CN113168233B - Shape memory alloy actuator - Google Patents

Abstract

The present technology generally relates to shape memory alloy actuators, and to methods of making such SMA actuators. We describe a shape memory alloy (SMA) actuator comprising: a static element (104); a movable element (106) movable relative to the static element; and a plurality of SMA wires (108) each connected to one or both of the static element and the movable element and causing movement of the movable element when contracted. At least one connector (110a, 110c), preferably a crimp connector, connects at least two of the plurality of SMA wires (108) to at least one of the static element and the movable element.

Description

Shape memory alloy actuator

The present technology relates generally to shape memory alloy actuators, and to methods of manufacturing such SMA actuators.

Consumer electronic devices such as laptop computers and smartphones may employ different types of controls to provide some feedback to the user of the device indicating that they have successfully pressed a button on the device. This is commonly referred to as tactile feedback, and tactile buttons or controls on the device may provide a tactile sensation to the user to confirm that they have successfully pressed the buttons/controls/switches. To generate a good tactile sensation, it is desirable that the actuator move with a high enough force to provide sufficient displacement. It should be appreciated that there are other applications, such as latches or medical devices, where high forces are also required to achieve relatively large displacements.

The present inventors have identified a need for an improved shape memory alloy actuator.

According to a first method of the present technology, a Shape Memory Alloy (SMA) actuator is provided that includes a static element, a movable element movable relative to the static element, a plurality of SMA wires each coupled to one or both of the static element and the movable element and causing movement of the movable element upon contraction, and a coupling element that couples at least two wires from the plurality of SMA wires to one of the static element and the movable element.

Preferably, the coupling element comprises a crimp connector (crimp connector) holding at least two wires.

According to a second method of the present technology, there is provided a haptic assembly comprising a touchable member (e.g. a button) and an actuator as described above, wherein when the user presses or releases the touchable member, the actuator assembly is activated to provide haptic feedback to the user by moving the touchable member using a movable element.

According to another method of the present technique, there is provided a method of manufacturing an SMA actuator (e.g., one as described above) comprising feeding a plurality of SMA wires into an open crimp connector, closing the crimp connector, and trimming any excess wires.

According to another method of the present technology, there is provided an apparatus comprising any SMA actuator described herein. The apparatus may be a smart phone, a camera, a foldable smart phone, a foldable image capturing device, a foldable smart phone camera, a foldable consumer electronic device, a camera with folding optics, an image capturing device, an array camera, a 3D sensing device or system, a servo motor, a consumer electronic device (including household appliances, such as vacuum cleaners, washing machines, and lawnmowers), mobile or portable computing devices, mobile or portable electronic devices, laptop computers, tablet computing devices, electronic readers (also known as e-book readers or e-book devices), computing accessories or computing peripherals (e.g., mice, keyboards, headphones, earphones, earplugs, and the like), audio devices (e.g., headphones, headsets, headphones), and the like, security systems, gaming systems, game accessories (e.g., controllers, headsets, wearable controllers, joysticks, and the like), robotic or robotic devices, medical devices (e.g., endoscopes), augmented reality systems, augmented reality devices, virtual reality systems, virtual reality devices, wearable devices (e.g., watches, smartwatches, fitness trackers, and the like), autopilots (e.g., unmanned vehicles), vehicles, tools, surgical tools, remote controls (e.g., for drones or consumer electronics devices), clothing (e.g., clothing, shoes, and the like), switches, dials or buttons (e.g., switches, dials, and the like), display screens, touch screens, and Near Field Communication (NFC) devices, this is a non-exhaustive list of possible devices.

Preferred features are set out in the appended dependent claims.

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

FIG. 1a is a schematic cross-sectional view of a first haptic assembly;

FIG. 1b is a schematic cross-sectional view of a second haptic assembly;

FIG. 1c is a schematic enlarged view of a detail in FIG. 1 b;

FIGS. 2a and 2b are schematic block diagrams of functional arrangements of the haptic components shown in FIGS. 1 a-1 c;

FIG. 3a is a graph plotting temperature change over time for a single wire of 60 μm diameter heated, for each of the middle wire (W2) and the outer wire (W1) in a set of three adjacent contact wires (each of 35 μm diameter and heated), and for each of the middle wire (W2) and the outer wire (W1) in a set of three wires (heated and each of 35 μm diameter but spaced apart such that the wires are adjacent but not touching);

FIG. 3b is a graph plotting temperature over time as the arrangement of lines of FIG. 3a is cooled;

FIG. 4a is a schematic cross-sectional view of another haptic assembly similar to that shown in FIG. 1 b;

FIG. 4b is a graph plotting temperature versus time for various distances (e.g., 420 μm to 40 μm) between the heat sink and the wire as the wire is cooled;

FIG. 4c is a graph plotting temperature as a function of distance between the heat sink and the wire as the wire is cooled, wherein temperature is a value after 100 milliseconds or 200 milliseconds of cooling, respectively;

FIG. 4d is a graph plotting temperature versus time for various distances (e.g., 420 μm to 40 μm) between the heat sink and the wire as the wire is heated;

FIG. 5 is a graph plotting time variations for restoring different displacements for each of three different arrangements;

FIGS. 6a and 6b are schematic partial views of different arrangements of crimps used in the assembly;

FIG. 7 is a schematic cross-sectional view of a third haptic assembly, and

Fig. 8 is a schematic diagram of a method of pressing wires in an SMA actuator.

The embodiments described below illustrate Shape Memory Alloy (SMA) actuators. Such SMA actuators may be any type of device that includes a static part (or element-these terms being used interchangeably) and a movable part that is movable relative to the static part. The movable part is moved by a plurality of SMA wires that are coupled (or connected-these terms being used interchangeably) between the static part and the movable part. The coupling element couples the at least two wires to at least one of the static part and the movable part. The coupling element may couple any number (N) of wires and is between two wires and six wires by way of example only.

The coupling element may provide a direct connection between the at least two SMA wires and one of the static element and the movable element. In an arrangement with direct connections at both ends of the SMA wire, "coupled between" means that there are only the SMA wire and the coupling element between the static element and the movable element. Alternatively, the coupling element may couple the at least two wires to the intermediate component to provide an indirect connection between the at least two wires and one of the static element and the movable element. The intermediate element itself may be connected to one of the static element and the movable element by a direct connection or an indirect connection. For an indirect connection, the intermediate element itself may be connected to at least one other intermediate element, and for a direct connection, the intermediate element is directly connected to one of the static element and the movable element.

The coupling element may comprise a fixed connector that provides a permanent (i.e. fixed) connection between the SMA wire and the static element or the movable element. Such a fixed connector may be in the form of a crimp connector, a welded component welded to at least two wires to form a weld, or other similar connector. When crimp connectors are used, the coupling element may comprise a single crimp connector holding a plurality of wires, or may comprise a plurality of adjacent crimp connectors, each holding a single wire. The or each crimp connector may have a width of between 500 μm and 750 μm. Adjacent crimp connectors may be vertically aligned, i.e. stacked. Alternatively, adjacent crimp connectors may be laterally offset from each other, or vertically offset from each other, or both laterally and vertically offset from each other.

The coupling element may optionally include a connector that provides a non-fixed connection between the plurality of SMA wires and the static element or the movable element. Such non-stationary connectors may be in the form of protruding elements, such as hooks, detents (dowel pin) or the like, around which the SMA wire is looped or similarly held in place.

There may be a first coupling element coupling one end of the SMA wire to the static element and a second coupling element coupling the opposite end of the SMA wire to the movable element. The first coupling element may be of the same type as the second coupling element, i.e. both the first coupling element and the second coupling element may be crimp connectors holding a plurality of wires or may be soldered points, the crimp connectors may comprise a plurality of adjacent crimp connectors, each of which holds a single wire. Alternatively, the first coupling element may be of a different type than the second coupling element, i.e. the first coupling element may comprise one or more crimp connectors and the second coupling element may be a protruding element, or the first coupling element may be a crimp connector holding a plurality of wires and the second coupling element may comprise a plurality of adjacent crimp connectors (each crimp connector holding a single wire).

The first coupling element and the second coupling element coupled to the same wire may be considered to form a pair of coupling elements. There may be multiple pairs of first and second coupling elements, with each pair coupling element coupling at least two different wires to both the static element and the movable element. In this way, a plurality of wires may be divided between pairs of coupling elements. For example, there may be six wires, with a first set of three wires coupled between a first pair of coupling elements and a second set of three wires coupled between a second pair of coupling elements.

When multiple wires are activated, such as in a haptic assembly, the SMA wires contract to move the movable part in response to detecting a need for haptic feedback. The first pair of coupling elements may couple the first set of at least two wires to the movable element and the second pair of coupling elements may couple the second set of at least two wires to the movable element, wherein the movable element moves in one direction when the wires coupled to the first pair of coupling elements and the second pair of coupling elements contract. For example, a first pair of coupling elements may couple at least two wires to one side of the movable element, and a second pair of coupling elements may couple at least two wires to an opposite side of the movable element, and the direction of movement may be substantially parallel to the opposite side of the movable element. Arranging the pairs of coupling elements on opposite sides of the movable element may result in balanced application of forces from contraction of the wire, i.e. rotation of the movable element may be avoided. Similar results are obtained by coupling at a position near the opposite edge of one end of the movable element. These are merely examples and any suitable coupling location on the movable element may be used.

The movable part is restorable to its original position by a restorative element (restoring element) that provides a restorative force. When activation of the SMA wire ceases, e.g. when power is removed, the SMA wire may also be restored to its original length by the restoring element. The restoring element may be a resilient element, such as a spring, a flexure (flexure), other SMA wire, or a force applied by a user's finger at the surface of the touchable member. For example, there may be a first pair of coupling elements coupling the first set of at least two wires to the movable element and a second pair of coupling elements coupling the second set of at least two wires to the movable element, wherein the movable element moves in a first direction when the first set of at least two wires is contracted and moves in a direction opposite to the first direction when the second set of at least two wires is contracted. For example, a first pair of coupling elements may couple a first set of at least two wires to one end of the movable element, and a second pair of coupling elements may couple a second set of at least two wires to an opposite end of the movable element. This is just one example and any suitable coupling location on the movable element may be used.

Embodiments of the present technology describe SMA actuators designed to deliver high forces, e.g., between 1.2 and 3N, more preferably between 1.2 and 10N, while maintaining strain in the wire within safe limits (e.g., a 2% -3% reduction in length from the original length). The force will depend on the desired target displacement. A plurality of relatively thin wires (e.g., about 25 μm or 35 μm in diameter, for example) are used in combination to provide the desired force. As explained in more detail below, the use of multiple wires provides a total cross section designed to deliver the desired force. Furthermore, the use of multiple wires allows the wires to cool faster than a single wire with a similar cross-section. Thus, the plurality of finer SMA wires are ready to be re-activated faster than a single wire having an equivalent cross-sectional area.

SMA actuators may be incorporated into a haptic assembly to move a button or other touchable element (movable element) contacted by a user relative to a housing or shell (static element) to impart a haptic sensation to a user pressing the button (or other touchable element). Embodiments of the present technology describe haptic assemblies that may be arranged to move a button laterally along an edge of a device, perpendicular to the edge of the device, helically around an axis perpendicular to the edge of the device, or in any other suitable direction, such as rotating in a plane parallel to the edge of the device or in a plane perpendicular to the device. Examples of actuators that move buttons in a lateral direction with respect to user contact are described for example in WO2018/046937 and GB 2551657. Examples of actuators that produce vertical movement are described in the inventors' GB1803084.1 and GB 1813008.8. Examples of arrangements that may be used to connect SMA actuators to crimps in a haptic assembly are described in WO2016/189314, GB1800484.6, GB1801291.4 and GB 1815673.7.

The present technique may provide localized haptic sensations caused by direct pulses rather than by inertial effects. For example, smartphones include inertial haptic actuators-when haptic effects are desired, a considerable mass is moved. The movement of the mass causes the entire smartphone to shake or vibrate. Thus, the haptic effect is global, not local. The present technology provides localized haptic feedback. Further, the haptic feedback provided by the present technology may be customized by the user by modifying software parameters. This allows different types of haptic feedback to be provided for different purposes or to suit different users.

Each haptic component described herein may be incorporated into any device in which it may be useful to provide haptic feedback to a user of the device. For example, the haptic component may be incorporated into any of the electronic or consumer electronic devices listed previously, including, but not limited to, computers, laptop computers, portable computing devices, smartphones, computer keyboards, gaming systems, portable gaming devices, gaming equipment/accessories (e.g., controllers, wearable controllers, etc.), medical devices, user input devices, and the like. It should be appreciated that this is a non-limiting, non-exhaustive list of possible devices that may incorporate any of the haptic components described herein. For example, the haptic components described herein may be incorporated into a smartphone or otherwise provided along an edge of the smartphone or on a surface of the smartphone.

Various SMA actuators will now be described with reference to the accompanying drawings. It should be understood that the elements or features described with respect to one particular drawing figure may be equally applied to any drawing figure described herein, e.g., a crimp holding multiple wires may be used in combination with a crimp holding a single wire, the total number of SMA wires may be selected to provide the desired force, and the heat sink(s) may be incorporated in any embodiment. Furthermore, while the figures illustrate the incorporation of SMA actuators in a haptic assembly, it should be understood that SMA actuators may be incorporated in other devices requiring high forces, such as latches or medical devices.

Fig. 1a shows a cross-sectional view of a first arrangement of SMA actuators within a haptic assembly 100. The haptic assembly 100 includes a button 102 (although it should be understood that other touchable members, surfaces or elements may be used interchangeably). The user may press the button 102 to perform a particular operation, such as making a selection, opening/closing the device, entering data (e.g., typing on a keyboard), scrolling, opening/closing a function of the device in which the assembly 100 is located, or adjusting the function (e.g., adjusting the volume of audio output from the device), etc. Pressing or releasing button 102 may cause haptic feedback or communicate a haptic sensation to the user, providing some sensory feedback (particularly touch-based feedback) to the user to indicate that the operation has been performed.

In many of the arrangements described herein, the button 102 may be a surface feature on an apparatus/device that includes a haptic component. Such a surface may be pressed in a similar manner to a button, and pressing or releasing the surface may be detected by a sensor and may trigger haptic feedback. However, instead of pressing or releasing a button (or surface) to trigger haptic feedback, the haptic feedback may be triggered by software in response to another event. For example, if a user makes a selection on the screen of their smartphone, the selection may cause haptic feedback to be triggered, where the feedback is provided by a button or surface feature. (software triggered haptic feedback may occur in a particular application, such as in a game and/or virtual/augmented reality device). Thus, in many of the arrangements and embodiments described herein, direct pressing of the tactile button 102 may not be necessary in order to communicate tactile feedback. However, in each case, the mechanism will determine which sensor records the need to provide haptic feedback, and in the case of multiple actuators to provide feedback, the mechanism can determine which appropriate actuator(s) will be activated to provide haptic feedback.

In the arrangement shown in fig. 1a, the haptic assembly 100 may include a housing 104 (also referred to herein as a "support," "chassis," "case," and "shell"). The housing 104 may include a cavity or recess. The button 102 may be disposed within a cavity of the housing 104. As shown, the button may be arranged with the cavity such that a contact surface (which may also be referred to as an exterior surface, or an upper surface) of the button is substantially level/flush with an exterior surface of the housing 104. Alternatively, the button may protrude from the housing. It should be appreciated that the housing 104 surrounds and encloses the button 102 such that only the contact surface 106 of the button is visible/accessible to the user.

The SMA actuator may include an intermediate movable element 106 disposed within a cavity below the button 102. The movable element 106 is movable relative to the stationary part (i.e., the housing) in a first direction perpendicular to the outer surface of the housing 104. Contact of the user's finger on the contact surface of the button may cause the button to move into or out of the housing as appropriate, such as in the direction of arrow 116. A sensor (not shown) may be mounted in the housing below the button 102 and the movable element 106. The sensor is any suitable sensor for determining that tactile feedback is required, for example by detecting a push of a button. The sensor may be coupled to a control circuit (not shown) and the sensor may be configured to communicate with the control circuit when haptic feedback is desired. For example, the sensor may detect when the force acting on the sensor changes, or when the force acting on the sensor has been applied for a minimum duration. As an example, detection of a button pressed by a user by a sensor results in haptic feedback being generated and applied by a haptic component.

The movable element 106 may also be movable relative to the housing in a second, different direction, which may be substantially perpendicular to the first direction, e.g., substantially parallel to the outer surface of the housing 102. Movement of the movable element 106 in the second direction may cause movement of the button 102 in the first direction to provide a tactile sensation to the user. The concept of moving the intermediate movable element 106 in one direction to cause the button 102 to move in the other direction may be implemented in a variety of ways.

There are a plurality of bearings 128 located between the sloped side of the movable element 106 and the adjacent sloped side of the button to reduce friction between the movable element and the button. Similarly, there are multiple bearings between the movable element 106 and the housing to facilitate movement of the movable element by reducing friction.

The term "bearing" is used interchangeably herein with the terms "sliding bearing", "sliding body bearing", "rolling bearing", "ball bearing", "flexure" and "roller bearing". The term "bearing" as used herein generally means any element or combination of elements that functions to limit movement to only the desired movement and reduce friction between moving parts. The term "plain bearing" is used to mean a bearing in which a bearing element slides over a bearing surface, and includes "slide bearings". The term "rolling bearing" is used to mean a bearing in which rolling bearing elements (e.g., balls or rollers) roll on a bearing surface. The bearing may be disposed on or may include a non-linear bearing surface. In some embodiments of the present technology, more than one type of bearing element may be used in combination to provide bearing functionality. Thus, the term "bearing" as used herein includes, for example, any combination of a sliding body bearing, a ball bearing, a roller bearing, and a flexure. In embodiments, a suspension system may be used to suspend the intermediate movable element and/or button within the haptic assembly and limit movement to only the desired movement. For example, a suspension system of the type described in WO2011/104518 may be used. Thus, it should be understood that the term "bearing" as used herein also means a "suspension system". In embodiments, the bearing may be disposed on or may include a non-linear bearing surface. The bearing may be formed of any suitable material, such as ceramic.

In this arrangement, the button 102 and the movable element 106 are wedge-shaped such that the wider end of the wedge-shaped button 102 is proximate to the narrower end of the wedge-shaped movable element 106. This arrangement means that when the movable element 106 is moved in a second direction within the housing 104 (i.e., substantially parallel to the surface of the housing), the button is moved in a first direction (i.e., substantially perpendicular to the surface of the housing). In this arrangement, the intermediate movable element 110 is a "single wedge" in that only one surface of the element is sloped/beveled.

The SMA actuator includes a plurality (e.g., N) of Shape Memory Alloy (SMA) actuator wires 108, for example, there may be 2 to 6 wires. As shown, the SMA wire 108 extends into another cavity 112 in the housing 104. The two ends of the SMA actuator wire 108 are connected to the housing 104 using a pair of coupling elements in the form of connectors/crimps 110a, 110b, the connectors/crimps 110a, 110b being electrical and mechanical connectors (for connecting the SMA actuator wire to a power source). Each connector holds the ends of a plurality of wires. Each of the SMA wires 108 hooks at its midpoint onto a hook 120 provided on one side of the movable element 106. Thus, the hook is another coupling element that couples and connects the plurality of SMA wires to the movable element. Each half of each wire may be considered to form one effective wire segment, and the two effective wire segments of each SMA actuator wire act mechanically in parallel, and thus each annular SMA actuator wire may provide twice the force of a single wire (which spans only once from the movable element to the housing).

In this arrangement there is a coupling element that couples each SMA wire to the movable element at its midpoint using a hook, and there are also two further coupling elements in the form of crimps, each of which couples a plurality of SMA wires to the static element at one end thereof. Thus, the coupling element coupling each SMA wire to the movable element has a different structure (i.e. is of a different type) than the coupling element coupling each SMA wire to the static element. Further, in this arrangement, the crimp is between each SMA wire and the static element, so each SMA wire has a direct connection with the static element, but it will be appreciated that the connection may also be indirect, so there may be one or more intermediate elements between each SMA wire and the static element.

When haptic sensation is desired, the request is communicated to a control circuit (not shown). Each SMA actuator wire 108 is then powered. When each SMA actuator wire 108 is energized, it heats up and contracts. Contraction of each SMA actuator wire 108 causes the intermediate movable element 106 to move laterally within the cavity and toward the other cavity 112. The wedge shape of the movable element 106 forces the button 102 to move upward as the movable element 106 moves laterally. In other arrangements, the wedge may be arranged to move the button downwardly or laterally. The intermediate movable element may move the button between 20 μm and 0.5mm, for example. In some embodiments, the button may move up to 1mm.

The haptic assembly may include a restoring element 126 that opposes the force of the SMA actuator wire 108. The restoring element 126 may be disposed within the other cavity 112 and may be coupled to the housing 104 at one end and to the movable element 106 at the other end. The return element 126 (e.g., a return spring or any suitable biasing resilient element) may be arranged to resist contraction of the SMA wire 108, thereby moving the movable element in the opposite direction when the SMA wire 108 is unpowered. It should also be appreciated that the recovery element 126 may include one or more additional SMA wires that pull the movable element 104 in an opposite direction from the plurality of SMA wires 108 when contracted.

There may be an end stop 114 formed as part of the housing within the cavity or may be a separate element within the cavity. The position of the end stop in the cavity may be arranged to limit the movement of the movable element. In general, if the SMA actuator wires are stretched too far (i.e., beyond a certain tension), the SMA actuator wires may weaken or break, even fracture. The force of the restoring element 126 on the intermediate movable element 110 may cause the SMA actuator wires to become overstretched. Thus, the end stops 114 may limit movement of the intermediate movable element 110 so that the SMA actuator wires 108 are not over stretched. Similarly, if there is no end stop, the force applied by the user's finger to the button surface may cause the wire to be over stretched.

Figure 1b shows a plan view of another haptic assembly 100' comprising three pairs of parallel SMA actuator wires. The function and structure of the haptic assembly 100' is the same as that shown in fig. 1a, except for the arrangement of the wires, and thus similar features are not described for the sake of brevity. In this arrangement, the actuator wires of each pair of actuator wires are coupled to opposite sides of the intermediate movable element 106. In some arrangements, opposite sides means that the actuator wire may be coupled to opposite sides of the intermediate movable element 106 parallel to the direction of movement of the intermediate movable element. In other arrangements, opposite sides may mean that the actuator wires may be coupled to the same end face of the intermediate movable element, but located on both sides of the end face. In both arrangements, the pair of wires acts in the same direction (i.e., can apply force to the intermediate movable element in the same direction) as compared to a single wire coupled to one side of the intermediate movable element to provide twice the force.

Three SMA actuator wires (one of each pair of wires) are coupled at one end to the intermediate movable element 106 via a coupling element in the form of a crimp 110c (or a crimp connector-these terms being used interchangeably) and at the other end to the housing 104 via a coupling element in the form of a crimp 110 a. The pair of crimps 110a, 110c may be considered to form a first pair of coupling elements coupling three wires to both the intermediate movable element 106 and the housing 104. Each crimp 110a, 110c holds opposite ends of three wires. In this arrangement, each SMA wire has a direct connection to the housing, but it will be appreciated that the connection may also be indirect, so that there may be one or more intermediate elements between each SMA wire and the housing.

Similarly, on the opposite side of the movable element (i.e., on the side not visible as shown in FIG. 1 b), there are three actuator wires, with one (not shown) of each pair being coupled at one end to the intermediate movable element 106 via a connector or crimp and at the other end to the housing 104 via a connector or crimp. Thus, the three SMA actuator wires are in turn coupled to both the intermediate movable element 106 and the housing by the pair of coupling members.

Fig. 1c schematically shows a detail of the crimp 110a connecting the end of each of the three wires to the housing. Although arrows are shown from fig. 1b, it should be understood that the details of the crimp in fig. 1c also apply to fig. 1a. In each individual crimp, there are three ends of the wires 108a, 108b, 108 c. There may be a spacing between each wire, and such spacing may be uniform. However, there may be no or very little spacing between the wires.

The width w of each crimp may be sufficient to hold and connect to each of the three wires. The crimp width w is the dimension of the crimp parallel to the SMA wire within the crimp. Thus, the width defines the amount by which each SMA wire is held in the crimp. The width may be between 400 μm and 750 μm, with standard crimps typically having a width of 500 μm. For example, the crimp holding three wires may have a standard width. A larger crimp may form a better mechanical connection between the crimp and the wire due to the presence of more crimp material. The length is the dimension of the crimp perpendicular to the width and is defined after the crimp is folded over the line. The length is typically 450 μm, i.e. the deployed crimp is typically 900 μm. The thickness of the crimp may depend on the material. Any suitable material that forms a mechanical and electrical connection may be used for the crimp, such as phosphor bronze or stainless steel. The crimp may be coated with, for example, gold or another suitable material to reduce corrosion and/or reduce the resistance of the electrical connection to the wire. A thick or thin piece of material may be more difficult to fold or may not form a good mechanical connection with the wire. For example, the folded crimp may have a total thickness of 100 μm. The size of the crimp can be selected to balance the requirements regarding the spacing between wires, as well as to provide acceptable mechanical and electrical connections.

Fig. 2a and 2b schematically show a functional arrangement of the SMA wires of fig. 1a and 1 b. Fig. 2a schematically shows an example of three annular SMA wires 208a, 208b, 208 c. As described with respect to fig. 1a, each of the three annular SMA wires may be located within an SMA actuator of the haptic assembly to provide the functionality described above. One end of each wire is connected to the housing 205 by a coupling element 210a (e.g., a crimp connector or a weld). As described above, each wire is looped around a hook, and the other end of each looped wire is connected to the housing 205 by a coupling element 210b (e.g., a crimp connector or weld). Thus, each coupling element 210a, 210b contains three wires, and each coupling element 210a, 210b is connected to a static part (i.e., housing). As mentioned above, such coupling may be direct as shown, or may be indirect, such as via an intermediate element (not shown).

Fig. 2b schematically illustrates an example of an SMA actuator using three pairs of tactile assemblies of SMA wires (218 a, 218 f), (218 b, 218 e), (218 c, 218 d). As described with respect to fig. 1b, each of the three pairs of SMA wires may be located within an SMA actuator of the haptic assembly to provide the functionality described above. The ends of each pair of SMA wires are connected to a coupling member, which may be a permanent connector such as a weld or crimp. The coupling members 210a, 210b are connected to the housing (i.e., static part) and may be referred to as static coupling members. Similarly, the coupling members 210c, 210d are connected to the movable element 206 and may be referred to as movable coupling members because they move with the movable element, but not individually. The static coupling member and the movable coupling member form two pairs of coupling members (210 a, 210 c), (210 b, 210 d) that couple the SMA wire to both the static element and the movable element. As mentioned above, such coupling may be direct as shown, or may be indirect, such as via an intermediate element (not shown).

The first or outer SMA actuator wire pair includes a first outer SMA actuator wire 218a and a second outer SMA actuator wire 218f. The first outer SMA actuator wire 218a is coupled at one end to the intermediate movable element 206 via the first movable coupling member 210c and at the other end to the housing via the first static coupling member 210 a. The second external SMA actuator wire 218f is coupled at one end to the intermediate movable element 206 via the second movable coupling member 210d and at the other end to the housing via the second static coupling member 210 b. Similarly, the second or intermediate SMA actuator wire pair includes a first intermediate SMA actuator wire 218b coupled to the first movable coupling member 210c and the first static coupling member 210a, and a second intermediate SMA actuator wire 218e coupled to the second movable coupling member 210d and the second static coupling member 210 b. The third or inner SMA actuator wire pair includes a first inner SMA actuator wire 218c coupled to the first movable coupling member 210c and the first static coupling member 210a, and a second inner SMA actuator wire 218d coupled to the second movable coupling member 210d and the second static coupling member 210 b. Thus, each of the first wires 218a, 218b, 218c in each pair of wires is connected to both the static part and the movable part by a first pair of coupling members 210a, 210c, and each of the second wires 218d, 218e, 218f in each pair of wires is connected by a second pair of second coupling members 210b, 210 d.

In fig. 1a (as schematically shown in fig. 2 a), the halves of the wire loop act mechanically in parallel, and thus each half of each wire can be considered to form an effective wire segment. Thus, the arrangement in fig. 1a effectively has six lines acting in parallel. Similarly, in fig. 1b (and fig. 2 b), the use of three pairs of wires also provides six parallel acting wires. Thus, both arrangements offer the potential to reach six-fold force compared to a single wire. This is because the maximum force available is proportional to the diameter of the wire. It should be understood that the SMA force will vary with the load applied to the wire, but some values are provided merely to illustrate the increased force generated by this arrangement. For example, a wire with a cross section of 25 μm will typically generate a maximum force of 120 to 200mN, so six wires (or six effective wire segments) will provide a force of about 720 to 1.2N. Increasing the diameter of each wire from 25 μm to 35 μm approximately doubles the cross-sectional area of each wire, thereby approximately doubling the force provided by each wire. Six wires (or six effective wire segments) with a diameter of 36 μm can provide a maximum total force in the range of 1.5N to 3N.

Thus, the arrangement of fig. 1a and 1b may provide significantly higher forces than known SMA actuators without compromising other properties of the assembly, as explained in more detail below. Typically, the SMA wire is operated to maintain the strain on the SMA wire within a lower limit (e.g., 2% -3%) to prevent damage to the wire. Providing higher forces with SMA wires may increase the stress within the wires unless other factors of the SMA wires are changed. For example, the force provided by an SMA wire is related to the cross-section of the wire. Increasing the cross section of the wire means an increase in the total force available. However, the volume of material that needs to be heated to activate the wire also increases, and the power also needs to be adjusted in order to obtain higher forces. There is a risk that the use of higher power for smaller diameter wires may damage the wires due to excessive strain. Another problem to be solved is that wires with larger cross sections cool down slower than wires with smaller cross sections, which may affect the performance as described below.

Figures 3a and 3b show simulated heating and cooling rates for three different arrangements, a single wire of 60 μm diameter, three adjacent contact wires of 35 μm diameter, and three wires of 35 μm diameter but spaced apart such that the wires are adjacent but not in contact. The cross-sectional area of a single wire of 60 μm diameter is 2.8xl0 ^-9 m², similar to the combined cross-sectional area of three wires of 2.9xl0 ^-9 m². For each of the three wire arrangements, the temperature of the middle wire W2 was simulated separately from the temperature of the outer wire W1, with the simulation parameters being an ambient temperature of 25 degrees celsius and a cooling initiation point of 150 degrees celsius.

As shown in fig. 3a, there is a minimal difference in temperature for both three wire arrangements during the first few milliseconds. The temperature of the middle wire W2 is also similar to the temperature of the outer wire W1. Initially, there was a minimal difference in temperature of a single wire arrangement over time compared to two three wire arrangements. However, after 10 milliseconds, the temperature of the three wire arrangement was about 6 degrees lower than the temperature of the single wire arrangement. After more than 10 milliseconds, the temperature of the single wire arrangement begins to rise faster than each of the three wire arrangements, so there is a temperature difference of about 18-20 degrees at 20 milliseconds.

The difference between the single wire arrangement and the three wire arrangement is more pronounced in terms of cooling. As shown in fig. 3b, when the two three wire arrangements cool, there is a minimal difference in their temperature over time. The temperature of the intermediate wire W2 is also similar to the temperature of the outer wire W1, with only a relatively small difference (e.g., 5 degrees) between the intermediate wire and the outer wire in the spaced arrangement after 10 milliseconds, and a smaller difference (e.g., 2 degrees) between the intermediate wire and the outer wire in the contact arrangement after 10 milliseconds. The three wire arrangement cools much faster than the single wire arrangement and is approximately 50 degrees lower after 200 milliseconds. For the same total cross section, a single wire arrangement takes about 3.2 times more time to cool than a three wire arrangement (i.e., 0.12 seconds and 0.38 seconds from 150 degrees to 60 degrees).

Thus, fig. 3a and 3b show that the three wire arrangement will heat up almost as fast as the single wire arrangement, so the heating event to activate the actuator and provide contraction to move the movable element is similar for both arrangements. However, the three wire arrangement provides significant advantages over the single wire arrangement for cooling. The cooling is much faster and thus the wires in the three wire arrangement will cool and return to their original shape faster than the thicker single wire. Thus, the three wire arrangement is ready to be re-activated faster than the single wire arrangement. The simulations in fig. 3a and 3b also show that when the wires are in contact, the heating and cooling of the three wire arrangement is similar to when the wires are spaced, which may be counter-intuitive. Furthermore, each wire in the multiple wire arrangement is at substantially the same temperature, and thus there is no performance penalty that would be expected if the wires were at different temperatures.

Thus, in summary, the heating and cooling problems associated with larger diameter wires can be solved by using several smaller diameter wires that provide substantially the same total volume of material, and thus the same maximum available total force. In addition to being able to provide greater force, the use of multiple wires may also improve the reliability of the device. This is because if one wire breaks at the crimp holding multiple wires, there is still at least one other wire in the crimp that is connected. Due to reliability issues, it is desirable in some industries not to have a single wire.

Radiator arrangement

Fig. 4a shows a variant of the arrangement of fig. 1 b. All unchanged elements retain the same reference numerals and the function and structure of these unchanged elements are not repeated for the sake of brevity. The haptic assembly 100 "includes a heat sink 130. In this arrangement, the heat sink 130 is a separate element on the housing 104 proximate the SMA wire. A single heat sink is shown, but it should be understood that multiple heat sinks may be combined. The distance between the heat sink and the wires may be less than 5 times the diameter of each wire. More preferably, the distance of the heat sink may be less than 3 diameters, still more preferably less than 2 diameters. The heat sink may contact the wire. The heat sink 130 may be made of any suitable material, such as aluminum, phosphor bronze, or steel, which increases the cooling rate of the wire. The heat sink 130 may have a substantial thermal mass and/or high thermal conductivity to achieve enhanced cooling.

In the arrangement schematically shown in fig. 4a, the heat sink is at a small distance from the wire, but it will be appreciated that an arrangement in which the heat sink is in contact with the wire may also be used. Direct contact may increase the cooling rate but may result in an increase in the power required by the instantaneous heater wire. However, such an arrangement may be desirable for tolerance reasons, as this means that the wires do not have to be positioned with high precision relative to the heat sink.

The heat sink and/or the wire may also be configured to be movable relative to each other between an active position in which the heat sink is adjacent (near or even in contact with) the wire and an equilibrium position in which the heat sink is far from the wire. Before activating the SMA wire, the SMA wire is at room temperature and the heat sink is in an equilibrium position. In this way, the SMA wire may be heated without any additional power. Once the SMA wire is heated, the wire is in a high temperature state and the heat sink can be moved from an equilibrium position to an activated position to ensure a good cooling rate of the wire. Additional cooling mechanisms, such as airflow around the wire, may also be triggered as the wire cools.

Fig. 4b to 4d are graphs for simulation of illustrating the effect of the radiator. The cooling and heating rates of a single wire with a diameter of 60 μm were calculated, with the heat sink being located in the range of 40 μm to 420 μm from the wire. It should be appreciated that similar results may be obtained for a multiple wire arrangement.

Fig. 4b plots the temperature change over time as the heat sink cools a single wire at different distances from the wire. As expected, the presence of the heat sink increases the cooling rate, especially when the heat sink is closer to the wire.

Fig. 4c plots temperature as a function of distance between the wire and the heat sink at 100 ms and 200 ms after the start of cooling. As expected, after 100 milliseconds of cooling, the temperature at each location of the heat sink was higher than after 200 milliseconds of cooling. However, both line graphs follow similar curves, and as the distance between the line and the heat sink increases, the temperature also increases after a fixed amount of time. After 200 milliseconds of cooling, the heat sink was cooled from 150 degrees celsius to 83 degrees celsius for lines 250 μm away from the line. After 200 milliseconds of cooling, the heat sink was cooled from 150 degrees celsius to 70 degrees celsius for lines 100 μm away from the line. Therefore, for a radiator that is farther away, there is less cooling. Similar results were obtained after cooling for 100 milliseconds. Thus, both graphs show that the proximity of the heat sink can significantly change the cooling rate, while a closer heat sink can improve cooling.

Fig. 4d plots the temperature change over time when a single wire is heated. As shown, the presence of the heat sink has no significant effect on the short term heating rate (e.g., before 30 milliseconds) until it is very close, e.g., only 40 μm apart. Furthermore, the period of driving the actuator is very short for some applications such as touch or latching, typically less than 10 milliseconds, and as shown, there is virtually no effect on the heating caused by the heat sink. Thus, any power increase required in such applications is very small, as it is not necessary to keep the wire at a higher temperature for a long time. Thus, the benefits of the cooling rate are not adversely affected by the adverse effects of heating. This is in contrast to other actuators in which the wire is driven longer, and therefore the heat sink is less desirable due to the increased power requirements of the heating wire.

Crimping arrangement

In the arrangement shown above, three wires are held together in each individual coupling member (e.g., crimp), although as noted above, there may be any number of wires in each coupling member, for example between 2 and 6 (or more). Fig. 5 is a graph showing recovery time versus displacement for a single wire of 60 μm diameter in the crimp, a single wire of 35 μm diameter in the crimp, and three wires of 35 μm diameter in the crimp. The results in fig. 5 were obtained from experimental data rather than from simulation data. As shown in fig. 5, and consistent with the above results, the recovery time of a single wire with a diameter of 60 μm was significantly worse than with other arrangements. Thus, more time will be required between actuation events to enable the wire to resume to produce the next contraction. Experimental data shows that the recovery time for a single wire with a diameter of 60 μm is about 1.75 times slower than for an arrangement of three wires with a diameter of 35 μm. This is less different than the simulation data, but nonetheless the three wire arrangement provides significantly improved cooling rates compared to a single wire arrangement with a similar cross section.

Fig. 5 also shows the cooling time for a single wire of diameter 35 μm. As expected, a single thinner wire has a significantly shorter recovery time than each of the arrangements with larger cross sections. For example, if in each arrangement the contraction of the wire(s) results in a displacement of 40 μm, a wire with a diameter of 60 μm requires about 275 milliseconds to recover, a wire with a diameter of 35 μm requires about 115 milliseconds to recover, and a three wire arrangement is between these two extremes with a recovery time of about 160 milliseconds.

Another variation of the arrangement shown in fig. 1a and 1b is to retain each wire in its respective independent crimp. Figure 6a shows a variation where each SMA wire has a single crimp. The arrangement of the movable and static elements is not shown for simplicity, but these components are supported on the chassis 600 for ease of assembly. In this arrangement, there are two pairs of wires (608 a, 608 c), (608 b, 608 d). The first pair of upper lines 608a, 608c is arranged above the second pair of lower lines 608b, 608 d. Thus, there are two wires on each side of the chassis 600.

The upper crimps 610a, 610b, 610c, 610d each have lower crimps 610a ', 610b', 610c ', 610d' therebelow, i.e., the crimps are vertically aligned. Each pair of stacked crimps (610 a, 610a ', 610 c'), (610 b, 610b ', 610 d') at either end of the wire may be considered to form a coupling element and thus each coupling element is coupled to multiple wires, although by using different parts, such as separate crimps at each end of each wire. The laminate crimp (610 a, 610a ') from the first pair of coupling elements (610 c, 610 c') has a first coupling element (610 c, 610c ') coupling one end of the two wires to the static element and a second coupling element (610 a, 610 a') coupling the opposite end of the two wires to the movable element. Similarly, the laminate crimp (610 b, 610b '), (610 d, 610 d') from the second pair of coupling elements has a first coupling element (610 d, 610d ') coupling one end of the two wires to the static element, and a second coupling element (610 b, 610 b') coupling the opposite end of the two wires to the movable element.

In this arrangement there are four wires in total, but it will be appreciated that the six wire arrangement of fig. 1b may be achieved by arranging three wires on either side of the chassis and corresponding sets of three pairs of crimps on either side of the chassis. If the wires are arranged vertically, as shown in fig. 6a, one on top of the other, the crimp can also be arranged as a vertical stack. Also, if two wires are required, there may be one wire on each side, or there may be a pair of wires on one side. The arrangement may have 2 to 6 wires in each coupling element comprising a plurality of crimps.

The first upper wire 608a is connected at one end to a first upper movable crimp 610a which will be connected to a movable part when the assembly is installed, for example an intermediate movable element as in the arrangement of fig. 1 b. The first upper wire 608a is connected at the other end to a first upper static crimp 610c that will be connected to a static portion, such as the housing in the arrangement of fig. 1a, when the assembly is installed. Similarly, the second upper wire 608c is connected at one end to the second upper movable crimp 610b and at the other end to the second upper static crimp 610d. For the lower wire, the first lower wire 608b is connected at one end to the first lower movable crimp 610a 'and at the other end to the first lower static crimp 610c', and the second lower wire 608d is connected at one end to the second lower movable crimp 610b 'and at the other end to the second lower static crimp 610d'.

Arranging the wires and crimp in a vertical stack achieves good separation of the wires, which may be advantageous for the cooling rate, as described above. However, the overall height is increased by using vertical stacking. In addition, there are additional parts (i.e., more crimps) and additional assembly steps. Some of the crimps, such as movable crimps 610a, 610b, 610a ', 610b', may be integrally formed with the chassis 600 to reduce the total number of parts. To assist in assembling some of the crimps, such as static crimps 610c, 610d, 610c ', 610d', may be formed on separate tabs 602, the tabs 602 being attached (e.g., welded) to the chassis 600 during the assembly procedure.

Fig. 6b shows a variation of the arrangement in fig. 6a, in which each SMA wire in the two pairs of wires (618 e, 618 c), (618 b, 618 d) has a single crimp. In this arrangement, the wires are still arranged in a vertical stack on either side of the chassis 600, but the upper and lower crimps are offset in both the lateral and vertical directions and thus are not arranged in a vertical stack as in the previous arrangements. It should be understood that this is only one arrangement and that the crimp may be offset laterally only or vertically only, not necessarily both as shown.

The crimps (620 a, 620a '), (620 c,620 c') from the first pair of coupling elements have a first coupling element (620 c,620c ') coupling one end of the two wires to the static element and a second coupling element (620 a, 620 a') coupling the opposite end of the two wires to the movable element. Similarly, the crimps (620 b, 620b '), (620 d, 620 d') from the second pair of coupling elements have a first coupling element (620 d, 620d ') coupling one end of the two wires to the static element and a second coupling element (620 b, 620 b') coupling the opposite end of the two wires to the movable element.

The first upper wire 618a is connected at one end to a first upper movable crimp 620a and at the other end to a first upper static crimp 620c, which first upper movable crimp 620c will be connected to the movable portion when the assembly is installed. Similarly, the second upper wire 618c is connected at one end to the second upper movable crimp 620b and at the other end to the second upper static crimp 620d. For the lower wire, the first lower wire 618b is connected at one end to the first lower movable crimp 620a 'and at the other end to the first lower static crimp 620c', and the second lower wire 618d is connected at one end to the second lower movable crimp 620b 'and at the other end to the second lower static crimp 620d'.

As shown, the upper wire is shorter than the lower wire because the upper crimp is positioned closer than the corresponding lower crimp. It should be appreciated that if each upper crimp is laterally offset from the lower crimp in the same direction, a similar spacing may be obtained between the upper and lower crimps. Thus, a similar offset arrangement may be used for the same length of wire. However, in some designs, wires having different lengths may be useful.

As with fig. 6a, arranging the wire and crimp in this way allows for good separation of the wire. Also, the overall height may be increased by vertical parting lines, but lateral offset means that the crimps may be formed simultaneously. This tradeoff may result in an overall increase in actuator width. As previously described, some of the crimps, such as movable crimps 620a, 620b, 620a ', 620b', may be integrally formed with the chassis 600 to reduce the total number of parts. To assist in assembling some of the crimps, such as static crimps 620c,620 d, 620c ', 620d', may be formed on separate tabs 602, the tabs 602 being attached to the chassis 600 during the assembly procedure.

It should be understood that the selection of the number of lines in the figures shown above is merely exemplary and that additional or fewer lines may be used. The use of additional wires, particularly if they are single crimps, may increase the size of the assembly, thus taking into account the balance between the number of wires and the overall size when designing the assembly. An arrangement with multiple crimps and multiple wires may have similar performance in terms of the force generated as an arrangement with the same number of wires remaining in a fewer number of wires, but may have an increased cooling rate as shown in fig. 5. However, the arrangement of multiple crimp portions may increase costs due to additional materials, an increase in assembly steps if the crimp portions are sequentially formed, and an increase in assembly size. In devices incorporating such SMA actuators, space is often limited and thus increasing size may be undesirable. However, the design may be selected to balance the desired cooling rate with other factors.

Third haptic component

Fig. 7 illustrates a ("third") haptic assembly that operates in a different manner than the haptic assemblies described above.

The third haptic assembly includes a movable element 706 mounted over the static element 704. Adjacent faces of the movable element and the static element have complementary shapes.

The third haptic assembly includes a plurality of wires 708 (only one of which is visible in the figure). Each wire is attached at its ends to a static element 704. Both ends of each wire are attached using a static coupling element 712a in the form of a crimp connector, where the same crimp connector preferably holds two or more of the plurality of wires 708. Each wire 708 defines a plurality of wire segments 708a, 708b (in this case ten wire segments). The first plurality of line segments 708a are substantially parallel to each other and the second plurality of line segments 708b are substantially parallel to each other and set, for example, at right angles to the other line segments 708 a. Thus, the line segments 708a, 708b may be considered to form a V-shaped pair of line segments 708a, 708 b.

Each of the line segments 708a, 708b engages the static element 704 and the movable element 706. A first end of the first wire segment 708a is attached to the static element 704 using a crimp connector 712a, and the other end of the first wire segment 708a is engaged with the movable element 704 via, for example, a locating pin 714. Similarly, a first end of the final wire segment 708b is engaged with the movable element 706 via the locating pin 714, and the other end of the final wire segment 708b is attached to the static element 704 using the crimp connector 712 a. Each of the other line segments 708a, 708b is engaged at one end with the static element 704 via a locating pin 712b (or other type of non-fixed connector, such as a hook) and at the other end with the movable element 706 via a locating pin 714.

The V-shape is located in a channel having a saw-tooth cross-section. It should be appreciated that if the line segments are designed to have different shapes, the channels may similarly be designed to have complementary mating shapes.

The plurality of wires 708 may be evenly spaced apart, may be parallel to one another, and/or may be aligned in separate channels (or single channels) between the static element 704 and the movable element 706.

It will be appreciated that when the plurality of wires 708 are contracted, the movable element 706 moves in a direction (upward) that extends generally (horizontally), e.g., 90 ° from the wires 708.

Manufacturing

FIG. 8 is a schematic illustration of one method that may be used to crimp multiple wires into a single crimp in the SMA actuator described above. The plurality of spools 70, 72, 74 simultaneously feed the wire through the guide wheel 76 and into the crimp 78. The guide wheel may help maintain the spacing between the wires in the crimp. Each wire may be made of any suitable shape memory alloy and may be coated (e.g., with polyimide or similar material) to reduce the risk of shorting the wires when they come into contact with other components in the SMA actuator. The number of wires is shown as three, but it should be understood that this is merely exemplary and that other numbers of wires may be used.

For optimum performance, the axis of each wire is preferably parallel to the axis of the crimp, but each wire is generally considered to leave the crimp at an angle due to a defect in the crimp. Bending of the wire at the nip point can increase fatigue. The guide wheels may also help maintain each wire at a desired angle relative to the crimp. A slight deviation from parallel may be acceptable. The magnitude of the deviation depends on the thickness of the wire, but for a wire with a diameter of 25 μm, the deviation is as high as 8 degrees of parallelism as possible. Moreover, the angular variation between each line may be within this range. The guide wheel may be omitted if each wire can be fed into the crimp at an acceptable angle.

Once the wire is within the crimp, the crimp may be crimped (i.e., folded or closed) to create a mechanical and electrical connection between the wire and the crimp. Any excess wire protruding from the crimp can then be trimmed. The crimping step may be performed at any suitable point in the assembly process.

The same procedure can be used to connect the same wire to a second crimp (e.g., a crimp as in the haptic assemblies of fig. 6 and 7).

Upon closing the crimp(s), the tension in each wire and/or the length of each of the plurality of SMA wires between the crimps are controlled such that in the final assembly, each wire has substantially the same tension and/or length between the crimps. As described above, this may be achieved by arranging a plurality of SMA wires to each follow an equivalent parallel path.

In general, if the wires do not cross (i.e., cross each other), a more reliable haptic assembly can be manufactured. However, in some cases (e.g., in high volume production), it may be impractical to completely prevent crossover. In such a case, the inventors have found that even if the wire crosses between the first crimp portion and the second crimp portion, satisfactory reliability can be achieved as long as the wire does not cross inside the crimp portion.

As an alternative to crimping, welding (e.g., arc welding, welding using a welding rod, laser/heat based welding) may be used to connect the ends of the wire in place (e.g., directly to the static or movable element or the intermediate element). By welding the wires in place, the spacing between the wires can be more precisely controlled. During the welding procedure, the weld needs to be carefully controlled in order to minimize damage to the wire (e.g., melting or material loss).

Those skilled in the art will appreciate that while the foregoing has described what are considered to be the best mode and other modes of carrying out the present technology, the present technology should not be limited to the particular configurations and methods disclosed in the description of the preferred embodiments. Those skilled in the art will recognize that the present technology has a wide range of applications and that the embodiments may be widely modified without departing from any of the inventive concepts as defined in the appended claims.

Claims (21)

1. A shape memory alloy (SMA) actuator, comprising: Static components; a movable element capable of moving relative to the static element; a plurality of SMA wires each coupled to one or both of the static element and the movable element and causing movement of the movable element when contracted; and a coupling element coupling at least two wires from the plurality of SMA wires to one of the static element and the movable element; Wherein, the coupling element comprises a crimping connector for holding the at least two wires. 2. The SMA actuator of claim 1, wherein the crimp connector holds between two wires and six wires. 3. An SMA actuator according to claim 1 or claim 2, wherein the crimp connector has a width of between 500 μm and 750 μm. 4. The SMA actuator according to any one of claims 1 to 3, comprising: a first crimp connector connecting one end of each of the at least two wires to the static element or the movable element; and a second crimp connector connecting the other end of each of the at least two wires to the static element or the movable element. 5. The SMA actuator of claim 4, wherein the first crimp connector and the second crimp connector are of the same type. 6. An SMA actuator according to claim 4 or claim 5, comprising a plurality of pairs of first and second crimp connectors, wherein each pair of crimp connectors connects each of at least two wires to one or both of the static element and the movable element. 7. The SMA actuator of claim 6, comprising a first pair of crimp connectors connecting each of a first set of at least two wires to the movable element, and a second pair of crimp connectors connecting each of a second set of at least two wires to the movable element, wherein when the first set of at least two wires is contracted, the movable element moves in a first direction, and when the second set of at least two wires is contracted, the movable element moves in a direction opposite to the first direction. 8. The SMA actuator of claim 6, comprising a first pair of crimp connectors connecting each of a first set of at least two wires to the movable element, and a second pair of crimp connectors connecting each of a second set of at least two wires to the movable element, wherein the movable element moves in one direction when the wires connected to the first pair of crimp connectors and the second pair of crimp connectors contract. 9. The SMA actuator of any one of claims 4 to 6, wherein the first crimp connector connects one end of the at least two wires to a first region of the static element, the second crimp connector connects the other ends of the at least two wires to a second region of the static element, the at least two wires extend generally in a first direction, and when the plurality of SMA wires contract, the movable element moves in a direction that makes an acute angle greater than zero with the first direction. 10. The SMA actuator according to any one of claims 4 to 9, wherein the at least two SMA wires do not cross between the first crimping portion and the second crimping portion. 11. The SMA actuator according to any one of claims 4 to 9, wherein the at least two SMA wires do not cross inside the crimp connector but cross between the first crimp portion and the second crimp portion. 12. The SMA actuator of any one of claims 1 to 11, wherein the at least two SMA wires do not cross inside the crimp connector. 13. An SMA actuator according to any one of claims 1 to 12, wherein the at least two wires extend substantially parallel to each other between the crimp connectors. 14. An SMA actuator according to any one of the preceding claims, wherein the coupling element provides a direct connection between the at least two wires and one of the static element and the movable element. 15. An SMA actuator according to any one of the preceding claims, wherein the coupling element couples the at least two wires to an intermediate component to provide an indirect connection between the at least two wires and one of the static element and the movable element. 16. The SMA actuator of any preceding claim, further comprising at least one heat sink adjacent the plurality of SMA wires. 17. The SMA actuator of claim 16, wherein the at least one heat sink is located at a distance from the plurality of wires that is less than five times the diameter of each wire. 18. An SMA actuator according to claim 16 or claim 17, wherein the at least one heat sink contacts the plurality of SMA wires. 19. An SMA actuator according to any one of claims 16 to 18, wherein the at least one heat sink and/or the plurality of wires are movable relative to each other between a first position in which the heat sink is adjacent to or in contact with the plurality of wires and a second position in which the heat sink is remote from the plurality of wires. 20. A haptic component comprising: Touchable parts; and An SMA actuator according to any one of claims 1 to 19, wherein when a user presses the touchable component, an actuator module is activated to provide tactile feedback to the user by moving the touchable component using the movable element. 21. A latch comprising a SMA actuator according to any one of claims 1 to 19.