Cross Reference to Related Application^ ^" )

[0001] The present application claims priority to United States Patent

Application Serial Number 12/332,004, filed December 10, 2008, the entire contents of which is hereby incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates generally to shape memory alloy apparatuses. In an embodiment, the disclosure relates to actuators and coupling apparatuses formed from a shape memory alloy.

BACKGROUND

[0003] A variety of apparatuses may be used for actuating objects or holding together objects that need to be later released. For example, an explosive bolt can be used to attach two or more objects and may later release the objects with an explosive force. An explosive bolt incorporates explosives that cause an explosion when initiated or triggered. The explosion breaks apart the explosive bolt to release the objects. The problem with explosive bolts is that they are dangerous to handle because of the explosives and the explosion may exert a large amount of shock load that may damage fragile machinery. In addition, shrapnel pieces or foreign object debris (FOD) resulting from the explosion can interfere with machinery or optics.

SUMMARY

[0004] In an embodiment, a separating apparatus is provided that comprises a pre-strained member formed from a shape memory alloy. This member is configured to separate upon application of heat and the separation is configured to actuate an object.

[0005] In another embodiment, an apparatus is provided that comprises a first object, a second object, and a separating apparatus that is configured to couple the first object to the second object. In this example, the separating apparatus is formed from a shape memory alloy and is configured to separate upon application of heat.

[0006] In yet another embodiment, a separating apparatus is provided that comprises a pre-strained member configured to couple a first object to a second object. The member is formed from a shape memory alloy and is configured to separate and release the first object from the second object upon application of heat.

[0007] In still yet another embodiment, a method is provided for actuating an object that is configured to be in contact with an actuator. The actuator has a pre-strained member formed from a shape memory alloy and is configured to be in contact with the actuator. In this method, heat is applied to the member and the application of heat is configured to cause the member to separate, where the separation is configured to actuate the object.

BRIEF DESCRIPTION OF DRAWINGS

[0008] The present disclosure is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:

[0009] Figures Ia, Ib, Ic, and Id illustrate the use of heat to separate a separating apparatus formed from a shape memory alloy, in accordance with an embodiment of the invention;

[0010] Figure 2 is a diagram illustrating the various solid phases of a shape memory alloy at different temperatures and stress states;

[0011] Figure 3 illustrates a plot of the mechanical behavior of a shape memory alloy with the application of heat, in accordance with an embodiment of the invention;

[0012] Figure 4 illustrates an example of a separating apparatus, in accordance with an embodiment of the invention;

[0013] Figures 5a and 5b illustrate another embodiment of a separating apparatus used in a telescope assembly;

[0014] Figure 6 illustrates yet another embodiment of a separating apparatus used in a multistage rocket; [0015] Figures 7a and 7b illustrate the use of a separating apparatus to actuate an object upon release, in accordance with an embodiment of the invention;

[0016] Figure 8 illustrates an exothermic reactive foil according to an embodiment of the invention that may be used to generate heat; and [0017] Figure 9 illustrates resistance wires according to another embodiment of the invention that may also be used to generate heat.

DETAILED DESCRIPTION [0018] The following description and the drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. Embodiments of the invention set forth in the claims encompass all available equivalents of those claims. Embodiments of the invention may be referred to, individually or collectively, herein by the term "invention" merely for convenience and without intending to limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. [0019] The embodiments described herein provide a variety of separating apparatuses formed from shape memory alloys. An embodiment of the apparatus is an actuator formed from a shape memory alloy. An "actuator," as used herein, refers to an apparatus, mechanism, or mechanical device that is configured to activate or put an object, which is configured to be in contact with the actuator, into motion by imparting directly or indirectly kinetic energy to the object. Another embodiment of the apparatus is a coupling apparatus formed from a shape memory alloy. A "coupling apparatus," as used herein, refers to a mechanical device or mechanism that is configured to couple or hold together two or more objects. A fastener is an example of a coupling apparatus, which, for example, includes bolts, hooks, snaps, screws, nails, pins, rings, pins, and other fasteners. The apparatuses or portions of the apparatuses are formed from a shape memory alloy that exhibits a shape memory effect where, as described in more detail below, the shape memory alloy can be deformed and then returned to its original shape when heated.

[0020] As illustrated in Figures Ia- Id, this shape memory effect may be used to separate a separating apparatus. Figure Ia illustrates a member 102 of a separating apparatus formed from a shape memory alloy, in accordance with an embodiment of the invention. As used herein, a "member" refers to a constituent part of a separating apparatus and, in the example of Figure Ia, the member 102 is in the shape of a bar having two opposing ends 104 and 106 that, as shown in Figure Ib, are held in place and pulled in opposite directions such that the member 102 is under strain. As illustrated in Figure Ic, the opposing ends 104 and 106 are fixed in place and a heating source 108 applies heat to the member 102, and upon application of heat, the member 102 separates into two pieces because of the shape memory effect. As used herein, to "separate" is to come apart caused by a break or fracture in the separating apparatus. As described in more detail below, such a unique property of shape memory alloys can be used as a release mechanism for a coupling apparatus or used to actuate an object. [0021] Figure 2 is a representative diagram 200 illustrating the various solid phases of a shape memory alloy at different temperatures and stress states. The diagram 200 includes a temperature reference 202 identifying a temperature increasing from a low temperature at the bottom of the diagram 200 to a high temperature at the top of the diagram 200. Additionally, the diagram 200 illustrates the different solid phases or crystal structures of a shape memory alloy at temperatures identified by the temperature reference 202. [0022] It should be appreciated that shape memory alloys undergo a temperature related phase change that is characterized by the memory of a mechanical configuration imposed on the material at an annealing temperature. When the shape memory alloy is below some lower temperature, the alloy possesses a particular crystal structure whereby it may be deformed into an arbitrary shape with relative ease. Upon heating the alloy above a higher temperature, the alloy undergoes a change in crystal structure and the shape memory effect is manifested by a resumption of the originally imparted shape, representing the onset of a restoring stress.

[0023] Figure 2 shows a pictorial diagram illustrating the shape memory effect of an example material formed from a shape memory alloy. At a low temperature (e.g., at room temperature), the shape memory alloy is in a martensite phase 204 where the shape memory alloy has a body centered tetragonal crystal structure and may be relatively soft and deformable. When stress 211 is applied to the martensite phase 204, the shape memory alloy is deformed and transformed into a deformed martensite phase 206. For example, the shape memory alloy in the martensite phase 204 may be stretched, compressed, and/or sheared such that it takes on a deformed shape that is in a deformed martensite phase 206. In the deformed martensite phase 206, the atoms may move past each other, but the bonds are not broken, and the atoms are still relatively placed to each other in the same position as the martensite phase 204.

[0024] Upon application of heat 208 to the shape memory alloy in the deformed martensite phase 206, which results in heating the shape memory alloy to a high temperature, the shape memory alloy inherently returns to its original shape. It should be noted that the imposition of stress 211 on the shape memory alloy in the martensite phase 204 is one way and causes the deformation of the material (e.g., into the deformed martensite phase 206) that will not go back to its unstressed or pre-stressed form until heat 208 is applied. On the other hand, stress 212 imparted in the austenite phase 210, which is explained in more detail below, is a bidirectional phase change in that when the stress 212 is removed, the shape memory alloy returns back to its unstressed form (e.g., deformed shape) without the addition of heat 208.

[0025] In the original shape, the shape memory alloy is in an austenite phase 210, which has a cubic crystal structure. When cooled to a low temperature, the shape memory alloy in the austenite phase 210 transitions back to the martensite phase 204. Unlike other metals, this transition between the phases (austenite phase 210 to martensite phases 204 and 206) is reversible and repeatable. It should be appreciated that a large amount of energy is stored in the deformed martensite phase 206, and this energy used by the shape memory alloy to return to its original shape can also be used to separate the shape memory alloy. Examples of shape memory alloys that exhibit the phases illustrated in Figure 2 include nickel-titanium alloys (e.g., Nitinol), titanium- nickel alloys, copper-zinc-aluminum alloys, copper aluminum nickel alloys, nickel titanium hafnium alloys, and other shape memory alloys. [0026] Figure 3 illustrates a plot 300 of the mechanical behavior of a shape memory alloy with the application of heat, in accordance with an embodiment of the invention. The plot 300 is a stress versus time curve of a shape memory alloy where the horizontal axis 350 defines time and the vertical axis 352 defines the stress applied to a shape memory alloy.

[0027] As depicted in Figure 3, the shape memory alloy is loaded or stressed (e.g., pulled, compressed, and/or sheared) for a duration of approximately 40 seconds at a constant strain rate at which point 302 the loading is stopped. Thereafter, at point 304, heat is applied to the shape memory alloy and as a result, the shape memory alloy is further stressed because it wants to return to its original shape. With sufficient stress (e.g., at approximately 160 ksi), the shape memory alloy separates or fails at point 306 of the plot 300. [0028] Figure 4 illustrates an example of a separating apparatus, in accordance with an embodiment of the invention. The separating apparatus may be in the form of a fracturing bolt 400, which is a type of coupling apparatus, that refers to a variety of fastening rods, pins, or screws that are configured to couple two or more objects together and also configured to separate (or fracture). The fracturing bolt 400 of Figure 4 comprises a threaded cylindrical shaft member 402 with a head member 401 attached to the cylindrical shaft member 402. Here, both the head member 401 and the cylindrical shaft member 402 are formed from a shape memory alloy. Additionally attached to the fracturing bolt 400 are electrical wires 404 (or electrical leads).

[0029] The fracturing bolt 400 is pre-strained. A separating apparatus

(e.g., the fracturing bolt 400) is pre-strained when it is preloaded to a predetermined strain value. That is, a separating apparatus is pre-strained when its body or structure is deformed as a result of an applied force. The fracturing bolt 400 is pre-strained such that when heat is applied to the member 402, the member 402 is configured to separate into two pieces. In an embodiment, the heat may be generated by resistance heating, which refers to a process in which heat is generated by passing an electric current through a conductor, such as the threaded cylindrical shaft member 402. In the example of Figure 4, an electric current may be applied to the cylindrical shaft member 402 by way of the electrical wires 404 to generate heat in the cylindrical shaft member 402. In addition to resistance heating, a variety of other techniques to generate heat may be used, in accordance with other embodiments, which is explained in more detail below.

[0030] Figures 5a and 5b illustrate another embodiment of a separating apparatus used in a telescope assembly 500. As depicted in Figure 5a, a telescope assembly 500 is comprised of objects, such as a cover 502 and a housing assembly 504, that are coupled together by a separating apparatus 506 in the form of a coupling apparatus. The separating apparatus 506 is a plate with two holes at both ends of the plate that fit into pegs of the cover 502 and the housing assembly 504, which, when fitted, prevents the cover 506 from being opened or detached from the housing assembly 504.

[0031] In this example, heat may be applied to the separating apparatus

506 by resistance heating where an electric current is applied to the separating apparatus 506. As depicted in Figure 5b, the separating apparatus 506 separates into two pieces when heated and the separation thereby releases the cover 502 from the housing assembly 504 such that the cover 502 can be opened. In another embodiment, the separating apparatus 506, as explained in more detail below, can also be an actuator configured to actuate the cover 502 when separated.

[0032] Figure 6 illustrates yet another embodiment of a separating apparatus 602 used in a rocket 600. The rocket 600 is a multistage rocket that comprises a first stage 606 mounted above a second stage 607 that are held together by a separating apparatus 602 in the form of a coupling apparatus. Each first stage 606 or second stage 607 contains its own engine and propellant. In effect, two rockets (first stage 606 and second stage 607) are stacked on top of each other. In this example, the separating apparatus 602 is a sleeve formed from a shape memory alloy and is configured to wrap around and couple the first stage 606 to the second stage 607.

[0033] Upon application of heat to the separating apparatus 602, the separating apparatus 602 separates to allow the first stage 606 to separate from the second stage 607. It should be noted that the location of the separation may be defined by machining a notch 604 into the separating apparatus 602 such that the separating apparatus 602 separates at the notch 604. The separating apparatus 602 illustrated in Figure 6 may be used to replace traditional explosive mandrels with sheared rivets or traditional explosive bolts currently used to separate the first stage 606 from the second stage 607 of the rocket 600. The separating apparatus 602 has fewer parts when compared with traditional explosive mandrels and traditional explosive bolts, thereby resulting in a more reliable mechanism to allow the separation of the first stage 606 from the second stage 607.

[0034] Figures 7a and 7b illustrate the use of a separating apparatus 506 to actuate an object upon release, in accordance with an embodiment of the invention. As illustrated in Figure 7a and also discussed above, a telescope assembly 500 includes a cover 502 and a housing assembly 504 that are coupled together by a separating apparatus 506 formed from a shape memory alloy. In this embodiment, the separating apparatus 506 is in the form of an actuator that stores a large amount of mechanical energy that, when released, may be used to actuate an object. [0035] For example, as illustrated in Figure 7b, the separating apparatus 506 separates upon the application of heat, and this separation releases or imparts a large amount of kinetic energy to the cover 502 such that the energy snaps open the cover 502. As a result, in addition to releasing the cover 502 from the housing assembly 504, heat may, in effect, also be used to actuate or open the cover 502. [0036] Figure 8 illustrates an exothermic reactive foil 804 according to an embodiment of the invention that may be used to generate heat. As discussed above, in addition to resistive heating, a variety of other heating techniques may be used to generate heat. For example, in an embodiment, a reactive foil 804 that may be used. In general, a reactive foil 804 is comprised of layers of metals or other materials (e.g., aluminum layers and/or nickel layers) that, when activated by an electric current, chemically react to deliver localized heat. An example of a reactive foil 804 is NANOFOIL®.

[0037] As illustrated in Figure 8, the reactive foil 804 is attached to or deposited on a surface 802 of a separating apparatus 802 by way of, for example, a conductive adhesive. When an electric current is applied to the reactive foil 804, the electric current initiates a chemical reaction in the reactive foil 804 that results in an almost immediate, localized heating of the separating apparatus 802 that is used to separate the separating apparatus 802. [0038] Figure 9 illustrates resistance wires 904 according to another embodiment of the invention that may also be used to generate heat. A resistance wire 904 is an electrical wire with a high electrical resistivity and is configured to generate heat upon application of an electric current. The resistance wire 904 may, for example, be formed from a nickel-chromium alloy. [0039] As depicted in Figure 9, resistance wires 904 are attached to a surface of the separating apparatus 802 using, for example, a conductive adhesive. When an electric current is applied to the resistance wires 904, the electric current causes the resistance wires 904 to generate heat, which is used to separate the separating apparatus 802.

[0040] In the foregoing detailed description, various features are occasionally grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, the invention may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment. [0041] Plural instances may be provided for components, operations or structures described herein as a single instance. Finally, boundaries between various components, operations, and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the invention(s). In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the invention(s).