WO2020222002A1

WO2020222002A1 - Sma actuator

Info

Publication number: WO2020222002A1
Application number: PCT/GB2020/051048
Authority: WO
Inventors: Peter van WYK; Stephen Matthew BUNTING; Alexander Doust
Original assignee: Cambridge Mechatronics Limited
Priority date: 2019-04-29
Filing date: 2020-04-29
Publication date: 2020-11-05
Also published as: GB2615663A; CN113767219A; GB2597208B; GB201905955D0; GB2615664A; GB2615663B; GB202305446D0; GB2597208A; GB2615664B; GB202305447D0; GB202116542D0

Abstract

An SMA actuation apparatus arranged to drive the operation of an iris element is provided, the actuation apparatus comprising: an iris drive mechanism arranged to open and close the aperture of the iris based on an input motion; and at least one SMA actuator wire arranged to provide, on contraction of the actuator wire, said input motion. The actuator apparatuses may have a low form factor, and which may be, for example, suitable for use in folded camera assemblies and other apparatuses in which the space available for control assemblies is limited.

Description

SMA ACTUATOR

The present techniques generally relate to the use of shape memory alloy (“SMA”) actuator wires to provide control of an iris.

There are a variety of apparatuses in which it is desired to provide control of a movable element. 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. WO 2011/104518 discloses examples of SMA actuation apparatuses which are suitable for use in miniature cameras.

Some miniature cameras have a folded optics arrangement, in which one or more lens elements have their optical axis arranged orthogonal to the axis along which light entering the camera first passes. A mirror or prism can be used to“fold” the optical path. Fig. 1 shows, schematically, the general configuration of a possible folded optics arrangement which is contained within a housing or cover 1. In Fig. 1, the optical axis of the lens element 10 lies along the z-axis between the prism/mirror 12 and the image sensor 20. Light enters the optics arrangement in the y-direction shown before being“folded” to pass along the z-axis. As shown in Fig. 1, movement in the x- and y-directions can provide for optical image stabilisation (“OIS”), whilst movement in the z-direction can provide for auto-focus (“AF”). In certain arrangements the lens element 10 may include multiple lenses which are movable relative to each other, with such relative movement providing for zoom.

Folded optics arrangements are particularly useful in devices where the thickness of the device in the direction of initial light entry (the y-direction in Fig. 1) is constrained. For example, smartphones are becoming thinner, such that it becomes more difficult to mount all elements of a camera device along a single optical axis in the thickness direction of the handset. Regardless of the configuration of the optical apparatus, an iris 14 may be placed on the optical path. For example, as shown in Fig. 1 , the iris may be placed between the prism/mirror 12 and the lens element 10 (it will be appreciate that the iris could be placed at a variety of other positions along the optical path as well). The iris controls the amount of light entering the lens element 10 (and thus reaching the image sensor 20). Many existing configurations of iris are known which could be used in such an apparatus. However, generally a significant range of mechanical movement is required to operate the iris which can be difficult to provide in the context of, for example, a miniature camera, and particularly for a folded optics arrangement where the available space around the optical elements for the actuators is constrained. For example, the space available for components of an actuator arrangement which operates the iris may, in some arrangements, be limited to a few millimetres in height, and in some cases less than 1mm.

An object of the present techniques is to provide assemblies which control the operation of an iris.

A further object of the present techniques is to provide assemblies which control the operation of an iris and which have a low form factor, and which are, for example, suitable for use in folded camera assemblies and other apparatuses in which the space available for control assemblies is limited.

Approaches of the present techniques aim to provide actuator assemblies which satisfy one or more of the above objects. At their broadest, approaches of the present techniques provide assemblies for controlling an iris which use SMA actuator wires.

A first approach of the present techniques provides an SMA actuation apparatus arranged to drive the operation of an iris element, the actuation apparatus comprising: an iris drive mechanism arranged to open and close the aperture of the iris based on an input motion; and at least one SMA actuator wire arranged to provide, on contraction of the actuator wire, said input motion. SMA actuator wires may be particularly useful in providing drive to an iris element where the available space is limited.

Preferably the apparatus is arranged to amplify the range of motion of the actuator wire to provide the input motion. This can allow an actuator wire which has a relatively small range of motion (or“stroke”), generally dictated by the length of the wire and the strain that it can create on contraction, to drive an iris drive mechanism which has a much greater range of motion between its extreme positions. In some arrangements the amplification is achieved by arranging the actuator wire at an angle to the direction of the input motion. In particular the angle between the direction of the length of the actuator wire and the direction of the input motion is may be greater than 45 degrees. In such arrangements a contraction of the actuator wire may cause the iris drive mechanism to move in a direction which moves the actuator wire closer to an orientation perpendicular to the direction of the input motion. For angles close to (but less than) 90 degrees, particularly, but not exclusively between 60-80 degrees and preferably around 75 degrees, a relatively small change in the length of the actuator wire can result in a significant extent of motion of the iris drive mechanism. The apparatus may include a plurality of SMA actuator wires which are arranged such that at least one of the actuator wires is arranged, on contraction, to provide said input motion in a first direction, and at least another one of the actuator wires is arranged, on contraction, to provide said input motion in a second direction which is opposite to said first direction. In this way the actuator wires can drive the iris drive mechanism in both directions.

The input motion may, in some arrangements, be a lateral motion. In other arrangements the input motion may be a rotational motion. When the input motion is rotational motion, the “direction” of that motion is the instantaneous direction of motion at the time of action (i.e. at any point in the range of motion) and includes, in particular, the direction of motion which occurs at a steady state or rest position of the iris mechanism, which may be, for example, at the extremes of the range of motion of the mechanism.

The apparatus may also include at least one group of a plurality of SMA actuator wires which is arranged, on contraction of all wires in the group, to provide said input motion in one or both directions. By arranging a plurality of wires in a group, the wires can be arranged such that, whilst they individually do not act entirely in a direction of input motion, when activated collectively they only exert a force in a direction of input motion. The apparatus may include two groups of this kind, one acting in each direction.

In certain arrangements the apparatus further comprises an intermediate movable element, wherein at least one SMA actuator wire is arranged between the iris drive mechanism and the intermediate element, and a further SMA actuator wire is arranged between the intermediate element and a fixed point. This arrangement can allow a plurality of SMA actuator wires to be connected“in series” to provide the input motion. Thus even if it is not possible to arrange a single actuator wire so as to generate sufficient stroke (even with the angling of the wire), a plurality of wires can be joined to create sufficient stroke across the combination.

In some arrangements the apparatus further includes a rigid element connecting the actuator wire to the iris drive mechanism. The rigid element may serve to change the direction of the motion generated by the actuator wire to the direction of the input motion desired by the iris drive mechanism. This may allow the actuator wire to be positioned in a location which is removed from the iris drive mechanism, which may allow a greater length of actuator wire to be used whilst retaining the desired form factor and dimensions for the apparatus in which the actuator apparatus is incorporated.

The rigid element may alternatively or additionally provide for its own amplification of the stroke of the actuator wire, for example by using lever principles. For example, in certain arrangements the rigid element is arranged to pivot about a pivot point, the actuator wire is arranged, on contraction, to cause rotational movement of the rigid element, and a point of connection of the iris drive mechanism to the rigid element is further from the pivot point than a point of connection of the actuator wire to the rigid element. By arranging the rigid element between the actuator wire and the iris drive mechanism in this manner, a lever with a displacement ratio of greater than 1 can be created, such that the stroke of the actuator wire which drives the rigid element is transformed into a greater stroke at the iris drive mechanism. The pivot in such levers may be a fixed point (which may include a bearing), or there may be a plurality of actuator wires arranged so as to apply a torque to the rigid element and pivot it about a point in space without the rigid element being attached to anything else at that point (and, by control of the relative activation of the actuator wires, that point may be in different positions).

In certain arrangements the actuator wire is arranged, on contraction, to cause translational movement of the rigid element, and the connection between the rigid element and the iris drive mechanism is configured to convert said translational movement into said input motion, wherein the directions of said translational movement and of said input motion are different. This can allow the actuator wires to be arranged in positions which allow longer wires to be used whilst still conforming, substantially at least, to the overall form and dimensions of the apparatus.

For example, the rigid element may have an engagement portion which engages with the iris drive mechanism, wherein the engagement portion includes an edge which engages with the iris drive mechanism, the edge being inclined relative to the direction of the input motion. This edge (or“ramp”) can be used to translate movement of the rigid element into motion in another plane, for example, one which is perpendicular to the plane of the motion of the rigid element. The configuration of the edge (or slot, which is, in effect, an arrangement of two substantially parallel edges), can also provide for mechanical advantage and/or an increase in displacement ratio between the motion of the rigid element and the input to the iris drive mechanism.

The apparatus may further include a bearing which is arranged to constrain movement of the rigid element. Such a bearing may allow the actuator wires to be angled relative to the desired direction of motion of the rigid element, whilst not requiring a balanced set of forces to be applied to the rigid element to achieve the desired motion. In other arrangements, a plurality of actuator wires are provided such that activation of a group of the wires creates an overall force in the desired direction of motion of the rigid element. In such arrangements a bearing may not be necessary. In certain arrangements there are a plurality of SMA actuator wires which are arranged such that at least one of the actuator wires is arranged, on contraction, to move the rigid element so as to provide said input motion in a first direction, and at least another one of the actuator wires is arranged, on contraction, to move the rigid element so as to provide said input motion in a second direction which is opposite to said first direction. In these arrangements there are actuator wires acting to drive the iris drive mechanism in opposite directions, so that the iris aperture can be both opened and closed by activation of different ones of the actuator wires. In some arrangements, the apparatus may further include a biasing element which urges the iris drive mechanism towards one extreme of its range of movement. This biasing element which may be, for example, a spring, can mean that the actuator wire or wires can be arranged to provide a force on the iris drive mechanism in only one direction, whilst the biasing element acts to return the iris drive mechanism when the actuator wire relaxes to its uncontracted state.

The apparatus may further include a bearing which is arranged to constrain movement of the iris drive mechanism to the directions of said input motion. This may allow the apparatus to include an arrangement of SMA actuator wires (or a single wire) which is asymmetrical as the asymmetry in the forces exerted by the actuator wires can be compensated for and accommodated by the bearing.

The apparatus may further comprise a control circuit electrically connected to the SMA actuator wires for supplying drive signals thereto.

The apparatus may further comprise an iris connected to the iris drive mechanism and having an aperture which is opened and closed by the input motion.

In certain arrangements, the apparatus is an optical apparatus and may further comprise an image sensor arranged to receive light passing through the iris. Such arrangements may, for example, be used in miniature cameras.

In certain arrangements the apparatus may further comprise a diverter element fixed to the support structure and arranged to change the direction of light entering the apparatus such that it passes through the iris to the image sensor. The diverter element may, for example, be a mirror or a prism. Such apparatuses may form part of a folded camera, where the iris and the image sensor are arranged along a different axis to the axis along which light enters the apparatus. In certain arrangements, the actuator wire(s) and the rigid element, if present, are configured so that their profile in at least one direction is very slim (e.g. less than 5mm, preferably less than 1mm). In the case of apparatuses which comprise a diverter element, this direction may be same as the direction of the light entering the apparatus.

In certain arrangements which comprise a diverter element, the non-optical elements of the apparatus (e.g. the actuator wires, the iris mechanism and/or the rigid element, if present) are arranged such that they do not increase the dimension of the apparatus in the direction of light entering the apparatus beyond the dimensions of the optical elements of the apparatus (e.g. the image sensor, the iris, the diverter element and/or any lenses).

The apparatus may further comprise a sensor arranged to generate output signals

representative of the amount or intensity of light arriving at the image sensor, the control circuit being arranged to generate the drive signals in response to said output signals to open or close the aperture and thereby adjust the amount of light arriving at the image sensor. In this way the aperture of the iris can be adjusted to automatically account for the intensity of light arriving at the image sensor.

The apparatus of this approach may include any combination of some, all or none of the above-described preferred and optional features.

The present techniques may in general be applied to any type of device that comprises a static part and a moveable part which is moveable with respect to the static part. By way of non- limitative example, the actuator assembly may be, or may be provided in, any one of the following devices: a smartphone, a protective cover or case for a smartphone, a functional cover or case for a smartphone or electronic device, a camera, a foldable smartphone, a foldable smartphone camera, a foldable consumer electronics device, a camera with folded optics, an image capture device, an array camera, a 3D sensing device or system, a servomotor, a consumer electronic device (including domestic appliances such as vacuum cleaners, washing machines and lawnmowers), a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader (also known as an e-book reader or e-book device), a computing accessory or computing peripheral device (e.g. mouse, keyboard, headphones, earphones, earbuds, etc.), an audio device (e.g. headphones, headset, earphones, etc.), a security system, a gaming system, a gaming accessory (e.g. controller, headset, a wearable controller, joystick, etc.), a robot or robotics device, a medical device (e.g. an endoscope), an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device (e.g. a watch, a smartwatch, a fitness tracker, etc ), a drone (aerial, water, underwater, etc.), an aircraft, a spacecraft, a submersible vessel, a vehicle, an autonomous vehicle (e.g. a driverless car), a tool, a surgical tool, a remote controller (e.g. for a drone or a consumer electronics device), clothing (e.g. a garment, shoes, etc.), a switch, dial or button (e.g. a light switch, a thermostat dial, etc.), a display screen, a touchscreen, a flexible surface, and a wireless communication device (e.g. near-field communication (NFC) device). It will be understood that this is a non-exhaustive list of example devices.

Actuator assemblies as described herein may be used in devices/systems suitable for image capture, 3D sensing, depth mapping, aerial surveying, terrestrial surveying, surveying in or from space, hydrographic surveying, underwater surveying, scene detection, collision warning, security, facial recognition, augmented and/or virtual reality, advanced driver- assistance systems in vehicles, autonomous vehicles, gaming, gesture control/recognition, robotic devices, robotic device control, touchless technology, home automation, medical devices, and haptics. Embodiments of the present techniques will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a schematic drawing of a folded optics arrangement and has already been described; Fig. 2 shows an SMA actuator assembly according to an embodiment of the present techniques;

Fig. 3 shows an SMA actuator assembly according to an embodiment of the present techniques;

Fig. 4 shows an SMA actuator assembly according to an embodiment of the present techniques; and

Fig. 5 is a schematic drawing of a control circuit which may be used in embodiments of the present techniques.

Figs. 2-4 show three embodiments of SMA actuator assemblies according to the present techniques. In these embodiments, like reference numerals are used to refer to

identical/similar features and, unless indicate otherwise or impractical, features described in relation to one embodiment are equally applicable to each of the other embodiments.

Fig. 2 shows three variations on a first embodiment of an SMA actuator assembly according to the present techniques. In the arrangements shown in Fig. 2, SMA actuator wires 51 are arranged at shallow angles to the perpendicular of the desired direction of motion. This shallow angle arrangement amplifies the normal movement (stroke) of the SMA actuator wires on contraction.

In the arrangement shown in Fig. 2A, a single SMA actuator wire 51a, 51b acts in each direction on the iris mechanism 30. The top actuator wire 51a depicted in Fig. 2A acts to urge the mechanism 30 downwards, whilst the lower actuator wire 5 lb acts to urge the mechanism 30 upwards. To open and close an iris, the mechanism 30 generally needs to be able to move through a distance of around 400 mm. To prevent rotation and/or transverse motion of the iris mechanism 30, the mechanism may be mounted on a bearing which constrains the motion of the mechanism to the desired linear motion (along the vertical axis of Fig. 2A).

The arrangement shown in Fig. 2B extends the arrangement in Fig. 2A by providing multiple actuator wires 51a, 51b (in this case two) on each side of the iris mechanism 30 to provide the respective actuations in either direction. This allows an increased force to be applied to the mechanism (if required) and also balances the transverse (in the left-right direction in Fig.

2B) and rotary forces on the mechanism, which may mean that it is not necessary to mount the mechanism 30 on a bearing. However, this arrangement may require more space to accommodate the extra actuator wires.

Fig. 2C shows an alternative arrangement in which a plurality of shallow-angled actuator wires, 51c, 5 Id are connected in a“chained” configuration. In the arrangement shown in Fig. 2C, the iris mechanism 30 is connected by a first set of actuator wires 51c to two rigid movable plates 52. Each of those plates is in turn connected to two further actuator wires 5 Id which connect it to the structure of the apparatus in which the arrangement is mounted. It will be appreciated that the“chain” of plates 52 and actuator wires 51 could be further extended so that there are two (or more) plates and three (or more) sets of actuator wires on each side of the mechanism 30.

In alternative arrangements, only a single actuator wire 51 may be used at each stage in the chain (between the mechanism 30 and the plate 52; and/or between subsequent plates; and/or between the final plate and the structure of the apparatus), with the single actuator wires operating in a similar manner to that shown in Fig. 2A. Such arrangements may use one or more bearings to constrain the motion of the mechanism 30 and/or the plates 52 to the desired direction.

The chaining of the actuator wires 51 with the plates 52 allows the displacement achievable in each direction to be multiplied by the number of“links” in the chain. The actuator wires 51 used at each stage could be identical, or could be different, thereby giving a range of control options for the actuation of the mechanism.

It will be appreciated that, although the arrangements shown in Figs. 2A-2C show single actuator wires 51, multiple wires could be used in any or all of the positions, for example by positioning additional wires in parallel to those shown in a direction perpendicular to the plane of the figures. This may allow increased force to be applied to the mechanism 30.

Further, whilst each of the arrangements shown in Figs. 2A-2C show (at least) a pair of actuator wires 51 which are arranged to act on the mechanism 30 in opposite directions, the wires causing motion in one of the directions could be replaced by a biasing element, such as a return spring, which can bias the mechanism into a position at one extreme of its range of motion, and against which the remaining wires act when causing the mechanism 30 to move. In testing, the applicant has determined that it is possible to achieve the desired stroke for an iris mechanism in a folded camera using an angled wire arrangement such as that shown in Figs. 2A and 2B. Specifically, using an SMA actuator wire which can provide up to 2% strain, the applicant has determined that it is possible to achieve 400 mm of vertical stroke (in the direction shown in Figs. 2A and 2B) of the iris mechanism whilst ensuring that the actuator assembly does not exceed a height (as shown in Figs. 2A and 2B; the y-direction in Fig. 1) of 5.5mm and a width (the x-direction in Fig. 1) of 12mm (and potentially down to 1 lmm). Using a known iris mechanism, this provides for a maximum iris opening of ~3mm. Figs. 3A-3D show four variations of a second embodiment of an SMA actuator assembly according to the present techniques. In this embodiment, the SMA actuator wires 51 are connected to mechanical arrangements which cause amplification of the range of motion of the actuator wires themselves. Each of Figs. 3A-3D show the potential positioning of the actuator assembly relative to an optical apparatus 1, such as a folded camera. The outline form of the optical apparatus 1 is shown by the dotted lines.

In the arrangement shown in Fig. 3 A, two SMA actuator wires 51 are connected with their fixed ends 54 attached to the optical apparatus 1, and their movable ends 53 connected to an arm 55 in a V-shape. The apparatus is configured so that the actuator wires 51 oppose each other and the actuator wires are arranged at a shallow angle to the arm 55. The arm 55 is pivoted about a pivot 56. The end of the arm 55 distal from the pivot drives the iris mechanism 30 which controls the opening and closing of the iris 14. In the arrangement shown, the distal end of the arm 55 is attached to a link 57 whose rotation about the centre of the iris 14 causes the leaves of the iris to reduce or increase the aperture at the centre of the iris. However, the distal end of the arm 55 could be connected to alternative mechanisms for controlling the iris.

The arm 55 acts to amplify the range of motion (also referred to as the“stroke”) available from the SMA actuator wires 51. The position of the connection of the movable ends 53 of the actuator wires 51 on the arm 55 relative to both the pivot 56 and the link 57 will determine the stroke and force available to drive the iris mechanism 30.

In the arrangement shown, the main moving parts of the apparatus (the actuator wires 51 and the arm 55) are positioned on the top of the optical apparatus 1. In the case of a folded camera oriented as shown in Fig. 1, this makes use of the large area available on the top of the camera, but will lead to an increase in the overall height of the camera in the y-direction, which may be undesirable. In such arrangements, the arm 55 and actuator wires 51 could be mounted on the side of the optical apparatus, like the arrangement shown in Fig. 3B. In an alternative arrangement, the pivot effect may be provided by a flexure which is arranged to guide the pivoting end of the arm 55, or another portion of the arm 55, to allow it to rotate. Fig. 3B shows a further alternative arrangement of an SMA actuator assembly. Again, two SMA actuator wires 51 are used in an opposed fashion and have their fixed ends 54 attached to the optical apparatus 1 and their movable ends attached to an arm 58. However, rather than causing rotational movement of the arm 58, the actuator wires 51 are mounted to cause lateral movement of the arm 58 (possibly in conjunction with a bearing, not shown) in the directions shown by the arrows.

The end of the arm 58 which engages with the link 57 of the iris mechanism 30 is inclined so as to form a slope or ramp 59. This ramp 59 engages with the link 57 to translate lateral movement of the arm 58 in one plane into movement of the link in a generally perpendicular direction which acts to open or close the iris 14. The angle of the ramp 59 and the length of the link 57 can be chosen based on the desired force and stroke required to operate the iris mechanism.

The link 57 may be urged in a direction which favours a positioning of the link at the“lower” end of the ramp 59 by a biasing element (not shown) such as a spring. This means that it is not necessary for the arm 58 to pull the link 57 back to the end position. Alternatively, the arm 58 may be provided with a slot into which the end of the link 57 is inserted, thus allowing the translational movement of the arm 58 in both directions to cause perpendicular motion of the link 57. Alternatively a further arm (not shown) may be provided with an opposing ramp to drive the link 57 in the opposite direction, or a second link may be provided as part of the iris mechanism 30 which provides for drive in the opposite direction (for example, mounted on the opposite side of the optical apparatus 1).

As well as the potential to amplify the stroke of the SMA actuator wires 51 by the choice of the angle of the ramp 59, the mounting of the actuator assembly along the side of the optical apparatus 1 allows for relatively long SMA actuator wires 51 to be used, which can provide the desired stroke to the link 57, despite the more restricted dimensions of the available space alongside the optical apparatus 1 in the plane of the link 57 itself. By mounting the actuator assembly on the“side” of the optical assembly 1 as shown in Fig. 3B, the actuator assembly does not add to the height of the optical assembly (the y-direction in Fig. 1) which is normally the most-constrained dimension in, for example, a folded camera.

Fig. 3C shows a further alternative arrangement which operates in a similar manner to the arrangement shown in Fig. 3B. In the arrangement shown in Fig. 3C, the SMA actuator wires 51 drive a further arm 60 which is connected to the drive arm 58. The drive arm 58 is kinked so that the further arm 60 is offset, in the plane of the assembly, from the ramp 59. For clarity, the iris mechanism has been omitted from this figure, but its interaction with the actuator assembly can be appreciated from the similarities with the arrangement shown in Fig. 3B.

The arrangement shown in Fig. 3C further amplifies the stroke available from the actuator wires 51 by arranging them in an angled and crossed configuration within the available footprint on the side (in this case the top) of the optical apparatus 1. This allows the longest available length of actuator wire to be used within that footprint.

Fig. 3D shows a further alternative arrangement in which an arm 55 is used to connect between the actuator wires 51 and the link 57 of the iris mechanism 30. In this arrangement, four actuator wires 51 are arranged with a pair of crossed wires on either side of the arm 55 with their fixed ends connected to the optical apparatus (not shown in this figure for clarity) approximately at the corners of the top surface of the apparatus. By appropriate activation of pairs of the actuator wires 51, the arm 55 can be made to rotate about a virtual axis in the approximate centre of the arm. In this respect, the motion and operation of the actuator assembly and the link 57 in the iris mechanism is similar to that described above in relation to Fig. 3 A. Alternatively, by a different approach to activation of pairs of the actuator wires 51, the arm 55 can be made to shift in the plane of the actuator assembly, either perpendicular to the optical axis passing through the iris 14 (substantially “up” and“down” in the orientation of Fig. 3D) or parallel to the optical axis (substantially “left” and“right” in the orientation of Fig. 3D). In the case of parallel motion, a ramp such as that described in relation to the arrangements in Figs. 3B and 3C above may be used to translate the motion of the arm 55 to the desired motion of the link 57. Fig. 4 shows a third embodiment of an actuator assembly according to the present techniques. The actuator assembly shown in Fig. 4 is similar in arrangement to those shown in Fig. 2. However, in the arrangement shown in Fig. 4, the actuator wires 51 are arranged on one side of the iris mechanism 30. This means that the fixed ends 54 of both wires 51 are located in a similar part of the apparatus, such that providing the appropriate electrical connections is simpler.

The iris mechanism 30 in the arrangement shown in Fig. 4 is arranged to rotate about an axis 61, such that the input forces from the actuator wires 51 are converted into rotary motion of the mechanism as indicated by the double-headed arrow. Whilst the arrangement shown in Fig. 4 has two actuator wires 51 arranged to operate the mechanism 30 in opposite directions, the arrangement could also be provided with a single actuator wire 51 which acts against a biasing element which urges the mechanism 30 in the opposite direction.

Fig. 5 shows a schematic arrangement of a control circuit 40 for controlling an SMA actuator assembly, such as those shown in Figs. 2-4. The control circuit 40 generates drive signals for each of the SMA actuator wires 51. The control circuit 40 derives the drive signals from the desired movement represented by movement signals 41.

The movement signals are supplied to a matrix controller 42 that may be implemented in a processor or in hardware. The matrix controller 42 generates a control signal for each of the SMA actuator wires 51 on the basis of the movement signals 41 by relating the necessary contraction of each of the actuator wires to achieve the movements desired in the movement signals 41. Further details of the operation of the controller and the driving of SMA actuator wires are known to the skilled person, for example from WO 2011/104518, the relevant contents of which are hereby incorporated by reference.

The movement signals 41 may be generated based on sensor inputs, for example based on the amount or intensity of light sensed on the image sensor 20.

Except where the context requires otherwise, the term“bearing” is used herein as follows. The term“bearing” is used herein to encompass the terms“sliding bearing”,“plain bearing”, “rolling bearing”,“ball bearing”,“roller bearing” and“flexure”. The term“bearing” is used herein to generally mean any element or combination of elements that functions to constrain motion to only the desired motion and reduce friction between moving parts. The term “sliding bearing” is used to mean a bearing in which a bearing element slides on a bearing surface, and includes a“plain bearing”. The term“rolling bearing” is used to mean a bearing in which a rolling bearing element, for example a ball or roller, rolls on a bearing surface. In embodiments, the bearing may be provided on, or may comprise, non-linear bearing surfaces.

In some embodiments of the present techniques, more than one type of bearing element may be used in combination to provide the bearing functionality. Accordingly, the term“bearing” used herein includes any combination of, for example, plain bearings, ball bearings, roller bearings and flexures.

Although some of the above approaches have been described with specific reference to cameras and camera assemblies, it will be appreciated that the configuration and/or control of the actuator assemblies involved can be applied in other fields where control of an iris is desired.

Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and where appropriate other modes of performing present techniques, the present techniques should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that present techniques have a broad range of applications, and that the embodiments may take a wide range of modifications without departing from any inventive concept as defined in the appended claims.

Claims

1. An SMA actuation apparatus arranged to drive the operation of an iris element, the actuation apparatus comprising:

an iris drive mechanism arranged to open and close the aperture of the iris based on an input motion; and

at least one SMA actuator wire arranged to provide, on contraction of the actuator wire, said input motion.

2, An apparatus according to claim 1 wherein the apparatus is arranged to amplify the range of motion of the actuator wire to provide the input motion.

3. An apparatus according to claim 2 wherein the actuator wire is arranged at an angle to the direction of the input motion.

4. An apparatus according to claim 3 wherein the angle between the direction of the length of the actuator wire and the direction of the input motion is greater than 45 degrees.

5. An apparatus according to claim 3 or claim 4, wherein the apparatus includes a plurality of SMA actuator wires which are arranged such that at least one of the actuator wires is arranged, on contraction, to provide said input motion in a first direction, and at least another one of the actuator wires is arranged, on contraction, to provide said input motion in a second direction which is opposite to said first direction.

6. An apparatus according to any one of claims 3 to 5 further comprising an intermediate movable element, wherein at least one SMA actuator wire is arranged between the iris drive mechanism and the intermediate element, and a further SMA actuator wire is arranged between the intermediate element and a fixed point.

7. An apparatus according to claim 2 wherein the apparatus further includes a rigid element connecting the actuator wire to the iris drive mechanism.

8. An apparatus according to claim 7 wherein the rigid element is arranged to pivot about a pivot point, the actuator wire is arranged, on contraction, to cause rotational movement of the rigid element, and a point of connection of the iris drive mechanism to the rigid element is further from the pivot point than a point of connection of the actuator wire to the rigid element.

9. An apparatus according to claim 8 wherein the actuator wire is arranged, on contraction, to cause translational movement of the rigid element, and the connection between the rigid element and the iris drive mechanism is configured to convert said translational movement into said input motion, wherein the directions of said translational movement and of said input motion are different.

10. An apparatus according to claim 9 wherein the rigid element has an engagement portion which engages with the iris drive mechanism, wherein the engagement portion includes an edge which engages with the iris drive mechanism, the edge being inclined relative to the direction of the input motion.

11. An apparatus according to any one of claims 7 to 10 further including a bearing which is arranged to constrain movement of the rigid element.

12. An apparatus according to any one of claims 7 to 11 wherein there are a plurality of SMA actuator wires which are arranged such that at least one of the actuator wires is arranged, on contraction, to move the rigid element so as to provide said input motion in a first direction, and at least another one of the actuator wires is arranged, on contraction, to move the rigid element so as to provide said input motion in a second direction which is opposite to said first direction.

13. An apparatus according to any one of the preceding claims further including a biasing element which urges the iris drive mechanism towards one extreme of its range of movement.

14. An apparatus according to any one of the preceding claims further including a bearing which is arranged to constrain movement of the iris drive mechanism to the directions of said input motion.

15. An apparatus according to any one of the preceding claims further comprising a control circuit electrically connected to the SMA actuator wire or wires for supplying drive signals thereto.

16. An apparatus according to any one of the preceding claims further comprising an iris connected to the iris drive mechanism and having an aperture which is opened and closed by the input motion.

17. An apparatus according to claim 16 further comprising an image sensor arranged to receive light passing through the iris.

18. An apparatus according to claim 17 further comprising a diverter element arranged to change the direction of light entering the apparatus such that it passes through the iris to the image sensor.

19. An apparatus according to claim 17 or claim 18, as dependent on claim 15, further comprising a sensor arranged to generate output signals representative of the amount or intensity of light arriving at the image sensor, the control circuit being arranged to generate the drive signals in response to said output signals to open or close the aperture and thereby adjust the amount of light arriving at the image sensor.

20. An apparatus as claimed in any one of the preceding claims where the apparatus is any one of: a smartphone, a protective case for a smartphone, a functional case for a smartphone, a camera, a foldable smartphone, a foldable image capture device, a foldable smartphone camera, a foldable consumer electronics device, a camera with folded optics, an image capture device, an array camera, a 3D sensing device or system, a servomotor, a consumer electronics device, a domestic appliance, a mobile or portable computing device, a mobile or portable electronic device, a laptop, a tablet computing device, an e-reader, a computing accessory, a computing peripheral device, an audio device, a security system, a gaming system, a gaming accessory, a robot or robotics device, a medical device, an augmented reality system, an augmented reality device, a virtual reality system, a virtual reality device, a wearable device, a drone, an autonomous vehicle, a vehicle, a tool, a surgical tool, a remote controller, clothing, a switch, a dial, a button, a display screen, a touchscreen, a flexible surface, and a wireless communication device.