Patent Grant
7928826
The present invention relates generally to the field of electrical switching devices, and more particularly to an electrical switching device having an actuator mechanism formed of a shape memory alloy (SMA).
Shape memory alloys (SMA), such as nickel-titanium alloys, copper-aluminum-nickel alloys, copper-zinc-aluminum alloys, iron-manganese-silicon alloys, and the like, are metallic alloys that remember their geometry. After such alloys are deformed, they regain their original geometry by themselves during heating (one-way effect) or, at higher ambient temperatures, simply during unloading (pseudo-elasticity). This capability results from a temperature-dependent martensitic phase transformation from a low-symmetry martensite structure to a highly symmetric crystallographic austennite structure. In most shape memory alloys, a temperature change of only about 10° C. is necessary to initiate this phase change. The most common shape memory alloy, a nickel-titanium alloy, was first developed in 1962-1963 by the Naval Ordnance Laboratory, White Oak, Md., and commercialized under the trade name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories).
Electrical switching devices, in particular, vacuum tube electrical switching devices such as relays, switches, resettable fuses, and the like, typically employ electromechanical actuators or solenoids which are prone to failure. Complex avionic equipment often employs large numbers of such devices, thereby limiting the reliability of the equipment and aircraft. For example, high frequency (HF) antenna couplers used in aircraft communications systems employ vacuum relays for connecting the capacitors and inductors in the coupler during the tuning phase to create an appropriate impedance match to the antenna. Typical HF Antenna Couplers may employ many such relays (e.g., 30 or more). During manufacture, each relay must be carefully hand soldered and tested. Assemblies of the relays are then functionally tested. The failure of any relay in an assembly may require additional companion relays to be removed and replaced, the assembly to be reassembled, tuned and retested. In the event a vacuum relay fails in use either before or during flight of the aircraft, the HF antenna coupler must be removed from the aircraft and replaced, which may result in undesirable grounding of the aircraft. Thus, the failure of a single relay is undesirably expensive.
Consequently, it would be advantageous to provide electrical switching devices, including but not limited to, vacuum tube electrical switching devices such as relays, switches, resettable fuses, and the like, which employ actuator mechanisms formed of a shape memory alloy (SMA) for improved reliability and reduced cost.
Accordingly, the present invention is directed to an electrical switching device which employs an actuator mechanism formed of a shape memory alloy (SMA) for improved reliability and reduced cost.
In exemplary embodiments, the electrical switching device includes a housing, at least one non-actuated electrical contact supported in the housing, and an actuator assembly contained within the housing. The actuator assembly includes a movable contact for engaging the contact and an actuator formed of a shape memory alloy (SMA). Application of a first electrical current to the actuator causes the actuator to move the movable contact to either engage or disengage the non-actuated electrical contact for one of allowing or preventing the flow of a second electrical current through the contact.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.
The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:
Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. It is to be appreciated that corresponding reference numbers refer to generally corresponding structures.
The actuator assembly 108 includes an actuator 112 formed of a shape memory alloy (SMA) which changes shape upon the application of an electric current (e.g., when heated by the application of an electric current). In this manner, the application of an electrical current to the actuator 112 causes the actuator 112 to move the movable contact 110 to either engage or disengage the non-actuated electrical contacts 104 & 106 so that the flow of an electric current through the contacts 104 & 106 is either allowed or inhibited. In exemplary embodiments, the actuator 112 is formed of a nickel-titanium alloy such as Nitinol. However, it is contemplated that the particular shape memory alloy (SMA) used will depend on a variety of factors, such as the specific application in which the electrical switching device 100 is to be used. Thus, it is contemplated that other shape memory alloys may be used. Such shape memory alloys may include, but are not necessarily limited to, copper-aluminum-nickel alloys, copper-zinc-aluminum alloys, iron-manganese-silicon alloys, and the like. These shape memory alloys (SMA) may be used in place of nickel-titanium alloys in specific applications of the invention without departing from the scope and intent of the present invention. In exemplary embodiments, the actuator may employ a shape memory alloy (SMA) exhibiting a one-way shape memory effect. In such embodiments, the actuator 112, upon being heated by the application of an electric current, acquires a predetermined shape, geometry or length without the application of an external force. A return mechanism may be provided to return the actuator to its original position prior to heating. In exemplary embodiments, the return mechanism may be mechanical (e.g., spring 126), hydraulic, pneumatic, or the like. Alternatively, in other embodiments, the actuator 112 may employ a shape memory alloy (SMA) exhibiting a two-way shape memory effect, wherein the actuator 112 acquires two different shapes: one a low temperature shape when no electrical current is applied, and the other a high temperature shape acquired upon application of an electrical current. Additionally, it is contemplated that the specific metallurgical content of the shape memory alloys (SMA) employed may be varied to provide the electrical switching device 100 with specific performance characteristics (e.g., response time, contact force, fatigue life, or the like).
In this embodiment, the actuator assembly 108 includes a flapper or diaphragm 124 supported in the case 114 of the housing 102 for supporting in the movable contact 110. A spring 126 (a coil spring is shown) extends between the bottom surface of the flapper 124 and the internal surface of the bottom of the case 114. As illustrated, the actuator 112 comprises a wire 128 formed of shape memory alloy (SMA) material extending between the bottom surface of the flapper 124 and the internal surface of the bottom of the case 114 within the spring 126. The wire 128 is electrically coupled to pins 130 & 132 mounted to the bottom of the case 114 and extending from the outer surface of the bottom of the case 114 so that an electric current may be applied to the wire 128.
The actuator assembly 108 is shown in the non-actuated state in
When the first electric current is removed from the wire 128, contraction of the wire ceases so that the wire 128 is allowed to extend. The spring 126, being no longer compressed by the wire 128, extends and pivots the flapper 124 upward, which pivots the movable contact 110 to the non actuated position shown in
In this embodiment, the actuator 112 comprises a coil or spiral 134 formed of shape memory alloy (SMA) material. The movable contact 110 comprises a rotor 136 coupled to the coil 134 via a shaft 138 which wipes non-actuated contacts 104 & 106 when rotated. The coil 136 is electrically coupled to pins 130 & 132 mounted to the bottom of the case 114 and extending from the outer surface of the bottom of the case 114.
When an electric current is applied to the coil 134, as shown in
In this embodiment, the actuator 112 comprises shaped block 140 formed of shape memory alloy (SMA) material having a generally funnel shaped cross-section. The movable contact 112 comprises a bar 142 coupled to the shaped block 140 via a shaft 144 so that the bar 142 engages or wipes the non-actuated contacts 104 & 106 when rotated. The shaped block 140 is electrically coupled to pins 130 & 132 extending from the outer surface of the bottom of the case 114 so that an electric current may be applied to the block 140. When the electric current is applied to the shaped block 140, as shown in
When the first electric current is removed from the shaped block 140, the twist of the block ceases so that the block 140 untwists, rotating the shaft 144 in the opposite (e.g., counterclockwise) direction. The shaft 144 in turn rotates the bar 142 to the non-actuated position shown in
As in the embodiments illustrated in
In this embodiment, the actuator 112 comprises a filament 146 of shape memory alloy (SMA) material having two control leads or pins 130 & 132 extending from the outer surface of the bottom of the case 114. As shown, all but a section 148 of the filament 146 is held (e.g., encased within a sleeve 150, or the like) which prevents movement of the filament 146. The section 150 not held within the sleeve is surrounded by movable contact 110, which is allowed to slide between a first position, wherein the movable contact 110 does not engage the non-actuated contacts 104 & 106 and a second position wherein the movable contact 110 engages the non-actuated electrical contacts 104 & 106. When an electric current is applied to the filament 146, the filament 146 contracts allowing the movable contact 110 to disengage the non-actuated contacts. When the first electric current is removed from the filament 146, the contraction of the filament 146 ceases so that the filament 146 is allowed to lengthen. As the filament lengthens, the exposed section 150 of filament 146 bows outward, as shown in
It is contemplated that, in exemplary embodiments, the diameter (gauge) of the filament 146 and the shape memory alloy (SMA) material from which the filament 146 is fabricated may be selected to achieve the specific response required by the application in which the vacuum relay electrical switching device 100 is used. The filament 146 may exhibit either one-way or two-way shape memory effect. If a filament 146 exhibiting one-way shape memory effect is employed, a return mechanism such as a mechanical device (e.g., a spring assembly), a hydraulic device, a pneumatic device, or the like, may be utilized to bias the movable contact 110 to either the opened (non-engaged) or closed (engaged) positions.
In exemplary embodiments, the electrical switching devices 100 illustrated may comprise vacuum tube electrical devices such as vacuum relays, switches, resettable fuses, or the like which employ a vacuum tube housing 102. However, it is contemplated that electrical switching devices 100 in accordance with the present invention need not be limited to such embodiments. Further, in the embodiments illustrated, single pole, single throw (SPST) relays are shown for purposes of illustration, however it is contemplated that double pole and/or double throw relays (e.g., SPDT, DPDT, etc.) or even multiple pole, multiple throw relays may also be implemented without departing from the scope and intent of the present invention, for example, by modifying the configuration of the contacts being used.
Accordingly, it is believed that the present invention and many of its attendant advantages will be understood by the forgoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.
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