Shape memory alloy actuator

Abstract

An SMA actuation device comprises: a support structure; a movable element; a spiral bearing mechanism, which supports the movable element on the support structure and is arranged to guide the spiral movement of the movable element relative to the support structure about a spiral axis; and a set of four SMA actuator wires, each wire being connected between the support structure and the movable element and located in a plane orthogonal to the spiral axis or at an acute angle to the plane orthogonal to the spiral axis, the set of wires comprising a first pair of wires and a second pair of wires, the first pair of wires being arranged to drive the movable element to rotate about the spiral axis in a first direction when contracted, and the second pair of wires being arranged to drive the movable element to rotate about the spiral axis in an opposite second direction when contracted, wherein the spiral bearing mechanism converts the rotation into spiral movement.

Description

[0001] The present disclosure relates to a shape memory alloy (SMA) actuation apparatus in which at least one SMA actuator wire drives a movable element relative to a support structure.

[0002] It is known to use SMA wires as actuators to drive translational movement of a movable element relative to a support structure. SMA actuator wires have particular advantages in micro-devices and can be applied to a variety of devices, including handheld devices (e.g., cameras and mobile phones). For example, such SMA actuator wires can be used in optical devices (such as cameras) to drive translational movement of a camera lens element along its optical axis, for example to achieve focusing (autofocus, AF) or zooming.

[0003] Some examples of SMA actuators for this type of camera are disclosed in WO-2007 / 113478. In this document, the movable element is a camera lens element supported on a support structure by a helical bearing arrangement that includes a flexure that guides translational movement along the optical axis. In one example described therein, the SMA actuator wire is a piece of SMA wire connected at its ends to the support structure and hooked onto a hook on the camera lens element to drive the translational movement. The straight SMA actuator wires, formed by the portions of the piece of SMA wire on either side of the hook, extend at an acute angle greater than 0 degrees relative to a direction of movement parallel to the optical axis. Tilting the SMA actuator wire in this manner increases the amount of movement compared to an SMA actuator wire extending in the direction of movement, while also reducing the range of the actuator in the direction of movement.

[0004] Miniaturization is an important design criterion for many types of SMA actuators. In many applications, it is desirable to minimize the size of the SMA actuator in the direction of movement. For example, where the SMA actuator includes a lens element that moves along an optical axis, it is desirable to minimize the size along the optical axis.

[0005] In SMA actuator devices where the SMA actuator wire extends at an acute angle to the direction of motion, such as in the camera disclosed in WO2007 / 113478, the SMA actuator wire itself must have a projected extent along the direction of motion. This imposes a minimum dimension on the SMA actuator device along the direction of motion, even though other components in that direction can be made smaller. In particular, the projected extent of the SMA actuator wire along the direction of motion is determined by the desired degree of translational motion, as the maximum change in length of the SMA actuator wire is a given percentage of the total length of the SMA actuator wire, due to the electromechanical properties of the SMA material.

[0006] According to a first aspect of the invention claimed, there is provided a shape memory alloy (SMA) actuation device comprising: a support structure; a movable element; a helical bearing mechanism supporting the movable element on the support structure and arranged to guide helical movement of the movable element relative to the support structure about a helical axis; and a set of four SMA actuator wires, each wire connected between the support structure and the movable element and located in a plane orthogonal to the helical axis or at an acute angle to the plane orthogonal to the helical axis, the set of wires comprising a first pair of wires and a second pair of wires, the first pair of wires being arranged to drive the movable element to rotate about the helical axis in a first direction when contracted, and the second pair of wires being arranged to drive the movable element to rotate about the helical axis in an opposite second direction when contracted, wherein the helical bearing mechanism converts the rotation into helical movement.

[0007] Four SMA actuator wires may provide an alternative and advantageous way of moving the movable element.

[0008] Further (optional) features are specified in the dependent claims, and further advantages are described below.

[0009] In some embodiments, the spiral bearing mechanism comprises at least one flexure arm extending between the support structure and the movable element.For example, the spiral bearing mechanism may comprise two flexure arms, preferably four flexure arms.

[0010] In some embodiments, the maximum extension of the flexure arm and the SMA wire along a first axis is substantially less than the maximum extension of the flexure arm and the four SMA wires along a second axis, wherein the first axis is perpendicular to the helical axis, and the second axis is perpendicular to the helical axis and perpendicular to the first axis. For example, the maximum extension of the flexure arm and the SMA wire along the first axis can be less than 90%, preferably less than 80%, of the maximum extension of the flexure arm and the four SMA wires along the second axis.

[0011] The SMA actuator may include a first side and a second side, wherein the first side includes at least one flexure arm and a first pair of four SMA wires, and the second side includes at least one flexure arm and a second pair of four SMA wires. The first side and the second side are located on opposite sides of the helical axis. The first side and the second side may be separate, non-overlapping, and contiguous.

[0012] The spiral bearing mechanism may include four flexure arms. The four flexure arms may be substantially equally spaced around the perimeter of the movable element. The flexure arms may protrude from the outer perimeter of the body of the movable element at four locations that are substantially offset by 90° from each other.

[0013] The four SMA wires may be substantially aligned with the first axis. For example, the angle between each of the four SMA wires and the axis may be less than 20°, preferably less than 10°, and further preferably less than 5°.

[0014] The four SMA wires may substantially occupy the maximum extension of the flexure arms and the SMA wires along the first axis. For example, the four SMA wires may occupy more than 80%, preferably more than 90%, and further preferably more than 95% of the maximum extension of the flexure arms and the SMA wires along the first axis.

[0015] In some embodiments, the movable element includes four movable connection portions, and the support structure includes four static connection portions. Each of the four SMA wires can be connected between each of the four movable portions and each of the four static connection portions. The four movable connection portions can extend from locations that are substantially equally spaced around the perimeter of the body of the movable element. These locations can be approximately offset by about 90° from each other.

[0016] The flexure arm and the movable connection portion can be unitary. For example, the flexure arm and the movable connection portion can be made from a single piece (e.g., a metal sheet). Alternatively, the flexure arm and the movable connection portion can be non-unitary and, for example, comprise different thicknesses and / or materials.

[0017] Particular advantages are realized when applied to SMA actuated devices in which the movable element is a lens element comprising at least one lens, e.g., where the helical axis is the optical axis of the lens element. In many applications, it is desirable to minimize the size along the direction of translational movement of such a lens element. For example, the SMA actuated device may be a camera in which the support structure has an image sensor mounted thereon, and the lens element is arranged to focus an image on the image sensor. The size reduction advantages achieved by the present technology are particularly valuable in handheld and miniature devices where space is at a premium (e.g., where at least one lens has a diameter of at most 30 mm, preferably at most 20 mm, preferably at most 15 mm, and preferably at most 10 mm).

[0018] However, the present technology can generally be applied to any type of device that includes a static portion and a movable portion that is movable relative to the static portion. By way of non-limiting example, the actuator assembly can be any of the following devices or can be provided in any of the following devices: a smartphone, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronic device, an image capture device, a foldable image capture device, an array camera, a 3D sensing device or system, a servo motor, 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, a security system, a gaming system, a gaming accessory, a robot or robotic device, a medical device, an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device, a drone, an aircraft, a spacecraft, a submersible, a vehicle, and an autonomous vehicle. It should be understood that this is a non-exhaustive list of example devices.

[0019] Certain embodiments of the claimed invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic diagram of an actuator assembly, the actuator assembly being a camera;

[0021] Figure 2 and Figure 3 It is a perspective view of two spiral bearings;

[0022] Figure 4 is a schematic cross-sectional view of an actuator assembly having different helical bearing mechanisms;

[0023] Figure 5 and Figure 6 Yes Figure 4 A perspective view of an example of an actuator assembly shown in FIG;

[0024] Figure 7 yes Figure 5 and Figure 6 a plan view of the actuator assembly shown in ;

[0025] Figures 8 to 10 is a schematic cross-sectional view of an actuator assembly having different helical bearing mechanisms;

[0026] Figure 11 yes Figure 9 A perspective view of a helical bearing mechanism of an actuator assembly;

[0027] Figure 12 yes Figure 9 a perspective view of a first example of an actuator assembly;

[0028] Figure 13 yes Figure 12 a side view of the actuator assembly shown in ;

[0029] Figure 14 yes Figure 12 a plan view of the actuator assembly shown in ;

[0030] Figure 15 yes Figure 9 a perspective view of a second example of an actuator assembly;

[0031] Figure 16 yes Figure 15 a plan view of the actuator assembly shown in ; and

[0032] Figure 17 is a perspective view of an actuator assembly having another possible helical bearing mechanism;

[0033] Figures 18 to 22 is a side view of a possible loading arrangement;

[0034] Figure 22A is a schematic cross-sectional view of an actuator assembly having yet another possible helical bearing mechanism;

[0035] Figure 23 is a cross-sectional view of a first alternative bearing taken perpendicular to the direction of movement of the bearing;

[0036] Figure 24 yes Figure 23 a side view of a first alternative bearing;

[0037] Figure 25 is a cross-sectional view of a second alternative bearing taken perpendicular to the direction of movement of the bearing;

[0038] Figure 26 yes Figure 25 A side view of an alternative bearing;

[0039] Figure 27 is a side view of an actuator assembly having a helical bearing mechanism including more than one flexure;

[0040] Figure 28 and Figure 29 yes Figure 27 A plan view of a spiral bearing mechanism having flexures of different forms;

[0041] Figure 29A is a perspective view of an alternative helical bearing mechanism including more than one flexure;

[0042] Figures 30 to 32are perspective views of various arrangements of SMA actuator wires, helical bearings, and biasing elements (where present);

[0043] Figure 33 is a perspective view of an alternative helical bearing mechanism;

[0044] Figure 34A-Figure 34B is a perspective view of a first spiral flexure assembly;

[0045] Figure 35 is a plan view of the second spiral flexure assembly;

[0046] Figure 36 is a plan view of the third spiral flexure assembly;

[0047] Figure 37 is a plan view of a fourth helical flexure assembly; and

[0048] Figure 38 is a plan view of the fifth helical flexure assembly.

[0049] Unless the context requires otherwise, the term "bearing" is used herein as follows. The term "bearing" as used herein includes the terms "sliding bearing," "plain bearing," "rolling bearing," "ball bearing," "roller bearing," "air bearing" (in which compressed air causes the load to float), and "flexure." The term "bearing" as used herein generally refers to any element or combination of elements that serves to limit motion to only the desired motion and to reduce friction between moving parts. The term "sliding bearing" is used to refer to a bearing in which a bearing element slides on a bearing surface and includes "plain bearings." The term "rolling bearing" is used to refer to a bearing in which a rolling bearing element (e.g., a ball or roller) rolls on a bearing surface. Such a rolling bearing element may be a compliant element, such as a gas-filled bladder. In embodiments, the bearing may be disposed on or may include a nonlinear bearing surface.

[0050] In some embodiments of the present disclosure, more than one type of bearing element may be used in combination to provide the bearing function.Thus, the term "bearing" as used herein includes, for example, any combination of sliding bearings, ball bearings, roller bearings, and flexures.

[0051] Actuator assembly

[0052] Figure 1 Schematically shown in FIG, is an actuator assembly 1 , which is a camera.

[0053] The actuator assembly 1 comprises a static part 2 having an image sensor 3 mounted thereon. The static part 2 may take any suitable form and typically comprises a base 4 to which the image sensor is fixed. The static part 2 may also support an IC chip 5, described further below.

[0054] The actuator assembly 1 further comprises a lens element 10, which in this example is a movable component. The lens element 10 comprises a lens 11, although alternatively the lens element may comprise more than one lens. The lens element 10 has an optical axis O aligned with the image sensor 3 and is arranged to focus an image on the image sensor 3.

[0055] The actuator assembly 1 is a microdevice.In some examples of microdevices, the lens 11 (or more than one lens, when provided) may have a diameter of at most 30 mm, preferably at most 20 mm, preferably at most 15 mm, preferably at most 10 mm.

[0056] Although actuator assembly 1 is a camera in this example, this is generally not required. In some examples, actuator assembly 1 may be an optical device in which the movable component is a lens element but lacks an image sensor. In other examples, actuator assembly 1 may be a device that is not an optical device and in which the movable component is not a lens element and lacks an image sensor. Examples include devices used for depth mapping, facial recognition, gaming consoles, projectors, and security scanners.

[0057] spiral bearing mechanism

[0058] The actuator assembly 1 also includes a spiral bearing mechanism 20 (in Figure 1 ), a helical bearing mechanism supports the lens element 10 on the static component 2. The helical bearing mechanism 20 is arranged to guide the helical movement of the lens element 10 relative to the static component 2 about a helical axis H. In this example, the helical axis H coincides with the optical axis O, and the helical movement is indicated by arrow M. Figure 1 . Preferably, the spiral motion is along a right-hand spiral, i.e. a spiral with a constant radius, but in general any spiral is possible. The pitch of the spiral can be constant or variable along the spiral motion. Preferably, the spiral motion is generally only a small fraction (less than a quarter) of a full turn of the spiral.

[0059] The helical motion of the lens element 10 guided by the helical bearing mechanism 20 includes components of translational movement along the helical axis H and rotational movement about the helical axis H. The translational movement along the helical axis H is a desired movement of the lens element 10, for example to change the focus of the image on the image sensor 3 and / or to change the magnification (zoom) of the image on the image sensor 3. In this example, the rotational movement about the helical axis H is not required for optical purposes, but is generally acceptable because the rotation of the lens element 10 does not change the focus of the image on the image sensor 3.

[0060] The screw bearing mechanism 20 may take a variety of forms.

[0061] One possibility is that the spiral bearing arrangement 20 comprises one or more spiral bearings 30 which are rolling bearings, examples of such spiral bearings are shown in FIG. Figure 2 and Figure 3 As shown in Figure 2 and Figure 3 In each of the spiral bearings 30, a pair of bearing surfaces 31 and 32 and one or more rolling bearing elements 33, such as balls, are provided between the bearing surfaces 31 and 32. One of the bearing surfaces 31 and 32 is provided on the static component 2, and the other of the bearing surfaces 31 and 32 is provided on the lens element 10.

[0062] The spiral bearing 30 guides the helical movement of the lens element 10 relative to the static component 2, as indicated by the arrow M. This can be achieved by the bearing surfaces 31 and 32 extending helically about the helical axis H (i.e., extending along the line of the helix). That is, in practical embodiments, if one or more spiral bearings in the spiral bearing mechanism 20 guide the helical movement of the lens element 10 relative to the support structure 2, the length of the bearing surfaces 31 and 32 can be short compared to their distance from the helical axis H, so that their shapes are close to straight or even each is straight. Typically, there is more than one spiral bearing 30, which are positioned at different angular positions about the helical axis H. In this case, the spiral bearings 30 have different orientations so that they cooperate and maintain sufficient constraint to guide the helical movement of the lens element 10 relative to the static component 2, even if the bearing surfaces 31 and 32 of a single spiral bearing 30 are straight.

[0063] exist Figure 2 In the example shown, the bearing surfaces 31 and 32 each include a corresponding groove 34 and 35, in which the rolling bearing element 33 is located. In this example, the grooves 34 and 35 constrain the lateral translation movement of the lens element 10 relative to the static component 2 (i.e., transverse to the direction of movement indicated by the arrow M). Figure 2The grooves shown in FIG are V-shaped in cross-section, but other cross-sections are possible, such as curved sections of a circle or ellipse. Typically, grooves 34 and 35 provide two contact points with the respective rolling bearing elements 33. Grooves 34 and 35 may extend helically. Alternatively, in practical embodiments, if one or more spiral bearings 30 in spiral bearing mechanism 20 guide the helical movement of lens element 10 relative to support structure 2, the length of bearing surfaces 31 and 32 may be short compared to their distance from the helical axis H, in which case grooves 34 and 35 may be straight or nearly straight.

[0064] exist Figure 3 In the example of FIG, the first bearing surface 31 includes a groove 36 in which the rolling bearing element 33 is located, and the bearing surface in the second bearing surface 32 is "flat". The first bearing surface 31 including the groove 36 can be provided on either the static component 2 or the lens element 10, and the second bearing surface 32 can be provided on the other of the static component 2 and the lens element 10. Figure 3 In the example shown, spiral bearing 30 does not constrain lateral translational movement of lens element 10 relative to static component 2 (i.e., transverse to the direction of movement indicated by arrow M). Bearing surface 32 is "planar" in the sense that it is a surface that is not grooved and provides only a single point of contact with the ball. In other words, bearing surface 32 is effectively planar across the entire width of rolling bearing element 33, although it is helical on a larger scale. For example, as shown, this "planar" surface is helical, appearing as a line that twists helically in the direction of movement in cross-section, maintaining a single point of contact with the ball at all times. Alternatively, and as described above, in practical embodiments, if one or more spiral bearings 30 in spiral bearing mechanism 20 guide helical movement of lens element 10 relative to support structure 2, the lengths of bearing surfaces 31 and 32 can be short, in which case bearing surface 32 can be planar or nearly planar.

[0065] Figure 2 and Figure 3 A single rolling bearing element 33 is shown by way of example in FIG. 3 , but generally any number of rolling bearing elements 33 more than one may be included.

[0066] In some examples, the spiral bearing 30 may comprise a single rolling bearing element 33. In that case, the spiral bearing 30 itself does not constrain the rotational movement of the lens element 10 relative to the static component 2 about the single rolling bearing element 33, i.e., about an axis transverse to the direction of movement indicated by the arrow M. However, this minimizes the overall size of the spiral bearing 30, and in particular the height of the spiral bearing 30 as projected along the spiral axis H, since it only needs to accommodate the size of the rolling bearing element 33 and the relative travel of the bearing surfaces 31 and 32.

[0067] In other examples, the spiral bearing 30 may include more than one rolling bearing element 33. In this case, the spiral bearing 30 constrains the rotational movement of the lens element 10 relative to the static component 2 about any one of the rolling bearing elements 33, i.e., about an axis transverse to the direction of movement indicated by the arrow M. However, this increases the overall size of the spiral bearing 30, and in particular increases the height of the spiral bearing 30 as projected along the spiral axis H, compared to the use of a single rolling bearing element 33.

[0068] The spiral bearing mechanism may generally include any number of spiral bearings 30, wherein the configuration of the spiral bearings 30 is selected to guide the spiral movement of the lens element 10 relative to the static component 2 while constraining the movement of the lens element 10 relative to the static component 2 in other degrees of freedom. Many spiral bearing mechanisms may include more than one spiral bearing 30, and at least one spiral bearing may include more than one rolling bearing element 30.

[0069] Some specific examples of actuator assemblies 1 with different possible helical bearing mechanisms are given in Figure 4 、 Figure 8 、 Figure 9 and Figure 10 , which are schematic plan views orthogonal to the screw axis, show the static component 2 , the lens element 10 and the screw bearing 30 .

[0070] Figure 4 A possible spiral bearing arrangement is shown which comprises only two spiral bearings 37 and 38. The spiral bearings 37 and 38 are arranged on opposite sides of the lens element 10.

[0071] The first spiral bearing 37 and Figure 2 The spiral bearing 30 shown is of the same type. Figure 2 The central bearing surfaces 31 and 32 each comprise a corresponding groove 34 and 35. The first spiral bearing 37 comprises more than one rolling bearing element 33 to constrain relative movement of the lens element 10 and the static component 2.

[0072] The second spiral bearing 38 and Figure 3The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 4 The illustration shows the case where the first bearing surface 31 of the second spiral bearing 38 is on the static component 2, but alternatively the first bearing surface 31 may be on the lens element 10. The second spiral bearing 38 may comprise a single rolling bearing element 33 or more than one rolling element 33 and primarily increases the constraint on the relative rotation of the lens element 10 and the static component 2 about the direction of movement (arrow M) of the first spiral bearing 37.

[0073] Figure 4 The spiral bearing mechanism includes a smaller number of spiral bearings (ie, two) than the following other examples, which simplifies the construction and reduces the occupied area of ​​the actuator assembly 1.

[0074] Figures 5 to 7 Pictured Figure 4 An example of an actuator assembly 1 is shown in FIG, wherein the static component 2 and the lens element 10 are formed from molded components. Figures 5 to 7 In FIG, the detailed form of the static component 2, the lens element 10 and the spiral bearings 37 and 38 can be seen. In addition, the actuator assembly 1 includes an elastic element 70, which is connected in a compressive manner between the support structure 2 and the lens element 10 and extends parallel to the spiral axis H, thereby providing a force along the spiral axis H. As a result, the elastic element 70 loads one or more spiral bearings. In this example, the elastic element 70 is a spring, but in principle it can be formed by any other element, such as a flexure or a piece of elastic material.

[0075] Figure 8 A possible spiral bearing arrangement is illustrated which comprises only three spiral bearings 39, 40 and 41. The three spiral bearings 39, 40 and 41 are equiangularly spaced around the spiral axis H, but alternatively they may be unequally spaced.

[0076] The first spiral bearing 39 and the second spiral bearing 40 are Figure 2 The spiral bearing 30 shown is of the same type. Figure 2 The center bearing surfaces 31 and 32 each include a respective groove 34 and 35 .

[0077] The third spiral bearing 41 and Figure 3 The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 8The case where the first bearing surface 31 of the third spiral bearing 41 is on the lens element 10 is illustrated, but it may alternatively be on the static component 2 .

[0078] Each of the three spiral bearings 39, 40 and 41 may comprise a single rolling bearing element or more than one bearing element 33. This is possible because the constraints imposed by the three spiral bearings 39, 40 and 41, and in particular the grooves of the first and second spiral bearings 39, 40, are sufficient to constrain the movement of the lens element 10 relative to the static component 2 in degrees of freedom other than the spiral movement. Since only a single rolling bearing element 33 is used in each of the three spiral bearings 39, 40, 41, the movement of the lens element 10 relative to the static component 2 is not limited. Figure 4 Compared with the spiral bearing mechanism of FIG. 1 , the overall size of the three spiral bearings 39 , 40 and 41 and in particular the height of the three spiral bearings 39 , 40 and 41 projected along the spiral axis H is reduced.

[0079] Figure 10 A possible spiral bearing arrangement is shown which comprises only four spiral bearings 42 to 45. The four spiral bearings 42 to 45 are equiangularly spaced about the spiral axis H.

[0080] The first spiral bearing 42 and Figure 2 The spiral bearing 30 shown is of the same type. Figure 2 The center bearing surfaces 31 and 32 each include a respective groove 34 and 35 .

[0081] The second spiral bearing 43, the third spiral bearing 44 and the fourth spiral bearing 45 are each Figure 3 The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 10 The case where the first bearing surface 31 of the second spiral bearing 43 , the third spiral bearing 44 and the fourth spiral bearing 45 is on the lens element 10 is illustrated, but alternatively it may be on the static component 2 .

[0082] Each of the second spiral bearing 43, the third spiral bearing 44 and the fourth spiral bearing 45 may comprise a single rolling bearing element 33, whereas the first spiral bearing 42 comprises two rolling bearing elements. This is possible because the constraints imposed by the four spiral bearings 42 to 45 are sufficient to constrain the movement of the lens element 10 relative to the static component 2 in degrees of freedom other than the spiral movement.

[0083] Figure 9Another possible screw bearing arrangement is illustrated, which comprises only four screw bearings 46 to 49. The four screw bearings 46 to 49 are equiangularly spaced around the screw axis H, but alternatively they may be unequally spaced.

[0084] The first spiral bearing 46 and the second spiral bearing 47 are Figure 2 The spiral bearing 30 shown is of the same type. Figure 2 The center bearing surfaces 31 and 32 each include a respective groove 34 and 35 .

[0085] The third spiral bearing 48 and the fourth spiral bearing 49 are Figure 3 The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 9 The case where the first bearing surface 31 of the third and fourth spiral bearings 48 , 49 is on the lens element 10 is illustrated, but it may alternatively be on the static component 2 .

[0086] Each of the four spiral bearings 46 to 49 may comprise a single rolling bearing element 33. This is possible because the constraints imposed by the four spiral bearings 46 to 49 are sufficient to constrain the movement of the lens element 10 relative to the static component 2 in degrees of freedom other than the spiral movement. Since only a single rolling bearing element 33 is used in each of the four spiral bearings 46 to 49, Figure 4 Compared to the spiral bearing mechanism of FIG. 4 , the overall size of the four spiral bearings 46 to 49 and in particular the height of the four spiral bearings 46 to 49 projected along the spiral axis H is reduced.

[0087] Figure 11 Pictured Figure 9 An example of a screw bearing mechanism 20 of an actuator assembly 1 is shown in FIG, wherein the static component 2 and the lens element 10 are formed from molded components. Figure 11 In FIG. 1 , the detailed form of the static part 2 , the lens element 10 and the spiral bearing 30 can be seen.

[0088] Figures 12 to 14 Pictured Figure 9 A first example of an actuator assembly 1 is shown in FIG. , which comprises Figure 11. In addition, the actuator assembly 1 comprises two elastic elements 70, which are connected in compression between the support structure 2 and the lens element 10 and extend at an acute angle to the screw axis H, so that the two elastic elements provide a force having a component that loads the four screw bearings 46 to 49. In this example, the elastic elements 70 are springs, but in principle can be formed by any other element, such as a flexure or a piece of elastic material.

[0089] Figure 15 and Figure 16 Pictured Figure 9 A second example of an actuator assembly 1 is shown in FIG. , which comprises Figure 11 . Furthermore, the actuator assembly 1 comprises two elastic elements 70 which are connected in compression between the support structure 2 and the lens element 10 and extend orthogonally to the screw axis H in a rotationally symmetrical manner about the screw axis H, so that the two elastic elements provide a force having a component which loads the screw bearings 46 to 49.

[0090] In each of the spiral bearing mechanisms described above, the bearing surfaces 32 on the lens element 10 are each arranged on the same side (either all above or all below) relative to the bearing surfaces 31 on the support structure 2. When the bearing surfaces 31 and 32 extend spirally, this means that Figure 8 In a cross-sectional view perpendicular to the helical axis H, all bearing surfaces 32 on the lens element 10 are to the right of the bearing surface 31 on the support structure 2, as seen from the outside of the helical axis H, and Figure 9 and Figure 10 In the view of FIG, when viewed from outside the screw axis H, all bearing surfaces 32 on the lens element 10 are to the left of the bearing surface 31 on the support structure 2. Due to this arrangement, all bearing surfaces 31 of the screw bearing on the support structure 2 face the same direction as each other, which facilitates the manufacture of the bearing surfaces 31 by the same tool. Similarly, the manufacturing advantages apply to the bearing surfaces 32 on the lens element 2, which also face the same direction as each other.

[0091] As a result of this arrangement, all spiral bearings 30 need to be loaded in the same spiral direction. Therefore, the loading of the spiral bearings 30 can be provided by applying a loading force along the spiral axis H, applying a loading force about the spiral axis H, or a combination thereof. In the arrangement described in more detail below, the loading force can be applied by a resilient biasing element 70.

[0092] Figure 17 Another possible helical bearing mechanism is shown. Figure 7Thus, the spiral bearing mechanism comprises only four spiral bearings 46 to 49, and the four spiral bearings 46 to 49 are equally angularly spaced around the spiral axis H, but alternatively, they may be unequally spaced.

[0093] As in Figure 11 In the spiral bearing mechanism, (a) the first spiral bearing 46 and the second spiral bearing 47 are Figure 2 The spiral bearing 30 shown is of the same type. Figure 2 The middle bearing surfaces 31 and 32 each include a corresponding groove 34 and 35, and (b) a third spiral bearing 48 and a fourth spiral bearing 49 are connected to Figure 3 The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 17 The case is shown where the first bearing surface 31 of the third and fourth spiral bearings 48 , 49 is on the lens element 10 , but it may alternatively be on the support structure 2 .

[0094] like Figure 17 In the embodiment of the present invention, the four spiral bearings 46 to 49 can each include a single rolling bearing element 33. This is possible because the constraints imposed by the four spiral bearings 46 to 49 are sufficient to constrain the movement of the lens element 10 relative to the support structure 2 in degrees of freedom other than the spiral movement. Since only a single rolling bearing element 33 is used in each of the four spiral bearings 46 to 49, the overall size of the four spiral bearings 46 to 49, and in particular the height of the four spiral bearings 46 to 49 projected along the optical axis, is reduced when each spiral bearing has only a single rolling element.

[0095] However, with Figure 11 compared to, Figure 17 The spiral bearing mechanism is modified to change the arrangement of the bearing surfaces 31 and 32 in each of the bearings 46 to 49, as described below. In the first spiral bearing 46, the bearing surface 32 on the lens element 10 is above the bearing surface 31 on the support structure 2 when viewed along the spiral axis H, while in the second spiral bearing 47, the bearing surface 32 on the lens element 10 is below the bearing surface 31 on the support structure 2 when viewed along the spiral axis H. Similarly, in the third spiral bearing 48, the bearing surface 32 on the lens element 10 is above the bearing surface 31 on the support structure 2 when viewed along the spiral axis H, while in the fourth spiral bearing 49, the bearing surface 31 on the lens element 10 is below the bearing surface 32 on the support structure 2 when viewed along the spiral axis H.

[0096] This can be understood by reference to the bearing constraints in a vertical plane (parallel to the screw axis) on the following basis: the first and third screw bearings 46, 48 prevent the lens element 10 from moving downward, and the second and fourth screw bearings 47, 49 prevent the lens element 10 from moving upward or rotating about the axis between the first and third screw bearings 46, 48.

[0097] As a result of this arrangement, the spiral bearings 46 to 49 do not need to all be loaded in the same spiral direction about the spiral axis H. This facilitates the loading of the spiral bearings 46 to 49. For example, the arrangement allows loading by a spring loading arrangement, as will now be described.

[0098] Alternatively, etching may be used to create spring loading of any bearing surfaces on the lens element 10 , in which case the same etching may be used to create the common connection between the support structure 2 and the lens element 10 .

[0099] Any type of screw bearing mechanism 20 may comprise a spring loading mechanism which loads a bearing surface of at least one of the rolling bearings against the rolling bearing element relative to a support structure or movable element on which the bearing surface is provided. Figures 18 to 22 Some examples of this type of spring-loaded mechanism are shown.

[0100] Figures 18 to 22 Each example is applied to a rolling bearing 100 comprising a first bearing surface 101, a second bearing surface 102, and a rolling bearing element 103 (e.g., a ball or roller) disposed between the first bearing surface 101 and the second bearing surface 102. The rolling bearing 100 can be applied to any one or more of the spiral bearings in any of the SMA actuation devices 1 described herein. When so applied, the first bearing surface 101 is disposed on one of the support structure 2 or the lens element 10, and the second bearing surface 102 is disposed on the other of the support structure 2 or the lens element 10, or vice versa. In each case, the first bearing surface 101 is movable relative to the support structure 2 or the lens element 10, which is disposed on the support structure 2 or the lens element 10. Conversely, the second bearing surface 102 is fixed relative to the other of the support structure 2 or the lens element 10, which is disposed on the other of the support structure 2 or the lens element 10.

[0101] exist Figure 18In the example of FIG, first bearing surface 101 is formed on a flexure element 104 connected to lens element 10 or support structure 2. Flexure element 104 is made of an elastic material, typically a metal such as steel, and is connected to an adjacent portion of lens element 10 or support structure 2. Flexure element 104 is thus an elastic element that both allows first bearing surface 101 to move relative to the adjacent support structure 2 or lens element 10 and acts as a spring-loaded mechanism that spring-loads first bearing surface 101 away from the adjacent portion of lens element 10 or support structure 2 against rolling bearing element 103.

[0102] exist Figure 19 In the example of FIG, first bearing surface 101 is formed on body 105. Body 105 is connected to lens element 10 or support structure 2 via a bridge portion 106, which is integrally formed with body 105 and an adjacent portion of lens element 10 or support structure 2 and allows first bearing surface 101 to move relative to the adjacent support structure 2 or lens element 10. Bridge portion 106 is configured as an elastic element disposed between body 105 and the adjacent portion of lens element 10 or support structure 2. Thus, bridge portion 106 acts as a spring-loaded mechanism that spring-loads body 106, and therefore first bearing surface 101, away from the adjacent portion of lens element 10 or support structure 2 against rolling bearing element 103.

[0103] Figure 20 Example with Figure 19 The example is the same as that of , except that the flexure element 107 is connected to the bridge portion 106. In this case, the flexure element 107 and the bridge portion 106 together allow the first bearing surface 101 to move relative to the adjacent support structure 2 or lens element 10, while the flexure element 107 is an elastic element that acts as a spring-loaded mechanism, spring-loading the body 106 and therefore the first bearing surface 101 away from the lens element 10 or the adjacent part of the support structure 2 against the rolling bearing element 103. Figure 19 The flexure element 107 can be designed to provide a primarily elastic effect, as compared to the example of FIG. 1 . The bridge portion 106 can be elastic and thus contribute to the loading in conjunction with the flexure element 107, or the bridge portion 106 can be substantially inelastic compared to the flexure element. In this way, compared to FIG. Figure 19 Compared to the example of FIG. 1 , the bridge portion 106 can be relatively thin. Advantageously, this arrangement reduces the occurrence of stress relaxation.

[0104] Figure 21 Example with Figure 20, except that the bridge portion 106 is omitted, so that the main body portion 105 is a separate element from the adjacent portion of the lens element 10 or the support structure 2, and is connected to the adjacent portion of the lens element 10 or the support structure 2 via the flexure element 107. As a result, the flexure element 107 alone acts as an elastic element, which acts as a spring loading mechanism to elastically load the main body 105, and therefore the first bearing surface 101, away from the adjacent portion of the lens element 10 or the support structure 2 against the rolling bearing element 103.

[0105] exist Figure 22 In the example shown, first bearing surface 101 is formed on a flexible arm 108 that is integrally formed with the lens element 10 or the adjacent portion of the support structure 2. Thus, flexible arm 108 allows first bearing surface 101 to move relative to the adjacent support structure 2 or lens element 10. Furthermore, a spring 109 (or other elastic element) is disposed between arm 108 and the adjacent support structure 2 or lens element 10. Spring 109 is in a compressed state. Thus, spring 109 serves as an elastic element that acts as a spring-loading mechanism, elastically loading first bearing surface 101 away from the adjacent portion of the lens element 10 or the support structure 2 against the rolling bearing element 103.

[0106] Another alternative to a spring loaded mechanism is that one of the bearing surfaces on either the support structure 2 or the lens element 10 is replaced by an etched thin wall section of the support structure 2 or lens element 10. Taking into account the thin walls or twists in the support structure 2 or lens element 10, these tolerance adjustments can be made fixed for each component by using glue. In the case where the SMA actuator 1 is a camera, the thin wall section or twist in the lens element 10 can be fixed in place when the lens is glued in place, or the thin wall section or twist in the chassis can be fixed in place when the shield is glued in place. Figures 18 to 22 In the same way as the example of , such thin walls or twisted portions can be made to dynamically adapt to changes in the bearing surface.

[0107] Figure 22A An example of an actuator assembly 1 having a helical bearing mechanism similar to Figure 10 The spiral bearing mechanism is similar to that of the embodiment of the present invention, but with some modifications, as will now be described. The spiral bearing mechanism comprises four spiral bearings 42 to 45, which are arranged in the same manner as described above. Figure 10 The spiral bearings 42 to 45 each comprise a single rolling bearing element 33, so that they provide a total of five constraints. The first spiral bearing 42 and Figure 2 The spiral bearing 30 shown is of the same type. Figure 2The middle bearing surfaces 31 and 32 each include a corresponding groove 34 and 35. The second spiral bearing 43, the third spiral bearing 44 and the fourth spiral bearing 45 are each connected to Figure 3 The spiral bearing 30 shown is of the same type. Figure 3 The first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is located, and the second bearing surface 32 is planar. Figure 10 As shown, the first bearing surface 31 of the second spiral bearing 43 , the third spiral bearing 44 and the fourth spiral bearing 45 is shown as being located on the lens element 10 , but may alternatively be on the support structure 2 .

[0108] The bearing surfaces 32 on the lens element 10 are each arranged on the same side (all above or all below) of the bearing surface 31 on the support structure 2. When the bearing surfaces 31 and 32 extend helically, this means that in a cross section perpendicular to the helical axis H, Figure 22A In the view of FIG, when viewed from the outside of the helical axis H, all bearing surfaces 32 on the lens element 10 are to the left of the bearing surface 31 on the support structure 2. Due to this arrangement, all spiral bearings 42 to 46 need to be in the same helical direction (corresponding to Figure 22A Clockwise rotation of the lens element 10) is loaded.

[0109] To provide this loading, Figure 10 In contrast, the spiral bearing mechanism is modified to include two additional rolling bearings 110, which are spiral bearings arranged as follows. The rolling bearing 110 includes a first bearing surface 111, a second bearing surface 112 and a rolling bearing element 113 (e.g., a ball or roller) arranged between the first bearing surface 111 and the second bearing surface 112. The first bearing surface 111 is movable relative to the support structure 2, and an elastic element 114 is arranged between the first bearing surface 111 and the support structure 2. The elastic element 114 loads the first bearing surface 111 away from the support structure 2, thereby acting as an elastic loading mechanism that elastically loads the first bearing surface 111 against the rolling bearing element 113. Alternatively, the rolling bearing element 110 can be reversed so that the second bearing surface 112 is movable relative to the lens element 10 and the elastic element 114 loads the second bearing surface 112 against the rolling bearing element 113. The additional rolling bearing 110 can have any suitable configuration, including Figures 18 to 22 The configuration of the rolling bearing 110 in any example.

[0110] The additional rolling bearing 110 is arranged in an opposite manner relative to the spiral bearings 42 to 46 so that they rotate in the same spiral direction (corresponding to Figure 22AClockwise rotation of the lens element 10) loads the spiral bearings 42 to 46. As a result, Figure 22A The screw bearing mechanism shown is highly balanced and has reduced tolerances, which aids manufacturing. Figure 10 The spiral bearing arrangement in which all bearing surfaces 31 on the support structure 2 face the same direction to each other and all bearing surfaces 32 on the lens element 10 face the same direction to each other facilitates the manufacture of the spiral bearings 42 to 46 .

[0111] Two additional rolling bearings 110 are shown here arranged on opposite sides of the lens element 10. More generally, any number of one or more additional rolling bearings 110 may be provided, but more than one additional rolling bearing 110 spaced around the lens element 10 is advantageous to aid in force balancing.

[0112] In the above examples, the spiral bearing 30 is a rolling bearing, but in each case the spiral bearing 30 may be replaced by a sliding bearing. Figures 23 to 26 Two examples of sliding bearings are shown in .

[0113] exist Figure 23 and Figure 24 In the first example shown, a slider bearing 81 includes an elongated bearing surface 83 located on one of the support structure 2 and the lens element 10. Slider bearing 81 also includes a protrusion 85 formed on the other of the support structure 2 and the lens element 10, with the end of protrusion 85 forming a bearing surface 86 that bears against the elongated bearing surface 83. Although two protrusions 85 are shown in this example, any number of one or more protrusions 85 may be provided. Elongated bearing surface 83 and bearing surface 86 are conformal, and in this example, both are planar, thereby allowing relative movement of the lens element 10 relative to the support structure 2. Ideally, elongated bearing surface 83 and bearing surface 86 have a coefficient of friction of 0.2 or less.

[0114] exist Figure 25 and Figure 26 In the second example shown, a slider bearing 91 includes a channel 92 located on one of the support structure 2 and the lens element 10, with the inner surface of the channel 92 forming a bearing surface 93. Slider bearing 91 includes a protrusion 95 formed on the other of the support structure 2 and the lens element 10, with the end of the protrusion 95 forming a bearing surface 96 that bears against the bearing surface 93. Although two protrusions 95 are shown in this example, any number of one or more protrusions 95 may be provided. The elongated bearing surface 93 and the bearing surface 96 are conformal, and in this example, both are planar, thereby allowing relative movement of the lens element 10 with respect to the support structure 2. Ideally, the elongated bearing surface 93 and the bearing surface 96 have a coefficient of friction of 0.2 or less.

[0115] In each of the plain bearings 81 and 91, the material of the bearing surfaces 83, 86, 93, 96 is selected to provide smooth movement and long life. The bearing surfaces 83, 86, 93, 96 may be integral with the underlying components or may be formed by a surface coating. Suitable materials include, for example, PTFE or other polymer bearing materials or metals.

[0116] In each of the slider bearings 81 and 91, a lubricant may be provided on the bearing surfaces 83, 86, 93, 96. For example, the lubricant may be a powder or a fluid. Suitable lubricants include graphite, silicon paste, or low-viscosity oil.

[0117] Although the spiral bearing arrangement 20 comprises a spiral bearing 30, which in the above example is a rolling bearing, another possibility is that the spiral bearing arrangement 20 comprises at least one flexure extending between the static component 2 and the lens element 10, e.g. Figure 27 As shown, the spiral bearing mechanism 20 includes two flexure elements 50, each flexure element includes four flexure members 51, and the flexure members 51 have the following characteristics: Figure 28 or Figure 29 The configuration shown. Figure 27 As shown, the flexures 51 are each pre-deflected along the helical axis H, and as shown Figure 28 and Figure 29 As shown, each flexure 51 extends in an arc shape about the helical axis H. Due to this configuration, the flexure 51 guides the helical movement of the lens element 10 about the helical axis H relative to the static component 2 . Figures 27 to 29 The specific number and arrangement of the intermediate flexures 51 are not required, and other configurations of flexures that are pre-deflected along the helical axis H and extend in an arc about the helical axis H may be used to provide the same functionality.

[0118] Figure 29A is a perspective view of an alternative spiral bearing mechanism 20 including more than one flexure 120, Figure 29A , four flexures 120 are shown, although any number of flexures 120 may be provided. In this example, the spiral bearing mechanism further includes a movable plate 121 mounted on the lens element 10 and a support plate 122 mounted on the support structure 2. The movable plate 121 and the support plate 122 are spaced apart along the spiral axis H, and the flexures 120 extend along the spiral axis H and are inclined relative to a plane orthogonal to the spiral axis H, with rotational symmetry about the spiral axis H. With this arrangement, the flexures 120 guide the spiral movement of the lens element 10 relative to the support structure 2 about the spiral axis H.

[0119] Flexure 120 is integrally formed with movable plate 120 and support plate 122. This form of connection is advantageous because it allows the screw bearing mechanism to be manufactured as a single component, for example during molding, thereby providing a precise constraint. Thus, this solution combines precision with low manufacturing costs. That is, in principle, flexure 120 can be a separate component connected to lens element 10 and support structure 2 in any suitable manner.

[0120] SMA actuator wire

[0121] Reference Figures 30 to 32 , the actuator assembly 1 comprises a set of four SMA actuator wires 60 (also simply referred to as “wires”) arranged to drive movement of the lens element 10 about the helical axis H relative to the static component 2 .

[0122] The wires 60 are each connected between the support structure 2 and the lens element 10 and are arranged as described in WO 2013 / 175197 A1 , which is incorporated herein by this reference.

[0123] In short, the wires 60 include a first pair of wires 60 and a second pair of wires 60. The first pair of wires 60 is arranged to drive the lens element 10 to rotate about the helical axis in a first direction when retracted. The second pair of wires 60 is arranged to drive the lens element 10 to rotate about the helical axis in an opposite second direction when retracted. The helical bearing mechanism 20 converts the rotation into helical movement.

[0124] The wires 60 are arranged in loops at different angular positions around the helical axis, and continuous wires 60 are connected between the support structure and the lens element 10 so as to apply torque in an alternating manner around the helical axis. Within each pair of wires, the wires 60 are arranged on opposite sides of the helical axis.

[0125] Lens element 10 includes a first pair of connecting portions (e.g., crimps, also referred to herein as "moving crimps") located at a first angular position about the helical axis and a second pair of connecting portions ("moving crimps") located at a second angular position about the helical axis. These first and second angular positions are offset by 180° from each other. The wires 60 of each of the first and second pairs of wires 60 are connected to lens element 10 via the first pair of moving crimps, and the wires of each of the first and second pairs of wires 60 are connected to lens element 10 via the second pair of connecting portions.

[0126] Special References Figure 30 In some examples, the spiral bearing mechanism 20 includes a set of three spiral bearings, specifically two ("pinned") bearings 401 ( Figure 2 of the type shown in the figure) and a ("slider") bearing 402 ( Figure 3 (type shown in the figure).

[0127] The three spiral bearings are a first pin-jointed bearing, a second slider bearing, and a third pin-jointed bearing. The second bearing is angularly spaced about 90° from the first bearing around the spiral axis, and the third bearing is angularly spaced about 90° from the second bearing around the spiral axis.

[0128] In some examples (including Figure 30 ), the actuator assembly 1 includes a biasing mechanism 90 configured to apply a biasing force to the lens element 10 in a direction at least substantially orthogonal to the spiral path along which the lens element 10 moves so as to at least partially load the spiral bearing mechanism 20, i.e., the bearings 401, 402. The biasing mechanism 90 may have any suitable form. For example, the biasing mechanism 90 may include an elastic element connected between the support structure 2 and the lens element. The elastic element may be a flexure or another elastic element. The biasing mechanism 90 may be a magnetic loading mechanism, for example including a permanent magnet located on one of the support structure 2 and the lens element 10 and a magnetic material (e.g., steel) located on the other of the support structure 2 and the lens element 10. As Figure 30 As illustrated in FIG, the biasing mechanism 90 may be angularly spaced approximately 90° from the third bearing about the screw axis.

[0129] In some examples, there may be no (separate) biasing mechanism, but rather four wires 60 may be arranged, for example at an acute angle to a plane normal to the helical axis, to apply a force to the lens element 10 in order to load the helical bearing mechanism 20, i.e. bearings 401, 402.

[0130] An example of this is Figure 31 This example is otherwise similar to Figure 30 The example shown in the figure is the same

[0131] Special References Figure 32 In other such examples, the space gained by omitting the (separate) biasing mechanism is used to include a fourth helical bearing. In particular, in such examples, there is one ("pinned") bearing 401 ( Figure 2 of the type shown in the figure) and three ("slider") bearings 402 ( Figure 3 ). Together, these bearings 401, 402 provide the required restraint. Adjacent pairs of spiral bearings 401, 402 are angularly spaced approximately 90° apart about the spiral axis. This distribution of spiral bearings 401, 402 provides a particularly stable arrangement (e.g., with respect to tilting, manufacturing tolerances, etc.) while also making efficient use of space (floor area).

[0132] from Figures 30 to 32 As can be seen, the lens element 10 comprises a portion 10a which at least partially extends outwardly from the screw axis and carries, for example, a portion of the bearings 401, 402 and, in turn, the mobile crimp. Preferably, the screw bearings 401, 402 are located within a square ring of four wires 60. This allows for efficient use of the available space (footprint) while maximizing the length of the wires 60 and, therefore, the maximum displacement (stroke).

[0133] The SMA actuator wires 60 are driven by control circuitry implemented in the IC chip 5. Specifically, the control circuitry generates a drive signal for each SMA actuator wire 60 and provides the drive signal to the SMA actuator wires 60. The control circuitry receives an input signal representing a desired position of the lens element 10 along the optical axis O and generates a drive signal selected to drive the lens element 10 to the desired position. The drive signal can be generated using a resistive feedback control technique, in which case the control circuitry 20 measures the resistance of a length of the SMA actuator wire 20 and uses the measured resistance as a feedback signal to control the power of the drive signal. This resistive feedback control technique may be implemented as disclosed in any of WO-2013 / 175197, WO-2014 / 076463, WO-2012 / 066285, WO-2012 / 020212, WO-2011 / 104518, WO-2012 / 038703, WO-2010 / 089529, or WO-2010029316, each of which is incorporated herein by reference. Alternatively, the control circuit may include a sensor that senses the position of the lens element 10, such as a Hall sensor that senses the position of a magnet affixed to the lens element 10. In this case, the drive signal uses the sensed position as a feedback signal to control the power of the drive signal.

[0134] Alternative to spiral flexure bearings

[0135] Figure 33 is a perspective view of an alternative spiral bearing mechanism 20 (referred to herein as a spiral flexure bearing 1090) comprising more than one flexure 1092 (also referred to herein as a flexure arm) arranged to extend between the static component 2 and the lens element 10. In this example, four flexure arms 10921, 10922, 10923, 10924 are shown, but in general any number of flexure arms 1092 may be provided.

[0136] Helical flexure bearing 1090 includes a circular ring 1091 having a central hole 1009. However, in general, central ring 1091 does not necessarily need to include central hole 1009. Circular ring 1091 is connected to four flexure arms 10921, 10922, 10923, and 10924. Instead of circular ring 1091, a central portion of any other shape may be commonly connected to flexure arms 1092. At the end not connected to circular ring 1091, each flexure arm 10921, 10922, 10923, and 10924 is connected to a corresponding spacer 10931, 10932, 10933, and 10934. Spacer 1093 is used to connect to static component 2. Circular ring 1091 is connected to lens element 10. The central axis of central hole 1009 coincides with optical axis O and helical axis H of lens element 10.

[0137] Each flexure arm 10921, 10922, 10923, 10924 is substantially tangential to the annular ring 1091 (in the same manner). The span of each flexure arm includes a first component parallel to a plane containing the first axis x and the second axis y and a second component parallel to the principal axis z. Therefore, the flexure arm is pre-deflected along the principal axis z. If the shims 10931, 10932, 10933, 10934 are clamped and a force is applied upward (in the positive z direction) to the annular ring 1091, in response, the flexure arms 10921, 10922, 10923, 10924 will deflect in the direction of that force. In doing so, in the xy plane, the end connected to the annular ring 1091 deflects closer to the corresponding shims 10931, 10932, 10933, 10934, thereby causing the annular ring 1091 to rotate clockwise about an axis parallel to the principal axis z. Conversely, a force applied downward (negative z direction) on the annular ring 1091 will result in downward movement of the annular ring 1091 and also in a counterclockwise (anti-clockwise) rotation of the annular ring 1091. It will be understood that the annular ring 1091 can rotate counterclockwise about an axis parallel to the main axis z, wherein the arrangement of the flexure arms 1092 is similar to Figure 33 The arrangement in is mirror symmetrical.

[0138] In this manner, the spiral flexure bearing 1090 serves to convert relative displacement parallel to the principal axis z into rotation about the principal axis z, and vice versa. These movements are not independent of one another. The spiral flexure bearing 1090 allows movement along one degree of freedom. The annular ring 1091 is constrained to move along a substantially helical path relative to the clamped spacers 10931, 10932, 10933, 10934.

[0139] Although the flexure arms 10921, 10922, 10923, 10924 are Figure 331090 is shown as being curved in the xy plane, but in other examples of the spiral flexure bearing 1090, the flexure arm 1092 can be straight in the xy plane. Further examples of the spiral flexure bearing 1090 are described in WO 2019 / 243849 A1, the contents of which are incorporated herein by reference in their entirety. Figures 19 to 22 The attached description on page 22, line 23 to page 23, line 24 particularly relates to the spiral flexure bearing 1090. Additional examples of implementing the spiral flexure bearing 1090 are shown and described below.

[0140] Spiral flexure bearing assemblies

[0141] refer to Figure 34A and Figure 34B , the four SMA actuator wires 60 (described above) will now be described. Figures 30 to 32 described) and the spiral flexure bearing 1090 (described above with respect to Figure 33 The example of the actuator assembly 1 will be referred to as the "first helical flexure assembly" 1000 below.

[0142] Figure 34A An exploded perspective view of the first spiral flexure assembly 1000 is shown and Figure 34B A perspective view of the first helical flexure assembly 1000 is shown.

[0143] As described above, the SMA actuator wires 60 connected between the static component 2 and the lens element 10 include a first pair of SMA actuator wires 60 and a second pair of SMA actuator wires 60. The first pair of SMA actuator wires 60 is arranged to drive the lens element 10 to rotate about the helical axis in a first direction when retracted. The second pair of SMA actuator wires 60 is arranged to drive the lens element 10 to rotate about the helical axis in an opposite second direction when retracted. The helical bearing mechanism 20 converts the rotation into helical movement.

[0144] The SMA actuator wires 60 are arranged in loops at different angular positions around the helical axis. Continuous SMA actuator wires 60 are connected between the static component 2 (also referred to herein as the support structure 2) and the lens element 10 to apply torque in an alternating manner around the helical axis. Within each pair of wires, the SMA actuator wires 60 are arranged on opposite sides of the helical axis.

[0145] The lens element 10 includes a first pair of connecting portions 19 (e.g., crimps, also referred to herein as "moving crimps") located at a first angular position about the helical axis and a second pair of connecting portions 19 ("moving crimps") located at a second angular position about the helical axis. These first and second angular positions are offset from each other by 180° about the helical axis. The SMA actuator wires 60 of each of the first and second pairs of SMA actuator wires 60 are connected to the lens element 10 via the first pair of moving crimps 19, and the other SMA actuator wire of each of the first and second pairs of SMA actuator wires 60, 60 is connected to the lens element 10 via the second pair of moving crimps 19.

[0146] The first spiral flexure assembly 1000 includes a movable plate 24, which in this example can be considered part of the lens element 10 because it provides or supports the lens element 10 and is fixed to the lens element 10. In the depicted embodiment, the movable plate 24 takes the form of an annular plate. The annular plate has an outer periphery that is rectangular in shape. The annular plate has a first corner 1511 and a second corner 1512 that are truncated in a diagonally opposing manner. The annular plate has a circular inner periphery that defines the central aperture 1009 of the first spiral flexure assembly 1000. However, in general, the movable plate 24 can have any other shape. The diagonally opposing third corner 1513 and fourth corner 1514 of the movable plate 24 support the first pair of movable crimps 19 and the second pair of movable crimps 19.

[0147] The static component 2 of the first spiral flexure assembly 1000 includes a static plate 149. In the depicted embodiment, the static plate 149 is formed as an annular plate having a rectangular outer perimeter and a circular inner perimeter defining a central aperture 1009. However, in general, the static plate 149 can have any other shape. The static component 2 also includes a first pair of connecting portions 18 (e.g., crimps, also referred to herein as "static crimps") located at a first angular position about the spiral axis and a second pair of connecting portions 18 ("static crimps") located at a second angular position about the spiral axis. These first and second angular positions are offset by 180° from each other and by 90° from the angular position of the moving crimp 19. The SMA actuator wires 60 of each of the first and second pairs of SMA actuator wires 60 are connected to the static component 2 via the first pair of static crimps 18 , and the SMA actuator wires of each of the first and second pairs of SMA actuator wires 60 are connected to the static component 2 via the second pair of static crimps 18 .

[0148] A first end of each of the four SMA actuator wires 60 is connected to the static component 2 via a static crimp 18 , and a second end of each of the four SMA actuator wires 60 is connected to the lens element 10 via a movable crimp 19 .

[0149] In the depicted embodiment, the static crimp 18 is supported by a first post 1521 and a second post 1522. The first post 1521 and the second post 1522 are attached (using welding, adhesive, or other suitable attachment method) to diagonally opposed corners of the static plate 149 to substantially align with the truncated corners 1511, 1512 of the movable plate 24.

[0150] Lens element 10 is coupled to static component 2 via movable plate 24, via helical flexure bearing 1090, via static plate 149. Spacer 1093 is secured to static plate 149 (also referred to herein as a "base" or "substrate"), for example, by welding, adhesive, or other suitable attachment methods. Circular ring 1091 is secured to movable plate 24 in the same or similar manner. Alternatively, circular ring 1091 may be integrally formed with movable plate 24.

[0151] Replacement for spiral flexure bearing assemblies

[0152] refer to Figure 35 A further example of an actuator assembly 1 including four SMA actuator wires 60' and a spiral bearing mechanism 20 having more than one flexure 1092' (also referred to as a spiral flexure bearing 1090') will now be described. In the depicted example, the spiral flexure bearing 1090' includes four flexure arms 10921', 10922', 10923', 10924', although generally any number of flexure arms may be provided. This example of an actuator assembly 1 will hereinafter be referred to as a "second spiral flexure assembly" 1000'.

[0153] The second helical flexure assembly 1000' comprises four SMA actuator wires 60'. The four SMA actuator wires 60' are arranged to drive the movement of the lens element 10 relative to the static component 2 about the helical axis H (e.g., in degrees about Figure 30-Figure 32 、 Figure 34A and Figure 34B described).

[0154] The four SMA actuator wires 60' include or consist of a first pair of SMA actuator wires 601' and a second pair of SMA actuator wires 602'. The first pair of SMA actuator wires 601' is arranged to rotate the lens element 10 in a first direction about the helical axis H when retracted. The second pair of SMA actuator wires 602' is arranged to rotate the lens element 10 in an opposite second direction about the helical axis H when retracted. The helical flexure bearing 1090' converts the rotation of the lens element 10 into a helical movement about the helical axis H. The four SMA actuator wires 60' can drive the movement of the lens element 10 in the manner described with respect to the previous embodiments.

[0155] As about Figure 33-34B As described above, spiral flexure bearing 1090 ′ may include a circular ring 1091 ′ having a central hole 1009 ′. Circular ring 1091 ′ is connected to the end of each of four flexure arms 10921 ′, 10922 ′, 10923 ′, and 10924 ′. At the end not connected to circular ring 1091 ′, each flexure arm 10921 ′, 10922 ′, 10923 ′, and 10924 ′ is connected to a spacer 10931 ′, 10932 ′, 10933 ′, and 10934 ′. Spacer 1093 ′ is used to connect to static component 2 . Circular ring 1091 ′ is connected to lens element 10 . The central axis of central hole 1009 ′, the optical axis O of lens element 10, the spiral axis H, and the principal axis z coincide. In general, the spiral flexure bearing 1090 ′ does not have to include a circular ring 1091 ′, but can include any central portion that is commonly connected to the flexure arm 1092 .

[0156] In the depicted embodiment, each spiral flexure arm 10921', 10922', 10923', 10924' of the spiral flexure bearing 1090' is substantially tangential to the annular ring 1091'. The span of the spiral flexure bearing 1090' includes a first component parallel to a plane containing the x- and y-axes and a second component parallel to the z-axis. If the shims 10931', 10932', 10933', 10934 are clamped and a force is applied upward (in the positive z-direction) to the annular ring 1091', the flexure arms 10921', 10922', 10923', 10924 will deflect in the direction of the force in response. In doing so, in the xy plane, the ends connected to the circular rings are also deflected closer to the corresponding pads 10931', 10932', 10933', 10934', thereby causing the circular ring 1091' to rotate clockwise about an axis parallel to the main axis z. Conversely, a force applied downwardly (negative z direction) on the circular ring 1091' will cause a downward movement of the circular ring 1091' and also cause a counterclockwise (anti-clockwise) rotation of the circular ring 1091'. It will be understood that when displaced upwardly, the circular ring 1091' can rotate counterclockwise about an axis parallel to the main axis z, wherein the arrangement of the flexure arms 1092' is the same as Figure 35 The arrangement in is mirror symmetrical.

[0157] In this manner, the spiral flexure bearing 1090' serves to convert relative displacement parallel to the principal axis z into rotation about the principal axis z, and vice versa. These movements are not independent of one another. The annular ring 1091' is constrained to move along a substantially helical path relative to the clamped spacers 10931', 10932', 10933', 10934'.

[0158] The second helical flexure assembly 1000' is typically asymmetric. The maximum extension of the helical flexure assembly 1000' along the first axis (which, in this example, is parallel to the y-axis) is substantially less than the maximum extension of the helical flexure assembly 1000' along the second axis (which, in this example, is parallel to the x-axis). The first and second axes are perpendicular to the helical axis H and to each other. In other words, typically, the maximum extension of the components of the helical flexure assembly 1000' (particularly the flexure arm 1092' and the SMA actuator wire 60') along the first axis is substantially less than the maximum extension of the components along the second axis. The maximum extension of the helical flexure assembly 1000' (and its components) along the first axis can be less than 95%, preferably less than 90%, more preferably less than 85%, and particularly preferably less than 80%. The maximum extension of the helical flexure assembly 1000' (and its components) along the first axis can be less than, for example, 70% or 60% of the maximum extension of the helical flexure assembly 1000' (and its components) along the second axis.

[0159] This asymmetric design helps minimize or reduce the extension of the actuator assembly 1 along one axis (i.e., the y-axis in this example). This can be useful, for example, in a smartphone with a front-facing camera, as the reduced extension along one axis can help reduce the gap between the screen and the front-facing camera. It can also reduce the gap between the top edge of the smartphone and the front-facing camera.

[0160] By placing the SMA actuator wires 60' on two opposing sides of the second helical flexure assembly 1000' (rather than on four sides of the first helical flexure assembly 1000, as in Figure 34A and Figure 34B ) to achieve an asymmetric design. Specifically, the SMA actuator wires 60' of each of the first pair of SMA actuator wires 601' and the second pair of SMA actuator wires 602' are completely arranged on a first side S1 of the spiral axis H (for ease of reference, these SMA actuator wires will be referred to as "S1 pair of SMA actuator wires 603'" below). The other SMA actuator wires 60' of the first pair of SMA actuator wires 601' and the second pair of SMA actuator wires 602' are completely arranged on an opposite second side S2 of the spiral axis H (for ease of reference, these SMA actuator wires will be referred to as "S2 pair of SMA actuator wires 604'" below). The first side S1 corresponds to the first half of the actuator assembly 1 and the second side S2 corresponds to the second half of the actuator assembly 1. The first side S1 and the second side S2 are separate, non-overlapping and adjacent. The first side S1 and the second side S2 are parallel to the spiral axis H (and parallel to Figure 35 1 and 2. The SMA actuator wires 60' extend generally parallel to the plane P and, therefore, generally parallel to the first axis. The SMA actuator wires 60' on each side S1, S2 are connected between the static component 2 and the lens element 10 to apply torque (as described above) in an alternating manner about the helical axis.

[0161] The helical flexure bearing 1090' includes a first pair of connecting portions 19' (e.g., crimps, also referred to herein as "moving crimps") on a first side S1 and a second pair of connecting portions 19' ("moving crimps") on a second side S2. The moving crimps 19' are each located at a different angular position about the helical axis H and are each located at a respective corner C of the actuator assembly 1.

[0162] Each mobile crimping component 19' is disposed at the end of a corresponding crimping arm 119' of the spiral flexure bearing 1090'. The crimping arm 119' can extend from the circular ring 1091' at the same locations as the flexure arms 10921', 10922', 10923', and 10924 extend from the circular ring 1091'. These locations are spaced approximately equally around the perimeter of the circular ring 1091'. The flexure arms 1092' extend along the spiral axis H (from the circular ring 1091' toward the base 4) and are substantially wrapped around the perimeter of the circular ring 1091'. The crimping arm 119' extends away from the spiral axis H and generally toward the corner C of the actuator assembly 1 (from the circular ring 1091'). The crimping arm 119' is generally flat and coplanar with the circular ring 1091' (i.e., the crimping arm 119' and the circular ring 1091' lie on a common plane perpendicular to the main axis z).

[0163] The static part 2 may have four columns (not shown, but similar to Figure 34B Each column is equivalent to the columns 1521, 1522, 1523, and 1524 in the base 4, each column standing upright from a corresponding corner C of the base 4 (in the positive z-direction). Each column has a connecting portion 18' (e.g., a crimp, also referred to herein as a "static crimp"). The four columns can be formed integrally with the base 4 or attached to the base 4 using welding, adhesive, or other suitable attachment methods.

[0164] A first pair of corners C and a first pair of static crimps 18' of the four corners C are on a first side S1 of the actuator assembly 1. A second pair of corners C and a second pair of static crimps 18' of the four corners C are on a second side S2 of the actuator assembly 1. The S1 pair of SMA actuator wires 603' are connected between the first pair of static crimps 18' and the first pair of moving crimps 19'. The S2 pair of SMA actuator wires 604' are connected between the second pair of static crimps 18' and the second pair of moving crimps 19'. The SMA actuator wires 60' extend generally from one corner to the other in a direction generally parallel to plane P (i.e., the y-axis in this example). In other words, the S1 pair of SMA actuator wires 603' extends from one corner of the first pair of corners C to the other corner of the first pair of corners C, and the S2 pair of SMA actuator wires 604' extends from one corner of the second pair of corners C to the other corner of the second pair of corners C. Thus, the SMA actuator wire 60' extends substantially along the entire length of the actuator assembly 1 along the first axis (the y-axis in this example).The SMA actuator wire 60' is substantially the same length between the moving crimp 19' and the static crimp 18'.

[0165] The flexure arm 1092 ′, the movable crimp member 19 ′, the static crimp member 18 ′, and the SMA actuator wire 60 ′ have a two-fold rotational symmetry about the helical axis H. As shown in FIG.

[0166] Similar to the flexure arm 1092 of the first spiral flexure assembly 1000, the flexure arm 1092' has shims 10931', 10932', 10933', 10934' at its lowermost end (i.e., the end closest to the base 4) for attaching the flexure arm 1092' to the base 4. The shims 10931', 10932', 10933', 10934' extend in a direction perpendicular to the plane P and, in this example, extend away from the plane P. As a result, the extension of the shims 10931', 10932', 10933', 10934' in a direction parallel to the plane P (and therefore the extension of the actuator assembly 1) is reduced. The first pair of four flexure arms 10921', 10923' (and their corresponding gaskets 10931', 10933') are on the first side S1 of the actuator assembly 1, and the second pair of four flexures 10922', 10924' (and their corresponding gaskets 10932', 10934') are on the second side S2 of the actuator assembly 1.

[0167] To minimize the extension of the actuator assembly 1 along the first axis, the static crimp component 18' (including the corresponding post), the helical flexure bearing 1090' (including the annular ring 1091', the crimp arm 119', the moving crimp component 19', the flexure arm 1092', the flexure spacer 1093'), and the SMA actuator wire 60' do not extend (or substantially do not extend) beyond the limits of the body of the lens element 10 in the first axis. Thus, the extension of the helical flexure bearing 1090' along the first axis is less than or equal to the extension of the body of the lens element 10 along the first axis.

[0168] The annular ring 1091', crimp arm 119', flexure arm 1092', and flexure pad 1093' can be formed from a single patterned metal sheet (e.g., an etched or machined sheet of stainless steel) and can be coated with an electrically insulating dielectric material. The dielectric coating or other type of dielectric layer can include one or more windows that allow electrical connections therethrough.

[0169] As described above with respect to first spiral flexure assembly 1000, lens element 10 is movably coupled to static component 2 via a spiral bearing mechanism 20 having more than one flexure 1092' (i.e., spiral flexure 1090'). Spacer 1093' is secured to base 4, for example, by welding, adhesive, or other suitable attachment method, while annular ring 1091' is secured to lens element 10 in the same or similar manner.

[0170] Alternatively, as described with respect to the first spiral flexure assembly 1000, the crimping arms 119' and the movable crimping portion 19' may instead be provided on the movable plate. The circular ring 1091' may then be secured to the movable plate by the attachment methods described above, and the movable plate may be secured to and / or form a portion of the lens element 10. Furthermore, the movable plate and the crimping arms 119' may be formed from a first single patterned metal sheet, and the circular ring 1091', the flexure arms 1092', and the flexure pads 1093' may be formed from a second single patterned metal sheet. Figure 36 and Figure 37 As shown in , such an arrangement would allow crimp arm 119' and flexure arm 1092' to be separately connected to lens element 10 and overlap along the z-axis. This would allow flexure arm 1092' to be longer, potentially reducing stress in the arm during AF actuation and increasing AF stroke. This would also allow flexure arm 1092' and crimp arm 119' to be made of different materials and have different thicknesses.

[0171] Other variants

[0172] It will be appreciated that many other variations of the helical flexure assembly examples described above are possible.

[0173] Although the above examples describe only providing a single SMA actuator wire between each static crimp and each corresponding moving crimp, any number of SMA actuator wires (or any length of SMA actuator wire) may be provided between the static and moving crimps.

[0174] Although the above examples only describe the column (supporting the static crimping portion) as being integrally formed with the base 4 or attached to the base 4 using welding, adhesive or other suitable attachment methods, the column can be integrally formed with any other component that is part of the static component 2 of the actuator assembly 1 or attached to such a component by any suitable attachment method.

[0175] Although the above examples focus on a helical flexure mechanism with four flexure arms, any number of flexure arms may be provided between the static component 2 and the lens element 10. For example, Figure 38 As shown, two flexure arms may be provided, although this would likely require additional components to limit undesirable movement of the lens element 10 (eg, tilting).

Claims

1. A shape memory alloy (SMA) actuator, comprising: Support structure; movable elements; a helical bearing mechanism supporting the movable element on the support structure and arranged to guide helical movement of the movable element relative to the support structure about a helical axis; as well as a set of four SMA actuator wires, each SMA actuator wire connected between the support structure and the movable element and located in a plane orthogonal to the helical axis or at an acute angle to the plane orthogonal to the helical axis, the four SMA actuator wires comprising a first pair of SMA actuator wires arranged to drive the movable element to rotate about the helical axis in a first direction when contracted and a second pair of SMA actuator wires arranged to drive the movable element to rotate about the helical axis in an opposite second direction when contracted, wherein the helical bearing mechanism converts the rotation into helical movement.

2. The SMA actuation device according to claim 1, wherein: The four SMA actuator wires are arranged in loops at different angular positions about the helical axis, and consecutive SMA actuator wires are connected to apply torque in an alternating manner about the helical axis.

3. The SMA actuation device of claim 2, wherein: Within each pair of SMA actuator wires, the SMA actuator wires are arranged on opposite sides of the helical axis.

4. The SMA actuation device of claim 3, wherein: The movable element comprises a first pair of connection portions located at a first angular position about the helical axis and a second pair of connection portions located at a second angular position about the helical axis, wherein the first angular position and the second angular position are offset from each other by 180°, wherein the SMA actuator wires in each pair of SMA actuator wires are connected to the movable element via the first pair of connection portions, and the SMA actuator wires in each pair of SMA actuator wires are connected to the movable element via the second pair of connection portions.

5. An SMA actuation device according to any preceding claim, wherein: The spiral bearing mechanism comprises a group of one or more spiral bearings, each of the group of one or more spiral bearings being a rolling bearing comprising bearing surfaces on the support structure and the movable element and at least one rolling bearing element arranged between the bearing surfaces.

6. The SMA actuation device of claim 5, wherein: The set of one or more spiral bearings comprises: at least one spiral bearing of a first type, wherein the bearing surface comprises grooves on each of the support structure and the movable element; and At least one helical bearing of a second type, wherein the bearing surface comprises a groove on one of the support structure and the movable element and a planar surface on the other of the support structure and the movable element.

7. The SMA actuation device of claim 6, wherein: The set of one or more spiral bearings comprises two spiral bearings of the first type and one spiral bearing of the second type.

8. The SMA actuation device of claim 7, wherein: The three spiral bearings consist of a first bearing, a second bearing and a third bearing, and the second bearing is angularly spaced substantially 90° from the first bearing around the spiral axis, and the third bearing is angularly spaced substantially 90° from the second bearing around the spiral axis.

9. An SMA actuation device according to any one of claims 1 to 4 and 6 to 8, comprising a biasing mechanism configured to apply a biasing force to the movable element in a direction at least substantially orthogonal to the helical path along which the movable element moves so as to at least partially load the helical bearing mechanism.

10. The SMA actuation device of claim 9, wherein: The biasing mechanism includes a resilient element connected between the support structure and the movable element.

11. The SMA actuation device of claim 10, wherein: The elastic element is a flexure.

12. The SMA actuation device of claim 9, wherein: The biasing mechanism is a magnetic loading mechanism.

13. An SMA actuation arrangement according to any one of claims 10 to 12 when dependent on claim 8, wherein At least a portion of the biasing mechanism is angularly spaced substantially 90° from the third bearing about the screw axis.

14. The SMA actuation device of claim 6, wherein: The four SMA actuator wires are arranged to apply a force to the movable element, which force loads the helical bearing mechanism.

15. The SMA actuation device according to any one of claims 1-4 and 7-8, wherein: The four SMA actuator wires are arranged to apply a force to the movable element, which force loads the helical bearing mechanism.

16. The SMA actuation device of claim 14, wherein: The set of one or more spiral bearings comprises one spiral bearing of the first type and three spiral bearings of the second type.

17. The SMA actuation device of claim 16, wherein: Adjacent pairs of spiral bearings are angularly spaced substantially 90° from each other about the spiral axis.

18. An SMA actuation device according to claim 4 or any one of claims 6-8, 10-12, 14 and 16-17 as appended thereto, wherein The spiral bearing mechanism comprises at least a first bearing and a second bearing, and wherein the movable element comprises a first part and a second part, each of the first part and the second part extending at least partially outward from the spiral axis, wherein the first part carries a part of the first bearing and a first connecting part, and the second part carries a part of the second bearing and a second connecting part.

19. An SMA actuation device according to claim 2 or any one of claims 3-4, 6-8, 10-12, 14 and 16-17 as appended thereto, wherein The spiral bearing mechanism is located within the loop of the four SMA actuator wires.

20. The SMA actuation device of any one of claims 1-4, 6-8, 10-12, 14, and 16-17, wherein: The helical bearing mechanism includes at least one flexure arm extending between the support structure and the movable element.

21. The SMA actuation device of claim 20, wherein: The maximum extension of the flexure arm and the four SMA actuator wires along a first axis is substantially less than the maximum extension of the flexure arm and the four SMA actuator wires along a second axis; wherein the first axis is perpendicular to the helical axis, and the second axis is perpendicular to the helical axis and perpendicular to the first axis.

22. The SMA actuation device of claim 21, wherein: A maximum extension of the flexure arm and the four SMA actuator wires along the first axis is less than 90% of a maximum extension of the flexure arm and the four SMA actuator wires along the second axis.

23. An SMA actuation device according to claim 21 or 22, wherein: The SMA actuation device comprises a first side and a second side, and wherein: the first side comprising at least one flexure arm and a first pair of the four SMA actuator wires, and the second side comprising at least one flexure arm and a second pair of the four SMA actuator wires; and Wherein the first side and the second side are located on opposite sides of the helical axis.

24. The SMA actuation device of claim 23, wherein: The first side corresponds to a first half of the SMA actuation device, and the second side corresponds to a second half of the SMA actuation device.

25. An SMA actuation device according to any one of claims 21-22 and 24, wherein: The helical bearing mechanism includes four flexure arms extending between the support structure and the movable element.

26. The SMA actuation device of claim 25, wherein: The four flexure arms are substantially equally spaced around the perimeter of the movable element.

27. An SMA actuation device according to any one of claims 21-22, 24 and 26, wherein: The four SMA actuator wires have equal lengths.

28. An SMA actuation device according to any one of claims 21-22, 24 and 26, wherein: The four SMA actuator wires are substantially aligned with the first axis.

29. An SMA actuation device according to any one of claims 21-22, 24 and 26, wherein: The four SMA actuator wires substantially occupy a maximum extension of the flexure arm and the four SMA actuator wires along the first axis.

30. The SMA actuation device of claim 23, wherein: The first pair of the four SMA actuator wires and the second pair of the four SMA actuator wires each comprise: a first SMA actuator wire arranged to actuate the movable element to rotate about the helical axis in a first direction, and A second SMA actuator wire is arranged to drive the movable element to rotate about the helical axis in a second, opposite direction.

31. An SMA actuation arrangement according to claim 24 or 26 as appended to claim 23, wherein The first pair of the four SMA actuator wires and the second pair of the four SMA actuator wires each comprise: a first SMA actuator wire arranged to actuate the movable element to rotate about the helical axis in a first direction, and A second SMA actuator wire is arranged to drive the movable element to rotate about the helical axis in a second, opposite direction.

32. An SMA actuation device according to any one of claims 21-22, 24 and 26, wherein the movable element comprises four movable connection parts, and the support structure comprises four static connection parts, and Wherein each of the four SMA actuator wires is connected between each of the four movable parts and each of the four static connection parts.

33. An SMA actuation device according to claim 32, wherein: The four movable connecting parts extend to four movable crimping parts, and the four static connecting parts include four static crimping parts, and wherein a first pair of the four movable crimps and a first pair of the four static crimps are positioned toward a first end of a maximum extension of the flexure arm and the four SMA actuator wires along the first axis, and The second pair of the four movable crimps and the first pair of the four static crimps are positioned toward opposite second ends of maximum extension of the flexure arm and the four SMA actuator wires along the first axis.

34. An SMA actuation device according to claim 33, wherein: The four movable connection portions extend from locations that are substantially equally spaced around the perimeter of the body of the movable element.

35. An SMA actuation arrangement according to any one of claims 33 to 34, wherein: The flexure arm and the four movable connecting parts are integral.

36. An SMA actuation arrangement according to any one of claims 33 to 34, wherein: The flexure arm and the four movable connection portions have a common connection point with the body of the movable element.

37. An SMA actuation arrangement according to any one of claims 33 to 34, wherein: The flexure arm and / or the four movable connection portions and / or the four static connection portions and / or the four SMA actuator wires have a two-fold rotational symmetry about the helical axis.

38. The SMA actuation device of any one of claims 1-4, 6-8, 10-12, 14, 16-17, 21-22, 24, 26, 30, and 33-34, wherein At least one SMA actuator wire is arranged to, when contracted, drive the movable element to rotate less than a quarter of a full turn about the helical axis.

39. The SMA actuation device of any one of claims 1-4, 6-8, 10-12, 14, 16-17, 21-22, 24, 26, 30, and 33-34, wherein: The movable element is a lens element comprising at least one lens, and the helical axis is an optical axis of the lens element.

40. The SMA actuation device of claim 39, wherein: The support structure has an image sensor mounted thereon, and the lens element is arranged to focus an image on the image sensor.

41. The SMA actuation device of claim 39, wherein: The at least one lens has a diameter of at most 30 mm.

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