Anchor for shape memory alloy wire and actuator

Abstract

The present invention is an anchor for a heat-responsive ligature that deforms when heated. The ligature has an engaging segment for engaging the anchor with two clamping portions and a curved portion. The anchor is made of a thermally and / or electrically conductive material and has an engaging surface for engaging a curved portion of the ligature. The clamping portions of the engaging segment of the ligature pass between the body and the clamping component when the curved portion of the engaging segment engages the engaging surface of the anchor body.Then, portions of the clamping component can be moved toward the anchor body to reconfigure the clamping component such that the portions of the clamping component press the clamping portions of the engaging segment of the ligature against the anchor body and maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to mechanisms for attaching a heat-responsive ligature to elements of a device, wherein the heat-responsive ligature exerts a force on the elements to move them relative to one another, and to actuators employing such mechanisms. GENERAL STATE OF THE ART

[0002] Active material elements, such as shape memory alloy (SMA) wires, are used in various devices, such as actuators and smart devices, to cause displacement of structural elements of the devices through activation of the active elements. This can be done, for example, by passing a current through SMA wire, causing it to heat up, resulting in the wire contracting and exerting force on the elements to which it is attached.

[0003] However, when an SMA wire is heated, typically all sections of the wire contract or attempt to contract, including those sections directly attached to a structural member. Such repeated deformation or contraction in the section(s) of the wire attached to members can lead to device failure. One failure mode is fatigue failure due to uneven stress distribution when contraction occurs along a curve. Another failure mode is slippage of the wire at the attachment point, resulting in pullout. EP 1 520 984 A2 discloses a bundle of shape memory alloy wires and actuators. JP H06-330 487 A discloses an apparatus for anchoring a wire in a socket pocket. US 9 145 903 B2 describes a shape memory alloy hydraulic accumulator and actuator plates.US 2013 / 0 199 172 A1 describes elements made of active material with reinforced structural connections. Furthermore, JP H09 31 877 A discloses a metal fitting for a wire rope end. SUMMARY OF THE INVENTION

[0004] The present invention provides an anchor for a heat-responsive ligature that deforms when heated. The ligature is configured to include an engaging segment for engaging the anchor, which is a segment of the ligature with two clamping portions and a curved portion between the clamping portions. The anchor includes a body and a configurable clamping component. The anchor body is made, at least in part, from a thermally and / or electrically conductive material and has an engaging surface for engaging the curved portion of the engaging segment of the ligature. The clamping component is configured to allow the clamping portions of the engaging segment of the ligature to pass between the body and the clamping component when the curved portion of the engaging segment engages the engaging surface of the anchor body.Then, portions of the clamping component near the clamping portions of the engaging segment of the ligature can be moved toward the anchor body to reconfigure the clamping component such that the portions of the clamping component press the clamping portions of the engaging segment of the ligature against the anchor body and maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body.

[0005] The anchor body may be attachable to a first element of a device having a second element connected to the first element by a heat-responsive ligature. When the anchor body is attached to the first element of the device, the engaging segment of the ligature is in thermal and / or electrical communication with the anchor body, the curved portion of the engaging segment of the ligature engaging the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal and / or electrical communication with the anchor body. Then, when the ligature is heated, the ligature deforms and exerts a force on the anchor body toward the second element, causing the two elements to move toward each other.When the ligature is heated, the temperature rise in the engaging segment of the ligature is sufficiently limited by heat transfer to the anchor body and / or by reducing the current flowing through the engaging segment of the ligature as current flows through the anchor body to prevent or substantially reduce deformation of the engaging segment relative to segments of the ligature not in contact with the anchor.

[0006] In some embodiments, the curved portion of the engaging segment of the ligature may include two curved subsections and a flattened subsection between these two curved subsections. In such embodiments, the engaging surface of the anchor body includes a flat portion for engaging a portion of the flattened subsection of the engaging segment of the ligature.

[0007] In some preferred embodiments, the engaging surface of the anchor body and the curved portion of the engaging segment are continuously curved such that when the clamping portions of the engaging segment of the ligature are clamped against the anchor body, the ligature engages the curved surface of the anchor body along the full length of the engaging segment of the ligature.

[0008] The curved portion of the engaging segment of the ligature may have a 180 degree curvature such that when the clamping portions of the ligature are pressed against opposite sides of the anchor body, the clamping portions of the ligature are substantially parallel to each other.

[0009] The ligature is preferably electrically conductive, and a portion of the anchor body including the engagement surface is preferably electrically conductive, such that when the engagement segment of the ligature is engaged with the anchor body, the electrically conductive portion of the anchor body electrically connects the clamping portions of the engagement segment of the ligature. The electrically conductive portion of the anchor body preferably has an electrical resistance less than the electrical resistance of the engagement segment of the ligature, such that when a current I flows through segments of the ligature not in contact with the anchor, the amount of current flowing through the engagement segment of the ligature is less than one-half of I, or in particular substantially less than I.The anchor body may be attachable to a first element of a device having a second element attached to the first element by a heat-responsive ligature. In this device, the engaging segment of the ligature may be electrically engaged with the anchor body, wherein the curved portion of the engaging segment of the ligature engages the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after the clamping component has been reconfigured to maintain the engaging segment of the ligature in electrical communication with the anchor body. Then, when sufficient current flows through the ligature to cause the ligature to become sufficiently heated to cause some portions of the ligature to deform, the ligature exerts a force on the anchor body toward the second element, causing the elements to move toward each other.Deformation of the engaging segment of the ligature is essentially prevented by limiting the fraction of the current flowing through the engaging segment of the ligature by that of the current flowing through the armature body. The armature body is preferably made of a metal, such as brass. The armature may further include an element for electrically connecting the electrically conductive portion of the armature body to a power source. The element for electrically connecting the electrically conductive portion of the armature body to a power source may be a solder pad, and the power source may then be connected to the element by a corresponding solder pad on a circuit board.

[0010] The ligature is preferably a shape-memory alloy wire. Alternatively, the ligature can be a shape-memory alloy band.

[0011] The anchor body and the clamping component may be integrally formed from a single piece of metal. The anchor body may be a U-shaped section of the piece of metal, and the clamping component may consist of two arms, each arm being bendably connected to one end of the anchor body and extending along a portion of one side of the anchor body near and spaced from the anchor body. In such embodiments, the anchor includes two openings sized to receive the ligature, each of the openings being located near the anchor body and one of the arms.In such embodiments, the clamping component is reconfigurable by applying a force to each of the two arms toward the anchor body such that the force causes the arms to flex such that when the curved portion of the engaging segment engages the engaging surface of the anchor body and the clamping portions of the engaging segment of the ligature are between the anchor body and the arms, each arm is then pressed against one of the clamping portions of the engaging segment of the ligature, maintaining the engaging segment of the ligature in thermal and electrical communication with the anchor body.

[0012] The clamping component may be a metal ring having an inner diameter greater than the sum of (a) twice the thickness of the ligature and (b) the thickness of the portion of the anchor body proximate the clamping portions of the engaging segment of the ligature.

[0013] The anchor may include positioning elements configured to receive the engaging segment of the ligature. The positioning elements may include two grooves as positioning features, each groove configured to receive one of the clamping portions of the engaging segment of the ligature.

[0014] The invention also provides an actuator comprising first and second members, a heat-responsive ligature connected to the second member, and an embodiment of an anchor, as described above, attached to the first member. The engaging segment of the ligature is thermally and / or electrically connected to the anchor body, wherein the curved portion of the engaging segment of the ligature engages the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal and / or electrical communication with the anchor body. When the ligature is heated, the ligature deforms and exerts a force on the anchor body toward the second member, causing the two members to move toward each other.

[0015] The actuator also preferably includes a biasing mechanism configured to move the first and second members back to their starting positions after heating has been discontinued and the ligature ceases to be deformed.

[0016] The invention also provides an anchoring device comprising a plurality of anchors, each anchor being an anchor as described above. The anchoring device is configured such that, for each of the anchors, the engaging surface of the anchor is engageable with an engaging segment of a heat-responsive ligature, such that the clamping portions of the ligature are pressed against the anchor body by the clamping component of the anchor after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1a and Fig. 1b are side views of a first embodiment of an anchor. Fig. 1b is labeled to indicate different sections of the anchor. Fig. 2a and Fig. 2b are side views of a section of an SMA wire having an engagement segment. Fig. 2b is labeled to indicate different sections of the anchor. Fig. 3 is a side view of the first embodiment of an anchor engaged with the engaging segment of an SMA wire before the clamping component of the anchor has been reconfigured to maintain the engaging segment of the SMA wire in thermal and electrical communication with the anchor body. Fig. 4 is a side view of the first embodiment of an armature fully engaged with the engaging segment of an SMA wire after the clamping component of the armature has been reconfigured to maintain the engaging segment of the wire in thermal and electrical communication with the armature body. Fig. 5 and Fig. 6 are perspective views of the first embodiment of an armature fully engaged with the engaging segment of an SMA wire after the clamping component of the armature has been reconfigured to maintain the engaging segment of the wire in thermal and electrical communication with the armature body. Fig. 7 is a perspective view of an anchoring device for anchoring multiple strands of a heat-responsive ligature using a second embodiment of an anchor. Fig. Figure 8 is a side view of the device of Fig. 7 with three engaging segments of an SMA wire engaged with three of the anchors in the device. Fig. 9 is a cross-sectional view through lines 9-9 of Fig. 8. Fig. 10 is a perspective view of a third embodiment of an anchor. Fig. 11a and Fig. 11b are side views of a simple actuator employing the third embodiment of an armature, with an SMA wire in Fig. 11b has deformed to cause two elements of the actuator to move towards each other. Fig. 12 is a perspective view of an actuator showing twelve armatures according to the first embodiment of an armature attached to the upper member of the actuator. DETAILED DESCRIPTION OF THE INVENTION

[0017] A first embodiment of an armature 100 is shown in Fig. 1 and also in Fig. 3 to 6 shown. Fig. Figure 1a is a side view of the generally "W"-shaped armature, which is preferably made from a single piece of metal, such as brass. The armature 100 has two main components, which are shown in Fig. 1b, namely an anchor body 101 and a clamping component. In this embodiment, the clamping component consists of two separate arms 102a and 102b, each arm connected to one end of the anchor body 101. The material used to form the anchor is selected such that the arms 102a, 102b are flexibly attached to the body 101 so that a force can be applied to the outer sides of the arms 102a, 102b toward the body, causing the arms 102a, 102b to move toward the body 101 and remain in the bent or deformed state after the force is removed. The anchor body 101 has an engagement surface 103 configured for engagement with an engagement segment of a heat-responsive ligature, such as an SMA wire or band.

[0018] A shape memory alloy (SMA, also known as smart metal, memory metal, memory alloy, muscle wire, and smart alloy) is an alloy that "remembers" its original shape and, when deformed, returns to its pre-deformation shape when heated. The two main types of shape memory alloys are copper-aluminum-nickel and nickel-titanium (NiTi) alloys, but SMAs can also be created by alloying zinc, copper, gold, and iron. Upon heating, an SMA wire is in the martensite state at a first threshold temperature (A s ) begin to deform, and at the time when it reaches a second (higher) temperature (A f) is reached, change to the austenite state. (The austenite state may be referred to herein as a deformed state.) In the present context, the wire is contracted in the austenite state, so that it is shorter in the austenite state than when it is in the martensite state. The wire will remain in the austenite state until the wire is below a certain threshold temperature (M s ), which is less than A f , has cooled down, when it will begin to return to the martensite state, and will be at the time when the wire reaches another certain temperature (M f ), which is generally less than A s , reaches, return to the martensite state.

[0019] The armature body 101 is preferably made of a thermally and electrically conductive material, such as brass or another metal. However, it is sufficient that a portion of the armature body 101, including a portion of the engagement surface 103, is thermally or electrically conductive. The conductive portion of the armature body comprises a subsection of the body on either side of the engagement surface 103, which are thermally and electrically connected to each other.

[0020] For example, although not preferable, the armature body may be formed of a non-conductive material with an electrically conductive coating. As another non-preferable example, the armature body may contain conductive material only in a central portion, such as the portion roughly described as the Fig. 1b, which will electrically connect (or "short-circuit") the clamping portions 203a, 203b of the wire 200, while the remainder of the armature 100 may be made of non-conductive material(s).

[0021] It is preferable that the entire armature 100 be formed from a single piece of metal, such as brass, so that the armature body 101 and the clamping component are integrally formed from a single piece of metal that is both thermally and electrically conductive. The armature may be manufactured by machining, stamping, cutting, forming, molding, or any combination of these approaches.

[0022] The anchor body 101 of the first embodiment of an anchor may be referred to as generally “U”-shaped, however, in such embodiments it is generally preferred that the two sides of the “U” be adjacent, as in Fig. 1a, have been pressed together, so that the entire anchor body 101 or at least a portion of the anchor body, such as the subsection 104 in Fig. 1b, is thermally and preferably also electrically connected. Of course, in some embodiments, the armature body 101 may be formed as a single unit, rather than from two sides of a U-shaped piece that have been pressed together.

[0023] Fig. Figure 2a shows a side view of a portion of a heat-responsive ligature, which is an SMA wire 200 having a curved portion 202 that is a gentle 180-degree bend. A portion of the wire 200 is designated as the engaging segment 201, as shown in Fig. 2b. The engagement segment 201 has the curved section 202 and two clamping sections 203a, 203b that are parallel to each other.

[0024] The anchor 100 has two openings sized and shaped to receive the ligature, which in the illustrated embodiment are slots 301, which are best Fig. 6. While in the case of SMA wire the openings could be circular, with a diameter slightly larger than the diameter of the wire, it has been shown that it is preferable to use slots because circular holes are more prone to deformation when the anchor is formed from a flat strip of material which is subsequently inserted into the Fig. 1a. The slots can be cut or punched out of the material strip before it is bent into the W shape shown.

[0025] To attach the wire 200 to the anchor 100, the wire 200 is placed as shown in Fig. 3, wherein the engaging segment 201 of the wire 200 engages (i.e., is in contact with) the engaging surface 103 of the anchor body 101. The placement of the wire 200 may be accomplished by braiding it through a slot 301, forming it over the anchor body 101, and passing it through the opposite slot 301. Alternatively, the wire 200 may be loosely braided through the anchor 100, and an external tool may be used to form the curved portion 202, at which point the anchor may be slid into position. In the embodiment of Fig. 1 and 3 to 6, the surface 103 of the anchor body 101 has a curved section with a curvature that matches the curvature of the curved section 202 of the wire 200, and two straight parallel sections, so that the wire 200 and the anchor body, as in Fig. 3, so that the engaging segment 201 of the wire 200 is in contact with the surface of the armature body 101 along its full length, the wire 200 passing through the two slots 301 in the armature 100.

[0026] The use of a curved surface allows the anchor to accommodate a ligature with a relatively small bend radius, allowing a high-density actuator design, for example with many strands of SMA wire (see e.g. Fig. 12), is possible.

[0027] It should be noted that, while preferable, it is not essential that all portions of the engaging segment of the wire be in direct engagement with the anchor body when the anchor is in use in a device. For example, if an upper portion of the engaging surface of the anchor body is flat, as in the Fig. 7, the wire does not touch any part of the flat portion of the armature body. However, when used in a device such as an actuator, it is essential that the clamping portions of the wire are firmly clamped to the armature body so that these clamping portions are electrically and / or thermally connected to each other via the armature body, and so that the wire can exert a force on the armature, which in turn is exerted on an element of the device to which the armature is attached.

[0028] Once the wire 200, as in Fig. 3, is engaged with the armature 100, a force (such as that shown as “F” in Fig. 3) is exerted on the outer portion of the two arms 102a, 102b towards the armature body 101, which bends the arms 102a, 102b relative to the armature body 101 to cause the arms 102a, 102b to be brought into contact with the clamping portions 203a, 203b of the wire 200 and to press the clamping portions 203a, 203b of the wire 200 against the sides of the armature body 101, thereby holding the engaging segment 201 of the wire 200 in thermal and electrical communication with the armature body 101, as shown in Fig. 4 to 6. If the force is applied only to a limited vertical extent of the arms, which is generally most convenient, it may result in indentations 301a, 301b in the outer portions of the arms 102a, 102b and corresponding bulges in the inner portions of the arms 102a, 102b that press against the clamping portions 203a, 203b of the wire 200. If the clamping component is made of a relatively soft material, such as brass, the application of a force may cause the brass to flow around the wire to some extent where the material forming the clamping component is softer than the SMA wire.

[0029] In addition to pressing the wire into thermal conduction with the armature body 101, applying such a squeezing force helps to ensure that any surface oxide on the wire is disrupted to enable a good electrical connection between the wire and the armature body 101.

[0030] In preferred embodiments, the material used to form the armature body 101 is chosen to have less electrical resistance than the wire, so that if a current I flows through the portions of the wire 200 outside the engaging segment 201 that are not in contact with the armature, most of the current then flows through the armature body 101, so that the current flowing through the engaging segment 201 of the wire 200 is substantially reduced. This is important because SMA wire is often activated by passing a current through it, causing Joule heating, which in turn activates the wire 200 to transform from martensite to austenite, as discussed above (thereby deforming by contraction and shortening).Such contraction of the wire 200 is generally useful in an actuator, for example, to cause a force to be exerted on the armature 100 (and therefore on any element to which the armature is attached) relative to another element (not shown in FIG. Fig. 3 to 6) connected to the wire 200 remote from the armature 100, which may be designed to cause the armature and the element to which it is connected, and a second element to which the wire 200 is connected, to move towards each other.

[0031] While the contraction in the segments of the wire 200 between the anchor and the other element is therefore useful and desirable, a contraction in the engaging segment 201 of the wire 200 is not desirable. Even if the engaging segment 201 of the wire 200 is fixed, such as by the Fig. 4, it is desirable to prevent the wire in the engagement segment 201 from reaching the threshold temperature A s reached, which would cause it to begin to contract, because such forces in the engaging segment 201, if repeated many times, can lead to fatigue and failure of the connection to the armature, for example, due to the wire breaking. The preferred design avoids this by effectively "short-circuiting" the engaging segment 201 of the wire 200, so that the current flowing through the engaging segment 201 of the wire 200 is significantly less than the current flowing through the rest of the wire 200, and so a current that induces heating of the rest of the wire sufficient to cause contraction can be employed and limited, so that it is insufficient to cause the engaging segment 201 of the wire 200 to move to the threshold A sheated, which consequently prevents or substantially reduces any thermally activated forces in the engagement segment 201 of the wire 200.

[0032] It should be noted that it is not essential that the electrical resistance of the armature body 101 be lower than the electrical resistance of the wire 200. For example, if the resistance of the armature body 101 is approximately equal to the resistance of the wire 200, then the current flowing through the engaging segment 201 of the wire 200 is reduced to approximately half the current flowing through the rest of the wire. If the resistance of the armature body 101 is approximately twice the resistance of the wire 200, then the current flowing through the engaging segment 201 of the wire 200 is reduced by a suitable choice of the current level to approximately two-thirds of the current flowing through the rest of the wire, which may still be adequate to prevent Joule heating of the engaging segment 201 of the wire 200 sufficient to reach the threshold temperature A s to reach the point where it would begin to deform

[0033] In some embodiments, for example, when the activation of the wire is accomplished by convective application of heat, the armature body, by being thermally conductive (and not necessarily electrically conductive), may prevent thermal activation of the engaging segment 201 of the wire 200 by having a combined thermal mass that absorbs enough of the heat applied to the engaging segment 201 of the wire 200 to maintain the temperature of the engaging segment 201 of the wire 200 below the threshold A s while the rest of the wire passes over the threshold A s Such activation is typically carried out for short periods of time insufficient for the thermally engaged armature body 101 and the engaging segment 201 of the wire 200 to reach the threshold temperature A s to reach.

[0034] Fig. 7 to 9 depict a device 700 including a plurality of anchors, each anchor 701 being a second embodiment of the invention. Each anchor has a generally "U"-shaped engagement surface with a flat upper surface. Vertical grooves 702 with a curved upper portion on each side and a relatively straight vertical lower portion define the anchor body and its outer engagement surface, which, as shown in Fig. 8 and Fig. 9, engages the engagement segment of the wire 200. The width of the grooves 702 is slightly larger than the diameter of the wire 200 and is used to position the engagement segment 201 relative to the armature 701. Once the wire 200 is engaged with the engagement surface of the armature 701, a force can be applied to the opposite sides of the armature toward the wire (e.g., in the plane of the Fig. 8 on the visible side and left and right to the wire 200 in Fig. 9) so that the clamping component of the anchor 701 presses against the wire on opposite sides and clamps the wire, holding it in engagement with the anchor. Where the forces are exerted over a limited vertical section of the anchor, they can lead to depressions 901a, 901b, as in Fig. 9. The material used to form the armature is chosen so that the two sections of the clamping components can bend towards the wire under such a force and remain in the bent / clamping position after the force is removed. It should be noted that the fact that a second embodiment of the armature 701 shown in the figures has an upper section having a curved outer surface to the left in Fig. 9 and a flat outer surface on the right in Fig. 9, has no relevance to the invention and is simply related to the process by which the device 700 and the anchors 701 were formed.

[0035] An integral power cable connection 703 is provided so that a power cable 704 can be connected to the device 700. This connection provides the electrical connection necessary to supply power to or remove power from the engaging segments of the wire 200. The connection 703, in this embodiment, is a two-tab wire clamp connection. Other connection methods, such as soldering or a screw connection, may alternatively be used.

[0036] Fig. 10 depicts a third embodiment of an armature 1000. The armature 100 is formed from a single piece of metal. The central portion 1001 is the armature body, and the clamping component consists of two portions 1003a, 1003b extending from the armature body 1001. The armature body 1001 has a gently curved engagement surface 1002 for engaging the curved portion 202 of the wire 200, and each of the two portions 1003a, 1003b of the clamping component has a hole or opening 1004 adjacent to the armature body 1001 and extending through the portion 1003a, 1003b of the clamping component. The opening 1004 is sized and shaped to allow the wire 200 to pass through the opening 1004 (as in Fig. 11a). Each section 1003a, 1003b of the clamping component also has a depression 1005, which facilitates the application of a force by a hard depression tool to each section toward the armature body 1001. The application of such forces causes a subsection of each section 1003a, 1003b of the clamping component to press against a portion of the wire passing through the hole 1004 in that section to press the wire against the armature body 1001 (with a portion of the inner surface of the hole 1004 immediately adjacent the armature body 1001). The use of a deformable, pliable material, such as brass, means that the deformed configuration is maintained and the engaging segment of the wire 200 is held in thermal and / or electrical communication with the armature body 1001. The underside of the Anchor 1000 is a flat surface to facilitate attachment to a structural element by soldering.When soldered to a pad of a printed circuit board (PCB), current can be applied to or drawn from the armature 1000. Alternatively, the armature can rest on the element and use the wire 200 and the mechanical biasing force to maintain its position relative to the element.

[0037] Fig. 11a and Fig. 11b show an actuator 1100 which is in Fig. 11a is not activated and in Fig. 11b is activated. The actuator 1100 has two elements 1101a, 1101b that are movable toward each other. The elements 1101a, 1101b are connected by an SMA wire 200, which connects to the upper element 1101a via an armature 1000 and connects to the lower element 1101b via two armatures 1000. The actuator 1100 also has a biasing mechanism, such as a spring or multiple springs, that biases the two elements away from each other, exerting a stretching force on the SMA wire 200.

[0038] When a current flows through the wire 200 in Fig. 11a, the wire 200 heats up until it reaches the threshold temperature A s at which point the wire contracts and pulls the two elements 1101a, 1101b closer together, as shown in Fig. 11b. The short-circuiting of the engaging segment of the wire at the point where it engages the armatures is essentially prevented by maintaining the temperature of the engaging segments of the wire below the threshold temperature A s that any deformation forces are exerted within these engaging segments of the wire.

[0039] After heating is interrupted and if the ambient temperature around the wire is lower than M f the pre-tension force will return the wire to its original state when the temperature of the wire at M s past on M f or less.

[0040] Fig. Figure 12 depicts a more complex actuator 1200 with an upper element 1201 and a lower element 1202 connected by an SMA wire 200. The wire 200 is connected by twelve W-shaped armatures 100, similar to the one shown in Fig. 3 through 6. The connection of wire 200 to lower member 1202 is not shown, but is made by a combination of anchors, which may include multiple embodiments of anchors used together, such as items 100 and 700. Wire 200 may be a single serpentine wire. Wire 200, anchors, and power cables 1203 form an electrical circuit. Passing sufficient current through the electrical circuit causes wire 200 to contract, causing members 1201, 1202 to move toward each other.

[0041] It is generally preferable that the engaging segment of the ligature has a (preferably gentle) curvature of 180 degrees (as in Fig. 2a) so that the clamping sections of the engagement segment of the ligature are substantially parallel, for example, to accommodate actuator designs such as those shown in Fig. 12. However, this is not essential, and the bend may be less than 180 degrees in some designs. However, the bend must be greater than zero degrees and normally at least 90 degrees, so that the ligature changes direction where it is connected to an anchor, so that the deformation of the wire, when activated, causes the curved section of the wire to exert a downward force (for example, in the direction shown in Fig. 4) on the engagement surface of the anchor body. The change in the direction of the wire in the engagement segment also helps to further reduce the likelihood of the wire being pulled out or slipping.

[0042] SMA tape can be used instead of SMA wire as the ligature. Such a tape is essentially flat, with a width significantly greater than its thickness. The curved portion of the ligature in such embodiments bends along an axis parallel to the width of the tape.

[0043] In an actuator, the ligature may be surrounded by gas (e.g., air) or liquid, or may be in a vacuum. Suspension in liquid, for example, may be used to reduce recovery time and assist heat dissipation after heating of the ligature is interrupted. When suspended in liquid, the liquid may be the working fluid of a hydraulic circuit. When suspended in liquid, the armatures may be placed on either side of the fluid boundary. A fluid boundary may be created by inserting a compliant sealing material between two plates around the wires. A fluid boundary may be created by creating a molded sealing surface using a potting compound, such as epoxy, around the armatures and the mounting plate. Objects in contact with the fluid boundary may be electrically insulated from the SMA electrical circuit.

[0044] It should be understood that the above-described embodiments of the present invention, especially any "preferred" embodiments, are merely exemplary implementations, presented solely for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention, as will be apparent to those skilled in the art. That is, those skilled in the art will recognize and understand that such modifications and variations are or will be possible for utilizing and practicing the teachings of the invention described herein.

[0045] Where in this document a list of one or more items is preceded by the phrase "such as" or "including", followed by the abbreviation "etc.", or preceded or followed by the phrase "for example" or "e.g.," this is done to expressly convey and emphasize that the list is not exhaustive, regardless of the length of the list. The absence of such a phrase or any other similar phrase is in no way intended to suggest that the list is exhaustive. Unless expressly stated or clearly meant to the contrary, such lists are to be read to include all comparable or equivalent variations of the listed item(s) and alternatives to the item(s) in the list that would be understood by a person skilled in the art to be suitable for the purpose for which the one or more items are listed.

[0046] The words "comprises" and "comprising" when used in this specification and the claims are used to specify the presence of stated features, elements, integers, steps, or components and do not preclude or imply the necessity of the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof.

[0047] The scope of the following claims is not limited by the embodiments set forth in the description. The claims should be given the broadest purposive interpretation consistent with the description and the figures as a whole.

Claims

[1] Anchor for a heat-responsive ligature that deforms when heated, the ligature being configured to have an engagement segment for engaging the anchor, the engagement segment being a segment of the ligature having two clamping portions and a curved portion therebetween, wherein the anchor comprises a body and a configurable clamping component, wherein the anchor body comprises a thermally conductive material or an electrically conductive material and has an engagement surface for engaging the curved portion of the engagement segment of the ligature, wherein the clamping component is configured to allow the clamping portions of the engaging segment of the ligature to pass between the body and the clamping component when the curved portion of the engaging segment engages the engaging surface of the anchor body, such that portions of the clamping component proximate the clamping portions of the engaging segment of the ligature can be moved toward the anchor body to reconfigure the clamping component such that the portions of the clamping component press the clamping portions of the engaging segment of the ligature against the anchor body and maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body. [2] The anchor of claim 1, wherein the anchor body is attachable to a first element of a device having a second element connected to the first element by the heat-responsive ligature, such that when the anchor body is attached to the first element of the device, the engaging segment of the ligature is in thermal or electrical communication with the anchor body, the curved portion of the engaging segment of the ligature engaging the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body wherein the ligature deforms when the ligature is heated and exerts a force on the anchor body towards the second element, causing the two elements to move towards each other, and wherein, when the ligature is heated, the temperature rise in the engaging segment of the ligature is sufficiently limited by heat transfer to the anchor body or by reducing the current flowing through the engaging segment of the ligature because current flows through the anchor body that deformation of the engaging segment of the ligature is prevented or substantially reduced relative to segments of the ligature not in contact with the anchor. [3] The anchor of claim 1, wherein the curved portion of the engaging segment of the ligature comprises two curved sub-portions and a flattened sub-portion therebetween, and the engaging surface of the anchor body comprises a flat portion for engaging a portion of the flattened sub-portion of the engaging segment of the ligature. [4] The anchor of claim 1, wherein the engaging surface of the anchor body and the curved portion of the engaging segment are continuously curved such that when the clamping portions of the engaging segment of the ligature are clamped against the anchor body, the ligature engages the curved surface of the anchor body along the full length of the engaging segment of the ligature. [5] The anchor of claim 1, wherein the ligature is electrically conductive and a portion of the anchor body having the engagement surface is electrically conductive such that when the engagement segment of the ligature is engaged with the anchor body, the electrically conductive portion of the anchor body electrically connects the clamping portions of the engagement segment of the ligature. [6] Anchor according to claim 5, wherein the electrically conductive portion of the anchor body has an electrical resistance that is less than the electrical resistance of the engaging segment of the ligature, such that when a current I flows through segments of the ligature that are not in contact with the anchor, the amount of current flowing through the engaging segment of the ligature is less than one-half of I. [7] An anchor according to claim 5, wherein the anchor body is attachable to a first element of a device having a second element secured to the first element by the ligature, such that when the anchor body is secured to the first element of the device, the engaging segment of the ligature is electrically connected to the anchor body, the curved portion of the engaging segment of the ligature engaging the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after it has been reconfigured to maintain the engaging segment of the ligature in electrical connection with the anchor body, wherein, when sufficient current flows through the ligature to cause the ligature to be heated sufficiently to cause some portions of the ligature to deform, the ligature exerts a force on the anchor body towards the second element, causing the elements to move towards each other, and wherein deformation of the engaging segment of the ligature is substantially prevented by limiting the fraction of the current flowing through the engaging segment of the ligature by the current flowing through the anchor body. [8] Anchor according to claim 5, wherein the anchor body is made of metal; and / or wherein the armature further comprises an element for electrically connecting the electrically conductive portion of the armature body to a power source. [9] An armature according to claim 8, wherein the element for electrically connecting the electrically conductive portion of the armature body to a power source is a solder pad and the power source is connectable to the element by a corresponding solder pad on a printed circuit board. [10] Anchor according to claim 1, wherein the ligature is a shape memory alloy wire; or where the ligature is a band made of shape memory alloy. [11] Anchor according to claim 1, wherein the anchor body and the clamping component are integrally formed from a single piece of metal. [12] The anchor of claim 11, wherein the anchor body includes a U-shaped portion of the piece of metal and the clamping component includes two arms, each arm being flexibly connected to an end of the anchor body and extending along a portion of a side of the anchor body proximate to and spaced from the anchor body, and wherein the anchor includes two openings sized and shaped to receive the ligature, each of the openings being proximate to the anchor body and one of the arms. [13] The anchor of claim 1, wherein the clamping component is a metal ring having an inner diameter greater than the sum of (a) twice the thickness of the ligature and (b) the thickness of the portion of the anchor body proximate the clamping portions of the engaging segment of the ligature. [14] The anchor of claim 1, wherein the anchor includes positioning elements configured to receive the engaging segment of the ligature. [15] The anchor of claim 14, wherein the positioning elements comprise two grooves, each groove configured to receive one of the clamping portions of the engaging segment of the ligature. [16] An actuator comprising: first and second members, a heat-responsive ligature connected to the second member, and the anchor of claim 1 attached to the first member, wherein the engaging segment of the ligature is in thermal or electrical communication with the anchor body, wherein the curved portion of the engaging segment of the ligature engages the engaging surface of the anchor body, and the clamping portions of the ligature are pressed against the anchor body by the clamping component after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body, wherein when the ligature is sufficiently heated, the ligature deforms and exerts a force on the anchor body toward the second member, causing the two members to move toward each other. [17] The actuator of claim 16, wherein the actuator further comprises a biasing mechanism configured to move the first and second members back to their starting positions after heating has been discontinued. [18] An anchoring device comprising a plurality of anchors, each anchor being an anchor according to claim 1, wherein the anchoring device is configured such that, for each of the anchors, the engaging surface of the anchor is engageable with an engaging segment of a heat-responsive ligature such that the clamping portions of the ligature are pressed against the anchor body by the clamping component of the anchor after the clamping component has been reconfigured to maintain the engaging segment of the ligature in thermal or electrical communication with the anchor body.

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