actuator assembly

Abstract

A shape memory alloy actuator assembly (2) is disclosed. The actuator assembly comprises a support (21), a first stage (22) movable in a first plane relative to the support in at least two different non-parallel directions, a first set of at least two shape memory alloy wires (271) configured to move the first stage in the first plane, a second stage (23) movable in a second plane parallel to or coplanar with the first plane relative to the first stage in at least two different non-parallel directions, and a second set of at least two shape memory alloy wires (272) configured to move the second stage in the second plane. The first stage is coupled to the support via the first set of shape memory alloy wires, and the second stage is coupled to the first stage via the second set of shape memory alloy wires, such that the movement of the second stage in the second plane relative to the support is a combination of the movement of the first stage relative to the support and the movement of the second stage relative to the first stage.

Description

[0001] TECHNICAL FIELD

[0002] The present application relates to an actuator assembly, in particular an actuator assembly comprising a multi-segment shape memory alloy (SMA) wire.

[0003] Background

[0004] Such an actuator assembly can be used in a camera, for example, to move a lens assembly in a direction perpendicular to the optical axis, thereby providing optical image stabilization (OIS). In case such a camera is to be incorporated into a portable electronic device such as a mobile phone, miniaturization can be important.

[0005] WO 2019 / 086855 A1 describes a camera having an actuator assembly comprising a support platform, a moving platform supporting a lens assembly, a SMA wire connected to the support platform and the moving platform, a bearing supporting the moving platform on the support platform, and two arms extending between the support platform and the moving platform.

[0006] SUMMARY

[0007] According to a first aspect of the application, there is provided a shape memory alloy actuator assembly. The actuator assembly comprises a support, a first stage, a first set of at least two shape memory alloy wires, a second stage, and a second set of at least two shape memory alloy wires, the first stage being movable relative to the support in at least two different non-parallel directions within a first plane; the first set of at least two shape memory alloy wires being configured to move the first stage in the first plane; the second stage being movable relative to the first stage in at least two different non-parallel directions in a second plane parallel to or coplanar with the first plane; the second set of at least two shape memory alloy wires being configured to move the second stage in the second plane. The first stage is coupled to the support via the first set of shape memory alloy wires, and the second stage is coupled to the first stage via the second set of shape memory alloy wires, such that the motion of the second stage in the second plane relative to the support frame is a combination (e.g. a sum) of the motion of the first stage relative to the support and the motion of the second stage relative to the first stage.

[0008] The first stage is preferably rigid. The first stage can be tilted during operation (in other words, when the stage is moved by the shape memory alloy wires).

[0009] The first set of at least two shape memory alloy wires preferably comprises four shape memory alloy wires, the four shape memory alloy wires comprising a first pair of wires acting in opposition for moving the first level in a first direction and a second pair of wires acting in opposition for moving the first level in a second direction different from the first direction. The second set of at least two shape memory alloy wires preferably comprises four shape memory alloy wires, the four shape memory alloy wires comprising a third pair of wires acting in opposition for moving the second level in the first direction or in a third direction and a fourth pair of wires acting in opposition for moving the second level in the second direction or in a fourth direction different from the third direction.

[0010] The shape memory alloy wires are preferably non-collinear. The first set of shape memory alloy wires is preferably configured such that they are able to move the first level (when suitably driven) without applying any net torque. The second set of shape memory alloy wires is preferably configured such that they are able to move the second level without applying any net torque.

[0011] The actuator assembly can further comprise a first terminal and a second terminal. A first shape memory alloy wire of the first set of shape memory alloy wires and a second shape memory alloy wire of the second set of shape memory alloy wires can be electrically connected in series between the first and second terminals, wherein the first and second shape memory alloy wires act in concert to move the first and second levels, respectively. Alternatively, a first shape memory alloy wire of the first set of shape memory alloy wires and a second shape memory alloy wire of the second set of shape memory alloy wires can be electrically connected in parallel between the first and second terminals, wherein the first and second shape memory alloy wires act in concert to move the first and second levels, respectively. The terminals can be comprised in or supported by the support.

[0012] The first and second shape memory alloy wires can be interconnected in the first level. The first level can comprise an electrically conductive layer supported by an insulating layer, wherein at least a portion of the electrically conductive layer interconnects the first and second shape memory alloy wires. The first and second shape memory alloy wires can be positioned on the same side of the actuator assembly, e.g. one above the other.

[0013] The actuator assembly can further comprise a common node, wherein at least a first shape memory alloy wire of the first set of shape memory alloy wires and at least a second shape memory alloy wire of the second set of shape memory alloy wires are connected to the common node, and wherein the common node is comprised in the first level. The actuator assembly can comprise a flexible electrical connection between the support and the common node. The actuator assembly can comprise a flexible electrical connection between the support and the second level to electrically connect to at least one second shape memory alloy wire.

[0014] The actuator assembly can further comprise a common node, wherein at least one pair of shape memory alloy wires consisting of one of the first set of shape memory alloy wires and one of the second set of shape memory alloy wires is electrically connected in series to the common node, and wherein the common node is comprised in the second level. The actuator assembly can comprise a flexible electrical connection between the support and the common node.

[0015] The actuator assembly can further comprise five terminals, the five terminals comprising first to fifth terminals, the fifth terminal being a common terminal, wherein the first set of shape memory alloy wires and the second set of shape memory alloy wires are connected to the terminals such that, in response to respective signals applied to the first to fourth terminals relative to the common terminal, the first set of shape memory alloy wires and the second set of shape memory alloy wires cause the first level and the second level to move in concert. The actuator assembly can comprise at least one additional level and at least one additional set of shape memory alloy wires, and the first set of shape memory alloy wires and the second set of shape memory alloy wires and the at least one additional set of shape memory alloy wires can be connected to the terminals such that, in response to respective signals applied to the first to fourth terminals relative to the common terminal, the first set of shape memory alloy wires and the second set of shape memory alloy wires and the at least one additional set of shape memory alloy wires cause the first level and the second level and the at least one additional level to move in concert. The terminals can be comprised in or supported by the support.

[0016] The actuator assembly can further comprise a set of electrically-conductive tracks formed on the support, the first level and / or the second level. The electrically-conductive tracks can comprise patterned tracks. The actuator assembly can further comprise a layer of dielectric material for electrically insulating different electrically-conductive parts of the actuator assembly from each other.

[0017] The actuator assembly preferably further comprises a support system configured to enable movement of the second level along at least two different non-parallel directions in the second plane. The second level is preferably directly supported on the support via the support system. The support system preferably comprises at least three supports, e.g. through-holes, a respective plurality of through-holes or through-cuts extending from an edge of the first level, through the first level.

[0018] The actuator assembly preferably further comprises a means for loading the support system by pushing the support and the second level together in the case that the first level is interposed between the support and the second level.

[0019] The loading means can comprise a set of at least two biasing springs. At least one of the springs carries an electrical connection between the support and the second level. The loading means can comprise at least one permanent magnet.

[0020] The at least two biasing springs can comprise at least two spring arms. The at least two spring arms and the second level or support can be formed as a single piece. The at least two spring arms can each have a first end fixed to the second level (e.g. by being integrally formed with said second level) and a second end fixed to the support (e.g. by attachment, e.g. by welding or another suitable attachment method). The first level and optional further levels can be interposed between the support level and the second level. The at least two spring arms can pass through the first level and any optional further levels on the outside (i.e. generally on the outside of the actuator assembly).

[0021] The first set of shape memory alloy wires and / or the second set of shape memory alloy wires can be tilted with respect to the first plane in order to facilitate pushing the support and the second level together.

[0022] The actuator assembly can comprise a third level and a third set of at least two shape memory alloy wires, the third level being movable relative to the second level in at least two different non-parallel directions in a third plane parallel to or coplanar with the first plane, the third set of at least two shape memory alloy wires being configured to move the third level, wherein the third level is interposed between the first level and the second level. This can be used to further expand the range of motion.

[0023] The actuator assembly can further comprise an additional level, which is movable perpendicular to the first plane, wherein the additional level is supported by the second level. For example, the first level and the second level can be used to provide motion in an x-y plane, while the additional level can be used to provide motion along a z-axis (perpendicular to the x-y plane).

[0024] The support, the first level and the second level can be stacked in a direction perpendicular to the first plane.

[0025] At least two of the support, the first level and the second level can be generally coplanar and nested.

[0026] At least some areas of the first and / or second opposite faces of the support, the first level and / or the second level can be coated with a dielectric material, such as a diamond-like carbon (DLC) coating or titanium carbide (TiC).

[0027] According to a second aspect of the present invention, there is provided a system comprising an actuator assembly of the first aspect of the present invention, a supply rail for delivering a drive voltage, a set of switching devices for applying a drive signal to respective shape memory alloy wires or respective pairs of shape memory alloy wires at the drive voltage, and a controller for individually controlling the switching devices.

[0028] According to a third aspect of the present application, there is provided an optical device comprising a main body, a first optical element (e.g. an image sensor) and a second optical element (e.g. a lens) and an actuator assembly according to the first aspect of the present application or a system according to the second aspect of the present application, wherein the first optical element and the second optical element are aligned substantially along an optical axis, and wherein the first optical element and the support of the actuator element are fixed relative to the main body, the second optical element being supported by the second level of optical elements.

[0029] According to a fourth aspect of the present application, there is provided a method of using an actuator assembly of the first aspect of the present application, the method comprising causing a drive signal to be applied to at least one shape memory alloy wire or at least one pair of shape memory alloy wires, each pair of shape memory alloy wires comprising one shape memory alloy wire of a first set of shape memory alloy wires and one shape memory alloy wire of a second set of shape memory alloy wires.

[0030] According to a fifth aspect of the present application, there is provided a method of manufacturing an actuator assembly of the first aspect of the present application, the method comprising providing a support element comprising a sacrificial support body and a crimp tab held apart by the sacrificial support body, unwinding a shape memory alloy wire over the crimp tab of the support element, folding and crimping the crimp tab over the shape memory alloy wire to form a crimp holding the shape memory alloy wire between the tabs, attaching the crimp to the support and the first level respectively, or to the first level and the second level respectively, and removing the sacrificial support, the crimp remaining attached to the support and the first level respectively, or to the first level and the second level respectively. BRIEF DESCRIPTION OF DRAWINGS

[0032] Certain embodiments of the present application will now be described, by way of example only, with reference to the accompanying drawings in which:

[0033] Figure 1 is a schematic cross-sectional view of a camera incorporating an SMA actuator assembly;

[0034] Figure 2 is Figure 1 is a top plan view of the SMA actuator assembly shown in Figure 1 ;

[0035] Figure 3 is Figure 1 is a top angled view of the SMA actuator assembly shown in Figure 1 ;

[0036] Figure 4 is Figure 2 is an exploded perspective view of the SMA actuator assembly shown in Figure 1 unwound along the optical axis O;

[0037] Figure 5 is Figure 2exploded perspective view of the SMA actuator assembly shown in Fig. 1, illustrating for a first SMA wire in a first tier and a corresponding second SMA wire in a second tier arranged in series, a current flow through the wires;

[0038] Figure 6 is a schematic circuit diagram of a first arrangement of SMA wires and transistors for controlling a current flow through the SMA wires in the SMA actuator assembly shown in Fig. 1; Figure 2

[0039] Figure 7 is a schematic circuit diagram of a second arrangement of SMA wires and transistors for controlling a current flow through the SMA wires;

[0040] Figure 8 is a schematic circuit diagram of a third arrangement of SMA wires and transistors for controlling a current flow through the SMA wires;

[0041] Figure 9 is a schematic circuit diagram of a fourth arrangement of SMA wires and transistors for controlling a current flow through the SMA wires;

[0042] Figure 10 schematically illustrates a process of attaching pre-crimped SMA wires to the actuator assembly; and

[0043] Figure 11 is a schematic circuit diagram of a fourth arrangement of SMA wires and transistors for controlling a current flow through the SMA wires; Figure 2 is a simple schematic plan view of a moving platform of the SMA actuator assembly shown in Fig. 1, illustrating additional motions of two tiers.

[0044] DETAILED DESCRIPTION

[0045] camera

[0046] With reference to Figure 1 Fig. 1 shows a camera 1 comprising an SMA actuator assembly 2 (also referred to herein as “SMA actuator” or simply as “actuator”).

[0047] The camera 1 comprises a lens assembly 3 suspended by the SMA actuator assembly 2 on a support structure 4, the SMA actuator assembly 2 supporting the lens assembly 3 in a manner allowing the lens assembly 3 to move relative to the support structure 4 in a direction perpendicular to the optical axis O.

[0048] The support structure 4 comprises a base 5. An image sensor 12 is mounted on a front side of the base 5. On a rear side of the base 5, an integrated circuit (IC) 7 (in which a control circuit is implemented) as well as a gyroscope sensor 8 are mounted. The support structure 4 further comprises a housing 9 protruding forward from the base 5 to enclose and protect other components of the camera 1.

[0049] ​The lens assembly 3 comprises a lens holder 10 in the form of a cylindrical body supporting two lenses 11 arranged along an optical axis O. In general any number of one or more lenses 11 can be included. Preferably each lens 11 has a diameter of at most about 20mm. The camera 1 can therefore be referred to as a miniature camera.

[0050] The lens assembly 3 is arranged to focus an image onto an image sensor 12. The image sensor 12 captures the image and can be of any suitable type, for example a CCD (Charge-Coupled Device) or CMOS (Complementary Metal-Oxide-Semiconductor) device.

[0051] The lenses 11 are supported on the lens holder 10 such that the lenses 11 are movable relative to the lens holder 10 along the optical axis O, for example to provide focusing or zooming. In particular, the lenses 11 are fixed to a lens carrier 13 which is movable relative to the lens holder 10 along the optical axis O. Although in this example all of the lenses 11 are fixed to the lens carrier 13, in general one or more of the lenses 11 can be fixed to the lens holder 10 and therefore not movable relative to the lens holder 10 along the optical axis O, leaving at least one lens 11 fixed to the lens carrier 13.

[0052] An axial actuator arrangement 14 is provided between the lens holder 10 and the lens carrier 13 and is arranged to drive the lens carrier 13 and the lenses 11 to move relative to the lens holder 10 along the optical axis O. The axial actuator arrangement 14 can be of any suitable type, for example a voice coil motor (VCM) or a device of SMA wire.

[0053] In operation, the lens assembly 3 is moved relative to the image sensor 12 orthogonal to the optical axis O, the effect of which is that the image on the image sensor 12 is moved. This is used to provide optical image stabilisation (OIS) to compensate for movement of the camera 1 which can be caused by hand shake or the like.

[0054] Actuator assembly

[0055] Reference will now be made to Figures 2 to 4 The SMA actuator assembly 2 will now be described in more detail.

[0056] The SMA actuator assembly 2 takes the form of an n-level SMA actuator assembly 2 (where in this case n = 2) which can provide an extended lateral motion (or "longer stroke") perpendicular to the optical axis O than a single-level SMA actuator assembly.

[0057] The actuator assembly 2 comprises a first sub-assembly 21 (hereinafter referred to as “support platform” or simply “support”), a second sub-assembly 22 (hereinafter referred to as “intermediate platform”, “intermediate moving part”, “intermediate stage” or in the present example as “first stage”) and a third sub-assembly 23 (hereinafter referred to as “moving platform”, “moving part”, “last stage” or in the present example as “second stage”) (see in particular Figure 2 ). The moving platform 23 supports the lens assembly 3 ( Figure 1 ) and is connected to the lens holder 10 ( Figure 1 ).

[0058] Each of the support platform 21, the intermediate moving platform 22 and the moving platform 23 generally takes the form of a flat thin ring having a rectangular outer edge (or “peripheral edge”) and a circular inner edge. The outer edges of the intermediate moving platform 22 and the moving platform 23 are located inside the outer edge of the support platform 21, but the inner edges of the platforms 21, 22, 23 generally have the same extension.

[0059] The first sub-assembly 21 is formed by two independent parts, i.e. a support part 24 and a conductive part 25, which are fixed to each other.

[0060] The actuator assembly 2 can comprise a base part 26 which is fixed to the support platform 21 and to the base 5 ( Figure 1 ) of the camera 1 ( Figure 1 ).

[0061] The support part 24, the conductive part 25 and the base part 26 can take the form of respective patterned metal sheets, e.g. etched or machined stainless steel, and can be coated with an electrically insulating dielectric material. The layer of dielectric material can comprise one or more windows (not shown) to allow electrical connections. Similarly, the intermediate moving platform 22 and the moving platform 23 can take the form of respective patterned metal sheet(s), e.g. stainless steel, which can be coated with a dielectric material.

[0062] Other example configurations can be used and further details are provided in WO 2017 / 055788 A1 and WO 2019 / 086855 A1, which are incorporated herein by reference.

[0063] The support platform 21, the intermediate moving platform 22, the moving platform 23 and the base part 26 are respectively provided with a respective central hole aligned with the optical axis O, allowing light to pass from the lens assembly 3 ( Figure 1 ) to the image sensor 12 ( Figure 1 ).

[0064] The movement of the intermediate mobile platform 22 and of the mobile platform 23, and thus of the lens assembly 3, relative to the support platform 21 is driven by transverse actuation means comprising SMA wires 27, in this case two sets of four SMA wires 271, 272.

[0065] The support platform 21 comprises a first set of crimping portions 31 (hereinafter referred to as "static crimping portions"). The intermediate mobile platform 22 comprises a second set of crimping portions 32 and a third set of crimping portions 33 (hereinafter referred to as "mobile intermediate crimping portions" and "static intermediate crimping portions", respectively). The mobile platform 23 comprises a fourth set of crimping portions 34 (hereinafter referred to as "mobile crimping portions").

[0066] The first set of crimping portions 31 and the second set of crimping portions 32 crimp the first set of four SMA wires 271 so as to connect them to the support platform 21 and to the intermediate mobile platform 22. Similarly, the third set of crimping portions 33 and the fourth set of crimping portions 34 crimp the second set of four SMA wires 272 so as to connect them to the intermediate mobile platform 22 and to the mobile platform 23. The SMA wires 27 can be perpendicular to the optical axis O or inclined at a small angle to a plane perpendicular to the optical axis O. Typically, in a set, the SMA wires 27 are non-collinear.

[0067] The crimping portions 31, 32, 33, 34 have respective arm portions 35, 36, 37, 38 which generally extend inwardly to landing points on the respective platforms 21, 22, 23, the arm portions 35, 36, 37, 38 being suitably attached to the landing points.

[0068] In operation, the SMA wires 27 are selectively driven to move the intermediate mobile platform 22 and / or the mobile platform 23 relative to the support platform 21 in any transverse direction, i.e. a direction perpendicular to the optical axis O.

[0069] Further details are also provided in WO 2013 / 175197 Al, which is incorporated herein by reference.

[0070] Taking the first group of four SMA lines 271 as an example, the SMA lines 271 are arranged in a ring at different angular positions around the optical axis O to provide two pairs of mutually perpendicular opposing SMA lines 271. Therefore, each pair of opposing SMA lines 271 can move the lens assembly 3 in one of the two perpendicular directions orthogonal to the optical axis O when selectively driven. Similarly, in the second group of four SMA lines 272, each pair of opposing SMA lines 271 can be selectively driven to move the lens assembly 3 in one of the two perpendicular directions orthogonal to the optical axis O. Therefore, the SMA lines 271 and 272 can be selectively driven to move the lens assembly 3 relative to the support structure 4 to any position within the range of movement in the two directions orthogonal to the optical axis O. The size of the range of movement depends on the geometry and contraction range of the SMA lines 271 and 272 within their normal operating parameters.

[0071] As will be explained in detail below, the movements of the two sets of SMA lines 271, 272 can be combined to move the moving platform 23, thereby moving the lens assembly 3. Figure 1 It moves further than using only one level and a set of SMA lines.

[0072] The position of lens assembly 3 relative to support structure 4 perpendicular to optical axis O ( Figure 1 The temperature is controlled by selectively altering the temperature of the SMA line 27. This is achieved by passing a selective drive signal that provides resistance heating through the SMA line 27. Heating is provided directly by the drive current. Cooling is provided by reducing or stopping the drive current to allow the SMA line 27 to cool through conduction, convection, and radiation with its surroundings.

[0073] When one of the SMA wires 27 is heated, the stress in the SMA wire 27 increases and the SMA wire 27 contracts, causing the lens assembly 3 to move. As the SMA temperature increases, a series of movements occur within the temperature range where the SMA material transitions from martensite to austenite. Conversely, when one of the SMA wires 27 is cooled to reduce the stress in the SMA wire 27, that SMA wire 27 expands under the force of the opposing SMA wire 27. This allows the lens assembly 3 ( Figure 1 It moves in the opposite direction.

[0074] SMA line 27 can be made of any suitable SMA material, such as Nitinol or another titanium alloy SMA material.

[0075] The drive signal for SMA line 27 is generated and provided by the control circuitry implemented in IC 7. Figure 1 The drive signal is received by the control circuit in response to the gyroscope sensor 8. Figure 1 The output signal of the lens assembly 3 is generated, thereby driving the movement of the lens assembly 3 to stabilize it.Figure 1 ) on the image sensor 12( Figure 1 ) to provide OIS. The drive signals can be generated using a resistive feedback control technique, for example as described in WO 2014 / 076463 Al, which is incorporated herein by this reference.

[0076] Reference is also made to Figure 5 , the electrical connection of the SMA wires 27 is achieved through a set of terminals 40 via conductive tracks 41 on the support platform 21, conductive tracks 42 on the intermediate moving platform 22 and conductive tracks 43 on the moving platform 23. In some examples, the moving platform 23 is a single conductive piece that provides a common node 44. The conductive tracks 42 on the intermediate moving platform 22 can be formed by patterning a metal sheet, for example stainless steel. The intermediate moving platform 22 can include insulating support for the tracks 42, for example a metal plate coated in a dielectric material.

[0077] Each wire in the first set of SMA wires 271 is in series with a respective wire in the second set of SMA wires 272 between a respective terminal 40 and the common node 44 (or "common connection"), which provides a return path to the common rail 46 (or "common connection") via a flexible interconnect. Described in another way, the current through one SMA wire 271 (for moving the first level 22, i.e. the intermediate moving platform 22) goes through one SMA wire 272 (for moving the second level 23, i.e. the moving platform 23). The current through each pair of SMA wires 271, 272 is controlled by a field effect transistor 47 or any suitable control circuit.

[0078] As will be explained in more detail hereinafter, the SMA wires 27 can be connected in different ways, resulting in different numbers of terminals.

[0079] Reference is again made to Figures 2 to 4 The actuator assembly 2 includes four planar bearings 50 spaced around the optical axis O to support the moving platform 23 on the support platform 21. In general, a different number of bearings 50 can be used. Preferably, at least three bearings 50 are used to help provide stable support.

[0080] Each planar support 50 comprises a support member 51, which in this case takes the form of a cylinder. The support member 51 can be fixed to the support platform 21, for example by adhesive. In this case, a surface 52 on the side of the support member 51 opposite the support platform 21 (“upper surface”) and a surface (not shown) of the moving platform 23 (“underside” or “downside”) are planar mating surfaces in contact with each other. Alternatively, the support member 51 can be fixed to the moving platform 23, for example by adhesive. In this case, a surface (not shown) on the side of the support member 51 opposite the moving platform 23 (“lower surface”) and a surface (not shown) of the support platform 21 (“topside” or “upside”) are planar mating surfaces in contact with each other. Each support member 51 passes through a (suitably enlarged) corresponding hole 53 in the intermediate moving platform 22.

[0081] Thus, the contact between the mating parts directly supports and bears the moving platform 23 on the support platform 21, allowing relative motion parallel to their extent (i.e. perpendicular to the optical axis O).

[0082] The supports 50 can be made of a suitable metal or alloy, for example phosphor bronze or stainless steel with a diamond-like carbon coating.

[0083] The actuator assembly 2 also comprises two arms 60 connected between the support platform 21 and the moving platform 23. The arms 60 are resilient and configured to provide a suitable holding force along the optical axis O, and also to allow lateral motion with a suitable lateral biasing force. The arms 60 also provide electrical connections from the support structure 21 to the moving platform 23, as described below.

[0084] In the assembled state of the actuator assembly 2, the arms 60 are deflected from their relaxed state so that they provide a force (i.e. a holding force) that biases the platforms 21, 23 together and maintains the contact in the planar supports 50. At the same time, the arms 60 can be deflected laterally to allow the moving platform 23 to move relative to the support platform 21 in a direction perpendicular to the optical axis O.

[0085] The arms 60 provide a force (i.e. a lateral biasing force) that biases the moving platform 23, and hence the lens assembly 3 ( Figure 1 ), from any direction around a central position to the central position, where the central position corresponds to the optical axis O of the lens assembly 3 being substantially aligned with the centre of the light-sensitive area of the image sensor 12 ( Figure 1 ). As a result, without driving lateral motion of the lens assembly 3 ( Figure 1 ), the lens assembly 3 ( Figure 1) will tend to centre from any direction around the central position. This ensures that even without driving of the SMA wires 27, the camera 1 still retains the ability to capture images normally. The magnitude of the lateral bias force is kept low enough so as not to impede OIS, while preferably high enough to centre the lens assembly 3 Figure 1 ) without driving.

[0086] Each arm 60 is generally "L" shaped and extends around the optical axis O. The angular extent of each arm 60 is preferably at least 90° (measured between the end points of the arm 60).

[0087] In the present example, the arms 60 are formed integrally with the moving platform 23 at one end of the moving platform 23 and are connected to the support platform 21 at the other end of the moving platform 23. Alternatively, the arms 60 can be formed integrally with the support platform 21 and connected to the moving platform 23, or the arms 60 can be separate parts connected to both platforms 21, 23. The arms 60 can be connected to the plates 21, 23 by welding (providing both mechanical and electrical connections).

[0088] The arms 60 are made from a suitable material that provides the desired mechanical properties and is electrically conductive. Typically, the material is a metal with a relatively high yield strength, for example steel, such as stainless steel.

[0089] Wire connections

[0090] With reference to Figure 5 and Figure 6 , the SMA actuator assembly 2 comprises two tiers 22, 23 that are mechanically connected together in series, and the SMA wires 271, 272 in both tiers 22, 23 are also electrically connected in series.

[0091] The support 21 provides four wire connections to the SMA wires 27, the intermediate moving part 22 has no connections (only the interconnection between the SMA wires 271, 272), and the moving part 23 provides a common connection.

[0092] With particular reference to Figure 5 , it is considered that the SMA wires 27 1，A to the intermediate moving part 22 (i.e. the first tier 22) can be provided to move the intermediate moving part 22 in the +x direction, potentially with two positions in which the SMA wires 27 1，A move the intermediate moving part 22 in the -x direction. 2、B SMA wires 27 2、B can be provided to the moving part 23 (i.e. the second tier 23) which will move the moving part 23 in the same direction. The SMA wires 27 1，A can be provided on the same side 61A or the opposite side 61B as the SMA wires 27

[0093] Figure 5current is shown flowing from a first terminal 40 on the support 21, via a wire 41 in the support 21, via the first SMA wire 27 1，A to the intermediate moving part 22, via a wire 42 in the moving intermediate part 23, via the second SMA wire 27 2、B to the moving part 23, and then back to the second terminal on the support 21 via another wire 41 in the moving part 23, the spring arm 60 and the support 21.

[0094] The use of two wires 27 1、A , 27 2、B arranged on the same side 61A can be helpful in one or more respects, namely (i) it can simplify the connections required on the intermediate moving part 22, e.g. the connections can be made by patterning a single layer of conductive material, (ii) the length of the wire 42 on the intermediate moving part 22 is shorter, which helps to reduce interference (i.e. image noise) with the image sensor caused by the PWM signals used to drive the wires, and (iii) the two wires 27 1，A , 27 2、B are in the same thermal environment, and so are more likely to be driven in a similar manner.

[0095] With particular reference to Figure 8 , in an alternative arrangement each SMA wire 271, 272 is independently controllable by a respective FET 47.

[0096] One end of each SMA wire 271 in the first set of SMA wires 271 is connected to a respective terminal 40 on the support 21. The other end of the SMA wire 271 is connected to a common node 441 (e.g. formed by a conductive layer) on the first tier 22, which is connected to a terminal 40 on the support 21 via a first flexible interconnect 701.

[0097] Similarly, one end of each SMA wire 272 in the second set of SMA wires 272 is connected to a terminal 40 on the support 21 via a second flexible interconnect 702. The other end of the SMA wire 272 is connected to a common node 442 on the second tier 23, which is connected to a terminal 40 on the support 21 via a third flexible interconnect 703.

[0098] The flexible interconnects 70 can be formed in any suitable manner. One or more of the flexible interconnects 70 can be formed in the arm 60 Figure 4) or other biasing springs (as described below). In this case, the flexible interconnections 70 can be formed by the arms 60 themselves, or by forming one or more conductive tracks on the arms 60 (particularly in the case where the flexible interconnections 70 involve multiple (e.g. four) connections). One or more of the flexible interconnections 70 can be formed in another way. For example, the flexible interconnections 70 can comprise a flexible printed circuit, e.g. as described in WO 2016 / 009200 Al, which is incorporated herein by this reference.

[0099] Figure 8 The arrangement of Figure 4 comprises ten terminals 40 and three flexible interconnections 70.

[0100] Another arrangement comprises effectively reversing the electrical connections to the two tiers 22, 23 relative to each other. In this case, the common connections (‘commoners’) for the two tiers are located on the intermediate moving part 22. These connections can be connected together and treated as one connection, reducing the number of connections.

[0101] Reference is made to Figure 9 An example of this arrangement will now be described.

[0102] In this case, the common nodes 441, 442 are connected to nodes 78 on the first tier 22. The nodes 78 are connected by a flexible interconnection 701 to a terminal 40 on the support 21. Thus, Figure 9 The arrangement of Figure 4 comprises ten terminals 40 and three flexible interconnections 70. Figure 8 The arrangement of Figure 4 comprises ten terminals 40 and three flexible interconnections 70.

[0103] In this case, each SMA wire 271, 272 is independently controllable by a respective FET 47.

[0104] Reference is made to Figure 7 An alternative electrical arrangement is shown in Figure 5, in which the SMA wires 271, 272 are electrically connected in parallel in both tiers 22, 23. Appropriate track arrangements are used on the support 41 and tiers 22, 23. Thus, Figure 7 The arrangement of Figure 4 comprises ten terminals 40 and three flexible interconnections 70.

[0105] Manufacture

[0106] Reference is again made to Figures 2 to 4 If the SMA wire 272 in the second tier 23 is directly above the SMA wire 271 in the first tier 22, it can be difficult to insert a crimping tool (not shown) into the correct position to allow the SMA wires 271, 272 to be crimped and thus attached to the rest of the actuator 2.

[0107] Reference is made to Figure 10To solve this problem, the SMA wire 27 can be crimped onto a strut element 85 (or "strut") away from the actuator subassembly (step S1). The strut 85, with corresponding crimps 32 at its distal ends between which the SMA wire 27 extends, is provided to the actuator subassembly 2' (step S2) and attached to the actuator subassembly 2' e.g. by welding (step S3). The strut 85 is detached from the crimps 32 using a cutting tool or laser (not shown) (step S4) and withdrawn (step S5).

[0108] Further details can be found in WO 2016 / 189314 Al, which is incorporated herein by this reference.

[0109] Thus, the actuator 2 is manufactured by first assembling the support 21, the intermediate moving part 22 and the moving part 23 together with the bearing 50 and held together with the spring arms 60. Next, the first set of wires 271 and corresponding crimps 31, 32 are attached to the support 21 and the intermediate moving part 22, and the second set of wires 272 and corresponding crimps 33, 34 are attached to the intermediate moving part 22 and the moving part 23.

[0110] Bearing arrangement and loading of bearings

[0111] In one arrangement, there is a first set of bearings between the intermediate moving part and the static part, and a second set of bearings between the moving part and the intermediate moving part. Furthermore, there is a set of biasing springs (or other biasing arrangements, e.g. magnets) between the intermediate moving part and the static part, and a second set of biasing springs (or other biasing arrangements) between the moving part and the intermediate moving part, where the biasing springs load the respective bearings.

[0112] However, the number of sets of bearings and / or biasing springs can be reduced in several ways. For example, there can be a single set of biasing springs which span from the moving part to the support and load all bearings. Alternatively or additionally, the moving part can be directly supported on the support.

[0113] With reference to Figures 2 to 4 , the actuator assembly 2 has a single set of biasing springs 60 which span from the moving part 23 to the support 21, and the moving part 23 is directly supported on the support 21.

[0114] In this case, the intermediate moving part 22 can be constrained e.g. by a small gap between the support 21 and the moving part 23, or there can be a weak spring force applied to the intermediate moving part 22 to press it against a secondary bearing surface on the moving part 23 or the support 21.

[0115] The intermediate moving portion 22 can be tilted during operation (in other words, when the intermediate moving portion 22 is moved by the SMA wires 271, 272).

[0116] Although not shown in the drawings, the moving portion 23 can be provided with end stops (also referred to herein as “second tier end stops”) to limit lateral movement of the moving portion 23. Furthermore, the intermediate portion can also be provided with its own end stops (also referred to herein as “first tier end stops”). In this way, the first set of SMA wires 271 and the second set of SMA wires 272 can be independently protected.

[0117] Both the first and second tier end stops can be formed by features having a fixed position relative to the support 21. For example, they can involve features of the housing 9 ( Figure 1 ) or the support 21 such as upstanding members. The first or second tier end stops can be formed between the intermediate portion 22 and the moving portion 23. For example, there can be a dependent member from the moving portion 23 that can engage with a corresponding upstanding member from the intermediate portion 22 in order to provide a limit to the relative lateral movement of the intermediate portion 22 and the moving portion 23 (where one or possibly both are limited in their movement relative to the support 21).

[0118] As previously mentioned, the bearings 50 between the moving portion 23 and the support pass through or are located in holes 53 in the intermediate moving portion 22. Although planar bearings are described, ball bearings or other forms of bearings can also be used.

[0119] Driving

[0120] Referring again Figure 8 and 9 , in the case where all eight SMA wires 271, 272 can be independently heated, stacked and overlapping PWM waveforms can be used to allow sufficient power to be delivered.

[0121] Both sets of SMA wires 271, 272 can be driven to the same amplitude.

[0122] Alternatively, in order to save power and / or when only a short small movement is required (for example, the camera is taking a still image rather than a video), only one set of SMA wires 271, 272 can be driven, leaving the other set of SMA wires 271, 272 unpowered or in a low power, zero displacement state.

[0123] Referring again Figure 5 , in the case where the pairs of SMA wires 271, 272 are connected in series, the resistance of the pairs of SMA wires 271, 272 can be high, which can make it difficult to deliver sufficient power to the actuator 2. One or more methods can be used to enable sufficient power to be delivered.

[0124] First, the drive voltage can be increased, e.g. from 2.8V to 3V, or even to 5V. Second, all four wire pairs can be driven simultaneously. Third, the diameter of the SMA wire can be increased from 25pm to 30pm, or even to 35pm.

[0125] Vertical or horizontal stacking

[0126] In the embodiments described above, the tiers are stacked vertically, i.e. one on top of the other (stacked in the z-axis direction). However, in alternative arrangements, two or more tiers can be nested. For example, the tiers can all be nested, with the support on the outside, the intermediate moving part generally on the inside of the support, and the moving part generally on the inside of the intermediate moving part.

[0127] Additional motion

[0128] Reference Figure 11 The two-tier SMA actuator assembly 2 is provided with elongated lateral motion (or “longer travel”) in the x-y plane (i.e. perpendicular to the optical axis O).

[0129] The moving platform 23 is centred on the optical axis O.

[0130] The first tier has a travel s 1x , s 1y , and the second tier has a travel s 2x , s 2y .

[0131] The moving platform 23 is able to move laterally (i.e. in the x-y plane) to any position within an elongated boundary 100, which is larger than the boundary 101 provided by just one of the tiers.

[0132] Other variations

[0133] It will be appreciated that there can be many other variations of the embodiments described above.

[0134] For example, there can be more than two tiers, e.g. three tiers including first and second intermediate moving tiers and a moving tier.

[0135] The moving platform does not have to move only in the x-y plane.

[0136] The actuator assembly does not need to be configured to support a lens assembly, and for example can be configured to support another type of optical element, image sensor, etc. The platform does not need to include an aperture.

[0137] The actuator assembly does not need to be used in a camera.

[0138] The z-axis need not correspond to the optical axis. The z-axis can correspond to a line normal to a plane defined by the plane of the mobile platform and / or support platform. The z-axis can correspond to a line normal to a plane defined by the direction of movement of the mobile platform.

[0139] The actuator assembly can be any type of assembly that includes a first portion and a second portion movable relative to the first portion. The actuator assembly can be or can be provided in any of the following devices: a smartphone, a protective cover or case for a smartphone, a functional cover or case for a smartphone or electronic device, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronic device, a camera with folding optics, an image capture device, an array camera, a three-dimensional sensing device or system, a servomotor, a consumer electronic device, a mobile or portable computing device, a mobile or portable electronic device, a laptop computer, a tablet computing device, an e-reader, a computing accessory or computing peripheral device, an audio device, a security system, a gaming system, a gaming accessory, a robot or robotic device, a medical device, a virtual reality system, a virtual reality device, a wearable device, a drone, an aircraft, a spacecraft, a submersible, a vehicle, an autonomous vehicle, a tool, a surgical tool, a remote control, clothing, a switch, a dial or button, a display screen, a touchscreen, a flexible surface, and a wireless communication device. It will be appreciated that this is a non-exhaustive list of example devices.

Claims

1. A shape memory alloy actuator assembly comprising: a support; a first stage movable in at least two different non-parallel directions within a first plane relative to the support; a first set of at least two shape memory alloy wires configured to move the first stage in the first plane; a second stage movable in at least two different non-parallel directions within a second plane parallel to or coplanar with the first plane relative to the first stage; and a second set of at least two shape memory alloy wires configured to move the second stage in the second plane; wherein the first stage is coupled to the support via the first set of shape memory alloy wires and the second stage is coupled to the first stage via the second set of shape memory alloy wires such that motion of the second stage in the second plane relative to the support is a combination of motion of the first stage relative to the support and motion of the second stage relative to the first stage.

2. The actuator assembly of claim 1, wherein: the first set of at least two shape memory alloy wires comprises four shape memory alloy wires including a first pair of wires acting in opposition to move the first stage in a first direction and a second pair of wires acting in opposition to move the first stage in a second direction different from the first direction, and the second set of at least two shape memory alloy wires comprises four shape memory alloy wires including a third pair of wires acting in opposition to move the second stage in the first direction or a third direction and a fourth pair of wires acting in opposition to move the second stage in the second direction or a fourth direction different from the third direction.

3. The actuator assembly of claim 1, further comprising: a first terminal and a second terminal; wherein a first shape memory alloy wire of the first set of shape memory alloy wires and a second shape memory alloy wire of the second set of shape memory alloy wires are electrically connected in series between the first terminal and the second terminal, and wherein the first shape memory alloy wire and the second shape memory alloy wire act in concert to move the first stage and the second stage, respectively.

4. The actuator assembly of claim 1, further comprising: a first terminal and a second terminal; wherein a first shape memory alloy wire of the first set of shape memory alloy wires and a second shape memory alloy wire of the second set of shape memory alloy wires are electrically connected in parallel between the first terminal and the second terminal, and wherein the first shape memory alloy wire and the second shape memory alloy wire act in concert to move the first stage and the second stage, respectively. the first shape memory alloy wire and the second shape memory alloy wire are interconnected in the first stage.

5. The actuator assembly of claim 3, wherein, ​ 6. The actuator assembly of claim 5, wherein, The first tier includes an electrically conductive layer supported by an insulating layer, wherein at least a portion of the electrically conductive layer interconnects the first shape memory alloy wire and the second shape memory alloy wire.

7. The actuator assembly of any of claims 3-6, wherein, The first and second shape memory alloy wires are on the same side of the actuator assembly.

8. The actuator assembly of any one of claims 1-6, further comprising: a common node; wherein at least a first shape memory alloy wire of the first set of shape memory alloy wires and at least a second shape memory alloy wire of the second set of shape memory alloy wires are connected to the common node; wherein the common node is included in the first tier.

9. The actuator assembly of claim 8, comprising: a flexible electrical connection between the support and the common node.

10. The actuator assembly of claim 8, comprising: a flexible electrical connection between the support and the second tier to electrically connect to the at least one second shape memory alloy wire.

11. The actuator assembly of any one of claims 1-6, further comprising: a common node; wherein at least a pair of shape memory alloy wires consisting of one of the first set of shape memory alloy wires and one of the second set of shape memory alloy wires are electrically connected in series to the common node; wherein the common node is included in the second tier.

12. The actuator assembly of claim 11, comprising a flexible electrical connection between the support and the common node.

13. The actuator assembly of any one of claims 1-6, 9-10, and 12, further comprising: five terminals including a first terminal to a fifth terminal, the fifth terminal being a common terminal; wherein the first set of shape memory alloy wires and the second set of shape memory alloy wires are connected to the terminals such that in response to respective signals applied to the first to fourth terminals relative to the common terminal, the first set of shape memory alloy wires and the second set of shape memory alloy wires cause the first tier and the second tier to move in unison.

14. The actuator assembly of any one of claims 1-6, 9-10, and 12, further comprising: a support system configured to enable the second tier to move in at least two different non-parallel directions in the second plane.

15. The actuator assembly of claim 14, wherein, The second tier is directly supported on the support via the support system.

16. The actuator assembly of claim 15, wherein, The support system includes at least three supports that pass through the first tier.

17. The actuator assembly of claim 14, further comprising: a loading device to load the support system by pushing the support and the second tier together with the first tier interposed therebetween.

18. The actuator assembly of claim 17, wherein, The loading device includes: a set of at least two biasing springs.

19. The actuator assembly of claim 18, wherein, At least one of the springs carries an electrical connection between the support and the second tier.

20. The actuator assembly of any of claims 17-19, wherein, The loading device includes at least one permanent magnet.

21. The actuator assembly of any of claims 1-6, 9-10, 12, and 15-19, wherein, The first set of shape memory alloy wires and / or the second set of shape memory alloy wires are tilted with respect to the first plane so as to facilitate pushing the support and the second stage together.

22. The actuator assembly of any one of claims 1-6, 9-10, 12, and 15-19, further comprising: a third stage movable relative to the second stage in at least two different non-parallel directions in a third plane parallel to or coplanar with the first plane; and a third set of at least two shape memory alloy wires configured to move the third stage; wherein the third stage is interposed between the first stage and the second stage.

23. The actuator assembly of any one of claims 1-6, 9-10, 12, and 15-19, further comprising: an additional stage movable perpendicular to the first plane; wherein the additional stage is supported by the second stage.

24. The actuator assembly of any of claims 1-6, 9-10, 12, and 15-19, wherein, The support, the first stage, and the second stage are stacked in a direction perpendicular to the first plane.

25. The actuator assembly of any of claims 1-6, 9-10, 12, and 15-19, wherein, At least two of the support, the first stage, and the second stage are approximately coplanar and nested.

26. A system comprising the actuator assembly of any one of claims 1-25, further comprising: a power supply track for delivering a drive voltage; a set of switching devices for applying a drive signal to a respective shape memory alloy wire or a respective pair of shape memory alloy wires at the drive voltage; and a controller for individually controlling the switching devices.

27. An optical device comprising: a main body; a first optical element; a second optical element; and the actuator assembly of any one of claims 1-25 or the system of claim 26; wherein the first optical element and the second optical element are approximately aligned along an optical axis, and wherein the first optical element and the support of the actuator element are fixed relative to the main body, and the second optical element is supported by the second stage of optical elements.

28. A method of using the actuator assembly of any one of claims 1-25, the method comprising: causing a drive signal to be applied to at least one shape memory alloy wire or at least one pair of shape memory alloy wires, each pair of shape memory alloy wires comprising one shape memory alloy wire of the first set of shape memory alloy wires and one shape memory alloy wire of the second set of shape memory alloy wires.

29. A method of manufacturing the actuator assembly of any one of claims 1-25, the method comprising: providing a support element comprising a sacrificial support body and crimp tabs held apart by the sacrificial support body; unfolding a shape memory alloy wire across the crimp tabs of the support element; folding the crimp tabs and crimping the crimp tabs over the shape memory alloy wire to form a crimp holding the shape memory alloy wire between the crimp tabs; attaching the crimp to the support and the first stage, respectively, or to the first stage and the second stage, respectively; and removing the sacrificial post body, leaving the crimp portions respectively attached to the support and the first tier or respectively attached to the first tier and the second tier.

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