GB2605640A

GB2605640A - Actuator fabrication

Info

Publication number: GB2605640A
Application number: GB2105051.3A
Authority: GB
Inventors: Hart Oliver; Bunting Stephen; Carr Joshua; Van Wyk Peter; Auchoybur Kiran
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2021-04-08
Filing date: 2021-04-08
Publication date: 2022-10-12
Also published as: CN117157584A; GB202317060D0; GB202105051D0; WO2022214831A1; GB2621278A

Abstract

A method of forming an actuator assembly 2, 30 includes crimping a first shape-memory alloy wire 12 to a first patterned sheet 14 which includes a frame 15, a features 16, 19 supporting or defining crimp heads 17, 20 and connected to the frame 15 by connecting members 18, 21. The first shape-memory alloy wire 12 is crimped between the crimp heads 17, 20. A second patterned sheet 22 similarly includes crimp heads which support a second SMA wire 13. The first and second patterned sheets 14, 22 and first and second parts 3, 4 are joined to form a first assembly, in which the SMA wires are attached between the first and second parts. The first and second parts are coupled by a bearing assembly configured to couple a rotation of the second part 4 relative to the first part 3 about a primary axis to a translation of the second part relative to the first part along the primary axis, thereby providing helical movement. After assembly, the first and second connecting members 18, 21 are severed to detach the frames from the crimp heads.

Description

ACTUATOR FABRICATION

Field

The present application relates to an actuator assembly, particularly methods of fabricating an actuator assembly.

Background

Such an actuator assembly may be used, for example, in a camera to move a lens assembly along an optical axis to provide automatic focussing (AF). Where such a camera is to be incorporated into a portable electronic device such as a mobile telephone, miniaturization can be important.

WO 2019/243849 Al describes a shape memory alloy actuation apparatus which comprises a support structure and a movable element. A helical bearing arrangement supported on the movable element on the support structure guides helical movement of the movable element with respect to the support structure around a helical axis. At least one shape memory alloy actuator wire is connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, so as to drive rotation of the movable element around the helical axis which the helical bearing arrangement converts into said helical movement.

Summary

According to a first aspect of the present invention, there is provided a method of forming an actuator assembly, including crimping a first shape-memory alloy wire to a first patterned sheet. The first patterned sheet includes a first frame, a first feature supporting or defining a first crimp head and connected to the first frame by one or more first connecting members, and a second feature supporting or defining a second crimp head and connected to the first frame by one or more second connecting members. The first shape-memory alloy wire is crimped between the first and second crimp heads. The method also includes crimping a second shape memory alloy wire to a second patterned sheet. The second patterned sheet includes a second frame, a third feature supporting a third crimp head and connected to the second frame by one or more third connecting members, and a fourth feature supporting or defining a fourth crimp head and connected to the second frame by one or more fourth connecting members. The second shape-memory alloy wire is crimped between the third and fourth crimp heads. The method also includes assembling the first patterned sheet, the second patterned sheet, a first part and a second part to form a first assembly. The first assembly is configured such that the first and third features are attached to the first part, the second and fourth features are attached to the second part, and the first part is coupled to the second part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis. The method also includes severing each of the first and second connecting members to detach the first frame and severing each of the third and fourth connecting members to detach the second frame.

A connecting member may be a sprue, or other structure having similar properties to a sprue. A connecting member may take the form of a thin, metal sheet (or foil or plate) portion. The connecting member in general may be any structure providing sufficient mechanical support to enable assembly, whilst being severable without the need to apply so much force that adjacent regions of a patterned sheet become distorted.

The first frame, the first feature and the second feature may be formed from a sheet having a uniform thickness. The second frame, the third feature and the fourth feature may be formed from a sheet having a uniform thickness.

When forming the first assembly, the first patterned sheet, the second patterned sheet, the first part and the second part may be stacked such that the primary axis is substantially parallel to the thickness of the first patterned sheet and the second patterned sheet.

The first part may also be referred to as a "static part" or a "chassis". The second part may also be referred to as a "moving part" or a "carriage".

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

Forming the first assembly may include attaching the first and second parts to the first patterned sheet, and attaching the second patterned sheet to the first and second parts so that the first and second parts are generally between the first and second patterned sheets. Forming the assembly may include stacking, in order, the first patterned sheet, the first part, the second part and the second patterned sheet. The first patterned sheet may be bonded to the first and second parts using adhesive. The first patterned sheet may be welded to the first and second parts. The second patterned sheet may be bonded to the first and second parts using adhesive. The second patterned sheet may be welded to the first and second parts. Welding may take the form of laser welding or electrical welding. Stacking along primary axis.

Forming the first assembly may include attaching the first patterned sheet to the second patterned sheet, and attaching the first and second patterned sheets to the first and second parts. The first patterned sheet may be bonded to the second patterned sheet using adhesive. The first patterned sheet may be welded to the second patterned sheet. The first and second patterned sheets may be bonded to the first and second parts using adhesive. The first and second patterned sheets may be welded to the first and second parts. Welding may take the form of laser welding or electrical welding.

One or more of the first connecting members may be formed as flexures configured to permit deflection of all or part of the first feature relative to the first frame along the primary axis. One or more of the second connecting members may be formed as second flexures configured to permit deflection of the second feature relative to the first frame along the primary axis. First and/or second flexures may be configured to constrain deflection of the corresponding feature(s) relative to the first frame in directions perpendicular to the primary axis.

One or more of the third connecting members may be formed as flexures configured to permit deflection of all or part of the third feature relative to the second frame along the primary axis. One or more of the fourth connecting members may be formed as fourth flexures configured to permit deflection of the fourth feature relative to the second frame along the primary axis. Third and/or fourth flexures may be configured to constrain deflection of the corresponding feature(s) relative to the second frame in directions perpendicular to the primary axis.

The bearing arrangement may be a helical flexure including a plurality of flexure arms, each flexure arm connecting the first part to the second part.

The bearing arrangement may be a helical bearing including a plurality of first bearing surfaces defined by the first part, and a plurality of second bearing surfaces defined by the second part. The first assembly may be configured such that each first bearing surface cooperates with a corresponding second bearing surface to define a bearing race which contains one or more ball bearings.

The first patterned sheet may include a fifth feature connected to the first frame by one or more fifth connecting members. The first assembly may be configured such that the fifth feature is attached to the first part or the second part and arranged to retain ball bearings within one or more bearing races. Detaching the first frame may include severing each of the fifth connecting members.

One or more of the fifth connecting members may be formed as fifth flexures configured to permit deflection of the fifth feature relative to the first frame along the primary axis. Fifth flexures may be configured to constrain deflection of the fifth feature relative to the first frame in directions perpendicular to the primary axis.

The fifth feature may be attached to the first or second part in the same way as the first to fourth features.

The second patterned sheet may include a sixth feature connected to the second frame by one or more sixth connecting members. The first assembly may be configured such that the sixth feature is attached to the first part or the second part and arranged to retain ball bearings within one or more bearing races. Detaching the second frame may include severing each of the sixth connecting members.

One or more of the sixth connecting members may be formed as sixth flexures configured to permit deflection of the sixth feature relative to the second frame along the primary axis. Sixth flexures may be configured to constrain deflection of the sixth feature relative to the second frame in directions perpendicular to the primary axis.

The sixth feature may be attached to the first or second part in the same way as the first to fifth features.

Forming the first assembly may include placing one or more ball bearings into each of the bearing races.

Placing each ball bearing may include using a suction tube to pick up the ball bearing from a hopper, locating the suction tube over an opening to a bearing race, and modifying the suction to drop the ball bearing into the bearing race.

The first and/or second bearing surfaces defining a bearing race may be chamfered to increase the size of an opening for ball bearing placement.

Two or more suction tubes may be used to place two or more ball bearings in a single step. The suction tubes may be attached to a tool which includes features configured to cooperate with one or more features of the assembly (for example features of the first and/or second frames) so as to locate the suction tubes relative to the bearing races. Two or more suction tubes attached to a tool may be configured to follow helical paths for insertion of ball bearings part-way along corresponding bearing races.

Placing each bearing may include applying grease to the first bearing surfaces, placing one or more ball bearings on each first bearing surface so as to be retained in position by the grease, and assembling the second part to the first part so as to complete the bearing races about the ball bearings.

The first bearing surfaces and/or the second bearing surfaces may include one or more moulded features configured to retain ball bearings within a run formed between the first and second bearing surface in the assembled actuator assembly.

Placing each bearing may include applying grease to the first bearing surfaces and/or the second bearing surfaces, assembling the second part to the first part so as to form the bearing races, and placing one or more ball bearings into each of the bearing races.

The first patterned sheet may also include a first flexure for connecting the second feature to the first part. The first patterned sheet may include a seventh feature connected to the first frame by one or more seventh connecting members. The first flexure may connect the second feature to the seventh feature. The first flexure may connect the second feature to the first feature.

The second patterned sheet may also include a second flexure for connecting the fourth feature to the first part. The second patterned sheet may include an eighth feature connected to the second frame by one or more eighth connecting members. The second flexure may connect the fourth feature to the eighth feature. The second flexure may connect the fourth feature to the third feature.

The first assembly may be configured such that each of the first, second, third and fourth connecting members is visible when the assembly is viewed along at least one direction parallel to the primary axis.

The first assembly may be configured such that each of the fifth and sixth connecting members is visible when the assembly is viewed along the at least one direction parallel to the primary axis.

The first and second frames may be detached using a laser to sever each of the first, second, third and fourth connecting members. The laser may be used to sever each of the fifth and sixth connecting members.

The first and second frames may be detached using a tool to physically sever each of the first, second, third and fourth connecting members. The tool may be used to physically sever the fifth and sixth connecting members.

One or more further lengths of shape memory alloy wire may be crimped to the first patterned sheet. One or more further lengths of shape memory alloy wire may connect between the first and second features. The first patterned sheet may include one or more additional features, each connected to the first frame by respective connecting members. One or more further lengths of shape memory alloy wire may connect between each additional feature and the first feature, the second feature and/or other additional features.

One or more further lengths of shape memory alloy wire may be crimped to the second patterned sheet. One or more further lengths of shape memory alloy wire may connect between the third and fourth features. The second patterned sheet may include one or more additional features, each connected to the second frame by respective connecting members. One or more further lengths of shape memory alloy wire may connect between each additional feature and the third feature, the fourth feature and/or other additional features.

The first patterned sheet may take the form of a metal sheet etched to form the first frame, the first, second and optionally fifth features, and the corresponding first, second and optionally fifth connecting members. The first patterned sheet may be formed by chemical etching. The first patterned sheet may be formed by laser etching. The first patterned sheet may be stamped from a metal plate.

The second patterned sheet may take the form of a metal sheet etched to form the second frame, the third, fourth and optionally sixth features, and the corresponding third, fourth and optionally sixth connecting members. The second patterned sheet may be formed by chemical etching. The second patterned sheet may be formed by laser etching. The second patterned sheet may be stamped from a metal plate.

The first patterned sheet may include one or more alignment features configured to cooperate with corresponding alignment features of the first part so as to align the first patterned sheet with the first part. The first patterned sheet may include one or more alignment features configured to cooperate with corresponding alignment features of the second part so as to align the first patterned sheet with the second part.

The second patterned sheet may include one or more alignment features configured to cooperate with corresponding alignment features of the first part so as to align the second patterned sheet with the first part. The second patterned sheet may include one or more alignment features configured to cooperate with corresponding alignment features of the second part so as to align the second patterned sheet with the second part.

The first and/or second patterned sheets may include one or more alignment features configured to cooperate with a tool or jig used to assemble the first assembly.

The first patterned sheet may include one or more first terminal connections extending from the first feature and/or the second feature. The second patterned sheet may include one or more second terminal connections extending from the third feature and/or the fourth feature. Assembling the first patterned sheet, the second patterned sheet, the first part and the second part to form the first assembly may include clamping the first patterned sheet, the second patterned sheet, the first part and the second part using a jig, wherein the jig is configured to leave the first terminal connections and the second terminal connections physically accessible. Assembling the first patterned sheet, the second patterned sheet, the first part and the second part to form the first assembly may include bending each of the first terminal connections to make an angle less than 90 degrees to the primary axis and bending each of the second terminal connections to make an angle less than 90 degrees to the primary axis. Assembling the first patterned sheet, the second patterned sheet, the first part and the second part to form the first assembly may include removing the jig after bending the first and second terminal connections.

The first terminal connections may be bent to be substantially parallel to the primary axis. The second terminal connections may be bent to be substantially parallel to the primary axis.

The clamping action of the jig may be provided by one or more blocks or other features, which in use are urged against one or more of the first patterned sheet, the second patterned sheet, the first part and the second part by one or more springs. The jig may be used to clamp the first patterned sheet, the second patterned sheet, the first part and the second part in position for attachment to one another as described hereinbefore using adhesives, welding, and so forth. The jig may be left in place as the first assembly sets, and kept in place to provide support and prevent deformation of the first, second, third and/or fourth features during bending of the first and second terminal connections. The jig may be removed before or after severing the first, second, third and/or fourth connecting members.

According to a second aspect of the invention, there is provided a method of fabricating a camera including providing an actuator assembly fabricated by a method according to the first aspect. The first part has a first attachment surface and the second part has a second attachment surface. The first attachment surface is offset from the second attachment surface in a first direction along the primary axis and the first shape memory alloy wire is offset from the second shape memory alloy wire in the first direction along the primary axis. The method of fabricating a camera also includes attaching the actuator assembly via the first attachment surface to a first camera component while orienting the actuator assembly such that a weight of the second part produces a torque on the second part about the primary axis that applies tension to the first shape memory alloy wire. The method of fabricating a camera additionally or alternatively includes attaching the actuator assembly via the second attachment surface to a second camera component while orienting the actuator assembly such that a weight of the second part produces a torque on the second part about the primary axis that applies tension to the second shape memory alloy wire.

The first camera component may include, or take the form of, a base and/or a screening can. The second camera component may include, or take the form of, one or more components of a lens assembly.

According to a third aspect of the invention there is provided an actuator assembly fabricated using the method according first aspect.

According to a fourth aspect of the invention there is provided an actuator assembly including a first shape-memory alloy wire crimped between a first crimp head supported by a first feature and a second crimp head supported or defined by a second feature. The actuator assembly also includes a second shape-memory alloy wire crimped between a third crimp head supported by a third feature and a fourth crimp head supported or defined by a fourth feature.

The actuator assembly also includes a first part, and a second part coupled to the first part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis. Tn the actuator assembly the first and third features are attached to the first part and the second and fourth features are attached to the second part. Each of the first, second, third and fourth features is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.

The actuator assembly may include any features corresponding to, or resulting from, any features described in relation to the method according to the first aspect and/or the method according to the second aspect.

The first and second features, the first and second parts, and the third and fourth features may be disposed in order along the primary axis. The first and second parts may be sandwiched between the first and second features and the third and fourth features along the primary axis.

The first and second features, the third and fourth features, and the first and second parts may be disposed in order along the primary axis. The first and second features may be disposed on the same side of the first and second parts as the third and fourth features, relative to the primary axis.

The first and second features may be bonded to the first and second parts respectively using adhesive. The first and second features may be welded to the first and second parts respectively. The third and fourth features may be bonded to the first and second parts respectively using adhesive. The third and fourth features may be welded to the first and second parts respectively. Welding may take the form of laser welding or electrical welding.

The bearing arrangement may be a helical flexure comprising a plurality of flexure arms, each flexure arm connecting the first part to the second part.

The actuator assembly may also include one or more ball retention features, each ball retention feature attached to the first part or the second part. Each ball retention feature may be formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.

Each ball retention feature may be attached to the first part or the second part in the same way as the first to fourth features. Additionally or alternatively, the first bearing surfaces and/or the second bearing surfaces may include moulded ball retention feature configured to retain one or more ball bearings in bearing race.

Each detachment site of the first, second, third and fourth features may be visible when the assembly is viewed along at least one direction parallel to the primary axis. Each detachment site of the one or more ball retention features may also be visible when the assembly is viewed along the at least one direction parallel to the primary axis.

The actuator assembly may also include a first flexure for connecting the second feature to the first part. The first flexure may connect the second feature to a seventh feature. The seventh feature may include one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members. The first flexure may connect the second feature to the first feature.

The actuator assembly may also include a second flexure for connecting the fourth feature to the first part. The second flexure may connect the fourth feature to an eighth feature. The eighth feature may include one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members. The second flexure may connect the fourth feature to the third feature.

The actuator assembly may also include one or more additional features attached to the same side of the first part and/or the second part as the first and second features. Each additional feature may be formed from a sheet and include one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members. The actuator assembly may also include one or more further lengths of shape memory alloy, each further length of shape memory alloy wire crimped between the first feature and one of the additional features, between the second feature and one of the additional features, or between a pair of the additional features.

The actuator assembly may also include one or more additional features attached to the same side of the first part and/or the second part as the third and fourth features. Each additional feature may be formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members. The actuator assembly may also include one or more further lengths of shape memory alloy, each further length of shape memory alloy wire crimped between the third feature and one of the additional features, between the fourth feature and one of the additional features, or between a pair of the additional features.

Each of the first, second, third and fourth features, the ball retention features and/or the additional features, along with respective frames and connecting members, may be formed by etching a metal sheet. The metal sheet may by etched using chemical etching or laser etching. Each of the first, second, third and fourth features, the ball retention features and/or the additional features, along with respective frames and connecting members, may be formed by stamping a metal sheet.

The first and second features may have been connected to a common, first frame by respective connecting members prior to completion of the actuator assembly. The third and fourth features may be connected to a common, second frame by respective connecting members prior to completion of the actuator assembly.

A camera may include the actuator assembly according to the first aspect, an image sensor, and a lens attached to the second part.

The camera may include a further actuator assembly attached to the first part and configured to move the first part relative to the image sensor in a direction perpendicular to the primary axis or to rotate the first part relative to the image sensor about two axes perpendicular to each other and to the primary axis.

According to a fifth aspect of the invention, there is provided a patterned metal sheet including a frame, a first feature supporting or defining a first crimp head and connected to the frame by one or more first connecting members, and a second feature supporting a second crimp head and connected to the frame by one or more second connecting members. One or more of the first connecting members are formed as first flexures configured to permit deflection of all or part of the first feature relative to the frame along a primary axis substantially perpendicular to the patterned metal sheet. Additionally or alternatively, one or more of the second connecting members are formed as second flexures configured to permit deflection of the second feature relative to the frame along the primary axis.

First and/or second flexures may be configured to constrain deflection of the corresponding feature(s) relative to the frame in directions perpendicular to the primary axis.

The patterned metal sheet may include any features corresponding to, or resulting from, any features described in relation to the method according to the first aspect, the method according to the second aspect and/or the actuator assembly according to the fourth aspect.

According to a sixth aspect of the invention, there is provided a method of forming an actuator assembly, including crimping a first shape-memory alloy wire to a first patterned sheet. The first patterned sheet includes a first frame, a first feature supporting or defining a first crimp head and connected to the first frame by one or more first connecting members, and a second feature supporting or defining a second crimp head and connected to the first frame by one or more second connecting members. The first shape-memory alloy wire is crimped between the first and second crimp heads. The method also includes assembling the first patterned sheet, a first part and a second part to form a second assembly. The second assembly is configured such that the first feature is attached to the first part, the second feature is attached to the second part, and the first part is coupled to the second part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis. The method also includes severing each of the first and second connecting members to detach the first frame.

The method according to the sixth aspect may include any features corresponding to, or resulting from, any features described in relation to the method according to the first aspect, the method according to the second aspect and/or the actuator assembly according to the fourth aspect.

The method may also include connecting a spring between the first and second parts such that contraction of the first shape-memory alloy wire causes extension of the spring.

The spring may be connected directly between the first part and the second part.

The spring may be connected to a second patterned sheet, the second patterned sheet comprising a second frame, a third feature connected to the second frame by one or more third connecting members, and a fourth feature connected to the second frame by one or more fourth connecting members, wherein the spring is connected between the third and fourth features.

The method may include connecting two or more springs between the first and second parts.

According to a seventh aspect of the invention, there is provided an actuator assembly including a first shape-memory alloy wire crimped between a first crimp head supported by a first feature and a second crimp head supported or defined by a second feature. The actuator assembly also includes a first part and a second part coupled to the first part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis. In the actuator assembly the first feature is attached to the first part and the second feature is attached to the second part. Each of the first and second features is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.

The actuator assembly may include any features corresponding to, or resulting from, any features described in relation to the method according to the first 25 aspect, the method according to the second aspect, the actuator assembly according to the fourth aspect and/or the method according to the sixth aspect.

The actuator assembly may also include a spring connecting between the first and second parts such that contraction of the first shape-memory alloy wire causes extension of the spring.

The spring may be connected between a third feature attached to the first part and a fourth feature attached to the second part. Each of the third and fourth features may be formed from a sheet and include one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.

Two or more springs may be connected between the first and second parts.

A camera may include the actuator assembly according to the seventh aspect, an image sensor, and a lens attached to the second part.

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a camera; Figure 2 is a schematic block diagram of an actuator assembly, for example for use in the camera shown in Figure 1; Figure 3 is a process flow diagram of a method of forming an actuator assembly; Figure 4 is an exploded projection view of an exemplary actuator assembly, as well as a base and screening can for attachment thereto; Figure 5 is a process flow diagram of a method of forming the exemplary actuator assembly; Figure 6 is a plan view of a first patterned sheet for use in forming the exemplary actuator assembly; Figure 7A is a plan view of a second patterned sheet for use in forming the 15 exemplary actuator assembly; Figure 73 is a partial plan view of the second patterned sheet shown in Figure 7A overlying a carriage and chassis shown in Figure 4, and the first patterned sheet shown in Figure 6; Figure 8 is a plan view of an alternative first patterned sheet; Figure 9 is a projection view of the exemplary actuator assembly supported on the base plate in a first orientation; Figure 10 is a projection view of the exemplary actuator assembly supported on a base plate, in a second orientation inverted relative to the first orientation; Figure 11 is a projection view of a lens assembly coupled to the base plate by the exemplary actuator assembly; Figure 12 is a plan view of a modified first patterned sheet; and Figures 13A to 13D are projection views illustrating a jig arrangement and a method for folding terminals of the exemplary actuator assembly.

Detailed Description

In the following, like parts are denoted by like reference numerals.

Camera Referring to Figure 1, a camera 1 incorporating a shape memory alloy (SMA) actuator assembly 2 (herein also referred to as an "SMA actuator" or simply an "actuator") is shown.

The camera 1 includes a first part in the form of a support structure 3, upon which a second part in the form of a lens assembly 4 is suspended by the SMA actuator assembly 2. The SMA actuator assembly 2 supports the lens assembly 4 in a manner allowing one or more movements (or degrees-of-freedom) of the lens assembly 4 relative to the support structure 3. The lens assembly 4 has an optical axis 0.

The first part in the form of the support structure 3 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 (i.e. the base 5 is interposed between the lens assembly 4 and the rear side), there is mounted an integrated circuit (IC) 7 in which a control circuit is implemented, and optionally a gyroscope sensor (not shown). The support structure 3 also includes a screening can 8 which protrudes forwardly from the base 5 to encase and protect the other components of the camera 1.

The second part in the form of the lens assembly 4 includes a lens carriage 9 in the form of a cylindrical body supporting one or more lenses 10 arranged along the optical axis 0. In general, any number of lenses 10 may be included. Preferably, each lens 10 has a diameter of up to about 30 mm. The camera 1 can therefore be referred to as a miniature camera.

The lens assembly 4 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-oxidesemiconductor (CMOS) device.

The lenses 10 are supported on the lens carriage 9 and the lens carriage 9 is supported by the SMA actuator assembly 2 such that the lens assembly 4 is movable along the optical axis 0 relative to the support structure 3, for example to provide focussing or zoom. Although all the lenses 10 are fixed to the lens carriage 9 in this example, in general, one or more of the lenses 10 may be mounted to a component other than the lens carriage 9, and may be fixed in place relative to the image sensor 6, leaving at least one of the lenses 10 attached to the lens carriage and movable along the optical axis 0 relative to the image sensor 6.

This specification is concerned with improved methods of fabricating SMA actuator assemblies 2 which may provide automatic focussing (AF) and/or zoom by translating one or more lenses 10 towards or away from the image sensor 6 along the optical axis 0.

Actuator schematic Referring also so Figure 2, a schematic block diagram of an actuator assembly 2 is shown.

The actuator assembly 2 includes a first, or static part 3 (e.g. the support structure of camera 1). A second, or moveable part 4 (e.g. the lens assembly of camera 1) is coupled to the first part 3 by a bearing arrangement 11. The bearing arrangement 11 is configured to couple a rotation of the second part 4 relative to the first part 3 about a primary axis z into a translation of the second part 4 relative to the first part 3 along the primary axis z. When used in a camera, the primary axis z should be aligned parallel to the optical axis 0. The bearing arrangement 11 may take the form of a helical bearing, or a helical flexure. WO 2019/243849 Al describes examples of helical bearings (see for example Figures 1 to 19 and accompanying description) and helical flexures (see for example Figures 20 to 22 and accompanying description.

Rotation in one sense (for example clockwise) about the primary axis z is provided by actuation of one or more first SMA wires 12 which are connected between the first and second parts 3, 4. Rotation in the opposite sense (for example anti-clockwise) about the primary axis z is provided by actuation of one or more second SMA wires 13 which are connected between the first and second parts 3, 4. An SMA wire 12, 13 may be actuated by passing currents through the SMA wires 12, 13 to generate resistive heating and raise the temperature of an actuated SMA wire 12, 13. Actuation and control of SMA wires is further described in WO 2014/076463. SMA wires 12, 13 may be formed of any SMA material suitable for drawing into wires, for example, Nitinol.

Actuation of the first SMA wire(s) 12 generates rotation in one sense, which is converted by the bearing arrangement 11 into movement of the second part 4 relative to the first part 3 and parallel to the primary axis z, for example away from the first part 3. To move the second part 4 back towards the first part 3, the second SMA wire(s) 13 are actuated instead. The actuator assembly 2 may also include springs, flexures, magnets or other suitable biasing means to urge the first and second parts 3, 4 towards a resting or neutral position when the first and second SMA wire(s) 12, 13 are unpowered.

The present specification concerns improved fabrication techniques for forming actuator assemblies 2, and in particular for providing faster, less complex and cheaper methods for connecting the first and second SMA wires 12, 13 between the first and second parts 3, 4.

Top down assembly method Referring also to Figures 3 to 7B, a method of forming an actuator assembly 2 shall be described.

A first SMA wire 12 is crimped to a first patterned sheet 14 (step Si). Figure 6 illustrates one example of the first patterned sheet 14. The first patterned sheet 14 includes a first frame 15 and a first feature 16 supporting or defining a first crimp head 17. The first feature 16 is connected to the first frame 15 by one or more first connecting members 18. The first patterned sheet 14 also includes a second feature 19 supporting or defining a second crimp head 20. The second feature 19 is connected to the first frame 15 by one or more second connecting members 21. The first SMA wire 12 is crimped between the first and second crimp heads 17, 20, for example as shown in Figure 4 (note Figure 4 shows the first patterned sheet 14 after removal of the first frame 15, described hereinafter).

The first and second connecting members 18, 21 may take the form of sprues, or other structures having similar properties to a sprue, for example a narrow portion of the first patterned sheet 14. Connecting members 18, 21 may be provided by any structure providing sufficient mechanical support to enable forming the actuator assembly 2, whilst being severable without the need to apply so much force/energy that adjacent regions of the patterned sheet 14 become distorted (for example by heat or stress). Any subsequently described connecting members should have the same properties as the first and second connecting members 18, 21.

A second SMA wire 13 is crimped to a second patterned sheet 22 (step 52).

Figure 7A illustrates one example of the second patterned sheet 22. The second patterned sheet 22 includes a second frame 23 and a third feature 24 supporting a third crimp head 25. The third feature 24 is connected to the second frame 23 by one or more third connecting members 26. The second patterned sheet 23 also includes a fourth feature 27 supporting or defining a fourth crimp head 28.

The fourth feature 27 is connected to the second frame by one or more fourth connecting members 29. The second shape-memory alloy wire 13 is crimped between the third and fourth crimp heads 25, 28.

Each of the patterned sheets 14, 22 is formed from a sheet having a uniform thickness. For example, the patterned sheets 14, 22 may be formed by etching (chemical or laser) metal sheets to form the respective frames 15, 23, features 16, 19, 24, 27 and connecting members 18, 21, 26, 29. Alternatively, either of both of the patterned sheets 14, 22 may be stamped from a metal plate, provided that any residual stresses do not cause excessive deformation of the patterned sheets 14, 22. The crimp heads 17, 20, 25, 28 are preferably formed by bending of the respective features 16, 19, 24, 27. Alternatively, the crimp heads 17, 20, 25, 28 may be initially separate components which are attached (e.g. bonded or welded) to the respective features 16, 19, 24, 27.

The first patterned sheet 14, the second patterned sheet 22, a first part 3 and a second part 4 are assembled to form a first assembly 69 (Figure 13A) (step 53). The first assembly is configured such that the first and third features 16, 24 are attached to the first part 3, whilst the second and fourth features 19, 27 are attached to the second part 4. As described hereinbefore, the first and second parts 3, 4 are coupled together by the bearing arrangement 11.

Forming the first assembly 69 (Figure 13A) may include attaching the first and second parts 3, 4 to the first patterned sheet 14, then attaching the second patterned sheet 22 to the first and second parts 3, 4 so that the first and second parts 3, 4 are generally between the first and second patterned sheets 14, 22. In other words, so that the first and second patterned sheets 14, 22 are generally parallel and sandwich the first and second parts 3, 4. Alternatively, forming the first assembly may include attaching the first patterned sheet 14 to the second patterned sheet 22, then attaching the first and second patterned sheets 14, 22 to the first and second parts 3, 4. In this way, the first and second patterned sheets 14, 22 may both be on the same side of the first and second parts 3, 4 with respect to the primary axis z (rotation axis of the bearing arrangement 11).

The patterned sheets 14, 22 may be attached to the first and second parts by one or a mixture of methods including bonding with adhesives, welding (laser or electrical), or any other suitable methods.

The first and second connecting members 18, 21 are severed to detach the first frame 15, and the third and fourth connecting members 26, 29 are severed to detach the second frame 23 (step 54).

In order to facilitate severing the connecting members 18, 21, 26, 29 to detach the frames 15, 23, the first assembly 69 (Figure 13A) is preferably assembled such that each of the first, second, third and fourth connecting members 18, 21, 26, 29 is visible when the assembly is viewed along at least one direction parallel to the primary axis z. For example, the second patterned sheet 22 may include one or more cut-out portions to leave connecting members 18, 21 of an underlying first patterned sheet 14 exposed, or vice versa. Additionally or alternatively, the third and fourth connecting members 26, 29 may be laterally offset relative to the underlying (relative to the primary axis z) first and second connecting members 18, 21, to assist with maintaining accessibility for severance. The same principle is preferably applied to any other connecting members described hereinafter, so that all connecting members may be visible and severable from at least one direction parallel to the primary axis z. The first to fourth connecting members 18, 21, 26, 29 (and any other connecting members described hereinafter) may be severed in any suitable way. Using a laser, for example a spot-welding laser, to melt and/or vaporise connecting members 18, 21, 26, 29 is preferred, although a physical tool may also be used. For example, to snip or shear connecting members 18, 21, 26, 29. Regardless of the method used to sever the connecting members 18, 21, 26, 29, the features 16, 19, 24, 27 of a finished actuator assembly 2 will have observable detachment sites. This is at least in part due to the impracticality of accessing and fine finishing (e.g. sanding) the detachment sites.

The actuator assembly 2 may be used as part of any device requiring translation of the second part 4 relative to the first part 3. Optionally, the actuator assembly 2 may be used as part of a camera 1. Assembly of the camera 1 may occur immediately after the detachment of the frames 14, 23, or after a delay. Assembly of the camera 1 may occur in the same location as fabrication of the actuator assembly 2, or in a different location The first part 3 may be attached to the base 5 for a camera 1, either directly or indirectly (step S5). In some examples, the first part 3 may be attached to the base 5 via a further actuator assembly (not shown) which provides optical image stabilisation functionality, for example by lateral translation (relative to the optical axis 0) and/or tilting of the first part 3 relative to the base 5.

One or more lenses 10 are attached to the second part 4, either directly or using a lens carriage 9 (step 56). In some examples, the second part 4 may be attached to one or more lenses 10 via a further actuator assembly (not shown) which provides optical image stabilisation functionality.

The method allows the first and second SMA wires 12, 13 to be crimped between the corresponding crimp heads 17, 20, 25, 28 whilst the frames 15, 23 maintain fixed relative positions. The frames 15, 23 help maintain the tension of the SMA wires 12, 13 through the process of attachment to the first and second parts 3, 4. It is also possible to simply stack the patterned sheets 14, 22 and the first and second parts 3, 4 so that bonding forces need only be applied in a single direction. This can enable the use of simple, 2D adhesive equipment, whilst ensuring strong and reliable connection of the SMA wires 12, 13 between the first and second parts 3, 4.

The method may be expanded to permit forming many other parts of an actuator assembly 2 as further features of the first and/or second patterned sheets 14, 22, including but not limited to ball-bearing retention features 40 (Figure 6), flexures 46, 50 (Figure 4), and so forth. The method may therefore reduce the number of parts, whilst simplifying and improving reliability when constructing an actuator assembly 2 by holding features in the correct relative positions and orientations to one another using the frames 15, 23. Once the first assembly 69 (Figure 13A) is securely formed, the frames 15, 23 may be detached by severing connecting members 18, 21, 26, 29 to finish the actuator assembly 2. The method may also utilise flexible connecting members, to facilitate assembling features formed as part of a single patterned sheet 14, 22 to different heights within an actuator assembly 2. These effects, amongst others, shall be further illustrated hereinafter with reference to an exemplary actuator assembly 30.

Exemplary actuator assembly Referring in particular to Figures 4 to 7B, a method of forming the exemplary actuator assembly 30 (hereinafter "exemplary actuator") shall be described.

The exemplary actuator 30 is one example of implementing an actuator assembly 2 as shown in Figure 2, and the exemplary actuator 30 is formed using one example of the method shown in Figure 3.

A first SMA wire 12 is crimped to the first patterned sheet 14 (step Si.) and the 35 second SMA wire 13 is crimped to the second patterned sheet 22 (step S2). The first and second patterned sheets 14, 22 as illustrated in the Figures include features beyond the first to fourth features 16, 19, 24, 27, and the properties and functions of these further features are explained hereinafter.

The first patterned sheet 14 is placed and the first and second parts 3, 4 are arranged over and attached to the first patterned sheet 14 (step S3-1). The method of attachment may be as described hereinbefore. The exemplary actuator 30 includes a first part 3 in the form of a chassis 31 and a second part 4 in the form of a carriage 32 (see for example Figure 4). The chassis 31 includes first bearing surfaces 33 which, when assembled, cooperate with second bearing surfaces 34 of the carriage 32 to form ball bearing races. The bearing surfaces 33, 34 are angled and/or curved to form a helical bearing to provide the bearing arrangement 11. Optionally, additional surfaces of the chassis 31 may bear against corresponding surfaces of the carriage 32 to provide additional plain bearings which guide movement of the bearing arrangement 11.

The chassis 31 and carriage 32 may be formed, for example, by injection moulding polymers, by casting of polymers or metals, by stamping and/or deep drawing of metal materials, or in any other suitable way. Preferably the chassis 31 and carriage 32 are formed of electrical insulating materials to avoid the need for additional insulation of the SMA wires 12, 13. Either or both of the chassis 31 and carriage 32 may optionally include protrusions 36 arranged to be received by registration through-holes 37 of the first and second features 16, 19. The protrusions 36 received into through-holes 37 may additionally function as heat stakes to provide additional strength to a bond between plastic and metal components.

One or more ball bearings 35 are inserted into each ball bearing race formed between the first and second bearing surfaces 33, 34 (step 53-2).

The second patterned sheet 22 is placed over and attached to the first pare 3 (chassis 31) and the second part 4 (carriage 32) (step 53-3). The method of attachment may be as described hereinbefore. Either or both of the chassis 31 and carriage 32 may optionally include protrusions 36 arranged to be received by registration through-holes 37 of the third and fourth features 24, 27.

The connecting members 18, 21, 26, 29 are severed to detach the frames 15, 23 (step 54) as described hereinbefore. Referring in particular to Figure 7B, connecting members 18, 21, 26, 29 of the first and second patterned sheets 14, 22 may be observed to be offset from one another so that all are visible and accessible to be severed after attachment of the second patterned sheet 22. Additionally, the second patterned sheet 22 includes a cut-out portion 38 to leave connecting members of the underlying first patterned sheet 14 exposed and accessible.

An annular plate 39 having a generally square or rectangular outer perimeter and a circular inner perimeter may optionally be attached (step S5) to the first patterned sheet 14 and/or the first part 3 before, after or concurrently with attaching the first patterned sheet 14 to the first and second parts 3, 4. The plate 39 may provide, or form part of, the base 5 of a camera 1.

When the exemplary actuator 30 is being included in a camera 1, a screening can 8 may be secured to cover the exemplary actuator 30 (step 56), either before or after attachment of one or more lenses 10 to the carriage 32.

Ball bearing handling There are a number of options for placing/inserting the ball bearings 35 (step S3-2).

The first and/or second bearing surfaces 33, 34 may be greased prior to assembly to form the bearing races, which may assist with insertion of the ball bearings 35 irrespective of the handling method used ball bearings 35. Ball bearing 35 positioning may be performed using known pick-and-place machinery, either off-the shelf or modified in accordance with the following

descriptions.

In one example, placing each ball bearing 35 (step 53-2) uses a suction tube (not shown) to pick up each ball bearing 35 from a hopper (not shown), followed by locating the suction tube (not shown) over an opening to a bearing race formed between bearing surfaces 33, 34, and modifying (e.g. decreasing) the suction to drop the ball bearing 35 into the bearing race. To assist this method, and any method described hereinafter, the first and/or second bearing surfaces 33, 34 defining a bearing race may be chamfered to increase the size of an opening for ball bearing 35 placement. Ball bearings 35 and associated suction tubes (not shown) may be of the order of 1 mm diameter.

Two or more suction tubes may (not shown) be used to place two or more ball bearings 35 in a single step. The suction tubes (not shown) may optionally be configured to follow helical paths for insertion of ball bearings part-way along corresponding bearing races formed between bearing surfaces 33, 34. The suction tubes (not shown) may be attached to a tool (for example hand held) which includes features configured to cooperate with one or more features of the first part 3, 31, the second part 4, 32, the first patterned sheet 14 and/or the second patterned sheet 22, so as to locate the suction tubes relative to the bearing races.

In another example, placing each ball bearing 35 (step S3-2) may include applying grease to the first bearing surfaces 33, followed by placing one or more ball bearings 35 on each first bearing surface 33, retained in position by the grease. The second part 4 (carriage 32) may then be positioned relative to the first part 3, 31 so as to complete the bearing races about the ball bearings 35. The placement may be made using one or more suction tubes (not shown) as described hereinbefore.

During the placement of ball bearings (step S3-2), it may be beneficial to orientate (twist and/or tilt) the second part 4 (carriage 32) relative to the first part 3 (chassis 31) so that the gaps between bearing surfaces 33, 34 are increased and the targeting accuracy requirements of the ball loading process are reduced. The second part 4 (carriage 32) is correctly aligned with the first part 3 (chassis 32) after the ball bearings 35 have been loaded.

The suction ball retention tubes could be replaced with one or more electromagnets that hold individual ball bearings.

Ball bearing retention There are a number of options for retaining ball bearings 35 within their respective races. For example, retaining features may be insert moulded into a chassis 31 and carriage 32 formed from plastic. Alternatively, retaining features may be formed as part of the base 5 (for example plate 39) and/or the screening can 8, for example by creating depressions in regions which will align with the bearing races formed between bearing surfaces 33, 34. Instead of depressions, retaining features may be formed as strips of metal cut out of the base 5 (for example plate 39) and/or screening can 8, then folded/deformed towards the openings of bearing races. Still another option is to weld, or otherwise attach, retaining features to the base 5 (for example plate 39) and/or the screening can 8. These options may provide good strength of the bearing retentions, and additional processing steps are not needed when constructing an actuator 2, 30 or camera 1. However, high precision of alignment between parts is needed.

An alternative approach is to form ball bearing retaining features 40 as part of the first and/or second patterned sheets. This may help to provide reliable alignment of retaining features with ball bearing races.

Referring in particular to Figure 6, the first feature 16 may include retaining features 40 in the form of widened regions, each arranged and dimensioned to at least partially occlude the entrance to one end of a bearing race formed between a pair of bearing surfaces 33, 34.

The first patterned sheet 14 also includes a retaining feature 40 in the form of a fifth feature 41 which is connected to the first frame 15 by one or more fifth connecting members 42. In the exemplary actuator 30, the fifth feature 41 is also connected to the second feature 19 by an optional, further connecting member 43. The fifth feature 41 is for attachment to the first part 3 in the form of the chassis 31, and is arranged and dimensioned to at least partially occlude the entrance to one end of a bearing race formed between a pair of bearing surfaces 33, 34. During assembly, the fifth connecting members 42 are severed in the same way as first to fourth connecting members 18, 21, 26, 29, preferably during the same process step (step 54). Any further connecting members 43 are also severed in the same way (and preferably during the same step), to enable movement of the second part 4 (carriage 32) relative to the first part 3 (chassis 31).

In other examples, the fifth feature 41 could instead by integrally formed with the second feature 19 for connection to the second part 4 (carriage 32).

Although only one fifth feature 41 is shown in Figure 6, in other examples, two or more fifth features 41 may be included, each providing one or more retaining features 40. Each fifth feature 41 may include further registration through-holes 37 for receiving protrusions 36 of the first part 3 (or second part 4).

The other ends of each bearing race may be at least partially occluded by retaining features 40 formed as part of the second patterned sheet 22. For example, referring in particular to Figure 7A, a retaining feature 40 is formed as part of the third feature 24 in the same (or an analogous) way as the retaining features 40 of the first feature 16. The second patterned sheet 22 also includes a pair of retaining features 40 in the form of sixth features 44 connected to the second frame 23 by sixth connecting members 45. One of the sixth features 44 is also connected to the fourth feature 27 by a further connecting member 43, however this is not essential. For the exemplary actuator 30, the sixth features 44 are for attachment to the first part 3 (chassis 31), and are arranged and dimensioned to at least partially occlude the entrance to one end of a bearing race formed between a pair of bearing surfaces 33, 34. During assembly, the sixth connecting members 45 are severed in the same way as first to fourth connecting members 18, 21, 26, 29, preferably during the same process step (step S4). Any further connecting members 43 are also severed in the same way (and preferably during the same step) to permit the second part 4 (carriage 32) to more relative to the first part 3 (chassis 31).

In other examples, the sixth features 44 could instead by integrally formed with the fourth feature 27 for connection to the second part 4 (e.g. carriage 32).

Although two sixth features 44 are shown in Figure 7A, in other examples, fewer or more sixth features 44 may be included, each providing a retaining feature 40. Each sixth feature 44 may include further registration through-holes 37 for receiving protrusions 36 of the first part 3 (or second part 4).

Hex ures The exemplary actuator 30 includes flexures 46, 50 to provide return paths 46, 50 for electrical currents used to actuate the SMA wires 12, 13. Alternatively or additionally, the flexures 46, 50 may have a role in loading the bearing arrangement 11 (for example, to maintain contact between the ball bearings 35 and the surfaces 33, 34 forming the bearing race) and/or urging the first and second parts 3, 4 towards a resting or neutral position when the first and second SMA wire(s) 12, 13 are unpowered.

In some examples, as illustrated in Figures 4 to 73, the flexures 46, 50 may be formed as parts of the first and/or second patterned sheets 14, 22. This may help to simplify assembly, as well as to reduce the number of parts and connections required.

Referring in particular to Figure 6, the first patterned sheet 14 further includes a first flexure 46 for connecting the second feature 19 to the first part 3 (chassis 31). The first patterned sheet 14 for the exemplary actuator 30 further includes a seventh feature 47, and the first flexure 46 take the form of a narrow, substantially arcuate strip connecting the second feature 19 to the seventh feature 47. The seventh feature 47 is attached to the first part 3 when assembled, and in this way the first flexure 46 connects the first and second parts 3, 4 via the second and seventh features 19, 47.

The seventh feature 47 is connected to the first frame 15 by seventh connecting members 48. The seventh connecting members 48 are relatively elongated to provide enough flexibility to enable deflection of the seventh feature 47 relative to the first frame 15 along the primary axis z during the assembly. This allows the seventh feature 47 to be assembled at a different vertical height than the first and/or second features 16, 19 during assembling. Referring in particular to Figure 4, the seventh feature 47 is connected to a downwardly protruding ridge 49 (relative to the primary axis z) of the chassis 31. This may be useful in order to preload the first flexure 46 in a direction parallel to the primary axis z. The seventh connecting members 48 are detached during assembly in the same way as the connecting members 18, 21, 26, 29, 42, 45 described hereinbefore. The seventh connecting members 48 need not all be detached in the same process step (see descriptions of folding electrical terminals hereinafter). The seventh connecting members 48 may be configured to resist lateral deflections (along x and/or y axes as illustrated), whilst permitting vertical deflections (along primary axis z). For example, by controlling the width of the seventh connecting members 48 to be larger than a thickness of the first patterned sheet 14.

In other examples, the seventh feature 47 may be omitted, and the first flexure 46 may be formed to connect directly between the first and second features 16, 19 (in such an example the first SMA wire 12 should be insulated from the first and second features 16, 19 to prevent shorting via the first flexure 46).

Additionally or alternatively, the second patterned sheet 22 may include a second flexure 50 for connecting the fourth feature 27 to the first part 3. Referring in particular to Figure 7A, the second patterned sheet 22 includes an arcuate second flexure 50 similar to the first flexure, except connecting between the fourth feature 27 and an eighth feature 51. The eighth feature 51 is connected to the second frame 23 by eighth connecting members 52 which, in the same way as the seventh connecting members 48, are configured to be flexible enough to permit deflection of the eighth feature 51 relative to the second frame 23 along the primary axis z during assembly. In the illustrated example, two of the eighth connecting members 52 are elongated along respective straight lines, whilst a third is elongated in a 3-shaped hairpin/switchback. Flexibility of the eighth connecting members 52 allows multi-level assembly in the same way as the seventh connecting members 47. In the exemplary actuator 30 the eighth feature 51 is attached to an upwardly protruding ridge 53 (relative to the primary axis z) of the chassis 31.

In other examples, the eighth feature 51 may be omitted, and the second flexure 50 may be formed to connect directly between the third and fourth features 24, 27 (in such an example the second SMA wire 13 should be insulated from the third and fourth features 24, 27 to prevent shorting via the second flexure 50).

In other examples, the seventh and/or eighth connecting members 47, 52, need not be formed to be flexible. Equally, any or all of the first to sixth connecting members 18, 21, 26, 29, 42, 45 may be made flexible in the same way as the seventh and eighth connecting members 47, 52, in order to facilitate multi-level assembly of features formed from the first and/or second patterned sheets 14, 22. Any or all such flexible connecting members 18, 21, 26, 29, 42, 45, 47, 52 may be formed to allow displacements along the primary axis z, whilst suppressing lateral displacements (along xly axes).

Advantages of using flexible connecting members 18, 21, 26, 29, 42, 45, 47, 52 may include, without being limited to, improved repeatability over forming to different heights within the assembly; improved accuracy because features can be on the same patterned sheet 14, 22 and consequently do not require alignment via holes, which would add extra components and extra tolerance to the overall tolerance loop; and requiring fewer parts which reduces cost, time and complexity of assembling and actuator 2, 30.

Electrical connections An advantage of using separate seventh and eighth features 47, 51 for connection of the first and second flexures 46, 50 is that the flexures 46, 50 may more conveniently provide electrical return paths for the SMA wires 12, 13.

Referring in particular to Figures 4, 6 and 7A, the first feature 16 includes a portion which, after attachment, is bent about a line perpendicular to the primary axis z to provide a first terminal 54. The seventh feature 47 also include a portion which, after attachment, is bent about a line perpendicular to the primary axis z to provide a second terminal 55. Once the first SMA wire 12 is connected between first and second crimp heads 17, 20, an electrical path between the first and second terminals 54, 55 is completed, allowing a current to be applied to actuate the first SMA wire 12 (by resistive heating).

Similarly, the third and eighth features 24, 51 include portions which, after attachment, are each bent about a line perpendicular to the primary axis z to provide respective third and fourth terminals 56, 57. Once the second SMA wire 13 is connected between third and fourth crimp heads 25, 28, an electrical path between the third and fourth terminals 56, 57 is completed, allowing a current to be applied to actuate the second SMA wire 13 (by resistive heating).

The first and/or second patterned sheets 14, 22 may include one or more alignment features configured to cooperate with a tool or jig used to assemble the first assembly. For example, referring in particular to Figures 6 and 7A, the first and second patterned sheets 14, 22 also include slots 58 and through holes 59 arranged to receive extensions of a tool/or jig (not shown) to facilitate accurate alignment during assembly.

The first and second patterned sheets 14, 22 of the exemplary actuator 30 each include an optional temporary support extension 60 of the respective frames 15, 23. The temporary support extensions 60 may be useful to provide additional mechanical support to features of the patterned sheets 14, 22 during the assembly process. The temporary support extensions 60 are subsequently removed along with the rest of the respective frames 15, 23.

Alternative first patterned sheet Referring also to Figure 8, an alternative first patterned sheet 61 is shown.

The alternative first patterned sheet 61 includes the same elements as the first patterned sheet 14, except that many are shaped differently. For example, the fifth feature 41 of the alternative first patterned sheet 61 is elongated and provides a pair of retaining features 40 at either end. Another difference is that the temporary support extension 60 of the alternative first patterned sheet 61 has an arcuate shape. The flexible seventh connecting member 48 of the alternative first patterned sheet 61 has a serpentine configuration, instead of a straight or J-shaped configuration. Other differences shall be apparent from comparison of Figures 6 and 8.

Although only an alternative first patterned sheet 61 has been described and illustrated, the same or similar modifications may be made to the second patterned sheet 22.

Anti-snagging assembly The use of first to fourth features 16, 19, 24, 27 to support (or form) crimp heads 17, 20, 25, 28, whilst being connected to respective frames 15, 23, allows the SMA wires 12, 13 to be easily crimped without excess slack. Nonetheless, some slack is inevitable, and freedom of movement provided between the first and second parts 3, 4 by the bearing arrangement 11 means that the weight of the second part 4 (e.g. carriage 32) will urge rotation of the second part 4, causing one SMA wire 12, 13 to be tensioned (pulled taut) whilst the other SMA wire 12, 13 is slackened. Which SMA wire 12, 13 is tensioned and which slackened depends on the sense of rotation urged by weight of the second part 4, and does not necessarily correspond with which SMA wire 12, 13 is uppermost relative to gravity. During further steps to assemble an actuator 2, 30 into a device, for example camera 1, there is a risk that a slackened SMA wire 12, 13 may become trapped between parts of the actuator 2, 30 and the base 5 (e.g. plate 39), the screening can 8, one or more lenses 10, or any other parts to be connected to the actuator 2, 30 (or close to it). A slackened SMA wire 12, 13 may also become fouled with adhesive, causing it to stick to other components even if not physically trapped.

One way to reduce the chance of snagging and/or fouling of SMA wires 12, 13 is to take advantage of the tensioning effect of the weight of the second part 4 (e.g. carriage 32) by varying the orientation of the assembly during the method.

Referring also to Figures 9 to 11, attachment of the exemplary actuator 30 to the plate 39 providing (or forming part of) base 5 (step S5) and a lens assembly 64 (step S6) of a camera 1 are illustrated.

The first part 3 has a first attachment surface 62, for example the bottom surface (relative to the primary axis z) of the chassis 31 and/or the first feature 16 attached thereto. Optionally, the bottom surface(s) of fifth and/or seventh features 41, 47 may also provide parts of the first attachment surface 62. Similarly, the second part 4 has a second attachment surface 63, for example the top surface (relative to the primary axis z) of the carriage 32 and/or the fourth feature 37 attached thereto. In the exemplary actuator 30, the first attachment surface 62 is offset from the second attachment surface 63 along the primary axis z, and the first SMA wire 12 is offset from the second SMA wire 13 along the primary axis z. The actuator assembly 2, 30 may be attached to a first camera component via the first attachment surface 62 while orienting the actuator assembly such that a weight of the second part 4 produces a torque on the second part 4 about the primary axis z that applies tension to the first shape memory alloy wire 12.

For example, for attaching the exemplary actuator 30 to the plate 39 providing (or forming part of) the base 5 (step S5), the exemplary actuator 30 is oriented with the primary axis z oriented downwards relative to gravity, as illustrated in Figure 10. The configuration of the exemplary actuator 30 causes the first SMA wire 12 to be tensioned by the weight of the carriage 32 acting on the bearing arrangement 11. The exemplary actuator 30 is then attached to the plate 39 (e.g. bonded with adhesive).

Once the attachment to the first camera component is completed and any adhesives have been cured or allowed time to dry/set, the actuator assembly 2, is subsequently attached to a second camera component via the second attachment surface 63, while orienting the actuator assembly 2, 30 such that a weight of the second part 4 produces a torque on the second part 4 about the primary axis z that applies tension to the second shape memory alloy wire 13.

For example, for attaching the exemplary actuator 30 to one or more lens(es) 10 (step S6), the exemplary actuator 30 is oriented with the primary axis z upwards relative to gravity, as illustrated in Figure 9. A lens assembly 64 including one or more lenses 10 is then attached to the carriage 32 (e.g. bonded with adhesives).

The lens assembly 64 bonded to the plate 39 via the exemplary actuator 30 is illustrated in Figure 11, once more oriented with the primary axis z oriented upwards relative to gravity.

When the screening can 8 is attached to the base 5 (plate 39) and/or the first part 3 (chassis 31), the exemplary actuator 30 is again oriented with the primary axis z downwards relative to gravity.

Balanced torque actuator The exemplary actuator 30 described hereinbefore uses a single SMA wire 12, 13 to impart rotation in each direction (clockwise and anti-clockwise). However, the same principles of assembly using patterned sheets 14, 22 may be applied to constructing actuator assemblies 2 which use two or more first SMA wires 12 and/or two or more second SMA wires 13. For example, torque may be applied using a pair of first SMA wires 12 and a pair of second SMA wires 13 so that there is no (or substantially no) net force applied perpendicular to the primary axis z. Referring also to Figure 12, a modified first patterned sheet 65 is shown, to which a pair of first SMA wires 12a, 12b are crimped.

The modified first patterned sheet 65 is similar to the first patterned sheet 14 and/or the alternative first patterned sheet 61, and only those aspects of the modified first patterned sheet 65 which are different shall be explicitly described.

The modified first patterned sheet 65 includes a pair of first features 16a, 16b, each of which supports (or forms) a respective first crimp head 17a, 17b. The first features 16a, 16b and first crimp heads 17a, 17b are illustrated as having two-fold rotational symmetry about a position 66 corresponding, when assembled, to the primary axis z of the bearing arrangement 11. Other types of symmetry may also provide the desired balancing of forces applied perpendicular to the primary axis z, for example three-fold symmetry and so forth.

Similarly, the modified first patterned sheet 65 includes a pair of second features 19a, 19b, each of which supports (or forms) a respective second crimp head 20a, 20b. The second features 19a, 19b and second crimp heads 20a, 20b are illustrated as having two-fold rotational symmetry about the position 66. The second features 19a, 19b are connected to one another by an annular ring structure 67, although in other examples the second features 19a, 19b need not be connected. Other types of symmetry may also provide the desired balancing of forces applied perpendicular to the primary axis z, for example three-fold symmetry and so forth.

Any features described in relation to the first patterned sheet 12, for example a first flexure 46 (or multiple first flexures), flexible connecting members, and so forth, may also be implemented for the modified first patterned sheet 65. Although only a modified first patterned sheet 65 has been described and illustrated, the second patterned sheet 22 may be modified in the same or an analogous way.

The configuration of the modified first patterned sheet 65 may apply a net torque about the primary axis z of the bearing arrangement 11 without applying a net force to the bearing arrangement. This may improve performance of the bearing arrangement 11 and/or permit use of helical flexures as an alternative to bearings.

Using two or more first SMA wires 12 and two or more second SMA wires 13 may also enable heavier lenses 10 to be coupled to the second part 4 without losing response speed. This effect may be obtained even in examples (not shown) which uses two or more first and/or second SMA wires 12, 13 which are not configured to reduced or eliminate net lateral forces.

Method and jig for terminal bending.

As described hereinbefore, first to fourth terminals 54, 55, 56, 57 may be integrally formed with the first, third, seventh and eighth features 16, 24, 47, 51.

This allows for convenient assembly, with minimum complexity and numbers of parts. However, the subsequent step of folding (bending) the terminals 54, 55, 56, 57 into their final orientations (aligned parallel or more towards parallel with the primary axis z than not), risks unwanted deformation of the attached first, third, seventh and/or eighth features 16, 24, 47, 51.

Referring also to Figures 13A to 13D, a jig arrangement 68 developed to mechanically support the patterned sheets 14, 22 during folding of the terminals 54, 55, 56, 57 is shown.

The jig arrangement 68 is utilised during the process of severing the connecting members 18, 21, 26, 29, 42, 45, 47, 52 (step S4), and divides the severing process into two stages.

Referring in particular to Figure 13A, the first assembly 69 (alternatively "stack") of the first patterned sheet 14, the first part 3, second part 4 and the second patterned sheet 22 is shown for the exemplary actuator 30, clamped in the jig arrangement 68.

The jig arrangement 68 includes a first block 70 and a second block 71. The first assembly 69 is clamped between the first and second blocks 70, 71. For example, as illustrated in Figure 13A, the first block 70 may include holes 72 for receiving bolts (not shown), which are screwed into threaded holes (not shown) of the second block 71. Such an arrangement is only for exemplary purposes, and any other suitable clamping arrangement may be used instead.

The first block 70 includes an aperture 73 into which a third block 74 is received. The first block 70 also includes a cut-away section 75 which leaves the part of the first assembly 69 in which the terminals 54, 55, 56, 57 exposed. The cutaway section 75 communications with the aperture 73 through a gap 76 in a wall 77. The sides of the aperture 73 constrain the third block to move along the primary axis z relative to the first assembly 69, and biasing means (not shown) press the third block 74 down against the second patterned sheet 22 which the first patterned sheet is 14 is supported.

The second block 71 also includes a cut-way portion or aperture (not shown), to leave space which terminals 54, 55, 56, 57 may be folded into. Similarly, the first patterned sheet 14 should include a cut-away 78 (illustrated in Figure 6) to allow folding the third and fourth terminals 56, 57 down through the nominal plane of the first patterned sheet 14.

Referring in particular to Figure 13B, a zoomed in view of the area of the first assembly 69 corresponding to the terminals 54, 55, 56, 57 is shown, with the first block 70 omitted for visual purposes.

The connecting members 18, 26, 48, 52 connecting the terminals 54, 55, 56, 57, 58 to the respective frames 15, 23 are severed, using the access provided by the cut-away section 75 in the first block 70. Other connecting members 18, 21, 26, 29, 42, 45, 47, 52 are left connected at this stage. The configuration of the stack 69 clamped in the jig arrangement 68 after severance of the connecting members 18, 26, 48, 52 connecting the terminals 54, 55, 56, 57, 58 is shown in Figure 13C.

The terminals 54, 55, 56, 57 are subsequently folded (bent) down in order to lie parallel, substantially parallel, or at least at an acute angle, with the normal to the first and second patterned sheets 14, 12. The force biasing the third block 74 against the second patterned sheet 22 needs to be sufficient to prevent the first, third, seventh and eighth features 16, 24, 47, 51, or significant parts thereof, from being deformed out of contact with the first part 3 (chassis 31) during the folding (bending) process. The bending of the terminals 54, 55, 56, 57 may involve a further block (not shown) which is applied laterally.

Once any adhesives used as set/cured, the stack 69 may be removed from the jig arrangement 68 for severance of all remaining connecting members 18, 21, 26, 29, 42, 45, 47, 52 to detach the frames 15, 23. In other examples, the jig arrangement 68 may be configured to allow access to all connecting members 18, 21, 26, 29, 42, 45, 47, 52, so that the first assembly 69 may be kept clamped in the jig arrangement 68 until whilst all remaining connecting members 18, 21, 26, 29, 42, 45, 47, 52 are severed.

The stack 69 may be assembled within the jig arrangement 68, for example the first patterned sheet 14, the first part 3, the second part 4 and the second patterned sheet 22 may be laid in sequence over the second block 71, along with any adhesives, prior to clamping the first block 70 and third block 74. The third block 74 may be fixed to the first block 70 via the biasing means (not shown), of the third block 74 may be entirely removable from the aperture 74 and the biasing may be provided by separate biasing means (not shown) such as a spring or flexure.

It will be appreciated that there may be many other variations of the above-5 described embodiments.

Actuator assemblies 2, 30 have been described which include first SMA wire(s) 12 which oppose (and are opposed by) second SMA wire(s) 13. In other words, contraction of the first SMA wire(s) 12 causes extension of the second SMA wire(s) 13 and vice versa. In this way, movement of the second part 4 relative to the first part 3 in either direction along the primary axis z is possible by actuation of the corresponding first or second SMA wire(s) 12, 13.

However, the assembly methods and features of patterned sheets described in relation to fabrication of the actuator assemblies 2, 30 are equally applicable to actuator assemblies (not shown) in which either (but not both) of the first and second SMA wire(s) 12, 13 is replaced by one or more springs (not shown). For example, the second SMA wire(s) 13 and second patterned sheet 22 may be omitted, and one or more springs (not shown) may be coupled directly between the first and second parts 3, 4. Alternatively, a spring (not shown) may be connected between the third and fourth features 24, 27 of a modified second patterned sheet 22 (e.g. replacing crimp heads 25, 28 with elements for connection to the spring(s)), and the second patterned sheet 22 may be assembled as described in relation to the actuator assemblies 2, 30. In either case, motion of the second part 4 in one direction is achieved by contracting the first SMA wire(s), whilst motion in the opposite direction is achieved by relaxing the first SMA wire(s) (e.g. by reducing the applied current to permit cooling) to permit contraction of the spring(s).

Alternatively, the first SMA wire(s) 12 may be replaced by one or more springs (whether coupled directly between the first and second parts 3, 4, or using a modified first patterned sheet 14).

The actuator assembly 2 may be any type of assembly that comprises a first part which is movable with respect to a second part.

Claims

Claims 1. A method of forming an actuator assembly comprising: crimping a first shape-memory alloy wire to a first patterned sheet, the first patterned sheet comprising a first frame, a first feature supporting or defining a first crimp head and connected to the first frame by one or more first connecting members, and a second feature supporting or defining a second crimp head and connected to the first frame by one or more second connecting members, wherein the first shape-memory alloy wire is crimped between the first and second crimp heads; crimping a second shape memory alloy wire to a second patterned sheet, the second patterned sheet comprising a second frame, a third feature supporting a third crimp head and connected to the second frame by one or more third connecting members, and a fourth feature supporting or defining a fourth crimp head and connected to the second frame by one or more fourth connecting members, wherein the second shape-memory alloy wire is crimped between the third and fourth crimp heads; assembling the first patterned sheet, the second patterned sheet, a first part and a second part to form a first assembly, wherein the first assembly is configured such that the first and third features are attached to the first part, the second and fourth features are attached to the second part, and the first part is coupled to the second part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis; severing each of the first and second connecting members to detach the first frame and severing each of the third and fourth connecting members to detach the second frame.
2. A method according to claim 1, wherein forming the first assembly comprises: attaching the first and second parts to the first patterned sheet; attaching the second patterned sheet to the first and second parts so that the first and second parts are generally between the first and second patterned 35 sheets.
3. A method according to claim 1, wherein forming the first assembly comprises: attaching the first patterned sheet to the second patterned sheet; attaching the first and second patterned sheets to the first and second parts.
4. A method according to any one of claims 1 to 3, wherein one or more of the first connecting members are formed as flexures configured to permit deflection of all or part of the first feature relative to the first frame along the primary axis; and/or one or more of the second connecting members are formed as second flexures configured to permit deflection of the second feature relative to the first frame along the primary axis.
5. A method according to any one of claims 1 to 4, wherein one or more of the third connecting members are formed as flexures configured to permit deflection of all or part of the third feature relative to the second frame along the primary axis; and/or one or more of the fourth connecting members are formed as fourth flexures configured to permit deflection of the fourth feature relative to the second frame along the primary axis.
6. A method according to any one of claims 1 to 5, wherein the bearing arrangement is a helical flexure comprising a plurality of flexure arms, each flexure arm connecting the first part to the second part.
7. A method according to any one of claims 1 to 5, wherein the bearing arrangement is a helical bearing comprising: a plurality of first bearing surfaces defined by the first part; a plurality of second bearing surfaces defined by the second part; wherein the first assembly is configured such that each first bearing surface cooperates with a corresponding second bearing surface to define a bearing race which contains one or more ball bearings.
8. A method according to claim 7, wherein the first patterned sheet comprises a fifth feature connected to the first frame by one or more fifth connecting members; wherein the first assembly is configured such that the fifth feature is attached to the first part or the second part and arranged to retain ball bearings within one or more bearing races; wherein detaching the first frame comprises severing each of the fifth connecting members.
9. A method according to claims 7 or 8, wherein the second patterned sheet comprises a sixth feature connected to the second frame by one or more sixth connecting members; wherein the first assembly is configured such that the sixth feature is attached to the first part or the second part and arranged to retain ball bearings within one or more bearing races; wherein detaching the second frame comprises severing each of the sixth connecting members.
10. A method according to any one of claims 7 to 9, wherein forming the first assembly comprises placing one or more ball bearings into each of the bearing races.
11. A method according to claim 10, wherein placing each ball bearing comprises: using a suction tube to pick up the ball bearing from a hopper; locating the suction tube over an opening to a bearing race; modifying the suction to drop the ball bearing into the bearing race.
12. A method according to claim 10, wherein placing each bearing comprises: applying grease to the first bearing surfaces; placing one or more ball bearings on each first bearing surface so as to be retained in position by the grease; assembling the second part to the first part so as to complete the bearing races about the ball bearings.
13. A method according to claim 10 or claim 11, wherein placing each bearing comprises: applying grease to the first bearing surfaces and/or the second bearing surfaces; assembling the second part to the first part so as to form the bearing races; placing one or more ball bearings into each of the bearing races.
14. A method according to any one of claims 1 to 13, wherein the first patterned sheet further comprises a first flexure for connecting the second feature to the first part.
15. A method according to any one of claims 1 to 14, wherein the second patterned sheet further comprises a second flexure for connecting the fourth feature to the first part.
16. A method according to any one of claims 1 to 15, wherein the first assembly is configured such that each of the first, second, third and fourth connecting members is visible when the assembly is viewed along at least one direction parallel to the primary axis.
17. A method according to any one of claims 1 to 16, wherein the first and second frames are detached using a laser to sever each of the first, second, third and fourth connecting members.
18. A method according to any one of claims 1 to 15, wherein one or more further lengths of shape memory alloy wire are crimped to the first patterned sheet and/or wherein one or more further lengths of shape memory alloy wire are crimped to the second patterned sheet.
19. A method according to any one of claims 1 to 18, wherein the first patterned sheet comprises one or more first terminal connections extending from the first feature and/or the second feature, and the second patterned sheet comprises one or more second terminal connections extending from the third feature and/or the fourth feature; wherein assembling the first patterned sheet, the second patterned sheet, the first part and the second part to form the first assembly comprises: clamping the first patterned sheet, the second patterned sheet, the first part and the second part using a jig, wherein the jig is configured to leave the first terminal connections and the second terminal connections physically accessible; bending each of the first terminal connections to make an angle less than 90 degrees to the primary axis and bending each of the second terminal connections to make an angle less than 90 degrees to the primary axis; removing the jig after bending the first and second terminal connections.
20. A method of fabricating a camera comprising: providing an actuator assembly fabricated by a method according to any one of claims 1 to 20, wherein the first part has a first attachment surface and the second part has a second attachment surface, wherein the first attachment surface is offset from the second attachment surface in a first direction along the primary axis and the first shape memory alloy wire is offset from the second shape memory alloy wire in the first direction along the primary axis; attaching the actuator assembly via the first attachment surface to a first 20 camera component while orienting the actuator assembly such that a weight of the second part produces a torque on the second part about the primary axis that applies tension to the first shape memory alloy wire; and/or attaching the actuator assembly via the second attachment surface to a second camera component while orienting the actuator assembly such that a 25 weight of the second part produces a torque on the second part about the primary axis that applies tension to the second shape memory alloy wire.
21. An actuator assembly fabricated using the method according to any one of claims 1 to 19 or a camera fabricated using the method of claim 20.
22. An actuator assembly comprising: a first shape-memory alloy wire crimped between a first crimp head supported by a first feature and a second crimp head supported or defined by a second feature; a second shape-memory alloy wire crimped between a third crimp head supported by a third feature and a fourth crimp head supported or defined by a fourth feature; a first part; a second part coupled to the first part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis; wherein in the actuator assembly the first and third features are attached to the first part and the second and fourth features are attached to the second part; wherein each of the first, second, third and fourth features is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or 15 more connecting members.
23. An actuator assembly according to claim 22, wherein first and second features, the first and second parts, and the third and fourth features are disposed in order along the primary axis.
24. An actuator assembly according to claim 22, wherein first and second features, the third and fourth features, and the first and second parts are disposed in order along the primary axis.
25. An actuator assembly according to any one of claims 22 to 24, wherein the bearing arrangement is a helical flexure comprising a plurality of flexure arms, each flexure arm connecting the first part to the second part.
26. An actuator assembly according to any one of claims 22 to 24, wherein the bearing arrangement is a helical bearing comprising: a plurality of first bearing surfaces defined by the first part; a plurality of second bearing surfaces defined by the second part; wherein the first assembly is configured such that each first bearing surface cooperates with a corresponding second bearing surface to define a bearing race which contains one or more ball bearings.
27. An actuator assembly according to claim 26, further comprising one or more ball retention features, each ball retention feature attached to the first part or the second part; wherein each ball retention feature is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.
28. An actuator assembly according to any one of claims 22 to 27, wherein each detachment site of the first, second, third and fourth features is visible when the assembly is viewed along at least one direction parallel to the primary axis.
29. An actuator assembly according to any one of claims 22 to 28, further comprising a first flexure for connecting the second feature to the first part.
30. An actuator assembly according to any one of claims 22 to 29, further comprising a second flexure for connecting the fourth feature to the first part.
31. An actuator assembly according to any one of claims 22 to 30, further comprising: one or more additional features attached to the same side of the first part and/or the second part as the first and second features, wherein each additional feature is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members; one or more further lengths of shape memory alloy, each further length of shape memory alloy wire crimped between the first feature and one of the additional features, between the second feature and one of the additional features, or between a pair of the additional features.
32. An actuator assembly according to any one of claims 22 to 31, further comprising: one or more additional features attached to the same side of the first part and/or the second part as the third and fourth features, wherein each additional feature is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members; one or more further lengths of shape memory alloy, each further length of 5 shape memory alloy wire crimped between the third feature and one of the additional features, between the fourth feature and one of the additional features, or between a pair of the additional features.
33. A camera comprising: the actuator assembly according to any one of claims 22 to 32; an image sensor; and a lens attached to the second part.
34. A patterned metal sheet, comprising: a frame; a first feature supporting or defining a first crimp head and connected to the frame by one or more first connecting members; a second feature supporting a second crimp head and connected to the frame by one or more second connecting members; wherein one or more of the first connecting members are formed as first flexures configured to permit deflection of all or part of the first feature relative to the frame along a primary axis substantially perpendicular to the patterned metal sheet; and/or one or more of the second connecting members are formed as second flexures configured to permit deflection of the second feature relative to the frame along the primary axis.
35. A method of forming an actuator assembly comprising: crimping a first shape-memory alloy wire to a first patterned sheet, the first patterned sheet comprising a first frame, a first feature supporting or defining a first crimp head and connected to the first frame by one or more first connecting members, and a second feature supporting or defining a second crimp head and connected to the first frame by one or more second connecting members, wherein the first shape-memory alloy wire is crimped between the first and second crimp heads; assembling the first patterned sheet, a first part and a second part to form a first assembly, wherein the first assembly is configured such that the first feature is attached to the first part, the second feature is attached to the second part, and the first part is coupled to the second part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis; severing each of the first and second connecting members to detach the first frame.
36. A method according to claim 35, further comprising connecting a spring between the first and second parts such that contraction of the first shape-memory alloy wire causes extension of the spring.
37. An actuator assembly comprising: a first shape-memory alloy wire crimped between a first crimp head supported by a first feature and a second crimp head supported or defined by a second feature; a first part; a second part coupled to the first part by a bearing arrangement configured to couple a rotation of the second part relative to the first part about a primary axis to a translation of the second part relative to the first part along the primary axis; wherein in the actuator assembly the first feature is attached to the first part and the second feature is attached to the second part; wherein each of the first and second features is formed from a sheet and comprises one or more detachment sites corresponding to locations where that feature was detached from a respective frame by severing one or more connecting members.
38. An actuator assembly according to claim 37, further comprising a spring connecting between the first and second parts such that contraction of the first shape-memory alloy wire causes extension of the spring.