap the moving crimp portions  1062 . This may help to ensure the separation  1064  is kept to a maximum. 
       FIG. 21  shows a top view of an alternative embodiment of the actuator assembly  2040  seen in  FIG. 18 . In this embodiment, the actuator assembly  2040  is essentially the same as the actuator assembly seen in  FIG. 18 , except that the flexure connection sections  2073   1 ,  2073   2  are arranged centrally such that they are equally spaced between the static crimp portions  2051  and moving crimp portions  2061 . 
     In this embodiment, the two flexures  2070   2 ,  2070   4  overlap the crimp support portions  2062  such that the two flexures  2070   2 ,  2070   4  are on top of the crimp support portions  2062 . This is contrasted to the embodiment seen in  FIG. 19  wherein the flexures  1070   2 ,  1070   4  and crimp support portions  1062  overlap such that the crimp support portions  1062  are on top of the flexures  1070   2 ,  1070   4 . 
       FIGS. 22A-22C  show cross sectional views through the line A 1 -A 2  seen in  FIG. 21 , focusing on the end of the line labelled A 1 , with various arrangements for providing a separation  2064 . The opposite end A 2  may have the same arrangement to that seen in at A 1  or an alternative arrangement. In each of the different versions shown in  FIGS. 22A-22C  the flexure  2070   2  is arched upwards so that at least in the portion overlapping the crimp support portion  2062  the flexure  2070   2  extends in a different plane to the crimp support portion  2062  to at least partially provide the separation between the flexure  2070   2  and the crimp support portion  2062 . The flexure  2070   2  may only be arched in this manner in the portion of the flexure  2070   2  proximal to the crimp support portion  2062 . 
     In at least the embodiment seen in  FIG. 22A , the crimp support portion  2062  is also attached to an underside of the moving part  2060 . This necessitates in an increase in the height of the bearing  2101  in order to accommodate the crimp support portion  2062  extending from the underside of the moving part. Additionally, in the embodiment seen in  FIG. 22A , the crimp support portion  2062  comprises a thinned section  2063  which also contributes to the formation of the separation  2064  between the flexure  2070   2  and the crimp support portion  2062 . 
       FIG. 22B  shows an alternative sub-embodiment which comprises all the features of the embodiment seen in  FIG. 22A . Additionally, in this sub-embodiment, the flexure  2070   2  comprises a thinned section  2072  which also contributes to the formation of the separation  2064 . 
       FIG. 22C  shows a further sub-embodiment which achieves a separation  2064  between the flexure  2070   2  and crimp support portion  2062 . In this embodiment, the crimp support portion  2062  is attached entirely on a bottom surface of the movable part  2060 . In order to ensure that the movable crimps  2061  are in the appropriate position along the primary axis, the crimp support portion  2062  initially extends in a direction perpendicular to the primary axis, away from the movable part  2060 , and then, once it no longer overlaps with the flexure  2070   2 , the crimp support portion  2062  extends upwards partially along the primary axis in order to ensure that the moving crimps  2061  sits in the correct plane. 
       FIG. 23A  shows a variation on the embodiment seen in  FIG. 20D . In addition to the thinned section  1063  and the section  1066  which extends along the primary axis away from the movable part  1060  to form the separation  1064  between the flexure  1070   2  and the crimp support portion  1062 , an insulation layer  1075  is also arranged on top of the flexure  1070   2 . The insulation layer  1075  is arranged on a surface of the flexure  1070   2  which faces the crimp support portion  1062 . This insulation layer  1075  may provide a further means for preventing the formation of a short circuit between the flexure  1070   2  and the crimp support portion  1062 . In this and other embodiments, a further insulation layer may be provided on the surface of the flexure which faces the static part so as to prevent the formation of a short circuit to the static part (or to component(s) mounted thereon). As will be appreciated, insulation layers on two surfaces of a flexure may be formed by way of a single process, e.g. by coating the flexure. 
       FIG. 23B  shows a variation on the embodiment seen in  FIG. 23A , and is identical, except that instead of the insulation layer  1075  being arranged on the flexure  1070   2  as seen in  FIG. 23A , an insulation layer  1077  is arranged on the crimp support portion  1062 . In this variation, the insulation layer  1077  is arranged in the thinned section  1063  on a surface which faces the flexure  1070   2 . Similarly to the insulation layer  1075  seen in  FIG. 23A , the insulation layer  1077  may also provide a further means for preventing the formation of a short circuit between the flexure  1070   2  and the crimp support portion  1062 . 
       FIG. 23C  shows a further variation which is effectively a combination of the embodiments seen in  FIGS. 23A and 23B . In this embodiment both the insulation layer  1075  provided on the flexure  1070   2  and the insulation layer  1077  provided on the crimp support  1062  are included. The inclusion of both insulation layers  1075 ,  1077  may further reduce the possibility of a short circuit forming between the crimp support  1062  and the flexure  1070   2 . 
     Whilst the insulation layers  1075 ,  1077  described above are shown on the embodiment of the actuator assembly depicted in  FIG. 20D , the insulation layers  1075 ,  1077  may be included in any of the embodiments described herein. 
       FIGS. 24-30  show top views of different movable parts  3060 , with up to four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  and some which have different arrangements of the flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  around the primary axis. Where present, each flexure  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  comprises a corresponding foot  3071   1 ,  3071   2 ,  3071   3 ,  3071   4 . The flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4 , where present, are connected to the movable part  3060  by up to four flexure connection sections  3073   1 ,  3073   2 ,  3073   3 ,  3073   4 . Whilst each of the movable parts  3060  is technically an eight-sided polygon, due to their specific proportions, each movable part may be approximated to be a square having four corners. For ease of reference, whilst each of the embodiments in  FIGS. 24-30  are different, the various components are given the same reference numeral. 
       FIG. 24A  shows a movable part  3060  comprising two flexures  3070   1 ,  3070   2  which extend around two corners of the movable part  3060 . The flexures  3070   1 ,  3070   2  are arranged and extend such that their feet  3071   1 ,  3071   2  come together to meet one another. As will be appreciated by those skilled in the art, and with reference to earlier Figures, one of the corners around which one of the flexures  3070   1 ,  3070   2  extend may comprise a crimp support portion.  FIG. 24B  shows a similar embodiment except that the feet  3071   1 ,  3071   2  are separated by a small amount. Table 1 (below) shows stiffness data in relation to the movable part  2060  seen in  FIG. 24A . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Finite element analysis data for the stiffnesses 
               
               
                 (in N/m) along various directions in the movement 
               
               
                 plane and the diagonal stiffness ratio of several of 
               
               
                 the arrangements shown in the drawings. 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 FIG. 
                 24A 
                 25 
                 26 
                 27A 
                 27B 
                 27C 
                 28 
                 29 
                 30 
                 31 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 X stiffness  
                 607.7 
                 70 
                 690 
                 664.6 
                 649.2 
                 418.5 
                 1116.9 
                 658.5 
                 1109 
                 326.2 
               
               
                 X stiffness  
                 320.8 
                 69 
                 436 
                 664.6 
                 0 
                 0 
                 0 
                 658.5 
                 1109 
                 142.8 
               
               
                 (unconst.) 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Y stiffness  
                 116.5 
                 10 
                 685 
                 661.5 
                 661.5 
                 415.4 
                 1109.2 
                 660 
                 1120 
                 329.2 
               
               
                 Y stiffness 
                 116.0 
                 10 
                 667 
                 661.5 
                 0 
                 0 
                 0 
                 660 
                 1120 
                 144.2 
               
               
                 (unconst.) 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Static diag. 
                 153.6 
                 38 
                 598 
                 657.1 
                 647.3 
                 417.7 
                 1116.1 
                 660.3 
                 1118 
                 81.81 
               
               
                 stiff. 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Moving 
                 153.5 
                 42 
                 772 
                 657.1 
                 645.1 
                 416.6 
                 1116.1 
                 660.3 
                 1120 
                 571.1 
               
               
                 diag. stiff. 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Diag. stiff. 
                 0.999 
                 1.11 
                 1.29 
                 1 
                 0.997 
                 0.997 
                 1 
                 1 
                 1.002 
                 6.981 
               
               
                 ratio 
               
               
                   
               
            
           
         
       
     
       FIG. 25  shows a movable part  3060  comprising two flexures  3070   1 ,  3070   2  each of which extends around two corners of the movable part  3060  and wherein the two flexures  3070   1 ,  3070   2  together extend ˜360° around the primary axis. In the illustrated example, each of the flexures  3070   1 ,  3070   2  start and end midway between two corners and are arranged with two-fold rotational symmetry. Other examples need not have one or both of these characteristics. Table 1 (above) shows stiffness data for the movable part  2060  seen in  FIG. 25 . 
       FIG. 26  shows a movable part  3060  which comprises three flexures  3070   1 ,  3070   2 ,  3070   3 . As can be seen in this Figure, the three flexures  3070   1 ,  3070   2 ,  3070   3  extend around over 270° around the primary axis. Table 1 (above) shows stiffness data in relation to the movable part  3060  seen in  FIG. 26 . As can be seen in the table, the ratio of the static diagonal stiffness and the moving diagonal stiffness is 1.29 and thus less than the ratio required by the third aspect of the invention. This is also true for the ratio of the stiffnesses in the x and y directions. 
       FIG. 27A  shows a movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  that are arranged to have both two-fold mirror symmetry and four-fold rotational symmetry.  FIG. 27B  shows a movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  having the same general arrangement as seen in  FIG. 27A , with the difference being that each of the flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  comprises a respective inward kinked portion  3100   1 ,  3100   2 ,  3100   3 ,  3100   4 .  FIG. 27C  shows another movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  having the same general arrangement as seen in  FIG. 27A , with the difference being that each of the flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  comprises a respective outward kinked portion  3100   1 ,  3100   2 ,  3100   3 ,  3100   4 . Table 1 (above) shows stiffness data for the movable parts  3060  seen in  FIGS. 27A, 27B and 27C . 
       FIG. 28  shows a movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4 , wherein one pair of flexures  3070   1 ,  3070   4 , share a common connection section  3073   1 , and wherein the other pair of flexures  3070   2 ,  3070   3  share another common connection section  3073   2 . Additionally, the connection sections  3073   1 ,  3073   2  are offset such that each of the connection sections  3073   1 ,  3073   2  is closer to one of the corners of the movable part than another corner. Table 1 (above) shows stiffness data for the movable member  3060  seen in  FIG. 28 . 
       FIG. 29  shows a top view of a movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  each of which is connected to the movable part  3060  by an individual respective connection section  3073   1 ,  3073   2 ,  3073   3 ,  3073   4 . The connection sections  3073   1 ,  3073   2 ,  3073   3 ,  3073   4  are arranged centrally between respective corners of the movable part  3060  and the four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  together extend 360° around the primary axis. Table 1 (above) shows stiffness data relating to the movable part  3060  seen in  FIG. 29 . 
       FIG. 30  shows a top view of a movable part  3060  which comprises four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4  each of which is connected to the movable part  3060  by an individual respective connection section  3073   1 ,  3073   2 ,  3073   3 ,  3073   4 . However, unlike the example shown in  FIG. 29 , the connection sections  3073   1 ,  3073   2 ,  3073   3 ,  3073   4  are offset such that they are not equally spaced between corners of the movable part. Table 1 (above) shows stiffness data for a movable part  3060  as seen in  FIG. 30 . 
     As can be seen from the data in Table 1 for  FIGS. 27-30 , all of which correspond to movable parts  3060  which comprise at least four flexures  3070   1 ,  3070   2 ,  3070   3 ,  3070   4 , taking the stiffness for each of the X and Y directions these two axis satisfy the ratio requirement of the third aspect of the invention, and additionally taking the stiffness for each of the static and moving diagonals satisfy the ratio requirement of the third aspect of the invention. For reference, the moving diagonal is the direction which corresponds to moving the movable part, and thus the flexures, in the direction of the moving crimps, and the static diagonal is the direction which corresponds to moving the movable part, and thus the flexures, in the direction towards the static crimps. Due to the configuration of the flexures in these embodiments, the ratio of the stiffnesses in the static and moving diagonals will be the highest, and thus the ratio of stiffnesses of any other pair of orthogonal axis will be less than the ratio for the static and moving diagonals. Therefore, these other orthogonal axes will also satisfy the requirement of the third aspect of the invention. These tables therefore demonstrate the improved symmetry of the of the stiffness in the movement plane. 
     In any of the embodiments with two feet that are adjacent to each other (see e.g.  FIGS. 24A, 26-28 ), these feet may be provided separately, as illustrated, or may be combined in a single, unitary foot. Each of these options may have its respective advantages in relation to e.g. noise, ease of manufacture, etc. 
       FIG. 31  shows a movable part  4060  which comprises only two flexures  4070   1 ,  4070   2  which do not overlap moving crimp portions. Table 1 (above) shows stiffness data for the movable part  4060  seen in  FIG. 31 . As is apparent from this table, the ratio of the diagonal stiffnesses is greater than the ratio required by the third aspect of the invention, and is significantly greater than the movable parts  3060  described above in accordance with the present invention. 
     Further Details of the Known Actuator Assembly 
     Referring in particular to  FIGS. 32 to 34 , the known actuator assembly  40  will now be described in further detail so as to aid understanding of the embodiments described below. 
     As described above with reference to  FIGS. 1, 2A and 2B , this actuator assembly  40  includes a base component  400 , a movable part  60  (also referred to herein as a ‘moving platform’), and a static part  50  (also referred to herein as a ‘support platform’). The static part  50  includes two separate components, i.e. a support component  500  and a conductive component  501 , which are affixed to each other. The actuator assembly  40  also includes four SMA wires  80 , each mechanically and electrically connected at one end to the static part  50  (specifically, the conductive component  501 ) via so-called static crimps  51 , and at the other end to the movable part  60  via so-called moving crimps  61 . 
     Two flexures  70 , i.e. first and second flexures  70   1 ,  70   2 , are connected between the static part  50  and the moving part  60 . In this example, the flexures  70  are formed integrally with the moving part  60  at one end thereof and are connected to the static part  50  at the other end thereof by welds  6001   a ,  6001   b  or any other suitable means for providing both mechanical and electrical connections. However, the flexures  70  can instead be integrally formed with the static part  50  or indeed be provided as independent parts. 
     The static crimps  51  and the moving crimps  61  are provided on the static part  50  and the moving part  60 , respectively, via crimp supports  50   d ,  60   d . In this example, the static crimp supports  50   d , which each include one static crimp  51 , are integral with the static part  50 , and the moving crimp supports  60   d , which each include two moving crimps  61 , are separate components attached to the moving part  60  by welds  6002  or other suitable means for providing both mechanical and electrical connections. 
     As described above with reference to  FIG. 18 , whilst the movable part  60  is technically an eight-sided polygon, due to its proportions, the movable part  60  can be considered to have a square shape with four corners. The moving crimps  61  are arranged on two diagonally-opposite corners of the moving part  60  and the static crimps  51  are arranged on the other two corners on the static part  50 . 
     The conductive component  501  of the static part  50  is split into six separate segments  5001 - 5006 . A first segment  5001  (hereinafter referred to as the ‘common static segment’) is electrically and mechanically connected to a first end of the flexure  70   1  via a weld  6001   a  and has a terminal at one end for electrically connecting to the integrated circuit (IC)  30 . A second segment  5006  is connected to a first end of the second flexure  70   2  via a weld  6001   b . In this embodiment, the second flexure  70   2  performs only a mechanical (i.e. biasing) function. In other embodiments, the second flexure  70   2  may also perform an electrical function similar to the first flexure  70   2 . The remaining four segments  5002 - 5005  (hereinafter referred to as the ‘wire segments’) each have a terminal at one end for connecting to the IC  30  and a static crimp  51  at the other end. Each segment  5001 - 5006  is electrically isolated from each other within the conductive component  501 . In other words, each segment  5001 - 5006  provides a separate current path within the conductive component  501 . 
     The base component  400 , the movable part  60 , and the static part  50  (i.e. the support component  500  and the conductive component  501 ) may each take the form of a patterned sheet of metal, e.g. etched or machined stainless steel, and may each be coated with an electrically-insulating dielectric material. The dielectric coating or other type of dielectric layer may include one or more windows allowing electrical connections therethrough. 
     Instead of the welds  6001   a  and  6001   b , any other suitable means for providing mechanical and electrical connections can be used to connect the segments  5001 ,  5006  and the flexures  70   1 ,  70   2 . 
     The conductive component  501 , the flexures  70 , the movable part  60 , the crimp supports  50   d ,  60   d , the crimps  51 ,  61 , and the SMA wires  80  are electrically connected. Thus, as illustrated in  FIG. 33 , when the terminals of the common static segment  5001  and the terminals of the wire segments  5002 - 5005  are connected to the IC  30 , current from the IC  30  can flow through the current paths provided by the segments  5001 - 5005 , the flexure  70   1 , the movable part  60 , the crimp supports  50   d ,  60   d , the crimps  51 ,  61 , and the SMA wires  80 . More specifically, current from the IC  30  can flow through the common static segment  5001  and the first flexure  70   1  ‘up’ to the movable part  60 , and can flow ‘down’ to the IC  30  through one or more of the four SMA wires  80  and corresponding wire segment(s)  5002 - 5005  of the static part  50 . This arrangement allows the IC  30  to control the amount of current that flows through each of the SMA wires  80  and thus allows the IC  30  to control the length of each SMA wire  80  so as to move the movable part  60  with respect to the static part  50  as described above. As will be appreciated, the current may flow in either direction. 
     As described above with reference to  FIG. 1 , the moving part  60  supports the lens assembly  20  and is connected to the lens carriage  21 . Moreover, an axial actuator arrangement  24 , provided between the lens carriage  21  and the lens holder  23 , is arranged to drive movement of the lens holder  21  and the lenses  22  along the optical axis O relative to the lens carriage  21  for focusing incoming light onto the image sensor  6  of the camera module  1 . The axial actuator arrangement  24  can be of any suitable type, for example a voice coil motor (VCM) or an arrangement of SMA wires. Hereinafter, the elements  21 ,  23 ,  24  will be collectively referred to as an autofocus (AF) actuator assembly  7000 . However, as will be appreciated, the actuator assembly  7000  may perform functions other than AF. 
       FIG. 34  shows an AF actuator assembly  7000  in the form of a closed-loop VCM AF actuator assembly mounted on the moving part  60  of the SMA actuator assembly  40  such that the AF actuator assembly  7000  moves with the moving part  60 . A flexible printed circuit (FPC)  7010  electrically connects the AF actuator assembly  7000  to its control circuitry, e.g. the IC  30 . 
     In this example, the FPC  7010  includes four electrical connections  7011 - 7014 . These connections  7011 - 7014  can include a power connection, a ground connection and two data connections (e.g. so-called Vdd, Vss, SDA and SCL connections). 
     Using an FPC for electrical connections between the AF actuator assembly  7000  and the IC  30  can have certain disadvantages. For example, since the FPC needs to fit within the camera module housing without hindering OIS and/or AF performance, e.g. by obstructing movement of the lens carriage, an accurately formed FPC can be required, and a complicated camera module assembly process can be required. Since both the AF actuator assembly and the FPC need to fit within the camera module housing, stricter size limitations (e.g. smaller lateral dimension limitations) may need to be applied to the AF actuator assembly to provide sufficient room for the FPC. The FPC can also increase the camera module bill of material (BOM) cost. 
     Further Embodiment of an SMA Actuator Assembly 
     Referring to  FIGS. 35 to 42 , a further embodiment of an SMA actuator assembly  8000  will now be described. When combined with an AF actuator assembly  7000 ′ such as the one described above with reference to  FIG. 34 , the actuator assembly  8000  eliminates the need to use an FPC to electrically connect the AF actuator assembly  7000 ′ and the IC  30 . 
     The actuator assembly  8000  is substantially the same as the above-described known actuator assembly  40  except for the differences described below. 
     Like the known actuator assembly  40 , the actuator assembly  8000  includes a static part  8002  (formed of a conductive component  8300  and a support component (not shown)), a movable part  8001 , and a set of flexures connected therebetween. However, as will be explained in more detail below, the actuator assembly  8000  has five such flexures. 
     Also like the known actuator assembly  40 , the actuator assembly  8000  has current paths (hereinafter referred to as ‘OIS current paths’  8000   a ) provided in the static part  8002 , the flexures, and the movable part  8001  for driving the SMA wires  80 ′. However, the actuator assembly  8000  includes four further current paths (hereinafter referred to as ‘AF current paths’  8000   b ). The AF current paths  8000   b  are also provided in (e.g. run via, through or on) the static part  8002 , the flexures, and the movable part  8001 . The AF current paths  8000   b  allow the AF actuator  7000 ′ to be electrically connected to the IC  30  via the SMA actuator assembly  8000  rather than e.g. via an FPC. This is achieved by:
         having five flexures  8201   a ,  8211   a ,  8212   a ,  8213   a ,  8214   a  electrically and mechanically connecting the static part  8002  and the movable part  8001 , as opposed to the two flexures  70   1 ,  70   2  of the known actuator assembly  40 ;   having the conductive component  8300  of the static part  8002  divided into nine segments  8301 - 8305 ,  8311 - 8314 , as opposed to the six segments  5001 - 5006  of the known actuator assembly  40 ; and   having the movable part  8001  divided into five segments  8101 / 8201 ,  8111 / 8211 ,  8112 / 8212 ,  8113 / 8213 ,  8114 / 8214 , as opposed to the undivided movable part  60  of the known actuator assembly  40 .       

     The five flexures include one flexure  8201   a  (hereinafter referred to as the ‘common flexure’) that forms part of the OIS current paths  8000   a . The remaining four flexures  8211   a - 8214   a  (also referred to herein as the ‘AF-connecting flexures’) each form part of one of the AF current paths  8000   b . In the illustrated embodiment, the five flexures  8201   a ,  8211   a - 8214   a  are integrally formed with the moving part  8001 . However, one or more of the five flexures  8201   a ,  8211   a - 8214   a  could instead be integrally formed with the static part  8002  or indeed be provided as independent parts. 
     As mentioned above, the conductive component  8300  of the static part  8002  is split into nine segments  8301 - 8305 ,  8311 - 8314 . Like the conductive component  501  of the known actuator assembly  40 , the conductive component  8300  includes one ‘common static segment’  8301  and four ‘wire segments’  8302 - 8305  forming part of the OIS current paths  8000   a . The common static segment  8301  is electrically and mechanically connected to a first end of the common flexure  8201   a  via a connection (e.g. weld)  9101  and has a terminal for electrically connecting to the IC  30 ; and the wire segments  8302 - 8305  each have a terminal at a first end for connecting to the IC  30  and a static crimp  8302   a - 8305   a  at a second end. 
     The conductive component  8300  includes four further segments  8311 - 8314  (hereinafter referred to as ‘static AF segments’). Each static AF segment  8311 - 8314  forms part of one of the AF current paths  8000   b . Each static AF segment  8311 - 8314  includes a terminal for electrically connecting to the IC  30 , and a connection (e.g. weld)  9111 - 9114  for mechanically and electrically connecting to a first end of a respective flexure  8211   a - 8214   a . As in the known actuator  40 , the segments  8301 - 8305 ,  8311 - 8314  of the conductive component  8300  are electrically isolated from each other within the conductive component  8300 . 
     As mentioned above, the movable part  8001  is split into five segments  8101 / 8201 ,  8111 / 8211 ,  8112 / 8212 ,  8113 / 8213 ,  8114 / 8214 . A first segment  8101 / 8201  (hereinafter referred to as the ‘movable common segment’) is electrically and mechanically connected to a second end of the common flexure  8201   a . The remaining four segments  8111 / 8211 ,  8112 / 8212 ,  8113 / 8213 ,  8114 / 8214  (hereinafter referred to as ‘movable AF segments’) are each electrically and mechanically connected to a second end of one of the AF-connecting flexures  8211   a - 8214   a . Hence the movable AF segments  8111 / 8211 ,  8112 / 8212 ,  8113 / 8213 ,  8114 / 8214  each form part of one of the AF current paths  8000   b.    
     In the illustrated embodiment, the movable part  8001  includes an upper layer  8100  (hereinafter referred to as the ‘crimp layer’) and a lower layer  8200  (hereinafter referred to as the ‘flexure layer’). The crimp layer  8100  includes the moving crimps  8101   a ,  8101   b , and the flexure layer  8200  includes connections to the flexures  8201   a ,  8211   a - 8214   a . The segments  8101 ,  8111 - 8114  of the crimp layer  8100  are electrically isolated from each other within the crimp layer  8100 . The segments  8201 ,  8211 - 8214  of the flexure layer  8200  are electrically isolated from each other within the flexure layer  8200 . The layers  8100 ,  8200  (in particular corresponding segments of the layers, e.g. segments  8101  and  8201 ) are mechanically and electrically connected to each other via connectors (e.g. welds)  9201 ,  9211 - 9214  (see  FIG. 39 ) passing through windows in an insulating layer (not shown). Hence, due also to the arrangement (e.g. overlap) of the segments  8101 ,  8111 - 8114 ,  8201 ,  8211 - 8214 , the movable part  8200  forms an integral structure. The insulating layer between the crimp layer  8100  and the flexure layer  8200  may be formed, for example, by coating at least one of the layers  8100 ,  8200 . The coating may be a polymer coating or it may be a coating such as DLC or CrC-DLC. This latter type of coating may be thin, hard wearing, and low friction and may also be used as part of the bearing arrangements involving the plain bearings  100 . Instead of welds, the connectors  9201 ,  9211 - 9214  may involve solder, conductive adhesive, or a pressure and heat sensitive conductive film such as ACF. 
     In other embodiments, the movable part  8001  may have a single-layer comprising both the moving crimps  8101   a ,  8101   b  and the connections to the flexures  8201   a ,  8211   a - 8214   a .  FIG. 47  shows a schematic circuit diagram of such an embodiment. 
     In the illustrated embodiment, four flexures  8201   a ,  8211   a ,  8213   a ,  8214   a  (hereinafter referred to as the ‘outer flexures’) extend in an arc around the optical axis O and substantially wrap around the outer perimeter of the flexible layer  8200 , and one flexure  8212   a  (hereinafter referred to as the ‘inner flexure’) extends in an arc around the optical axis O and substantially wraps around the inner perimeter of the flexible layer  8200 . However, other embodiments may have other arrangements. The inner flexure  8212   a  can be configured so as to provide a small amount of stiffness relative to the outer flexures  8201   a ,  8211   a ,  8213   a ,  8214   a  such that the diagonal stiffness ratio provided by the flexures  8201   a ,  8211   a - 8214   a  is mainly determined by the four outer flexures  8201   a ,  8211   a ,  8213   a ,  8214   a . The outer flexures  8201   a ,  8211   a ,  8213   a ,  8214   a  may be arranged as described above in relation to the actuator assembly  1040  or  2040  (see  FIGS. 18-20D, 23A-23C ;  FIGS. 21-22 ). 
     The movable part  8001  generally includes terminals  8000   c  (see  FIG. 42 ) for connecting to the AF actuator assembly  7000 ′. The terminals  8000   c  may be provided on the crimp layer  8100 . The terminals  8000   c  may take the form of solder pads, for example. The terminals  8000   c  may be provided on formed-up structures to facilitate the connections. The specific arrangement of the terminals  8000   c  may depend on the specific AF actuator assembly  7000 ′ with which the actuator assembly  8000  is configured to be used. 
     As illustrated in  FIG. 38 , each of the five segments  8201 ,  8211 - 8214  of the flexure layer  8200  is connected via a flexure  8201   a ,  8211   a - 8214   a  (and by a weld  9101 ,  9111 - 9114 ) to one of the segments  8301 ,  8311 - 8314  of the conductive component  8300 . 
     As illustrated in  FIG. 39 , each of the five segments  8101 ,  8111 - 8114  of the crimp layer  8100  and the corresponding five segments  8201 ,  8211 - 8214  of the flexure layer  8200  are connected by connections (e.g. welds)  9201 ,  9211 - 9214 . 
     Referring in particular to  FIG. 40 , the conductive component  8300 , the flexure layer  8200  and the crimp layer  8100  are each provided with a central aperture aligned with the optical axis O (z axis) allowing the passage of light from the lens assembly  20  to the image sensor  6 . The SMA wires (not shown in  FIG. 40 ) can be perpendicular to the optical axis O or inclined at a small angle to the plane perpendicular to the optical axis O. These aspects are similar to the known actuator assembly  40 . 
     In a similar way to the known actuator assembly  40 , the SMA wires  80 ′ are electrically connected within the actuator assembly  8000  such that, when the terminal of the common static segment  8301  and the terminals of the wire segments  8302 - 8305  are connected to the IC  30 , current can flow to and from the IC  30  through the common static segment  8301 , the common flexure  8201   a , the common movable segment  8201 / 8101 , the SMA wires  80 ′ (not shown in  FIG. 41 ), and the wire segments  8302 - 8305 . This is illustrated by the solid lines in  FIG. 41 . More specifically, current from the IC  30  can flow through the common static segment  8301  and the common flexure  8201   a  ‘up’ to the common movable segment  8201 / 8101  (i.e. to one of the segments  8201  of the flexure layer  8200  and then to the corresponding segment  8101  of the crimp layer  8100 ), and can flow ‘down’ to the IC  30  through one or more of the four SMA wires  80 ′ (not shown in  FIG. 41 ) and corresponding wire segment(s)  8302 - 8305  of the static part  8300 . This arrangement allows the IC  30  to drive the movement of the movable part  8001  with respect to the static part  8002  as described above with respect to actuator assembly  40 . 
     Furthermore, as illustrated by the dashed lines in  FIG. 41 , when the terminals of the static AF segments  8311 ,  8312 ,  8313 ,  8314  of the static part  8002  are connected to the IC  30  and the AF actuator  7000 ′ is mounted on the movable part  8001  (i.e. the AF actuator  7000 ′ is electrically connected to the terminals  8000   c , etc.), current can flow between the IC  30  and the AF actuator  7000 ′ via the actuator assembly  8000  through the four AF current paths  8000   b  provided by the four static AF segments  8311 - 8314 , the four AF-connecting flexures  8211   a - 8214   a , and the four movable AF segments  8111 / 8211 ,  8112 / 8212 ,  8113 / 8213 ,  8114 / 8214  (via the connections  9111 - 9114  between the static AF segments  8311 - 8314  and the AF-connecting flexures  8211   a - 8214   a  and via the connections  9211 - 9214  between the flexure layer  8200  and the crimp layer  8100  of the movable part  8001 ). 
     In this embodiment, the static AF segment  8314  and the movable AF segment  8114 / 8214  provide a power connection to the AF actuator  7000 ′ via a first AF current path  8000   b , the static AF segment  8311  and the movable AF segment  8111 / 8211  provide a ground connection to the AF actuator  7000 ′ via a second AF current path  8000   b , and the static AF segments  8312 ,  8313  and the movable AF segments  8112 / 8212 ,  8113 / 8213  provide two data connections to the AF actuator  7000 ′ via respective third and fourth AF current paths  8000   b . However, each of the connections to the AF actuator  7000 ′ can be provided by any of the four AF current paths  8000   b.    
       FIG. 42  shows a schematic circuit diagram of the actuator assembly  8000  when the AF actuator  7000 ′ is mounted on the movable part  8001  of the actuator assembly  8000  (i.e. the AF actuator  7000 ′ is electrically connected to the terminals  8000   c , etc.). As described above, the static part  8002 , the flexures (specifically the AF-connecting flexures  8211   a - 8214   a ), and the movable part  8001  (specifically the flexure layer  8200  and the crimp layer  8100 ) include four AF current paths  8000   b  within the actuator assembly  8000  for connecting the IC  30  and the AF actuator assembly  7000 ′. Also, as described above, the static part  8002 , the flexures (specifically the common flexure  8201   a ), and the movable part  8001  (specifically the flexure layer  8200  and the crimp layer  8100 ) include four OIS current paths  8000   a  for driving/controlling the SMA wires  80 ′. 
     Alternative Embodiments 
     In the actuator assembly  8000  described above, all four AF current paths  8000   b  are provided via the actuator assembly  8000 . However, one or more of the current paths to the AF actuator assembly  7000 ′ can be provided in a different way, e.g. via an FPC. Hence the number of segments of the conductive component  8300 , the number of segments of the movable part  8001 , the number of AF-connecting flexures, and the number of connections therebetween would change (reduce) accordingly. 
     For example, as illustrated in  FIG. 43 , only one AF current path  8000   b  may be provided and/or used to connect the IC  30  and the AF actuator assembly  7000 ′ via the actuator assembly  8000 . In this example, the remaining current paths are provided by an FPC  7010 ′. Hence, the conductive component  8300  would only need to be divided into six segments (five for the OIS current paths  8000   a  and one for the AF current path  8000   b ), the movable part  8001  would only need to be divided into two segments (one for the OIS current paths  8000   a  and one for the AF current path  8000   b ), and the flexures would only need to provide two current paths (one for the OIS current paths  8000   a  and one for the AF current path  8000   b ), e.g. there would only need to be two flexures. 
     Alternatively, only, two, or three AF current paths  8000   b  can be provided and/or used to connect the IC  30  and the AF actuator assembly  7000 ′ via the actuator assembly  8000 . Again, in such examples, the remaining current path(s) can be provided by an FPC. In a configuration with only two AF current paths, the conductive component  8300  would only need to be divided into seven segments, the movable part  8001  would only need to be divided into three segments, and e.g. only three flexures would be needed. In a configuration with only three AF current paths, the conductive component  8300  would only need to be divided into eight segments, the movable part  8001  would only need to be divided into four segments, and e.g. only four flexures would be needed. 
     In the embodiments described above, the four AF current paths  8000   b  are separate from the OIS current paths  8000   a . However, one of the AF current paths  8000   b  and one of the OIS current paths  8000   a  can be shared. 
     For example, as illustrated in  FIG. 44 , the OIS current path  8000   a  (hereinafter referred to as the ‘common current path’) provided by the common static segment  8301 , the common flexure  8201   a , and the common movable segment  8201 / 8101  can be configured to also connect to the AF actuator assembly  7000 ′. In other words, the common current path can also provide an AF current path  8000   b  (e.g. providing the power connection to the AF actuator assembly  7000 ′). In this example, the conductive component  8300  would only need to be divided into eight segments, the movable part  8001  would only need to be divided into four segments, and the flexures would only need to provide four current paths (e.g. only four flexures would be needed, wherein each flexure provides a separate current path). 
     The above embodiments of actuator assembly  8000  describe that four AF current paths are required for the AF actuator assembly  7000 ′. However, the actuator assembly  8000  can be electrically connected to an AF actuator requiring less than four connections to the IC  30  or more than four connections to the IC  30 . Hence the number of segments of the movable part  8001 , the number of flexures, and the number of connections required to be provided in the actuator assembly  8000  would change accordingly. 
     For example, as shown in  FIG. 45 , the actuator assembly  8000  can be electrically connected to an AF actuator assembly  7000 ″ only requiring three AF current paths connecting the IC  30  and the AF actuator assembly  7000 ″ (e.g. an SMA auto-focus actuator comprising two SMA wires). In which case, the conductive component  8300  would only need to be divided into eight segments, each providing a separate current path; the movable part  8001  would only need to be divided into four segments, of which three segments would be for the three AF current paths; and the flexures would only need to provide four current paths (i.e. only four flexures would be needed, wherein each flexure provides a separate current path). 
     Alternatively, as shown in  FIG. 46 , the actuator assembly  8000  can be electrically connected to the AF actuator assembly  7000 ″ and the AF current path providing the power connection to the AF actuator  7000 ′ and the current path providing the power connection to the SMA wires  80 ′ can be shared. In which case, the conductive component  8300  would only need to be divided into seven segments, each providing a separate current path; the movable part  8001  would only need to be divided into three segments, of which all three segments would be for the three AF current paths; and the flexures would only need to provide three current paths (i.e. only three flexures would be needed, wherein each flexure provides a separate current path). 
     Where there are three flexures, these may be arranged as described above in relation to flexure plate  3060  (see  FIG. 26 ). Where there are four flexures, these may be arranged as described above in relation to the actuator assembly  1040  or  2040  (see  FIGS. 18-20D, 23A-23C ;  FIGS. 21-22 ). 
     Other Variations 
     It will be appreciated that there may be many other variations of the above-described embodiments. 
     For example, the crimp layer  8100  may be an upper layer and the flexure layer  8200  may be a lower layer of the movable part  8001 . 
     The actuator assemblies described above with reference to  FIGS. 35 to 47  are only described as configured to be connectable to an AF actuator. However, as the person skilled in the art would appreciate, these actuator assemblies can instead be configured to be connectable to any other device with electronic connections. 
     The OIS current paths  8000   a  and the AF current paths  8000   b  in the actuator assemblies  8000  described above are described as being provided by having the conductive component  8300  and the movable part  8001  divided into a number of electrically conductive segments, and having the segments of the conductive component  8300  and respective segments of the movable part  8001  electrically connected via electrically conductive flexures  8211   a - 8214   a  (wherein each of the segments of the conductive component  8300  are electrically isolated from each other within the conductive component  8300 , each of the segments of the movable part  8001  are electrically isolated from each other within the movable part  8001 , and each flexure  8211   a - 8214   a  provides one current path). However, the OIS current paths  8000   a  and the AF current paths  8000   b  can instead be provided by electrically conductive tracks running on (or through, or in) the conductive component  8300 , the movable part  8001  and at least one of the flexures  8211   a - 8214   a , wherein the conductive tracks are electrically isolated from each other within the parts of the actuator assembly  8000  they sit on. Alternatively, the OIS current paths  8000   a  and the AF current paths  8000   b  can be provided by a combination of both (i.e. provided by electrically conductive tracks, electrically conductive segments of the conductive component  8300 , electrically conductive segments of the movable part  8001 , and electrically conductive flexures  8211   a - 82114   a ).