Actuator assembly

Abstract

An actuator assembly comprises: a first component (20) and a second component (10), wherein a principal axis (P) is defined with reference to the second component; a plurality of lengths of shape memory alloy wire (30) connected between the first component and the second component, wherein each length of the wire is configured to cause three-dimensional movement of the first component relative to the second component when selectively energized; and a mechanism configured to maintain the first component in at least one position and / or orientation relative to the second component against gravity for any orientation of the second component when each length of the wire is not energized.

Description

[0001] field

[0002] The present application relates to actuator assemblies, and more particularly to actuator assemblies including multiple lengths of shape memory alloy (SMA) wire.

[0003] background

[0004] WO 2011 / 104518 A1 describes an actuator assembly that uses SMA wires to move a movable element supported on a support structure, for example to provide optical image stabilization. Eight SMA wires are arranged obliquely relative to an imaginary main axis, with a pair of SMA wires on each of the four sides around the main axis. The SMA wires are connected so that when contracted, the forces provided by the two groups of four SMA wires have components in opposite directions along the main axis, so that these groups can provide movement along the main axis. Each group of SMA wires has a 2-fold rotational symmetry around the main axis, so that there are SMA wires that are opposite to each other that can provide lateral movement.

[0005] Overview

[0006] According to a first aspect of the present invention, an actuator assembly is provided, comprising: a first component and a second component; a plurality of sections of SMA wire connected between the first component and the second component, wherein each section of the wire is configured to cause three-dimensional (3D) movement of the first component relative to the second component when selectively energized; and a mechanism configured to maintain the first component relative to the second component in at least one position and / or orientation against gravity for any orientation of the second component when the sections of the wire are not energized.

[0007] A number of advantages derive from being able to hold the first component in this manner.

[0008] The mechanism should be configured so as to avoid undue influence on the ability of the SMA wire to induce 3D motion of the first component.

[0009] For example, the first component may correspond to the movable element, the second component may correspond to the supporting structure, and the plurality of lengths of SMA wire may correspond to the eight SMA wires described in WO 2011 / 104518 A1.

[0010] A principal axis (eg an optical axis) may be defined with reference to the second component.

[0011] 3D motion may correspond to, for example, a translational motion with three degrees of freedom.

[0012] At least one position in which the first component is held may correspond to a range of positions. The range of positions may correspond to at least a portion of the first component having moved a distance <100 μm from a central position relative to the second component. The distance may be <50 μm or <25 μm.

[0013] The distance may be a transverse distance relative to the main axis. In certain applications, controlling such a distance is particularly important.

[0014] The mechanism may include: a set of one or more end stops formed on the second component; and a set of one or more elastic elements connected between the first component and the second component to bias the first component so that when the wire segments are not energized, the first component moves into contact with the set of end stops. This may provide another effective way to implement the mechanism.

[0015] The movement may be at least partially along the primary axis.

[0016] The set of end stops may include a first set of surface areas configured to contact a first set of surface areas of the first component to control an orientation of the first component relative to the primary axis.

[0017] The set of end stops may include a second set of surface areas configured to contact a second set of surface areas of the first component to control a lateral position of at least a portion of the first component relative to the primary axis.

[0018] The second set of surface regions may define a cone to guide the first component to at least one position and / or orientation from a range of positions and / or orientations associated with 3D movement of the first component.

[0019] The first component may have a first portion and a second portion spaced apart from each other along the main axis. The second set of surfaces may be configured to control a lateral position of the second portion relative to the main axis, and the set of resilient elements may be further configured to bias the first portion toward a central lateral position relative to the main axis, thereby controlling the orientation of the first component relative to the main axis.

[0020] The mechanism may comprise a set of one or more resilient elements connected between the first component and the second component to bias the first component towards at least one position and / or orientation. This may provide an efficient way of implementing the mechanism.

[0021] At least one of the set of elastic elements may extend in one or more directions at least partially perpendicular to the main axis. This may be advantageous due to space considerations.

[0022] The set of resilient elements may comprise two or more resilient elements spaced apart from each other along the main axis.This may provide a relatively high stiffness with respect to rotation of the first component relative to the main axis, which may be advantageous.

[0023] The set of resilient elements may produce a biasing force on the first component such that for any orientation of the second component where the major axis is horizontal, at least a portion of the first component is at a distance of 80 μm to 100 μm below the center relative to the second component. The distance may be 40 μm to 50 μm or 16 μm to 20 μm. Thus, the biasing force may be just sufficient to achieve a certain degree of retention, in which case any effect on the ability of the SMA wire to induce 3D motion of the first component may be minimized (or suitably small).

[0024] One or more of the set of elastic elements may form part of the electrical connection to the moving end of each length of shape memory alloy wire. Thus, one or more elastic elements may have a dual function, thereby reducing the number of components.

[0025] For ease of reference, actuator assemblies having one or more of the following features are sometimes referred to below as second type actuator assemblies.

[0026] The mechanism can be configured to provide a non-linear biasing force that biases the first component toward at least one position and / or orientation. The non-linear biasing force can be relatively large when the first component is in at least one position and / or orientation, and the non-linear biasing force can be relatively small when the first component is within a range of positions and / or orientations associated with 3D motion of the first component (e.g., a range associated with standard operation).

[0027] The mechanism may include a latch that couples the first component and the second component when the first component is in at least one position and / or orientation.

[0028] These mechanisms may be particularly suited to minimise the impact on the ability of the SMA wire to induce 3D motion of the first component.

[0029] The actuator assembly may include a control circuit configured to move the first component relative to the second component to a position and / or orientation in which the non-linear biasing force is relatively large and / or the latch is engaged before de-energizing the wire segments.

[0030] The mechanism may be configured to provide a non-linear biasing force that is greater than the force of gravity on the first component for any operating position and orientation of the first component relative to the second component. In this case, a control circuit configured as described above may not be required.

[0031] The mechanism may include magnetic elements on each of the first and second components. At least one of the magnetic elements may include a permanent magnet. The magnetic elements may be close to each other when the first component is in at least one position and / or orientation.

[0032] The permanent magnet may be a quadrupole magnet. Such a magnet has a field that decreases rapidly with increasing distance from the magnet and is therefore particularly suitable for generating non-linear biasing forces.

[0033] Optionally, at least one position and / or orientation may be achieved by a substantially translational movement of the first component relative to the second component along the principal axis from a central operating position and orientation of the first component. Thus, the orientation and lateral position of the first component relative to the principal axis may be the same in at least one position and the central operating position. As described below, this may allow the camera lens to be aligned with the optical axis in both positions.

[0034] The central operating position and orientation may correspond to a position and orientation that maximizes a range of motion of the first component relative to the second component that may be induced by selective energization of the plurality of lengths of shape memory alloy wire, and may correspond to a central position within the range.

[0035] The first component and the second component may each include a first set of end stop surface areas configured to contact each other to guide the first component to at least one position and / or orientation.

[0036] The first component and the second component may each include a second set of end stop surface areas configured to contact each other to define at least a portion of a wire protection envelope. The first set of end stop surface areas may intercept the wire protection envelope so that at least one position and / or orientation is within the wire protection envelope.

[0037] The first component and the second component may each include a set of end stop surface areas configured to contact each other to at least partially define the position of the first component along the primary axis when the first component is in at least one position and / or orientation.

[0038] The mechanism may be configured to provide a non-linear biasing force that guides the first component to at least one position and / or orientation.

[0039] The first component may have a first portion and a second portion spaced apart from each other along a main axis. At least one position and / or orientation may correspond to a position and orientation range where the first portion generally has a smaller position range than the second portion. Controlling the position of a particular portion of the first component (i.e., the first portion) may be particularly important. For example, when the actuator assembly is included in a device, the first portion may be more visible than the second portion.

[0040] An optical assembly comprising the actuator assembly may be provided. The first component may comprise a component of an optical system. The principal axis may correspond to an optical axis of the optical system.

[0041] A camera assembly including the optical assembly may be provided.The first component may include a camera lens, and the second component may include an image sensor.

[0042] In the case where the camera assembly includes a second type of actuator assembly, the position and / or orientation of the camera lens relative to at least a portion of the mechanism can be at least partially defined so as to at least partially define the position and orientation of the camera lens relative to the optical axis when the first component is in at least one position and / or orientation. The camera lens can have an orientation defined by a first axis, and another portion of the first component can have an orientation defined by a second axis, the angle of the second axis relative to the first axis being greater than zero and less than, for example, about 5°. In other words, the camera lens may not be aligned with other portions of the first component. This enables the camera lens to be aligned with the optical axis when the first component is in at least one position and / or orientation and is in an operational center position, even if other portions of the first component cannot be so aligned.

[0043] According to a second aspect of the present invention, there is provided a method of assembling an actuator assembly of a second type, the method comprising:

[0044] selectively energizing the plurality of shape memory alloy wires to move the first component to at least one position and / or orientation; and

[0045] In maintaining the first component in the at least one position and / or orientation, at least a portion of the securing mechanism is relative to the position and / or orientation of the first component.

[0046] Moving the first component to at least one position and / or orientation may include moving the first component to an operational center position and orientation and then moving the first component along the primary axis to at least one position and / or orientation.

[0047] Fixing the position and / or orientation of at least a portion of the mechanism may include positioning at least one of the magnetic elements such that the magnetic elements are proximate to each other.

[0048] Fixing the position and / or orientation of at least a portion of the mechanism may include adhering at least one of the magnetic elements to the first component and / or the second component.

[0049] A method of assembling a camera assembly including a second type of actuator assembly may be provided, the method comprising: a method according to the second aspect of the invention; and fixing the position and / or orientation of the camera lens relative to the optical axis while the mechanism holds the first component in at least one position and / or orientation.

[0050] Thus, when the first component is in an operationally central position and orientation, the camera lens may be aligned with the optical axis without having to selectively energize the plurality of lengths of shape memory alloy wire.

[0051] Fixing the position and / or orientation of the camera lens may include adhering the camera lens to a portion of the first component.

[0052] According to a third aspect of the present invention, there is provided a method of operating an actuator assembly or a camera assembly, the method comprising:

[0053] calibrating one or more offsets based on measuring the electrical resistance of one or more lengths of shape memory alloy wire when the first component is in at least one position and / or orientation,

[0054] The offsets are used to adjust one or more aspects of the control scheme so that the actual position and / or orientation of the first component relative to the second component substantially matches the target position and / or orientation in at least one degree of freedom.

[0055] The method may include performing the measurement of the resistance at least in part as part of a power up process and prior to moving the first component to the operative position.

[0056] The method may include performing the measurement of the resistance in part during manufacture of the actuator assembly.

[0057] The method may include determining a change in at least one of the one or more offsets based on a change in at least one measured resistance or a change in a measured resistance response to a known drive signal.

[0058] The method may include calibrating one or more offsets based on measuring the electrical resistance of one or more lengths of the shape memory alloy wire when the first component is in another position and / or orientation.

[0059] The first component may include a camera lens and the second component may include an image sensor. Another position and / or orientation may correspond to a position and / or orientation of the camera lens relative to the image sensor, the position and / or orientation being determined based on properties of an image formed on the image sensor by the camera lens.

[0060] The at least one degree of freedom may include rotation of the first component relative to the second component about at least one axis perpendicular to the main axis.

[0061] The method may include controlling the three-dimensional movement using a control scheme.

[0062] Controlling 3D motion can include:

[0063] setting a target resistance value representing a desired position of the first component relative to the second component;

[0064] Detecting a measured value of the resistance of each section of the shape memory alloy wire;

[0065] deriving errors from the target resistance value and the detected resistance measurement, the errors being adjusted by the offset; and

[0066] The power of the driving signal provided to each section of the shape memory alloy wire is controlled according to the adjusted error. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0069] Figure 1 is a perspective view of an example of an actuator assembly;

[0070] Figure 2 yes Figure 1 A side view of an actuator assembly;

[0071] Figure 3 yes Figure 1 An exploded perspective view of an actuator assembly;

[0072] Figure 4 yes Figure 1 A schematic view of an actuator assembly;

[0073] Figure 5 is a schematic view of another example of an actuator assembly;

[0074] Figure 6 is a schematic view of another example of an actuator assembly;

[0075] Figure 7 is a schematic view of another example of an actuator assembly;

[0076] Fig. 8A and Figure 8B is in the operating position ( Fig. 8A ) and hold position ( Figure 8B ) is a schematic view of another example of an actuator assembly;

[0077] Fig. 9A , Fig. 9B and Fig. 9C is in the operating position ( Fig. 9A ), in the position corresponding to the maximum operating movement ( Fig. 9B ) and in holding position ( Fig. 9C ) is a schematic view of another example of an actuator assembly;

[0078] Fig.10 Shows Figure 9A-9C A motion envelope of a lens holder of an actuator assembly;

[0079] Fig.11A , Fig. 11B and Fig. 11C are schematic views of an example of a camera assembly at several different stages of assembly;

[0080] Fig. 12A , Fig. 12B and Fig. 12C is a schematic view of another example of a camera assembly at several different stages of assembly; and

[0081] Fig.13 is a schematic view of a control circuit that may be used with any of the actuator assemblies shown.

[0082] Detailed Description

[0083] First Component

[0084] refer to Figures 1 to 4 , a first example of an actuator assembly 1 suitable for a miniature camera will now be described.

[0085] The actuator assembly 1 comprises a stationary part 10 and a moving part 20. The moving part 20 has a cylindrical opening 20a for holding a camera lens 25 (only in Figure 4 ). The camera lens 25 includes a lens or a lens assembly. Therefore, the moving part 20 is referred to as the lens holder hereinafter. As described in more detail below, the lens holder 20 is supported on the stationary part 10 by eight SMA wires 30. The lens holder 20 can move relative to the stationary part 10 under the drive of the SMA wires 30, and has six degrees of freedom, namely three orthogonal translational degrees of freedom and three orthogonal rotational degrees of freedom.

[0086] The position and orientation of the various features of the actuator assembly 1 may be conveniently described with reference to a principal axis P, which is defined with reference to the stationary component 10. Broadly speaking, the principal axis P corresponds to an axis of (two-fold) rotational symmetry of the actuator assembly 1. When the camera lens 25 is arranged in the center of the actuator assembly 1, the principal axis P typically corresponds to the optical axis of the camera lens 25.

[0087] The actuator assembly 1 includes a set of two arms 5 that connect the stationary component 10 to the lens holder 20. The arms 5 provide, among other things, an electrical connection from the stationary component 10 to the moving end of the SMA wire 30 (i.e., the end of the SMA wire 30 that is connected to the lens holder 20). Therefore, the arms 5 are sometimes referred to as a common connection.

[0088] The actuator assembly 1 further includes a shielding layer 14 and a shielding cover 15 (from Figure 1 and Figure 2 These components 14, 15 are fixedly connected to the stationary component 10. The shield 15 extends around the lens holder 20 with a clearance sufficient to allow the movement of the lens holder 20. The shield 15 protects the actuator assembly 1 from physical damage and the ingress of dust.

[0089] The stationary component 10 includes a substrate 10a and two stationary posts 10b disposed at opposite corners of the substrate 10a. The stationary posts 10b may be fixedly connected to the substrate 10a or formed integrally with the substrate 10a as a whole. Two crimping assemblies 13 are fixedly connected to each of the two stationary posts 10b. The substrate 10a is configured to hold an image sensor (not shown).

[0090] The lens holder 20 includes two moving posts 20b, which are aligned with the corners of the substrate 10a between the stationary posts 10b. Two crimping assemblies 23 are fixedly connected to each of the two moving posts 20b. Figure 1 Two of the crimping assemblies 23 are omitted. )

[0091] The SMA wire 30 is connected between the stationary component 10 and the lens holder 20 by being crimped to the crimping assembly 13 of the stationary component at one end and to the crimping assembly 23 of the lens holder 20 at the other end. The crimping assemblies 13, 23 serve as both mechanical and electrical connections. The crimping assemblies 23 on the same moving column 20b are all electrically connected to one of the arms 5 (i.e., a common connection).

[0092] The SMA wires 30 have the same configuration around the lens holder 20 as the SMA wires in the actuator assembly described in WO 2011 / 104518 A1. Specifically, two SMA wires 30 are arranged on each of the four side surfaces around the main axis P, and viewed perpendicularly to the main axis P, the two SMA wires 30 are inclined in opposite directions relative to the main axis P (i.e., inclined at an acute angle greater than 0°) and cross each other. Therefore, specifically, each SMA wire 30 is inclined relative to the main axis P and relative to each other. For further details on the arrangement of the SMA wires 30, refer to WO 2011 / 104518 A1.

[0093] The selective contraction of the SMA wire 30 can drive the lens holder 20 to move in any one of the six degrees of freedom. Such motion is sometimes referred to as three-dimensional (3D) motion hereinafter. The contraction and expansion of the SMA wire 30 are generated by selectively applying a drive signal thereto. The SMA wire 30 is resistively heated by the drive signal and is cooled by heat conduction with the surrounding environment when the power of the drive signal is reduced.

[0094] Therefore, the SMA wire 30 can be used to provide the following two functions: providing an auto focus (AF) function through the translation movement of the lens holder 20 along the main axis P, and providing an initial image stabilization (OIS) function through the translation movement of the lens holder 20 perpendicular to the main axis P.

[0095] The drive signal may be generated by a control circuit (not shown) and provided to the SMA wire 30. Such a control circuit may receive an input signal representing a desired position of the lens holder 20 and generate a drive signal having a power selected to drive the lens holder 20 to the desired position. The power of the drive signal may be linear or may be varied using pulse width modulation. The drive signal may be generated using a resistive feedback control technique, in which case the control circuit measures the resistance of the SMA wire 30 and uses the measured resistance as a feedback signal to control the power of the drive signal.

[0096] In this example, the set of arms 5 is also configured to generate a biasing force to bias the lens holder 20 toward a position in which the lens holder 20 (particularly the cylindrical opening 20a for holding the camera lens 25) is centered on and aligned with the main axis P. This position and orientation of the lens holder is referred to as the central arrangement hereinafter. The arm 5 is configured to maintain the lens holder 20 and the camera lens 25 together in a substantially central arrangement when the SMA wire 30 is not driven. In addition, the arm 5 is configured to do so for any orientation of the actuator assembly 1. Specifically, the arm 5 is configured to generate a biasing force so that in these cases, the lens holder 20 is maintained within a specific range of positions and orientations around the central arrangement. It should be understood that the required biasing force will depend on the weight of the camera lens 25 (and any other components on the lens holder 20). The range of positions and orientations may, for example, correspond to at least a portion of the lens holder 20 moving no more than a specified distance (e.g., 100 μm) from its position when the lens holder 20 is in the central arrangement. The specified distance may be a lateral distance relative to the main axis P. The portion of the lens holder 20 for which the distance is specified may be, for example, the upper surface 20d of the lens holder 20, since this determines, for example, the view of the camera lens 25 visible to a user when the camera is included in the device (see in particular Figure 4 ).

[0097] At the same time, the biasing force generated by the arm 5 should not excessively affect the 3D movement of the lens holder 20 caused by the selective contraction of the SMA wire 30 (this movement is referred to as the "operating movement" hereinafter). It will be appreciated that the biasing force in any given direction cannot exceed the maximum force that can be applied by the SMA wire 30 in the opposite direction. In practice, the biasing force may be much lower than this upper limit. Therefore, the arm 5 should be configured to generate a biasing force that is just sufficient to achieve a particular degree of retention. For example, for any orientation in which the main axis P of the actuator assembly 1 is horizontal, the arm 5 can be configured to generate a biasing force so that a portion of the lens holder 20 (e.g., the upper surface 20d) is a distance of 80μm to 100μm below the center position. The biasing force is preferably substantially symmetrical, such as substantially symmetrical in a transverse direction relative to the main axis P.

[0098] The arm 5 may have any suitable characteristics to produce the biasing force as described above.

[0099] In this example, the arms 5 are located within a plane region perpendicular to the main axis P. Broadly speaking, each arm 5 extends a portion (e.g., slightly less than about 180°) around a circle centered on the main axis P. More specifically, each arm 5 first extends in one direction (e.g., clockwise), and then extends around a hairpin bend, and then extends in another direction (e.g., counterclockwise).

[0100] In other examples, there may be a different (eg, larger) number of arms 5 and / or each arm 5 may follow a different path.

[0101] The arm 5 may also be made of any suitable (elastic) material and / or may have any suitable cross-section.

[0102] Second example

[0103] refer to Figure 5 , a second example of an actuator assembly 21 will now be described.

[0104] The actuator assembly 21 comprises the same features as in the first example, and further comprises another (“second”) set of arms 6 connecting the stationary component 10 to the lens holder 20 .

[0105] The second set of arms 6 is located in a ("second") planar region that is perpendicular to the main axis. The second planar region is spaced apart from the ("first") planar region in which the first set of arms 5 is located. For example, the first set of arms 5 can be located toward the lower end of the actuator assembly 21, while the second set of arms 6 can be located toward the upper end of the actuator assembly 21 (where "upper" and "lower" are defined with respect to the actuator assembly 21, which is oriented so that the main axis P is vertical, as shown in the figure).

[0106] In other respects, the second set of arms 6 may be substantially identical to the above-described ("first") set of arms 5, for example, they may be the same in number, may follow the same path within the relevant planar region, may be made of the same material and / or may have the same cross-section.

[0107] The first set of arms 5 and the second set of arms 6 are together configured to generate a biasing force to bias the lens holder 20 towards the central arrangement in a manner similar to that described above with respect to the first example.

[0108] In this example, because there are arms 5, 6 spaced apart along the main axis P, the arms 5, 6 are more effective in limiting the tilt of the lens holder 20 relative to the main axis. In other words, the lens holder 20 can be maintained within a given range of orientations arranged about the center, and furthermore, this can be achieved with each set of arms 5, 6 being independent, each set of arms 5, 6 having generally lower stiffness (and therefore reduced effect on the operational movement of the lens holder 20).

[0109] The second set of arms 6 can generate a different biasing force strength than the first set of arms 5. In particular, the second set of arms 6 can be stiffer than the first set of arms 5. Therefore, the portion of the lens holder 20 to which the second set of arms 6 is attached (i.e., the "upper portion") can be kept more centered than the portion of the lens holder 20 to which the first set of arms 5 is attached (i.e., the "lower portion"). This is advantageous because, as described above, when the camera is included in a device, the position of such an upper portion determines, for example, the view of the camera lens 25 visible to a user.

[0110] In some examples, the first set of arms 5 may generate a relatively weak biasing force, and may be used primarily to provide an electrical connection to the moving end of the SMA wire 30 .

[0111] In some examples, there may be only one set of arms that are connected to the upper portion of the lens holder 20 and provide electrical connections. However, for some technical reasons, it may not be desirable to position the common connection(s) near the top of the lens holder.

[0112] There may be more than two groups of arms, and each group may include any number of arms.

[0113] Third Example

[0114] refer to Figure 6 , a third example of an actuator assembly 31 will now be described.

[0115] The actuator assembly 31 includes the same or similar features as in the first example. However, the arm 5' may be used only to provide an electrical connection to the moving end of the SMA wire 30, without generating the biasing force described above. Instead, in this example, the actuator assembly 31 includes a set of springs 7 and a set of end stops 40, which together hold the lens holder 20' in a desired manner, i.e., in a substantially central arrangement, when the SMA wire 30 is not driven and for any orientation of the actuator assembly 31.

[0116] The spring 7 is connected between the stationary component 10' and the lens holder 20', and is configured to bias the lens holder 20' so that when the SMA wire 30' is not driven, the lens holder 20' moves into contact with the end stop 40. In this example, the spring 7 is connected to the lower portion of the lens holder 20' and biases the lens holder 20' in an upward direction along the main axis P so that the upper portion of the lens holder 20' engages with the end stop 40.

[0117] The end stop 40 includes a first set of surface areas 40a that contact a first set of surface areas 200a of the lens holder 20' to force the lens holder 20' into alignment with the principal axis P. The first set of surfaces 40a, 200a are planar and oriented perpendicular to the principal axis P in this example.

[0118] The end stop 40 includes a second set of surface areas 40b that contact a second set of surface areas 200b of the lens holder 20' to control the lateral position of the upper portion of the lens holder 20' relative to the main axis P. In addition, the second set of surface areas 40b, 200b define a cone to guide the lens holder 20' from any operating position and / or orientation to its final position and / or orientation, i.e., when the SMA wire 30 is selectively driven. In this example, the second set of surface areas 40b, 200b corresponds to a portion of the surface of a cone whose main axis corresponds to the main axis P.

[0119] In some examples, the first set of surfaces 40a, 200a or the second set of surfaces 40b, 200b may be omitted.

[0120] The end stop 40 may be attached to the stationary component 10 and / or the shield 15 or may be formed by a portion of the stationary component 10 and / or the shield 15 .

[0121] As described above, the spring 7 may have any suitable properties to bias the lens holder 20'. Compared to the arms 5 and / or 6 in the first and second examples, the stiffness of the spring 7 may be relatively low, especially in the direction perpendicular to the main axis P, and thus the effect on the operating movement of the lens holder 20' may also be relatively low.

[0122] In some examples, the arm 5 may perform the function of the spring 7 while also providing an electrical connection to the moving end of the SMA wire 30 , without the need for a separate spring 7 .

[0123] Fourth Example

[0124] refer to Figure 7 , an actuator assembly 41 of a fourth example will now be described.

[0125] The fourth example of the actuator assembly 41 is generally similar to the third example, except that the spring 7' is connected to the upper portion of the lens holder 20" and biases the lens holder 20" in a downward direction along the main axis P so that the lower portion of the lens holder 20" engages the end stop 40'.

[0126] In this example, the spring 7' also biases the upper part of the lens holder 20" laterally relative to the main axis P towards a central position.

[0127] In the third example, if the end stop 40 is some distance from the top (i.e., the front) of the actuator assembly 31, then when the lens holder 20' contacts the end stop 40, the rotation of the lens holder 20' will cause, for example, the top of the camera lens to be misaligned. A large biasing force may be required to ensure that the top of the camera lens does not move under the influence of gravity, and such a large force may impair the performance of the actuator. In the fourth example, this problem is solved by placing the spring 7' near the top of the actuator assembly 41 and using the lateral stiffness of the spring 7' to help ensure that the top of the camera lens remains in the desired position.

[0128] Fifth example

[0129] refer to Fig. 8A and Figure 8B , the actuator assembly 51 of the fifth example will now be described.

[0130] The actuator assembly 51 includes the same or similar features as in the first example. However, the arm 5' can be used only to provide an electrical connection with the moving end of the SMA wire 30, without generating the above-mentioned biasing force. Moreover, in this example, the actuator assembly 51 includes magnetic elements 45, 46 on each of the stationary component 10 and the lens holder, and the magnetic elements 45, 46 together hold the lens holder 20 in a desired manner.

[0131] In this example, there is a set of, for example three, permanent magnets 45 that are attached to the stationary component 10, and a set of three corresponding regions of ferromagnetic material (e.g. steel) 46 that are attached to the lens holder 20 or form part of the lens holder 20. In other examples, the permanent magnets 45 may instead be attached to the lens holder 20, and the regions of ferromagnetic material 46 may be attached to the stationary component 10 or form part of the stationary component 10.

[0132] The permanent magnet 45 may be a magnetic quadrupole which may have a size comparable to the distance over which the magnetic force needs to act. Typically this may be several hundred microns.

[0133] When the lens holder 20 is within its range of operating positions and / or orientations (see Fig. 8A ), the magnetic elements 45, 46 on the respective components are relatively far from each other (and therefore the force between them is relatively small). Therefore, the magnetic elements 45, 46 do not affect the operational movement of the lens holder 20 in any significant way.

[0134] When the lens holder 20 is in the holding position (see Figure 8B ), the magnetic elements 45, 46 on the respective components are relatively close to or in contact with each other (and therefore the force between them is relatively large).

[0135] In this example, for any operating position and orientation of the lens holder 20 relative to the stationary component 10, the magnetic force is greater than the gravitational force on the lens holder 20. Therefore, as long as the SMA wire 30 is not energized, the lens holder 20 can be pulled into the retaining position.

[0136] In some other examples, the actuator assembly 51 is used with, or includes, a control circuit that is configured to move the lens holder 20 into a holding position (or close enough to a holding position so that the magnetic force is high enough to pull the lens holder 20 into the holding position) before the SMA wire 30 is energized.

[0137] In this example, the components 10, 20 each include a set of end stop surface areas that are configured to contact each other to at least partially define the position of the lens holder 20 along the main axis P when the first component is in the holding position. For example, the end stop surface areas can be planar ("flat") and perpendicular to the main axis, as shown. In such an example, the magnetic force can guide the lens holder 20 to a relevant position and / or orientation on the "flat" end stop, i.e., to the holding position.

[0138] Instead of a magnetic element, in some examples, the actuator assembly 51 may include another mechanism for providing a nonlinear bias force as described above. In some examples, the actuator assembly 51 may have a latch mechanism (e.g., a mechanical latch) that connects the stationary component 10 and the lens holder 20 when the lens holder 20 is brought to (close to) the holding position by the control circuit.

[0139] Sixth Example

[0140] refer to Figure 9A-9C and Fig.10 , the actuator assembly 61 of the sixth example will now be described.

[0141] The actuator assembly 61 comprises the same features as the fifth example, in particular the magnetic elements (although only the magnetic element 46 on the lens holder 20 is shown). The actuator assembly 61 also comprises a set of end stops 100.

[0142] The end stop 100 defines the lower part of the motion envelope 300 of the lens holder 20. The remaining part of the envelope 300 is defined by one or more further end stops (not shown).

[0143] Each end stop 100 is formed by a partial upwardly facing surface area 101a , 101b on the stationary component 10 (for the illustrated orientation of the actuator assembly 61 ) and a partial downwardly facing surface area 102a , 102b on the lens holder 20 .

[0144] The end stop surface area on the stationary component 10 includes a first group of areas 101a and a second group of areas 101b. Similarly, the end stop surface area on the lens holder includes a first group of areas 102a and a second group of areas 102b. In use, the first group of areas 101a, 102a can engage with each other, and the second group of areas 101b, 102b can engage with each other.

[0145] In this example, the end stop surface areas correspond to the surfaces of (truncated) cones, the axes of which are parallel to the main axis P. In other examples, one or more end stops 100 may have flat surface areas forming a channel having a substantially uniform surface area with respect to the main axis P. Figure 9A-9C The same cross section is shown. A flat surface may be preferred for withstanding stress and / or dust generation.

[0146] The first set of regions 101a, 102a are at a smaller angle relative to the main axis P and are spaced further from the central axis of each end stop 100. In contrast, the second set of regions 101b, 102b are at a larger angle relative to the main axis P and extend to a point on the central axis of each end stop 100.

[0147] The first set of regions 101a, 102a defines a portion 300aa of the "wire protection" envelope 300a in which the SMA wire 30 is safe from damage, e.g., due to overextension. In conventional actuators, the wire protection envelope 300a is interrupted horizontally, e.g., by a horizontal end stop surface, thereby defining the (lower portion) of the operating envelope (see Fig.10 In this example, the wire protection envelope 300a is interrupted by the second set of surface areas 101b, 102b (see Fig.10 The second set of surface areas 101b, 102b are used to guide the lens holder 20 to a center point 300d, which is below the horizontal envelope 300c of a conventional actuator (and therefore below a typical operating envelope) and above the wire protection envelope 300a (and therefore safe for the SMA wire 30).

[0148] The second set of regions 101b, 102b assist in guiding the lens holder 20 into and out of a low center position (i.e., a holding position) in which the magnetic elements are close to each other. Thus, the second set of regions 101b, 102b assist in "parking" the lens holder 20, as described above, using the SMA wire 30 before the SMA wire 30 is not energized.

[0149] The second set of regions 101b, 102b reduces the amount of Z-axis travel required to park the lens holder 20, and therefore reduces the amount of space required for the actuator 61, while also reducing the risk of strain damage to the SMA wire 30 in the extra Z-axis travel area.

[0150] In other examples, the first set of surface regions 101a , 102a may be separated from the second set of surface regions 101b , 102b while still providing a similar envelope 300 , rather than being combined in a single end stop 100 .

[0151] Assembly Method

[0152] refer to Figure 11A-11C Now, an example of a method of assembling the components of the camera assembly (i.e., the actuator assembly 61' and the lens assembly 25) will be described. Here, the actuator assembly 61' is similar to the actuator assembly 61 of the sixth example, i.e., includes magnetic elements 45, 46 on each of the stationary component 10 and the lens holder 20.

[0153] In the first step (see Fig.11A), maintaining the lens holder 20 in a position and orientation referred to hereinafter as the "operating center". This can be achieved by selectively energizing the SMA wires 30. The operating center may correspond to a position and orientation that maximizes the range of (translational) motion of the lens holder 20 that can be caused by the SMA wires 30, and more specifically may correspond to a central position within this range. Alternatively, the operating center may be an approximation of such a position and orientation. The operating center may be defined in any suitable manner, for example with reference to a target resistance of the SMA wires 30. Due to, for example, changes in the tension of the SMA wires 30 after they are attached between the stationary component 10 and the lens holder 20, the operating center does not generally correspond to an arrangement in which the lens holder 20 is centered on and aligned with the main axis P. For example, the operating center, which may correspond to the main axis of the lens holder 20, may have a deviation of up to about 1° from the main axis P.

[0154] In the second step (see Fig. 11B ), with the lens holder 20 held at the operational center by the SMA wire 30, introduce the lens assembly 25 (if not already done), arrange the lens assembly in the desired position and orientation using the clamp 250, and attach the lens assembly to the lens holder 20. The desired position and orientation of the lens assembly 25 is arranged relative to the stationary component 10 so as to be substantially parallel to the main axis P. The lens assembly 25 can also be arranged in a substantially laterally (and vertically) central position. The clamp 250 can have any suitable shape to achieve this. The lens assembly 25 can be attached to the lens holder 20 by a curable adhesive 26 that is cured at this stage.

[0155] For further details related to the above steps, refer to WO 2018 / 073585 A1.

[0156] refer to Fig. 11C , in this example, the magnetic elements 45, 46 are symmetrically arranged on the stationary part 10 and the lens holder 20. Therefore, when the lens holder 20 is in the holding position, the orientation of the lens holder 20 relative to the main axis P is substantially different from its orientation when it is in the operating center. Therefore, when the lens holder 20 is in the holding position, the lens assembly 25 is substantially not parallel to the main axis P. This can be at least partially compensated by arranging the actuator assembly 61' relative to the hole 150 (for example, in a device including it) so that when the lens holder 20 is in the holding position, the lens assembly 25 appears to be centered in the hole 150. This may require additional (adjustment) measures during assembly, which may be disadvantageous.

[0157] Sixth Example and Assembly Method

[0158] refer to Figure 12A-12C, an example of a seventh example actuator assembly 71 and a method involving assembly thereof will now be described.

[0159] The actuator assembly 71 includes the same or similar features as the sixth example 61. However, as will be explained in more detail below, the position and orientation of the magnetic element 46 relative to the lens holder 20 may be adjusted during assembly.

[0160] In the first step (see Fig. 12A ), as described above, the lens holder 20 is brought to the operating center and then lowered to a final position corresponding to the holding position in which the magnetic elements 45, 46 engage each other. This lowering corresponds to a movement along the main axis P toward the stationary part 10 and is performed without substantially changing the orientation of the lens holder 20 (i.e., it is a translational movement). This movement can be performed by appropriately energizing the SMA wire 30.

[0161] In other examples, the lens holder 20 may be raised to a holding position above the operating center.

[0162] In the second step (see Fig. 12B ), with the lens holder 20 held in the “held” position by the SMA wires 30 , introduce the magnetic elements 46 (if not already done), arrange them in the desired position and orientation, and attach them to the lens holder 20 .

[0163] In this example, the magnetic element 46 (hereinafter referred to as "magnet") is a permanent magnet and is bar-shaped. Each magnet 46 and, for example, a certain amount of curable adhesive 47 are contained in the cavity 20f of the lens holder 20. The cavity 20f has a relatively large top opening to allow the magnet 46 and the adhesive 47 to be introduced into the cavity 20f. The cavity 20f has a relatively small lower opening, and the magnet 46 can pass through the lower opening within a range of orientations relative to the lens holder 20. In the desired position and orientation, each magnet 46 passes through the lower opening in the cavity 20f and engages with the corresponding magnetic element 45 on the stationary component 10. The magnet 46 can be attached to the lens holder 20 by, for example, a curable adhesive 47 that is cured at this stage.

[0164] The first and second steps described above need not involve the lens assembly 25. In other words, they may correspond to actuator assembly steps rather than camera assembly steps. In addition, these steps provide an actuator assembly 71 in which the position and orientation of the lens holder 20 at an operational center is defined at least in part relative to a holding position in which the magnetic elements 45, 46 engage each other. In particular, the operational center is a distance above (or below) the holding position. As will now be explained, this enables the lens assembly 25 to be arranged in a desired position and orientation without having to selectively energize the SMA wire 30, which can simplify the camera assembly process.

[0165] In the third step (see Fig. 12C ), with the lens holder 20 held in a retaining position by the magnetic elements 45, 46, introduce the lens assembly 25 (if not already done), arrange the lens assembly in the desired position and orientation using the clamp 250, and attach it to the lens holder 20.

[0166] The desired position and orientation corresponding to the lens assembly 25 is substantially parallel to the main axis P, and is preferably in a substantially transverse central position relative to the main axis P. Because the operating center is a certain distance above the holding position, the desired position of the lens assembly 25 at this stage is a corresponding distance below the operating center. The fixture 250 can have any suitable shape to achieve this position and orientation. The fixture 250 can have an adjustable height, or can be adjustably positioned to compensate for changes in the distance between the operating center and the holding position (which can be recorded in the previous step). However, a certain amount of change in the height of the lens assembly 25 may be acceptable, so such compensation may not be necessary. The lens assembly 25 can be attached to the lens holder 20 by a curable adhesive 26 that is cured at this stage.

[0167] Thus, an assembly can be produced in which the lens assembly 25 is properly aligned with (and may be centered about) the principal axis P in both the operational center and the retained position.

[0168] Control and calibration methods

[0169] As described above, the drive signal to the SMA wire 30 may be generated by a control circuit using a resistive feedback technique.

[0170] refer to Fig.13 , such a circuit and such a technique will now be briefly described. Further details are provided in WO 2017 / 098249A1, which is incorporated herein by this reference. The relevant calibration method will then be described.

[0171] The control circuit 12 includes a drive circuit 12a that generates a drive signal for each SMA wire 30 according to the control signal for each SMA wire 30. The drive circuit 12a may include a constant voltage or constant current source for each SMA wire 30. The drive signal generated by the drive circuit 12a may be a pulse width modulated (PWM) signal.

[0172] The control circuit 12 also includes a detection circuit 12b that detects a resistance measurement of each SMA wire 30, the resistance of the wire being related to its length. In the case where the drive circuit 12a includes a constant current source, the detection circuit 12b may include, for example, a voltage detection circuit to detect the voltage across each SMA wire 30. Alternatively or additionally, the detection circuit 12b may include a current detection circuit.

[0173] The control circuit 12 also includes a setting unit 12c for setting a target resistance value. The target resistance value can be set for each wire or different combinations of wire resistances. In addition, combinations of wire resistances can be selected that correspond to the degrees of freedom of the 3D movement of the lens holder 20 relative to the stationary component 10. In the example to be described now, a target resistance value is set for each degree of freedom, namely tx, ty and tz (indicating translational positions along the x-axis, y-axis and z-axis) and rx, ry and rz (indicating rotational positions around the x-axis, y-axis and z-axis, where the z-axis corresponds to the main axis P). The setting unit 12c sets the target resistance value according to the desired position and orientation of the lens holder 20, for example, by changing tz to perform autofocus and / or by changing tx and ty to perform OIS, while keeping rx, ry and rz constant.

[0174] The control circuit 12 further comprises an error detector 12d for each degree of freedom. Each error detector 12d is provided with a respective target resistance value and a detected resistance measurement value of the SMA wire 30.

[0175] Each error detector 12d comprises a feedback measurement unit 12e which determines a feedback value for the relevant degree of freedom. The feedback value is a linear sum of the resistance measurements of the detected SMA wires 30, with a proportionality factor corresponding to the contribution of the SMA wires 30 to the motion of the relevant degree of freedom. This depends on the geometry of the SMA wires 30. For example, the rotational position rotx of the lens holder 20 about the x-axis may be a function of the lengths and therefore the resistances R of the four SMA wires 30, labeled a, b, e and f, and furthermore, the SMA wires 30 may have a symmetrical configuration such that rotx=K×(Ra-Rb+Re-Rf), where K is a proportionality constant.

[0176] Each error detector 12d also includes a comparator 12f, which determines the error between the target resistance value and the feedback value for the associated degree of freedom. This error is further adjusted by an offset O. In this example, the adjustment is applied by offsetting the error determined by the comparator 12f. However, it should be understood that the adjustment can be made in different ways, such as by offsetting the target resistance value or the feedback value.

[0177] The adjusted error is provided from the error detector 12d to the matrix controller 12g, which determines a control signal for each SMA wire 30 to control the power of the drive signal according to the adjusted error. The matrix controller 12g uses a closed loop control algorithm to reduce the adjusted error.

[0178] It will be appreciated that the setup unit 12c, error detector 12d and matrix controller 12g may be implemented in one or more processors (operating jointly or independently).

[0179] The offset O (see above) is used to improve the accuracy with which the actual position and orientation of the lens holder 20 matches the target position and orientation represented by the target resistance value. For example, the offset O is used to correct for changes in the actual position and orientation of the lens holder 20 driven by the control circuit 12 due to manufacturing tolerances of the SMA wire 30 or in response to changes in the SMA wire 30 over time.

[0180] When the lens holder 20 is in a known position and / or orientation relative to the stationary component 10 (hereinafter referred to as a calibrated position), the offset O can be determined based on a measurement of the resistance of the SMA wire 30 .

[0181] As mentioned above, the resistance of the SMA wire 30 may be determined by applying a current to the SMA wire 30 and measuring its resistance. The resistance used to determine the offset O may be the maximum resistance of each wire measured, or may be the resistance measured at a predetermined wire temperature, or may be the resistance measured at a predetermined time after starting to apply current to the wire (in which case the predetermined time and / or the profile of the applied current may depend on the ambient temperature).

[0182] A suitable calibration position is one in which the optical axis of the camera lens 25 is normal to the image sensor and the image is therefore optimally focused on the image sensor. This position is preferably determined during manufacturing, for example using a planar image target arranged parallel to the image sensor. In this state, the resistance of each SMA wire 30 can be measured and used to derive a suitable offset O. For example, a first offset roff1 can be determined with respect to the rotational position of the lens holder 20 around the x-axis, i.e. rotx. It will be appreciated that the sum of the resistances of the associated SMA wires 30, i.e. (Ra-Rb+Re-Rf), is typically non-zero even in this calibration position. The offset for the rotational position roty of the lens holder 20 around the y-axis can be determined in an equivalent manner.

[0183] Another suitable calibration position corresponds to the above-mentioned center arrangement, ie, the position and orientation in which the lens holder 20 is maintained when the SMA wire 30 is not energized.

[0184] The resistance of each SMA wire 30 at this calibration position can be measured at different times and used to compensate for changes that may occur in the actuator assembly over time. For example, such measurements can be made during manufacturing and subsequently, such as as part of the power-up process before moving the lens holder 20 to the operating position. Thus, calibration can be performed without unduly interfering with normal operation.

[0185] For example, such measurements can be used to correct for tilt variations relative to the z-axis, ie, rotations around the x-axis and y-axis (rotx and roty).

[0186] This may be implemented in an actuator assembly (not shown) which is a variation of the sixth example and comprises:

[0187] (i) magnetic elements in the form of two permanent magnets on the lens holder 20 and corresponding elements in the form of two metal plates on the stationary part 10; and

[0188] (ii) three or more end stop surfaces arranged such that when the SMA wire 30 is not energized, the magnetic force generated holds the lens holder 20 in a predetermined tilt relative to the z-axis, which may be nominally zero (depending on manufacturing tolerances).

[0189] During manufacturing, a measurement of the absolute rotational position of the lens holder 20 in the center arrangement can be obtained. For example, with respect to the rotational position of the lens holder 20 about the x-axis, i.e., rotx, the absolute position can correspond to the difference between the first offset roff1 and the second offset roff2, which is equal to K×(Ra-Rb+Re-Rf) and is determined based on the resistance of the associated SMA wire 30 when the lens holder 20 is in the center arrangement.

[0190] Subsequent measurements of the resistance of the SMA wire 30 when the lens holder 20 is in the central arrangement can be used to determine any changes. For example, with respect to rotx, subsequent measurements can be used to determine a third offset roff3 (equivalent to the first and second offsets), and thus determine the total offset in rotational position, i.e., r 总 =(roff1+roff3-roff2).

[0191] The total offset of the rotational position of the lens holder 20 about the y-axis, roty, can be determined in an equivalent manner. Similar techniques can be used to obtain the offset O of one or more other degrees of freedom, such as translational motion in the x-, y- and / or z-directions.

[0192] These techniques may also be implemented with respect to any actuator assemblies described herein, or variations of such actuator assemblies.

[0193] Other variants

[0194] It will be appreciated that many other variations of the above described embodiments are possible.

[0195] For example, the actuator assembly may be used in applications other than cameras.

[0196] Any reference to centering and / or aligning the lens holder 20 may alternatively refer to centering and / or aligning the lens assembly 25 (which may be off-center and / or misaligned with the lens holder 20 ).

[0197] Instead of a combination of wire resistances corresponding to the degrees of freedom, the control method may use any suitable target value, such as individual wire resistances. Furthermore, the offset O may take any suitable form.

[0198] It is not necessary to determine the offset O for each degree of freedom.

[0199] The offset O can be used in different control methods, including different closed-loop techniques and open-loop techniques.

Claims

1. An actuator assembly comprising: a first component and a second component, wherein the principal axis is defined with reference to the second component; a plurality of lengths of shape memory alloy wire connected between the first component and the second component, wherein each length of the wire is configured to cause three-dimensional movement of the first component relative to the second component when selectively energized; as well as A mechanism is configured to maintain the first component relative to the second component in at least one position and / or orientation against gravity for any orientation of the second component when the wire segments are not energized.

2. The actuator assembly according to claim 1, wherein: The at least one position corresponds to a range of positions corresponding to at least a portion of the first component, the range of positions corresponding to at least a portion of the first component being moved relative to the second component by a distance <100 μm from a center position.

3. The actuator assembly according to claim 2, wherein: The distance is a lateral distance relative to the main axis.

4. The actuator assembly according to any one of claims 1 to 3, wherein: The institutions include: a set of one or more end stops formed on the second component; and A set of one or more resilient elements connected between the first component and the second component to bias the first component so that the first component moves into contact with the set of end stops when the wire sections are not energized.

5. The actuator assembly according to claim 4, wherein: The set of end stops includes a first set of surface areas configured to contact a first set of surface areas of the first component to control an orientation of the first component relative to the primary axis.

6. An actuator assembly according to claim 4 or 5, wherein: The set of end stops includes a second set of surface areas configured to contact a second set of surface areas of the first component to control a lateral position of at least a portion of the first component relative to the primary axis.

7. The actuator assembly according to claim 6, wherein: The second set of surface regions defines a cone to guide the first component to the at least one position and / or orientation from a range of positions and / or orientations associated with three-dimensional movement of the first component.

8. An actuator assembly according to claim 6 or 7, wherein: The first component has a first portion and a second portion spaced apart from each other along the main axis, wherein the second set of surfaces is configured to control a lateral position of the second portion relative to the main axis, and wherein the set of elastic elements is further configured to bias the first portion toward a central lateral position relative to the main axis to control the orientation of the first component relative to the main axis.

9. An actuator assembly according to any one of claims 1 to 4, wherein: The mechanism comprises a set of one or more resilient elements connected between the first component and the second component to bias the first component towards the at least one position and / or orientation.

10. The actuator assembly of claim 9, wherein: At least one elastic element of the set of elastic elements extends in one or more directions at least partially perpendicular to the main axis.

11. The actuator assembly of claim 10, wherein: The set of elastic elements includes two or more elastic elements, and the two or more elastic elements are spaced apart from each other along the main axis.

12. An actuator assembly according to any one of claims 4 to 11, wherein: The set of resilient elements generates a biasing force on the first component such that for any orientation of the second component with the major axis being horizontal, at least a portion of the first component is between 80 μm and 100 μm below a central position relative to the second component.

13. An actuator assembly according to any one of claims 4 to 12, wherein: One or more of the set of elastic elements forms part of the electrical connection to the moving end of each length of shape memory alloy wire.

14. An actuator assembly according to any preceding claim, wherein: The mechanism is configured to provide a non-linear biasing force that biases the first component toward the at least one position and / or orientation, wherein the non-linear biasing force is relatively large when the first component is in the at least one position and / or orientation, and the non-linear biasing force is relatively small when the first component is within a range of positions and / or orientations associated with three-dimensional movement of the first component.

15. The actuator assembly of claim 14, wherein: The mechanism includes a latch connecting the first component and the second component when the first component is in the at least one position and / or orientation.

16. An actuator assembly according to claim 15, wherein the actuator assembly includes a control circuit, and the control circuit is configured to move the first component relative to the second component to a certain position and / or orientation before the respective wire segments are energized, in which the nonlinear bias force is relatively large and / or the latch is engaged.

17. The actuator assembly of claim 14, wherein: The mechanism is configured to provide a non-linear biasing force that is greater than a gravitational force on the first component for any operational position and orientation of the first component relative to the second component.

18. An actuator assembly according to any one of claims 14 to 17, wherein: The mechanism comprises magnetic elements located on each of the first component and the second component, wherein at least one of the magnetic elements comprises a permanent magnet, and wherein the magnetic elements are in proximity to each other when the first component is in the at least one position and / or orientation.

19. The actuator assembly of claim 18, wherein: The permanent magnet is a quadrupole magnet.

20. An actuator assembly according to any one of claims 14 to 19, wherein: The at least one position and / or orientation is attainable by a substantially translational movement of the first component relative to the second component along the primary axis from a central operating position and orientation of the first component.

21. The actuator assembly of claim 20, wherein: The central operating position and orientation corresponds to a position and orientation that maximizes a range of motion of the first component relative to the second component, the motion being induced by selective energization of the plurality of lengths of shape memory alloy wire, and corresponds to a central position within the range.

22. An actuator assembly according to any one of claims 14 to 21, wherein: The first component and the second component each include a first set of end stop surface areas configured to contact each other to guide the first component to the at least one position and / or orientation.

23. The actuator assembly of claim 22, wherein: the first component and the second component each comprising a second set of end stop surface areas configured to contact each other to define at least a portion of a wire protection envelope, Wherein said first set of end stop surface areas interrupts said wire protection envelope such that said at least one position and / or orientation is within said wire protection envelope.

24. An actuator assembly according to any one of claims 14 to 21, wherein: The first component and the second component each include a set of end stop surface areas configured to contact each other when the first component is in the at least one position and / or orientation to at least partially define the position of the first component along the primary axis.

25. The actuator assembly of claim 24, wherein: The mechanism is configured to provide a non-linear biasing force that guides the first component to the at least one position and / or orientation.

26. An actuator assembly according to any preceding claim, wherein: The first component has a first portion and a second portion spaced apart from each other along the primary axis, and the at least one position and / or orientation corresponds to the first portion having a generally smaller position range and orientation range than the second portion.

27. An optical assembly comprising an actuator assembly according to any preceding claim, wherein the first component comprises a component of an optical system, and wherein, The main axis corresponds to the optical axis of the optical system.

28. A camera assembly comprising the optical assembly of claim 27, wherein the first component comprises a camera lens and the second component comprises an image sensor.

29. A camera assembly according to claim 28 as appended to claim 20 or 21, wherein: The position and / or orientation of the camera lens relative to at least a portion of the mechanism is at least partially defined, such that when the first component is in the at least one position and / or orientation, the position and orientation of the camera lens relative to the optical axis is at least partially defined.

30. The camera assembly of claim 29, wherein: The camera lens has an orientation defined by a first axis, and another portion of the first component has an orientation defined by a second axis that makes an angle greater than zero and less than 5° relative to the first axis.

31. A method of assembling an actuator assembly according to claim 20 or 21, the method comprising: selectively energizing the plurality of lengths of shape memory alloy wire to move the first component to the at least one position and / or orientation; as well as While maintaining the first component in the at least one position and orientation, the position and / or orientation of at least a portion of the mechanism relative to the first component is fixed.

32. The method of claim 31, wherein: The mechanism comprises magnetic elements on each of the first component and the second component, wherein at least one of the magnetic elements comprises a permanent magnet, and wherein the magnetic elements are in proximity to each other when the first component is in the at least one position and / or orientation; and Fixing the position and / or orientation of at least a portion of the mechanism includes positioning at least one of the magnetic elements such that the magnetic elements are proximate to each other.

33. The method according to claim 32, wherein: Fixing the position and / or orientation of at least a portion of the mechanism comprises adhering at least one of the magnetic elements to the first component and / or the second component.

34. A method of assembling a camera assembly according to claim 29 or 30, the method comprising: A method according to any one of claims 31 to 33; as well as When the mechanism holds the first component in the at least one position and / or orientation, the position and / or orientation of the camera lens relative to the optical axis is fixed.

35. The method of claim 34, wherein: Fixing the position and / or orientation of the camera lens includes adhering the camera lens to a portion of the first component.

36. A method of operating an assembly according to any one of claims 1 to 30, the method comprising: calibrating one or more offsets based on measuring the electrical resistance of one or more lengths of the shape memory alloy wire when the first component is in the at least one position and / or orientation, The offset is used to adjust one or more aspects of a control scheme so that an actual position and / or orientation of the first component relative to the second component substantially matches a target position and / or orientation in at least one degree of freedom.

37. The method of claim 36, comprising measuring the resistance at least in part as part of a power up process and prior to moving the first component to an operative position.

38. A method according to claim 36 or 37, comprising carrying out the measurement of the resistance partly during manufacture of the actuator assembly.

39. A method according to any one of claims 36 to 38, the method comprising determining a change in at least one of the one or more offsets based on a change in at least one measured resistance or a change in a measured resistance response to a known drive signal.

40. A method according to any one of claims 36 to 39, comprising calibrating the one or more offsets based on measuring the electrical resistance of one or more lengths of the shape memory alloy wire when the first component is in another position and / or orientation.

41. The method of claim 40, wherein: The first component comprises a camera lens and the second component comprises an image sensor, and wherein the further position and / or orientation corresponds to a position and / or orientation of the camera lens relative to the image sensor, the position and / or orientation being determined at least in part based on properties of an image formed on the image sensor by the camera lens.

42. The method according to any one of claims 36 to 41, wherein: The at least one degree of freedom comprises a rotation of the first component relative to the second component about at least one axis perpendicular to the main axis.

43. A method according to any one of claims 36 to 42, comprising: The three-dimensional motion is controlled using the control scheme.

44. The method of claim 43, wherein: Controlling the three-dimensional motion includes: setting a target resistance value representing a desired position of the first component relative to the second component; Detecting a measured value of the resistance of each section of the shape memory alloy wire; deriving an error from the target resistance value and the detected resistance measurement, the error being adjusted by the offset; and The power of the driving signal provided to each section of the shape memory alloy wire is controlled according to the adjusted error.

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