ACTUATOR ASSEMBLY

The actuator assembly comprises a first part (102), a second part (110) and a helical bearing arrangement. The helical bearing arrangement is arranged to guide helical movement of the second part with respect to the first part around a helical axis H such that rotation of the second part around the helical axis is converted into helical movement of the second part. The first and second parts comprise respective stops (152, 162) that are arranged such that the stops are spaced from each other throughout an operating range of said helical movement of the second part relative to the first part. The stops are configured to engage if the second part is moved relative to the first part in at least one direction other than the direction of said helical movement such that the engagement of the stops restricts relative movement of the first and second parts.

FIELD

The present disclosure relates to an actuator assembly and to a camera system comprising an actuator assembly.

BACKGROUND

It is known to use SMA wires in actuators to drive movement of a movable element with respect to a support structure. Such SMA actuators have particular advantages in miniature devices such as smartphones. SMA actuators may be used for example in optical devices such as compact camera modules for driving movement of lenses along their optical axis, for example to effect focussing (e.g. autofocus, AF) or zoom.

For example, WO 2019/243849 A1 describes a shape memory alloy actuation apparatus which comprises a support structure and a movable element. A helical bearing arrangement supported on the movable element on the support structure guides helical movement of the movable element with respect to the support structure around a helical axis. At least one shape memory alloy actuator wire is connected between the support structure and the movable element in, or at an acute angle to, a plane normal to the helical axis, so as to drive rotation of the movable element around the helical axis which the helical bearing arrangement converts into said helical movement.

If such an actuator is subjected to an impact, for example by being dropped from a height, then this can cause the moveable element to be urged relative to the support structure by way of a non-helical motion, which may damage components of the actuation apparatus. It would be desirable to reduce the likelihood of damage to the components of the actuator in such circumstances.

SUMMARY

According to a first aspect of the present invention, there is provided an actuator assembly comprising: a first part; a second part; and, a helical bearing arrangement arranged to guide helical movement of the second part with respect to the first part around a helical axis such that rotation of the second part around the helical axis is converted into helical movement of the second part, wherein the first and second parts comprise respective stops that are arranged such that the stops are spaced from each other throughout an operating range of said helical movement of the second part relative to the first part, and wherein the stops are configured to engage if the second part is moved relative to the first part in at least one direction other than the direction of said helical movement such that the engagement of the stops restricts relative movement of the first and second parts.

The stops help to prevent damage to the components of the actuator assembly if the actuator assembly is subjected to an impact.

In some embodiments, the actuator assembly is a shape memory alloy (SMA) actuator assembly and/or a miniature actuator assembly.

The at least one direction other than the direction of said helical movement may involve translational and/or rotational degrees of freedom of the second part relative to the first part (or their equivalents in a helical coordinate system).

The directions—i.e. the direction of said helical movement and the at least one direction other than the direction of said helical movement—may be defined with reference to the relative movement of the stops (or points near the stops). Generally, movements of the second part relative to the first part can be approximated by a ‘local’ translational relative movement of the stops.

In some embodiments, the at least one direction other than the direction of said helical movement is perpendicular to the direction of said helical movement, e.g. at the stops.

In some embodiments, the at least one direction other than the direction of said helical movement is perpendicular to the helical axis.

In some embodiments, the stop of the first part comprises a first surface.

In some embodiments, the stop of the second part comprises a second surface.

In some embodiments, the first surface does not face in a direction that is normal (and/or parallel) to an axis parallel to the helical axis and/or the second surface does not face in a direction that is normal (and/or parallel) to an axis parallel to the helical axis.

In some embodiments, the first and/or second surface is helically arranged. In other words, the first and/or second surface is substantially parallel with the direction of the helical movement thereof.

In some embodiments, the stops are spaced by a substantially constant distance in a first direction during at least a portion of said helical movement of the second part relative to the first part, and wherein the stops are configured to engage if the stop of the second part is moved relative to the stop of the first part in said first direction.

In some embodiments, the stops are arranged such that the stops are spaced by the substantially constant distance in the first direction over the entire range of said helical movement of the second part relative to the first part.

In some embodiments, the stops are arranged such that the stops are spaced by a substantially constant distance in the first direction during a first portion of said helical movement of the second part relative to the first part.

In some embodiments, the first and second parts each comprise respective second stops that are arranged such that the second stops are spaced by a substantially constant distance during a second portion of said helical movement of the second part relative to the first part.

In some embodiments, one of the first and second parts comprises a track that comprises the stop of said one of the first and second parts.

In some embodiments, the other one of the first and second parts comprises a protrusion for being received in the track, wherein the protrusion comprises the stop of said other one of the first and second parts.

In some embodiments, the track extends into an inner surface of said one of the first and second parts and the protrusion protrudes from an outer surface of the other one of the first and second parts.

In some embodiments, the first part comprises the track and the second part comprises the protrusion.

In some embodiments, the second part is at least partially located within the first part.

In some embodiments, the first part comprises a space and at least a portion of the second part is received within the space. The space may be an aperture that extends through the first part.

In some embodiments, the substantially constant distance is at least 50 microns and, preferably, is at least 75 microns, at least 100 microns, at least 125 microns or at least 150 microns.

In some embodiments, the substantially constant distance is less than 250 microns and, preferably, is less than 200 microns or less than 150 microns.

Rather than being substantially constant, the actuator assembly may be configured such that the distance changes by less than a predetermined relative or absolute amount during at least the portion of said helical movement of the second part relative to the first part.

In some embodiments, the helical bearing arrangement comprises a plurality of tracks and a plurality of bearings that are each received in a respective track and, preferably, the helical bearing arrangement comprises three tracks.

In some embodiments, the helical bearing arrangement does not itself limit the range of helical movement of the second part relative to the first part.

In some embodiments, the tracks are spaced apart, and wherein the stops are substantially equidistant from the two nearest tracks.

In some embodiments, the tracks are substantially equally spaced apart.

In some embodiments, the tracks are disposed at first, second and third positions respectively about the helical axis and wherein the stops are located at a fourth position about the helical axis, and wherein the first, second, third and fourth positions are spaced at about 90 degrees intervals about the helical axis.

In some embodiments, the actuator assembly further comprises a loading arrangement, wherein the stops are disposed in closer proximity to the loading arrangement than to the helical bearing arrangement.

In some embodiments, the loading arrangement is a magnetic loading arrangement.

In some embodiments, at least a portion of the loading arrangement is fixed relative to (e.g. on) the protrusion.

In some embodiments, the protrusion comprises first and second surfaces, wherein the first surface comprises said other one of the first and second stops and wherein said portion of the loading arrangement is mounted to the second surface.

In some embodiments, the first and second surfaces face in generally opposite directions.

In some embodiments, the loading arrangement is configured to urge the second part relative to the first part in a direction generally perpendicular to the helical motion of the second part relative to the first part.

In some embodiments, the first direction is at an angle to the helical axis and, preferably, is substantially perpendicular to the helical axis.

In some embodiments, the first part comprises one or more further stops and the second part comprises one or more further stops each corresponding to the one or more further stops of the first part, wherein corresponding ones of the further stops are arranged so as to be spaced from each other throughout an operating range of said helical movement of the second part relative to the first part.

The further stops may have one or more of the features of the stops described above.

For example, in some embodiments, each further stop of the first part and corresponding further stop of the second part are spaced by a substantially constant distance in a further direction during at least a portion of said helical movement of the second part relative to the first part and are configured to engage if the further stop of the second part is moved relative to the further stop of the first part in said further direction.

In some embodiments, at least one of the one or more further directions is substantially parallel to the first direction.

In some embodiments, at least one of the one or more further directions is at an angle to the first direction and, preferably, is perpendicular to the first direction.

In some embodiments, the engagement of the stops restricts at least one degree of freedom of movement of the second part relative to the first part.

In some embodiments, the engagement of the stops restricts at least two degrees of freedom of movement of the second part relative to the first part and, preferably, three degrees of freedom.

In some embodiments, the stops and further stops together restrict at least two degrees of freedom of movement of the second part relative to the first part and, preferably, three, four, or five degrees of freedom of movement of the second part relative to the first part.

In some embodiments, the stops and further stops together restrict movement of the second part relative to the first part other than said helical movement of the second part relative to the first part.

In some embodiments, at least one of the one or more further directions is perpendicular to the helical axis.

In some embodiments, at least one of the one or more further directions is perpendicular to the direction of said helical movement, e.g. at the stops.

In some embodiments, the or each further stop of the first part comprises a first surface.

In some embodiments, the or each further stop of the second part comprises a second surface.

In some embodiments, the first surface of the or each further stop does not face in a direction that is normal to an axis parallel to the helical axis and/or the second surface of the or each further stop does not face in a direction that is normal to an axis parallel to the helical axis. In some embodiments, the first and/or second surface of the or each further stop is helically arranged.

In some embodiments, at least one of the further stops is arranged such that the corresponding further stops are spaced by the substantially constant further distance in the further direction over the entire range of said helical movement of the second part relative to the first part.

In some embodiments, at least one of the further stops is arranged such that the corresponding further stops are spaced by a substantially constant further distance in the further direction during a first portion of said helical movement of the second part relative to the first part.

In some embodiments, one of the first and second parts comprises a further track that comprises the further stop of said one of the first and second parts.

In some embodiments, the other one of the first and second parts comprises a further protrusion for being received in the further track, wherein the further protrusion comprises the stop of said other one of the first and second parts.

In some embodiments, one of the first and second parts comprises a plurality of such further tracks, each forming one of the further stops of said one of the first and second parts, and the other one of the first and second parts comprises a plurality of protrusions, each forming one of the further stops of said other one of the first and second parts.

In some embodiments, the substantially constant further distance is at least 50 microns and, preferably, is at least 75 microns, at least 100 microns, at least 125 microns or at least 150 microns. In some embodiments, the substantially constant further distance is less than 250 microns and, preferably, is less than 200 microns or less than 150 microns.

In some embodiments, the engagement of corresponding further stops restricts at least one degree of freedom of movement of the second part relative to the first part.

In some embodiments, the engagement of corresponding further stops restricts at least two degrees of freedom of movement of the second part relative to the first part and, preferably, three degrees of freedom.

The actuator assembly may have further, different stops that face in directions normal (and/or parallel) to the helical axis. However, such further stops are generally less effective at restricting relative movement of the first and second parts. For example, such further stops may only engage if a portion of the second part moves relative to the first part beyond a range of positions along (and/or away from) the helical axis defined by the normal movement envelope of the second part.

In some embodiments, the second part comprises first and second sides and an end stop that is arranged on one of the first and second sides and, preferably, wherein the first part comprises an end stop, and wherein the end stop of the second part moves towards or away from the end stop of the first part during helical movement of the second part relative to the first part.

In some embodiments, the end stop of the first part faces in a direction normal to an axis parallel to the helical axis. In some embodiments, the end stop of the second part faces in a direction normal to an axis parallel to the helical axis. The end stop of the first part may face in generally the opposite direction to the end stop of the second part.

In some embodiments, the first part comprises a support structure.

In some embodiments, the second part comprises a moveable mount and, preferably, a movable lens mount.

In some embodiments, the actuator assembly comprises a drive mechanism configured to drive rotation of the second part around the helical axis which the helical bearing arrangement converts into the helical movement of the second part.

In some embodiments, the drive mechanism is configured to move the second part relative to the first part throughout the operating range between extreme first and second positions.

In some embodiments, the actuator assembly is a shape memory alloy actuator.

According to another aspect of the present invention, there is provided an autofocus system comprising the actuator assembly according the first aspect of the present invention.

According to another aspect of the present invention, there is provided a camera system comprising: the actuator assembly of the first aspect of the present invention; an image sensor; and, a lens system, wherein the image sensor is mounted to one of the first part and the second part, and wherein the lens system is mounted to the other one of the first part and second part.

DETAILED DESCRIPTION

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”, an “air bearing” (where pressurised air floats the load) 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. Such a rolling bearing element may be a compliant element, for example a sac filled with gas. 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.

A shape memory alloy (SMA) actuation apparatus1that is a camera is shown schematically inFIG.1.

The SMA actuation apparatus1comprises a support structure2that has an image sensor3mounted thereon. The support structure2may take any suitable form, typically including a base4to which the image sensor is fixed. The support structure2may also support an IC chip5. The SMA actuation apparatus1also comprises a lens element10that is the movable element in this example. The lens element10comprises a lens11, although it may alternatively comprise plural lenses. The lens element10has an optical axis O aligned with the image sensor3and is arranged to focus an image on the image sensor3.

The SMA actuation apparatus1is a miniature device. In some examples of a miniature device, the lens11(or plural lenses, when provided) may have a diameter of at most 20 mm, preferably at most 15 mm, preferably at most 10 mm.

Although the SMA actuation apparatus1in this example is a camera, that is not in general essential. In some examples, the SMA actuation apparatus1may be an optical device in which the movable element is a lens element but there is no image sensor. In other examples, SMA actuation apparatus1may be a type of apparatus that is not an optical device, and in which the movable element is not a lens element and there is no image sensor. Examples include apparatuses for depth mapping, face recognition, game consoles, projectors and security scanners.

The SMA actuation apparatus1also comprises a helical bearing arrangement20(shown schematically inFIG.1) that supports the lens element10on the support structure2. The helical bearing arrangement20is arranged to guide helical movement of the lens element10with respect to the support structure2around a helical axis H. The helical axis H in this example is coincident with the optical axis O and the helical movement is shown inFIG.1by the arrow M. Preferably, the helical motion is along a right helix, that is a helix with constant radius, but in general any helix is possible. The pitch of the helix may be constant or vary along the helical motion. Preferably, the helical movement is generally only a small portion (less than one quarter) of a full turn of the helix.

The helical motion of the lens element10guided by the helical bearing arrangement20includes a component of translational movement along the helical axis H and rotational movement around the helical axis H. The translational movement along the helical axis H is the desired movement of the lens element10, for example to change the focus of the image on the image sensor3and/or to change the magnification (zoom) of the image on the image sensor3. The rotational movement around the helical axis H is in this example not needed for optical purposes, but is in general acceptable as rotation of the lens element10does not change the focus of the image on the image sensor3.

The helical bearing arrangement20may take a variety of forms.

One possibility is that the helical bearing arrangement20comprises one or more helical bearings30that are rolling bearings, examples of which are shown inFIGS.2and3. In each ofFIGS.2and3, the helical bearing30comprises a pair of bearing surfaces31and32and plural rolling bearing elements33, for example balls, disposed between the bearing surfaces31and32. One of the bearing surfaces31and32is provided on the support structure2and the other of the bearing surfaces31and32is provided on the lens element10.

The helical bearing30guides the helical movement of the lens element10with respect to the support structure2as shown by the arrow M. This may be achieved by the bearing surfaces31and32extending helically around the helical axis H, that is following a line that is helical. In practical embodiments, the length of the bearing surfaces31and32may be short compared to the distance of the bearing surfaces31and32from the helical axis H, such that their shape is close to straight or even each being straight, provided that the one or more helical bearings of the helical bearing arrangement20guide helical movement of the lens element10with respect to the support structure2. Plural helical bearings30are typically present, located at different angular positions around the helical axis H, in which case the helical bearings30have different orientations so that they cooperate and maintain adequate constraints to guide the helical movement of the lens element10with respect to the support structure2, even if the bearing surfaces31and32of an individual helical bearing30are straight.

In the example ofFIG.2, the bearing surfaces31and32each comprise respective grooves34and35in which the rolling bearing elements33are seated. In this example, the grooves34and35constrain transverse translational movement of the lens element10with respect to the support structure2, that is transverse to the direction of movement shown by arrow M. The grooves shown inFIG.2are V-shaped in cross-section, but other cross-sections are possible, for example curved as in portions of a circle or an oval. In general, the grooves34and35provide two points of contact with the respective rolling bearing elements33. The grooves34and35may extend helically. Alternatively, in practical embodiments, the length of the bearing surfaces31and32may be short compared to the distance of the bearing surfaces31and32from the helical axis H, in which case the grooves34and35may be straight or close to straight, provided that the one or more helical bearings30of the helical bearing arrangement20guide helical movement of the lens element10with respect to the support structure2.

In the example ofFIG.3, a first bearing surface31comprises a groove36in which the rolling bearing elements33are seated and a second bearing surface32wherein the bearing surface is ‘planar’. The first bearing surface31comprising a groove36may be provided on either one of the support structure2and the lens element10, with the second bearing surface32being provided on the other one of the support structure2and the lens element10. In the example ofFIG.3, the helical bearing30does not constrain transverse translational movement of the lens element10with respect to the support structure2, that is transverse to the direction of movement shown by arrow M. The bearing surface32is ‘planar’ in the sense that it is a surface which is not a groove and one which provides only a single point of contact with the ball. In other words, the bearing surface32is effectively planar across a scale of the width of the rolling bearing element33, although be helical at a larger scale. For example, as pictured, the ‘planar’ surface is helical, being a line in cross section which twists helically along the movement direction, maintaining a single point of contact with the ball at any time. Alternatively and as mentioned above, in practical embodiments the length of the bearing surfaces31and32may be short, in which case the bearing surface32may be planar or close to planar, provided that the one or more helical bearings30of the helical bearing arrangement20guide helical movement of the lens element10with respect to the support structure2.

A single rolling bearing element33is shown inFIGS.2and3by way of example, but in general may include any plural number of rolling bearing elements33.

In some examples, the helical bearing30may include a single rolling bearing element33. In that case, the helical bearing30by itself does not constrain the rotational movement of the lens element10with respect to the support structure2about the single rolling bearing element33, that is around an axis transverse to the direction of movement shown by arrow M. However, this minimises the overall size of the helical bearing30, and in particular the height of the helical bearing30projected along the helical axis H as it is only needed to accommodate the size of the rolling bearing element33and the relative travel of the bearing surfaces31and32.

In other examples, the helical bearing30may include plural rolling bearing element33. In that case, the helical bearing30constrains the rotational movement of the lens element10with respect to the support structure2about either one of the rolling bearing elements33, that is around an axis transverse to the direction of movement shown by arrow M. However, compared to use of a single rolling bearing element33, this increases the overall size of the helical bearing30, and in particular the height of the helical bearing30projected along the helical axis H.

The helical bearing arrangement may in general comprise any number of helical bearings30with a configuration chosen to guide the helical movement of the lens element10with respect to the support structure2while constraining the movement of the lens element10with respect to the support structure2in other degrees of freedom. Many helical bearing arrangements may comprise plural helical bearings30and at least one which comprises plural rolling bearing elements30.

Some specific examples of the SMA actuation apparatus1with different possible helical bearing arrangements are illustrated inFIGS.4to6which are schematic plan views normal to the helical axis showing the support structure2, the lens element10and the helical bearings30.

FIG.4illustrates a possible helical bearing arrangement that includes two helical bearings37and38only. The helical bearings37and38are arranged on opposite sides of the lens element2.

The first helical bearing37is of the same type as the helical bearing30shown inFIG.2wherein the bearing surfaces31and32each comprise respective grooves34and35. The first helical bearing37includes plural rolling bearing elements33to constrain the relative movement of the lens element10and the support structure2.

The second helical bearing38is of the same type as the helical bearing30shown inFIG.3wherein the first bearing surface31comprises a groove36in which the rolling bearing elements33are seated and the second bearing surface32is planar.

FIG.4illustrates the case that the first bearing surface31of the second helical bearing38is on the support structure2, but it could alternatively be on the lens element10. The second helical bearing38may comprise a single rolling bearing element33or plural rolling elements33and principally adds a constraint against relative rotation of the lens element10and the support structure2around the direction of movement (arrow M) of the first helical bearing37.

The helical bearing arrangement ofFIG.4includes a smaller number of helical bearings (i.e. two) than the other examples below, which simplifies the construction and reduces footprint of the SMA actuation apparatus1.

FIG.5illustrates a possible helical bearing arrangement that includes three helical bearings39,40and41only. The three helical bearings39,40and41are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

The first and second helical bearings39and40are of the same type as the helical bearing30shown inFIG.2wherein the bearing surfaces31and32each comprise respective grooves34and35. The third helical bearing41is of the same type as the helical bearing30shown inFIG.3wherein the first bearing surface31comprises a groove36in which the rolling bearing element33is seated and the second bearing surface32is planar.FIG.5illustrates the case that the first bearing surface31of the third helical bearing41is on the lens element10, but it could alternatively be on the support structure2.

Each of the three helical bearings39,40and41may comprise a single rolling or plural bearing elements33. This is possible because the constraints imposed by three helical bearings39,40and41, and in particular the grooves of the first and second helical bearings39and40sufficient to constrain the movement of the lens element10with respect to the support structure2in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element33in each of the three helical bearings39,40and41, the overall size of the three helical bearings39,40and41, and in particular the height of the three helical bearings39,40and41projected along the helical axis H is reduced compared to the helical bearing arrangement ofFIG.4.

FIG.6illustrates a possible helical bearing arrangement that includes four helical bearings42to45only. The four helical bearings42to45are equally angularly spaced around the helical axis H.

The first helical bearing42is of the same type as the helical bearing30shown inFIG.2wherein the bearing surfaces31and32each comprise respective grooves34and35.

The second, third and fourth helical bearings43,44and45are each of the same type as the helical bearing30shown inFIG.3wherein the first bearing surface31comprises a groove36in which the rolling bearing element33is seated and the second bearing surface32is planar.FIG.6illustrates the case that the first bearing surface31of the second, third and fourth helical bearings43,44and45is on the lens element10, but it could alternatively be on the support structure2.

Each of the second, third and fourth helical bearings43,44and45may comprise a single rolling bearing element33while the first helical bearing42comprises two rolling bearing elements. This is possible because the constraints imposed by four helical bearings42to45are sufficient to constrain the movement of the lens element10with respect to the support structure2in degrees of freedom other than the helical movement.

FIG.7illustrates another possible helical bearing arrangement that includes four helical bearings46to49only. The four helical bearings46to49are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

The first and second helical bearings46and47are of the same type as the helical bearing30shown inFIG.2wherein the bearing surfaces31and32each comprise respective grooves34and35.

The third and fourth helical bearings48and49are of the same type as the helical bearing30shown inFIG.3wherein the first bearing surface31comprises a groove36in which the rolling bearing element33is seated and the second bearing surface32is planar.FIG.7illustrates the case that the first bearing surface31of the third and fourth helical bearings48and49is on the lens element10, but it could alternatively be on the support structure2.

Each of the four helical bearings46to49may comprise a single rolling bearing element33. This is possible because the constraints imposed by four helical bearings46to49are sufficient to constrain the movement of the lens element10with respect to the support structure2in degrees of freedom other than the helical movement. As a result of using only a single rolling bearing element33in each of the four helical bearings46to49, the overall size of the four helical bearings46to49, and in particular the height of the four helical bearings46to49projected along the helical axis H is reduced compared to the helical bearing arrangement ofFIG.4.

In each of the helical bearing arrangements ofFIGS.4to7, the bearing surfaces32which are on the lens element10are each arranged on the same side of (all above or all below) the bearing surfaces31on the support structure2. As the bearing surfaces31and32extend helically, this means that in the view ofFIG.5which is a cross-section perpendicular to the helical axis H, all the bearing surfaces32which are on the lens element10are on the right of the bearing surfaces31on the support structure2as viewed outwardly of the helical axis H, and in the view ofFIGS.6and7all the bearing surfaces32which are on the lens element10are on the left of the bearing surfaces31on the support structure2as viewed outwardly of the helical axis H. As a result of this arrangement, the helical bearings all the bearing surfaces31on the support structure2face in the same direction as each other, which assists in manufacture of the bearing surfaces31by the same tool. For instance, in embodiments wherein the first and second parts are moulded, then the above arrangement reduces the amount of actions on a tool, namely the number of directions that the tool must move to be removed from the first/second part. Similarly, manufacturing advantages apply to the bearing surfaces32on the lens element2which also face in the same direction as each other.

As a result of this arrangement, all the helical bearings30need to be loaded in the same helical sense. The helical bearings30are loaded normal to their respective helical faces. Thus loading of the helical bearings30may be provided by applying a loading force along the helical axis H, a loading force around the helical axis H, or, preferably, a suitable combination thereof that minimises interaction between the loading force and the force applied by the at least one SMA actuator wire60, e.g. by being perpendicular to the direction of helical movement. For example, this loading force may be applied by the loading arrangement170described below in connection with the actuator assembly101.

FIG.8illustrates another possible helical bearing arrangement that is a modification of the helical bearing arrangement ofFIG.7. Thus, the helical bearing arrangement includes four helical bearings46to49only, and the four helical bearings46to49are equally angularly spaced around the helical axis H, but they could alternatively be spaced unequally.

As in the helical bearing arrangement ofFIG.7, (a) the first and second helical bearings46and47are of the same type as the helical bearing30shown inFIG.2wherein the bearing surfaces31and32each comprise respective grooves34and35, and (b) the third and fourth helical bearings48and49are of the same type as the helical bearing30shown inFIG.3wherein the first bearing surface31comprises a groove36in which the rolling bearing element33is seated and the second bearing surface32is planar.FIG.8illustrates the case that the first bearing surface31of the third and fourth helical bearings48and49is on the lens element10, but it could alternatively be on the support structure2. As in the helical bearing arrangement ofFIG.7, each of the four helical bearings46to49may comprise a single rolling bearing element33. This is possible because the constraints imposed by four helical bearings46to49are sufficient to constrain the movement of the lens element10with respect to the support structure2in degrees of freedom other than the helical movement. In some embodiments, one of the bearings has a resilient element to load the other bearings, as described in WO2019/243849A1.

As a result of using only a single rolling bearing element33in each of the four helical bearings46to49, the overall size of the four helical bearings46to49, and in particular the height of the four helical bearings46to49projected along the optical axis is reduced when each of the helical bearings has a single rolling element only.

However, the helical bearing arrangement ofFIG.8is modified compared to that ofFIG.7to change the arrangement of the bearing surfaces31and32in the individual bearings46to49, as follows. In the first helical bearing46, the bearing surfaces32on the lens element10are above the bearing surfaces31on the support structure2as viewed along the helical axis H, whereas in the second helical bearing47, the bearing surfaces32on the lens element10are below the bearing surfaces31on the support structure2as viewed along the helical axis H. Similarly, in the third helical bearing48, the bearing surfaces32on the lens element10are above the bearing surfaces31on the support structure2as viewed along the helical axis H, whereas in the fourth helical bearing49, the bearing surfaces31on the lens element10are below the bearing surfaces32on the support structure2as viewed along the helical axis H.

This may be understood on the following basis with reference to a constraint of the bearings in the vertical plane, parallel to the helical axis. The first and third helical bearings46and48constrain the lens element10from moving down, and the second and fourth helical bearings47and49constrain the lens element10from moving up, or rotating around an axis between first and third helical bearings46and48.

While the helical bearing arrangement20comprises helical bearings30that are rolling bearings in the above example, another possibility is that the helical bearing arrangement20comprises at least one flexure extending between the support structure2and the lens element10as shown for example inFIG.9wherein the helical bearing arrangement20comprises two flexure elements50that each comprise four flexures51having a configuration as shown either inFIG.10or inFIG.11. As shown inFIG.9, the flexures51are each pre-deflected along the helical axis H, and as shown inFIGS.10and11, the flexures51each extend in an arc around the helical axis H. As a result of this configuration, the flexures51guide the helical movement of the lens element10with respect to the support structure2around the helical axis H. The specific number and arrangement of flexures51inFIGS.9to11is not essential and other configurations of flexures that are pre-deflected along the helical axis H and extend in an arc around the helical axis H may be used to provide the same function.

FIG.12is a perspective view of an alternative helical bearing arrangement20comprising plural flexures120, four flexures120being shown inFIG.12although in general any number of flexures120could be provided. In this example, the helical bearing arrangement also comprises a movable plate121mounted on lens element10and a support plate122mounted on the support structure2. The movable plate121and the support plate122are spaced along the helical axis H and the flexures120extend along the helical axis H and are inclined with respect to a plane normal to the helical axis H helical axis with rotational symmetry around the helical axis H. With this arrangement, the flexures120guide the helical movement of the lens element10with respect to the support structure2around the helical axis H.

The flexures120are integrally formed with the movable plate120and the support plate122. This form of connection is advantageous because it allows the helical bearing arrangement to be made as a single part, for example in a moulding, providing exact constraints. This solution therefore combines precision with a low manufacturing cost. That said, in principle the flexures120could be separate elements connected to the lens element10and the support structure2in any suitable way.

The use of one or more SMA actuator wires60to rotate the lens element10will now be described.

The SMA actuation apparatus1includes at least one SMA actuator wire60for the purpose of rotating the lens element10. The or each SMA actuator wire60is connected between the support structure2and the lens element10, for example as shown inFIGS.13and14. The SMA actuator wire60is connected to the support structure2and lens element10by crimp portions61which crimp the SMA actuator wire60to provide both mechanical and electrical connection. In the case ofFIG.13, the SMA actuator wire60extends in a plane normal to the helical axis H. In the case ofFIG.14, the SMA actuator wire60extends at an acute angle Q to a plane normal the helical axis H. The SMA actuator wire60is offset from the helical axis. Thus, in both the caseFIG.13andFIG.14, contraction of the SMA actuator wire60drives rotation of the lens element10around the helical axis H. Accordingly, either of the orientations of the SMA actuator wire60ofFIG.13orFIG.14may be used in any of the arrangements described below.

As the helical bearing arrangement20guides helical movement of the lens element10with respect to the support structure2and constrains movement in other degrees of freedom, the rotation driven by contraction of the SMA actuator wire60is converted by the helical bearing arrangement20into helical movement of the lens element10with respect to the support structure2. Thus, as well as the component of rotational movement, a component of translational movement of the lens element10with respect to the support structure2is achieved along the helical axis H. This changes the focus of the image on the image sensor3as described above.

As the SMA actuator wire60has the primary purpose of driving rotation of the lens element10, the extent of the SMA actuator wire projected along the helical axis H may be minimised. As such, other components of the SMA actuation apparatus1constrain the reduction in size along the helical axis H. Typically, the height projected along the helical axis H becomes dependent on the helical bearing arrangement20, for example the geometry of the helical bearing arrangement20. The helical bearing arrangement20is illustrated schematically inFIGS.13and14.

Various different arrangements of the at least one SMA actuator wire60may be used in the SMA actuation apparatus1, provided that the at least one SMA actuator wire60drives rotation of the lens element10with respect to the support structure2. Some examples of possible arrangements of the at least one SMA actuator wire60are as follows with reference toFIGS.15and16which are each schematic drawings of the SMA actuation apparatus1including schematically illustrated connection portions65that are part of the lens element10and to which the SMA actuator wire60is connected. In each case, the or each SMA actuator wire60is connected between the support structure2and the lens element10in the respective orientations shown.

In a first type of embodiment, the SMA actuation apparatus1further comprises a resilient biasing element70connected between the support structure2and the lens element10, as inFIG.15. The resilient biasing element70is typically a spring, as in the examples below, but in principle could be formed by any other element for example being a flexure or a piece of resilient material.

Such a resilient biasing element70is arranged to resiliently bias the at least one SMA actuator wire60. In general terms, use of a resilient biasing element70with an SMA actuator wire is known, the resilient biasing element70applying a stress to the SMA actuator wire60and driving movement in the opposite direction from contraction of the SMA actuator wire60. Thus, such a resilient biasing element70may be employed with a single SMA actuator wire60or plural SMA actuator wires60. In the specific case of the SMA actuation1, the resilient biasing element70may be arranged in various ways, some examples of which are as follows.

FIG.15shows an example where the SMA actuation apparatus1comprises a single SMA actuator wire60only and the resilient biasing element70extends around the helical axis H and so provides a force around the helical axis H. InFIG.15, the resilient biasing element operates in tension, but alternatively could operate in compression, for example being arranged alongside the SMA actuator wire60. The use of a resilient biasing element70extends around the helical axis H minimises the extent of the resilient biasing element70projected along the helical axis H.

FIG.16shows an example where the SMA actuation apparatus1comprises a single SMA actuator wire60only and the resilient biasing element70extends parallel to the helical axis H and so provides a force along the helical axis H. In this case, the forces applied by the resilient biasing element70acts in a different direction from the SMA actuator wire60, but resilient biasing is still provided due to the effect of the helical bearing arrangement20. InFIG.16, a helical spring is the resilient biasing element70, shown with its axis parallel to the optic axis. The spring axis could alternatively be at an angle to the optic axis.

The examples shown inFIGS.15and16include a single SMA actuator wire60, but may be modified to include plural SMA actuator wires60acting in parallel. For example, the SMA actuator wire60and the resilient biasing element70may be duplicated on opposite sides of the lens element10. The SMA actuator wires60and the resilient biasing elements70have rotational symmetry around the helical axis, and so the SMA actuator wires60are complimentary and drive rotation of the lens element10with respect to the support structure2in parallel, that is in the same sense around the helical axis H, and so are actuated together. However, as the SMA actuator wires60are arranged on opposite sides of the helical axis H, the SMA actuator wires60also provide translational forces on the lens element10in opposite directions in a plane normal to the helical axis H. Thus, the net translational force applied by the SMA actuator wires60is minimised, thereby reducing the force applied to the helical bearing arrangement20.

In another configuration, no resilient biasing element is provided, and instead the SMA actuation apparatus1comprises at least one pair of SMA actuator wires60that are arranged to drive rotation of the lens element10in opposite senses around the helical axis H. Similar to known uses of opposed SMA actuator wires to provide opposed forces in translation of an object that moves linearly, the or each pair of SMA actuator wires60apply opposed torques around the helical axis H. Thus, the SMA actuator wires60of the pair apply a stress to each other, which may act through the helical bearing arrangement20, and drive rotation of the lens element10in the opposite directions around the helical axis H.

In general terms, any of the forms of the helical bearing arrangement20described herein, including any helical bearing arrangement or the flexure arrangement, may be used with any of the arrangements of at least one SMA actuator wire60described herein.

In all of the examples above, the SMA actuator wires60are driven by the control circuit implemented in the IC (Integrated Circuit) chip5. In particular, the control circuit generates drive signals for each of the SMA actuator wires60and supplies the drive signals to the SMA actuator wires60. The control circuit receives an input signal representing a desired position for the lens element10along the optical axis O and generates drive signals selected to drive the lens element10to the desired position. The drive signals may be generated using a resistance feedback control technique, in which case the control circuit20measures the resistance of the lengths of SMA actuator wire20and uses the measured resistance as a feedback signal to control the power of the drive signals. Such a resistance feedback control technique may be implemented as disclosed in any of WO-2013/175197; WO-2014/076463; WO-2012/066285; WO-2012/020212; WO-2011/104518; WO-2012/038703; WO-2010/089529 or WO-2010029316, each of which is incorporated herein by reference. As an alternative, the control circuit may include a sensor which senses the position of the lens element10, for example a Hall sensor which sense the position of a magnet fixed to the lens element10. In this case, the drive signals use the sensed position as a feedback signal to control the power of the drive signals.

Referring now toFIGS.17to25, a first embodiment of an actuator assembly101is shown.

The actuator assembly101comprises a first part102and a second part110. In the present embodiment, the first part102is a support structure102and the second part110is a moveable element110, for example, a lens element110. However, it should be recognised that the first and second parts102,110may be other components. In one alternative embodiment (not shown), the first part is a moveable element and the second part is a support structure.

The actuator assembly101further comprises a helical bearing arrangement120. The helical bearing arrangement120is arranged to guide helical movement of the second part110with respect to the first part102around a helical axis H.

Thus, rotation of the second part110around the helical axis H is converted into helical movement of the second part110. The helical bearing arrangement120may have the configuration of any of the examples described above in reference toFIGS.1to16, or may have an alternate configuration.

In the present example, the helical bearing arrangement120has a similar arrangement to the helical bearing arrangement20shown inFIG.5, comprising first, second and third helical bearings139,140,141.

The first helical bearing139is spaced from the second helical bearing140in a first direction about the helical axis H and the third helical bearing141is spaced from the second helical bearing141in a second direction about the helical axis H. The first and third helical bearings139,141may be substantially equally spaced from the second helical bearing140.

The first and second helical bearings139and140are of the same type as the helical bearing30shown inFIG.2. Each of the first and second helical bearings139,140comprises first and second bearing surfaces131and132. Each first bearing surface131comprises a groove134and each second bearing surface132comprises a groove135.

The third helical bearing141is of the same type as the helical bearing30shown inFIG.3. The third helical bearing141comprises a first bearing surface131comprising a groove136in which a rolling bearing element133is seated. The third helical bearing141further comprises a second bearing surface132that is planar. In the present example, the first bearing surface131of the third helical bearing141is on the second part110, but it could alternatively be on the first part102.

In the present example, each of the three helical bearings139,140,141comprises a single rolling bearing element133. However, in an alternative embodiment (not shown), one, two, or all of the helical bearings comprises a plurality of rolling bearing elements.

The actuator assembly101further comprises a drive mechanism that is configured to drive rotation of the second part110relative to the first part102around the helical axis H, which the helical bearing arrangement120converts into the helical movement of the second part110.

The drive mechanism may comprise an SMA actuator, such as an SMA wire, having the configuration of any of the examples described above in reference toFIGS.1to16, or may comprise an SMA actuator with an alternate configuration. In yet further embodiments, the drive mechanism may be of a type other than an SMA actuator. For example, the drive mechanism may instead, or additionally, comprise an electric motor (not shown), such as a voice coil motor (VCM) that is configured to drive rotation of the second part110relative to the first part102.

In the present example, the drive mechanism is an SMA actuator of the type shown inFIG.15, comprising a single SMA actuator wire60and a resilient biasing element70for providing resilient biasing, with the resilient biasing element70extending around the helical axis H to load the helical bearings. Any other SMA wire arrangements and/or loading arrangements are also possible. In some embodiments, an electrical connection element (not shown) is mounted on the second part110to provide an electrical connection from the end of the SMA actuator wire60which is connected to the second part110to the first part102. A detailed description of the operation of the SMA actuator will not be repeated hereinafter.

The first part102comprises a track150that extends into an inner surface151of the first part102. The inner surface151faces generally towards the helical axis H. In the present example, the track150is a slot150in the first part102.

The first part102has opposing first and second sides102A,102B, which in some embodiments are a top side102A and bottom side102B.

In some embodiments, the track150extends through the first part102from the first side102A to the second side102B. In other embodiments, the track150only extends part of the way between the first and second sides102A,102B.

The track150extends generally helically. The track150may extend generally coincident or parallel to the helical movement M of the second part110relative to the first part102.

The track150comprises a first surface152that forms a stop152. The first surface152is arranged generally parallel to the helical movement M of the second part110relative to the first part102.

The second part110comprises a protrusion160that extends from an outer surface161of the second part110. The outer surface161faces generally away from the helical axis H. In the present example, the protrusion160is a rib160.

The second part110has opposing first and second sides110A,110B, which in some embodiments are a top side110A and bottom side110B.

In some embodiments, the protrusion160extends from the first side110A to the second side110B. In other embodiments, the protrusion160only extends part of the way between the first and second sides110A,110B.

The protrusion160extends generally helically. The protrusion160may extend generally coincident or parallel, to the helical movement M of the second part110relative to the first part102.

The protrusion160comprises a first surface162that forms a stop162. The first surface162is arranged generally parallel to the helical movement M of the second part110relative to the first part102.

The protrusion160is configured to be received in the track150such that the first surface152of the track150faces towards the first surface162of the protrusion160. During normal operation of the actuator assembly101, the first surfaces152,162are separated by a constant or substantially constant distance (shown by arrow ‘D’ inFIG.24) in a first direction (shown by arrow ‘X’ inFIG.24). Normal operation refers, for example, to movement driven by the drive mechanism.

The first surfaces152,162are generally helically arranged such that, during normal operation of the actuator assembly101, when the drive mechanism is operated such that the helical bearing arrangement120guides helical movement of the second part with respect to the first part about the helical axis (shown by dashed line ‘H’ inFIG.18), the first surfaces152,162are spaced by said substantially constant distance D in the first direction X. That is, as the second part110moves helically with respect to the first part102, the first surfaces152,162are arranged to permit said helical movement without the first surfaces152,162engaging each other.

In some embodiments, the first surfaces152,162are arranged such that there is a less than 50% deviation of the distance D between the first and second surfaces152,162during helical motion of the second part about the helical axis.

In the present example, the first surfaces152,162, remain said substantially constant distance D in the first direction X over the entire, or substantially the entire, range of helical movement of the second part110relative to the first part102. However, it should be recognised that in alternative embodiments the first surfaces152,162, remain said substantially constant distance D in the first direction X over only a portion of the range of helical movement of the second part110relative to the first part102and thereafter the distance D may, for example, increase.

In some embodiments, one or both of the first surfaces152,162extend helically around the helical axis H, that is following a line that is helical. In practical embodiments, the length of the or each first surface152,162may be short compared to the distance of the first surfaces152,162from the helical axis H, such that their shape is close to straight or even each being straight, provided that one or more first surfaces152,162is arranged such that the first surfaces152,162are spaced by said substantially constant distance D in the first direction X during at least a portion of said helical movement of the second part110relative to the first part102. It should be recognised that in some embodiments the first and/or second surface152,162may comprise a plurality of planar portion that together form a generally helical arrangement.

In some embodiments, the substantially constant distance is at least 50 microns and, preferably, is at least 75 microns, at least, 100 microns, at least 125 microns or at least 150 microns.

In some embodiments, the substantially constant distance is less than 250 microns and, preferably, is less than 200 microns or less than 150 microns.

The first surfaces152,162are configured to engage (as shown inFIG.25) if the first surface162of the second part110is moved relative to the first surface152of the first part102by said distance D in the first direction X. The engagement of the first surfaces152,162restricts relative movement of the first and second parts102,110.

Relative movement of the first surfaces152,162that causes the first surfaces151,161to engage may occur, for example, if the actuator assembly101is dropped. For instance, if the actuator assembly101is dropped, then upon impact with the ground or other object the first part102will deaccelerate quicker than the second part110thereby causing relative movement of the second part110relative to the first part102. This movement of the second part110relative to the first part102may be in a direction generally perpendicular to the helical axis H such that portions of the first and second parts102,110are pressed together, or components of the actuator assembly101are compressed between said portions of the first and second parts102,110, which may cause damage to the first and second parts102,106and/or said components.

Movement of the second part110relative to the first part102in a direction perpendicular to the helical axis H may also cause components of the actuator assembly101to be deformed, for example, stretched, which may damage said components. For instance, in embodiments wherein the drive mechanism comprises an SMA actuator wire, the actuator wire may be stretched, which may damage the actuator wire.

The arrangement of the stops152,162, which in the present embodiment are first surfaces152,162, helps to prevent damage to the actuator assembly101. For example, if the actuator assembly101is dropped and the second part110is urged relative to the first part102in the first direction X, then the stops152,162will engage to limit the amount of movement of the second part110relative to the first part102. Once the first surface162of the second part110has moved said distance D towards the first part102in the first direction X, the first surfaces152,162abut to resist further movement and thus help to prevent damage to the components of the actuator assembly101. Since the stops152,162are a substantially constant distance D over at least said portion of the helical movement of the second part110relative to the first part102, the stops152,162provide a reliable limit of the amount of movement of the second part110relative to the first part102regardless of the position of the second part110relative to the first part102within said portion of the helical movement.

In the present example, the first surfaces152,162are also arranged such that, during normal operation of the actuator assembly101, when the drive mechanism is operated such that the helical bearing arrangement120guides helical movement of the second part with respect to the first part about the helical axis (shown by dashed line ‘H’ inFIG.18), the first surfaces152,162are spaced by a substantially second constant distance E in a second direction Y. The second direction is different to the first direction X and, in some embodiments, the second direction Y is perpendicular to the first direction X. In the present example, the first surfaces152,162are also configured to engage if the first surface162of the second part110is moved relative to the first surface152of the first part102by said second distance E in the second direction Y. Again, the engagement of the first surfaces152,162restricts relative movement of the first and second parts102,110.

The distance D may be equal, or substantially equal, to the second distance E, or may be different.

In some embodiments, the engagement of the stops152,162restricts at least one degree of freedom of movement of the second part110relative to the first part102. In some embodiments, the engagement of the stops152,162restricts at least two, three, four or five degrees of freedom of movement of the second part relative to the first part.

In some embodiments, the first and second parts102,110each comprise a plurality of stops and wherein each stop of the first part102is configured to engage a corresponding stop of the second part110. The stops together restrict movement of the second part110relative to the first part102in at least two, three, four or five degrees of freedom. For instance, if the second part110is moved relative to the first part102in a first direction then first stops of the first and second parts102,110will engage to prevent further movement in the first direction, whilst if the second part110is moved relative to the first part102in a second direction then second stops of the first and second parts102,110will engage to prevent further movement in the second direction. In some embodiments, the first direction is opposite to the second direction or is at an angle to the second direction, for example, perpendicular to the second direction. The first and second directions may both be perpendicular to the helical axis.

The first, second and third helical bearings139,140,141are spaced apart about the helical axis H. In some embodiments, the first, second and third helical bearings139,140,141are spaced at regular intervals about the helical axis H. The first, second and third bearings139,140,141may be ordered sequentially about the helical axis H.

In some embodiments, the stops152,162are substantially equidistant from the two nearest helical bearings which, in the present example, is the first and third helical bearings139,141. The part of the second part110that is furthest from any of the bearings139,140,141has been found to have the most movement relative to the first part102if a non-helical movement of the second part110is induced, for example, if the actuator assembly101is dropped. Positioning the stops152,162at this location of the most relative movement of the second part110relative to the first part102increases the effectiveness of the stops152,162at reducing unwanted non-helical movement of the second part110relative to the first part102.

In some embodiments, the first surface152of the first part102is substantially equally spaced to the groove134of the first bearing surface131of the first helical bearing139and the groove136of the first bearing surface131of the third helical bearing141, in a plane normal to the helical axis H.

In some embodiments, the first surface152of the first part102, the groove134of the first bearing surface131of the first helical bearing139, the groove134of the first bearing surface131of the second helical bearing140, and the groove136of the first bearing surface131of the third helical bearing141are substantially equally spaced about the helical axis H in a plane normal to the helical axis H. The first surface152of the first part102, the groove134of the first bearing surface131of the first helical bearing139, the groove134of the first bearing surface131of the second helical bearing140, and the groove136of the first bearing surface131of the third helical bearing141may be spaced at substantially 90 degree intervals about the helical axis H in a plane normal to the helical axis H.

In some embodiments, the first surface162of the second part110is substantially equally spaced to the groove135of the second bearing surface132of the first helical bearing139and the first bearing surface131of the third helical bearing141, in a plane normal to the helical axis H.

In some embodiments, the second surface162of the second part110, the groove135of the second bearing surface132of the first helical bearing139, the groove135of the second bearing surface132of the second helical bearing140, and the second bearing surface132of the third helical bearing141are substantially equally spaced about the helical axis H in a plane normal to the helical axis H. The first surface162of the first part102, the groove135of the second bearing surface132of the first helical bearing139, the groove135of the second bearing surface132of the second helical bearing140, and the second bearing surface132of the third helical bearing141may be spaced at substantially 90 degree intervals about the helical axis H in a plane normal to the helical axis H.

The actuator assembly101further comprises a loading arrangement170configured to load one or more of the first, second and third helical bearings139,140,141. The loading arrangement170is configured to load the helical bearings139,140,141. That is, the loading arrangement170is configured to load one or more of the helical bearings139,140,141in a direction normal to one or more of the bearing surfaces.

In the present example, the loading arrangement170is a magnetic loading arrangement170. However, in other embodiments the loading arrangement170may be of a different configuration, for example, instead comprising a resilient element such as a spring to load the bearings139,140,141.

The magnetic loading arrangement170comprises a first magnet171mounted to the first part102and a second magnet172mounted to the second part110.

In the present example, the first and second magnets171,172are configured to attract each other such that the portion of the second part110to which the second magnet172is mounted is urged towards the portion of the first part102to which the first magnet171is mounted, in order to load the helical bearings139,140,141. However, in an alternate embodiment the first and second magnets171,172are configured to repel each other such that the portion of the second part110to which the second magnet172is mounted is urged away from the portion of the first part102to which the first magnet171is mounted, in order to load the helical bearings139,140,141.

In some embodiments, the first, second and third helical bearings139,140,141are arranged on three corners of the actuator assembly101and the stops152,162are arranged on a fourth corner of the actuator assembly101.

The first magnet171is provided at an edge of the track150or on a surface of the track150. The second magnet172is mounted to the protrusion160. In some embodiments, the protrusion160comprises a second surface163and the second magnet172is mounted to the second surface163. The second surface163generally faces in the opposite direction to the first surface162of the protrusion160that forms the stop162. In some embodiments, the first and second surfaces162,163of the protrusion160face in generally opposite directions.

Advantageously, since a portion of the loading arrangement170is mounted to the same protrusion160that comprises the stop162, the size, weight and complexity of manufacture of the actuator assembly101is reduced compared to embodiments (not shown) wherein said portion of the loading arrangement is mounted to a first protrusion and the stop162is provided on a separate second protrusion.

In one alternative embodiment, the magnetic loading arrangement170comprises a single magnet that is mounted to one of the first or second parts102,110. The other one of the first and second parts102,110comprises a ferrous material, or has a portion of ferrous material attached thereto, arranged such that the magnet is attracted towards the ferrous material to load the bearings139,140,141.

In some embodiments, the loading arrangement170is configured to urge the second part110relative to the first part102in a second direction that is generally opposite to the first direction.

In some embodiments, the stops152,162are disposed in closer proximity to the loading arrangement170than to the helical bearing arrangement120. That is, the stops152,162are in closer proximity to the loading arrangement170than to any of the first, second or third helical bearings139,140,141.

In the above described embodiment, the first part102comprises the first bearing surfaces131and the second part110comprises the second bearing surfaces132. However, in an alternative embodiment, the second part110comprises the first bearing surfaces131and the first part102comprises the second bearing surfaces132.

In the above described embodiment, the first part102comprises the track150and the second part110comprises the protrusion160. However, in one alternative embodiment (not shown), the first part102comprises the protrusion and the second part110comprises the track that receives the protrusion.

In the above described embodiment, the stop152of the first part102comprises a surface152and the stop162of the second part110comprises a surface162. However, in alternate embodiments, one or both of the stops152,162may have a different configuration, for example, instead comprising an edge, ridge or protrusion. For example, an edge or ridge may extend generally helically to permit helical movement of the second part110relative to the first part102.

In some embodiments, the second part110further comprises an end stop180that is arranged on one of the first and second sides110A,110B.

In some embodiments, the first part102comprises a corresponding end stop (not shown), wherein the end stop180of the second part110moves towards or away from the end stop of the first part102during helical movement of the second part110relative to the first part102.

In some embodiments, the end stop (not shown) of the first part102faces in a direction normal to an axis parallel to the helical axis H. In some embodiments, the end stop180of the second part11faces in a direction normal to an axis parallel to the helical axis H. The end stop of the first part102may face in generally the opposite direction to the end stop180of the second part110. The end stop of the first part102may be generally parallel to the end stop180of the second part110.

The end stops of the first and second parts102,110are configured to engage to limit rotation of the second part110relative to the first part102, for example, rotation about an axis extending through bearing elements133of two of the first, second and third helical bearings139,140,141. In the present example, the end stops of the first and second parts102,110are configured to engage to limit rotation of the second part110relative to the first part102about an axis extending through bearing elements133of the first and third helical bearings139,141. That is, if the actuator assembly100is subjected to an impact that causes the second part110to rotate relative to the first part102about said axis extending through the bearing elements133of the first and third helical bearings139,141, the end stops will engage to prevent any further such rotation.

In some embodiments, the second part110comprises a further end stop (not shown) that is arranged on the other one of the first and second sides110A,110B. In some embodiments, the first part102comprises a corresponding further end stop (not shown). Again, the further end stops are configured to engage to limit rotation of the second part110relative to the first part102, for example, rotation about an axis extending through bearing elements133of two of the first, second and third helical bearings139,140,141.

Referring now toFIGS.26to27B, components of an actuator assembly according to a second embodiment are shown. The actuator assembly of the second embodiment ofFIGS.26to27Bis similar to that of the first embodiment ofFIGS.17to25and thus a detailed description will not be repeated hereinafter. A difference is that the second part210of the actuator assembly of the second embodiment has a different arrangement of stop262. More particularly, the stop262comprises a generally cylindrical protrusion262that extends radially outwardly from a circumferential outer surface261of the second part210.

As with the first embodiment, the first part202comprises a first surface252that is generally helically arranged such that, during normal operation of the actuator assembly, when the drive mechanism is operated such that the helical bearing arrangement (not shown) guides helical movement of the second part210with respect to the first part202about the helical axis, the first surface252is spaced from the protrusion262by a substantially constant distance (shown by arrow ‘D’ inFIG.27A) in the first direction (shown by arrow ‘X’ inFIG.27A).

That is, as the second part210moves helically with respect to the first part202, the first surface252of the first part202is arranged to permit said helical movement without the protrusion262(or other configuration of stop in alternative embodiments) abutting the first surface252.

In some embodiments, the stops252,262are arranged such there is a less than 50% deviation of the distance D between the stops252,262during helical motion of the second part about the helical axis.

In the present example, the stops252,262remain a substantially constant distance D in the first direction X over the entire, or substantially the entire, range of helical movement of the second part210relative to the first part202. However, it should be recognised that in alternative embodiments the stops252,262, remain said substantially constant distance D in the first direction X over only a portion of the range of helical movement of the second part210relative to the first part202and thereafter the distance D may, for example, increase.

In some embodiments, the first surface252of the first part202extends helically around the helical axis H, that is following a line that is helical. In practical embodiments, the length of the first surface252may be short compared to the distance of the first surface252from the helical axis H, such that the shape of the first surface252is close to straight or even being straight, provided that one or more first surfaces252is arranged such that the first surface(s)252is spaced by said substantially constant distance D in the first direction X during at least a portion of said helical movement of the second part210relative to the first part202. In some embodiments, the first surface252comprises a plurality of planar portions that together form a generally helical arrangement.

The protrusion262is configured to engage the first surface252of the first part202(as shown inFIG.27B) if the protrusion262is moved relative to the first surface252of the first part202by said distance D in the first direction X. The engagement of the protrusion262with the first surface252restricts relative movement of the first and second parts202,210. As explained above in respect of the first embodiment of the actuator assembly101shown inFIGS.17to25, restricting relative movement of the first and second parts202,210helps to prevent damage to the components of the actuator assembly, for example, if the actuator assembly is dropped or otherwise impacted.

In an alternative embodiment (not shown), the first part202comprises a generally cylindrical protrusion that extends radially inwardly from an inner surface of the first part202, and the second part210comprises a first surface that is arranged such that the protrusion is spaced a substantially constant distance during helical movement of the second part210relative to the first part210.

It should be recognised that the protrusion262may have any shape and does not need to be cylindrical. For instance, the protrusion262could instead have a square, triangular or rectangular cross-section. In some embodiments, the protrusion262is a rod.

Referring now toFIGS.28to30D, components of an actuator assembly according to a third embodiment are shown. The actuator assembly of the third embodiment ofFIGS.28to30Dis similar to that of the second embodiment ofFIGS.26to27Band thus a detailed description will not be repeated hereinafter. A difference is that the second part310of actuator assembly of the third embodiment comprises first and second stops362A,362B. Each stop362A,362B comprises a generally cylindrical protrusion362A,362B that extends radially outwardly from an outer surface361of the second part310.

The first part (not shown) comprises first and second stops352A,352B. The first stop352A of the first part is arranged in proximity to the first stop362A of the second part310and the second stop352B of the first part is arranged in proximity to the second stop362B of the second part310.

The first stop352A of the first part comprises a first surface352A of the first part and the second stop352B of the first part comprises a second surface352B of the first part.

The first surface352A extends over a first distance (shown by arrow ‘Y1’ inFIGS.29B and30B) in the direction of the helical axis H, from the top side of the first part towards, but stopping short of, the bottom side of the first part. The second surface352B extends over a second distance (shown by arrow ‘Y2’ inFIGS.29B and30B) in the direction of the helical axis, from the bottom side of the first part towards, but stopping short of, the top side of the first part.

When the second part310is moved relative to the first part over a first portion of helical movement, the first stop362A is aligned with the first surface352A in the direction along the helical axis.

The first surface352A of the first part is generally helically arranged such that, during normal operation of the actuator assembly, when the drive mechanism is operated such that the helical bearing arrangement (not shown) guides helical movement of the second part310with respect to the first part about the helical axis over the first portion of the helical movement, the first stop362A of the second part310is spaced from the first surface352A by a substantially constant distance (shown by arrow ‘D1’ inFIG.29A) in the first direction (shown by arrow ‘X’ inFIG.29A). That is, as the second part310moves helically with respect to the first part over the first portion of helical movement, the first surface352A of the first part is arranged to permit said helical movement without the first stop362A of the second part310abutting the first surface352A.

The first stop362A of the second part310is configured to engage the first surface352A of the first part (as shown inFIG.29B) if the first stop362A is moved relative to the first surface352A of the first part by said distance D1in the first direction X. The engagement of the first stop362A of the second part310with the first surface352A restricts relative movement of the first and second parts. As explained above in respect of the first embodiment of the actuator assembly101shown inFIGS.17to25, restricting relative movement of the first and second parts helps to prevent damage to the components of the actuator assembly, for example, if the actuator assembly is dropped or otherwise impacted.

When the second part310is moved relative to the first part over the first portion of helical movement, the second stop362B of the second part310is not aligned with the second surface352B along the helical axis and is instead spaced from the second part by a distance (depicted by arrow ‘D2’ inFIG.30A) that may vary according to the position of the second part310along the first portion of helical movement, but is greater than said distance Dl. Thus, movement of the second part310relative to the first part in the first direction X by the first distance D1will result in the second stop362B of the second part310still being spaced from the second part310by a distance (depicted by arrow ‘D3’ inFIG.30B) that may vary according to the position of the second part310along the first portion of helical movement.

When the second part310is moved relative to the first part over a second portion of helical movement, the second stop362B is aligned with the second surface352B in the direction along the helical axis. The second surface352B of the first part is generally helically arranged such that, during normal operation of the actuator assembly, when the drive mechanism is operated such that the helical bearing arrangement (not shown) guides helical movement of the second part310with respect to the first part about the helical axis over the second portion of the helical movement, the second stop362B of the second part310is spaced from the second surface352B by a substantially constant distance (shown by arrow ‘D1’ inFIG.30C) in the first direction (shown by arrow ‘X’ inFIG.30C). That is, as the second part310moves helically with respect to the first part over the second portion of helical movement, the second surface352B of the first part is arranged to permit said helical movement without the second stop362B of the second part310abutting the second surface352B.

The second stop362B of the second part310is configured to engage the second surface352B of the first part (as shown inFIG.30D) if the second stop362B is moved relative to the second surface352B of the first part by said distance D1in the first direction X. The engagement of the second stop362B of the second part310with the second surface352B restricts relative movement of the first and second parts. As explained above in respect of the first embodiment of the actuator assembly101shown inFIGS.17to25, restricting relative movement of the first and second parts helps to prevent damage to the components of the actuator assembly, for example, if the actuator assembly is dropped or otherwise impacted.

When the second part310is moved relative to the first part over the second portion of helical movement, the first stop362A of the second part310is not aligned with the first surface352A along the helical axis and is instead spaced from the second part by a distance (depicted by arrow ‘D2’ inFIG.29C) that may vary according to the position of the second part310along the first portion of helical movement, but is greater than said distance D1. Thus, movement of the second part310relative to the first part in the first direction X by the first distance D1will result in the first stop362A of the second part310still being spaced from the second part by a distance (depicted by arrow ‘D3’ inFIG.29D) that may vary according to the position of the second part310along the first portion of helical movement.

The first and second stops352A,362A,352B,362B therefore permit helical movement of the second part310relative to the first part, and together provide a stopping function over the entire range of helical movement of the second part.

The actuator assembly may be any type of assembly that comprises a first part and a second part movable with respect to the first part. 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, and 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.

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.