Patent Description:
In the case of a camera lens element, movement orthogonal to the optical axis may be utilised to provide optical image stabilisation (OIS) of an image focused by the camera lens element on an image sensor.

The purpose of OIS is to compensate for camera shake, that is vibration of the camera apparatus, typically caused by user hand movement, that degrades the quality of the image captured by the image sensor. OIS typically involves detecting the vibration by a vibration sensor such as a gyroscope sensor, and controlling, on the basis of the detected vibration, an actuator arrangement that adjusts the camera apparatus to compensate for the vibration. Several techniques for adjusting the camera apparatus are known. OIS by processing of a captured image is possible in principle but requires significant processing power. Accordingly, there has been developed mechanical OIS in which the optical system of the camera is adjusted mechanically.

A number of actuator arrangements employing mechanical OIS techniques are known and applied successfully in relatively large camera apparatuses, such as digital still cameras, are difficult to miniaturise. Cameras are becoming very common in a wide range of portable electronic equipment, for example mobile telephones and tablet computers, and in many such applications miniaturisation of the camera is important. The very tight packaging of components in miniature camera apparatuses presents great difficulties in adding OIS actuators within the desired package.

In one type of mechanical OIS, a camera lens element is moved orthogonal to the optical axis of the at least one lens. Such a type of OIS will be referred to herein as "OIS-shift". OIS-shift has the potential to reduce the size of the overall package for the camera as compared to a type of OIS in which a camera unit comprising an image sensor and a camera lens assembly for focussing an image on the image sensor is tilted relative to the support structure around two notional axes that are perpendicular to each other and to the optical axis of the lens assembly, for example as disclosed in <CIT> and <CIT>. This is because only the camera lens element is moved and the lateral movement thereof requires less clearance than tilting the entire camera.

<CIT> discloses an SMA actuator arrangement that employs OIS-shift. In <CIT>, there is employed a suspension system for suspending the camera lens element on the support structure that uses at least one ball to permit movement of the camera lens element relative to the support structure orthogonal to the optical axis but prevent movement along the optical axis. This provides good performance in operation. However, balls are difficult to handle in assembly, particularly in a miniature camera lens assembly. This has a negative impact of the manufacturing yield. Also, in practice the balls have a minimum size that limits miniaturisation of the arrangement.

It would therefore be desirable to provide an alternative method of suspension that does not suffer from these problems, but maintains the operation performance in permitting movement of the camera lens element relative to the support structure. Many types of suspension have high friction which makes them unsuitable for a camera lens element.

According to a first aspect of the present invention, there is provided a shape memory alloy actuator arrangement for a camera lens element, the shape memory alloy actuator arrangement comprising: a support structure; a movable element for supporting a camera lens assembly comprising at least one lens having an optical axis; plural shape memory alloy actuator wires connected between the support structure and the movable element in an arrangement wherein the shape memory alloy actuator wires are arranged, on selective driving, to move the movable element relative to the support structure in any direction orthogonal to the optical axis; and at least one plain bearing that bears the movable element on the support structure, allowing movement of the movable element relative to the support structure orthogonal to the optical axis.

Thus, at least one plain bearing is used to bear the camera lens element on the support structure, allowing movement of the camera lens element relative to the support structure orthogonal to the optical axis. A plain bearing is a bearing comprising two surfaces in contact with each other and permitting relative sliding motion. Of course, a plain bearing is a simple type of bearing which is known for use in other applications. Inevitably the contact provides friction which adversely affects the performance, particularly in a miniature arrangement. However, surprisingly, plain bearings can in fact be used to provide good performance in which the friction is sufficiently low to allow movement perpendicular to the optical axis. This is possible, in part, because the SMA actuator wires provide a high actuation force compared to other forms of actuator.

Furthermore, plain bearings may be formed with inherently small size along the height of the bearing, that is along the optical axis, especially compared to a suspension system employing balls. This allows the size of the arrangement to be reduced along the optical axis compared to that disclosed in <CIT>.

As the present motion orthogonal to the optical axis of the at least one lens, the plain bearing may comprise conforming surfaces in contact with each other which are planar. By using a plain bearing comprising planar conforming surfaces, it is possible to avoid contact at a point or along a line. Such contact at a point or along a line may be disadvantageous, as wear would be concentrated in a small area, which could over time cause changes in the area of contact and hence the properties of the bearing. In contrast, the advantage of a plain bearing comprising planar conforming surfaces is that wear is distributed across a larger area, which area remains stable over time.

Similar problems to those described above for a camera lens element occur also in the more general case of an SMA actuator arrangement for a movable element of any other type. <CIT> and <CIT> disclose optical image stabilization OIS arrangements to correct camera shake using shape memory alloys in the lens barrel.

Thus, according to a second aspect of the present invention, there is provided a shape memory alloy actuator arrangement, the shape memory alloy actuator arrangement comprising: a support structure; a movable element; at least one shape memory alloy actuator wire connected between the support structure and the movable element in an arrangement wherein the shape memory alloy actuator wire is arranged, on driving thereof, to move the movable element relative to the support structure; and at least one plain bearing that bears the movable element on the support structure, allowing movement of the movable element relative to the support structure.

In this more general case, the movement may be in a plane in which case the at least one plain bearing may comprise conforming surfaces that are planar, or may be rotational in which case the at least one plain bearing may comprise conforming surfaces that are cylindrical sections.

To allow better understanding, an embodiment of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:.

A camera apparatus <NUM> that incorporates an SMA actuator arrangement <NUM> in accordance with the present invention is shown in <FIG>, which is a cross-sectional view taken along the optical axis O. The camera apparatus <NUM> is to be incorporated in a portable electronic device such as a mobile telephone, or tablet computer. Thus, miniaturisation is an important design criterion.

The camera apparatus <NUM> comprises a camera lens assembly <NUM> suspended on a support structure <NUM> by an SMA actuator arrangement <NUM> that supports the camera lens assembly <NUM> in a manner allowing movement of the camera lens assembly <NUM> relative to the support structure <NUM> in two orthogonal directions each perpendicular to the optical axis O.

The support structure <NUM> is a camera support supporting an image sensor <NUM>. The support structure <NUM> comprises a base <NUM>, the image sensor <NUM> being mounted on the front side of the base <NUM>. On the rear side of the base <NUM>, there is mounted an IC (integrated circuit) chip <NUM> in which a control circuit is implemented, and also a gyroscope sensor <NUM>. The support structure <NUM> also comprises a can <NUM> protruding forwardly from the base <NUM> to encase and protect the other components of the camera apparatus <NUM>.

The camera lens assembly <NUM> comprises a lens carriage <NUM> in the form of a cylindrical body supporting two lenses <NUM> arranged along the optical axis O, although in general any number of one or more lenses <NUM> may be provided. The camera apparatus <NUM> is a miniature camera in which the lenses <NUM> (or lens <NUM> if a single lens is provided) have a diameter of at most <NUM>.

The camera lens assembly <NUM> is arranged to focus an image onto the image sensor <NUM>. The image sensor <NUM> captures the image and may be of any suitable type, for example a CCD (charge-coupled device) or a CMOS (complimentary metal-oxide-semiconductor) device.

In this example, the lenses <NUM> are supported on the lens carriage <NUM> in a manner in which the lenses <NUM> are movable along the optical axis O relative to the lens carriage <NUM>, for example to provide focussing or zoom. In particular, the lenses <NUM> are fixed to a lens holder <NUM> which is movable along the optical axis O relative to the lens carriage <NUM>. Although all the lenses <NUM> are fixed to the lens holder <NUM> in this example, in general one or more of the lenses <NUM> may be fixed to the lens carriage <NUM> and so not movable along the optical axis O relative to the lens carriage <NUM>, leaving at least one of the lenses <NUM> fixed to the lens holder <NUM>.

An axial actuator arrangement <NUM> provided between the lens carriage <NUM> and the lens holder <NUM> is arranged to drive movement of the lens holder <NUM> and lenses <NUM> along the optical axis O relative to the lens carriage <NUM>. The axial actuator arrangement <NUM> may be any suitable type, for example being a voice coil motor (VCM) or an arrangement of SMA actuator wires, such as is described in <CIT>.

In operation, the camera lens assembly <NUM> is moved orthogonally to the optical axis O in two orthogonal directions, shown as X and Y, relative to the image sensor <NUM>, with the effect that the image on the image sensor <NUM> is moved. This is used to provide OIS, compensating for image movement of the camera apparatus <NUM>, caused by for example hand shake.

The SMA actuator arrangement <NUM> will now be described in more detail with reference to <FIG> and <FIG>, <FIG> being an exploded view of the SMA actuator arrangement <NUM> omitting the SMA actuator wires <NUM>, and <FIG> being a side view of the SMA actuator arrangement <NUM> expanded along the optical axis O.

The SMA actuator arrangement <NUM> comprises a support plate <NUM> that forms part of the support structure <NUM> and is connected to the base <NUM>. The SMA actuator arrangement <NUM> further comprises a moving plate <NUM>. In this embodiment the moving plate <NUM> is the moving element, but it could equally form part of a movable element including other components. The moving plate <NUM> supports the camera lens assembly <NUM> and is connected to the lens carriage <NUM>. The support plate <NUM> and the moving plate <NUM> are integral sheets made of metal, for example steel such as stainless steel.

Each of the support plate <NUM> and the moving plate <NUM> is provided with a central aperture aligned with the optical axis O allowing the passage of light from the camera lens assembly <NUM> to the image sensor <NUM>.

Movement of the camera lens assembly <NUM> relative to the support structure <NUM> is driven by a lateral actuation arrangement comprising plural SMA actuator wires <NUM> connected between the support structure <NUM> and the movable element. Specifically, the support plate <NUM> is formed with crimps <NUM> and the moving plate <NUM> is formed with crimps <NUM>, the crimps <NUM> and <NUM> crimping the four SMA actuator wires <NUM> so as to connect them to the support plate <NUM> and the moving plate <NUM>. The SMA wires <NUM> may be perpendicular to the optical axis O or inclined at a small angle to the plane perpendicular to the optical axis O. Each of the SMA actuator wires <NUM> is held in tension, thereby applying a force between the support plate <NUM> and the moving plate <NUM> in a direction perpendicular to the optical axis O. In operation, the SMA actuator wires <NUM> are selectively driven to move the camera lens assembly <NUM> relative to the support structure <NUM> in any direction orthogonal to the optical axis O. The overall arrangement of the SMA wires <NUM> to achieve this is the same as described in <CIT>, as follows.

SMA material has the property that on heating it undergoes a solid-state phase change which causes the SMA material to contract. At low temperatures the SMA material enters the Martensite phase. At high temperatures the SMA enters the Austenite phase which induces a deformation causing the SMA material to contract. The phase change occurs over a range of temperature due to the statistical spread of transition temperature in the SMA crystal structure. Thus heating of the SMA actuator wires <NUM> causes them to decrease in length.

The SMA actuator wires <NUM> may be made of any suitable SMA material, for example Nitinol or another Titanium-alloy SMA material. Advantageously, the material composition and pre-treatment of the SMA actuator wires <NUM> is chosen to provide phase change over a range of temperature that is above the expected ambient temperature during normal operation and as wide as possible to maximise the degree of positional control.

On heating of one of the SMA actuator wires <NUM>, the stress therein increases and it contracts, causing movement of the camera lens element <NUM>. A range of movement occurs as the temperature of the SMA increases over the range of temperature in which there occurs the transition of the SMA material from the Martensite phase to the Austenite phase. Conversely, on cooling of one of the SMA actuator wires <NUM> so that the stress therein decreases, it expands under the force from opposing ones of the SMA actuator wires <NUM>. This allows the camera lens element <NUM> to move in the opposite direction.

The SMA actuator wires <NUM> have an arrangement in a loop at different angular positions around the optical axis O to provide two pairs of opposed SMA actuator wires <NUM> that are perpendicular to each other. Thus each pair of opposed SMA actuator wires <NUM> is capable on selective driving to move the camera lens element <NUM> in one of two perpendicular directions X and Y orthogonal to the optical axis O. As a result, the SMA actuator wires <NUM> are capable of being selectively driven to move the camera lens element <NUM> relative to the support structure <NUM> to any position in a range of movement in two directions orthogonal to the optical axis O. The magnitude of the range of movement depends on the geometry and the range of contraction of the SMA actuator wires <NUM> within their normal operating parameters.

The position of the camera lens assembly <NUM> relative to the support structure <NUM> perpendicular to the optical axis O is controlled by selectively varying the temperature of the SMA actuator wires <NUM>. This is achieved by passing through SMA actuator wires <NUM> selective drive signals that provide resistive heating. Heating is provided directly by the drive current. Cooling is provided by reducing or ceasing the drive current to allow the SMA wire <NUM> to cool by conduction, convection and radiation to its surroundings.

The drive signals for the SMA actuator wires <NUM> are generated and supplied by the control circuit implemented in the IC chip <NUM>.

The control circuit uses the output signals of the gyroscope sensor <NUM> which is a vibration sensor. The gyroscope sensor <NUM> detects the vibrations that the camera apparatus <NUM> is experiencing and its output signals represent the angular velocity of the camera lens element <NUM>. The gyroscope sensor <NUM> is typically a pair of miniature gyroscopes, for detecting vibration around two axes perpendicular to each other and the optical axis O, although in general larger numbers of gyroscopes or other types of vibration sensor could be used.

The drive signals are generated by the control circuit in response to the output signals of the gyroscope sensor <NUM> so as to drive movement of the camera lens element <NUM> to stabilise an image focused by the camera lens element <NUM> on the image sensor <NUM>, thereby providing OIS. The drive signals may be generated using a resistance feedback control technique for example as disclosed in any of<CIT>;<CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT> or <CIT>.

In addition, the SMA actuator arrangement <NUM> comprises three plain bearings <NUM> spaced around the optical axis O to bear the moving plate <NUM> on the support plate <NUM>. Each plain bearing <NUM> is arranged as follows and as illustrated in more detail in <FIG>.

Each plain bearing <NUM> comprises a bearing member <NUM>. The bearing member <NUM> separates the moving plate <NUM> and the support plate <NUM>, and the thickness of the bearing members <NUM> is chosen accordingly. Due to the simplicity of the bearing members <NUM>, it possible to minimise the separation and hence the height of the SMA actuator arrangement <NUM> along the optical axis O.

In one alternative, the bearing member <NUM> is fixed to the support plate <NUM>, for example by adhesive. In this case, the bearing member <NUM> also bears on the moving plate <NUM>. That is, a surface <NUM> of the bearing member <NUM> on the opposite side from the support plate <NUM> and a surface <NUM> of the moving plate <NUM> are planar, conforming surfaces which contact one another.

In another alternative, the bearing member <NUM> is fixed to the moving plate <NUM>, for example by adhesive. In this case, the bearing member <NUM> also bears on the support plate <NUM>. That is, a surface <NUM> of the bearing member <NUM> on the opposite side from the moving plate <NUM> and a surface <NUM> of the support plate <NUM> are planar, conforming surfaces which contact one another.

Thus, the contact between the conforming surfaces <NUM> and <NUM> or between the conforming surfaces <NUM> and <NUM> supports and bears the movable plate <NUM> on the support plate <NUM>, allowing relative motion parallel to their extent, that is perpendicular to the optical axis O.

The material properties of the conforming surfaces <NUM> and <NUM> or the conforming surfaces <NUM> and <NUM> are chosen to provide a low friction and low wear plain bearing. One option is that the conforming surface <NUM> or <NUM> of the bearing member <NUM> is coated by a material having suitable properties. Another option is that the conforming surface <NUM> or <NUM> of the bearing member <NUM> is not coated, but instead the material of the bearing member <NUM> is chosen to have suitable properties. With either option, the other conforming surface <NUM> or <NUM> may also be coated with a material having suitable properties, but that is not essential. Where coatings are used, the coating has lower friction and/or lower wear than the material which is coated. The bearing member <NUM> or the coating, where used, may be made from a polymer, for example nylon, polytetrafluoroethylene (PTFE) (e.g. Teflon), an acetal (e.g. Delrin) or an Ultra High Molecular Weight Polyethylene (UHMWPE).

Although <FIG> illustrates an example having three bearing members <NUM>, in general there may be any number of one or more bearing members <NUM>. Inclusion of at least three bearing members <NUM> spaced around the optical axis O assists in providing stable support and many practical embodiments include three or four bearing members <NUM>.

The total area of contact of the bearing member <NUM>, that is the area of the conforming surfaces <NUM> or <NUM> of the bearing member <NUM> summed over all bearing members present, is chosen to control the friction in the bearing.

Surprisingly, the plain bearings <NUM> can in fact provide good performance with friction that is sufficiently low to allow movement perpendicular to the optical axis O, having regard to the force applied by the SMA actuator wires. Typically, in order to limit the friction, the total area of contact is at most <NUM><NUM>, preferably at most <NUM><NUM>.

Equally, the plain bearings maintain a relatively high total area of contact, due to the contact over the conforming surfaces, compared to a bearing having a point or line contact. This reduces the impact of wear occurring over time and changing the area of contact and hence the bearing properties. Typically, the total area of contact is at least <NUM><NUM>, preferably at least <NUM><NUM>.

In addition, the SMA actuator assembly <NUM> comprises two flexures <NUM> connected between the support structure and the movable element to act as a biasing arrangement that biases the support structure and the movable element against each other whilst permitting the movement of the movable element relative to the support structure orthogonal to the optical axis O. The flexures <NUM> are arranged as follows.

The flexures <NUM> each extend between the support plate <NUM> and the movable plate <NUM>. The flexures <NUM> have a dual purpose of providing a mechanical function as described below and providing electrical connections from the support structure <NUM> to the camera lens assembly <NUM>.

In this example, the flexures <NUM> are formed integrally with the movable plate <NUM> at one end thereof and are mounted to the support plate <NUM> at the other end thereof. Alternatively, the flexures <NUM> could be formed integrally with the support plate <NUM> and are mounted to the movable plate <NUM>, or else could be separate elements mounted to each of the support plate <NUM> and the movable plate <NUM>. The mounting of the flexures <NUM> may be achieved by soldering which provides both mechanical and electrical connection.

The flexures <NUM> are arranged as follows to provide their mechanical function. Each flexure <NUM> is an elongate beam connected between the support structure <NUM> and the camera lens assembly <NUM>.

The flexures <NUM>, due to their intrinsic resilience, bias the support structure <NUM> and the camera lens element <NUM> together, the biasing force being applied parallel to the optical axis O. This maintains the contact in the plain bearings <NUM>. At the same time, the flexures <NUM> may be laterally deflected to permit said movement of the camera lens assembly <NUM> relative to the support structure <NUM> orthogonal to the optical axis O, to permit an OIS function.

The flexures <NUM>, again due to their intrinsic resilience, provide a lateral biasing force that biases the camera lens assembly <NUM> towards a central position from any direction around the central position in which the optical axis O of the camera lens assembly is aligned with the centre of the light-sensitive region of the image sensor <NUM>. As a result, in the absence of driving of the lateral movement of the camera lens assembly <NUM>, the camera lens assembly <NUM> will tend towards the central position from any direction around the central position. This ensures that the camera apparatus <NUM> remains functional to capture images, even in the absence of driving of the SMA actuator wires <NUM>.

The flexures <NUM> are designed as follows to provide a suitable retaining force along the optical axis O for the plain bearings <NUM>, and also to permit lateral movement with a lateral biasing force. The magnitude of the lateral biasing force is kept low enough as not to hinder OIS, whilst being high enough to centre the camera lens assembly <NUM> in the absence of driving.

Each flexure <NUM> has a cross-section with an average width orthogonal to the optical axis O is that is greater than its average thickness parallel to the optical axis O. Each flexure <NUM> extends in an L-shape around the optical axis O, it in general being desirable that the angular extent is at least <NUM>° as measured between the ends of the flexure <NUM>.

In the assembled state of the SMA actuator assembly <NUM>, the flexures <NUM> are deflected from their relaxed state to provide a pre-loading force that biases the support structure <NUM> and the movable element together. This is illustrated in <FIG>, wherein <FIG> shows the flexures <NUM> in their relaxed state and <FIG> shows the flexures <NUM> in their assembled state where the flexures are deflected from their relaxed state by a distance d.

The flexures <NUM> are made of a suitable material that provides the desired mechanical properties and is electrically conductive. Typically the material is a metal having a relatively high yield, for example steel such as stainless steel.

The SMA actuator arrangement <NUM> shown in <FIG> employs a particular configuration of plain bearings <NUM> as an example, but plain bearings may be applied in a any other suitable configuration. By way of non-limitative example, some alternative configurations of plain bearings will now be described. Such alternative configurations of plain bearings may be applied as alternatives to the plain bearings <NUM>, but with the SMA actuator arrangement <NUM> being otherwise as described above.

In <FIG>, the bearing member <NUM> is fixed to one of the support plate <NUM> and the moving plate <NUM>, and the other of the support plate <NUM> and the moving plate <NUM> provide a conforming surface which contacts the conforming surface of the bearing member <NUM>. <FIG> illustrates an alternative in which the plain bearing <NUM> comprises bearing members <NUM> fixed to both of the support plate <NUM> and the moving plate <NUM>. In this case, the bearing members <NUM> provide conforming surfaces <NUM> and <NUM> which contact one another.

In <FIG>, the bearing members <NUM> are separate elements. <FIG> illustrates in plan view an alternative in which the bearing members <NUM> are integrally formed with an annular ring <NUM> of the same material. In this example, the bearing members <NUM> and the annular ring <NUM> are fixed to the support plate <NUM> (but the arrangement could be reversed so that the annular ring <NUM> is fixed to the movable plate <NUM>). The annular ring <NUM> extends around the optical axis O outside the aperture <NUM> in the support plate <NUM> but inside the aperture <NUM> in the moving plate <NUM>, so that the annular ring <NUM> does not contact the moving plate <NUM>. The bearing members <NUM> protrude outwardly of the annular ring <NUM> beyond the aperture <NUM> so that they overlap and bear on the moving plate <NUM>. This arrangement provides an advantage in manufacture that the annular ring <NUM> and bearing members <NUM> may be formed as an integral element at the same time, which facilitates manufacture and improves yield.

As an alternative to providing plural plain bearings <NUM> spaced around the optical axis O, it is possible to use a single plain bearing that is an annular bearing extending around the optical axis O. By way of example, <FIG> illustrates in plan view a single plain bearing <NUM> that is modified to be annular. The plain bearing <NUM> comprises an annular bearing member <NUM> fixed to one of the support plate <NUM> and the movable plate <NUM> and bears on the other of the support plate <NUM> and the movable plate <NUM> (although for clarity the other of the support plate <NUM> and the movable plate <NUM> is not shown in <FIG>). Such an arrangement provides a stable support. The annular plain bearing <NUM> is formed as a single annular member, which facilitates manufacture and improves yield.

A potential risk with a plain bearing is that wear particles may be formed by wear of the plain bearing and that such wear particles may obscure the image capture or create mechanical or electrical problems within the SMA actuator assembly <NUM>. It is therefore desirable to provide means for containing wear particles formed at the plain bearing. A variety of such means are possible. There will now be described some non-limitative examples of means for containing wear particles that may be applied to any of the plain bearings <NUM> described above.

<FIG> illustrates in cross-section a plain bearing <NUM> comprising a labyrinth path <NUM> as a means for containing wear particles. The labyrinth path <NUM> is formed between the support plate <NUM> and the movable plate <NUM>, by shaping those components.

<FIG> illustrates in cross-section a plain bearing <NUM> comprising a trap <NUM> comprising an adherent surface <NUM> as a means for containing wear particles. The trap <NUM> is formed in a recess <NUM> in the support plate <NUM>, but could be formed additionally or instead on the movable plate <NUM>. The recess <NUM> contains a material <NUM> providing the adherent surface <NUM>. The material <NUM> is chosen to be adherent to the wear particles. For example, the material may be silicone or an adhesive.

<FIG> illustrates in cross-section another plain bearing <NUM> comprising a trap <NUM> comprising an adherent surface <NUM> as a means for containing wear particles. However, in this case the trap <NUM> is formed in a recess <NUM> in the bearing member <NUM> of the plain bearing <NUM>. Again, the recess <NUM> contains a material <NUM> providing the adherent surface <NUM>. The material <NUM> is chosen to be adherent to the wear particles. For example, the material may be silicone or an adhesive.

<FIG> illustrates in cross-section a plain bearing <NUM> comprising a wiper portion <NUM> as a means for containing wear particles. The wiper portion <NUM> is formed in the member <NUM> of the plain bearing <NUM>. In this example, the bearing member <NUM> is fixed to the support plate <NUM> and the wiper portion <NUM> extends to the surface of the movable element <NUM>, but this could be reversed. The wiper portion <NUM> wipes the movable element and collects wear particles <NUM>.

The arrangements of <FIG> are effective in containing wear particles, although the structures do require sufficient height and so may increase the overall height of the SMA actuator assembly along the optical axis O, albeit to a lesser extent than a suspension system employing balls.

Claim 1:
A shape memory alloy actuator arrangement (<NUM>), the shape memory alloy actuator arrangement comprising:
a support structure (<NUM>);
a movable element (<NUM>);
at least one shape memory alloy actuator wire (<NUM>) connected between the support structure (<NUM>) and the movable element (<NUM>) in an arrangement wherein the shape memory alloy actuator wires (<NUM>) are arranged, on driving thereof, to move the movable element (<NUM>) relative to the support structure (<NUM>); and
at least one plain bearing (<NUM>) that bears the movable element (<NUM>) on the support structure (<NUM>), allowing movement of the movable element (<NUM>) relative to the support structure (<NUM>).