WO2008134699A1

WO2008134699A1 - Developments in smart memory alloy retention

Info

Publication number: WO2008134699A1
Application number: PCT/US2008/061965
Authority: WO
Inventors: Paul Kudrna; Lee David Blattmann; Dickory Rudduck
Original assignee: Telezygology, Inc.
Priority date: 2007-04-30
Filing date: 2008-04-30
Publication date: 2008-11-06

Abstract

This invention relates to an integrated SMA retention system for a fastener 2 comprising an actuating means 4 including a material adapted to contract when activated 6, a biasing means 34; a core 8 having a catch head 10 for said material adapted to contract when activated 6 and an engagement means 26, The material adapted to contract when activated 6 is shaped into a 'Z', 'L', or 'C' shape around the catch head 10 within the core 8 thereby eliminating the need for crimping of the material adapted to contract when activated 6 to mechanically retain and electronically ground the material adapted to contract when activated 6 within that fastener or device

Description

Developments in Smart Memory Alloy Retention FIELD OF THE INVENTION

This invention is concerned with developments in fasteners. More specifically this invention relates to an SMA retention system within a fastener or device that has solved the problem of needing a secondary component to mechanically retain and electronically ground an SMA wire within that fastener or device. It also relates to a support that aids in uniform heating and cooling of the SMA wire and post tensioning of the wire.

BACKGROUND OF THE INVENTION Fasteners, such as the beam type fastener, were disclosed in International Patent

Application Nos. PCT/AU03/000759 and PCT/AU06/001874. The contents of those International Applications are incorporated herein by reference. It will be appreciated by one skilled in the art that a substantial part of the disclosure in the International Applications will also be applicable to the invention disclosed below. The beam type fasteners discussed in the above applications required a secondary component to mechanically retain and electrically ground an SMA wire or strip within the fasteners. This secondary component retains the SMA wire or strip onto the fastener via a crimp, screw, solder, clasp, adhesive, or other type of fastener. While this secondary component is successful in achieving its goal of mechanically retaining and electrically grounding an SMA wire it is commonly expensive and can over time be a less reliable means of retention and grounding. Attaching the secondary component to the SMA wire or strip is a two step process. First, the SMA wire needs to be cut to a desired length while in its hot state. Second, the crimp needs to be attached to that wire. The tolerance for both processes quickly stacks up and it is more desirable to have only one action to achieve the desired results. This invention has successfully removed the secondary component while still maintaining the capability to mechanically retain and electrically ground an SMA wire. The beam type fastener also can suffer from problems due to loss of heat while attempting to achieve a desired temperature within the SMA wire or strip, prolonged cooling of the SMA wire due to the added energy needed to heat to that desired temperature and uneven contraction of the SMA wire. The SMA wire in a fastener is typically wrapped around a support. This convention support simply supports the SMA wire in its place. However as the SMA wire is heated and then cooled around the support certain features of the wire may be lost due to the loss of heat while in contact with the surface support. As such, there is a need for a support that does not cause the wire to lose as much heat while trying to achieve a desired temperature and for a support that aid in the problem of prolonged cooling and uneven contraction. This invention provides such a solution.

At times it may be desirable to adjust the position of the wire to tension the wire or to loosen the wire depending on the situation. Typical SMA wires are placed about a support at a desired length. This typical structure does not allow for the wire to be adjusted to different lengths. At times, it may be appropriate to tension the SMA wire to achieve a desired length or result. The above mentioned support can also assist in solving this problem.

SMA wires are also prone to experiencing overstress situations. When the wire is overstressed, it may snap and break rendering the fastener useless. As such, it is desirable to include an overstress prevention feature in fasteners so that the SMA wire doesn't break resulting in the need for a new fastener or a replaced wire. This invention includes features to prevent overstress situations.

SUMMARY OF THE INVENTION This invention relates to an integrated SMA retention system for a fastener comprising: an actuating means including a material adapted to contract when activated; a biasing and a core located between said actuating means and said biasing means, having a catch head for said material adapted to contract when activated and an engagement means.

The material adapted to contract when activated is preferably shape memory alloy wire or strips. Shape memory alloys are known and are usually made predominantly or wholly of titanium and nickel. They may also include other material, such as aluminium, zinc and copper. A shape memory alloy is capable of adopting one shape below a predetermined transition temperature and changing to a second shape once its temperature exceeds the transition temperature. Conversely, when the shape memory alloy cools below the transition temperature, it is capable of adopting the first shape again. In connection with the various aspects of the present invention, the shape memory alloy contracts when heated in situ. Shape memory alloy wire currently available, such as that sold under the trade mark Nitinol, is capable of contracting by about 3% when activated by heating. Activation of the material adapted to contract when activated is preferably achieved through electrical resistance heating, with a wire feed to the assembly. Activation of the shape memory alloy wire can be initiated from a central location, using the wiring system of, for example, a security system. It is also within the scope of this invention that the activation is initiated by remote means, such as a hand held tool operating through the use of any suitable form of energy, including microwave, electric magnetic, sonic, infra-red, radio frequency and so on.

The scope of the invention in its various aspects is not necessarily limited to the use of shape memory alloy. Other material may also be useful. Also, while activation may take place through heating, other means of activation may be suitable and are within the scope of this invention.

For purposes of this invention, the core will be discussed in terms of a beam type fastener however one skilled in the art will recognize that the core may take on any number of embodiments. This reference does not limit the type of fastener this invention may be useful on, it is simply for purposes of reference and explanation; any fastener utilizing SMA wire may benefit from this invention. This core of this invention comprises a clip that aids in retention and grounding but also supplies power throughout the core. This clip may be seen as a blade but other embodiments such as a spring clip may also be acceptable. Within this invention, the SMA wire or strips are shaped and fed through a catch head within the core. The SMA wires are formed into a "Z", "L", or "C" shape about the core. Tension from the clip aids in holding the SMA wire in place. One skilled in the art will recognize that the SMA wire in these shapes do not necessarily need the clip to stay in place; the SMA wire will not move in most circumstances while it is in place within the catch head. Because the SMA wire stays in place after it is fed through the catch head, there is no need for a secondary component to mechanically retain or electrically ground the SMA wire. This arrangement completely resolves the need for the secondary component. This catch head prevents the SMA wire from moving even when it is activated and there is a force pulling on the SMA wire.

Shaping the SMA wire or strips in this manner provides for a simpler, cheaper manufacturing process. Instead of the two step process of cutting the SMA wire and attaching the crimp, this invention simply utilizes on step of cutting and instantly shaping. This can be done with the aid of a tool designed in the desired "Z", "L", or "C" shape.

The combination of the clip with the catch head leads to a condition where the SMA wire will not activate in the area where power is grounded. This means that any formed shape that is integrated into the wire will retain its form and will allow the SMA wire to act as its own "retainer" without using additional secondary components.

One skilled in the art will recognize that this invention improves the accuracy of the wire since there is reduced tolerance. It also improves the holding strength of the SMA wire while also improving the pulling strength of the SMA wire.

When the actuating means is activated the SMA wire will contract moving the engagement means fastening or unfastening the fastener depending on the setting. The biasing means will then bias the action of the actuating means when to once again fasten or unfasten. Another embodiment of this invention relates to an integrated SMA support system comprising: an actuating means including a material adapted to contract when activated; a biasing means a core locating between said actuating means and said biasing means, said core having an engagement means; and a support for the material adapted to contract when activated wherein said support has a plurality of support peaks and a plurality of troughs; the support being adapted to slidably support the wire from one support peak to another support peak while bridging a trough therebetween; said support further including a cam post tensioning feature. For purposes of uniformity, this embodiment will also be discussed in terms of a beam type fastener but this should not be construed as limiting the types of fasteners it may be useful on.

In a fastener, there is concern about uniform heating of the SMA wire or strip. Other concerns for the SMA wire is prolonged cooling and smooth wire contraction. The SMA wire is typically wrapped around a conventional support and when the SMA wire is heated, some heat is lost due to the contact between the SMA wire and the surface of the conventional support. This is known as the heat sink effect. Because of this situation, it takes longer to heat the SMA wire to its desired point and me energy must be put into the SMA wire. This triggers another situation in that the added heat can cause prolonged cooling of that same SMA wire or can cause lack of uniformity in transition of the wire from a heated state to a cooled state.

While this invention was prompted by experience with contact of the wire with the surface of a conventional support that may be cylindrical in shape, one skilled in the art will recognize that the invention is not limited to this setting and other circumstances may find this invention appropriate. This invention is also not limited to fasteners but may be useful wherever uniform heating of an SMA wire is required and it is desired to avoid prolonged cooling.

The design of the current invention's support peaks and troughs may be varied according to application. Where the support is cylindrical, the support may resemble a cog. If the support is planar, it may resemble a line of scalloping. Because the SMA wire effectively spans a trough from one peak to another, the contact of the wire with the surface of support is reduced, thus reducing the heat sink effect and requiring less energy to achieve a desired result. When the heat is applied to the SMA wire on a support, the regions of the wire bridging the troughs respond first, contracting and drawing the SMA wire over the support. This motion pulls those regions of the wire which were in contact with the support, at the peaks, into the regions between the peaks, over the troughs, allowing them to heat rapidly. As a result, the SMA wire on a support of the invention will heat more uniformly, more quickly and will cool more quickly then an equivalent SMA wire on a conventional support.

This above mentioned embodiments may also include an overstress prevention mechanism. When overstressed, SMA wires may snap and break. There are a variety of overstress prevention methods. One may include a situation whereby the support can be pulled forward in an overstress situation thereby causing the SMA wire to contract and preventing a possible break. Another variation of this overstress protection mechanism is one where the support can collapse in an overstress situation allowing the SMA wire to contract without breaking. Another example may be a situation where an insert is placed under the SMA wire on the core. This insert comprises of a stiff yet slightly flexible material that can deflect downward towards the core when the SMA is overstressed thereby preventing breakage. Another solution to the overstress problem may include an extension to the actuating means. This extension is stifFer then the working portion of the actuation means. During normal operation of the SMA wire, the working portion of the actuating means will bend. During an overstress situation, the extension will be pulled in and straighten the working portion of the actuator thus allowing the SMA wire to contract and prevent damage to the wire.

The above mentioned embodiments may also be housed into a body. This housing provides support for the engagement means so that when engaged it is engaged tightly and has very little movement about the x, y, or z axis. This housing allows the fastener added security and can provide for many different mounting situations

One skilled in the art may recognize that the two embodiments discussed above may be joined together into a third embodiment having the option of overstress protection or housing.

Other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and the detailed description of a preferred embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a beam type fastener

FIG. 2 depicts a beam type fastener utilizing a support having peaks and plurality of troughs. FIG. 3 depicts a cross-sectional view of a fastener detailing the material adapted to contract when activated formed into a "Z" shape through the catch head.

FIG. 4 is another view of a fastener detailing the material adapted to contract when activated formed into a "Z" shape through the catch head.

FIG. 5 A depicts the support utilizing overstress protection. FIG. 5B is the flip side of FIG. 5 A detailing the location of the overstress protection.

FIG. 6 is a view of the insert as overstress protection.

FIG. 7 is a view of the extension to the actuating means as overstress protection.

FIG. 8 depicts a fastener within housing. FIG. 9 depicts a fastener within housing utilizing the support with peaks and troughs.

FIG. 10 depicts a view of an overstress protection mechanism utilizing a collapsible support.

FIG. 1OA is a detailed view of the collapsible portion of the support. FIGS. 1 IA and 1 IB depict the cam post tensioning feature of the support.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a preferred embodiment, this invention relates to an integrated SMA retention system for a fastener 2 comprising an actuating means 4 including a material adapted to contract when activated 6; a biasing means 34; a core 8 having a catch head 10 for said material adapted to contract when activated 6 and an engagement means 26.

The core 8 includes a spring clip 12. This spring clip 12 will ultimately provide support, power, and grounding for the material adapted to contract 6. The material adapted to contract when activated 6 is fed through a catch head 10 as seen in FIGS. 3 and 4. As seen in FIGS. 3 and 4, the material adapted to contract when activated 6 is formed into a "Z" shape. This shape prevents movement of the material adapted to contract when activated 6 within the core upon activation of said actuating means 4 or said biasing means 20. This also resolves the need for a secondary component. This embodiment may also include housing 22 as seen in FIGS. 8 and 9 over overstress protections as seen in FIGS. 5A-7 and 10. FIG. 5A details the movement of the support 28 when the SMA wire 6 is in an overstress situation. The support 28 is slidable along the core 8. FIG 10 details another variation of using the support 28 as a mode of overstress protection. Here, the support 28 has collapsible features 36. When the SMA wire 6 is overstressed, the support 28 will simply collapse allowing the SMA wire 6 to contract. FIG. 6 details the insert 30 as a mode of overstress protection. As the SMA wire 6 is overstressed, the insert 30 will deflect downward to prevent breakage. FIG. 7 details the extension 32 as overstress protection. As the SMA wire 6 becomes overstressed the extension 32 will flex allowing the SMA wire 6 to contract. Another preferred embodiment comprises an actuating means 4 including a material adapted to contract when activated 6; a biasing means 34; a core 8 having an engagement means 26, and a support 28 for the material adapted to contract when activated 6. This support 28 as seen in Figures has a plurality of support peaks 40 and troughs 42. The support 28 is adapted to sliably support the material adapted to contract when activated 6 from one support peak 40 to the other support peak while bridging a trough 42. This may also include a cam post tensioning feature 42 that adjust the wire tension as the wire bridges from one support peak 40 to another. This embodiment may also include housing 22 as seen in FIGS. 8 and 9 over overstress protections as seen in FIGS. 5A-7 and 10 and described above.

The invention may be described in terms of claims that can assist the skilled reader in understanding the various aspects and preferments of the invention. It will be appreciated by those skilled in the art that many modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the invention.

Industrial Applicability

As will be appreciated by those skilled in the various arts, this invention disclosed herein is not limited to the examples set our above and has wide application in many areas. This invention represents a significant advance in the art of SMA retention.

Claims

CLAIMSWhat is claimed is:

1. An integrated SMA retention system for a fastener comprising: an actuating means including a material adapted to contract when activated; a biasing and a core located between said actuating means and said biasing means, having a catch head for said material adapted to contract when activated and an engagement means.

2. The integrated SMA retention system as in Claim 1 wherein said core further comprises a clip.

3. The integrated SMA retention system as in Claim 2 wherein said clip is a retainer, has grounding capabilities, and supplies power.

4. The integrated SMA retention system as in Claim 1 wherein said material adapted to contract when activated is shaped through said catch head within said core.

5. The integrated SMA retention system as in Claim 4 wherein said material adapted to contract when activated is shaped into a "Z", "L", or "C" shape around said catch head within said core.

6. The integrated SMA retention system as in Claim 5 wherein said assumed "Z", "C", or "C" shape of said material adapted to contract when activated retains shape and grounds said material adapted to contract within said flexible against a pulling force.

7. The integrated SMA retention system as in Claim 6 wherein said actuating means is activated about said core when material adapted to contract is activated; said biasing means re-bias said material adapted to contract to a set position; the action of said actuation means and said biasing means is maintained by said material adapted to contract when activated is through said catch head.

8. The integrated SMA retention system as in Claim 1 further comprises overstress protection and/or housing.

9. An integrated SMA support system comprising: an actuating means including a material adapted to contract when activated; a biasing means a core locating between said actuating means and said biasing means, said core having an engagement means; and a support for the material adapted to contract when activated wherein said support has a plurality of support peaks and a plurality of troughs; the support being adapted to slidably support the wire from one support peak to another support peak while bridging a trough therebetween; said support further including a cam post tensioning feature.

10. The integrated SMA support system as in Claim 9 wherein said actuating means is activated about said core when material adapted to contract is activated; said biasing means re-bias said material adapted to contract to a set position; the action of said actuation means and said biasing means is maintained by said material adapted to contract about said support.

11. The integrated SMA support system of claim 9 further comprising overstress protection and/or housing.