Blade for variable aperture assembly

Abstract

A blade 40 for a variable aperture assembly (VA) or iris where the blade connects to a base and to a rotatable part via a first 21 and second 31 protrusion. The blade is configured to resiliently defo

Description

Field The present application relates to a blade, a variable aperture (VA) assembly and a camera assembly. Background There are a variety of apparatuses in which it is desired to provide control of a movable element. SMA elements, for instance SMA wires, may be advantageous as actuators in such apparatuses, for example due to their high energy density which means that the SMA actuator required to apply a given force to the movable element can be relatively small. One type of apparatus in which SMA wire is known for use as an actuator is in miniature cameras, for example those used in smartphones or other portable electronic devices. WO2011 / 104518 discloses examples of SMA actuation apparatuses which are suitable for use in miniature cameras. A VA assembly can be used to provide an aperture of a controlled size. For example, in the context of a camera, a VA assembly may be used to control the size of the aperture. For example, different aperture sizes may be used for different focal lengths. A VA assembly may comprise blades that move so as to define the VA. Variable aperture assemblies within a camera may use SMA elements (for instance, SMA wires) to move the blades so as to adjust the size of the variable aperture. An example of such a variable aperture assembly is disclosed in WO2024 / 057042: the variable aperture assembly comprises a base, a rotatable part, and an actuator assembly configured to drive rotation of the rotatable part relative to the base about a primary axis to any rotational position within a range of movement. The actuator assembly includes at least one SMA element coupled between the base and the rotatable parts. A plurality of blades is connected to the base and the rotatable part. Rotation of the rotatable part drives rotation of each blade of the plurality of blades to change the size of the variable aperture. Typically, each blade of a variable aperture assembly is driven by a drive element such as pin or other protrusion. For instance, each blade may be driven by a first pin formed on the base and a second pin formed on the rotatable part. The first and second pins interface with the blades via holes or slots formed in each blade. Due to manufacturing tolerances for the base and the rotatable (particularly the pins) and also for the holes or slots formed in the blades, there will be backlash (that is, a degree of play between the various parts) in the variable aperture assembly. As an example, a hole or slot may be larger than the corresponding pins (which typically is the case partly due to the previously mentioned manufacturing tolerances, and partly also to facilitate assembly of the variable aperture assembly). For a set position of the rotatable part and the base, the corresponding blade position for each blade may differ from one another. This backlash reduces the accuracy and reproducibility of the aperture size. Furthermore, as well as reducing the accuracy of the aperture diameter, the shape of the aperture may be less accurate if the backlash differs between blades. This problem of backlash is pronounced for systems with higher gearing to move the blades. SMA driven variable aperture assemblies, such as those disclosed in WO2024 / 057042, typically include high gearing due to the limited stroke length deliverable by an SMA actuator, which results in a limited range of motion of the rotatable part relative to the base. This invention details options that can used to mitigate against this backlash. It is desirable to reduce the possibility of the blades being out of position (e.g. for circularity and / or concentricity of the VA), particularly without unduly increasing the difficulty of manufacturing and / or assembling a VA assembly. It is an aim of certain embodiments of the present invention to provide a variable aperture assembly that is less affected by backlash than previous variable aperture assemblies. Consequently, it is an aim of certain embodiments of the present invention to provide a variable aperture assembly in which the size and shape of the aperture can be more accurately controlled. Summary According to an aspect of the present invention, there is provided a blade for a VA assembly comprising a base and a rotatable part, wherein the blade is configured to be connectable to the base via a first protrusion, and connectable to the rotatable part via a second protrusion, wherein the blade is configured to resiliently deform to bias the second protrusion and the first protrusion relative to each other. Advantageously, by configuring the blade to resiliently deform to bias the protrusions relative to each other, the problem of backlash in a VA mechanism can be mitigated. The result is that for a given relative position of rotatable part and base, the angular position of each blade is more closely similar to one another. Accordingly, the shape of the aperture will be rendered more accurately (that is, more evenly rotationally symmetrical) and the size of the aperture will be more accurately and consistently set. By providing that the blade provides the biasing, there is greater design freedom for other components of the VA assembly. For example, it may not be necessary to provide the base and the rotatable part with biasing features. It can be difficult to manufacture such a base and rotatable part with biasing features. It can be difficult to assemble the VA assembly when the base or rotatable part is provided with biasing features. An embodiment of the invention is expected to make it easier to manufacture and / or assemble a VA assembly. Optionally, the blade is configured to resiliently deform so as to accommodate a change in distance between the second protrusion and the first protrusion. By accommodating the change in distance, the blades may be kept in continuous engagement with the base and the rotatable part. This can help to improve the accuracy with which movement of the blades can be controlled. This can help to improve the position and / or shape of the VA defined by the blades. Optionally, the blade comprises an engaging arm configured to accommodate a change in distance between the second protrusion and the first protrusion. Optionally, the blade is configured such that the engaging arm moves toward a main body of the blade as the distance increases. Optionally, the blade is configured such that the engaging arm moves away from a main body of the blade as the distance increases. Optionally, the engaging arm comprises a flexure arm. Optionally, the engaging arm is configured to engage with the first protrusion and / or the second protrusion. The blade itself can provide for biasing of the blades relative to the base and the rotatable part. The engaging arm provides a mechanically simple way of providing the biasing force. The blade comprising the engaging arm may be manufactured cheaply and easily. Optionally, the blade comprises at least one edge configured to engage with the first protrusion and at least one edge configured to engage with the second protrusion. The edges allow the flexibility of the blade to be used to provide the biasing force. Meanwhile by engaging with the edges, the blades may have sufficient stiffness to reliably function to define the VA, i.e. without buckling. Optionally, the at least one edge configured to engage with the first protrusion is curved around the first protrusion and / or the at least one edge configured to engage with the second protrusion is curved around the second protrusion. The curvature may help to reduce undesirable wear between the blades and the protrusions. This can help to reduce the possibility of undesirable deformation of the components and can help to reduce the possibility of particles being generated which could otherwise interfere with the VA mechanism. Optionally, the at least one edge configured to engage with the first protrusion faces away from the at least one edge configured to engage with the second protrusion. Optionally, the blade is configured to bias the second protrusion and the first protrusion away from each other. The biasing force may add to the actuation force urging the blades to the maximum size and the minimum size of the VA. The biasing force may help the actuator towards the ends of the actuation stroke. This can improve the accuracy of control of the VA. Optionally, the at least one edge configured to engage with the first protrusion faces toward the at least one edge configured to engage with the second protrusion. Optionally, the blade is configured to bias the second protrusion and the first protrusion toward each other. The biasing force may help the VA assembly to be more stable when the VA has a medium size. Optionally, the blade comprises the first protrusion and / or the second protrusion. Optionally, the first protrusion and / or the second protrusion are secured to a main body of the blade or are formed integrally as part of the blade. The protrusions may couple with holes in the base and the rotatable part. The design of the base and the rotatable part may be simplified. This may help to reduce the cost of manufacturing the VA assembly. According to another aspect of the invention, there is provided a blade for a variable aperture assembly comprising a base and a rotatable part, wherein the blade is configured to be connectable to the base via a first protrusion, and connectable to the rotatable part via a second protrusion; and wherein the blade comprises a single first slot configured to receive the first and second protrusions, the blade being configured to resiliently deform such that edge portions of the first slot maintain contact between the blade and the first and second protrusions as the rotatable part rotates relative to the base. At least a part of a first edge of the first slot may be defined by a first resilient beam formed between the first slot and a second slot, the first resilient beam being configured to deform to accommodate one or both of the first and second protrusions within the first slot. At least a part of a second edge of the first slot opposite to the first edge may be defined by a second resilient beam formed between the first slot and a third slot, the second resilient beam being configured to deform to accommodate one or both of the first and second protrusions within the first slot. At least one resilient beam may be fixed at both ends to the blade so that the first slot is separated from the respective second or third slot. At least one resilient beam may be fixed at a first end to the blade and has a free second end so that the first slot communicates with the respective second or third slot. The first slot may be configured such that at least one of the first and second protrusions can slide within the first slot so as to accommodate a change in distance between the first protrusion and the second protrusion. An edge portion of the first slot may be shaped to receive the first protrusion or the second protrusion so as to restrict that protrusion from sliding within the first slot. According to another aspect of the invention, there is provided a blade for a variable aperture assembly comprising a base and a rotatable part, wherein the blade is configured to be connectable to the base via a first protrusion, and connectable to the rotatable part via a second protrusion; and wherein the blade comprises at least one slot or hole and the blade has at least one portion configured to be deformed along a deformation axis normal to a plane defined by surrounding portions of the blade when at least one of the first and second protrusions is received in the slot or hole. The deformation may comprise a portion of the blade being turned out of the plane of surrounding portions of the blade. Or it may comprise a portion of the blade being crumpled or formed with a zigzag pattern (viewed side on, looking at an edge of the plane defining the majority of the blade). The blade may comprise a first slot or hole configured to receive the first protrusion, and a second slot or hole configured to receive the second protrusion. For at least one slot or hole an edge portion of the slot or hole may be configured to be deformed out of a plane defined by surrounding portions of the blade when at least one of the first and second protrusions is received in the slot or hole. The part that deformed need not be an edge portion of the hole or slot: it may be a further component coupled to the remainder of the blade. At least one slot may be configured such that at least one of the first and second protrusions can slide within the slot to accommodate a change in distance between the first protrusion and the second protrusion. An edge portion of at least one slot may be shaped to receive the first protrusion or the second protrusion so as to restrict that protrusion from sliding within the slot. Optionally, the blade comprises an aperture defining edge configured to partly define a variable aperture of the variable aperture assembly. Optionally, the blade is substantially planar. Optionally, the blade is substantially planar. Optionally, the blade has a thickness of at most 100pm, optionally at most 50pm, and optionally at most 30pm. According to another aspect of the present invention, there is provided a VA assembly comprising: a base; a rotatable part; an actuator assembly configured to drive rotation of the rotatable part relative to the base about a primary axis to any rotational position within a range of movement; a plurality of the blade as described above connected to the base via a plurality of first protrusions, and connected to the rotatable part via a plurality of second protrusions, and arranged to define a variable aperture with a central axis which coincides with the primary axis; wherein said rotation of the rotatable part drives each second protrusion to move along a path, which drives rotation of the plurality of blades about the first protrusions, wherein said rotation of the plurality of blades changes the size of the variable aperture. An embodiment of the invention is expected to make it easier to manufacture and / or assemble a VA assembly. Optionally, the path is an arc of a circle centred around the primary axis. The protrusions may have a consistent radial position during rotation. This can help to simplify the design of components such as the rotatable part. Optionally, the at least one edge configured to engage with the first protrusion engages with the first protrusion at a point on a straight line connecting a centre of the first protrusion with a centre of the second protrusion; and / or the at least one edge configured to engage with the second protrusion engages with the second protrusion at a point on a straight line connecting a centre of the first protrusion with a centre of the second protrusion. The biasing force may be applied more directly, and therefore more efficiently. The magnitude of the biasing force required may be reduced. Optionally, the blades are configured to bias respective second protrusions and respective first protrusions relative to each other such that the respective blades are bistable. The amount of friction needed in the system to achieve zero hold power, at least at the maximum and minimum sizes of the VA, may be reduced. Optionally, the second protrusions are rigid. Optionally, the first protrusions are rigid. Optionally, the rotatable part is rigid. Optionally, the base is rigid. It is not necessary to provide such components with biasing features. It can be difficult to manufacture such a base and rotatable part with biasing features. It can be difficult to assemble the VA assembly when the base or rotatable part is provided with biasing features. An embodiment of the invention is expected to make it easier to manufacture and / or assemble a VA assembly. According to another aspect of the present invention, there is provided a camera assembly comprising: a variable aperture assembly as described above; a lens assembly; and an image capture device; wherein light passing through the variable aperture assembly passes is focused by the lens and is received by the image capture device. An embodiment of the invention is expected to make it easier to manufacture and / or assemble a camera assembly. Optionally, the optical axis of the lens assembly coincides with the primary axis. Optionally, the camera assembly comprises: a further actuator assembly; a (single) drive chip operatively connected to the actuator assembly and the further actuator assembly for controlling the actuator assembly and the further actuator assembly; wherein the drive chip comprises at least four drive channels; and wherein the actuator assembly is configured to be (fully) controlled (only) via a first channel and a second channel of the at least four drive channels, and the further actuator assembly is configured to be (fully) controlled (only) via a third channel and a fourth channel of at least four drive channels. Optionally, the further actuator assembly is a focus (e.g. auto-focus (AF)) actuator assembly (e.g. configured to drive movement of one or more lenses along the primary axis, and, optionally, comprising one or more SMA elements configured to drive said movement). According to another aspect of the present invention, there is provided a camera assembly comprising: a variable aperture assembly as described above; and a lens assembly; wherein the variable aperture assembly (e.g. the base of the variable aperture assembly) is mounted on the lens assembly, and the optical axis of the lens assembly coincides with the primary axis. Optionally, the lens assembly is (at least partially) provided / nested within a (through) hole that extends through the base along the primary axis. Optionally, more than 50%, 60%, 70%, 80%, or 90% of the variable aperture assembly overlaps with the lens assembly along the primary axis (i.e. as viewed across the primary axis). Optionally, the actuator assembly fully overlaps with the lens assembly along the primary axis (i.e. as viewed across the primary axis). According to another aspect of the invention, there is provided an electronic device incorporating the camera as described above. Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic plan view of a VA assembly; Figure 2 is a schematic plan view of a blade of a VA assembly; Figure 3 is a schematic plan view of a VA assembly comprising the blade of Figure 2; Figure 4 is a schematic plan view of an alternative blade of a VA assembly; Figure 5 is a schematic plan view of an alternative blade of a VA assembly; Figure 6 is a schematic cross-sectional side view of the VA assembly of Figure 1 mounted on a lens assembly; Figure 7 is a schematic perspective view of the VA assembly of Figure 1 mounted on a lens assembly; Figures 8 and 9 are schematic plan views of portions of a VA assembly including alternative blades; Figures 11 and 12 are schematic cross section views of portions of a VA assembly including alternative blades; Figures 13 and 14 are schematic plan views of alternative blades of a VA assembly; Figures 15a and 15b are respectively a schematic plan view and a schematic cross section view of an alternative blade of a VA assembly; and Figures 16a to 24 illustrate various jigs and portions of a VA assembly incorporating sprung pins. Detailed description VA assembly Figure 1 shows a VA assembly 1 comprising: a base 30, a rotatable part 20, a plurality of blades 40 which are connected to the base 30 and the rotatable part 20 via pins 21, 31 and which define a VA and, and an actuator assembly 10 (not shown in Figure 1 but schematically illustrated in Figures 6 and 7) configured to drive rotation of the rotatable part 20 relative to the base 30 about a primary axis O to any rotational position within a range of movement so as to change the size of the VA defined by the blades 40. The primary axis O may be the longitudinal axis of the VA assembly 1. The primary axis O may be the longitudinal axis of the actuator assembly 10. The base 30 may be described as a hollow tube with a base plate, provided on the lower end of the base 30, which radially protrudes outwards from the main body of the base 30 away from the optical axis O. The base 30 comprises a plurality of pivot protrusions 31 (also referred to as first protrusions or pivot pins) protruding from an upper surface of the main body of the base 30 in an upward direction parallel to the primary axis O. The plurality of pivot protrusions 31 form a loop around the primary axis O and are equally distanced from each other and equally distanced from the primary axis 0. The main body of the rotatable part 20 is nested or provided within a hole or opening that extends through the base 30 along the primary axis O. The rotatable part 20 is mounted onto the base 30 such that it is capable of rotating relative to the base 30 about the primary axis O. A bearing arrangement (e.g. a sliding / plain bearing, ball bearing, or a roller bearing) may be provided between the base 30 and the rotatable part 20. This bearing arrangement may guide, allow and / or facilitate the rotational movement of the rotatable part 20 relative to the base 30. The rotatable part 20 comprises a plurality of moving protrusions 21 (also referred to as second protrusions or moving pins) protruding from an upper surface of the rotatable part 20 in an upward direction parallel to the primary axis O. The plurality of moving protrusions 21 form a loop around the primary axis 0 and are equally distanced from each other and equally distanced from the primary axis 0. The moving protrusions 21 are connected to the main body of the rotatable part 20. The plurality of blades 40 are arranged to define a VA with a central axis which coincides with the primary axis O. The plurality of blades 40 are connected to the base 30 via the plurality of pivot protrusions 31 and connected to the rotatable part 20 via the plurality of moving protrusions 21. The plurality of blades 40 are provided on the upper sides of the base 30 and the rotatable part 20. In other words, the plurality of blades 40 (at least partially) cover or are provided at sides of the base 30 and the movable part 20 that generally face in upwards. The plurality of blades 40 (at least partially) overlap with the base 30 and / or the rotatable part 20 as viewed along the primary axis O. The plurality of blades 40 (at least partially) overlap with each other as viewed along the primary axis 0. The plurality of blades 40 generally lie in a plane perpendicular to the primary axis O which sits on top of the rotatable part 20 and the base 30. The plurality of blades 40 are provided at sides of the base 30 and the movable part 20 that generally face in the same direction (e.g. upwards). Each blade 40 is connected to the base 30 via a single pivot protrusion 31 and connected to the rotatable part 20 via a single moving protrusion 21. The pivot protrusions 31 and the moving protrusions 21 extend through holes provided in the blades 40. The plurality of blades 40 are arranged such that, throughout the range of movement, the (variable) aperture defined by the plurality of blades 40 is continuously generally circular as viewed along the primary axis 0, and / or the shape of the (variable) aperture defined by the plurality of blades 40 does not comprise any acute angles, and / or the shape of the (variable) aperture defined by the plurality of blades 40 is continuously an equilateral shape. The plurality of blades 40 are distributed around the primary axis O. In Figure 1, the plurality of blades 40 comprises a total of six blades 40. The plurality of blades 40 are stacked in two layers of three blades 40 on top of each other, and the layers overlap when viewed along the primary axis O. It will be appreciated that, the plurality of blades 40 may comprise any number of blades and any number of layers. For example, the plurality of blades may comprise six blades, the blades stacked in layers of two blades on top of each other wherein the layers overlap when viewed along the primary axis. For example, the plurality of blades may comprise eight blades, the blades stacked in layers of four blades on top of each other wherein the layers overlap when viewed along the primary axis. The plurality of blades 40 may, for example, comprise five or six blades 40. The moving protrusions 21 are connected to the blades 40 in a manner that prevents or restricts (any significant amount of) relative translational movement between each connected moving protrusion 21 and blade 40 in directions perpendicular to the primary axis O. The pivot protrusions 31 are also connected to the blades 40 in a manner that prevents or restricts (any significant amount of) relative translational movement between each connected pivot protrusion 31 and blade 40 in directions perpendicular to the primary axis 0. In the illustrated embodiments, the moving protrusions 21 are fixed (e.g. integrally formed with, attached, welded, glued or soldered) to the rotatable part 20, and the moving protrusions 21 are engaged with the blades 40 in a manner that allows each connected moving protrusion 21 and blade 40 to slidably rotate relative to each other, i.e. the moving protrusions 21 are rotatably / slidably engaged with edges of the blades 40. However, it will be appreciated that in another example, the moving protrusions 21 may be rotatably / slidably engaged within openings in the rotatable part 20 and also rotatably / slidably engaged with edges of in the blades 40. In the illustrated embodiments, the pivot protrusions 31 are fixed (e.g. integrally formed with, attached, welded, glued or soldered) to the base 30, and the pivot protrusions 31 are engaged with the blades 40 in a manner that allows each connected pivot protrusion 31 and blade 40 to slidably rotate relative to each other, i.e. the pivot protrusions 31 are rotatably / slidably engaged with edges of the blades 40. However, it will be appreciated that in another example, the pivot protrusions 31 may be rotatably / slidable mounted within openings in the base 30 and also rotatably / slidable engaged with edges of the blade 40. The VA assembly 1 is configured such that rotation of the rotatable part 20 relative to the base 30 about the primary axis O, drives relative movement between the pivot protrusions 31 and the moving protrusions 21, more specifically drives rotation of the moving protrusions 21 about the primary axis 0. In other words, the rotation of the rotatable part 20 drives each moving protrusion 21 to move along a path that is an arc of a circle centred around the primary axis O. In other words, rotation of the rotatable part 20 relative to the base 30 about the primary axis O drives the moving protrusions 21 to move along circular paths centred around the primary axis O (i.e. drives each moving protrusion 21 to move along a circular path centred around the primary axis O). This in turn drives rotation of the plurality of blades 40 about the pivot protrusions 31. The rotation of the plurality of blades 40 changes the size of the VA. In other words, the rotation of the moving protrusions 21 relative to the pivot protrusions 31 drives rotation of the plurality of blades 40 about the pivot protrusions 31, and the rotation of the plurality of blades 40 about the pivot protrusions 31 changes the size of the VA. The moving protrusions 21 and the pivot protrusions 31 may be configured (e.g. are close enough to each other) to provide, per degree of rotation of the rotatable part 20 about the primary axis O (relative to the base), at least 5,10, or 20 degrees of rotation of the blades 40 about the pivot protrusions 31. Optionally, the VA assembly comprises a holding arrangement configured to releasably hold the rotatable part at one or more positions within the range of positions that the rotatable part is capable of being driven to relative to the base by the actuator assembly. The protrusions may be integrally formed with the base 30 or the rotatable part 20. For example, the moving protrusions 21 and the base 30 or the rotatable part 20 may be formed as a single part by injection moulding or sheet material fabrication. The moving protrusions 21 and the rotatable part 20 or the base 30 may be etched portions of a single sheet of material (e.g. sheet metal). The pivot protrusions 31 and the base 30 or the rotatable part 20 may be formed as a single part by injection moulding or sheet material fabrication. The pivot protrusions 31 and the rotatable part 20 or the base 30 may be etched portions of a single sheet of material (e.g. sheet metal). Backlash mitigation As noted above in the background section, backlash (that is, play between connected components) within a variable aperture assembly can result from manufacturing tolerance of holes and slots formed in blades and the tolerance of the protrusion. The following embodiments disclose modified VA blades incorporating biasing. In particular, the blades incorporate portions configured to deform to mitigate backlash by ensuring that a selected bearing surface of the blade bears against the corresponding protrusion. The deformable portion may be an integrally formed portion of the blade or attached to the blade. This reduces blade position inaccuracy for a given rotational position of the rotatable part resulting in more accurate and consistent aperture size and more even aperture shape. Figure 2 is a schematic illustration of a blade 40. The blade 40 is for a VA assembly 1, for example of the type shown in 1. Such a VA assembly 1 may comprise a plurality of blades 40. The blade 40 is configured to be connectable to the base 30 via either a pivot protrusion 31 or a moving protrusion 21. For example, in the arrangement shown in Figure 1, the blades 40 are connectable (and connected) to the base 30 via respective pivot protrusions 31. The blade is configured to be engageable with the rotatable part 20 via the other of the pivot protrusion 31 and the moving protrusion 21. For example, in the arrangement shown in Figure 1, the blades 40 are engageable (and engaged) with the rotatable part 20 via respective moving protrusions 21. The blade 40 is configured to resiliently deform. For example, the blade 40 may be configured to resiliently deform to bias the moving protrusion 21 and the pivot protrusion 31 relative to each other. During use of the VA assembly 1, the rotatable part 20 is rotated relative to the base 30. As the rotatable part 20 rotates, the moving protrusions 21 rotate around the primary axis O. The moving protrusions 21 are secured to the rotatable part 20. For example, the moving protrusions 21 may be fixed to the rotatable part 20. The moving protrusions 21 may be formed integrally with the rotatable part 20. As the rotatable part 20 rotates, the radial position of the moving protrusions 21 may remain substantially constant throughout the rotation. The radial position of the moving protrusions 21 corresponds to the distance between the moving protrusions 21 and the primary axis O. Optionally, the moving protrusions 21 are substantially rigid. The moving protrusions 21 may not significantly bend during the rotation. During the rotation of the rotatable part 20, the pivot protrusions 31 remain substantially stationary. As the rotatable part 20 rotates relative to the base 30, the distance between the moving protrusion 21 and the pivot protrusion 31 associated with the same blade 41 varies. Optionally, the VA assembly 1 is arranged such that the distance between the moving protrusions 21 and their respective pivot protrusions 31 is generally greater towards the ends of the rotational stroke and smaller at a mid-point of the rotational stroke. The end points of the rotational stroke correspond to the VA having its greatest size or its smallest size. For example, Figure 1 shows the VA having its smallest size. Figure 7 shows the VA having its greatest size. The distance between the moving protrusion 21 and its respective pivot protrusion 31 may be at a minimum when the moving protrusion 21 is located directly between the respective pivot protrusion 31 and the primary axis O. The moving protrusion 21 may be located along an imaginary straight line between the pivot protrusion 31 and the primary axis 0. This may correspond to the VA having a medium size between its greatest size and its smallest size. As the rotatable part 20 is rotated so as to increase the size of the VA, the moving protrusion 21 moves away from the line between the pivot protrusion 31 and the primary axis O. This causes the distance between the pivot protrusion 31 and the moving protrusion 21 to increase. Similarly, as the rotatable part 20 is rotated so as to decrease the size of the VA from its mid-point, then the moving protrusion 21 moves away from the line between the pivot protrusion 31 and the primary axis O. This causes the distance between the moving protrusion 21 and the pivot protrusion 31 to increase. In the arrangement shown in Figure 1, the moving protrusions 21 are radially inward of the pivot protrusions 31. However, this is not necessarily the case. In an alternative arrangement, the moving protrusions 21 are radially outward of the pivot protrusions 31. In such an arrangement, the moving protrusions 21 may not be located on an imaginary straight line between the pivot protrusion 31 and the primary axis O. However, the moving protrusion 21 may be located to coincide with the continuation of such an imaginary straight line between the pivot protrusion 31 and the primary axis 0. This may correspond to the midpoint of the rotational stroke of the rotatable part 20, when the distance between the moving protrusion 21 and the pivot protrusion 31 is at a minimum. Biasing the moving protrusion 21 and the pivot protrusion 31 relative to each other helps to keep the blades 40 positioned correctly. Positioning the blades 40 correctly helps to improve the accuracy of the VA having its target shape. The target shape may be a circle. By positioning the blades 40 correctly, circularity of the VA may be improved. By positioning the blades 40 correctly, the position of the VA within the plane of the blades 40 may be improved. For example, the concentricity of the VA may be improved. By configuring the blade 40 to resiliently deform to provide the bias force, the accuracy of control of the blades 40 may be improved. The resilient deformation of the blade 40 helps to keep the blade 40 engaged with the moving protrusion 21 and the pivot protrusion 31 during use of the VA assembly 1. The blade 40 may be arranged such that the blade 40 remains in contact with the moving protrusion 21 and the pivot protrusion 31 during rotation of the rotatable part 20 relative to the base 30. By maintaining engagement between the blade 40 and the moving protrusion 21 and the pivot protrusion 31, the possibility of the rotational stroke being lost on clearances between the blade 40 and the protrusions is reduced. If the blade 40 is not engaged with the moving protrusion 21 and / or the pivot protrusion 31, then part of the rotational movement of the rotatable part 20 may bring the moving protrusion 21 into engagement with the blade 40. In other words, the clearance between the blade 40 and the moving protrusion 21 may be reduced to zero. As the clearance is reduced, the rotation of the rotatable part 20 does not lead to a corresponding rotation of the blade 40. This reduces the accuracy with which movement of the blade 40 can be controlled. Configuring the blade 40 to provide the bias force helps to improve the accuracy of control of movement of the blades 40. Any clearance between the blade 40 and the moving protrusion 21 could potentially be reduced by manufacturing the blade 40 and / or the moving protrusion 21 to tighter tolerances. By configuring the blade 40 to resiliently deform to bias the moving protrusion 21, the manufacturing tolerance for the blade 40 and / or the moving protrusion 21 may be increased, without unduly decreasing the accuracy of control of movement of the blades 40. The blades 40 may be configured to bias the moving protrusions 21 (more specifically, at least the portions of the moving protrusions 21 engaging the blades 40) relative to the pivot protrusions 31. In other words, the blades 40 may be elastically-deformable so as to bias each of the moving protrusions 21 into engagement with a respective blade 40 of the plurality of blades 40. If the blade 40 comprises an engaging arm 22 that comprises a flexure arm, the flexure arm itself may be configured to provide this biasing. This biasing may ensure that the moving protrusions 21 are in constant engagement with the blades 40 throughout the range of movement, e.g. wherein the moving protrusions 21 are not fixed to the blades 40. In other words, each moving protrusion 21 may be biased (e.g. in a direction perpendicular to the primary axis O) against a respective blade 40 of the plurality of blades 40 (i.e. the blade the moving protrusion 21 is connected to) such that, throughout the range of movement, the moving protrusions 21 are in constant (e.g. slidable) engagement with respective blades 40. This biasing may also bias the blades 40 into engagement with the pivot protrusions 31 such that the blades 40 are in constant engagement with the pivot protrusions 31 throughout the range of movement, e.g. wherein the pivot protrusions 31 are not fixed to the blades 40. In other words, the biasing of the moving protrusions 21 against respective blades 40 may also bias (e.g. in a direction perpendicular to the primary axis O) each blade 40 against a respective pivot protrusion 31 of the plurality of pivot protrusions 31 (i.e. the pivot protrusion 31 the blade 40 is connected to) such that, throughout the range of movement, the blades 40 are in constant (e.g. slidable) engagement with respective pivot protrusions 31. The engaging arms 45 and the elastically-deformable blades 40 may be configured to act as compression springs (i.e. be under compression) or as extension springs (i.e. be under tension) throughout the range of movement. The biasing forces applied to the moving protrusions 21 may generally be towards respective pivot protrusions 31. Alternatively, the biasing forces applied to the moving protrusions 21 may generally be in directions away from respective pivot protrusions 31. In other words, each moving protrusion 21 may be biased at least partially towards or away from a respective pivot protrusion 31 of the plurality of pivot protrusions 31 (i.e. the pivot protrusion 31 the moving protrusion 21 is connected to via one of the blades 40). The biasing forces provided may generally be inwardly, i.e. in directions towards the primary axis O. Alternatively, the biasing forces provided may generally be outwardly, i.e. in directions away from the primary axis 0. In other words, each moving protrusion 21 may be biased at least partially towards or away from the primary axis O. Arrangement of Figure 2 Optionally, the blade 40 is configured to resiliently deform so as to accommodate a change in distance between the moving protrusion 21 and the pivot protrusion 31. For example, as shown in Figure 2, optionally the blade 40 comprises at least one edge 41 configured to engage with the pivot protrusion 31 and at least one edge 42 configured to engage with the moving protrusion 21. The blade 40 shown in Figure 2 comprises two edges 41a, 41b configured to engage with the pivot protrusion 31 and two edges 42a, 42b configured to engage with the moving protrusion 21. In an alternative arrangement, the blade 40 may comprise only one edge or more than two edges configured to engage with the pivot protrusion 31. In an alternative arrangement, the blade 40 may comprise only one edge or more than two edges configured to engage with the moving protrusion 21. Although not shown in Figure 2, the pivot protrusion 31 may be located so as to be in contact with the edges 41a, 41b configured to engage with it. This may be seen in Figure 1. Although not shown in Figure 2, the moving protrusion 21 may be located so as to be in contact with the edges 42a, 42b configured to engage with it. As shown in Figure 2, optionally the blade 40 comprises an aperture 43. The aperture 43 may be configured to accommodate the moving protrusion 21. In an alternative arrangement, the aperture 43 may be configured to accommodate the pivot protrusion 31. When the distance between the moving protrusion 21 and the pivot protrusion 31 is small (e.g. at the midpoint of the rotational stroke), then the two edges 41a, 41b configured to engage with the pivot protrusion 31 may be pushed away from each other. Similarly, the edges 42a, 42b configured to engage with the moving protrusion 21 may be forced generally away from each other. As the distance between the moving protrusion 21 and the pivot protrusion 31 increases, the edges 41a, 41b configured to engage with the pivot protrusion 31 may move closer towards each other. Similarly, the edges 42a, 42b configured to engage with the moving protrusion 21 may move generally towards each other. In this way, the blade 40 may resilient deform so as to accommodate the change in distance between the moving protrusion 21 and the pivot protrusion 31. Optionally, the blade 40 is arranged such that for substantially all distances between the moving protrusion 21 and the pivot protrusion 31 during the rotational stroke, the blade 40 remains in contact with the moving protrusion 21 and the pivot protrusion 31. For example, the blade 40 may be arranged such that when it is assembled onto the moving protrusion 21 and the pivot protrusion 31, the blade 41 is tensed so as to generally urge the edges 41a, 41b configured to engage with the pivot protrusion 31 generally towards each other. Similarly, the blade 40 may be tensed (once assembled onto the moving protrusion 21 and the pivot protrusion 31) so as to generally urge the edges 42a, 42b configured to engage with the moving protrusion 21 generally towards each other. As shown in Figure 2, optionally the blade comprises an engaging arm 45. The engaging arm 45 is configured to accommodate the change in distance. The engaging arm 45 may be referred to as a thin wall. The engaging arm 45 corresponds to a relatively narrow part of the blade 40. For example, as shown in Figure 2, a slit 44 may generally define a boundary between the engaging arm 45 and a main body 46 of the blade 40. The engaging arm 45 is generally elongate. The engaging arm 45 is connected with the main body 46, for example at a location beyond the end of the slit 44. The engaging arm 45 may be formed integrally with the main body 46 of the blade 40. Figure 3 shows an enlarged view of part of the VA assembly 1. The locations of the moving protrusion 21 and the pivot protrusion 31 relative to the blade 40 are shown in Figure 3. Figure 3 shows the VA assembly 1 at a large size of VA. The moving protrusion 21 is located a distance away from an imaginary line between the pivot protrusion 31 and the primary axis. The distance between the moving protrusion 21 and the pivot protrusion 31 is relatively large. As shown in Figure 3, as the moving protrusion 21 rotates clockwise from a large VA size towards a midsize, the distance to the pivot protrusion 31 decreases. As the moving protrusion 21 continues to rotate clockwise towards the small size of the VA, the distance to the pivot protrusion 31 increases. The blade 40 is configured to interface with each of the moving protrusion 21 and the pivot protrusion 31 at two points on the faces (or edges). Optionally, the blade 40 is arranged such that these points are an interference fit at all sizes of the VA. The blade 40 is forced apart as the moving protrusion 21 rotates clockwise from the large size of the VA towards the mid-size position, increasing the bias force on the moving protrusion 21 and the pivot protrusion 31. The biasing force decreases as the moving protrusion 21 continues to rotate clockwise from the mid-size of the VA towards the small size of the VA. As the rotatable part 20 rotates, the engaging arm 45 may be configured to move away from or towards the main body 46 of the blade 40. For example, when the distance between the moving protrusion 21 and the pivot protrusion 31 is smaller, the engaging arm 45 may be forced away from the main body 46. For example, the engaging arm 45 may generally pivot with respect to the main body 46 about a pivot point generally where the engaging arm 45 is connected to the main body 46 (i.e. beyond the end of the slit 44). As the distance between the moving protrusion 21 and the pivot protrusion 31 increases, the engaging arm 45 may generally move towards the main body 46. This may be due to a resilient force or an elastic force. The engaging arm 45 may comprise a flexure arm. As shown in Figure 2, optionally the engaging arm 45 is configured to engage with the pivot protrusion 31 and / or the moving protrusion 21. In the arrangement shown in Figure 2, the engaging arm 45 is configured to engage with the pivot protrusion 31 and the moving protrusion 21. As shown in Figure 2, the engaging arm 45 comprises one of the edges 41a configured to engage with the pivot protrusion 31. The engaging arm 45 comprises one of the edges 42a configured to engage with the moving protrusion 21. In an alternative arrangement, the engaging arm 45 may be configured to engage with only one of the pivot protrusions 31 and the moving protrusion 21. As shown in Figure 2, optionally the blade 40 is arranged so as to generally push the moving protrusion 21 and the pivot protrusion 31 away from each other. The blade 40 may be configured to bias the moving protrusion 21 and the pivot protrusion 31 away from each other. For example, as shown in Figure 2, optionally the at least one edge 41 configured to engage with the pivot protrusion 31 faces away from the at least one edge 42 configured to engage with the moving protrusion 21. By biasing the moving protrusion 21 and the pivot protrusion 31 away from each other, the bias force combines with the force of the actuator 10 that drives rotation of the rotatable part 20 towards the ends of the rotational stroke. In other words, the biasing helps the actuator 10 where the actuator 10 may need some help. For example, it is possible that the force imparted by the actuator 10 may be generally lower towards the ends of the stroke. The biasing force effectively increases the force that drives rotation of the rotatable part 20 towards the maximum and minimum sizes of the VA. Arrangement of Figure 4 Figure 4 schematically depicts an alternative blade 40. The blade 40 may be for a VA assembly 1 of the type shown in Figure 1, for example. The blade 40 shown in Figure 4 may have the same features as described with reference to Figure 2 and Figure 3, with the exception of the differences set out below. In the arrangement shown in Figure 2, the blade is configured to bias the moving protrusion 21 and the pivot protrusion 31 away from each other. This is also a feature of the blade of Figure 4. In the arrangement shown in Figure 2, the engaging arm 45 is configured to engage with both the moving protrusion 21 and the pivot protrusion 31. In the arrangement shown in Figure 4, the engaging arm 45 is configured to engage with only the pivot protrusion 31. In an alternative arrangement, the engaging arm 45 may be configured to engage with only the moving protrusion 21. As shown in Figure 4, optionally the engaging arm 45 comprises the edge 41 configured to engage with the pivot protrusion 31. As shown in Figure 4, the blade 40 may comprise only one edge 41 configured to engage with the pivot protrusion 31. Alternatively, the blade 40 may comprise a plurality of edges configured to engage with the pivot protrusion 31. As shown in Figure 4, the moving protrusion 21 is accommodated within an aperture 43. In the arrangement shown in Figure 4, the aperture 43 is surrounded by the material of the blade 40. In other words, the aperture 43 is fully defined by the blade 40. In contrast, in the arrangement of Figure 2, the aperture 43 is open to the edges 41a, 41b that engage with the pivot protrusion 31. The blade 40 comprises an aperture defining edge 47. The aperture defining edge 47 is configured to partly define the VA of the VA assembly 1. As shown in Figure 1, the VA may be fully defined by the aperture defining edges 47 of the plurality of blades 40. As shown in Figure 2, for example, optionally the aperture defining edge 47 is curved. Alternatively, the aperture defining edge 47 may be straight. As shown in Figure 4, optionally the engaging arm 45 is located generally on the radially outer side of the blade 40, when the blade 40 is assembled as part of the VA assembly 1. The engaging arm 45 may generally be on the radially opposite side of the blade 40 from the aperture defining edge 47. In contrast, as shown in Figure 2, optionally the engaging arm 45 is located at a generally radially inward side of the blade 40. The engaging arm 45 may be located generally on the same radial side of the blade 40 as the aperture defining edge 47. As shown in the arrangement of Figure 4, optionally the aperture 43 is defined in the main body 46 of the blade 40. Alternatively, as shown in Figure 2, optionally the aperture 43 is defined between the engaging arm 45 and the main body 46. The engaging arm 45 may partly define the aperture 43. The main body 46 may partly define the aperture 43. As shown in Figure 4, optionally the at least one edge 41 configured to engage with the pivot protrusion 31 engages with the pivot protrusion 31 at a point on a straight line connecting a centre of the pivot protrusion 31 with a centre of the moving protrusion 21. The edge 41 may impart a force on the pivot protrusion 31 more directly away from the moving protrusion 21. In contrast, Figure 2 shows an alternative arrangement in which the forces applied by the edges 41a, 41b act on the pivot protrusion 31 in a direction that is oblique with respect to the direction between the moving protrusion 21 and the pivot protrusion 31. The arrangement shown in Figure 4 may increase the efficiency of the biasing force. Similarly, as shown in Figure 4, optionally the at least one edge 42 configured to engage with the moving protrusion 21 may engage with the moving protrusion 21 at a point on a straight line connecting a centre of the pivot protrusion 31 with a centre of the moving protrusion 21. As shown in Figure 4, optionally part of the blade 40 is located directly between the moving protrusion 21 and the pivot protrusion 31. This may help to allow the blade 40 to provide a biasing force edging the moving protrusion 21 and the pivot protrusion 31 more directly away from each other. Alternatively, as shown in Figure 2, the space between the pivot protrusion 31 and the moving protrusion 21 is filled by a gap. That is, none of the material of the blade 40 is located on the imaginary straight line between the centre of the pivot protrusion 31 and the centre of the moving protrusion 21. This may make it easier to manufacture the blade 40. The small space between the moving protrusion 21 and the pivot protrusion 31 may be so small as to make it difficult to manufacture part of the leaf 40 to be between the moving protrusion 21 and the pivot protrusion 31. The arrangement shown in Figure 2 is expected to make it easier to manufacture the blade 40. Arrangement of Figure 5 Figure 5 schematically depicts an alternative blade 40. The blade 40 is for a VA assembly 1, for example of the type shown in Figure 1. The blade 40 shown in Figure 5 may have features that are the same as described with reference to Figure 2 or Figure 4. These features are not described again, for brevity. Features that are different from the blade of Figure 2 and Figure 4 are described below. In the arrangements shown in Figure 2 and Figure 4, the blade 40 is configured to bias the moving protrusion 21 and the pivot protrusion 31 away from each other. However, this is not an essential feature. As shown in Figure 5, optionally the blade 40 is configured to bias the moving protrusion 21 and the pivot protrusion 31 toward each other. For example, the at least one edge 41a, 41b configured to engage with the pivot protrusion 31 may face towards the at least one edge 42a, 42b configured to engage with the moving protrusion 21. As shown in Figure 5, optionally two edges 41a, 41b may be provided to engage with the pivot protrusion. Two edges 42a, 42b may be configured to engage with the moving protrusion 21. Alternatively, the blade 40 may comprise only one edge 41 configured to engage with the pivot protrusion 31. The blade 40 may comprise only one edge configured to engage with the moving protrusion 21. For example, optionally the at least one edge 41 configured to engage with the pivot protrusion 31 may be curved. For example, the edge 41 may be curved around the pivot protrusion 31. Optionally, the at least one edge 42 configured to engage with the moving protrusion 21 is curved. For example, the edge 42 may be curved around the moving protrusion 21. By providing that the edges may be curved, the possibility of undesirable wear between the protrusions and the edges may be reduced. Any such wear may result in the undesirable generation of particles. Such particles could undesirably interfere with the mechanism of the VA assembly 1. Wear between the protrusions and the edges may lead to undesirable deformation of the protrusions and / or the blade 40. However, it is not essential for the edges 41, 42 to be curved. In an alternative arrangement, one or more of the edges 41, 42 is straight. As shown in Figure 5, optionally the engaging arm 45 is configured to engage with only the pivot protrusion 31. The pivot protrusion 31 and the moving protrusion 21 may be separated by a gap. This may make it easier to manufacture the blade 40. In the arrangement shown in Figure 5, the blade 40 is configured to urge the moving protrusion 21 and the pivot protrusion 31 together as the size of the VA increases or decreases from its mid-size. This may increase the force needed to be imparted by the actuator 10 so as to reach the largest and smallest sizes for the VA. In the arrangement shown in Figure 5, the blade 40 is configured such that the engaging arm 45 moves away from the main body 46 of the blade 40 as the distance between the moving protrusion 21 and the pivot protrusion 31 increases. As the distance decreases, the engaging arm 45 resiliently returns towards the main body 46. The blade 40 may be assembled onto the moving protrusion 21 and the pivot protrusion 31 so as to be tensed to urge the moving protrusion 21 and the pivot protrusion 31 towards each other. Bistability Optionally, the blades 40 are configured to bias respective moving protrusions 21 and respective pivot protrusions 31 relative to each other such that the respective blades are bistable. As mentioned above, optionally the blades 40 are arranged such that the biasing force adds to the actuation force for actuating the VA assembly 1 towards its maximum and minimum sizes of VA. By configuring the blade 40 so as to increase the biasing force, the blade 40 may be bistable. The VA assembly 1 may have a first stable position that corresponds to the VA having a maximum size. The VA assembly 1 may have a second stable position that corresponds to the VA having a minimum size. Optionally, the VA assembly 1 is configured such that the size of the VA may be kept substantially constant. Optionally, the size of the VA may be kept substantially constant while the actuator 10 is not being powered. This may be referred to as zero hold power. By providing the biasing force, the biasing force may contribute to the VA having a stable size without the actuator 10 being powered. For example, the biasing force may help to keep the VA assembly 1 in one of its first stable position and its second stable position without requiring the actuator 10 to be powered. The blades 40 may be configured and the VA assembly 1 may be arranged to apply biasing forces (e.g. in directions at least partially towards respective pivot protrusions 31, and / or at least partially towards the primary axis O), to the moving protrusions 21, such that the respective blades 40 are bistable, i.e. configured to cause the plurality of blades 40 to have a first stable equilibrium position and a second stable equilibrium position. In other words, the moving protrusions 21 may be biased such that the plurality of blades 40 are bistable. The first and second stable equilibrium positions may correspond to the ends of the range of movement of the plurality of blades 40 (which e.g. may be defined by endstops). The VA assembly 1 may be arranged so as to generate frictional forces that constrain the movement of the rotatable part 20 relative to the base 30 at any position within the range of movement (i.e. at any position within the range of positions that the rotatable part 20 is capable of being driven to relative to the base 30 by the actuator assembly 10) when the actuator assembly 10 is not actuated. When the plurality of blades 40 are bistable, the frictional forces needed to constrain the movement of the rotatable part 20 relative to the base 30 may be reduced. Dimensions Optionally, the blade 40 is substantially planar. For example, the blade 40 may be formed from a planar piece of material. For example, the blade 40 may be cut out or punched from a sheet. Optionally, the blade 40 comprises an elastic material. For example, optionally the blade comprises a plastic. The blade 40 may be formed from a sheet of plastic. In an embodiment the blade 40 has a thickness of at most 200 pm, optionally at most 100 pm and optionally at most 50 pm. By reducing the thickness of the blade 40, the blade 40 may be easier to deform so as to provide the biasing force. Optionally, the blade 40 has a thickness of at least 5 pm, optionally at least 10 pm and optionally at least 20 pm. By increasing the thickness of the blade 40, the blade 40 may be more robust and may be able to impart a greater biasing force. Merely as an example, the blade 40 may have a thickness of about 30 pm to 40 pm. Optionally, the moving protrusions 21 have a diameter of at least 0.1 mm and optionally at least 0.2 mm. Optionally the moving protrusions 21 have a diameter of at most 1 mm, and optionally at most 0.5 mm. For example, the moving protrusions 21 may have a diameter of about 0.3 mm. Optionally, the pivot protrusions 31 have a diameter of at least 0.1 mm and optionally at least 0.2 mm. Optionally the pivot protrusions 31 have a diameter of at most 1 mm, and optionally at most 0.5 mm. For example, the pivot protrusions 31 may have a diameter of about 0.3 mm. Optionally, the slit 44 has a length of at least 0.5 mm, optionally at least 1 mm and optionally at least 2 mm. Optionally, the slit 44 has a length of at most 5 mm, and optionally at most 2 mm. Holding arrangement The VA assembly 1 may comprise a holding arrangement (not shown) configured to releasably hold the rotatable part 20 at one or more positions within the range of positions that the rotatable part 20 is capable of being driven to relative to the base 30 by the actuator assembly 10. The holding arrangement may, for example, be any suitable latch or catch arrangement known in the art, such as a roller ball catch arrangement. Assembling the VA assembly By providing that the blades 40 provide the biasing force, it may be easier to assemble the VA assembly 1. For example, optionally the blades 40 are pushed down onto the moving protrusions 21 and the pivot protrusions 31. The flexibility of the blades 40 allows the blade 40 to be located onto the moving protrusion 21 and the pivot protrusion 31 without requiring independent manipulation of the moving protrusion 21 or the pivot protrusion 31. Optionally, the moving protrusions 21 are rigid. Optionally, the pivot protrusions 31 are rigid. Optionally, the rotatable part 20 is rigid. Optionally, the base 30 is rigid. The moving protrusions 21, the pivot protrusions 31, the rotatable part 20 and the base 30 can be rigid because the biasing force is provided by the blade 40 itself. For example, it is not necessary to provide any flexure arms as part of the rotatable part 20 or the base 30. It is not necessary for the moving protrusions 21 or the pivot protrusions 31 to be able to flex so as to provide the biasing force. The present invention is expected to make it easier to manufacture the VA assembly 1. Camera assembly As shown in Figures 6 and 7, the base 30 of the VA assembly 1 may be mounted onto a lens assembly 50. The central axis of the VA also coincides with the optical axis of the lens assembly 50. The base 30 is mounted such that the lens assembly 50 is nested or provided within a through hole or opening of the base 30 which extends along a primary axis O of the VA assembly 1. The primary axis O coincides with the optical axis of the lens assembly 50. The rotatable part 20 may be rotatably / slidably mounted onto the lens assembly 50 such that the rotatable part 20 can rotate relative to the lens assembly 50 about the primary axis O. The actuator assembly 10 is provided between the base 30 and the rotatable part 20. In Figures 6 and 7, the actuator assembly 10 is mounted onto the base plate of the base 30 but it will be appreciated that this may not necessarily be the case. The actuator assembly 10 is configured to, on actuation, drive rotation of the rotatable part 20 relative to the base 30 about a primary axis O in both clockwise and anticlockwise directions. The actuator assembly 10 may be a shape memory alloy (SMA) actuator assembly. However, it will be appreciated that the actuator assembly 10 may be any suitable actuator assembly, for example, be a voice coil motor (VCM) actuator assembly or a piezoelectric actuator assembly, instead of a SMA actuator assembly. The VA assembly 1 (e.g. the base 30 of the VA assembly 1) may be mounted on a lens assembly 50 of a camera assembly, such that the optical axis of the lens assembly 50 coincides with the primary axis O. The lens assembly 50 may be (at least partially) provided / nested within a (through) hole that extends through the base 30 along the primary axis O. More than 50%, 60%, 70%, 80%, or 90% of the VA assembly 1 may overlap with the lens assembly 50 along the primary axis O, i.e. as viewed across the primary axis O. The actuator assembly 10 may fully overlap with the lens assembly 50 along the primary axis O, i.e. as viewed across the primary axis. SMA actuator assembly The actuator assembly 10 may be an SMA actuator assembly 10 comprising one or more SMA elements configured to, upon contraction (e.g. upon heating the SMA elements by passing a current through them), (directly or indirectly) drive the rotation of the rotatable part 20 relative to the base 30. An example of an SMA actuator assembly 10 is described in detail in WO2013175197 which is incorporated herein by reference. The actuator assembly 10 may comprises a total of four SMA elements; a support structure fixed to the base 30; and a movable part coupled to the rotatable part 20. The SMA elements are configured to, upon contraction, drive relative movement between the movable part and the support structure so as to drive the rotation of the rotatable part 20 relative to the base 30. The movable part is fixed to the rotatable part 20; and the one or more SMA elements are configured to, upon contraction, drive rotation of the movable part relative to the support structure (e.g. around the primary axis O) so as to drive the rotation of the rotatable part 20 relative to the base 30. The VA assembly 1 may comprise a holding arrangement (not shown) configured to releasably hold the movable part at one or more positions within the range of positions that the movable part is capable of being driven to relative to the support structure, e.g. by the one or more SMA elements. The holding arrangement may be any suitable latch or catch arrangement known in the art, such as a roller ball catch arrangement. The four SMA elements are configured to, indirectly via the movable part, drive the rotation of the rotatable part 20 relative to the base 30. The four SMA elements are arranged in a loop at different angular positions around the primary axis O. Successive SMA elements around the primary axis O are configured, on contraction, to, indirectly via the movable part, apply a force to the rotatable part 20 in alternate senses around the primary axis O. In an alternative embodiment, the four SMA elements may be configured to directly drive the rotation of the rotatable part 20 relative to the base 30. Successive SMA elements around the primary axis O may be configured, on contraction, to directly apply a force to the rotatable part 20 in alternate senses around the primary axis O. A first pair of SMA elements may be electrically connected together (in series or parallel), and arranged to apply a torque to the rotatable part 20 (directly, or indirectly via the movable part) for rotating the rotatable part 20 about the primary axis O in a first sense (e.g. anticlockwise); and a second pair of SMA elements may be electrically connected together (in series or parallel) and arranged to apply a torque to the rotatable part 20 (directly, or indirectly via the movable part) for rotating the rotatable part 20 about the primary axis O in a second sense (e.g. clockwise), wherein the second sense is opposite to the first sense. In an alternative example the SMA actuator assembly 10 may comprise: a first SMA element arranged to (directly, or indirectly via the movable part) rotate the rotatable part 20 about the primary axis O in a first sense relative to the base 30; and a second SMA element arranged to (directly, or indirectly via the movable part) rotate the rotatable part 20 about the primary axis O in a second sense relative to the base 30, wherein the second sense is opposite to the first sense. The actuator assembly 10 may comprise one or more SMA elements (e.g. a total of two SMA elements) that are wound around (i.e. bent or folded around) corner elements which may be flexures, pulley wheels, posts and / or rocking arms. Blade Flexure Features The blades of Figures 2, 4 and 5 described above have in common that the blade has been modified from a conventional variable aperture blade having holes or slots driven by protrusions to incorporate one or more flexure feature that generates an anti-backlash force. Specifically, the anti-backlash force comprises a force that biases the protrusions relative to one another - towards or away from one another. Further alternative blade configurations with different flexure features will be apparent to the skilled person, having in common that a portion of the blade or a component coupled to the blade serves to generate a biasing force acting upon the protrusions on which the blade is mounted or driven so that relative play between the protrusions and the blade (for instance, due to manufacturing tolerances or deliberately introduced to facilitate assembly) is eliminated. Such flexure features could be a blade cutout profile, with either a single flexure for both protrusions, or one flexure for each protrusion. Configuration of the flexure feature permits the biasing force to be radial, tangential, or have a radial component and a tangential component (defined relative to the primary axis). A radial biasing force may in some embodiments reduce the effect upon the aperture from shaking or dropping the device. Arrangement of Figure 8 Figure 8 schematically depicts an alternative blade 40, that is functionally similar to the arrangement of Figure 5. The blade 40 is for a VA assembly 1, for example of the type shown in Figure 1. The blade 40 shown in Figure 8 may have features that are the same as described with reference to Figure 5. These features are not described again, for brevity. Like the arrangement of Figure 5, the blade 40 is configured to bias the moving protrusion 21 and the pivot protrusion 31 toward each other. For example, at least one edge 41a, 41b is configured to engage with the pivot protrusion 31 and is formed upon an engaging arm 45 which is divided from the main body 46 of the blade 40 by slit 44. Upon the side of the body 45 the pivot protrusion is engaged by surfaces 60a, 60b. The paired surfaces 41a, 41b and 60a, 60b may be respectively replaced by single engagement surfaces, for instance curved surfaces. Moving protrusion 21 is received within hole 61 and bears against surface 62. Engagement arm 45 is configured to bias the pivot protrusion 31 towards the main body 46 of the blade 40. The main body 46 may be sized so that the gap between hole 61, specifically surface 62, and surfaces 60a, 60b is less than the minimum distance between protrusion 21, 31 such that the engaging arm serves to engage protrusion 21 against surface 62. As the protrusions 21, 31 move relative to one another, engaging arm 45 flexes or deforms further to accommodate this change in relative distance. As for the arrangement shown in Figure 5, for the arrangement of Figure 8, the blade 40 is configured to urge the moving protrusion 21 and the pivot protrusion 31 together as the size of the variable increases or decreases from its mid-size. Accordingly, there is a higher anti-backlash biasing force applied to the protrusions at the minimum and maximum aperture positions (corresponding to maximum distance between the protrusions) which provides a small centring force. This centring force may need to be considered when configuring the actuator 10. Arrangements of Figures 9 and 10 Figure 9 presents an alternative approach to generating an anti-backlash biasing force. In place of the engagement arm of the preceding embodiments, blade 100 incorporates an engagement arm 101 that is separated from the main body 102 of the blade 100 by a slit 103 and upturned, for instance generally normally to the plane of the blade body 102. The engagement arm 101 may be deformed upon assembly such that it bears upon and applies a biasing force to the pivot protrusion 31 extending from base 30 (or the moving protrusion 21 extending from rotatable part 20) that serves to bias the protrusions apart. The effect of biasing the protrusions apart is generally the same as already described in connection with Figures 2 and 4. The blade 100 including engagement arm 101 may be a stamped and formed profile. In a further embodiment there may be a second engagement arm to engage the other pin (acting in the same direction as engagement arm 101, or in an opposite direction). Figure 10 is generally the same as Figure 9 except that blade 110 has a separate component 111 mounted upon it (for instance, by glueing or welding) to form an engagement arm 112 that functions as described for engagement arm 101. Arrangements of Figures 11 and 12 Figure 11 presents an alternative approach to adding flexure features to the blades to generate an antibacklash force. Blade 120 is shown edge on mounted upon pivot protrusion 31 (the same arrangement may apply also to the moving protrusion 21, or only to the moving protrusion 21). Figure 12 shows that the flexure may comprise a cutout profile that flexes up out of plane to generate a clamping load on the protrusion. Specifically, the hole or slot formed within the blade 120 to receive protrusion 31 may be formed smaller than the diameter of the protrusion 31 but with a portion of the edge of the hole or slot that is free to deform out of plane as the protrusion 31 is engaged. Figure 11 shows that first and second portions of the hole edge form flexure features 121, 122 deformed out of the plane of blade 120. Instead, only one side may form a flexure feature. Only a single flexure 121, 122 per protrusion may create a torque risking the blade tilting. Using two or more flexures 121, 122 per protrusion reduces any resulting torque applied to the blade. The arrangement of Figure 11 may provide for significantly lower normal force applied to the blade 120 than for the previously presented flexure options. Figure 12 is generally the same as for Figure 11 except that the flexure feature 123 formed on an edge portion of a hole or slot formed in blade 120 is formed with a zigzag pattern or other folding feature to bear against protrusion 31 (or protrusion 21). The flexure 120 effectively forms a compression spring and allows the protrusion to fun on the face of blade material rather than on an edge, which may reduce wear. This arrangement may also reduce the risk of the blade material buckling as it engages the protrusion 31. Arrangements of Figures 13,14,15a, 15b Figures 13,14,15a, 15b represent further options for incorporating anti-backlash biasing features into a blade for a variable aperture assembly. Figure 13 illustrates a blade 130 incorporating a single slot 131 configured to receive the pivoting protrusion 31 and the moving protrusion 21. One side of slot 131 is configured to deform such that an edge portion 132 of the first slot 131 maintain contact between the blade 130 and the protrusions 21, 31. Specifically, edge portion 132 of first slot 131 is defined by a resilient beam 133 formed between the first slot 131 and a second slot 134. Resilient beam 133 is configured to deform to accommodate the protrusions 21, 31 within the slot 131. Resilient beam 133 is shown as fixed at both ends so that slots 131,134 are separated. Within slot 131 pivoting protrusion 31 is prevented from sliding by being engaged by edge portions 135a, 135b that together with edge portion 132 form a restriction that prevents protrusion 21 from sliding. Moving protrusion 21 on the other hand is free to slide within the slot 131. Resilient beam provides an anti-backlash biasing force to protrusions 21, 31, biasing the protrusions against the other side of the slot, while permitting relative movement of the protrusions 21, 31 during variable aperture actuation. Assembly of the blade 130 upon the protrusions may require the resilient beam 133 to be deformed towards slot 134 and then released once the protrusions are received in slot 131 such that both sides of slot 131 bear upon protrusions 21, 31. Figure 14 differs from Figure 13 in that for blade 140 both protrusions 21, 31 are free to slide within slot 131. In an alternative, the pivoting protrusion 31 may be restricted from sliding. For instance, one wall of slot 141 may include an angled wall portion similar to that of Figure 13 configured to engage the pivoting protrusion 31 to restrict sliding movement. For slot 141 at least part of each side is defined by resilient beams 142,143 which are fixed first ends to the body of blade 140 and free at second ends. Each resilient beam 142,143 is defined between slot 141 and a further slot 144,145 respectively. Slots 141,144, 145 are interconnected. The arrangement of resilient beams 142, 143 is such that they each apply an anti-backlash biasing force upon the protrusions 21, 31 such that side portions 146,147 of slot 141 bear upon the protrusions. Figure 15a is a plan view of a further blade 150, similar in certain respects to Figure 11. Figure 15b is a cross section along line A:A in the direction of the arrows. Protrusions 21, 31 are received in separate slots 151, 152. As for Figure 11 an edge portion 153,154 of each slot is formed as a flexure configured to be deformed out of the plane of the blade 150 to bear against the respective protrusions. The deformation of flexure portion 154 is visible in the cross section of Figure 15b. Pivot protrusion 31 is prevented from sliding within slot 152 by the edge of slot 152 opposed to flexure portion 154 being formed with angled surfaces 155. However, moving protrusion 21 is free to slide within slot 151 while flexure portion 153 applies a biasing force pushing protrusion 21 against opposite wall 156. SMA element The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. The SMA element may be described as an SMA wire. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element 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 element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA wire, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling or deposition and / or other forming process(es). The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field. Variations It will be appreciated that there may be many other variations of the above-described examples. Optionally the pivot protrusion 31 and / or the moving protrusion 21 are part of the blade 40 instead of part of the base 30 and rotatable part 20. The blade 40 may comprising the pivot protrusion 31 and / or the moving protrusion 21. The protrusions 21, 31 may be fixed to / formed integrally with the blades 40. The protrusions 21, 31 may be configured to couple with corresponding holes in the base 30 and the rotatable part 20. For example, the base 30 and / or the rotatable part 20 may comprise apertures or slits configured to accommodate the respective protrusions 31, 21. The blade 40 is configured to resiliently deform so as to bias the protrusions 31, 21 relative to each other. Optionally, the engaging arm 45 comprises an edge 41 configured to engage with the pivot protrusion 31 and an edge 42 configured to engage with the moving protrusion 21. The edges 41, 42 may be arranged so as to urge the pivot protrusion 31 and the moving protrusion 21 toward each other. Optionally, instead of having the rotatable part 20 nested within the base 30, the base 30 may be nested within the rotatable part 20. In the illustrated embodiments, the moving protrusions 21 comprise part of the rotatable part 20 and the pivot protrusions 31 comprise part of the base 30. However, the rotatable part 20 may instead comprise the pivot protrusions 31, and the base 30 may instead comprise the moving protrusions 21, wherein the moving protrusions 21 are configured to rotate around the primary axis O (as described above). In other words, each blade 40 may be connected to the base 30 via a single moving protrusion 21 and connected to the rotatable part 20 via a single pivot protrusion 31. It will be appreciated that the moving protrusions 21 and the pivot protrusions 31 may not be pins but may be any suitable protrusions, such as protrusions that protrude from a sheet of material (e.g. sheet metal) especially wherein the base 30 or the rotatable part 20 comprises, or is formed of, said sheet of material. The protrusions may be etched portions of the sheet of material that are bent upwards or downwards from the sheet of material. The protrusions may protrude from the base 30 or the rotatable part 20 in directions parallel to the primary axis O. The base 30 or the rotatable part 20 may comprises or be formed of a sheet of material, such as sheet metal. At least some of the electrical connections required for the operation of the actuator assembly 10 may be laid (e.g. printed or attached) onto a (coated or non-coated) surface (e.g. the top surface) of the sheet of material in the form of electrical tracks. In the illustrated embodiments, the VA assembly 1 is only described as being for use with a lens assembly and / or a camera assembly. However, it will be appreciated that the VA assembly 1 may instead be used for other applications and with other devices. For example, the VA assembly 1 may be used to control the flow of liquids or gases in a flow control device. It will be appreciated that any electrical connections required for the actuator assembly 10 may be e.g. insert moulded into the rotatable part 20 and / or the base 30. It will also be appreciated that any electrical connections required for the actuator assembly 10 may be e.g. laid (e.g. printed or attached) onto a (coated or non-coated) surface (e.g. the top surface) of the rotatable part 20 and / or the base 30. Manufacturing ofVA with biased pins The embodiments described above address the problem of backlash within the blade drive mechanism of a variable aperture assembly in which the pivot protrusion and the moving protrusion move together or apart as the size of the aperture changes. The above embodiments address this by incorporating compliance within the blades such that this change in protrusion spacing can be accommodated within the blade. Portions of the blades define flexures or other deformable elements that bear against one or both protrusions to reduce or remove backlash. An alternative approach to backlash mitigation is to mount one or both protrusion upon flexures forming part of the base and / or the rotatable part such that as the rotatable part rotates relative to the base the protrusions remain a fixed distance apart. An example of such a variable aperture assembly is given in WO2024 / 057042A1 which is hereby incorporated by reference. Each blade may be provided with a pair of holes / slots to receive a respective pair of protrusions. The effect is that as the rotatable part is driven, the moving protrusion rotates about the pivot protrusion (or vice versa). This biasing of the protrusions, built into the base and / or the rotatable part addresses the problem of backlash by removing some tolerances associated with a protrusion in a slot. This means that "at rest" (that is, prior to assembly, the protrusions and the holes in the blades do not align (they require biasing) which presents an issue for assembly - there is a risk that if forced into place the blades could be damaged. Figures 16 to 24 disclose various methods for aligning the protrusions and blade holes during assembly where at least one protrusion is mounted on a flexure such that it can move radially. Assembly Jig Figures 16a and 16b illustrate assembly jig could be used to bias the protrusion positions during assembly of blades within a variable aperture assembly. Figure 16a shows a blade 200 including first and second holes 201, 202 to receive a pivot protrusion 203 and a moving protrusion 204 mounted on base 205 and rotatable part 206 respectively. It can be seen that at rest the holes 201, 202 and protrusions 203, 204 are misaligned. Other than one protrusion being radially biased, the arrangement of base and rotatable part may be generally the same as described for Figures 1, 6, and 7. For the example of a sprung moving protrusion 204 a jig 207 interfaces between each spring arm 209 and the base 205. Specifically, jig 207 larger than the at rest gap between the moving protrusion spring arm 209 and the base 205 such that as it is inserted in the direction of arrow 208 the jig pushes these components further apart as shown in Figure 16b, with spring arm 209 moving in the direction of arrow 210. The biasing feature 211 upon jig 207 is slightly wider than the nominal gap 212 between the base 205 and the spring arm 209 (shown in Figure 16a) in order to push the spring arm 209 and has a lead in to allow easy insertion. The biasing feature 211 is sized so that once inserted between base 205 and spring arm 209 the protrusions 203, 204 are appropriately spaced to be received in the corresponding holes 201, 202 in the blades. It will be appreciated that there may be a separate jig 207 provided for each pair of protrusions, for each blade. Those jigs may be interconnected (and thus viewed as a single overall jig) so that they may be inserted at all points around the aperture in one go. The jig 207 could be brought in from the bottom (as shown above) or from the top, providing it has sufficient clearance to the blades themselves. This is shown in Figure 17: the dashed boxes 215 illustrate suitable jig insertion locations where the gap between spring arms 209 and base 205 is accessible from either above or below the variable aperture assembly. Alternatively, as shown in Figures 18a, 18b the jig biasing features 220 could be slightly elliptical pins inserted between spring arms 209 and base 205 which when rotated push the spring arms 209 to achieve the desired biasing spacing. Figures 18a and 18b show each biasing feature in respective first and second rotational positions. Figure 19 shows a further alternative jig in which two layers of rotating wedges 225, 226 are used to move the arms into correct position. A first ring 227 (only part of which is shown) supports a first plurality of wedges 225 configured to rotate clockwise to deflect a first subset of spring arms 209 whilst simultaneously a second ring 228 (only part of which is shown) supports a first plurality of wedges 226 is configured to rotated anticlockwise to deflect a second subset of spring arms 209. Rings 227, 228 may also be used to centre the base 205 and rotatable part 206 relative to each other. The motion may be largely linear. The ring part of the jig may be retractable so that the wedges 225, 226 overlap and can then be removed vertically through a gap in the blades 200. Figure 20 shows a side view of the variable aperture assembly and jig of Figure 19 and the planes the two rings 227, 228 are positioned in. The wedges 225, 226 may engage with the spring arms 209, similarly, to as described for the preceding embodiments, or they may engage directly with the protrusions 203, 204. If the protrusions are deflected directly, the blades 200 will need to be pushed down onto the protrusions once the wedges are removed. In a further alternative shown in Figure 21, instead of the wedge features being part of an external jig, wedges 230 may be part of the base 205 (as illustrated) and / or the rotatable part 206, such that when the rotatable part 206 is rotated beyond its operational range, the wedges 230 interact with the spring arms 209 and push the protrusions 203, 204 to the required distance apart. In one implementation the rotatable part 206 is rotated in one direction to add half the blades using a first subset of wedges 230 to position the protrusions 203, 204 and then rotated in the other direction to add the remaining blades using a second subset of wedges 230 to position the protrusions 203, 204. Endstops to define the normal range of motion of the variable aperture assembly can be added separately after the blades are assembled or the blade mechanism may be constructed as a self-contained subassembly and then added to the main assembly later. A further option for wedges forming part of the base or rotatable part is for them to be sacrificial: once the blades have been added by prising the protrusions to the correct spacing the wedges can removed from the assembly. This would allow for the rotation required to space the protrusions for assembly to be within the normal range of motion of the variable aperture assembly and so not interfere when fully assembled during operation. As shown in Figures 22 and 23, the protrusions 203, 204 on both the base 205 and rotatable part 206 may be made conical (Figures 22) or have their facing surfaces 240 chamfered (Figure 23). This allows blades to be held on a vacuum chuck and pushed onto the protrusions. The vacuum force needs to be low enough to allow movement of the leaf as it positions itself on the static pin and correctly positions the moving spring arm 209. The moving spring arms 209 could be directly pushed in a radial pattern through clearance features in the base 205. In some examples the moving spring arms 209 may be extended so that they can be deflected without clearance being needed in the base 205. A further option is that the moving protrusion 204 could be made longer than the pivot protrusion 203. The blade 200 can be positioned on to the moving protrusion 204 and then shifted to align with the shorter pivoting protrusion 203 and lowered to the bottom of both protrusions. Essentially a lateral force applied to the moving protrusion via the blade 200 deforms the spring arm 209. A further option is for the blade to be angled during loading so the pivot protrusion is inserted through the blade hole before the moving protrusion (or vice versa). Once the pivot protrusion is fully inserted through the blade, the blade is rotated into a horizontal position and the moving protrusion is pushed away from the pivot protrusion until it engages with the moving protrusion hole and slides through the blade. The blade holes can be elongated or enlarged to allow the protrusions to be inserted through the angled blade. A further option is for the rotatable part to be offset in XY relative to the base to position individual moving protrusions so they align with holes in one blade at a time. A further option is for blade holes to be oversized relative to the protrusion because the pins are biased towards each other. A further option is to extend the rotation of rotatable part so that the protrusions align with the blade 5 holes. A further option illustrated in Figure 25 is to rotate the rotatable part 206 such that the distance between the protrusions 203, 204 matches that of the holes in the blades 200. This may be beyond the normal stroke window of the variable aperture assembly. This approach may be simplified if the blade 10 mechanism is assembled as a subassembly and then added to the actuator assembly complete with endstops which define the correct stroke window. In some of the embodiments of Figures 16a to 24 the blades are designed to take up a certain amount of deformation so will not be damaged when pressed into place on the protrusions.

Claims

1. A blade for a variable aperture assembly comprising a base and a rotatable part, wherein the blade is configured to be connectable to the base via a first protrusion, and connectable to the rotatable part via a second protrusion,wherein the blade is configured to resiliently deform to bias the second protrusion and the first protrusion relative to each other.

2. A blade according to claim 1, wherein the blade is configured to resiliently deform so as to accommodate a change in distance between the second protrusion and the first protrusion.

3. A blade according to claim 1 or 2, comprising an engaging arm configured to accommodate a change in distance between the second protrusion and the first protrusion.

4. A blade according to claim 3, configured such that the engaging arm moves toward a main body of the blade as the distance increases.

5. A blade according to claim 3 or 4, configured such that the engaging arm moves away from a main body of the blade as the distance increases.

6. A blade according to any of claims 3-5, wherein the engaging arm comprises a flexure arm.

7. A blade according to any of claims 3-6, wherein the engaging arm is configured to engage withthe first protrusion and / or the second protrusion.

8. A blade according to any preceding claim, comprising at least one edge configured to engage with the first protrusion and at least one edge configured to engage with the second protrusion.

9. A blade according to claim 8, wherein the at least one edge configured to engage with the first protrusion is curved around the first protrusion and / or the at least one edge configured to engage with the second protrusion is curved around the second protrusion.

10. A blade according to claim 8 or 9, wherein the at least one edge configured to engage with the first protrusion faces away from the at least one edge configured to engage with the second protrusion.

11. A blade according to any preceding claim, wherein the blade is configured to bias the second protrusion and the first protrusion away from each other.

12. A blade according to claim 8 or 9, wherein the at least one edge configured to engage with the first protrusion faces toward the at least one edge configured to engage with the second protrusion.

13. A blade according to any of claims 1-9 or 12, wherein the blade is configured to bias the second protrusion and the first protrusion toward each other.

14. A blade according to any of claims 1-6 comprising the first protrusion and / or the second protrusion.

15. A blade according to any preceding claim, comprising an aperture defining edge configured to partly define a variable aperture of the variable aperture assembly.

16. A blade according to any preceding claim, wherein the blade has a thickness of at most 100pm, optionally at most 50pm, and optionally at most 30pm.

17. A variable aperture assembly comprising:a base;a rotatable part;an actuator assembly configured to drive rotation of the rotatable part relative to the base about a primary axis to any rotational position within a range of movement;a plurality of the blade of any preceding claim connected to the base via a plurality of first protrusions, and connected to the rotatable part via a plurality of second protrusions, and arranged to define a variable aperture with a central axis which coincides with the primary axis;wherein said rotation of the rotatable part drives each second protrusion to move along a path, which drives rotation of the plurality of blades about the first protrusions, wherein said rotation of the plurality of blades changes the size of the variable aperture.

18. A variable aperture assembly according to claim 17, wherein the path is an arc of a circle centred around the primary axis.

19. A variable aperture assembly according to claim 17 or 18, wherein:the at least one edge configured to engage with the first protrusion engages with the first protrusion at a point on a straight line connecting a centre of the first protrusion with a centre of thesecond protrusion; and / orthe at least one edge configured to engage with the second protrusion engages with the second protrusion at a point on a straight line connecting a centre of the first protrusion with a centre of the second protrusion.

520. A variable aperture assembly according to claim 19, wherein the blades are configured to bias respective second protrusions and respective first protrusions relative to each other such that the respective blades are bistable.10 21. A camera comprising:the variable aperture assembly of any one of claims 17 to 20;a lens assembly; andan image capture device;wherein light passing through the variable aperture assembly passes is focused by the lens and 15 is received by the image capture device.

22. An electronic device incorporating the camera of claim 21.38

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