Actuator assembly

Abstract

Actuator assembly (1) comprising a plurality of actuator sub-assemblies, each actuator sub-assembly comprising a support structure (2), a movable part (10a, 10b, 10c), a bearing arrangement (30) arranged to guide movement of the movable part relative to the support structure and at least one actuator component arranged, on actuation, to drive the movable part relative to the support structure and a loading arrangement (90) arranged to apply a loading force between the movable part of a first actuator sub-assembly of the actuator sub-assemblies and the movable part of a second actuator sub-assembly of the actuator sub-assemblies for loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly.

Description

[0001] ACTUATOR ASSEMBLY

[0002] Field

[0003] The present application relates to an actuator assembly.

[0004] Background

[0005] It is known to use an actuator, for example a shape memory alloy, SMA, wire, to drive translational movement of a movable element with respect to a support structure. SMA actuator wires have particular advantages in miniature devices and may be applied in a variety of devices including handheld devices, such as cameras and mobile phones. Such SMA actuator wires may be used for example in an optical device such as a camera for driving translational movement of a camera lens element along its optical axis, for example to effect focussing (autofocus, AF) or zoom.

[0006] Some examples of an SMA actuation apparatuses which are cameras of this type are disclosed in WO- 2007 / 113478. Herein, the movable element is a camera lens element supported on a support structure by a helical bearing arrangement comprising flexures that guide translational movement along the optical axis. In one example described herein, the SMA actuator wire is a piece of SMA wire connected at its ends to a support structure and hooked over a hook on a camera lens element for driving 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 of greater than 0 degrees to the movement direction parallel to the optical axis. Angling the SMA actuator wires in this way increases the amount of movement compared to an SMA actuator wire extending along the movement direction and also reduces the extent of the actuator in the movement direction.

[0007] Optionally, the apparatus may comprise a bearing arrangement arranged to guide movement of the movable element relative to the support structure along a movement axis across a surface. The bearing arrangement may be loaded by applying a force urging the movable part onto the bearing arrangement. Two opposed SMA wires may be arranged to, on contraction thereof, apply forces that reduce frictional forces, thereby increasing the control over the movement of the movable element.

[0008] An apparatus may have multiple movable elements. Components are needed to load the bearing arrangements for the movable elements. It is desirable to reduce the size of such an apparatus.

[0009] Summary

[0010] According to an aspect of the present invention, there is provided an actuator assembly comprising: a plurality of actuator sub-assemblies, each actuator sub-assembly comprising: a support structure; a movable part; a bearing arrangement arranged to guide movement of the movable part relative to the support structure; and at least one actuator component arranged, on actuation, to drive the movable part relative to the support structure; and a loading arrangement arranged to apply a loading force between the movable part of a first actuator sub-assembly of the actuator sub-assemblies and the movable part of a second actuator sub-assembly of the actuator sub-assemblies for loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly.

[0011] By providing the loading directly between movable parts, it is not necessary to apply loading forces by separate mechanisms between each movable part and a static component. The space required for the loading arrangement may be reduced. The number of components of the actuator assembly may be reduced.

[0012] Optionally, the loading arrangement is located between the movable part of the first actuator subassembly and the movable part of the second actuator sub-assembly. The space required for the loading arrangement may be reduced. In particular, it may be possible to reduce elements provided radially and / or axially outwardly of the movable parts.

[0013] Optionally, the at least one actuator component is arranged to apply an unloading force so as to reduce loading of the corresponding bearing arrangement. By applying the unloading force, the motion of the movable part can be made easier when required. This can help to reduce the possibility of the movable part undesirably sticking.

[0014] Optionally, the bearing arrangement is arranged to have sufficient friction when loaded that the movable part remains in position when the at least one actuator component is not driving the movable part. Optionally, the bearing arrangement is arranged to have sufficient friction when loaded that the movable part, over a continuum of positions, remains in position when the at least one actuator component is not driving the movable part. Optionally, the loading arrangement is arranged to load the bearing arrangement of the first actuator sub-assembly so as to generate frictional forces therein that constrain the movement of the movable part of the first actuator sub-assembly relative to the support structure at any position within a range of movement when the at least one actuator component of the first actuator sub-assembly is not actuated. Optionally, the loading arrangement is arranged to load the bearing arrangement of the second actuator sub-assembly so as to generate frictional forces therein that constrain the movement of the movable part of the second actuator sub-assembly relative to the support structure at any position within a range of movement when the at least one actuator component of the second actuator sub-assembly is not actuated. By providing sufficient friction, the power and / or energy requirements to maintain the position of the movable part may be reduced. By providing sufficient friction, the power and / or energy requirements to maintain an arbitrary position of the movable part may be reduced.

[0015] Optionally, the at least one actuator component of the first actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement of the first actuator sub-assembly. Optionally, the at least one actuator component of the second actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement of the second actuator subassembly. Optionally, the at least one actuator component is arranged to reduce loading of the bearing arrangement by less than loading applied by loading arrangement. By reducing the frictional force, the motion of the movable part can be made easier when required. This can help to reduce the possibility of the movable part undesirably sticking.

[0016] Optionally, the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly is a helical bearing arrangement arranged to guide movement of the movable part relative to the support structure around a helical axis. Optionally, the loading arrangement is arranged to apply a loading torque about an axis perpendicular to the helical axis for loading the helical bearing arrangement. Optionally, the at least one actuator component is arranged to apply an unloading torque about an axis perpendicular to the helical axis so as to reduce loading of the corresponding bearing arrangement.

[0017] By applying the unloading torque, the load on the helical bearing arrangement can be controlled. As one example, this allows the load to be made lower when movement of the movable part is desired and made higher when movement is not desired. By applying the unloading torque with the actuator components, the number of parts may be minimised. By applying the loading torque perpendicular to the helical axis, the lateral forces imposed by the loading arrangement may be reduced. This can help to increase the accuracy of control of the position of the movable part.

[0018] Optionally, the loading arrangement comprises a resilient loading arrangement for resiliently loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly. Optionally, the resilient loading arrangement comprises at least one resilient element disposed between the movable part of the first actuator sub-assembly and the movable part of the second actuator sub-assembly. By providing a resilient loading arrangement, the loading may be provided without increasing power requirements. Optionally, the resilient loading arrangement comprises at least one resilient element between the movable part of the first actuator sub-assembly and the movable part of the second actuator subassembly, wherein the resilient element is stressed in its mounted position disposed between the movable part of the first actuator sub-assembly and the movable part of the second actuator subassembly so as to load the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly. By providing a stressed resilient element, the loading torque may be applied in a mechanically simple way that is relatively easier to manufacture.

[0019] Optionally, the loading arrangement comprises a magnetic loading arrangement. By providing a magnetic arrangement, the lateral forces on the movable part may be reduced. This can help to increase the accuracy of control of the position of the movable part.

[0020] Optionally, the at least one actuator component arranged, on actuation, to drive rotation of the movable part relative to the support structure about an axis parallel to a primary axis defined by the actuator assembly.

[0021] Optionally, the movable part of the first actuator sub-assembly and the movable part of the second actuator sub-assembly overlap when viewed along the primary axis. The overall space taken up by the actuator assembly may be reduced.

[0022] Optionally, the actuator assembly comprises at least three of the actuator sub-assemblies, wherein the loading arrangement is arranged between the movable part of the first actuator sub-assembly and the movable part of a third actuator sub-assembly of the actuator sub-assemblies for loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the third actuator sub-assembly. Optionally, the loading arrangement is arranged between the movable part of the second actuator sub-assembly and the movable part of the third actuator sub-assembly for loading the bearing arrangement of the second actuator sub-assembly and / or the bearing arrangement of the third actuator sub-assembly.

[0023] Optionally, the actuator component of at least one of the actuator sub-assemblies is a shape memory alloy, SMA, element. By providing an SMA element, the actuation may be effected particularly accurately and simply.

[0024] Optionally, the movable part is a lens element comprising at least one lens. By providing a lens element, the control of the position of the movable part may be implemented in the context of an optical focusing system, for example. Optionally, the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor. By providing an image sensor, the actuator assembly may be implemented as a camera, for example.

[0025] Optionally, the support structure has a display mounted thereon, the lens element being arranged to focus an image generated by the display. By providing a display, the actuator assembly may be implemented as a head-mounted display, for example.

[0026] Optionally, the movable part has an image sensor mounted thereon. By providing an image sensor, the actuator assembly may be implemented as a camera, for example.

[0027] Optionally, the support structure has a lens element comprising at least one lens, the lens element being arranged to focus an image on the image sensor. By providing a lens element, the control of the position of the movable part may be implemented in the context of an optical focusing system such as a camera, for example.

[0028] Brief description of the drawings

[0029] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0030] Figure 1 is a schematic view of an actuator assembly with a helical bearing arrangement;

[0031] Figure 2 is a schematic view of an actuator assembly with a loading arrangement;

[0032] Figure 3 is a schematic side view of the actuator assembly shown in Fig. 2;

[0033] Figure 4 is a schematic view of a rolling bearing;

[0034] Figure 5 is a schematic view of a possible helical bearing arrangement;

[0035] Figure 6 is a schematic side view of a possible bearing arrangement;

[0036] Figure 7 is a plan view of an actuator assembly comprising three movable parts;

[0037] Figure 8 is a perspective view of an overlapping region of the movable parts shown in Figure 7;

[0038] Figure 9 is a schematic side view of a possible bearing arrangement for two movable parts;

[0039] Figure 10 is a schematic view of a resilient loading arrangement;

[0040] Figure 11 is a schematic side view of part of the resilient loading arrangement of Figure 10;

[0041] Figure 12 is a plan view of an actuator assembly comprising three movable parts;

[0042] Figure 13 is a schematic view of a resilient loading arrangement for the movable parts shown in Figure 12;

[0043] Figure 14 is a schematic side view of a possible bearing arrangement for two movable parts; and Figure 15 is a schematic view of a loading arrangement for two movable parts.

[0044] Detailed description

[0045] Actuator assembly

[0046] An actuator assembly 1 is shown schematically in Fig. 1. The actuator assembly 1 may be a camera. The actuator assembly 1 is described primarily in the context of the actuator assembly 1 being a camera. However the actuator assembly 1 is not required to be a camera and may be embodied as a different type of apparatus.

[0047] The actuator assembly 1 comprises a support structure 2. The support structure 2 may have one or more components fixed to it, for example mounted onto it. For example when the actuator assembly 1 is a camera, the support structure 2 may have an image sensor 3 mounted thereon. The support structure 2 may take any suitable form, typically including a base 4 to which the image sensor is fixed. The support structure 2 may also support an IC chip 5.

[0048] The actuator assembly 1 also comprises a movable part 10 (or movable element). Optionally the movable part 10 is or comprises a lens element. The movable part 10 may comprise a lens 11, although it may alternatively comprise plural lenses. The movable part 10 has an axis O (for example an optical axis) aligned with the image sensor 3 and may be arranged to focus an image on the image sensor 3.

[0049] The actuator assembly 1 may be a miniature device. In some examples of a miniature device, the lens 11 (or plural lenses, when provided) may have a diameter of at most 20mm, preferably at most 15mm, preferably at most 10mm.

[0050] Although the actuator assembly 1 in this example is a camera, that is not in general essential. In some examples, the actuator assembly 1 may be an optical device in which the movable part 10 is a lens element but there is no image sensor. In other examples, actuator assembly 1 may be a type of apparatus that is not an optical device, and in which the movable part is not a lens element and there is no image sensor. Examples include apparatuses for depth mapping, face recognition, game consoles, projectors and security scanners.

[0051] The actuator assembly 1 also comprises a helical bearing arrangement 20 (shown schematically in Fig. 1) that supports the movable part 10 on the support structure 2. The helical bearing arrangement 20 is arranged to guide helical movement of the movable part 10 with respect to the support structure 2 around a helical axis H. The helical axis H in this example is coincident with the optical axis O and the helical movement is shown in Fig. 1 by the arrow M. Preferably, the helical motion is along a right helix, that is a helix with constant radius, but in general any helix is possible. The pitch of the helix may be constant or vary along the helical motion. Preferably, the helical movement is generally only a small portion (less than one quarter) of a full turn of the helix.

[0052] The helical motion of the movable part 10 guided by the helical bearing arrangement 20 includes a component of translational movement along the helical axis H and rotational movement around the helical axis H. The translational movement along the helical axis H is the desired movement of the movable part 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. The rotational movement around the helical axis H is in this example not needed for optical purposes, but is in general acceptable as rotation of the movable part 10 does not change the focus of the image on the image sensor 3.

[0053] Driving rotation of the movable part

[0054] Fig. 2 is a schematic view of an actuator assembly 1. The actuator assembly 1 comprises at least one actuator component. Optionally the actuator component is an SMA element, for example an SMA wire 40. The actuator assembly 1 depicted in Fig. 2 comprises SMA wires 40 as the actuator components. However, other types of actuator components may be used.

[0055] The actuator component is arranged, on actuation, to drive rotation of the movable part 10 around the helical axis H. The helical bearing arrangement 20 converts the rotation of the movable part 10 into the helical movement of the movable part 10 relative to the support structure 2 around the helical axis H.

[0056] Optionally only one actuator component is provided. The actuator component may be arranged, on actuation, to drive rotation of the movable part 10 in one sense around the helical axis H. The helical bearing arrangement 20 converts the rotation into helical movement in one helical direction (i.e. in one sense). Another component such as a resilient member may drive rotation of the movable part 10 in the opposite sense around the helical axis H which the helical bearing arrangement 20 converts into helical movement in the opposite sense.

[0057] Alternatively, optionally the actuator assembly 1 comprises a plurality of actuator components. For example as shown in Fig. 2 the actuator assembly 1 may comprise two SMA wires 40 as actuator components. Only one of the SMA wires 40 is visible from the angle of Fig. 2. As shown in Fig. 2, optionally the SMA wire is connected between the support structure 2 and the movable part 10. The SMA wire 40 may be connected to the support structure 2 via a fixing such as a static crimp 41. The SMA wire 40 may be connected to the movable part 10 via a fixing such as a moving crimp 42. The second SMA wire 40 which is not visible in Fig. 2 is provided at the lower side (in the orientation shown in Fig. 2) of the actuator assembly 1. The moving crimp 42 for connecting the second SMA wire 40 to the movable part 10 can be seen in Fig. 2.

[0058] Optionally, the actuator assembly 1 comprises at least one pair of actuator components (e.g. SMA wires 40) arranged, on actuation, to drive rotation of the movable part 10 in opposite senses around the helical axis H. The helical bearing arrangement converts the rotation of the movable part 10 into the helical movement. The two SMA wires 40 can be actuated to cause helical movement along the helical axis H in opposite senses. The SMA wires 40 may be controlled (i.e. actuated) so as to control the helical position of the movable part 10 along the helical axis H.

[0059] Optionally, the SMA wires 40 are driven by a control circuit implemented in the IC chip 5. In particular, the control circuit may generate drive signals for each of the SMA wires 40 and supply the drive signals to the SMA wires. The control circuit receives an input signal representing a desired position for the movable part 10 along the optical axis O and generates drive signals selected to drive the movable part 10 to the desired position.

[0060] The drive signals may be generated using a resistance feedback control technique, in which case the control circuit measures the resistance of the lengths of the SMA wires 40 and uses the measured resistance as a feedback signal to control the power of the drive signals.

[0061] As an alternative, the control circuit may include a sensor which senses the position of the movable part 10, for example a Hall sensor which senses the position of a magnet fixed to the movable part 10. In this case, the drive signals use the sensed position as a feedback signal to control the power of the drive signals.

[0062] Loading arrangement

[0063] As shown in Fig. 2, the actuator assembly 1 comprises a loading arrangement 50 (which may also be referred to as a biasing arrangement). The loading arrangement 50 is arranged between the support structure 2 and the movable part 10. The loading arrangement 50 is for loading the helical bearing arrangement 20. Loading the helical bearing arrangement 20 means urging the different parts (e.g. bearing surfaces) of the helical bearing arrangement 20 towards each other.

[0064] If the helical bearing arrangement 20 is not loaded (i.e. is unloaded), then the helical bearing arrangement 20 may not be capable of converting rotation of the movable part 10 into helical movement. If the helical bearing arrangement 20 is not loaded, then the bearing surfaces of a sliding bearing may lose contact with each other and / or bearing surfaces may lose contact with a rolling bearing between the bearing surfaces. By loading the helical bearing arrangement 20, the helical bearing arrangement 20 may guide helical movement of the movable part 10 relative to the support structure 2 around the helical axis 2.

[0065] In the actuator assembly 1 shown in Fig. 2, the loading arrangement 50 comprises a pair of resilient elements 51 (e.g. springs). The resilient elements 51 exert a force that urges the helical bearing arrangement 20 together. The loading arrangement 15 may be provided in a variety of different forms, as explained in further detail below.

[0066] As shown in Fig. 2, optionally each resilient element 51 is disposed (e.g. connected) between the support structure 2 and the movable part 10. The resilient element 51 may comprise a static part 52 that engages with the support structure 2. For example, the static part 52 may be fixed directly to the support structure 2. The resilient element 51 may comprise a moving part 53 that engages with the movable part 10. For example, the moving part 53 may be fixed to the movable part 10.

[0067] As shown in Fig. 2, optionally the moving part 53 of the resilient element 51 and the moving crimp 42 may be provided as an integral component. However, this is not essential. In an alternative arrangement the moving part 53 of the resilient element 51 and the moving crimp 42 may be provided as separate components. The moving part 53 of the resilient element 51 and the moving crimp 42 may both be fixed relative to the movable part 10.

[0068] Unloading torque

[0069] Fig. 3 is a schematic side view of the actuator assembly 1 shown in Fig. 2. The two SMA wires 40 that are the actuator components can be seen in Fig. 3.

[0070] Fig. 3 shows force arrows 45 indicating the direction of forces applied by the SMA wires 40. These are forces that are applied to the movable part 10. The upper force arrow 45 shown in Fig. 3 shows the force applied to the movable part 10 to urge the movable part in the direction from right to left. This force is applied when the SMA wire 40 at the top of Fig. 3 is contracted. At the bottom of Fig. 3 the other force arrow 45 shows the force applied to the movable part 10 by contraction of the SMA wire 40 shown at the bottom of Fig. 3.

[0071] Fig. 3 further shows an unloading torque arrow 46. The unloading torque arrow 46 indicates the general direction of the unloading torque formed by a combination of the force arrows 45 applied by the SMA wires 40 as actuator components. As shown in Fig. 3, optionally the at least one pair of actuator components (e.g. SMA wires 40) is arranged to apply an unloading torque 46 about an axis perpendicular to the helical axis H so as to reduce loading of the helical bearing arrangement 20. In the actuator assembly shown in Fig. 3, the axis about which the unloading torque 46 is applied is an axis that extends into and out from the paper. The axis may be generally perpendicular to the directions of the SMA wires 40 and perpendicular to the helical axis H.

[0072] By providing at the actuator components by an unloading torque so as to reduce loading of the helical bearing arrangement 20, the extent of loading of the helical bearing arrangement 20 may be varied in a controlled manner. For example, when it is desirable to move the movable element 10 along the helical axis H, then the loading of the helical bearing arrangement 20 may be reduced by applying the unloading torque 46. By reducing loading of the helical bearing arrangement 20, the friction in the helical bearing arrangement 20 may be reduced. This allows the movable part 10 to move more freely relative to the support structure 2. Of course, it is desirable for the helical bearing arrangement 10 to remain loaded at least to some extent so that the helical bearing arrangement 20 can continue to convert rotation of the movable part 10 into the helical movement during use of the actuator assembly 1. It is desirable for the unloading torque 46 to be less than the threshold amount which would result in the helical bearing arrangement 20 becoming unloaded.

[0073] By providing that the unloading torque 46 is applied by the actuator components that drive rotation of the movable part 10 and cause the movable part 10 to move helically, the loading of the helical bearing arrangement 20 can be controlled without requiring additional components for controlling the loading of the helical bearing arrangement 20. The actuator components may be provided already in such an actuator assembly 1. The actuator components are controlled in a new way so as to control loading of the helical bearing arrangement 20.

[0074] By providing that the loading of the helical bearing arrangement 20 is reduced by an unloading torque 46 about an axis perpendicular to the helical axis H, the possibility of the unloading torque 46 itself directly resulting in helical movement of the movable part 10 is reduced. For example, if the reduction in loading of the helical bearing arrangement 20 were achieved by applying a force that acts primarily or purely along the helical axis H, then the unloading force itself may cause the movable part 10 to move along the helical axis H. Hence the helical movement of the movable part 10 may be affected in an undesirable way. By providing the unloading torque 46 about the axis perpendicular to the helical axis H, undesirable effects on the helical movement may be reduced. Meanwhile, when helical movement of the movable part 10 is not desired (for example when it is desired for the movable part 10 to maintain its position relative to the support structure 2), the loading of the helical bearing arrangement 20 may be increased. For example, the unloading torque 46 may be reduced so as to reduce any reduction in loading of the helical bearing arrangement 20 caused by the unloading torque 46. By increasing loading of the helical bearing arrangement 20, friction within the helical bearing arrangement 20 may be increased. The friction may help to reduce the amount of power required by the actuator components in order to keep the position of the movable part 10 relative to the support structure 2. It is possible that the power required to maintain the position of the movable part 10 along the helical axis H may be eliminated. In other words, when the actuator components are not actuated, the friction within the helical bearing arrangement 20 may be sufficient to keep the movable part 10 in position relative to the support structure 2. This may be referred to as zero hold power.

[0075] Loading torque

[0076] Fig. 3 further shows loading force arrows 55. The loading force arrows 55 show the forces applied to the movable part 10 by the resilient elements 51 of the loading arrangement 50. For example, the moving part 53 of the resilient element 51 which is engaged with the movable part 10 may urge the movable part 10 by a force that acts generally in parallel with the helical axis H. As shown in Fig. 3, optionally the loading arrangement 50 is arranged to apply a loading torque 56 about an axis perpendicular to the helical axis H for loading the helical bearing arrangement 20. Similarly, Fig. 6 shows loading force arrows 60. The loading force arrows 60 show the forces applied to the movable part 10 by resilient elements (not shown in Fig. 6) of a loading arrangement. As shown in Fig. 6, the loading arrangement is arranged to apply a loading torque for loading the bearing arrangement comprising the bearing surfaces 31, 32.

[0077] As shown in Fig. 3, the forces applied by the resilient elements 51 on the movable part 10 act generally in the directions parallel to the helical axis H. However, the two forces applied by the two resilient elements 51 of the loading arrangement 50 act on either side of the helical axis H. The helical axis H is between the loading force arrows 55. This creates a loading torque 56. The axis about which the loading torque 56 is applied is an axis that extends into and out from the Figure.

[0078] By providing that the loading of the helical bearing arrangement 20 is achieved by a loading torque 56 about an axis perpendicular to the helical axis H, the possibility of the forces that load the helical bearing arrangement 20 undesirably affecting the helical movement is reduced. It is desirable for the forces that load the helical bearing arrangement 20 do not act in a direction that could cause helical movement of the movable part 10 relative to the support structure 2. For example, as shown in Fig. 3 the two loading force arrows 55 for the resilient elements 51 of the loading arrangement 50 act generally in opposite directions to each other. As a result, the overall force in the direction of the helical axis H may be small or even zero. As a result, the loading arrangement 50 itself may not significantly drive helical movement of the movable part 10 relative to the support structure 2. This may help the helical movement of the movable part 10 to be controlled more accurately by controlling rotation of the movable part 10 by the actuator components.

[0079] As shown in Fig. 3, optionally the at least one pair of actuator components (e.g. SMA wires 40) are arranged to apply forces to the movable part 10 relative to the support structure 2 that are offset from each other along the helical axis H. This offset along the helical axis H allows the forces to combine to form the unloading torque 46 about an axis perpendicular to the helical axis H. In the example shown in Fig. 3, the actuator components are SMA wires 40. In such a case, the SMA wires 40 may be arranged to be offset from each other along the helical axis H. The axis about which the unloading torque 46 is applied may be between the forces applied by the actuator components, for example between the SMA wires 40 when the SMA wires 40 are the actuator components. The forces applied by the SMA wires 40 act in the direction of the SMA wires 40.

[0080] As shown in Fig. 3, optionally the at least one pair of actuator components are arranged to apply forces in opposite directions perpendicular to the helical axis H such that the unloading torque 46 can be applied without applying an overall force perpendicular to the helical axis H. The force arrows 45 shown in Fig. 3 generally oppose each other. The force arrows 45 are generally perpendicular to the helical axis H. The force arrows 45 are in the direction of the SMA wires 40 themselves. The SMA wires 40 may be generally perpendicular to the helical axis H. Of course the SMA wires 40 may be oriented at an acute angle relative to the perpendicular to the helical axis H. When the movable part 10 moves along the helical axis H relative to the support structure 2, the angle of orientation of the SMA wires 40 may vary. However, the forces and the SMA wires 40 may remain generally approximately perpendicular to the helical axis H (or at least at an acute angle perpendicular to the helical axis H). Optionally, the forces applied by the SMA wires 40 could be equal to each other in magnitude but applied in opposite directions. This would result in no overall force perpendicular to the helical axis H. However, the unloading torque 46 could still be applied. This means that the loading of the helical bearing arrangement 20 can be controlled without adversely affecting the control of the helical position of the movable part 10 relative to the support structure 2.

[0081] Of course, it may be desirable to apply different forces by the different SMA wires 40. For example, it may be desirable to drive rotation of the movable part 10 so as to move the movable part 10 in the helical direction. Additionally or alternatively, it may be desirable to control a difference in forces applied by the SMA wires 40 in order to counteract other external forces such as gravity.

[0082] Zero hold power

[0083] Zero hold power actuators have a benefit of using no power when holding a position. This is a particularly large advantage for devices that have limited power (e.g. a limited peak power) and / or energy (e.g. a limited average power). For example, wearables may have limited power and / or energy. Other battery powered devices may similarly have limited power and / or energy available.

[0084] It may be desirable for a bearing arrangement, for example the helical bearing arrangement 20, to have high friction to provide the friction to hold against inertial roads. The helical bearing arrangement 20 is generally good at resisting linear forces caused by shocks, for example. Such a linear force may increase friction on one or more of the helical bearings of the helical bearing arrangement 20. This can actually increase the resistance to motion.

[0085] Optionally, a bearing arrangement is arranged to have sufficient friction when loaded that the movable part 10 remains in position when the actuator components are not driving rotation of the movable part 10. This allows the power and energy requirements of the actuator assembly 1 to be reduced while allowing the position of the movable part 10 to be controlled and maintained. For example, the actuator assembly 1 may be used in the context of an autofocus function of a camera. It may be desirable to maintain a focussed position of the movable part 10 relative to the support structure 2 between shots taken by the camera.

[0086] Optionally, the bearing arrangement is arranged to have sufficient friction when loaded that the movable part 10, over a continuum of positions, remains in position when the actuator components are not driving rotation of the movable part 10. This may allow the movable part 10 to be controlled to maintain any arbitrary position relative to the support structure 2. This is an improvement over ratchettype systems which may maintain the position of a component but only at a set of discrete intervals. The friction within the bearing arrangement may allow the movable part 10 to be kept at any of a continuum of positions.

[0087] Optionally, the loading arrangement 50 is arranged to load the bearing arrangement so as to generate frictional forces therein that constrain the movement of the movable part 10 relative to the support structure 2 at any position within a range of movement when the actuator components are not actuated. The constraining of the movable part 10 may be such that the position of the movable part 10 is maintained relative to the support structure 2. Once a desirable position of the movable part 10 has been found, it is not necessary to again control the movement of the movable part 10 in order to maintain that desirable position for a subsequent process (e.g. taking of a photograph with a camera).

[0088] Optionally, the actuator components are arranged, on actuation, to apply the unloading torque 46 so as to reduce the frictional forces in the bearing arrangement. As shown in Fig. 3, the unloading torque 46 counteracts the loading torque 56. The loading torque 56 of the unloading torque 46 may be about the same axis perpendicular to the axis O. The unloading torque 46 acts to cancel out part of the loading torque 56. Of course, the loading torque 56 may overall remain greater than the unloading torque 46 such that the bearing arrangement remains loaded, at least to an extent. By reducing the frictional forces in the bearing arrangement, the ease of movement of the movable part 10 relative to the support structure 2 may be controlled. For example, when it is desirable to maintain the position of the movable part 10, the friction can be increased by reducing the unloading torque 46. When it is desirable to move the movable part 10, then the unloading torque 46 may be increased so as to reduce the friction within the bearing arrangement.

[0089] Bearing arrangement

[0090] The bearing arrangement may take a variety of forms. For example, the bearing arrangement may be a helical bearing arrangement. Alternatively, the bearing arrangement may be linear or curved, for example.

[0091] One possibility is that the bearing arrangement comprises one or more bearings 30 that are rolling bearings, an example of which is shown in Fig. 4. In Fig. 4, the bearing 30 comprises a pair of bearing surfaces 31 and 32 and plural rolling bearing elements 33, for example balls, disposed between the bearing surfaces 31 and 32. One of the bearing surfaces 31 and 32 is provided on the support structure 2 and the other of the bearing surfaces 31 and 32 is provided on the movable part 10.

[0092] The helical bearing 30 guides the movement of the movable part 10 with respect to the support structure 2 as shown by the arrow M. The movement may be helical. This may be achieved by the bearing surfaces 31 and 32 extending helically around the helical axis H, that is following a line that is helical. That said, in practical embodiments, the length of the bearing surfaces 31 and 32 may be short compared to the distance of the bearing surfaces 31 and 32 from the helical axis H, such that their shape is close to straight or even each being straight, provided that the one or more helical bearings of the helical bearing arrangement 20 guide helical movement of the movable part 10 with respect to the support structure 2. Plural helical bearings 30 are typically present, located at different angular positions around the helical axis H, in which case the helical bearings 30 have different orientations so that they cooperate and maintain adequate constraints to guide the helical movement of the movable part 10 with respect to the support structure 2, even if the bearing surfaces 31 and 32 of an individual helical bearing 30 are straight.

[0093] In the example of Fig. 4, the bearing surfaces 31 and 32 each comprise respective grooves 34 and 35 in which the rolling bearing elements 33 are seated. In this example, the grooves 34 and 35 constrain transverse translational movement of the movable part 10 with respect to the support structure 2, that is transverse to the direction of movement shown by arrow M. The grooves shown in Fig. 4 are V- shaped in cross-section, but other cross-sections are possible, for example curved as in portions of a circle or an oval. In general, the grooves 34 and 35 provide two points of contact with the respective rolling bearing elements 33. The grooves 34 and 35 may extend helically. Alternatively, in practical embodiments, the length of the bearing surfaces 31 and 32 may be short compared to the distance of the bearing surfaces 31 and 32 from the helical axis H, in which case the grooves 34 and 35 may be straight or close to straight, provided that the one or more helical bearings 30 of the helical bearing arrangement 20 guide helical movement of the movable part 10 with respect to the support structure 2.

[0094] Another possibility is that the bearing arrangement comprises one or more bearings 30 that are sliding bearings. In the example of Fig. 6, the bearing surface 32 comprises a groove. The other bearing surface 31 comprises a ridge. The ridge is complementary to the groove. In this example, the groove and the ridge constrain transverse translational movement of the movable part 10 with respect to the support structure 2. The groove and the ridge shown in Fig. 6 are V-shaped in cross-section, but other crosssections are possible, for example curved as in portions of a circle or an oval. In general, the bearing surfaces 31, 32 provide a point of contact.

[0095] Fig. 5 illustrates a possible helical bearing arrangement that includes three helical bearings 71, 72 and 73 only. Optionally the three helical bearings 71, 72 and 73 are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

[0096] Optionally the first and second helical bearings 71 and 72 are of the same type as the helical bearing 30 shown in Fig. 8 wherein the bearing surfaces 31 and 32 each comprise respective groove 34 and 35.

[0097] The third helical bearing 73 is of the same type as the helical bearing 30 shown in Fig. 9 wherein the first bearing surface 31 comprises a groove 36 in which the rolling bearing element 33 is seated and the second bearing surface 32 is planar. Fig. 5 illustrates the case that the first bearing surface 31 of the third helical bearing 73 is on the movable part 10, but it could alternatively be on the support structure 2. Each of the three helical bearings 71, 72 and 73 may comprise a single rolling or plural bearing elements 33. This is possible because the constraints imposed by the three helical bearings 71, 72 and 73, and in particular the grooves of the first and second helical bearings 71 and 72 are sufficient to constrain the movement of the movable part 10 with respect to the support structure 2 in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element 33 in each of the three helical bearings 71, 72 and 73, the overall size of the three helical bearings 71, 72 and 73, and in particular the height of the three helical bearings 71, 72 and 73 projected along the helical axis H is reduced.

[0098] Optionally, one or more of the helical bearings shown in Fig. 5 may be replaced with one or more sliding bearings. For example, a sliding bearing may comprise a groove in one of the support structure 2 and the movable part 10, with a complementarily shaped member in the other of the support structure 2 and the movable part 10. This may provide sufficient constraints to constrain movement of the movable part 10 with respect to the support structure 2 in degrees of freedom other than the helical movement.

[0099] Optionally the at least one pair of actuator components is arranged to reduce loading of the helical bearing arrangement 20 by less than the loading applied by the loading arrangement 50. This allows the helical bearing arrangement 20 to continue to convert the rotation of the movable part 10 accurately into the helical movement.

[0100] Multiple moving parts

[0101] Optionally, the actuator assembly comprises a plurality of movable parts 10. For example, the actuator assembly 1 may comprise a plurality of actuator sub-assemblies. Each actuator sub-assembly may have the features and characteristics of an actuator assembly 1 described elsewhere in this document. In particular, each actuator sub-assembly may comprise a support structure 2, a movable part 10, a bearing arrangement 30 arranged to guide movement of the movable part 10 relative to the support structure 2, and at least one actuator component (e.g. SMA wire 40) arranged, on actuation, to drive movement of the movable part 10 relative to the support structure 2.

[0102] Fig. 7 is a plan view of an actuator assembly comprising a plurality of actuators sub-assemblies. The movable parts 10 of the actuator sub-assemblies are shown. As shown in Fig. 7, optionally the actuator assembly 1 comprises three actuator sub-assemblies, each comprising a respective movable part 10. Alternatively, an actuator assembly 1 may comprise two actuator sub-assemblies or more than three actuator sub-assemblies. In the arrangement shown in Fig. 7, the movable part 10 of each actuator sub-assembly is generally cylindrical. The movable part 10 may have features as described elsewhere in this document, and as shown in Fig. 1, Fig. 5 and Fig. 6, for example. In the arrangement shown in Fig. 7, a first actuator subassembly comprises a first movable part 10a. A second actuator sub-assembly comprises a second movable part 10b. A third actuator sub-assembly comprises a third movable part 10c.

[0103] As shown in Fig. 7, optionally the movable parts 10 overlap each other. When viewed along the axis O, the first movable part 10a overlaps with the second movable part 10b at an overlapping region 70. Similarly, the second movable part 10b overlaps partially with the third movable part 10c. Similarly, the third movable part 10c overlaps partially with the first movable part 10a.

[0104] Fig. 8 is a perspective view of part of the first movable part 10a and the second movable part 10b. As shown in Fig. 8, in the overlapping region 70, part of the first movable part 10a is above part of the second movable part 10b. As shown in Fig. 8, there may be a gap in the axial direction between the first movable part 10a and the second movable part 10b with in the overlapping region 70. Optionally, the first movable part 10a and the second movable part 10b are arranged such that they do not directly contact each other during use of the actuator assembly 1. There may be sufficient space and gaps provided such that during movement of the movable parts 10, they do not interfere with each other.

[0105] Fig. 9 is a schematic side view of the first movable part 10a and the second movable part 10b shown in Fig. 7 and Fig. 8. Fig. 9 is a cross-sectional view cutting through the cylinders of the first movable part 10a and the second movable part 10b. The overlapping region 70 is shown in the middle of Fig. 9. In the overlapping region 70, part of the first movable part 10a is shown above the second movable part 10b.

[0106] Loading between movable parts

[0107] Fig. 9 shows force arrows 60, 61 corresponding to forces applied for loading the bearing arrangements 30. The force arrow 60 shown at the left-hand side of Fig. 9 is for loading the bearing surfaces 31, 32 for the first movable part 10a. The force arrow 60 shown at the right-hand side of Fig. 9 is for loading the bearing surfaces 31, 32 for the bearing arrangement of the second movable part 10b. The force arrows 61 shown in the middle of Fig. 9 represent forces between the first movable part 10a and the second movable part 10b.

[0108] As shown in Fig. 9, optionally the actuator assembly 1 comprises a loading arrangement arranged between the movable part 10a of the first actuator sub-assembly and the movable part 10b of the second actuator sub-assembly. The loading arrangement may be for loading the bearing arrangement 30 of the first actuator sub-assembly. For example, the force arrow 61 shown at the top of Fig. 9 represents a force urging the right-hand side of the first movable part 10a downwards. This contributes to a torque for urging the first movable part 10a into engagement with the support structure 2 via the bearing arrangement 30. Additionally or alternatively, the loading arrangement may be for loading the bearing arrangement 30 of the second actuator sub-assembly. The force arrow 61 shown at the bottom of Fig. 9 represents a force for contributing to a torque applied to the second movable part 10b. The torque applied to the second movable part 10b loads the bearing arrangement 30 for the second movable part 10b.

[0109] The loading arrangement being between the movable parts 10a, 10b means that the loading arrangement is arranged to apply a force between the movable parts 10a, 10b. The loading arrangement may be located physically between the movable parts 10a, 10b. Alternatively, the loading arrangement may be partly embedded in one or both of the movable parts 10a, 10b, or may be located beyond a gap between the movable parts 10a, 10b.

[0110] Loading forces may be applied for loading the bearing arrangements 30. The loading forces may be applied directly between neighbouring (e. g. adjacent) movable parts 10. By applying the loading forces directly between multiple movable parts 10, loading forces applied between a movable part 10 and a static element may be reduced. This may reduce the space required for the loading arrangement. The number of components required for manufacturing the actuator assembly 1 may be reduced.

[0111] For example, as explained above, the force arrows 60 may correspond to forces that are applied by an element such as a spring between the movable part 10 and a static element (i.e. a component that has a fixed position relative to the support structure 2). Comparing Fig. 9 to Fig. 6, it can be seen that one of the force arrows 60 shown in Fig. 6 is replaced by a different force arrow 61 in Fig. 9. The different force arrow 61 is for a force applied directly between the movable parts 10a, 10b. A corresponding force arrow 61 represents a corresponding force applied to the second movable part 10b. The forces corresponding to the force arrows 61 may be applied by the same arrangement, rather than requiring separate arrangements for a force on each of the movable parts 10a, 10b. Accordingly, the number of components may be reduced. The space taken up by the loading arrangement may be reduced. The actuator assembly 1 may be more compact.

[0112] As shown in Fig. 9, the loading arrangement is arranged to apply a loading force between the movable part 10a of the first actuator sub-assembly and the movable part 10b of the second actuator subassembly. The force can be applied between the movable parts 10a, 10b directly. Optionally, the force applied between the movable parts 10a, 10b contributes to friction of the bearing arrangement. Optionally, the friction is sufficient when the bearing arrangement is loaded that the movable part 10 remains in position when the at least one actuator component (e.g. SMA wire 40) is not driving the movable part 10. In other words, the loading force supplied between the movable parts 10a, 10b, may be used in the context of a zero hold power assembly as described above. For example, optionally the loading arrangement is arranged to load the bearing arrangement 30 of the first actuator sub-assembly so as to generate friction or forces therein that constrain the movement of the movable part 10a of the first actuator sub-assembly relative to the support structure 2 at any position within a range of movement when the at least one actuator component of the first actuator sub-assembly is not actuated. Optionally, the at least one actuator component of the first actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement 30 of the first actuator sub-assembly.

[0113] Additionally, or alternatively, the loading arrangement may be arranged to load the bearing arrangement 30 of the second actuator sub-assembly so as to generate frictional forces therein that constrain the movement of the movable part 10b of the second actuator sub-assembly relative to the support structure 2 at any position within a range of movement when the at least one actuator component of the second actuator sub-assembly is not actuated. Optionally, the at least one actuator component of the second actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement 30 of the second actuator sub-assembly.

[0114] Optionally, the support structure 2 of a plurality of the actuator sub-assemblies are fixed relative to each other. The support structure 2 of a first actuator sub-assembly may have a fixed location relative to the support structure 2 of a second actuator sub-assembly. Optionally, the support structures 2 of all of the sub-assemblies have a fixed position relative to each other. For example, the support structures 2 may be secured to each other. Alternatively, the support structures 2 may be formed integrally with each other. In other words, there may be a single support structure 2 for a plurality of actuator subassemblies. Even when the support structure 2 is the same between a plurality of actuator subassemblies, the movable parts 10 are separate from each other. The movable parts 10 of the actuator sub-assemblies are independently movable.

[0115] Magnetic loading arrangement

[0116] As shown in Fig. 9, optionally the loading arrangement comprises a magnetic loading arrangement. For example, magnets 80 may be provided for applying the loading forces directly between the first movable part 10a and the second movable part 10b. As shown in Fig. 9, optionally the magnets 80 may be embedded within the movable parts 10. Alternatively, the magnets 80 may be mounted to a surface of the movable parts 10. For example, the magnets 80 may be mounted to opposing (i.e. facing) surfaces of the movable parts 10a, 10b. The magnets 80 may be attracting magnets so as to apply an attractive force between the first movable part 10a and the second movable part 10b. the magnets 80 may be located on opposite sides of a gap between the first movable part 10a and the second movable part 10b within the overlapping region 70.

[0117] Resilient loading arrangement

[0118] Fig. 10 is a schematic view of a resilient loading arrangement 90. The resilient loading arrangement 90 is for resiliently loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly. As shown in Fig. 10, optionally the resilient loading arrangement 90 comprises a plurality of resilient elements 91-96. The resilient elements 91-96 are between the movable part 10a of the first actuator sub-assembly and the movable part 10b of the second actuator sub-assembly.

[0119] As shown in Fig. 10, a single component may be provided for applying the loading forces to a plurality (e.g. 3) movable parts 10a, 10b, 10c. Optionally, each of the resilient elements 91-96 is configured to contact one of the movable parts 10a, 10b, 10c. Each resilient element 91-96 is configured to apply a loading force or urging the movable part 10 onto its bearing arrangement. The resilient elements 91-96 are configured to load the bearing arrangements.

[0120] For example, optionally the first resilient element 91 is configured to apply a force on the first movable part 10a. This is shown in Fig. 11. Fig. 11 is a schematic side view of the first resilient element 91 and the second resilient element 92 of the resilient loading arrangement 90 shown in Fig. 10. As shown in Fig. 11, the first resilient element 91 is in contact with the first movable element 10a within the overlapping region 70. The first resilient element 91 may be secured to the first movable part 10a. For example, the first resilient element 91 may be adhered (e.g. glued) to the first movable part 10a. The first resilient element 91 may be in contact with a surface of the first movable part 10a that faces in the axial direction. As shown in Fig. 11, optionally the second resilient element 92 is configured to apply a loading force to the second movable part 10b. For example, the second resilient element 92 may be secured to a surface of the second movable part 10b.

[0121] Optionally, the resilient loading arrangement 90 shown in Fig. 10 is substantially plainer when not in use. For example, the component may be formed from a sheet of material (e.g. metal or plastic). When the actuator assembly 1 is manufactured, the resilient elements 91-96 of the resilient loading arrangement 90 may be secured to surfaces of the movable parts 10a, 10b, 10c. In use, the resilient element 91-96 may be stressed. For example, as shown in Fig. 11, the first resilient element 11 is bent upwards due to it being secured to the first movable part 10a. The first resilient element 91 applies a force pulling the first movable part 10a downwards (i.e. towards the second movable part 10b).

[0122] Similarly, the second resilient element 92 is bent downwards in Fig. 11 due to it being secured to the second movable part 10b. The second resilient element 92 applies a force pulling the second movable part 10b upwards, (i.e. towards the first movable part 10a).

[0123] The other resilient element 93-96 may be configured to apply loading forces to the movable parts 10a, 10b, 10c in corresponding fashion. In particular, optionally the third resilient element 93 is configured to apply a force pulling the second movable part 10b towards the third movable part 10c in an overlapping region between the second movable part 10b and the third movable part 10c. The fourth resilient element 94 may be configured to pull the third movable part 10c towards the second movable part 10b in that overlapping region.

[0124] Similarly, the fifth resilient element 95 may be configured to pull the third movable part 10c downwards towards the first movable part 10a in an overlapping region between the third movable part 10c and the first movable part 10a. The sixth resilient element 96 may be configured to pull the first movable part 10a upwards towards the third movable part 10c in that overlapping region.

[0125] The resilient elements 91-96 may be referred to as arms. Each of the six arms may be attached to a corresponding movable part. Adjacent arms may be configured to apply opposing forces to adjacent movable parts 10.

[0126] SMA wire

[0127] The above-described actuator assembly 1 comprises actuator components. Optionally the actuator components are SMA elements, for example SMA wires. The term SMA wire may refer to any element comprising SMA. The SMA wire may have any shape that is suitable for the purposes described herein. The SMA wire may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA wire. It is also possible that the length of the SMA wire (however defined) may be similar to one or more of its other dimensions. The SMA wire may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two elements, the SMA wire can apply only a tensile force which urges the two elements together. In other examples, the SMA wire may be bent around an element and can apply a force to the element as the SMA wire tends to straighten under tension. The SMA wire may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA wire may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA wire may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA wire' may refer to any configuration of SMA wire acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA wire may comprise two or more portions of SMA wire that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA wire may be part of a larger piece of SMA wire. Such a larger piece of SMA wire might comprise two or more parts that are individually controllable, thereby forming two or more SMA wires.

[0128] Other variations

[0129] It will be appreciated that there may be many other variations of the above-described examples.

[0130] For example, the actuator assembly 1 may comprise a mixture of sliding bearing and rolling bearings. As a further alternative the bearing arrangement may comprise a flexure arrangement.

[0131] It is not essential for the movable parts 10 to overlap with each other. Fig. 12 shows an alternative actuator assembly 1 comprising a plurality of movable parts 10a, 10b, 10c. As shown in Fig. 12, optionally the movable parts 10a, 10b, 10c are non-overlapping. When viewed along the axis O, the first movable part 10a is distanced from the second movable part 10b. Similarly, the second movable part 10b is distanced from the third movable part 10c. Similarly, the third movable part 10c is distanced from the first movable part 10a.

[0132] As shown in Fig. 12, optionally the movable parts 10a, 10b, 10c are relatively closely spaced to each other. The gaps between the movable parts 10 may be relatively small. For example, the spaces between the movable parts 10 may be less than the dimension of the movable parts themselves. In particular, the gap between the first movable part 10a and the second movable part 10b when viewed along the axis O, may be smaller than the diameter of the first movable part 10a or the diameter of the second movable part 10b. Optionally, the gap between the adjacent movable parts 10a, 10b is less than 0.5, optionally less than 0.2 and optionally less than 0.1 of the diameter of each of the individual movable parts 10a, 10b.

[0133] Optionally, the construction of each movable part 10 is substantially the same. Alternatively, the movable parts 10a, 10b, 10c may have different sizes or may be formed from different materials, for example.

[0134] Fig. 13 is a schematic view of a resilient loading arrangement 90 for the movable parts 10 shown in Fig.

[0135] 12. The resilient loading arrangement 90 shown in Fig. 13 is similar to the resilient loading arrangement

[0136] 90 shown in Fig. 10. Accordingly, the function of the resilient elements 91-96 are not repeated below. In the resilient loading arrangement 90 of Fig. 13, the resilient elements 91-96 may be spaced further apart from each other compared to in the resilient loading arrangement 90 shown in Fig. 10. This may allow larger resilient elements 91-96 to be used. This may help to increase the force that the resilient elements 91-96 can apply for loading the bearing arrangements.

[0137] As described above, optionally the loading forces applied between the movable parts 10a, 10b generally act to urge the movable parts 10a, 10b towards each other. However, this is not necessarily the case. Fig. 14 shows an alternative arrangement in which the loading arrangement between the first movable part 10a and the second movable part 10b acts to urge the movable parts 10a, 10b away from each other. This is indicated by the direction of the force arrows 61 in Fig. 14.

[0138] As shown in Fig. 14, optionally the loading arrangement comprises repulsive magnets 80. The magnets 80 repel each other, thereby generating the forces corresponding to the force arrows 61.

[0139] Alternatively, the loading arrangement may be a resilient loading arrangement. The resilient loading arrangement may be configured to urge the movable parts 10a, 10b away from each other. For example, a resilient loading arrangement 90 of the type shown in Fig. 10 or Fig. 13 may be pre-stressed such that the resilient elements 91-96 urge the movable parts 10a, 10b generally away from each other. For example, the first resilient element 91 and the second resilient element 92 may be bent before the actuator assembly is manufactured to have a greater curve shown in Fig. 11. As a result, when the actuator assembly 1 is assembled, the resilient elements 91, 92 act to urge the movable parts 10a, 10b away from each other.

[0140] As mentioned above, the support structure 2 may have an image sensor 3 mounted thereon. The lens element may be arranged to focus an image on the image sensor 3. Alternatively, the support structure 2 may have a display mounted thereon. The lens element may be arranged to focus an image on the display. Additionally or alternatively, the support structure 2 may have a light source mounted thereon. The lens element may be arranged to focus light from the light source.

[0141] Alternatively, the support structure 2 may have at least one lens element mounted thereon. The movable parts 10 may comprise respective image sensors. The at least one lens element may be arranged to focus images on the image sensors.

[0142] A head-mounted display may comprise the actuator assembly 1. A pair of virtual or augmented reality glasses may comprise the actuator assembly 1. Fig. 15 shows a schematic view of an alternative arrangement. In the arrangement shown in Fig. 15, the bearing arrangements are linear. In particular, magnets 80 may be arranged to attract between adjacent movable parts 10a, 10b. Each movable part 10a, 10b is in contact with a corresponding surface 106a, 106b. The movable part 10 is arranged to move in the left-right direction shown in Fig. 15 along the corresponding surface 106. The magnets load the movable part 10 onto the corresponding surface 106.

[0143] The SMA wires 40 are arranged, on contraction, to reduce the friction between the movable part 10 and the surface 106. The support structures 2 may be connected to each other or may be formed integrally with each other. Although magnets 80 are shown in Fig. 15, alternatively a resilient loading arrangement may be provided for loading the bearings.

Claims

Claims1. An actuator assembly comprising: a plurality of actuator sub-assemblies, each actuator sub-assembly comprising: a support structure; a movable part; a bearing arrangement arranged to guide movement of the movable part relative to the support structure; and at least one actuator component arranged, on actuation, to drive the movable part relative to the support structure; and a loading arrangement arranged to apply a loading force between the movable part of a first actuator sub-assembly of the actuator sub-assemblies and the movable part of a second actuator subassembly of the actuator sub-assemblies for loading the bearing arrangement of the first actuator subassembly and / or the bearing arrangement of the second actuator sub-assembly.

2. An actuator assembly of claim 1, wherein the loading arrangement is located between the movable part of the first actuator sub-assembly and the movable part of the second actuator subassembly.

3. An actuator assembly according to claim 1 or 2 wherein the at least one actuator component is arranged to apply an unloading force so as to reduce loading of the corresponding bearing arrangement.

4. An actuator assembly according to any preceding claim, wherein the bearing arrangement is arranged to have sufficient friction when loaded that the movable part remains in position when the at least one actuator component is not driving the movable part.

5. An actuator assembly according to claim 4, wherein the bearing arrangement is arranged to have sufficient friction when loaded that the movable part, over a continuum of positions, remains in position when the at least one actuator component is not driving the movable part.

6. An actuator assembly according to any preceding claim, wherein the loading arrangement is arranged to load the bearing arrangement of the first actuator sub-assembly so as to generate frictional forces therein that constrain the movement of the movable part of the first actuator sub-assembly relative to the support structure at any position within a range of movement when the at least one actuator component of the first actuator sub-assembly is not actuated.

7. An actuator assembly according to claim 6, wherein the at least one actuator component of the first actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement of the first actuator sub-assembly.

8. An actuator assembly according to any preceding claim, wherein the loading arrangement is arranged to load the bearing arrangement of the second actuator sub-assembly so as to generate frictional forces therein that constrain the movement of the movable part of the second actuator subassembly relative to the support structure at any position within a range of movement when the at least one actuator component of the second actuator sub-assembly is not actuated.

9. An actuator assembly according to claim 8, wherein the at least one actuator component of the second actuator sub-assembly is arranged, on actuation, to reduce the frictional force in the bearing arrangement of the second actuator sub-assembly.

10. An actuator assembly according to any preceding claim, wherein the at least one actuator component is arranged to reduce loading of the bearing arrangement by less than the loading applied by the loading arrangement.

11. An actuator assembly according to any preceding claim, wherein the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly is a helical bearing arrangement arranged to guide movement of the movable part relative to the support structure around a helical axis.

12. An actuator assembly according to claim 11, wherein the loading arrangement is arranged to apply a loading torque about an axis perpendicular to the helical axis for loading the helical bearing arrangement.

13. An actuator assembly according to claim 11 or 12, wherein the at least one actuator component is arranged to apply an unloading torque about an axis perpendicular to the helical axis so as to reduce loading of the corresponding bearing arrangement.

14. An actuator assembly according to any preceding claim, wherein the loading arrangement comprises a resilient loading arrangement for resiliently loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly.

15. An actuator assembly according to claim 14, wherein the resilient loading arrangement comprises at least one resilient element disposed between the movable part of the first actuator subassembly and the movable part of the second actuator sub-assembly.

16. An actuator assembly according to claim 14 or 15, wherein the resilient loading arrangement comprises at least one resilient element between the movable part of the first actuator sub-assembly and the movable part of the second actuator sub-assembly, wherein the resilient element is stressed in its mounted position disposed between the movable part of the first actuator sub-assembly and the movable part of the second actuator sub-assembly so as to load the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the second actuator sub-assembly.

17. An actuator assembly according to any preceding claim, wherein the loading arrangement comprises a magnetic loading arrangement.

18. An actuator assembly according to any preceding claim, wherein the at least one actuator component is arranged, on actuation, to drive rotation of the movable part relative to the support structure about an axis parallel to a primary axis defined by the actuator assembly.

19. An actuator assembly according to claim 18, wherein the movable part of the first actuator subassembly and the movable part of the second actuator sub-assembly overlap when viewed along the primary axis.

20. An actuator assembly according to any preceding claim comprising at least three of the actuator sub-assemblies, wherein the loading arrangement is arranged between the movable part of the first actuator sub-assembly and the movable part of a third actuator sub-assembly of the actuator subassemblies for loading the bearing arrangement of the first actuator sub-assembly and / or the bearing arrangement of the third actuator sub-assembly.

21. An actuator assembly according to claim 20, wherein the loading arrangement is arranged between the movable part of the second actuator sub-assembly and the movable part of the third actuator sub-assembly for loading the bearing arrangement of the second actuator sub-assembly and / or the bearing arrangement of the third actuator sub-assembly.

22. An actuator assembly according to any preceding claim, wherein the actuator component of at least one of the actuator sub-assemblies is a shape memory alloy, SMA, element.

23. An actuator assembly according to any preceding claim, wherein the movable part is a lens element comprising at least one lens.

24. An actuator assembly according to claim 23, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

25. An actuator assembly according to claim 23, wherein the support structure has a display mounted thereon, the lens element being arranged to focus light emitted by the display.

26. An actuator assembly according to any preceding claim, wherein the movable part has an image sensor mounted thereon.

27. An actuator assembly according to claim 26, wherein the support structure comprises a lens element comprising at least one lens, the lens element being arranged to focus an image on the image sensor.

Images