GB2588965A

GB2588965A - An actuator and a method of controlling thereof

Info

Publication number: GB2588965A
Application number: GB1916721.2A
Authority: GB
Inventors: Armstrong Samuel; Howarth James; Langhorne Robert; Eddington Robin; Mcgrath Joel; Pantelidis Konstantinos
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2019-11-16
Filing date: 2019-11-16
Publication date: 2021-05-19
Anticipated expiration: 2039-11-16
Also published as: CN214311057U; GB201916721D0; GB2588965B

Abstract

An actuator 10 comprises a first part 11 a second part 12, movable relative to the first. Lengths of shape memory alloy (SMA) wire 2 connect the respective parts, each length of wire, on contraction, effect movement in the second part. Included is a means for reducing abrasion of the wire when one length(s) of the actuator wire is in an unenergized state, where there may be a degree of slack. Preferably the lengths of wire are angled to, and cross, each other at a point. The abrasive reduction means may comprise a protrusion extending from one of the parts and components of the actuator towards an unenergized wire, integrally formed with the respective parts. The means may comprise a barrier between each of the wires of a coating (530, fig 5) covering the surface of a portion of wire covering only the surface at and/or in the vicinity of the crossing point, which may be either a polymer, powder, lubricant, viscous fluid or damping gel (630, fig 6). The means may comprise a shock absorber (930, fig 9). A method of control is also claimed.

Description

AN ACTUATOR AND A METHOD OF CONTROLLING THEREOF

The present application generally relates to an actuator and method of controlling thereof.

Summary

The present invention provides an SMA actuator having various means for reducing abrasion of the SMA actuator wires therein. Advantageously, the present invention may increase the longevity the SMA actuator wires and thereby it may improve the reliability of the actuator. Moreover, in some embodiments, the means may prevent contact between energised wires and thus eliminating electrical damage.

According to a first aspect of the present invention, there is provided an actuator 15 comprising: a first part; a second part movable relative to the first part; plural lengths of shape memory alloy (SMA) wire connecting the first part and the second part, each length of SMA wire is configured to, on contraction, effect movement in the second part; and means for reducing abrasion of the lengths of SMA wire when at least one length of SMA actuator wire is in an unenergized state.

The actuator may be a micro-actuator for a camera or a mobile phone, wherein multiple lengths of SMA actuator wire are used for moving a second part, e.g. lens carriage along multiple axes. Such arrangement enables autofocus (AF) and optical image stabilisation (OIS) to be carried out upon actuating some or all of the lengths of SMA wire. The lengths of SMA wire may extend in different directions and in close proximity to each other. This may increase the likelihood of contact and therefore abrasion between the lengths of wire, as well as with components of the actuator.

By providing suitable means, each length of SMA actuator wire may be isolated, or having their movement limited when it is in an unenergized state. Thereby the present invention significantly reduces or eliminates abrasion on the SMA wires.

The means is configured to reduce abrasion of the lengths of SMA actuator wire when at least one length is in an unenergized state, i.e. when the actuator is inactive. For example, the at least one length of the unenergized SMA wires may have a degree of slack, wherein upon energising the said length of unenergized SMA wire may contract and thereby eliminates the slack therein. More specifically, a length of unenergized SMA wire, as well as the lens carriage, may have a degree of free movement when the actuator is powered off. Therefore, when the device is in motion, e.g. during transit, the lengths of SMA wire may experience a substantial amount of wear over time.

The SMA actuator wires may form from any suitable shape memory alloy material, typically a nickel-titanium alloy (e.g. Nitinol), but they may also contain tertiary components such as copper. The SMA actuator wires may have any cross-sectional profile and diameter suitable for the application. For example, the SMA wires may have a cross section diameter of 25,1m capable of generating a maximum force of between 120mN to 200mN whilst maintaining the strain in the SMA wire within safe limits (e.g. 2-3% reduction in length over original length). Increasing the diameter of each SMA wire from 25pm to 35pm approximately doubles the cross-sectional area of the SMA wire and thus approximately doubles the force provided by each SMA wire. Preferably, the SMA wire may be capable to deliver a high force, e.g. between 1.2 to 3N, more preferably between 1.2 to 10N, whilst maintaining the strain in the SMA wire within safe limits (e.g. 2-3% reduction in length over original length). The force may be dependent on the target displacement required.

Optionally, the lengths of SMA wire are angled to, and cross, each other at a crossing point when viewed from a first direction, wherein the lengths of SMA wire are susceptible to abrasion with each other when at least one length of SMA wire is in an unenergized state. For example, the lengths of SMA wire may not come into contact with each other at the crossing point when they are energised and tensioned. However, in an unenergized state they may make contact with, and rubbing on, each other at the crossing point, i.e. when the actuator is powered off.

Optionally, the movement of the lengths of SMA wire, in an energised state, is free of interference from the means. In some embodiments, the means is configured to limit movement of the lengths of unenergized SMA wire, thereby preventing contact between the wires. More specifically, the means is arranged such that it only limits the movement of SMA wires when they are unenergized or slacked. Once the SMA wires are energised and tensioned, the means does not present any hinderance or interference to the movement of SMA wires or indeed the second part. Advantageously, the means may function in an automated manner as required.

Optionally, the means comprises a barrier disposed between each length of the SMA wires. The barrier may provide a physical means for separating the wires. The barrier may form from a material having a lower toughness than the SMA wires, and therefore upon contacting the wires it serves as a sacrificial layer to reduce wire wear. Alternatively or in addition, the barrier may have a surface with a lower friction coefficient than that of the SMA wires, and thereby allows the wires to slide thereon. In some embodiments, the barrier may form from an electrical insulation material for eliminating electrical conduction between adjacent wires.

Optionally, the barrier comprises a coating covering the surface of at least a portion of one or more lengths of SMA actuator wire. Optionally, the coating covers only the surface of the one or more lengths of SMA wire locally at and/or in the vicinity of the crossing point. Optionally, the coating comprises one or more of a polymer, powder, lubricant, viscous fluid and damping gel. The coating may be a Teflon coating. The coating may be a block of damping gel deposited on one or more surfaces of the first part, the second part, and other components of the actuator, wherein the block of damping gel encloses one or more lengths of the SMA wires at the crossing point.

Alternatively, the coating comprises a wire sheath formed together with, or separated to, the lengths of SMA wire. For example, the SMA wires may form with a wire sheath extending the length of SMA wires, wherein the portions of wire sheath away from the crossing point are stripped off. Alternatively, the SMA wires are unsheathed when formed, with the wire sheath being added to the portion of the wire at or adjacent to the crossing point. The sheath may be an electrical insulating wire sheath and/or a length of adhesive tapes.

Optionally, the barrier comprises a film or a partition wall extending between the lengths of SMA actuator wire and along a plane substantially parallel to the SMA wires. Optionally, the film or the partition wall extends between a pair of crimps connecting one or more lengths of SMA actuator wire to the first part and the second part. For example, the film or the partition wall does not come into contact with the SMA wires when they are tensioned or energised, but it acts as a preventive measure for preventing contact between lengths of unenergized SMA wires.

The film or the partition wall may be rigid, or it may be flexible and/or deformable. The film or the partition wall may be attached to the crimps by heat sealing or any other methods. The film or partition wall may not restrict movement of the SMA wires once they are energised and under tension.

Optionally, the means comprises a protrusion extending from one of the second part, the first part and components of the actuator towards a length of unenergized SMA wire, to support the said length of unenergized SMA wire.

Optionally, the protrusion is integrally formed with the respective second part, the first part and/or components of the actuator. Optionally, the protrusion is formed integrally with the crimps. The protrusion may extend from the first part, second part and/or the crimps along the first direction, wherein the extent of protrusion may be limited such that it does not interfere with energised SMA wires once they are tensioned.

Optionally, the means comprises a resilient element for exerting a biasing force against at least one length of unenergized SMA wire and thereby tensions the length of unenergized SMA wire, wherein upon contraction the length of SMA actuator wire overcomes the biasing force to effect movement of the second part. The resilient element may be configured to bias the at least one length of unenergized SMA wire away from other SMA wires and/or components of the actuator. The resilient element may be positioned at one of more of the first part, the second part, and the crimps. The resilience element may comprise one of more of a spring, a flexure, a structured foam such as a sponge and elastomer.

Optionally, the means comprises a magnet or an adhesive surface configured to retain at least one length of unenergized SMA wire, wherein upon contraction the SMA wire overcomes such retention to effect movement of the second part.

Advantageously, the magnet or the adhesive surface may be configured to attract or adhere to the at least one length of unenergized SMA wire, so as to retain it away from other SMA wires and/or components of the actuator. The magnet or the adhesive surface may be positioned at one or more of the first part, the second part, or the crimps. The adhesive surface may comprise a glue, or an adhesive tape.

Optionally, the means comprises shock absorber for absorbing impact of the lengths of SMA wires against each other and/or components of the actuator. Optionally, the shock absorber comprises a deformable element deposited on a surface of the components. For example, the deformable element may be a pad formed from a structured foam or a gel deposited on the first part, second part, e.g. lens carriage or other components such as a screening can surrounding the lens carriage. Advantageously, the shock absorber may limit the freedom of movement in the SMA wires, as well as reducing the impact of collisions between the adjacent lengths of SMA wire or between the SMA wires and an adjacent surface.

Optionally, the deformable element is configured to deform and receive at least one length of unenergized SMA wire, thereby shielding the said length of SMA wire from abrasion with other lengths of SMA actuator wire and/or components of the actuator. For example, the deformable element may be a gel for absorbing the an SMA wire therein upon its impact on the gel, thereby the SMA wire is submerged beneath the surface of the gel. Advantageously, such arrangement may reduce the likelihood of impact between the submerged SMA wire and another SMA wires.

Upon energising, the submerged SMA wire is configured to contract and thereby emerges from the gel.

Optionally, the lengths of SMA wire are connected to the first part and the second part by respective crimps. The crimp may at least partially form from any electrically conductive material, such as carbon steel, stainless steel and copper alloy, e.g. phosphorus bronze. The conductive material may advantageously be ductile and capable of mechanically crimping the SMA wires thereat. Alternatively, the lengths of SMA wire are connected to the first part and the second part by hooks, dowel pins, clips or any other suitable connectors for effecting mechanical connection with the SMA wires.

Optionally, the means comprises a restrain provided on at least one of the crimps, the restrain is configured to restrain a lateral movement of the respective length of SMA wire extending from the crimp when it is in an unenergized state. More specifically, the restrain may be provided on an end of the crimp where the SMA wire emerges. The restrain may be a resilient element such as a flexure, a spring or an elastomer, or the restrain may be a gel or an adhesive. Therefore advantageously, the restrain maintains the exit angle of the SMA wire emerging from the crimp, thereby restrains any free movement of the wire.

Optionally, the means comprises an extender provided on at least one of a pair of crimps that are connected to adjacent lengths of SMA wire, wherein the extender is configured to extend the offset between the pair of the crimps in the first direction, thereby reducing abrasion between adjacent lengths of SMA wire. That is, by increasing the separation between the adjacent SMA wires through an increased offset position, it may advantageously reduce the chance of adjacent SMA wires colliding with each other. Moreover, it may reduce the risk of wires rubbing on each other when they are energised, partly due to tolerances and the tilting of the lens carriage. The offset may be created by providing an angled portion at the crimp, increasing an angle of the angled portion of the crimp and/or extending an angled portion of the crimp.

Optionally, the crimps are arranged such that adjacent lengths of unenergized actuator wire are angled away from each other. For example, the crimp heads coupling adjacent SMA wires may be arranged so as to direct adjacent SMA wires away from each other. That is, the crimp heads may be pointing away from each other. When the adjacent lengths of SMA wires are energised, they may contract and cause the crimp heads to rotate, such that the said crimp heads may be parallel to each other when the SMA wires are energised.

According to a second aspect of the present invention, there is provided a method of controlling an actuator, the actuator having a first part connected to a second part by plural lengths of SMA actuator wire, the method comprising: supplying a first electrical current to the lengths of unenergized SMA actuator wire, the first electrical current is sufficient to tension the lengths of SMA actuator wire; measuring an electrical characteristic in each length of the SMA actuator wire; determining the degree of slack in each length of SMA actuator wire based on its respective electrical characteristic; and supplying a second electrical current to one or more lengths of the SMA wire to effect movement in the second part, once it is determined that all lengths of the SMA wires are tensioned; wherein the second electrical current is higher than the first electrical current.

Optionally, the first current is arranged increased in a gradual manner for tensioning the lengths of SMA wires.

More specifically, the method implements a gradual start-up procedure that changes how the lengths of SMA wires are driven at start-up. This may allow the voltage difference between the SMA wires to be minimised and therefore reduce the likelihood of damage resulting from arcing.

For example, at the start of actuation, all the adjacent lengths of SMA wires may be energised at the same time, with a reduced current flow. This may activate the SMA wires together with a reduced risk of arcing. Once the SMA wires are tensioned, the wires are not in contact and thereon a higher current flow may be supplied.

According to a third aspect of the present invention, there is providing an electronic device having the actuator of the first aspect and/or implementing the method of the second aspect. For example, the electronic device may be a camera or smart phone whereby the actuator is configured to move a lens carriage for effecting autofocus (AF) and optical image stabilisation (OIS).

Brief Description of the Drawings

Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an exploded view of SMA actuator wire arrangements in a camera; Figures 2A and 2B are respective side and plan sectional views of an SMA actuator according to a first embodiment of the present invention; Figures 3A and 3B are respective side and plan sectional views of an SMA actuator according to a second embodiment of the present invention; Figures 4A and 4B are respective side and plan sectional views of an SMA actuator according to a third embodiment of the present invention; Figures 5A and 5B are respective side and plan sectional views of an SMA actuator according to a fourth embodiment of the present invention; Figure 6A is a side view of an SMA actuator according to a fifth embodiment of the present invention, and Figures 6B and 6C are plan sectional views of the SMA actuator in respective energised and unenergised states; Figures 7A and 7B are respective side and plan sectional views of an SMA actuator according to a sixth embodiment of the present invention; Figures 8A and 8B are respective side and plan sectional views of an SMA actuator according to a seventh embodiment of the present invention; Figures 9A is a plan view of an SMA actuator according to an eighth embodiment of the present invention, and Figures 9B and 9C are sectional views of the SMA actuator wires interacting with a means, when view along the length of one of the SMA wires; Figures 10A is a side sectional view of an SMA actuator according to a ninth embodiment of the present invention, and Figures 10B and 10C are plan views of the SMA actuator at two different planes along direction of view; Figures 11A and 11B are respective plan and side sectional views of an SMA actuator according to a tenth embodiment of the present invention; Figures 12A and 12B are respective plan and side sectional views of an SMA actuator according to an eleventh embodiment of the present invention; Figure 13A is a plan sectional view of an SMA actuator according to a twelfth embodiment of the present invention, and Figures 13B and 13C are side sectional views of the SMA actuator where the SMA wires are respectively in an unenergized and in an energised state; Figures 14A and 14B are respective plan and side sectional views of an SMA actuator according to a thirteenth embodiment of the present invention; Figures 15A, 15B, 15C illustrates various stages of operation in a tensioning mechanism according to a fourteenth embodiment of the present invention; Figure 16 is a plan sectional view of an SMA actuator according to a fifteenth embodiment according of the present invention; and Figures 17A, 17B and 17C are side sectional views of SMA actuators according to respective sixteenth, seventeenth and eighteenth embodiments of the present invention.

Detailed Description

Figure 1 shows an exploded view of a shape memory alloy (SMA) actuator wire arrangement 10 in a miniature camera. The SMA actuator arrangement 10 includes a static part 5, or a first part, that comprises a base 11 that is an integrated chassis and sensor bracket for mounting an image sensor, and a screening can 12 attached to the base 11. The SMA actuator arrangement 10 includes a moving part 6, or a second part, that is a camera lens assembly comprising a lens carriage 13 carrying at least one lens (not shown).

In this example, the actuator 10 includes eight SMA wires 2 each attached between the static part 5 and the moving part 6. A pair of SMA wires 2 that cross each other are provided on each of four sides of the SMA actuator arrangement 10 as viewed along an optical axis, along a first direction. The SMA wires 2 are attached to the static part 5 and the moving part 6 in such a configuration that upon heating, they contract and thereby provide relative movement of the moving part 5 with multiple degrees of freedom for providing both autofocus (AF) and optical image stabilisation (OIS).

Thus, in respect of each pair of SMA wires 2, the SMA wires 2 are attached at one end to two static mount portions 15, which are themselves mounted to the static part 5 for attaching the SMA wires 2 to the static part 5. The static mount portions are adjacent one another but are separated to allow them to be at different electrical potentials.

Similarly, in respect of each pair of SMA wires 2, the SMA wires 2 are attached at 20 one end to a moving mount portion 16 which is itself mounted to the moving part 6 for attaching the SMA wires 2 to the moving part 6. The moving part 6 further comprises a conductive ring 17 connected to each of the moving mount portions 16 for electrically connecting the SMA wires 2 together at the moving part 6.

The static mount portions 15 and the moving mount portions 16 comprise crimp tabs 23 which may be formed into crimps and used to hold the SMA wires 2. The moving mount portions 16 may comprise electrical connection tabs 31 for providing electrical connection to the conductive ring 17. Thus, in the example shown in Figure 1, the crimp tabs 23 that are formed into crimps are integral parts of the static and moving portions of the actuator arrangement 10. Methods for forming the crimps and trapping the SMA wires within the crimp tabs 23 are described in International Patent Publication No. W02016/189314.

In practice, when the SMA wires 2 are unenergized, i.e. when the SMA actuator 10 is powered off, they may no longer under tension. In some cases, a degree of slack may be observed in the unenergized SMA wires 2. This may cause free movement in the SMA wires, and in some cases in the lens carriage. Such free movement causes the SMA wires to contact and rub over each other, leading to abrasion and wear of the wire. As such the present invention provides various means for reducing abrasion on SMA wires when they are in an unenergized state.

The means may be applied together or each on their own, wherein the means may be applicable to any SMA actuator arrangement having a pair of adjacent SMA wires.

Figures 2A and 2B show a SMA actuator 210 according to a first embodiment according of the present invention. In the illustrated embodiment, a pair of SMA wires 202 connect the movable part 213 and the base 211 by respective crimps 216 and 215. In the side view of Figure 2A, it is shown that the pair SMA wires 202 are angled to, and crossed, at a crossing point around the mid-point of each of the wires. As shown in Figure 2B, the wires 202 are extended in parallel and do not come into contact with each other when it is energised and tensioned. However, when the wires 202 are unenergized, they may no longer be tensioned and in some cases, they may have a degree of slack. Therefore, it may be possible that when in an unenergized state, they may come into contact with each other unless a means is provided to reduce or prevent abrasion of the SMA wires 202 due to contact.

In this embodiment, the means comprises a film 230 extends between, and parallel to, the pair of wires. The film 230 is adhered to the pair of crimps 215, 216, and isolates the SMA wires 202 extending therebetween. The film 230 is tensioned to prevent contact with the pair of SMA wires 202. The film 230 as shown in this embodiment is formed from a polymer and is sufficiently thin to be flexible, i.e. it accommodates the movement of the SMA wires 202 and the movable part 213. Due to its flexibility, as well as a lower toughness and a lower friction coefficient in the polymer material, it reduces abrasion of the SMA wires 202 even if it comes in contact with the SMA wires. The polymer film 230 also serves as an electrical insulator and therefore it is capable of electrically insulating the pair of SMA wires 202.

In other embodiments, the film may be replaced by a rigid partition wall hingedly connected to the respective crimps. Such arrangement provides longevity to the partition wall between the SMA actuator wires.

Figures 3A and 3B show a SMA actuator 310 according to a second embodiment of the present invention. The SMA actuator 310 is structurally similar to the actuator 210 as shown in Figures 2A and 2B. However, the SMA actuator 310 comprises additional films 330 shielding the SMA wires 302. As shown in Figure 3B, the means comprises additional films 330 extending along the side of the pairs of SMA wires 302, e.g. the internal and external sides of the group of SMA wires with respect to the movable part 313. As with the film 230 as illustrated in Figure 2, the film 330 is adhered to and tensioned between the pair of crimps 315, 316, and isolates the SMA wires 302 extending therebetween. The additional films 330 shield the wire against abrasion and electrical conduction with components of the actuator 310, such as the movable part 313, the base 311, as well as the screening can (not shown) enclosing the SMA wires 302.

Figures 4A and 4B show a SMA actuator 410 according to a third embodiment of the present invention. The SMA actuator 410 is structurally similar to the actuator 410 as shown in Figures 2A and 2B. However, SMA actuator 410 comprises a wire sheath 430 in place of the film. As shown in Figure 4B, the means comprises a wire sheath 430 covering one of the SMA wires 402 at the crossing point, whilst the surface of remainder of the SMA wires 402 are exposed. Advantageously, such selective coverage of the SMA wires 402 allows the majority of the wire 402 surface to remain uncovered, therefore such arrangement allows efficient heat dissipation critical to the operation of SMA wires 402. The wire sheath 430 reduces the abrasion of the SMA wires 402 at and in the vicinity of the crossing point. In this embodiment, the wire sheath 430 is formed by stripping portions of existing wire sheath on sheathed SMA wires 402 at positions away from the crossing point.

The wire sheath 430 may be applied at the crimp prior to assembling the SMA wires 402 to the SMA actuator 410, e.g. before the crimps 415, 416 are removed from its corresponding crimp coupon, or it may take place at any stage of the actuator assembly process.

In other embodiments, the wire sheath is formed by sheathing unsheathed SMA wires at the crossing point with a coating or a tape. Preferably, the sheath may form from a PTFE tape or coating for reducing friction at the surface, thereby reducing abrasion on the surface of SMA wires.

In some other embodiments, the wire sheath may be provided on both the SMA wires at the crossing point. Advantageously, this provides additional protection for the SMA wires, i.e. against abrasion against other components of the actuator.

Figures 5A and 5B show a SMA actuator 510 according to a fourth embodiment according of the present invention. The SMA actuator 510 is structurally similar to the actuator 410 as shown in Figures 4A and 4B. However, SMA actuator 510 comprises a coating 530 in place of the wire sheath. The coating in the illustrated embodiment is a damping gel 530 covering the surface of both SMA wires 502 at the crossing point for reducing friction at the said surface. Therefore, such arrangement reduces abrasion on the surface of SMA wires 502 against other SMA wires, as well as against surfaces of the other components of the actuator 510. The damping gel 530 is configured to electrically insulate the SMA wires 502. The damping gel 530 preferably has properties such as low thermal capacity and high thermal conductivity, so as to avoid hindering the heat dissipation of the SMA wires. The coating 530 may be of a thin layer of coating, in the orders of tens or hundreds of microns.

In some other embodiments, only one of the SMA wires comprises the coating to reduce abrasion between the SMA wires. This advantageously reduces the impact of coating on the heat dissipation rate.

In some other embodiments, the coating may be a grease, or it may be other friction reducing coating such as a Teflon coating.

Figures 6A is a side view of an SMA actuator 610 according to a fifth embodiment of the present invention, and Figures 6B and 6C are plan sectional views of the SMA actuator in respective energised and unenergized state. In this embodiment, the means comprises a block of damping gel 630 positioned on the surface the movable part 613 at or adjacent to the crossing point. More specifically, as shown in the plan view in Figure 6A, a receptacle 632 is provided adjacent to the crossing point for receiving the block of damping gel 630. The damping gel 630 is configured to receive or enclose a portion of at least one of the SMA wires at the crossing point. As shown in Figure 6A and 66, the damping gel 630 reduces wire abrasion by physically shielding the enclosed wires 602 from other SMA wires 602.

The damping gel is sufficiently viscous, non-flowable, at the operating temperature of the SMA wires 602, yet it is able to absorb the impact of SMA wires 602 impinging thereon.

In other embodiments, the damping gel extends from the receptacle and encloses both of the SMA wires. For example, the damping gel is configured not to hinder the movement of the an energised SMA wire during operation, e.g. the viscosity of the damping gel reduces with the temperate, therefore during operation of the actuator, the damping gel does not impose any friction or resistance on the SMA wires.

Figures 7A and 7B show a SMA actuator 710 according to a sixth embodiment of the present invention. Figures 8A and 8B show a SMA actuator 810 according to a seventh embodiment of the present invention. Both SMA actuators 710, 810 are structurally similar to the actuator 510 as shown in Figures 4A and 4B. In each of these embodiments, a block of damping gel 730, 830 is positioned at the leading edge of the respective crimp 715,716,815,816 where the SMA wires 702,802 emerge. In Figure 7, the damping gel 730 is configured to bias the SMA wires 702 away from each other (along the direction of the arrows). As a result, when the SMA wires 702 are in an unenergized state, they emerge from respective crimps deflected away from each other, wherein their free movement is limited by the biasing force.

Alternatively, as shown in Figure 8, the damping gel 830 is configured to held in place or to stabilise the SMA wires 802. As a result, when the SMA wires 802 are 30 in an unenergized state each of SMA wires 802 emerges from the respective crimp with limited free movement, however they may not be deflected.

The damping gel 730, 830 in providing in SMA actuators 710, 810 are arranged to reduce abrasion of unenergized SMA wires 702, 802, and not to cause interference when they are energised. For example, the viscosity of the damping gel may reduce with temperate, therefore during operation of the actuator, i.e. when the SMA actuators are heated, the damping gel does not impose any force, friction or resistance on the SMA wires.

Figures 9A is a plan view of an SMA actuator according to an eighth embodiment of the present invention, and Figures 9B and 9C are sectional views of the SMA actuator wires interacting with a means, when view along the length of one of the SMA wires. The SMA actuator 910 is structurally similar to the actuator 510 as shown in Figures 4A and 4B. The SMA actuator 910 comprises a shock absorbing surface, or a shock absorber 930, provided on a surface of a component adjacent to the SMA wires 902. In the illustrated embodiment, the shock absorber 930 may be a pad of structured foam such as a sponge, a pad of gel, an adhesive. The shock absorber 930 is shown adhered to a sidewall of the screening can 912. Alternatively, or in addition, the shock absorber 930 may be adhered to a surface of the movable part 913 or base 911.

This shock absorber 930 is configured to either limit the freedom of movement in the SMA wires 902 or to reduce the impact of collisions between the wires and the adjacent surface or between the SMA wires when one of the wires impacts against an adjacent surface. For example, the shock absorber reduces the maximum impact force on the wire during a collision. This has the potential to reduce the likelihood of damage when colliding with an adjacent surface, e.g. the shock absorber 930 is configured to reduce the kinetic energy in the SMA wire 902 and therefore it produces a damping effect. The shock absorber is configured to reduce the amount of wire rebound after an impact. For example, in embodiments where the shock absorber 930 is an adhesive, the adhesive 930 is configured to attract and thereby prevents the SMA wire 902 from ricocheting off the impacted surface before colliding with the adjacent SMA wire 902. By attracting, or slowing down the SMA wire 902, the number of collisions may be reduced.

In some embodiments, the shock absorber 930 is configured to protect an SMA wire 902a from colliding with an adjacent SMA wire 902b. This mechanism is illustrated in Figures 9B and 9C, where upon impact a first SMA wire 902a is indented or received into the surface of the shock absorber 930. Such arrangement shields the first SMA wire 902a and thereby reducing or eliminating the impact of the second SMA wire 902b thereon.

Figures 10A is a side sectional view of an SMA actuator 1010 according to a ninth embodiment of the present invention, and Figures 10B and 10C are plan views of the SMA actuator 1010 at two different planes along the direction of view. In this embodiment, the moving part 1013 comprises a pair of protrusions, or wire guards 1030a extending form the corresponding sidewall. As shown in Figure 10B, the pair of wire guards 1030a are configured to support one of the SMA wires 1002 when it is in an unenergized state, thereby constraining or restricting free lateral movement in the SMA wires. Although a pair of wire guards 1030a are shown in this example, a single wire guard providing support anywhere along the length of the SMA wire would be sufficient for preventing free movement in the unenergized SMA wire.

In addition, an additional wire guard 1030b protrusion from the surface of a support element, which in turn is attached to the sidewall of the screening can (not shown). The additional wire guard 1030b is configured to support the other one of the SMA wires 1002 when it is in an unenergized state, thereby constraining or restricting its free lateral movement. In some other embodiment, a plurality of additional wire guards 1030b may be provided to lend further support on the said SMA wire 1002.

The wire guards 1030a and additional wire guards 1030b protruded respectively from the movable part 1013 and the screening can, at a predetermined distance that would provide support only when the SMA wires 1002 are unenergized and/or slack. The wire guards 1030a and additional wire guards 1030b are configured not to hinder or interfere with the movement of SMA wire 1002 when they are energised and/or tensioned.

Alternatively, there are other embodiments that offer more compact or simplistic wire guard designs. Figures 11A and 11B are respective plan and side sectional views of an SMA actuator according to a tenth embodiment of the present invention. In this embodiment, a single wire guard 1130 extends from an edge of the base 1111 in a direction towards the movable part 1113, and between the pair of SMA wires 1102 at their crossing point. The wire guard 1130 provides a low friction surface, e.g. the surface of the wire guard 1130 has to lower friction coefficient than the surface of the SMA wires 1102. Therefore, the wire guard 1130 not only ensures the pair of SMA wires 1102 do not come into contact with each other, it also minimises abrasion of the SMA wires 1102.

Figures 12A and 12B are respective plan and side sectional views of an SMA actuator 1210 according to a tenth embodiment of the present invention. The SMA actuator 1210 is structurally similar to the SMA actuator 1110 shown in Figure 11.

However, the SMA actuator 1210 in this embodiment comprises a pair of wire guards 1230 extending from an edge of the base 1211 in a direction towards the movable part 1113, and between the pair of SMA wires 1102 at their halves closest to the base 1211. That is, the extent of each of the wire guards 1230 is less than that of the wire guard 1130 shown in Figure 11. Thus, it may reduce the likelihood of interfering with the movement of the movable part 1213.

Figures 13A is a plan sectional view of an SMA actuator 1310 according to a twelfth embodiment of the present invention, and Figures 13B and 13C are side sectional views of the SMA actuator 1310 where the SMA wires 1302 are respectively in an unenergized and in an energised state. As shown in Figure 13A and 13B, the SMA actuator 1310 comprises a pair of flexures 1330 mounted on the base 1311 each configured to bias one of the SMA wires 1302 away from each other. The flexures may alternatively, or in addition, mounted on the movable part 1313 to bias the other ends of the SMA wires 1302 away from each other. Such arrangement keeps the wire tensioned when they are in an unenergized state or slacked. Upon energising, the SMA wires 1302 contract and thereby overcome the biasing force to effect movement in the movable part 1313, as shown in Figure 13C. The biasing force as exerted by the flexures 1330 should be sufficient to at least support and thereby ridding of any slack in the respective SMA wire 1302, but not high enough to cause a tangible effect on the movement of the movable part 1313.

Figures 14A and 14B are respective plan and side sectional views of an SMA actuator 1410 according to a thirteenth embodiment of the present invention. Similar to the SMA actuator 1310 of Figure 13, the means in this embodiment 35 comprises tensioning mechanism 1430 for tensioning the SMA wires 1402 when they are in an unenergized state. As shown in Figures 14A and 14B, there is provided elastic cords 1430 connecting the crimps at the base 1411 and their respective SMA wires 1402. Such arrangement tensions the SMA 1402 when they are in an unenergized state / having a degree of slack. In other embodiments, the elastic cords 1430 may alternatively, or additionally, provided between the SMA wires 1402 and the corresponding crimps at the movable part 1413. The tensioning force as exerted by the elastic cords 1430 should be sufficient to at least tension and thereby ridding of any slack in the respective SMA wire 1402, but not high enough to cause a tangible effect on the movement of the movable part 1413.

Figures 15A, 15B, 15C illustrate various stages of operation in a tensioning mechanism according to a fourteenth embodiment of the present invention. The tensioning mechanism 1530 may replace or used in tandem with the flexures 1330 and/or the elastic cords 1430 respectively shown in Figures 13 and 14. The tensioning mechanism comprises a coil spring 1530 that is configured to bias against the contraction of the SMA wire 1502. In Figure 15A, when the SMA wire 1502 is in an unenergized state, the coil spring 1503 biases a crimp head 1516b (coupled to the SMA wire 1502), slidably on a crimp base 1516a, against a direction in which the SMA wire 1502 contracts. More specifically, the coil spring 1503 acts as a returning mechanism. Thereby, the SMA wire 1502 maintains tensioned when it is in an unenergized state. In Figure 15B, the SMA wires 1502 is energised and begins to contract, in the process overcomes the biasing force of the coil spring 1503 and moves the crimp head 1516b. The crimp head 1516b moves in the direction of contraction until it reaches an end stop, as shown in Figure 15C. In other words, the end stop defines a nominal active position of the crimp. Once the crimp head 1516b reaches this position further contraction in the SMA wire 1502 causes movement in the movable element. In order to maintain accurate wire exit positions, e.g. where the SMA wire 1502 exits the crimp, the SMA wire 1502 would need to maintain a tension greater than the force from the coil spring 1530.

Figure 16 is a plan sectional view of an SMA actuator according to a fifteenth embodiment of the present invention. In this embodiment, the means for reducing wire abrasion comprises a pair of adjacent angled crimps 1715 each connecting a respective SMA wire 1702. The angled crimps 1715 are arranged such that the adjacent SMA wires 1702 exiting the crimps are angled away from each other. More specifically, the crimp heads of the angled crimps 1715 may be modified such that adjacent crimp heads are angled away from each other, as shown in Figure 17. For example, the crimp head closest to the movable element 1713 is angled towards the centre of the said movable element 1713, wherein the crimp head furthest from the movable element 1713 is angled away therefrom.

In some embodiments, as the SMA wires energise and contract, the crimp head may rotate such that the adjacent crimps are parallel to each other when the SMA wires are under tension.

Alternatively, or in addition, the means may comprise redirecting one or more of the SMA wires along its length, e.g. via a hook, so as to avoid contact between adjacent SMA wires.

Figures 17A, 17B and 17C are side sectional views of SMA actuators according to respective sixteenth, seventeenth and eighteenth embodiments of the present invention. All of these embodiments comprise modified, or radially (with respect to an axis extending through the centre of the base and the movable element) extended, crimps to increase the offset between two adjacent SMA wires. By increasing the distance between adjacent SMA wires through the use of an increased offset position, it reduces the likelihood of wire collisions when the SMA wires are in an unenergized state. It also reduces the risk of abrasion between SMA wires when they are in an energised state, e.g. due to tolerances and the tilting of the lens carriage.

One of the current restrictions on the available offset (denoted by the arrows) is the limited space between the base 1711 and the shielding can 1712 as shown in Figure 17A. To increase the available offset, the length or angle of a jog 1830, e.g. the inclined surface relative to the plane of a crimp head, may increase as shown in Figure 17B. That is, an extender may be provided to extend the length of the jog, thus the offset. However, this required trimming off a leading edge of the base 1811 to allow room for the additional offset.

Alternatively, additional jog 1930 may be provided at other crimp heads of the crimp, as shown in Figure 17C. This requires part of the leading edge of the base 1911 to be trimmed off to provide the necessary space for accommodating the additional jog 1930.

In additional, the abrasion of SMA wires at the crossing point can be reduced by an improved control system. According to a nineteenth embodiment of the present invention, there is method comprising a soft start-up feature that changes how the SMA wires are driven when they start to energise. This would allow, for example, the voltage difference between the SMA wire pairs to be minimised during start-up. As such, the wire pairs may tension gradually, reducing the potential for damage from arcing.

According to this method, it is proposed to start driving the adjacent SMA wires simultaneously at the start-up. This would involve activating all the SMA wires concurrently, resulting in a reduced risk of arcing. Once the SMA wires are tensioned, as detected by resistance measurement in each of the wires, they can no longer come into contact with each other. Thereon, the power supply to the SMA wires, as well as SMA wire operation, may resume normal operation.

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

Claims

Claims 1. An actuator comprising: a first part; a second part movable relative to the first part; plural lengths of shape memory alloy (SMA) wire connecting the first part and the second part, each length of SMA wire is configured to, on contraction, effect movement in the second part; and means for reducing abrasion of the lengths of SMA wire when at least one length of the SMA actuator wire is in an unenergized state.
2. An actuator according to claim 1, wherein the at least one length of SMA wire has a degree of slack in the unenergized state, wherein upon energising the said length of SMA wire contracts and thereby eliminates the slack therein.
3. An actuator according to claim 1 or 2, wherein the plural lengths of SMA wire are angled to, and cross, each other at a crossing point when viewed from a first direction, wherein the lengths of SMA wire are susceptible to abrasion with each other when at least one length of the SMA wire is in an unenergized state.
4. An actuator according to any preceding claims, wherein the movement of the lengths of SMA wire, in an energised state, is free of interference from the means.
5. An actuator according to the any one of the preceding claims, wherein the means comprises a protrusion extending from one of the second part, the first part and components of the actuator towards a length of unenergized SMA wire, to support the said length of unenergized SMA wire.
6. An actuator according to claim 5, wherein the protrusion is integrally formed with the respective second part and/or the first part.
7. An actuator according to any one of the preceding claims, wherein the means comprises a barrier disposed between each length of the SMA wire.
8. An actuator according to claim 7, wherein the barrier comprises a coating covering the surface of at least a portion of one or more lengths of SMA wire.
9. An actuator according to claim 8, wherein the coating covers only the surface of the one or more lengths of SMA wire locally at and/or in the vicinity of the crossing point.
10. An actuator according to claim 8 or 9, wherein the coating comprises any one or more of a polymer, powder, lubricant, viscous fluid and damping gel.
11. An actuator according to any one of claims 8 to 10, wherein the coating comprises a wire sheath formed together with, or separated to, the lengths of SMA wire.
12. An actuator according to claim 7, wherein the barrier comprises a film or a partition wall extending between the lengths of SMA wire and along a plane substantially parallel to the lengths of SMA wire.
13. An actuator according to claim 12, wherein the film or the partition wall extends between a pair of crimps connecting one or more lengths of SMA actuator wire to the first part and the second part.
14. An actuator according to any one of the preceding claims, wherein the means comprises a resilience element for exerting a biasing force against at least one length of unenergized SMA wire, and thereby tensions the length of unenergized SMA wire, wherein upon contraction the at least one length of SMA wire overcomes the biasing force to effect movement of the second part.
15. An actuator according to the any one of the preceding claims, wherein the means comprises a magnet or an adhesive surface configured to retain a length of unenergized SMA wire, wherein upon contraction the length of SMA wire overcomes such retention to effect movement of the second part.
16. An actuator according to any one of the preceding claims, wherein the means comprises shock absorber for absorbing impact of the lengths of SMA wires against each other and/or components of the actuator.
17. An actuator according to claim 16, wherein the shock absorber comprises a deformable element deposited on a surface of the components.
18. An actuator according to claim 17, wherein the deformable element is configured to deform and receive at least one length of unenergized SMA actuator wire, thereby shielding the said length of SMA wire from abrasion with other lengths of SMA actuator wire and/or components of the actuator.
19. An actuator according the any one of the preceding claims, wherein the lengths of SMA wires are connected to the first part and the second part by respective crimps.
20. An actuator according to claim 19, wherein the means comprises a restrain provided on at least one of the crimps, the restrain is configured to restrain a lateral movement of the respective length of SMA wire extending from the crimp when it is in an unenergized state.
21. An actuator according to claim 20, wherein the restrain comprises one or more of a damping gel, a resilient means and an adhesive.
22. An actuator according to any one of claims 19 to 21, wherein the means comprises an extender provided on at least one of a pair of crimps that are connected to adjacent lengths of SMA wire, wherein the extender is configured to extend the offset between the pair of the crimps in the first direction, thereby reducing abrasion between adjacent lengths of SMA wire.
23. An actuator according to any one of claims 19 to 22, wherein the crimps are arranged such that adjacent lengths of unenergized SMA wire are angled away from each other.
24. A method of controlling an actuator, the actuator having a first part connected to a second part by plural lengths of SMA actuator wire, the method 35 comprising: supplying a first electrical current to the lengths of unenergized SMA actuator wire, the first electrical current is sufficient to tension the lengths of SMA actuator wire; measuring an electrical characteristic in each length of the SMA actuator wire; determining the degree of slack in each length of SMA actuator wire based on its respective electrical characteristic; and supplying a second electrical current to one or more lengths of the SMA wire to effect movement in the second part, once it is determined that all lengths of the SMA wires are tensioned; wherein the second electrical current is higher than the first electrical current.
25. A method of controlling an actuator according to claim 24, wherein the first current is arranged increased in a gradual manner for tensioning the lengths of 15 SMA wires.