EP3737861A1

EP3737861A1 - Manufacture of shape memory alloy actuator assemblies

Info

Publication number: EP3737861A1
Application number: EP19701006.9A
Authority: EP
Inventors: Marc-Sebastian SCHOLZ; Stephen Matthew BUNTING; James Howarth; Andrew Benjamin Simpson Brown
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2018-01-11
Filing date: 2019-01-11
Publication date: 2020-11-18
Also published as: WO2019138239A1; GB201815673D0; CN111566344A; GB2570177A

Abstract

An SMA sub-assembly comprises at least one body portion (3) holding apart a pair of crimp portions/connection components (10) that are at least partly crimped around, or welded to, a length of SMA wire (20) which is slack between the crimp portions/connection components. The slackness of the SMA wire in the SMA sub-assembly may subsequently be adjusted and/or the SMA sub-assembly may be used to manufacture an SMA assembly wherein at least one length of slack shape memory alloy wire is connected between a static part and a movable part, thereby providing an advantage of increasing the available stroke of the SMA wire.

Description

Manufacture of Shape Memory Alloy Actuator Assemblies

The present application generally relates to manufacture of shape memory alloy (SMA) actuator assemblies.

In a first approach of the present techniques, there is provided a shape memory alloy sub-assembly comprising at least one body portion holding apart a pair of crimp portions, the crimp portions being at least partly closed around a length of shape memory alloy wire which is slack between the crimp portions.

In a second approach of the present techniques, there is provided a method of manufacture of a shape memory alloy sub-assembly comprising: providing at least one body portion holding apart a pair of open crimp portions; laying a length of shape memory alloy wire on the or each pair of open crimp portions; and at least partly closing the crimp portions around the length of shape memory alloy wire and providing the length of shape memory alloy wire with slack between the crimp portions. The SMA sub-assembly thus manufactured may be in accordance with the first approach of the present techniques.

In the first and second techniques, as the SMA wire is slack between the crimp portions, it is not necessary to apply a controlled tension to the SMA wire while closing the crimp portions around the length of SMA wire with the result that manufacture is simplified, increasing the speed of manufacture and reducing the unit cost.

Generally speaking, the term "slack wire" may mean a wire which has zero tension. Alternatively, the term "slack wire" may mean a wire which has zero tension when the wire is unpowered. Alternatively, the term "slack wire" may mean a wire which has zero tension when it is unpowered and at ambient temperature (which may, in some cases be, 25°C). In other words, the term "slack wire" may mean a wire which is held between two crimps/crimp portions (i.e. is mechanically coupled at two points along its length to some other element), does not lie in a straight line between those two crimp portions when the wire is unpowered and at ambient temperature. Thus, in some cases, the slackness is present when the length of SMA wire is at a temperature of 25°C (which is a typical ambient temperature). When a drive signal is applied in use to the length of SMA wire to cause contraction, its temperature rises significantly above 25°C. Typically, when SMA wire is pulled from a spool (in which the wire is under tension), in some cases the wire may retain some tension due to hysteresis. Thus, alternatively, the term "slack wire" may mean that the wire is slack after any residual tension has been removed. The tension may be removed by, for example stretching the wire at ambient temperature. Once the tension is removed, if the length of the wire between the two crimps is greater than the distance between the crimps, the wire may be considered to be slack. A further definition of the term "slack wire" is a wire which is slack when the SMA wire is substantially martensitic. It will be understood that any of these definitions may be used in the present techniques to provide slack wire.

As an alternative to crimping, the SMA wire may be connected in place using welding. The SMA wire may be welded to the crimps/crimp portions. Alternatively, the crimps/crimp portions may be replaced by suitable connection components (e.g. tabs) to which the SMA wire may be welded. Thus, it will be understood that where crimping is described herein, the crimping may be replaced by welding.

Thus, in a third approach of the present techniques, there is provided a shape memory alloy (SMA) sub-assembly comprising at least one body portion holding apart a pair of connection components that are welded to a length of SMA wire which is slack between the connection components.

As for the crimped arrangement, the body portion may be a sacrificial body portion that is removable from the connection components. The connection components may be formed integrally with the body portion. The connection components may be formed integrally with the body portion from a sheet of material.

The SMA sub-assembly may comprise a single body portion.

The SMA sub-assembly may be a composite SMA sub-assembly comprising a one-dimensional or two-dimensional array of body portions that are connected together. The body portions may be connected together by being formed integrally. The lengths of SMA wire in respect of each body portion may be lengths of the same piece of SMA wire.

In a fourth approach of the present techniques, there is provided a method of manufacture of a shape memory alloy (SMA) sub-assembly comprising : providing at least one body portion holding apart a pair of connection components; laying a length of SMA wire on the or each pair of connection components; and welding the SMA wire to the connection components. The step of welding the SMA wire to the connection components may comprise any one of: arc welding, welding using a weld bar, heat-based welding, laser welding.

The method may further comprise: adjusting, prior to welding, the degree of slackness or tension of the length of SMA wire.

The step of laying the length of SMA wire on the or each pair of connection components may be performed with the length of SMA wire under tension, and the method may further comprise: applying a tool that deflects the length of SMA wire laterally between the connection components and removing the tool after welding the connection components to the length of SMA wire.

Alternatively, the step of laying the length of SMA wire on the or each pair of connection components may be performed with the length of SMA wire under tension, and the method may further comprise: deforming the body portion so as to provide the length of SMA wire with the slack between the connection components.

The step of laying a length of SMA wire on each pair of connection components may comprise laying the same piece of SMA wire across all the pairs of connection components.

The SMA sub-assembly may be used to manufacture an SMA actuator assembly. Thus, in a fifth approach of the present techniques, there is provided a method of manufacture of a shape memory alloy actuator assembly, the method comprising: providing a static part, a movable part that is movable with respect to the static part, and a shape memory alloy sub-assembly in accordance with the first approach of the present techniques; attaching the crimp portions to the static part and the movable part, respectively; and removing the body portion, leaving the crimp portions attached to the static part and the moving part, respectively.

Similarly, in a sixth approach of the present techniques, there is provided a method of manufacture of a shape memory alloy (SMA) actuator assembly, the method comprising: providing a static part, a movable part that is movable with respect to the static part, and a SMA sub-assembly comprising a body portion holding apart a pair of connection components, the connection components being welded to a length of shape memory alloy wire which is slack between the connection components; attaching the connection components to the static part and the movable part, respectively; and removing the body portion, leaving the connection components attached to the static part and the moving part, respectively.

The presence of slack SMA wire in the SMA sub-assembly does not prejudice the use of the sub-assembly in manufacture of an SMA actuator assembly as might be expected. This is for the following reasons.

In a first case, the degree of slackness or tension of the SMA wire may be adjusted either (a) after manufacture of the SMA sub-assembly but prior to manufacture of the SMA actuator assembly, (b) during manufacture of the SMA actuator assembly (e.g. after the step of attaching the crimp portions to the SMA actuator assembly but before removal of a body portion of the SMA sub-assembly; or (c) after manufacture of the SMA actuator assembly. In this manner, as the SMA wire is subsequently adjusted, the degree of slackness of the SMA wire in the SMA sub-assembly does not matter, which facilitates speedy and cost-efficient manufacture.

By way of example, to facilitate such adjustment, the crimp portions may be partly closed around a length of shape memory alloy wire during manufacture of the SMA sub-assembly. In this state, the crimp portions may hold the SMA wire, but with a compressive force that is sufficiently low to allow the SMA wire to be adjusted to vary the degree of slackness or tension. Thereafter, the crimp portions may be fully closed around the SMA wire to hold the SMA wire with a compressive force that is sufficiently high to resist the tension developed in the SMA wire under application of drive signals.

In a second case, the SMA sub-assembly may be used to manufacture an SMA actuator assembly in which the SMA wire is slack in the unpowered state.

That is, in a seventh approach of the present techniques, there is provided a shape memory alloy actuator assembly comprising : a static part; a movable part that is movable with respect to the static part; and at least one length of shape memory alloy wire connected between the static part and the movable part and which is slack.

It has been appreciated by experiment and analysis that it is not necessary to hold the SMA wire in tension in the unpowered state. In this case, the SMA wire is configured so that a tension suitable for driving the SMA actuator assembly may be applied to the SMA wire by application of a suitable drive signal. This may be achieved by controlling the degree of slackness in the SMA wire. The length of the SMA wire in its driven state can be controlled during manufacture, for example by accurately controlling the relative positions of the crimp portions.

In addition, such a case of slack SMA wire in the unpowered state provides significant advantages. If an SMA wire is under tension in the unpowered state, then the SMA actuator assembly typically loses a large amount of its theoretical stroke, for example of the order of 50pm to lOOpm in typical optical device. This is significant because the achievable stroke is often a limiting factor in miniaturisation of the SMA actuator assembly. On the other hand, if the SMA wire is slack in the unpowered state, the length of the SMA wire length is increased, improving the stroke capability of the SMA actuator assembly, possibly up to its theoretical maximum.

An SMA actuator assembly according to the seventh approach of the present techniques may be manufactured in accordance with the fifth or sixth approach of the present techniques. By way of example, to facilitate this, the crimp portions may be completely closed around a length of shape memory alloy wire during manufacture of the SMA sub-assembly. In this state, the crimp portions hold the SMA wire with a compressive force that is sufficiently high to resist the tension developed in the SMA wire under application of drive signals.

In embodiments, an SMA actuator assembly may be manufactured by providing a static part, a movable part that is movable with respect to the static part, and a shape memory alloy sub-assembly comprising at least one body portion holding apart a pair of crimp portions, the crimp portions being at least partly closed around a length of shape memory alloy wire; attaching the crimp portions to the static part and the movable part, respectively; and removing the body portion, leaving the crimp portions attached to the static part and the moving part, respectively. The method may further comprise fully closing the crimp portions (if these were not fully closed prior to attachment to the SMA actuator assembly). The method may further comprise forming or deforming at least a part of the SMA actuator assembly in a way that the SMA wire between the crimp portions becomes slack. That is, this technique involves coupling a tense or taut SMA wire to an SMA actuator assembly, and deforming or forming or shaping the SMA actuator assembly such that the SMA wire becomes slack.

Alternatively, an SMA actuator assembly according to the seventh approach of the present techniques may be manufactured by any other technique that provides an SMA wire that is slack. Some non-limitative examples include:

• accurately cutting over-length SMA wire at a known tension;

• providing a removable element such as a pin to ensure the SMA wire is not straight when attached to the crimp portions, and then removing the removable element;

• moving the movable part to a known position within the stroke of the SMA wire, for example using a jig, before attaching the SMA wire thereto; or

• attaching the SMA wire in a heated state where it is partially transformed and contracted, such that it can be attached in the tensioned state and becomes slack when cool.

The SMA sub-assembly will now be further discussed. The body portion may be a sacrificial body portion that is removable from the crimp portions/connection components.

The crimp portions/connection components may be formed integrally with the body portion, for example from a sheet of material.

The SMA sub-assembly may comprise a single body portion. In that case, the SMA sub-assembly holds a single length of SMA wire. When used to manufacture an SMA actuator assembly comprising plural lengths of SMA wire, plural SMA sub-assemblies may be used.

Alternatively, the SMA sub-assembly may be a composite SMA sub- assembly comprising an array of body portions that are connected together, which may be a one-dimensional array or a two-dimensional array. The term "composite SMA sub-assembly" is used herein to mean the SMA sub-assembly may be part of (i.e. one of) a larger array of SMA sub-assemblies, and individual SMA sub- assemblies may be disconnected or removed from the array during the actuator manufacturing process. For example, the body portions may be connected together by being formed integrally. In that case, the SMA body portions each hold a single length of SMA wire. Such a composite SMA sub-assembly may further increase the speed and cost-effectiveness of manufacture by assembling plural lengths of SMA wire at the same time. For example, the lengths of SMA wire in respect of each body portion may be lengths of the same piece of shape memory alloy wire. This allows the piece of SMA wire to be applied to all the body portions. Individual SMA sub-assemblies may be removed from the composite SMA sub- assembly.

The eighth and ninth approach of the present techniques are concerned with simplifying the manufacture of shape memory alloy sub-assemblies.

In the eighth approach of the present techniques, there is provided a method of manufacture of shape memory alloy sub-assemblies comprising : providing a sheet of material comprising plural pairs of open crimp portions; laying a length of shape memory alloy wire on each pair of open crimp portions; at least partly closing the crimp portions around the length of shape memory alloy wire; and cutting out from the sheet of material plural shape memory alloy sub- assemblies each comprising a body portion formed integrally with a pair of crimps holding a length of SMA wire.

In a ninth approach of the present techniques, there is provided a method of manufacture of shape memory alloy (SMA) sub-assemblies comprising: providing a sheet of material comprising plural pairs of connection components; laying a length of SMA wire on each pair of connection components; welding the SMA wire to each pair of connection components; and cutting out from the sheet of material plural SMA sub-assemblies each comprising a body portion formed integrally with a pair of connection components holding a length of SMA wire.

The method may further comprise: adjusting, prior to welding, the degree of slackness or tension of the length of shape memory alloy wire.

The step of welding the length of SMA wire to the connection components may be performed with the length of shape memory alloy wire slack between the connection components, optionally when the length of shape memory alloy wire is at a temperature of 25°C.

The step of laying the length of SMA wire on the or each pair of connection components may be performed with the length of shape memory alloy wire under tension, and the method may further comprise: applying a tool that deflects the length of SMA wire laterally between the crimp portions before welding the length of SMA wire, and removing the tool after welding the connection components to the length of SMA wire.

These methods may increase the speed and cost-effectiveness of manufacture by assembling plural lengths of SMA wire at the same time. For example, the lengths of SMA wire in respect of each body portion may be lengths of the same piece of shape memory alloy wire. This allows the piece of SMA wire to be applied to all the SMA sub-assemblies.

The length of SMA wire may be slack between the crimp portions, for example, when the length of shape memory alloy wire is at a temperature of 25°C, as in the approaches of the present techniques discussed above and providing the same advantages.

The SMA actuator assembly will now be further discussed.

In general, the SMA actuator assembly may be any type of device that comprises a static part and a movable part which is movable with respect to the static part.

The SMA actuator assembly may be, or may be provided in, any one of the following devices: a smartphone, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, an image capture device, a foldable image capture device, an array camera, a periscope camera, a 3D sensing device or system, a servomotor, a consumer electronic device (including domestic appliances such as vacuum cleaners, washing machines and lawnmowers), a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader (also known as an e-book reader or e-book device), a computing accessory or computing peripheral device (e.g. mouse, keyboard, headphones, earphones, earbuds, etc.), an audio device (e.g. headphones, headset, earphones, etc.) a security system, a gaming system, a gaming accessory (e.g. controller, headset, a wearable controller, joystick, etc.), a robot or robotics device, a medical device (e.g. an endoscope, inhaler, drug dispenser, etc.), e-cigarettes, an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device (e.g. a watch, a smartwatch, a fitness tracker, etc.), a drone (aerial, water, underwater, etc.), an aircraft, a spacecraft, a submersible vessel, a vehicle, and an autonomous vehicle (e.g. a driverless car), a tool, a surgical tool, a remote controller (e.g. for a drone or a consumer electronics device), clothing (e.g. a garment, shoes, etc.), a display screen, a touchscreen, a sensor, and wireless communication devices (e.g. a near-field communication (NFC) device). It will be understood that this is a non-exhaustive list of example devices.

The SMA actuator assembly may be an optical device in which the movable element comprises an optical element. The movable part may be movable along an optical axis of the optical element.

The optical element may, for example, be a lens element comprising at least one lens, for example a miniature device in which the at least one lens has a diameter of at most 20mm. In that case, the SMA actuator assembly may be a camera wherein the static part has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor. However, the SMA actuator assembly may be any other type of optical device.

The movable part may be supported on the static part by a suspension system arranged to guide movement of the movable element with respect to the static part. The static part may, for example, comprise a bearing arrangement.

The slack wire used in the present techniques may be coated with an electrically insulating layer. Such a coated slack wire is described in International Patent Publication No. WO2015/036761. When crimping a coated SMA wire, the electrically insulating layer may need to be removed from at least the portion of the coated SMA wire that will be in a crimp, in order to achieve an electrical connection between the wire and crimp. The electrically insulating layer may be removed by, for example, laser ablation. An advantage of the present techniques in which the SMA wire is welded in place may be that if the SMA wire is coated with an electrically insulating layer, the coating may not need to be removed prior to the welding process. In embodiments, the present techniques may be used to provide an eight- wire actuator, such as the actuator described in International Patent Publication No. W02011/104518. Preferably, the eight-wire actuator is formed using the present techniques and coated slack wire.

The present techniques may be used to provide a haptic assembly or device arranged to deliver haptic feedback, such as the haptic assembly described in United Kingdom patent applications GB1803084.1 and GB1813008.8. Thus, in the SMA actuator assembly, the movable part may be movable with respect to the static part to deliver haptic feedback. The slack wire may be coated or uncoated in such a haptic assembly or device.

The present techniques may be used to provide a 3D sensing device or system, such as those described in International Patent Publication No. WO2018/096347 and United Kingdom Patent Application Nos. GB1808804.7 and GB1812818.1. The slack wire may be coated or uncoated in such a 3D sensing device or system.

Preferred features are set out in the appended dependent claims.

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

Figure 1 is a top view of an SMA sub-assembly comprising a single body portion;

Figures 2 and 3 are perspective views of the crimp portion in partly and fully crimped states;

Figure 4 is a flowchart of a manufacturing method of the SMA sub- assembly;

Figure 5 is a flowchart of a modified manufacturing method of the SMA sub- assembly; Figure 6 is a perspective view of a use of a tool to deflect the length of SMA wire in the method of Figure 5;

Figure 7 is a flowchart of a further modified manufacturing method of the SMA sub-assembly;

Figures 8 and 9 are perspective views of the SMA sub-assembly before and after deformation in the method of Figure 7;

Figure 10 is a top view of a one-dimensional array of plural separate SMA sub-assemblies during manufacture;

Figure 11 is a top view of a composite SMA sub-assembly comprising a one- dimensional array of plural connected SMA sub-assemblies;

Figure 12 is a top view of a two-dimensional array of plural separate SMA sub-assemblies during manufacture;

Figure 13 is a top view of a composite SMA sub-assembly comprising a two- dimensional array of plural connected SMA sub-assemblies;

Figure 14 is a flowchart of a manufacturing method of plural SMA sub- assemblies;

Figure 15 is a top view of a sheet of material in which plural SMA sub- assemblies are manufactured in a one-dimensional array;

Figure 16 is a top view of a sheet of material in which plural SMA sub- assemblies are manufactured in a two-dimensional array;

Figure 17 is a flowchart of a modified manufacturing method of plural SMA sub-assemblies;

Figure 18 is a flowchart of a further modified manufacturing method of plural SMA sub-assemblies; Figures 19 and 20 are perspective views of SMA actuator assemblies which are cameras;

Figures 21 to 23 are flowcharts of three methods of manufacturing an SMA actuator assembly; and

Figures 24 to 27 are flowcharts of three methods of manufacturing SMA sub-assemblies.

Broadly speaking, embodiments of the present techniques generally relate to manufacture of shape memory alloy (SMA) actuator assemblies. An SMA sub- assembly comprises at least one body portion holding apart a pair of crimp portions (or connection components) that are at least partly closed around a length of SMA wire (or welded to the length of SMA wire) which is slack between the crimp portions (or connection components). The slackness of the SMA wire in the SMA sub-assembly may subsequently be adjusted and/or the SMA sub- assembly may be used to manufacture an SMA assembly wherein at least one length of slack shape memory alloy wire is connected between a static part and a movable part, thereby providing an advantage of increasing the available stroke of the SMA wire.

SMA actuators are known for use in handheld electronic devices, such as cameras and mobile phones. Such actuators may be used for example in miniature cameras to effect focus, zoom or optical image stabilization (OIS). By way of example, International Patent Publication No. WO2007/113478 discloses an SMA actuator arrangement for a camera providing autofocus using a single SMA wire and International Patent Publication No. WO2013/175197 discloses a compact SMA actuator arrangement for a camera providing OIS using four SMA wires. Further, International Patent Publication No. W02011/104518 discloses an SMA actuator arrangement comprising eight SMA wires capable of effecting both autofocus and OIS. Such actuators may also be used to deliver haptic feedback to a user of the device. By way of example, United Kingdom patent application no. GB1813008.8 discloses delivering haptic feedback using one or more SMA wires. In each of these disclosures, each SMA wire is fixed at its ends to a static part and a moving part. One method of fixing the SMA wire to the static and moving parts is crimping in which a crimp portion is closed (or crimped) around the SMA wire to form a crimp holding the SMA wire. Another method of fixing the SMA wire to the static and moving parts is welding, in which segments of the SMA wire is welded either directly to the static and moving parts, or by welding segments of the SMA wire to a connection component.

In the prior art examples mentioned above, it has been assumed that it is necessary during manufacture to attach the SMA wire under tension such that its length and tension can be accurately known in the unpowered state. In such an actuator, the SMA wire is under tension in the unpowered state.

International Patent Publication No. WO2016/189314 discloses a method of manufacture of an SMA actuator assembly by first making a sub-assembly in the form of a strut element comprising a sacrificial strut body and crimp portions closed (or crimped) around the SMA wire under application of a controlled tension, so that the crimp portions hold the SMA wire therebetween. The crimp portions are attached to the static part and the moving part, respectively. Then, the sacrificial strut body is removed, leaving the crimp portions attached to the static part and the moving part, respectively. WO2016/189314 teaches that this provides advantages including the provision of tight control of the length of the SMA wire in the manufactured SMA actuator assembly, because the sacrificial strut body of the strut element holds the relative locations of the crimp portions and thereby maintains the length of the SMA wire therebetween.

While the use of the sub-assembly disclosed in WO2016/189314 provides such advantages, there remain difficulties in manufacturing the sub-assembly while applying a controlled tension to the SMA wire.

In the following, SMA sub-assemblies that comprise crimp portions are described (and illustrated in the Figures). However, it will be understood that the crimp portions of the SMA sub-assemblies may be replaced by connection components to which SMA wire may be welded. Similarly, it will be understood that the manufacturing processes described with respect to crimping may be adapted for a welding process. Figure 1 shows an SMA sub-assembly 1 comprising a fret 2 including a body portion 3. The fret 2 is formed from a sheet of material as a flat strip. The material of the fret 2 may be metal, for example phosphor bronze, steel or laminate containing conductive components.

The fret 2 also comprises a pair of crimp portions 10 formed integrally with the body portion 3 from the same sheet of material. In particular, the body portion 3 comprises an elongate portion 4 and laterally protruding arms 5 at the extremes of the elongate portion 4, the crimp portions 10 being formed by tabs on the ends of the arms 5. Thus, the crimp portions 10 are held apart by the body portion 4.

The SMA sub-assembly 1 may have a similar construction and arrangement to the fret disclosed in WO2016/189314.

The crimp portions 10 are partly or fully closed around a length of SMA wire 20, so that they hold the SMA wire 20. The crimp portions 10 therefore crimp the length of SMA wire 20 to provide both mechanical and electrical connection. The SMA wire 20 may be made of any suitable SMA material, for example Nitinol or another Titanium-alloy SMA material.

In contrast to WO2016/189314 wherein the length of SMA wire 20 is under tension in the fret, the length of SMA wire 20 is slack, the term "slack" being used herein with its normal meaning that the length of SMA wire 20 (i.e. the length of its three-dimensional path) between the crimp portions 10 is greater than the distance between the crimp portions 20. Typically, the length of SMA wire 20 will have zero tension when it is slack, except that this may be affected by hysteresis effects. That is, when a length of SMA wire 20 is pulled under tension, e.g. from a spool, even if the wire is slack when between the crimped portions, it may retain some tension. Such tension may be removed by stretching the length of SMA wire 20 (before or after the crimp portions 10 are crimped), for example at a tension of 300MPa.

In general, the slackness or tension of the length of SMA wire 20 depends on its temperature and in use a drive signal is applied to the length of SMA wire 20 to cause contraction. However, references herein to the length of SMA wire 20 being slack refer to the length of SMA wire being slack when at ambient temperature, for example at a temperature of 25°C which is significantly below the temperature of the SMA wire with the drive signal is applied in use. The length of SMA wire 20 may be brought to a temperature of 25°C simply by placing it within an ambient temperature 25°C and waiting a sufficient time to reach thermal equilibrium of the length of SMA wire 20 and any surrounding components.

The body portion 3 is sacrificial and is removable from the crimp portions 10, for example by mechanical or laser cutting.

The crimp portions 10 may be partly closed around the length of SMA wire 20 as shown in Figure 2. In that case, the crimp portions 10 hold the SMA wire 20 with a compressive force that is sufficiently low to allow the SMA wire 20 to be moved along its length to vary the degree of slackness or introduce tension.

Alternatively, the crimp portions 10 may be fully closed around the length of SMA wire 20 as shown in Figure 3. In that case, the crimp portions 10 hold the SMA wire 20 with a compressive force that is sufficiently high to resist the tension developed in the SMA wire 20 under application of drive signals in normal use.

Figure 4 illustrates a method of manufacturing the SMA sub-assembly 1.

In step SI, the fret 2 comprising the body portion 3 and the pair of crimp portions 10 is provided with the crimp portions 10 being open. The fret 2 may be made, for example by cutting the body portion and the pair of crimp portions 10 from a sheet of material, for example by mechanical or laser cutting, stamping or pressing.

In step S2, a length of SMA wire 20 is laid on the pair of open crimp portions 10 in a predetermined position. The SMA wire 20 is not under tension and so is slack.

In step S3, the crimp portions 10 are closed around the length of SMA wire 20. This may be done by folding the open crimp portions 10 over the SMA wire 20 and pressing them, for example using a conventional crimp tool. Thus the crimp portions 10 hold the length of SMA wire 20 in a state in which it is slack between the crimp portions 10, the degree of slackness being controlled by the slackness of the length of SMA wire when the crimp portions 10 are crimped around the length of SMA wire 20. The body portion 3 of the SMA sub-assembly 1 holds the crimp portions 10 and maintains the length of the SMA wire 20 when it is subsequently tensioned, as described below.

As the SMA wire 20 is slack between the crimp portions 10, it is not necessary to apply a controlled tension to the SMA wire 20 while closing the crimp portions 10 around the length of SMA wire 20. As a result, manufacture is simplified, increasing the speed of manufacture and reducing the unit cost.

Step S3 may be performed by completely closing the crimp portions 10 around the length of SMA wire 20. In that case, as mentioned above, the crimp portions 10 hold the SMA wire 20 with a compressive force that is sufficiently high to resist the tension developed in the SMA wire 20 under application of drive signals in normal use.

In that case, the method ends and the further steps shown in Figure 4 are omitted.

Alternatively, step S3 may be performed by partly closing the crimp portions 10 around the length of SMA wire 20. In that case, as mentioned above, the crimp portions 10 hold the SMA wire 20 with a compressive force that is sufficiently low to allow the degree of slackness or introduce tension into the SMA wire 20 by applying a force along the length of the SMA wire 20. Accordingly, the further steps shown in Figure 4 may be performed to adjust the SMA wire 20 in that manner, in particular as follows.

In step S4, a force is applied along the length of the SMA wire 20 to vary the degree of slackness (i.e. without introducing tension) or to introduce tension into the length of SMA wire 20. This force may be applied by a tool which clamps the length of SMA wire 20 on opposite sides of the fret 2. In step S5, the crimp portions 10 are completely closed around the length of SMA wire 20. In that case, as mentioned above, the crimp portions 10 hold the SMA wire 20 with a compressive force that is sufficiently high to resist the tension developed in the SMA wire 20 under application of drive signals in normal use.

Steps S4 and S5 may be performed after manufacture of the SMA sub- assembly 1 but prior to use of the SMA sub-assembly in the manufacture of an SMA actuator assembly 30 which is described below. Alternatively, steps S4 and S5 may be performed during manufacture of the SMA actuator assembly 30, as will be described further below.

The example manufacturing steps shown in Figure 4 may be modified when the fret comprises a pair of connection components instead of crimp portions. Specifically, steps S3, S4 and S5 may be replaced with a step to weld the SMA wire to the connection components of the fret. The modified manufacturing process is show in Figure 24. Steps SI and S2 are the same as in Figure 4. Once the SMA wire has been positioned in the correct place on the fret (i.e. over the pair of connection components of the fret, which are held apart by a body portion), the SMA wire is welded to the connection components of the fret (step S30), Any suitable welding technique may be used to weld the SMA wire to the connection components, such as spot-welding, arc welding, welding using a weld bar, heat- based welding, and laser welding.

Figure 5 shows a modified method of manufacturing the SMA sub-assembly 1 using a different technique to control the degree of slackness in the length of SMA wire 20, and which is performed as follows. The steps of the method are the same as shown in Figure 4, except for the following modifications.

In step SI, the fret 2 comprising the body portion 3 and the pair of crimp portions 10 is provided with the crimp portions 10 being open, as described above.

In step S2, a length of SMA wire 20 is laid on the pair of open crimp portions 10 in a predetermined position, as described above except that the length of SMA wire 20 is under tension. In step S8 which is an addition step, a tool 15 is applied to the length of SMA wire 20 between the crimp portions 10 which are open, as shown in Figure 6. The tool 15 deflects the length of SMA wire 20 laterally.

In step S3, the crimp portions 10 are crimped around the length of SMA wire 20, or welded to the SMA wire, as described above. As the length of SMA wire 20 is in tension, a good mechanical contact is made between the crimp portions 10 and the length of SMA wire 20.

In step S9, the tool 11 is removed. This leaves the length of SMA wire 20 slack. The amount of slack is controlled by the amount of deflection applied by the tool 15 in step S8. Accordingly, this alternative method provides good control over the degree of slack.

The example manufacturing steps shown in Figure 5 may be modified when the fret comprises a pair of connection components instead of crimp portions. Specifically, step S3 may be replaced with a step to weld the SMA wire to the connection components of the fret. The modified manufacturing process is show in Figure 25. Steps SI, S2 and S8 are the same as in Figure 5. Once the SMA wire has been positioned in the correct place on the fret (i.e. over the pair of connection components of the fret, which are held apart by a body portion), the wire is deflected and then the SMA wire is welded to the connection components of the fret (step S30), Any suitable welding technique may be used to weld the SMA wire to the connection components, such as spot-welding, arc welding, welding using a weld bar, heat-based welding, and laser welding. The tool used to deflect the SMA wire is then removed (step S9) as per Figure 5.

Figure 7 shows another modified method of manufacturing the SMA sub- assembly 1 using a different technique to control the degree of slackness in the length of SMA wire 20 and which is performed as follows. The steps of the method are the same as shown in Figure 4, except for the following modifications.

In step SI, the fret 2 comprising the body portion 3 and the pair of crimp portions 10 is provided with the crimp portions 10 being open, as described above. In step S2, a length of SMA wire 20 is laid on the pair of open crimp portions 10 in a predetermined position, as described above except that the length of SMA wire 20 is under tension.

In step S10, the body portion 3 is deformed so as to provide the length of SMA wire 20 with slack between the crimp portions 10 by decreasing the distance between the crimp portions 10. This may be performed for example as shown in Figures 8 and 9 which show the SMA sub-assembly 1 before and after step S14. Dotted lines 16 in Figure 8 show the edges of a part 17 of the body portion 3 that is deformed out of the plane of the body portion 3.

Further improvements may be achieved by applying a similar method to manufacture of an array of plural SMA sub-assemblies 1, for example as will now be described.

Figure 10 shows a one-dimensional array of SMA sub-assemblies 1 which are separate from each other. The frets 2 of each SMA sub assembly 1 may be cut from the same sheet of material.

Figure 11 shows a composite SMA sub-assembly 11 comprising a one- dimensional array of plural SMA sub-assemblies 1 that are connected together by being formed integrally from the same sheet of material, for example by cutting out from a larger sheet.

Figure 12 shows a two-dimensional array of SMA sub-assemblies 1 which are separate from each other. The frets 2 of each SMA sub-assembly 1 may be cut from the same sheet of material.

Figure 13 shows a composite SMA sub-assembly 12 comprising a two- dimensional array of plural SMA sub-assemblies 1 that are connected together by means of being formed integrally from the same sheet of material, for example by cutting out from a larger sheet.

Each of the arrays shown in Figures 10-13 may be made using the method shown in Figure 4. In this case, the plural SMA sub-assemblies may first be cut out from a larger sheet and arranged in an array as shown in Figures 10-13. In each case, the cutting may be performed for example by mechanical or laser cutting, stamping or pressing.

In principle, separate lengths of SMA wire 20 could be laid across each SMA sub-assembly in step S3, but manufacture is improved by instead laying the same piece of SMA wire 21 across all the pairs of open crimp portions 10 (or connection components), so that parts of that piece of SMA wire 21 between each pair of crimp portions 10 form the respective lengths of SMA wire 20. The piece of SMA wire 21 is then cut into the respective lengths of SMA wire 20 in respect of each SMA sub-assembly, as shown by the dotted lines.

Such manufacture of an array of plural SMA sub-assemblies 1 allows high volume processing which reduces the unit cost.

In the case of the composite SMA sub-assembly 11 or 12, there may subsequently be performed a step of removing the individual SMA sub-assemblies from the composite shape memory alloy sub-assembly 11 or 12, for example by cutting along the dotted lines 16 shown in Figs 8 and 9 using mechanical or laser cutting.

Figure 14 illustrates a method of manufacturing plural SMA sub-assemblies 1 together and which is performed as follows. The steps of the method are the same as shown in Figure 4 and described above, except for the following modifications.

In step Sll, there is provided a sheet of material 18 from which plural SMA assemblies 1 arranged in a one-dimensional or two-dimensional array are later to be cut out. However in step Sll only the pairs of crimp portions 10 of each SMA sub-assembly 1 are cut out, for example using mechanical or laser cutting. Figures 15 and 16 illustrate examples of such a sheet of material 18, Figure 15 illustrating the case of a one-dimensional array of SMA sub-assemblies and Figure 16 illustrating the case of a two-dimensional array of SMA sub-assemblies. In Figures 15 and 16 the cut pairs of crimp portions are shown by solid lines and the rest of the SMA sub-assemblies which are later to be cut out are shown in dotted outline.

In step S2, a length of SMA wire 20 is laid on each pair of open crimp portions 10 in a predetermined position. The SMA wire 20 is not under tension and so is slack. This step is the same as step S2 of the method of Figure 4, except that the same piece of SMA wire 21 is laid across all the pairs of open crimp portions 10, so that parts of that piece of SMA wire 21 between each pair of crimp portions 10 form the respective lengths of SMA wire 20. In the case of a two-dimensional array of SMA sub-assemblies, as shown for example in Figure 16, the single piece of SMA wire 21 is bent around to lie across successive rows of SMA sub-assemblies 1, but alternatively, separate straight pieces of SMA wire may be laid across each row of SMA sub-assemblies 1.

In step S3, the crimp portions 10 are crimped around the length of SMA wire 20, as described above. The above description of step S3 of the method of Figure 4 applies to the method of Figure 14 also.

Steps S4 and S5 may optionally be performed, as described above for the method of Figure 4.

The example manufacturing steps shown in Figure 14 may be modified when the fret comprises a pair of connection components instead of crimp portions. Specifically, steps S3, S4 and S5 may be replaced with a step to weld the SMA wire to the connection components of the fret.

In step S12, the SMA sub-assemblies 1 are cut out from the sheet of material 18, for example using mechanical or laser cutting. The cutting process may simultaneously cut (1) the sheet of material 18 to cut out the body portions 3 and (2) the piece of SMA wire 21 to separate the lengths of SMA wire 20.

Figures 17 and 18 show modified method of manufacturing plural SMA sub- assemblies 1 together which are modified as compared to the method of Figure 14 in the same way that the methods of Figures 5 and 7 are modified as compared to the method of Figure 4. Accordingly, for brevity, in respect of those modifications reference is made to the description of Figures 5 and 7 and is not repeated here. Similarly, Figures 26 and 27 show manufacturing methods in which the step to crimp the SMA wires (S3) is replaced by a step to weld the SMA to the connection components of the fret instead (step S30).

SMA sub-assemblies 1 as described above may be used to manufacture an SMA actuator assembly, as will now be described.

Figure 19 shows an example of an SMA actuator assembly 30 which is a camera arranged as follows.

The SMA actuator assembly 30 comprises a support structure 32 that has an image sensor 33 mounted thereon. The support structure 32 includes a base 34 which is a rigid plate. The image sensor 33 is fixed to the front side of the base 34. The support structure 32 also includes a chassis 36 that protrudes from the base 34 and may be a moulded component. The chassis 36 has a central aperture 37 aligned with the image sensor 33.

The SMA actuator assembly 30 further comprises a lens element 40 positioned in the aperture 37 and comprising a lens carriage 42 which holds a lens 41, although alternatively plural lenses may be present. The lens 41 may be made of glass or plastic. The SMA actuator assembly 30 is a miniature optical device in which the lens 41 has a diameter of at most 20 mm, preferably at most 15 mm, more preferably at most 10 mm.

The lens element 40 has an optical axis O aligned with the image sensor 33 and is arranged to focus an image on the image sensor 33. The lens element 40 also has a protrusion 43 that is formed on one side protruding laterally of the optical axis O. The SMA actuator assembly 30 also comprises a suspension system 50 that supports the lens element 40 on the support structure 32. The suspension system 50 is configured to guide movement of the lens element 40 with respect to the support structure 32 along the optical axis O, while constraining movement of the lens element 40 with respect to the support structure 32 in other degrees of freedom. Such relative movement of the lens element 40 changes the focus of the image on the image sensor 33, for example for providing autofocus or zoom. Accordingly, in this example the support structure 32 is a static part and the lens element 40 is a movable part that is movable with respect to the support structure 32 along the optical axis O. The terms "static" and "movable" refer to that relative motion.

In particular, the suspension system 50 comprises a bearing arrangement of plural rolling bearings 51. Each of the rolling bearings 51 comprises a bearing surface 53 on the support structure 32, in particular on the chassis 36, and a bearing surface 52 on the lens element 40, in particular on the lens carriage 42. Each of the rolling bearings 51 also comprises balls 54 disposed between the bearing surfaces 52 and 53. The balls 54 therefore act as rolling bearing elements, although as an alternative other types of rolling bearing element could be used, for example a roller.

As an alternative, the rolling bearings 51 may be replaced by plain bearings comprising bearing surfaces on each of the support structure 32 and the lens element 40 that conform and bear on each other to guide the relative movement.

The SMA actuator assembly 30 also comprises two lengths of SMA wire 20 (one of which is visible in Figure 19 that are arranged as follows to drive movement of the lens element 40 along the optical axis O. Each length of SMA wire 20 is connected to the support structure 32 at one end and to the lens element 40 at the other end by crimp portions 10 (which are the crimp portions 10 of an SMA sub-assembly as described in more detail below).

The lengths of SMA wire 20 have an angled-V arrangement of a similar type to that disclosed in International Patent Publication No. WO2007/113478. That is, each length of SMA wire 20 is inclined in the same sense and at the same acute angle Q with respect to a plane normal to the optical axis O which is the movement direction in this example. The angle Q is selected to provide gain between the change in length of the SMA wire 20 and the movement along the optical axis O, while also reducing the height projected along the optical axis, typically being in a range from a lower limit of 5 degrees, or more preferably 8 degrees, to an upper limit of 20 degrees, preferably 15 degrees, or more preferably 12 degrees, with respect to a plane normal to the optical axis O. The lengths of SMA wire 20 also have an angle therebetween of 90 degrees as viewed along the optical axis O which is the movement direction in this example.

In an alternative, simpler arrangement, one of the lengths of SMA wire 20 may be omitted.

The SMA actuator assembly 30 further comprises a compression spring 45 that is connected between the support structure 32 and the lens element 40 and acts a resilient biasing element for the lengths of SMA wire 20. Thus, when the lengths of SMA wire 20 cool, the compression spring 45 drives movement along the optical axis O in the opposite direction (downwards in Figures 19 and 20). As a result, the temperature of the lengths of SMA wire 20 and hence the position of the lens element 40 along the optical axis O can be controlled by control of the power of the drive signals.

The lengths of SMA wire 20 are arranged to be slack in the absence a drive signal being applied thereto, for example when the length of SMA wire 20 is at a temperature of 25°C. It has been appreciated by experiment and analysis that it is not necessary to hold the lengths SMA wire 20 in tension in the unpowered state. The SMA wire 20 is however configured so that a tension suitable for driving the SMA actuator assembly 30 may be applied to the SMA wire by application of suitable drive signals to heat the wire and cause it to contract. This may be achieved by controlling the degree of slackness in the lengths of SMA wire 20.

In addition, such a case of slack SMA wire in the unpowered state provides significant advantages. If an SMA wire is under tension in the unpowered state, then the SMA actuator assembly typically loses a large amount of its theoretical stroke, for example of the order of 50pm to 100pm in typical optical device. This is significant because the achievable stroke is often a limiting factor in miniaturisation of the SMA actuator assembly. On the other hand, by providing lengths of SMA wire 20 that are slack in the unpowered state, the length of the SMA wires 20 is increased, improving the stroke capability of the SMA actuator assembly 30, possibly up to its theoretical maximum.

A control circuit implemented in an IC chip (not shown) generates the drive signals and supplies them to the lengths of SMA wire 20, to which the control circuit is connected. The control circuit receives an input signal representing a desired position for the lens element 40 along the optical axis O and generates drive signals having powers selected to drive the lens element 40 to the desired position. The power of the drive signals may be either linear or varied using pulse width modulation.

The drive signals may be generated using a resistance feedback control technique, in which case the control circuit 20 measures the resistance of the lengths of SMA wire 20 and uses the measured resistance as a feedback signal to control the power of the drive signals. Such a resistance feedback control technique may be implemented as disclosed in any of the following International Patent Publications each of which is incorporated herein by reference: WO2013/175197; WO2014/076463; WO2012/066285; W02012/020212; W02011/104518; W02012/038703; W02010/089529 or W02010/029316.

Alternatively, the drive signals may be generated using closed-loop control based on the output of a Hall sensor which senses the position of the lens element 40 along the optical axis O.

Figure 20 shows an example of an SMA actuator assembly 30 which is a camera similar to that shown in Figure 19 but with the following modification to provide an angled-V arrangement of the type disclosed in International Patent Publication No. WO2007/113478. Instead of providing two lengths of SMA wire 20 that are separate pieces of SMA wire each connected by crimp portions 10 at each end as in Figure 19, a single length of SMA wire 20 is connected at each end to the support structure 32 by crimp portions 10 and is connected to the lens element 40 by being hooked over a hook feature 44 formed on the protrusion 43. As a result, the two parts of the length of SMA wire 20 on either side of the protrusion 43 form respective lengths of SMA wire 22 which have the same configuration, and hence the same function and operation, as the two lengths of SMA wire 20 in Figure 19.

Although particular SMA actuator assemblies 30 are shown in Figures 19 and 20 as an example, the SMA sub-assembly 1 could be used to manufacture other types of SMA actuator assembly 30. In one alternative, the SMA actuator assembly 30 may be a camera providing OIS of the type disclosed in International Patent Publication No. WO2013/175197, or a camera providing multiple functions of the type disclosed in International Patent Publication No. W02011/104518. In other alternatives, the SMA actuator assembly 30 may be an optical device in which the movable element is a lens element but there is no image sensor. In other alternatives, the SMA actuator assembly 30 may be an optical device wherein the movable part is an optical element other than a lens element, for example a diffractive optical element, a filter, a prism, a mirror, a reflective optical element, a polarising optical element, a dielectric mirror, a metallic mirror, a beam splitter, a grid, a patterned plate, or a grating, which may be a diffraction grating. In other examples, SMA actuator assembly 30 may be a type of device that is not an optical device and in which the movable element is not an optical element.

There will now be described methods of manufacturing the SMA actuator assembly 30 which may be for example of the type shown in Figures 19 or 20, using the SMA sub-assembly 1.

Figure 21 is a flow chart of a first method of manufacturing an SMA actuator assembly which is performed as follows.

In step Tl, there is provided a static part of the SMA actuator assembly 30, a movable part of the SMA actuator assembly 30 and an SMA sub-assembly 1 of the type described above. The movable part, for example the lens element 40 in the example of Figures 19 and 20, is movable with respect to the static part, for example the support structure 32 of Figures 19 and 20. In the first method of Figure 21, in the SMA sub-assembly 1, the crimp portions 10 are completely crimped around the SMA wire 20, or the connection components are welded to the SMA wire, as described above.

In step 12 the crimp portions 10 are attached to the static part and the movable part, respectively. This may be done by placing the SMA sub-assembly 1 onto the static part and the movable part with the crimp portions/connection components in the desired location and then fixing the crimp portions/connection components 10 themselves to the static part and the moving part, for example by setting of adhesive or mechanical fixing. The manner of fixing the crimp portions/connection components 10 allows some latitude in the placing of the SMA sub-assembly 1, such that the distance between the crimp portions/connection components 10 and the length of the SMA wire 20 remain the same as set by the configuration of the body portion 3 of the SMA sub-assembly 1.

In step T3, the body portion 3 is removed from the SMA sub-assembly, for example by mechanical or laser cutting. This leaves the crimp portions/connection components attached to the static part and the moving part, respectively. However, the length of the length of SMA wire 20 remains that correctly set by the separation between the crimp portions/connection components 10 in the SMA sub-assembly.

In the first method of Figure 21, as the crimp portions/connection components 10 are completely crimped around, or welded to, a length of shape memory alloy wire, then no further steps are carried out.

In an alternative case of using an SMA sub-assembly 1 wherein the crimp portions 10 are partly crimped around the length of shape memory alloy wire 20, then a second method shown in Figure 22 or a third method shown in Figure 23 may be used. Each of these methods includes the steps T1 to T3 of the first method, as described above, but with additional steps as follows.

In the second method of Figure 22, additional steps T4 and T5 are carried out during the manufacture of the SMA actuator assembly 30, in particular after step T2 of attaching the crimp portions 10 to the static part and the movable part, but before step T3 of removing the body portion 3 of the SMA sub-assembly 1. The additional steps T4 and T5 correspond to steps S4 and S5 in the method of manufacture of the SMA sub-assembly. That is, in step T4, a force is applied along the length of the SMA wire 20 to vary the degree of slackness (i.e. without introducing tension) or to introduce tension into the length of SMA wire 20, and, in step T5, the crimp portions 10 are completely crimped around the length of SMA wire 20, as described above.

In the third method of Figure 23, the same additional steps T4 and T5 are carried out but after the manufacture of the SMA actuator assembly 30, and in particular after step T3 of removing the body portion 3 of the SMA sub-assembly 1.

Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and where appropriate other modes of performing present techniques, the present techniques should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that present techniques have a broad range of applications, and that the embodiments may take a wide range of modifications without departing from any inventive concept as defined in the appended claims.

Claims

1. A shape memory alloy sub-assembly comprising at least one body portion holding apart a pair of crimp portions, the crimp portions being at least partly closed around a length of shape memory alloy wire which is slack between the crimp portions.

2. The shape memory alloy sub-assembly according to claim 1, wherein the crimp portions are partly closed around a length of shape memory alloy wire.

3. The shape memory alloy sub-assembly according to claim 1, wherein the crimp portions are completely closed around a length of shape memory alloy wire.

4. The shape memory alloy sub-assembly according to any preceding claim, wherein the body portion is a sacrificial body portion that is removable from the crimp portions.

5. The shape memory alloy sub-assembly according to any preceding claim, wherein the crimp portions are formed integrally with the body portion.

6. The shape memory alloy sub-assembly according to claim 5, wherein the crimp portions are formed integrally with the body portion from a sheet of material.

7. The shape memory alloy sub-assembly according to any preceding claim, comprising a single body portion.

8. The shape memory alloy sub-assembly according to any one of claims 1 to 6, being a composite shape memory alloy sub-assembly comprising a one- dimensional or two-dimensional array of body portions that are connected together.

9. The shape memory alloy sub-assembly according to claim 8, wherein the body portions are connected together by being formed integrally.

10. The shape memory alloy sub-assembly according to claim 8 or 9, wherein the lengths of shape memory alloy wire in respect of each body portion are lengths of the same piece of shape memory alloy wire.

11. A method of manufacture of a shape memory alloy sub-assembly comprising:

providing at least one body portion holding apart a pair of open crimp portions;

laying a length of shape memory alloy wire on the or each pair of open crimp portions; and

at least partly closing the crimp portions around the length of shape memory alloy wire and providing the length of shape memory alloy wire with slack between the crimp portions.

12. The method according to claim 11, wherein the crimp portions are completely closed around a length of shape memory alloy wire.

13. The method according to claim 11, wherein the crimp portions are partly closed around a length of shape memory alloy wire.

14. The method according to claim 13, further comprising :

adjusting the degree of slackness or tension of the length of shape memory alloy wire; and

completely closing the crimp portions around the length of shape memory alloy wire.

15. The method according to any one of claims 11 to 14, wherein the step of laying the length of shape memory alloy wire on the or each pair of open crimp portions is performed with the length of shape memory alloy wire under tension, and the method further comprises:

applying a tool that deflects the length of SMA wire laterally between the crimp portions before closing the crimp portions around the length of shape memory alloy wire and removing the tool after closing the crimp portions around the length of shape memory alloy wire.

16. The method according to any one of claims 11 to 13, wherein the steps of laying the length of shape memory alloy wire on the or each pair of open crimp portions and closing the crimp portions around the length of shape memory alloy wire are performed with the length of shape memory alloy wire under tension, and the method further comprises:

deforming the body portion so as to provide the length of shape memory alloy wire with the slack between the crimp portions.

17. The method according to any one of claims 11 to 16, wherein the body portion is a sacrificial body portion that is removable from the crimp portions.

18. The method according to any one of claims 11 to 17, wherein the crimp portions are formed integrally with the body portion.

19. The method according to claim 18, wherein the crimp portions are formed integrally with the body portion from a sheet of material.

20. The method according to any one of claims 11 to 19, wherein a single body portion is provided.

21. The method according to any one of claims 11 to 19, wherein a one- dimensional or two-dimensional array of body portions are provided.

22. The method according to claim 21, wherein the body portions are separate.

23. The method according to claim 21, wherein the body portions are connected together.

24. The method according to claim 23, wherein the body portions are connected together by being formed integrally.

25. The method according to any one of claims 21 to 24, wherein the step of laying a length of shape memory alloy wire on each pair of open crimp portions comprises laying the same piece of shape memory alloy wire across all the pairs of open crimp portions.

26. A method of manufacture of shape memory alloy sub-assemblies comprising:

providing a sheet of material comprising plural pairs of open crimp portions; laying a length of shape memory alloy wire on each pair of open crimp portions;

at least partly closing the crimp portions around the length of shape memory alloy wire; and

cutting out from the sheet of material plural shape memory alloy sub- assemblies each comprising a body portion formed integrally with a pair of crimps holding a length of SMA wire.

27. The method according to claim 26, wherein the crimp portions are completely crimped around a length of shape memory alloy wire.

28. The method according to claim 26, wherein the crimp portions are partly crimped around a length of shape memory alloy wire.

29. The method according to claim 28, further comprising :

30. The method according to any one of claims 26 to 29, wherein the step of at least partly closing the crimp portions around the length of shape memory alloy wire is performed with the length of shape memory alloy wire slack between the crimp portions, optionally when the length of shape memory alloy wire is at a temperature of 25°C.

31. The method according to any one of claims 26 to 29, wherein the step of laying the length of shape memory alloy wire on the or each pair of open crimp portions is performed with the length of shape memory alloy wire under tension, and the method further comprises:

32. The method according to any one of claims 26 to 29, wherein the steps of laying the length of shape memory alloy wire on the or each pair of open crimp portions and closing the crimp portions around the length of shape memory alloy wire are performed with the length of shape memory alloy wire under tension, and the method further comprises:

33. The method according to any one of clause 26 to 32, wherein the plural shape memory alloy assemblies are arranged in a one-dimensional or two- dimensional array.

34. The method according to any one of clauses 26 to 33, wherein the step of laying a length of shape memory alloy wire on each pair of open crimp portions comprises laying the same piece of shape memory alloy wire across all the pairs of open crimp portions.

35. A method manufacture of a shape memory alloy actuator assembly, the method comprising:

providing a static part, a movable part that is movable with respect to the static part, and a shape memory alloy sub-assembly comprising a body portion holding apart a pair of crimp portions, the crimp portions being at least partly closed around a length of shape memory alloy wire which is slack between the crimp portions;

attaching the crimp portions to the static part and the movable part, respectively; and

removing the body portion, leaving the crimps attached to the static part and the moving part, respectively.

36. The method according to claim 35, wherein, when the shape memory alloy sub-assembly is provided, the crimp portions are partly crimped around a length of shape memory alloy wire.

37. The method according to claim 36, wherein the method further comprises adjusting the degree of slackness or tension of the shape memory alloy wire and thereafter fully closing the crimp portions around the shape memory alloy wire.

38. The method according to claim 37, wherein the steps of adjusting the degree of slackness or tension of the shape memory alloy wire and thereafter fully closing the crimp portions around the shape memory alloy wire are performed : after the step of attaching the crimp portions to the static part and the movable part, respectively; and before or after the step of removing the body portion.

39. The method according to claim 35, wherein, when the shape memory alloy sub-assembly is provided, the crimp portions are completely crimped around a length of shape memory alloy wire.

40. The method according to any one of claims 35 to 39, wherein the crimp portions are formed integrally with the body portion.

41. The method according to claim 40, wherein the crimp portions are formed integrally with the body portion from a sheet of material.

42. The method according to any one of claims 35 to 41, wherein the step of providing a shape memory alloy sub-assembly comprises:

providing a composite shape memory alloy sub-assembly comprising an array of body portions that are connected together; and

removing the shape memory alloy sub-assembly comprising a body portion from the composite shape memory alloy sub-assembly.

43. The method according to any one of claims 35 to 42, wherein the movable part is supported on the support structure by a suspension system arranged to guide movement of the movable element with respect to the static part.

44. The method according to claim 43, wherein the suspension system comprises a bearing arrangement.

45. The method according to any one of claims 35 to 44, wherein the movable part is an optical element.

46. The method according to claim 45, wherein the movable part is movable with respect to the static part along an optical axis of the optical element.

47. The method according to claim 45 or 46, wherein the movable part is a lens element comprising at least one lens.

48. The method according to claim 47, wherein the at least one lens has a diameter of at most 20 mm.

49. The method according to claim 47 or 48, wherein the static part has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

50. A shape memory alloy actuator assembly comprising:

a static part;

a movable part that is movable with respect to the static part; and at least one length of shape memory alloy wire connected between the static part and the movable part and which is slack.

51. The shape memory alloy actuator assembly according to claim 50, wherein the movable part is supported on the support structure by a suspension system arranged to guide movement of the movable element with respect to the static part.

52. The shape memory alloy actuator assembly according to claim 51, wherein the suspension system comprises a bearing arrangement.

53. The shape memory alloy actuator assembly according to any one of claims 50 to 52, wherein the movable part is an optical element.

54. The shape memory alloy actuator assembly according to claim 53, wherein the movable part is movable with respect to the static part along an optical axis of the optical element.

55. The shape memory alloy actuator assembly according to claim 53 or 54, wherein the movable part is a lens element comprising at least one lens.

56. The shape memory alloy actuator assembly according to claim 55, wherein the at least one lens has a diameter of at most 20 mm.

57. The shape memory alloy actuator assembly according to claim 55 or 56, wherein the static part has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

58. A shape memory alloy (SMA) sub-assembly comprising at least one body portion holding apart a pair of connection components that are welded to a length of SMA wire which is slack between the connection components.

59. The SMA sub-assembly as claimed in claim 58 wherein the body portion is a sacrificial body portion that is removable from the connection components.

60. The SMA sub-assembly as claimed in claim 58 or 59 wherein the connection components are formed integrally with the body portion.

61. The SMA sub-assembly as claimed in claim 60 wherein the connection components are formed integrally with the body portion from a sheet of material.

62. The SMA sub-assembly according to any one of claims 58 to 61 comprising a single body portion.

63. The SMA sub-assembly according to any one of claims 58 to 61 being a composite SMA sub-assembly comprising a one-dimensional or two-dimensional array of body portions that are connected together.

64. The SMA sub-assembly according to claim 63 wherein the body portions are connected together by being formed integrally.

65. The SMA sub-assembly according to claim 63 or 64 wherein the lengths of SMA wire in respect of each body portion are lengths of the same piece of SMA wire.

66. A method of manufacture of a shape memory alloy (SMA) sub-assembly comprising:

providing at least one body portion holding apart a pair of connection components;

laying a length of SMA wire on the or each pair of connection components; and

welding the SMA wire to the connection components.

67. The method according to claim 66 wherein the step of welding the SMA wire to the connection components comprises any one of: arc welding, welding using a weld bar, heat-based welding, laser welding.

68. The method according to claim 66 or 67 further comprising:

adjusting, prior to welding, the degree of slackness or tension of the length of SMA wire.

69. The method according to any one of claims 66 to 68 wherein the step of laying the length of SMA wire on the or each pair of connection components is performed with the length of SMA wire under tension, and the method further comprises:

applying a tool that deflects the length of SMA wire laterally between the connection components and removing the tool after welding the connection components to the length of SMA wire.

70. The method according to any one of claims 66 to 68 wherein the step of laying the length of SMA wire on the or each pair of connection components is performed with the length of SMA wire under tension, and the method further comprises:

deforming the body portion so as to provide the length of SMA wire with the slack between the connection components.

71. The method according to any one of claims 66 to 70 wherein the step of laying a length of SMA wire on each pair of connection components comprises laying the same piece of SMA wire across all the pairs of connection components.

72. A method of manufacture of shape memory alloy (SMA) sub-assemblies comprising:

providing a sheet of material comprising plural pairs of connection components;

laying a length of SMA wire on each pair of connection components;

welding the SMA wire to each pair of connection components; and cutting out from the sheet of material plural SMA sub-assemblies each comprising a body portion formed integrally with a pair of connection components holding a length of SMA wire.

73. A method of manufacture of a shape memory alloy (SMA) actuator assembly, the method comprising :

providing a static part, a movable part that is movable with respect to the static part, and a SMA sub-assembly comprising a body portion holding apart a pair of connection components, the connection components being welded to a length of shape memory alloy wire which is slack between the connection components;

attaching the connection components to the static part and the movable part, respectively; and

removing the body portion, leaving the connection components attached to the static part and the moving part, respectively.

74. The SMA actuator assembly according to claim 50 wherein the movable part is movable with respect to the static part to deliver haptic feedback.