WO2021229228A1

WO2021229228A1 - A shape memory alloy actuator assembly and a method of manufacturing thereof

Info

Publication number: WO2021229228A1
Application number: PCT/GB2021/051147
Authority: WO
Inventors: Robin Eddington
Original assignee: Cambridge Mechatronics Limited
Priority date: 2020-05-13
Filing date: 2021-05-13
Publication date: 2021-11-18
Also published as: GB202218614D0; GB2610767A; CN115516203A; GB2610767B

Abstract

A shape memory alloy (SMA) actuator assembly comprising: a support structure; a moveable component supported on the support structure; one or more SMA components connected between the moveable component and the support structure and arranged to, on contraction, drive movement of the moveable component in a direction orthogonal to a primary axis extending through the moveable component; and wherein the support structure comprises: a support component and a bearing component arranged to conplanarly extend along a plane orthogonal to the primary axis; a conductive component provided on the support component to form electrical paths for the one or more SMA components; one or more bearing portions defined on the bearing component, each bearing portion comprising a bearing surface provided on the bearing component and arranged to guide relative movement of the moveable component and the support structure; and wherein the bearing component is separated from the support component so as to electrically insulate the one or more bearing portions from the support component.

Description

A Shape Memory Alloy Actuator Assembly and A Method of Manufacturing Thereof

Field

The present application generally relates to a shape memory alloy (SMA) actuator assembly and techniques for manufacturing the SMA actuator assembly, and in particular to an SMA actuator assembly for a camera assembly.

Background

Shape memory alloy (SMA) actuators are used in camera assemblies for effecting a range of motions of a lens carriage. For example, WO 2019/086855 A1 describes a camera with an SMA actuator assembly including a support structure, a moveable part that supports a lens assembly, plural SMA wires connected between the support structure and the moving part, and bearings to bear the moving part on the support structure. This actuator assembly also includes two flexure arms extending between the support structure and the moving part for providing a lateral biasing force that biases the lens assembly towards a central position. The SMA wires are configured to, on contraction, move the moveable part in directions perpendicular to an optical axis to provide optical image stabilization (OIS).

Figures 1A, IB show a prior art actuator assembly comprising a support structure 550 having a conductive component 554 stacked on top of a support component 552. The support component 552 has bearing posts 557 extended therefrom and supports the moveable part 560. That is, the bearing posts 557 are provided on top of the support component 552 in the prior art actuator assembly. A hard wearing electrically insulating coating is typically required on a surface of the bearing 557 to prevent it from short circuiting with a moveable part 560 to which it contacts. In this prior art example, the support component 552 is also tasked with conducing drive current for one of the SMA wires. The current path is shown as the dotted line in Figure IB.

However, prolonged use may lead to extensive wear on the insulative coating and a short circuit can occur upon failure of the bearing insulation coating on two or more bearings. As shown in Figure 1C, this may lead to an electrical path being established between the two or more bearings with damaged insulation through the moveable part 560. Therefore, a potential difference across the moveable part 560 may drive a varying current flow which results in resistance noise in the position feedback of the SMA actuator which can cause performance deterioration. Worse still, in embodiments such as that in Figure IB where the support component 552 serves as a conductor to conduct a drive current, a damaged insulation may cause the SMA actuator assembly to shut down or cause damage to the SMA actuator drive circuit.

Summary

The present techniques provide an SMA actuator assembly where the support component is physically isolated from the bearing. Advantageously, such an arrangement may, in an event of damaged insulation, provide additional safeguard against unintentional current flow. Thus, the present techniques may improve the reliability of the SMA actuator assembly.

Furthermore, the present techniques provide a method in which the support component and the bearing may be attached onto a component as a sub- assembly, thus advantageously simplifying the assembly process.

According to a first aspect of the present invention, there is provided a shape memory alloy (SMA) actuator assembly comprising: a support structure; a moveable part supported on the support structure; one or more SMA components connected between the moveable part and the support structure and arranged to, on contraction, drive movement of the moveable part in a direction orthogonal to a primary axis extending through the moveable part; and wherein the support structure comprises: a support component and a bearing component arranged to conplanarly extend along a plane orthogonal to the primary axis; a conductive component provided on the support component to form electrical paths for the one or more SMA components; one or more bearing portions defined on the bearing component, each bearing portion comprising a bearing surface provided on the bearing component and arranged to guide relative movement of the moveable component and the support structure; and wherein the bearing component is separated from the support component so as to electrically insulate the one or more bearing portions from the support component.

The bearing component may be separated from the support component in the plane so as to electrically insulate the one or more bearing portions from the support component. There may thus be an uniterruped gap, when viewed along the primary axis, between the support component and the bearing component.

The SMA actuator assembly may be a micro-actuator for a camera or a mobile phone. The SMA actuator assembly may comprises one or more (e.g. elongate) SMA components that may connect directly between the support structure and the moveable part (e.g. a lens carriage), or through another component such as a flexure arm. The SMA components may also be referred to as SMA wires.

The SMA components may be configured to, on contraction, effect movement of the moveable part in at least one direction substantially orthogonal to an optical axis, e.g. along the moveable plane. The optical axis may correspond to the primary axis. Such an arrangement may enable at least optical image stabilisation (OIS) to be performed upon actuating the or each of the SMA components. For example, the SMA components may extend in a direction substantially perpendicular to the optical axis. In some embodiments, the SMA components may be each provided on a respective side of the support structure. The SMA components may preferably be lengths of SMA wire, or it may be strips, or rods formed from SMA materials.

The SMA wires may form from any suitable shape memory alloy material, typically a nickel-titanium alloy (e.g. Nitinol), but they may also contain tertiary components such as copper. The SMA wires may have any cross-sectional profile and diameter suitable for the application. For example, the SMA wires may have a cross section diameter of 25mGh, or 30mGh, or 35mGh, capable of generating a maximum force of between 120mN to 200mN whilst maintaining the strain in the SMA wire within safe limits (e.g. 2-3% reduction in length over original length). Increasing the diameter of each SMA wire from 25mGh to 35mGh approximately doubles the cross-sectional area of the SMA wire and thus approximately doubles the force provided by each SMA wire.

The moveable part may comprise a spring plate (or flexure) for applying a biasing force against the moveable part in at least a lateral direction. The base of the spring plate is arranged to slide on the bearing surface. Thus, in use, (optional) coatings on the bearing surface may wear out over time and thereby expose conductive portions on respective parts.

The support component and the bearing component may be attached to a component, such as a conductive component, preferably by an electrically insulating adhesive. A base layer supporting the support component and the bearing component may also be provided with an electrically insulating coating. Therefore, the bearing component may be described as an island on a base layer separate to, or isolated from, the support component. More specifically, gaps or separations are provided between the support component and the bearing component. Advantageously, such an arrangement may eliminate the risk of establishment of an unintended conductive path, and thus may significantly improve the reliability of the SMA actuator assembly.

In contrast to some known embodiments (e.g. as shown in Figure 1C), where a conductive component and a bearing component are both supported on the support component (which in turn may be supported by a base layer), the bearing component and the support component according to the present invention extend coplanarly in the same plane. That is, the support component and the bearing component are positioned at substantially the same level along the primary axis.

Optionally, the SMA actuator assembly comprises a plurality of bearing portions and wherein the bearing component is separated from the support component so as to electrically insulate each bearing portion from the other bearing portions. Such an arrangement may advantageously eliminate, or reduce, resistance noise in the position feedback of the SMA actuator due to unintended current flow, which can cause performance deterioration. Optionally, the support component comprises a current-carrying portion that forms an electrical path for one of the SMA components, and wherein the bearing component is separated from the support component so as to electrically insulate the one or more bearing portions from the current-carrying portion of the support component. Such an arrangement may advantageously eliminate, or reduces, the risk of short-circuiting due to damaged insulation, which may cause the SMA actuator assembly to shut down or may cause damage to the SMA actuator drive circuit.

Optionally, the support component surrounds the bearing component along the plane. For example, the support component may comprise an aperture and the bearing component may be provided in the said aperture. Such an arrangement may provide a more compact SMA actuator assembly. Alternatively, depending on the application, some or all of the bearing components may be provided externally to the support component in the plane.

Optionally, edges of the support component and the bearing component at least partially conform to each other. For example, at least a portion of the physical gap, or separation, between the support component and the bearing component in the plane may be constant.

Optionally, the support component and at least a portion of the bearing element are of the same thickness when viewed along the plane. For example, the support component and the bearing element may be formed from the same material, e.g. cut out from the same metal sheet.

Optionally, the support component is integrally formed with the bearing component in a sub-assembly, wherein the support component is separated from the bearing component during assembly of the SMA actuator assembly. The sub- assembly may adhere to the base layer, such that the support component and the bearing component may be precisely aligned at their respective positions.

Optionally, the separation comprises severing or removing a sacrificial body portion connecting the bearing component and the support component in the pre assembly. For example, such separation may be achieved by cutting a connection extending between the bearing component and the support component. Preferably, the sacrificial body portion may be one or more tabs that secure the bearing component with the support component, whereby the separation may be achieved by removing the tab after the sub-assembly is attached to the conductive component or the base layer.

Optionally, the bearing component comprises plural bearing portions, wherein the plural bearing portions are distributed around the primary axis. The plural bearing portions may be evenly distributed around the primary axis, or they may be distributed in any manner depending on the application. The provision of plural bearing portions allows the moveable part to be supported by multiple points on the support structure.

Optionally, the bearing surface comprises a coating for electrical insulation and/or reducing friction and/or wear. Optionally, the surfaces of the bearing portion comprise a coating. Optionally, the coating comprising one or more of: a lubricant, a dry film lubricant, a diamond-like carbon coating, hard chrome, and a tungsten carbon carbide coating, a polymer coating. Some examples include CrC-DLC, TiC, S1O2, PTFE coatings.

Optionally, the bearing portion comprises a protrusion, wherein the bearing surface is provided on the protrusion. For example, the protrusion stands proud of a major surface of the bearing portion, and hence it also elevates above the support component. Thus, the protrusion may be coated with the coating for electrical insulation and/or reducing friction and/or wear.

Optionally, the surfaces of the bearing component are coated with the coating for electrical insulation and/or reducing friction and/or wear. Optionally, the surfaces of the support component are coated with the coating for electrical insulation. Optionally, at least the base of the moveable part contacting the bearing surface is coated with the coating for electrical insulation and/or reducing friction and/or wear. Optionally, at least the base of the conducting portion contacting the bearing component is coated with the coating for electrical insulation. Optionally, the protrusion is integrally formed with the bearing component. For example, the protrusion may be formed by stamping or partially etching the bearing component. Or, the protrusion may be produced by up-forming a tab portion of the bearing component. Preferably, the protrusion is formed in the sub- assembly prior to attaching onto the conductive component or the base layer.

Optionally, the protrusion comprises a polymer or metal element attached to the bearing component. For example, the polymer or metal element may be in the form of a block attached onto the surface of the bearing component by adhesive or by weld. The protrusion may be attached to the bearing component in the sub- assembly prior to attaching onto the base layer. Or, it may be attached directly onto the bearing component after the sub-assembly has been attached onto the base layer and/or sacrificial body portion has been severed or removed.

Optionally, the support component and the bearing component are formed from a metal or metal alloy. Optionally, the base layer may be formed from a metal or metal alloy laminated or coated with an electrical insulating and/or low friction and/or hard wearing top layer.

Optionally, the moveable part comprises a contacting portion for contacting the bearing surface, wherein the said contacting portion is provided with a coating for electrical insulation and/or reducing friction and/or wear. More specifically, an end of the flexure arm may be coated with the coating. Said coating may be the same, or different, to that provided on the bearing surface.

According to a second aspect of the present invention, there is provided a method for manufacturing a shape memory alloy (SMA) actuator assembly, comprising: forming a support component and a bearing component in a sub- assembly, the support component and the bearing component being integrally formed and connected by a sacrificial body portion; attaching the sub-assembly onto a component of the SMA actuator; and severing or removing the sacrificial body portion so as to separate the support component and the bearing component. The sacrificial body portion forms a template, where it is arranged to hold the support component and the bearing component with a defined separation between the components. Advantageously, when the sub-assembly is attached onto the component, e.g. the conductive component or the base layer the support component and the bearing component may be accurately positioned at their desirable locations. This reduces the risk of contact between the bearing component and the support component arising from any defect in the manufacturing process. Furthermore, the manufacturing process may be more efficient because, in the case of plural bearing components, all of the components can be aligned in a single step.

Optionally, the method further comprises providing a bearing surface on a bearing portion of the bearing component. For example, the providing may comprise coating a portion of the bearing portion and/or the surfaces of the bearing component with a coating for electrical insulation and/or reducing friction and/or wear. Similarly, the method may further comprise coating a contacting surface on the moveable part that is in contact with the bearing surface for electrical insulation and/or reducing friction and/or wear. Similarly, the method may further comprise coating the conductive component and/or base layer for electrical insulation and/or reducing friction and/or wear. The coating material applied on the various parts may be the same or different to each other.

Optionally, said providing comprises forming a protrusion on the bearing portion. This may be achieved by attaching a polymer or metal element on the bearing component by weld or adhesive, either before or after the sub-assembly is attached onto the base layer.

Alternatively, said providing comprises partially-etching or stamping the bearing portion, and/or by cutting tab portions in the bearing component and forming-up the tab portions. Preferably, the partially-etching, stamping, of the bearing portion, or cutting and forming up of tab portion, are carried out before the sub- assembly is attached to the conductive component or the base layer.

Optionally, the attaching comprises adhering the sub-assembly to the base layer. Preferably, the adhering may be achieved with the use of an electrically insulative adhesive. Alternatively, the surface of the base layer may be coated or laminated with an electrically insulating layer prior to attaching the sub-assembly.

Optionally, the forming comprises forming the sub-assembly from a single metal sheet. For example, the forming may be achieved by cutting or etching the metal sheet.

Subject matter from the first aspect and the second aspect may be combined.

Brief Description of the Drawings

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

Figures 1A and IB are respective persepctive and top plan views of an SMA actuator assembly according to a prior art embodiment;

Figure 1C is a side section view of the SMA actuator assembly according to the prior art embodiment;

Figure 2A is a side schematic view of a camera assembly according to a first embodiment of the present invention;

Figure 2B is a perspective view of a SMA actuator assembly of the first embodiment;

Figure 2C is an exploded perspective view of a SMA actuator assembly of the first embodiment;

Figure 2D is an enlarged side sectional view showing an SMA actuator assembly of the first embodiment;

Figure 3A is a top plan view showing a showing a support component and bearing component of the SMA actuator assembly illustrated in Figures 2B and 2C; Figure 3B is an enlarged perspective view showing a showing a bearing component of the SMA actuator assembly illustrated in Figures 2B and 2C;

Figure 3C is a top plan view showing a support structure of the SMA actuator assembly illustrated in Figures 2B and 2C;

Figure 3D is a top plan view showing a sub-assembly for the SMA actuator assembly illustrated in Figures 2B and 2C;

Figure 3E is a top plan view showing a sub-assembly attached to a conductive component;

Figure 3F is an enlarged side sectional view showing a support component and a bearing component coplanarly extending in a plane;

Figures 4A and 4B are respective enlarged perspective and side section views of an integrated bearing;

Figures 4C, 4D and 4E are respective enlarged perspective, side section and top plan views of an alternative integrated bearing;

Figure 4F is a side section view of another alternative integrated bearing;

Figure 5 is a flow diagram illustrating the steps in a method of manufacturing the sub-assembly for the SMA actuator assembly;

Figure 6A is a top plan view showing a support component and a bearing component according to a second embodiment of the present invention;

Figures 6B and 6C are top plan views of a sub-assembly for producing the support component and the bearing component of Figure 6A;

Figure 7A is a top plan view showing a support component and a bearing component according to a third embodiment of the present invention; and Figure 7B is a top plan view showing a support structure formed from the support component and bearing component of Figure 7A.

Detailed Description

Figure 2A is a schematic cross-sectional view of a camera incorporating an SMA actuator assembly 2 according to a first embodiment of the present invention. In Figure 2A, a camera assembly 1 incorporating an SMA actuator assembly 2 (herein also referred to as an "SMA actuator" or simply an "actuator") is shown.

The camera assembly 1 includes a lens assembly 21 suspended on a support structure 4 by an SMA actuator assembly 2 that supports the lens assembly 21 in a manner allowing movement of the lens assembly 21 relative to the support structure 4 in directions perpendicular to the optical axis 0.

The support structure 4 includes a base 5. An image sensor 6 is mounted on a front side of the base 5. On a rear side of the base 5, there is mounted an integrated circuit (IC) 30 in which a control circuit is implemented, and also a gyroscope sensor 31. The support structure 4 also includes a can 7 which protrudes forwardly from the base 5 to encase and protect the other components of the camera 1.

The lens assembly 21 includes a lens carriage 23 in the form of a cylindrical body supporting two lenses 22 arranged along the optical axis 0. In general, any number of one or more lenses 22 may be included. Preferably, each lens 22 has a diameter of up to about 20 mm. The camera 1 can therefore be referred to as a miniature camera.

The lens assembly 21 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 22 are supported on the lens carriage 23 such that the lenses 22 are movable along the optical axis 0 relative to the image sensor 6, for example to provide focusing or zoom. In particular, the lenses 22 are fixed to a lens carriage 23 which is movable along the optical axis 0 relative to the lens assembly 21. Although all the lenses 22 are fixed to the lens carriage 23 in this example, in general, one or more of the lenses 22 may be fixed to the lens assembly 21 and so not movable along the optical axis 0 relative to the image sensor 6.

An axial actuator arrangement 24 provided between the lens assembly 21 and the lens carriage 23 is arranged to drive movement of the lens carriage 23 and the lenses 22 along the optical axis 0 relative to the image sensor 6. The axial actuator arrangement 24 may be of any suitable type, for example, a voice coil motor (VCM) or an arrangement of SMA wires.

Further details are also provided in WO 2013/175197 Al, which is incorporated herein by this reference.

Figures 2B and 2C are respective perspective and exploded perspective views of the SMA actuator 2. An enlarged sectional side view of the SMA actuator 2 is also shown in Figure 2D.

The SMA actuator assembly 2 comprises a support structure 50 and a moveable part 60 moveable relative to the support structure 50. Each of the support structure 50 and the moveable part 60 generally takes the form of a flat, thin annulus with a rectangular outer edge (or "peripheral edge") and a circular inner edge. The outer edge of the moveable part 60 lies inside the outer edge of the support structure 50, but the inner edges of the support structure 50 and moveable part 60 are generally co-extensive.

The moveable part 60 supports the lens assembly 21 (Figure 1) and thereby connects to the lens carriage 23 (Figure 1). The support structure 50 is formed from two separate components, namely a support component 52 and a conductive component 54, which are affixed to each other. The support structure 50 is affixed to a base layer 58. Each of the moveable part 60, the support component 52 and the conductive component 54 may take the form of a patterned sheet of metal, e.g., etched or machined stainless steel. The support component 52 may be coated with an electrically-insulating dielectric material. The electrically-insulating dielectric material may also be provided on the plain bearings for reducing friction and increasing the longevity of the plain bearings. Other example configurations may be used, and further details are provided in WO 2017/055788 A1 and WO 2019/086855 Al, which are incorporated herein by this reference. The support structure 50 and the moveable part 60 are each provided with a respective central aperture aligned with the optical axis O allowing the passage of light from the lens assembly 21 (Figure 1) to the image sensor 6 (Figure 1). Movement of the moveable part 60 and, thus, the lens assembly 21 relative to the support structure 50, is driven by a lateral actuation arrangement comprising four SMA wires 80 crimped to the respective crimps 51, 61. In operation, the SMA wires 80 are selectively driven to move the moving part 60 relative to the support structure 50 in any lateral direction (i.e. direction perpendicular to the optical axis O). This is used to provide optical image stabilization (OIS), compensating for movement of the camera 1, which may be caused by hand shake, etc.

The support structure 50 and the movable part 60 each have a flat, planar body portion. Each body portion has four major side surfaces. Each body portion also has a central circular hole (i.e. the above-described aperture). The body portions are each perpendicular to the optical axis O (Z-axis), i.e. parallel to the XY-plane. The body portions are each centred on the optical axis (Z-axis) at a central position and have a similar size, shape, and orientation to each other.

The support structure 50 comprises further portions supporting the crimps 51. In this example, the support structure 50 has four crimp supports, each of which supports a crimp 51 (or "static crimp"). The crimp supports for the static crimps

51 are positioned at diagonally opposite corners of the support structure 50. The static crimps are configured to mechanically attach the first ends of SMA wires to the support structure 50. Movement of the moving element 60 relative to the support platform 50 is driven by a lateral actuation arrangement comprising four SMA wires 80. The support platform 50 is formed with crimps 51 (hereinafter referred to as 'static crimps') and the moveable part 60 is formed with crimps 61 (hereinafter referred to as 'moving crimps'). The crimps 51, 61 crimp the four SMA wires 80 so as to connect them to the support platform 50 and the moveable part 60. The SMA wires 80 may be perpendicular to the optical axis O or inclined at a small angle to the plane perpendicular to the optical axis O.

In operation, the SMA wires 80 are selectively driven to move the moveable part 60 relative to the support platform 50 in any lateral direction (i.e. direction perpendicular to the optical axis O), as will now be explained.

The SMA wires 80 have an arrangement in a loop at different angular positions around the optical axis O to provide two pairs of opposed SMA wires 80 that are perpendicular to each other. Thus, each pair of opposed SMA wires 80 is capable of selective driving to move the lens assembly 21 in one of two perpendicular directions orthogonal to the optical axis O. As a result, the SMA wires 80 are capable of being selectively driven to move the lens assembly 21 relative to the support structure 50 to any position in a range of movement in two directions orthogonal to the optical axis O. The magnitude of the range of movement depends on the geometry and the range of contraction of the SMA wires 80 within their normal operating parameters.

The position of the lens assembly 21 relative to the support structure 50 perpendicular to the optical axis O is controlled by selectively varying the temperature of the SMA wires 80. This is achieved by passing through SMA wires 80 selective drive signals that provide resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the SMA wire 80 to cool by conduction, convection, and radiation to its surroundings. On heating of one of the SMA wires 80, the stress in the SMA wire 80 increases and it contracts, causing movement of the lens assembly 21. A range of movement occurs as the temperature of the SMA increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA wires 80 so that the stress in the SMA wire 80 decreases, it expands under the force from opposing ones of the SMA wires 80. This allows the lens assembly 20 to move in the opposite direction.

The SMA wires 80 may be made of any suitable SMA material, for example Nitinol or another titanium-alloy SMA material.

The drive signals for the SMA wires 80 are generated and supplied by the control circuit implemented in the IC 30. The drive signals are generated by the control circuit in response to output signals of the gyroscope sensor 31 so as to drive movement of the lens assembly 20 to stabilise an image focused by the lens assembly 21 on the image sensor 6, thereby providing OIS. The drive signals may be generated using a resistance feedback control technique for example as described in WO 2014/076463 Al, which is incorporated herein by this reference.

The SMA actuator assembly 2 further comprises a suspension system (also referred to as a bearing arrangement) for suspending the moveable part on the support structure. The suspension may comprise at least one bearing to permit relative orthogonal movement between the moveable part 60 and the support structure 50 but to prevent movement along the optical axis. In the preferred embodiment as shown in Figure 3A, the suspension system comprises plural plain bearings (bearing components) 56 spaced around the optical axis O to bear the movable part 60 at respective bearing portions. The bearing components 56 may be attached to the base layer 58, for example by an electrically insulating adhesive. The base layer 58 may be provided with an electrically insulating coating or laminated with an electrically insulating layer, such that it is electrically insulated from the support component 52 (and the conductive component 54) and the bearing component 56. In this embodiment, the support component 52 conducts a drive current, shown as a dotted line in Figure 3C. The bearing components 56 are separated from, and therefore electrically insulated from, the support component 54 along the base layer 58. More specifically, as shown in Figures 3D and 3F, the bearing components 56 extend coplanarly with the support component 52 in the X-Y plane, which is orthogonal to the movement axis (Z-axis). For example, in contrast to known actuators, where a conductive component and a bearing component are both supported on the support component (which in turn may be supported on a base layer), the bearing component 56 and the support component 52 according to the present invention extend coplanarly in the same plane. That is, the support component and the bearing component are positioned at the same level along the movement axis.

In contrast to prior art embodiments, such an arrangement does not rely only on an electrically insulating coating provided on the bearing surface. Thus, it is much less susceptible to short circuiting due to excessive wear of the coating.

In some embodiments, a bearing surface is provided across the surface of the bearing portion of the bearing component . That is, the moveable part has a contacting portion that is slidable directly on the surface of respective bearing portions. This permits a simplified manufacturing process. In a preferred embodiment, as shown in the enlarged perspective view of Figure 3B, the bearing component 56 comprises a protrusion 57 extending upwardly from a bearing portion of the bearing component 56. The protrusion 57 may be in any shape or size, for example a ridge, a cone, a truncated cone, a dome, a cylinder, a cube and a cuboid. The protrusion 57 may comprises plural protrusions 57 of the same or different sizes /shapes. As shown, the protrusion 57 comprises a single raised dome with a planar bearing surface.

In some embodiments, the protrusion 57 may a polymer or metal bearing block formed separately to the bearing component. For example, the bearing block may be adhered to the bearing component 56 by an adhesive or a weld to form the protrusion.

Preferably, the protrusion 57 is formed integrally with the bearing component 56. Therefore, such protrusion 57 may be referred to as an integrated bearing 57. In Figure 3B, the integrated bearing 57 is formed by stamping or other metal forming techniques to form the bearing component 56 prior to adhering to the conductive component 54 or the base layer 58.

Other methods of forming integrated bearings 57 of various shapes may be used. Figures 4A to 4F show various forms of integrated bearings 57. It will be understood that these are just some examples of the form/shape of the integrated bearings 57 and are non-limiting. Figure 7A shows a perspective view of an integrated bearing 57 that has a raised boss-like structure, and Figure 7B shows how the raised boss 57 may be formed from the bearing component 56. The raised bosses 57 could be created by using a metal forming process on the bearing component 56 which is formed of a thin sheet of metal. Alternatively, the raised bosses 57 may be formed by domed impressions or structures in the base layer 58: when the bearing component 56 is attached to the base layer 58, the domed structures of the base layer 58 may cause the raised bosses 57 to be formed.

In some cases, forming a raised boss may be difficult. Figures 7C to 7E show how an integrated bearing 157 may be formed by etching reliefs 90 into the material of the bearing component 56 such that the bearing 157 may be formed without tearing the material.

Figure 7F shows how an integrated bearing 257 may be formed by etching/cutting a tab into the bearing component 56, and forming-up the tab (e.g. using a two bend-point forming operation) to provide a bearing 257.

In summary, the integrated bearings 57 may be formed by partially etching the bearing component 56. Alternatively, the integrated bearings 57 may be provided by forming raised portions in a surface of the bearing component 56. Alternatively, the integrated bearings 56 may be provided by etching and forming raised portions in a surface of the bearing component 56. Alternatively, the integrated bearings 57 may be provided by cutting tab portions in the bearing component 56 and forming-up the tab portions 257.

The entire bearing component 56, or at least the bearing surface, is coated with a coating layer. The coating serves one or more of the following purposes: 1) to provide electrical insulation, 2) to reduce wear of the bearing surface, 3) to reduce friction. Preferably, the bearing surface and/or the entire bearing component 56 is coated with a polymer coating, e.g. a PTFE coating.

According to another aspect of the present invention, there is provided a method 100 of manufacturing the SMA actuator assembly 2. The key steps 110-130 of the method 100 are illustrated in Figure 5.

In a first step 110 of the method 100, the support component 52 and the bearing component 56 are integrally formed in a sub-assembly 51 as shown in Figure 3b, with sacrificial body portions (tabs) 59 structurally connecting the two components. The sacrificial body portion fix the position of the bearing component 56 relative to the support component 52. More specifically, the sub-assembly 51 is produced from a (metal) sheet with any suitable metalworking techniques, such as cutting and stamping. This way, the separation between the bearing component

56 and the support component 52 are well defined by the extent of the tabs 59.

The formed sub-assembly 51 can optionally be provided with bearing surfaces in a second step 110. For example, coatings (e.g. for reducing friction/wear and electrical insulation) such as PTFE coatings may be applied to the surfaces of the bearing component 56 and/or the support component 52. Alternatively, the coating may be a PTFE layer laminated on the metal sheet. In addition, protrusions

57 or integrated bearings 57, 157, 257 may be formed.

In some embodiments, the second step 110 need not to be applied. For example, the bearing component 56 and the support component 52 may not be provided with a coating, nor do they require protrusions 57 to be formed. Thus, in these embodiments, the bearing portion of the bearing components 56 are the bearing surface.

The order of the first step 110 and the second step 120 may be reversed. For example, the metal sheet may be coated with coatings or laminated with a polymer layer, and/or forming protrusions 57 and integrated bearings 57,157,257 at defined positions, prior to forming the sub-assembly. In a third step 130 of the method 100, the sub-assembly is aligned at a predetermined position on the base layer 58 before being adhered to either the conductive component 54 or the base layer 58, for example by adhesive or weld 53 as shown in Figure 3E. The surface of the base layer 58 and/or at least the base of the conductive component 54 is electrically insulated, e.g. by an electrical insulating coating or a laminated polymer layer, such that it prohibits current flow between the bearing component 56 and the support component 52. The use of the sub-assembly allows the plural bearing components 56 to be accurately aligned with respect to the support component 52.

In a fourth step 140 of the method 100, the tab portions 59 are removed from the sub-assembly. The removing may comprise severing the ends of the tab portions 59 along the dotted line in Figure 3D. Alternatively, the tab portions 59 may be severed such that they no longer connects between the support component 52 and the bearing component 56.

Figure 6A is a top plan view showing a support component 352 and a bearing component 356 according to a second embodiment of the present invention. The support component 352 and the bearing component 356 are functionally similar to those of the first embodiment. In this embodiment, there is only a single bearing component 356 on which plural protrusions 357 are provided. Each of the plural protrusions forms a bearing surface that bears, and allows a relative sliding movement relative to, the moveable part 60. The bearing component 356 is a "ring" shaped component nested in the aperture of the support component 352. An annular gap is thus defined between the bearing component 356 and the support component 352.

The second embodiment as shown in Figure 6A is one of the many possible options for the bearing component. While, there may be a risk of current flow between the bearing surfaces, the bearing component is relatively narrow and so can reduce the current flow in case of damaged electrically insulative coatings. Nevertheless, the risk of short-circuiting between the conductive component 54 and the bearing component 356 is largely mitigated. Figures 6B and 6C are respective top plan views of a sub-assembly for producing the support component 352 and bearing component 356 of Figure 6A. Both embodiments comprise sacrificial body portions (tabs) 359 that are removed or severed after the sub-assembly is adhered onto the conductive component 354.

The tabs in Figures 6B and 6C eliminate the risk of short circuiting between the support component 352 and the bearing component 356 and simplifies the process of tabs removal by reducing the number of tabs required. In some other embodiments, more tabs are provided to better secure the bearing component 356 in the sub-assembly.

Figure 7A is a top plan view showing a support component and a bearing component according to a third embodiment of the present invention. Figure 7B is a top plan view showing a support structure formed from the support component and a bearing component of Figure 7A. The support component 452 and the bearing component 456 are functionally similar to that of the second embodiment. In this embodiment, there is only a single bearing component 456 on which plural protrusions 457 are provided. Each of the plural protrusions 457 forms a bearing surface that bears, and allows sliding movement relative to, the moveable part 60.

In this embodiment, the single bearing component 456 can broadly be described as a "ring". However, in contrast to the support component 352 of the second embodiment, the support component 472 carrying direct current for an SMA component is positioned on a side of the bearing component 456. This arrangement has the advantage that the two isolated components 452, 456 can be connected by external manufacturing tabs sites 455 and therefore minimises the need to redesign the manufacturing process. In addition, such an arrangement also removes the need for internal tabs, thus providing a simplified, and more efficient, manufacturing process.

Claims

1. A shape memory alloy (SMA) actuator assembly comprising: a support structure; a moveable component supported on the support structure; one or more SMA components connected between the moveable component and the support structure and arranged to, on contraction, drive movement of the moveable component in a direction orthogonal to a primary axis extending through the moveable component; and wherein the support structure comprises: a support component and a bearing component arranged to coplanarly extend along a plane orthogonal to the primary axis; a conductive component provided on the support component to form electrical paths for the one or more SMA components; one or more bearing portions defined on the bearing component, each bearing portion comprising a bearing surface provided on the bearing component and arranged to guide relative movement of the moveable component and the support structure; and wherein the bearing component is separated from the support component so as to electrically insulate the one or more bearing portions from the support component.

2. An SMA actuator assembly according to claim 1, comprising a plurality of bearing portions and wherein the bearing component is separated from the support component so as to electrically insulate each bearing portion from the other bearing portions.

3. An SMA actuator assembly according to claim 1, wherein the support component comprises a current-carrying portion that forms an electrical path for one of the SMA components, and wherein the bearing component is separated from the support component so as to electrically insulate the one or more bearing portions from the current-carrying portion of the support component.

4. An SMA actuator assembly according to any one of the preceding claims, wherein the support component surrounds the bearing element along the plane.

5. An SMA actuator assembly according to any one of the preceding claims, wherein edges of the support component and the bearing element are at least partially conformed with each other.

6. An SMA actuator assembly according to any one of the preceding claims, wherein the support component and at least a portion of the bearing element are of the same thickness when viewed along the plane.

7. An SMA actuator assembly according to any one of the preceding claims, wherein the support component is integrally formed with the bearing component in a sub-assembly, wherein the support component is separated from the bearing component during assembly of the SMA actuator assembly.

8. An SMA actuator assembly according to claim 7, wherein the separation comprises severing or removing a sacrificial body portion connecting the bearing component and the support component in the pre-assembly.

9. An SMA actuator assembly according to any one of the preceding claims, wherein the bearing component comprises plural bearing portions, wherein the plural bearing portions are distributed around the primary axis.

10. An SMA actuator assembly according to any one of the preceding claims, wherein the bearing surface comprises a coating for electrical insulation and/or reducing friction and/or wear.

11. An SMA actuator assembly according to 10, wherein the coating comprising one or more of: a lubricant, a dry film lubricant, a diamond-like carbon coating, hard chrome, a tungsten carbon carbide coating, and a polymer coating.

12. An SMA actuation assembly according to any one of the preceding claims, wherein the bearing portion comprises a protrusion, wherein the bearing surface is provided on the protrusion.

13. An SMA actuation assembly according to claim 12, wherein the protrusion is integrally formed with the bearing component.

14. An SMA actuation assembly according to claim 13, wherein the protrusion comprises a polymer or metal element attached to the bearing component.

15. The SMA actuation apparatus according to any one of the preceding claims, wherein the support component and the bearing component are formed from a metal or metal alloy.

16. The SMA actuation apparatus according to any one of the preceding claims, wherein the moveable element comprises a contacting portion for contacting the bearing surface, wherein the said contacting portion is provided with a coating for electrical insulation and/or reducing friction and/or wear.

17. A method for manufacturing a shape memory alloy (SMA) actuator assembly, comprising: forming a support component and a bearing component in a sub- assembly, the support component and the bearing component are integrally formed and connected by a sacrificial body portion; attaching the sub-assembly onto a component of the SMA actuator assembly; and severing or removing the sacrificial body portion so as to separate the support component and the bearing component.

18. A method according to claim 17, the method further comprises providing a bearing surface on a bearing portion of the bearing component.

19. A method according to claim 18, wherein the said providing comprises coating a portion of the bearing component with a coating for reducing friction and/or wear.

20. A method according to claim 17 or claim 18, wherein the said providing comprises forming a protrusion on the bearing portion.

21. A method according to claims 20, wherein the protrusion is formed by attaching a polymer or metal element on the bearing component.

22. A method according to claim 20, wherein the protrusion is formed by partially-etching or stamping the bearing portion.

23. A method according to claim 20 or 22, wherein the protrusion is formed by cutting tab portions in the bearing portion and forming-up the tab portions.

24. A method according to any one of claims 17 to 23, further comprising coating a contacting surface on the moveable element that is in contact with the bearing surface for electrical insulation and/or reducing friction and/or wear.

25. A method according to any one of claims 17 to 24, wherein the attaching comprises adhering the sub-assembly to the component.

26. A method according to any one of the claims 17 to 25, wherein the forming comprises forming the sub-assembly from a single metal sheet.