Abstract:
A device for restraining and then quickly releasing objects, comprising two half-spools that are held in place by a coil spring. The spring is attached at one end to one of the spools and at another end is held in place by a frangible wire, which is in turn connected to redundant power supplies. Insulation is provided by coating a base portion with aluminum oxide and attaching an insulator hub to the end of the spring held by the frangible wire. Cut-outs within the coils are provided to maximize separation force.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to non-explosive, frangible actuator devices for quickly releasing loads. 
     BACKGROUND OF THE INVENTION 
     Non-explosive frangible actuators are used to perform a task, often releasing a tensile load (such as a stowed solar array or antennae on a satellite) upon electronic command. Because of the damage of explosion in aerospace applications, and the weight of the satellite and other loads to be released, actuators must first restrain and then quickly release tremendous loads with a minimum mechanical shock imparted to the surrounding separate components or devices. Typically, such actuators will utilize a multi-part spool held together by a wound restraining wire (with memory). A load is restrained by the barrier formed by the intersection of the parts of the spool (when held together by the restraining wire). A pin is provided which bares against the spool at one end of the pin and holding the load at the other end of the pin. A small frangible fuse keeps the restraining wire from unraveling until a weak electrical current causes the frangible fuse to fail in tension, allowing the restraining wire to unwind and thus freeing the parts of the spool to separate, eliminating the resistance to the load. Some actuators apply the full force of the load to the spool, while others utilize a series of moving parts to create a mechanical advantage, so that only a small portion of the load need be resisted by the spool. Typically prior art devices used a single power supply. As detailed below, prior art devices have exhibited a number of problems. 
     In many applications, such as aerospace, the device must function properly the first time, and at a precise, predetermined time. The lack of a redundant power supply and electrical wiring can cause the device to fail or not operate successfully. 
     Prior art devices have also employed plastic actuators. In the past, metal actuators were thought to be impractical because the power to the fuse wire could short or ground on the entire device, causing the fuse wire not to actuate and perform the required function. Such devices are limited in the load that can be directly restrained by the actuator spool by the tensile strength of the plastic. One prior art device by G &amp; H Technology (“G &amp; H 8024”) attaches an insulator on the fuse wire, which unfortunately becomes debris after actuation. The G &amp; H 8024 also utilizes a ceramic actuator, made of aluminum oxide ( Al 2 O 3 ) to make their device as non-conductive as possible. Just as with plastic actuator spools, aluminum oxide lacks the tensile strength of steel. 
     Prior art “mechanical advantage devices” have an additional problem. In such devices, the load is released almost instantaneously, risking high mechanical shock output. Although “mechanical advantage” actuators have a series of events that precede release (e.g., fuse failure causing spool separation resulting in a series of parts moving and releasing other parts), the actual release of the load is quite sudden. 
     Prior art devices can only be loaded from one side (i.e., the load can either be pulling on one side or pushing against the other direction). Thus separately designed actuators must be employed for different applications. 
     Additionally, prior art units, such G &amp; H model no. 8024, use a conical (or funnel) shape for the top of a release pin. As discussed within, this allows no tolerance for misalignment. 
     What is needed is a frangible actuator that uses a direct release mechanism, has a redundant power supply, allows use of a metal spool release without grounding the fuse, and avoids failure due to excessive friction during release. 
     SUMMARY OF THE INVENTION 
     In a first embodiment, the present invention provides a redundant power supply for an actuator with two actuator terminals, which block and then release a load responsive to current from the power supply, which includes at least two power supplies, each connected to the actuator in parallel whereby should one fail upon activation, the other will still actuate the device. 
     In a second embodiment, the present invention provides a frangible actuator comprising an actuation barrier with a plurality of restraining parts, having a blocked position and an open position; a frangible restraint for maintaining and releasing said plurality of parts from the blocked position, the frangible restraint failing in tension upon the application of an electrical current; a restraining wire having a secured position and a release position, for holding and releasing the plurality of parts; an insulator hub made of a nonconductive material surrounding a loop end of the restraining wire, with the frangible restraint passing over and holding the restraining wire in the secured position and allowing said restraining wire to move into said release position when said frangible restraint fails in tension in response to the application of electrical current. 
     In a third embodiment, the present invention also provides an actuation barrier comprising a plurality of restraining parts with a blocked and open position and an interior surface; an activation pin having a head portion and a load portion interconnected to a load to be released adjacent to the load position and bearing against the restraining parts at said head portion when the restraining parts are in the blocked position and passing beyond the restraining parts in said open position; and the interior surfaces have at least one depression section against which the head portion of the activation pin does not bear when the restraining parts are in their blocked position. 
     In a fourth embodiment, the present invention also provides a base portion and restraining parts made primarily of steel at least partially coated with aluminum oxide. 
     In a fifth embodiment, the present invention also provides at least one and ideally two restraining pins, pin rigidly connected to the base portion and bearing against at least one of the plurality of restraining parts when the actuation barrier is in a blocked position, restraining movement of the actuation barrier relative to the base portion when the barrier is in the blocked position. 
     In a sixth embodiment, the present invention also provides a restraining wire wound around the actuation barrier at least once when in the blocked position to hold the restraining parts together, and unwinding to release the parts to move the barrier into the open position, and the diameter of said actuation barrier is equal to 0.8 times the square product of the diameter of the wire divided by a constant in the range of 0.021 to 0.031 and ideally 0.026. 
     In a seventh embodiment, the present invention also provides a head portion with two parallel flat sides and at least one restraining channel, located between the restraining parts, each restraining channel having a lower end and an upper end, said restraining channel restraining rotational movement of said head portion as the head portion passes through the channel but allowing rotational movement as the head portion passes above the channel so that the head portion may be inserted into the actuator and received by the lower end of the restraining channel with or without a load attached, passed through the channel and above the upper end thereof, rotated, ninety degrees, lowered and allowed to bare against and be resisted by said actuation barrier. 
    
    
     These and other features and advantages of this invention will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the present invention in a restrained state, showing it connected to redundant power supplies. 
     FIG. 2 is a schematic drawing of the circuitry of the present invention, showing both the frangible actuator ( 12 ) and redundant power supplies. 
     FIG. 3 is a cross sectional view of the present invention in a restrained state. 
     FIG. 4 is a cross sectional view of the present invention in a released state. 
     FIG. 5 is an isometric view of the present invention in a restrained state, with the restraining wire removed and the release pin ( 76 ) in place. 
     FIG. 6 is an isometric view of the present invention in a released state, with the restraining wire removed and without the release pin ( 76 ). 
     FIG. 7 is an isometric view of one of the two half-spools ( 16 ) and the release pin ( 76 ) of the present invention. 
     FIG. 8 is an isometric view of an alternative embodiment suitable for rear loading, with a modified shaft aperture ( 112 ) and also showing a flattened restraining head portion ( 106 ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a frangible actuator  12  constructed according to the present invention. The frangible actuator  12  has a base portion  14 , a first half-spool  16 , a second half-spool  18 , and two restraining pins, a first restraining pin  22 , and a second restraining pin  24 . The two restraining pins  22  &amp;  24  are rigidly mounted to the base portion  14 , while the two half-spools  16  &amp;  18  rest movably on an upper surface  26  of the base portion  14 . The half-spools  16  &amp;  18  and base portion  14  can be made of any number of materials, however it has been found that when loads are directly applied to the spool (as opposed to prior art mechanical advantage devices) metals such as stainless steel have a higher tensile strength and can handle greater loads. Half-spools made of 15-5 PH stainless steel have been found to be most satisfactory for many applications. 
     As noted above, it is desirable to make the half-spools  16  &amp;  18  and base portion  14  non-conductive. Therefore, in a preferred embodiment, the stainless steel is coated with a layer of aluminum oxide (Al 2 O 3 ) ideally {fraction (1/1000)} to {fraction (3/1000)} of an inch. The half-spools can be made in any number of sizes, depending upon the application, however it has been found that half-spools of diameter 0.8 inches and a height of 0.7 inches are well suited for loads of up to about 7,500 pounds. Similarly, the dimensions of the base portion  14  may be 2.0 inches by 1.5 inches, and the restraining pins 0.125 inches in diameter and 0.7 inches in height in a preferred embodiment suitable for many aerospace applications. The upper surface  26  of the base portion  14  may also be coated with aluminum oxide to further prevent accidental grounding. 
     The frangible actuator  12  is held in a restrained position by a restraining wire  28  which has two ends, a loop-shaped release end  32  and an attachment end (not shown). The restraining wire  28  may be made of any number of materials with memory, such that if released it will return to its uncoiled state. Stainless steel wire has been found to be quite effective. A restraining wire  28  which is approximately five feet long will wrap around a spool of the above dimensions approximately twenty times and allow loads up to about 7,500 pounds with a minimum actuation current of about 2.0 amperes and ideally about 4.5 amperes. It has been found that the optimal relationship between wire and spool (formed of the two half-spools  16  &amp;  18 ) can be calculated from the following formula: 
     
       
         S=0.8(W/0.026) 2   
       
     
     where: 
     
       
         S=Spool Diameter 
       
     
     
       
         W=Wire Diameter 
       
     
     and the figure 0.026 may be anywhere in the range of 0.021 to 0.031. The attachment end is permanently mounted to one of the two half-spools  16  &amp;  18 . Mounting can be accomplished in any number of ways, such as welding, bolting, and other means customary in the trade. Referring to FIGS. 1 &amp; 2, the loop-shaped release end  32  forms an open loop which passes over an insulator hub  34 . The insulator hub  34  has a pair of parallel ridges  36  which form a central depression  38 . The insulator hub  34  may be made of any number of non-conductive materials, such as polyamide imid (also known as TORLON® made by Amoco Chemical), and in a preferred embodiment need be no longer than ⅛ inch. A fuse wire  42  passes through the insulator hub  34  and is attached thereto. The fuse wire  42  has two ends (shown in FIG.  2 ). As can be seen schematically in FIG. 2, the fuse wire  42  connects two terminals, fuse terminal  44  and fuse terminal  46 , both terminals beneath the upper surface  26  of the base portion  14  (FIG.  1 ). For a frangible actuator  12  designed to handle loads of 7,500 pounds and having spools of the above dimensions, a fuse wire of a diameter of 0.004 inches has been found to be more than adequate. Such a wire will fail in tension with a current of about 2.0 amperes, however to provide a margin for error, in a preferred embodiment, a current of about 4.5 amperes may be employed. 
     A power supply  50  is provided which comprises at least two redundant power supplies, a primary power supply  48  and a secondary power supply  52 . Three or more power supplies may be employed for added security, however for many applications two has been found to be adequate. In a preferred embodiment, both power supplies are direct current, with an output of about 4.5 amperes suitable for most applications. Each power supply has a positive and a negative terminal, such that primary power supply  48  has positive terminal  54  and negative terminal  58 , and secondary power supply  52  has positive terminal  56  and negative terminal  62 . Positive terminal  54  is connected by connecting wire  54 - a  to fuse terminal  46  via diode  64 , which is wired in series and in a direction to permit the flow of current only in the direction from positive terminal  54  to fuse terminal  46 . Similarly, positive terminal  56  is connected by connecting wire  56 - a  to fuse terminal  46  via diode  66 , which also limits the flow of current to the direction from positive terminal  56  to fuse terminal fuse terminal  46 . This prevents positive terminal  54  from grounding on positive terminal  56 , and vice versa. 
     Negative terminal  58  and negative terminal  62  are directly connected to negative terminal  44  via connecting wires  58 - a  and  62 - a,  respectively. Thus if primary power supply  48  or secondary power supply  52  is activated, a current will be generated of at least about 2.0 amperes, which will pass through fuse wire  42  causing fuse wire  42  to fail in tension. In the embodiment disclosed, the redundant power supply of the present invention is used with a frangible actuator. However, the redundant power supply may be used with virtually any kind of actuator. For instance, the redundant power supply of the present invention may be used to directly actuate explosive bolts or other squibs, or to actuate a heater used to increase the temperature of a bimetal strip or other metals with memory (i.e., shape memory alloys) which will then return to its original configuration releasing a load, paraffin devices in which paraffin liquefies in response to heat eliminating the paraffins resistance to force, or other actuators. 
     As can be seen from FIGS. 1-6, the frangible actuator  12  comprises two half-spools, first half-spool  16  and second half-spool  18 . Three third-spools, four forth-spools, or other combinations can be employed depending upon the application. The herein described half-spool embodiment has been found to work well in many aerospace applications. 
     A release pin  76  is provided that rests between the two half-spools, and extends through an aperture  78  formed in the base portion  14 . The release pin  76  has a shaft section  84  and a restraining head portion  86 . In an embodiment suitable for aerospace applications in which loads of about 3,500 to 6,000 pounds must be supported, a release pin  76  fabricated of 15-5 PH stainless steel and having the diameter of ¼ inch, with an restraining head portion  86  fabricated of 15-5 PH stainless steel and having the dimensions of a spherical diameter of about 0.5 inches have proven useful. 
     The two half-spools are quite similar, so only first half-spool  16  need be discussed in detail. Referring to FIGS. 6 &amp; 7, first half-spool  16  has a generally vertical exterior wall  82  which when mated with the exterior wall  82  of the other second half-spool  18  has a generally tubular shape. The first half-spool  16  has an interior surface  70  which is somewhat conical in shape, being an approximately sixty degree cone having a base diameter of about 0.83 inches at a shaft aperture  92  (which is sized to allow the shaft section  84  of the release pin  76  to pass through, but to restrain the restraining head portion  86 ). The conical interior receives the restraining head portion  86  of the release pin  76 . 
     In a preferred embodiment, the half-spools  16  &amp;  18  are of a greater hardness than the restraining head portion  86  of the release pin  76  (e.g., the half-spools  16  &amp;  18  being made of 15-5 PH stainless steel, and the restraining head portion  86  of 15-5 PH stainless steel). Were the restraining head portion  86  and half-spools  16  &amp;  18  made of materials of the same hardness, a cold welding could take place, resulting in possible failure of the device (of course, were the restraining head portion  86  of a harder material than the half-spools  16  &amp;  18  could mold around the restraining head portion  86 , again resulting in failure). 
     The first half-spool  16  has a pair of pin recesses, pin recess  94  and pin recess  96 , each of which have a semicircular cross section, which when mated with their counterparts in second half-spool  18  form apertures surrounding the first restraining pin  22  and the second restraining pin  24 . 
     First half-spool  16  also has a pair of elliptical cut-outs, cut-out  98  and cut-out  102 . Because the interior surface  70  is shaped and sized to receive the restraining head portion  86 , much of the surface area of the interior surface  70  actually touches the restraining head portion  86 . However, the cut-outs  98  &amp;  102  provide an area that does not touch any part of the restraining head portion  86 , the advantages of which will be elaborated upon below. Each of the cut-outs  98  &amp;  102  are recesses in the interior surface  70  of approximately {fraction (1/16)} of an inch in depth. The pin recesses  94  &amp;  96  each represent a half-sleeve, which when first half-spool  16  is mated to second half-spool  18  forms a complete sleeve having a diameter of about ⅛ of an inch and a height of about 0.7 inches. 
     In operation, the frangible actuator  12  will be prepared by bringing first half-spool  16  and second half-spool  18  together atop the upper surface  26 , such that the first restraining pin  22  and second restraining pin  24  fit within the cavities created by the pin recess  94  and pin recess  96 , and wrapping the restraining wire  28  around the mated spool. The insulator hub  34  is fitted over and attached to the loop-shaped release end  32  of the restraining wire  28 . 
     The restraining wire  28  is held in place (wound around the spool section  68 ) by the fuse wire  42  passing over and restraining the insulator hub  34 . The shaft section  84  of the release pin  76  is passed into a central aperture  104  until further movement is restrained by the restraining head portion  86  bearing against the interior surface  70 . The load is then attached to the end of the release pin  76  distant from the restraining head portion  86  (in various embodiments the load may be attached at some other stage). 
     Actuation may be triggered automatically, by time, location, or any other variable. Actuation may also be triggered manually, providing a switch for use by an astronaut, pilot, or ground technician. Upon activation, the primary power supply  48  and secondary power supply  52  are both activated. Current from the primary power supply  48  flows from positive terminal  54  to fuse terminal  46  over connecting wire  54 - a,  over fuse wire  42  to fuse terminal  44  and over connecting wire  58 - a  to negative terminal  58 , completing the circuit. The current in that completed circuit (in the above-described embodiment, about 2.0 amperes minimum and about 4.5 amperes ideally) is adequate to cause a failure in tension in fuse wire  42 , which in turn releases loop-shaped release end  32  and the restraining wire  28 . The restraining wire  28  unravels, thus no longer restraining movement of the first half-spool  16  and the second half-spool  18 . The load is typically exerting some force against the release pin  76 , in this embodiment pulling “downward”. Prior to release of the restraining wire  28 , movement had been resisted by the restraining head portion  86  bearing against the interior surface  70  of the first half-spool  16  and second half-spool  18 . When the restraining wire  28  unravels, the half-spools are free to move aside, allowing the release pin  76  to drop thorough the frangible actuator  12  releasing the load. Should the primary power supply  48  fail for any reason, current will flow from the secondary power supply  52  (which is activated simultaneously with the primary power supply  48 ) completing the circuit and causing the fuse wire  42  to fail in tension. Diodes  64  &amp;  66  prevent either of the two positive terminals ( 54  or  56 ) from serving as a ground for the other. 
     Failure during activation is a risk with any actuator. This risk is reduced in the present invention by the cut-outs  98  &amp;  102  (in which material is removed adjacent to the two pins). As can be seen from FIG. 6 where the line between first restraining pin  22  and second restraining pin  24  is described as C-D, and a line passing through the center of the space between the two pins and perpendicular to C-D is described as A-B, because the units separate along the line A-B, C-D will receive more force than A-B. There can be no movement along C-D; thus the structures along that line are capable of resisting much more force than are those along A-B. Thus, the friction along line C-D may be so great as to cause enough force dissipation that the A-B force will not be enough to overcome that friction, and the device will fail. G &amp; H model no. 8014 attempts to solve this problem by flattening one of more of the sides of the restraining head portion of the release pin. Unfortunately, if the pin is turned 90 degrees, the device will fail because the line C-D will have maximum surface area contact and thus friction. In the present invention, the cut-outs in each half-spool along line C-D (for example, cut-outs  98  &amp;  102  in first half-spool  16 ) reduce the surface area, and thus the friction, resulting in a dissipation of force along line C-D, allowing proper movement along line A-B. 
     As described above, prior art mechanical advantage devices used an elaborate system of levers, planes, etc. which although taking some time after actuation to release a load, result in a very sudden release. This may damage the load due to mechanical shock. The present invention allows the load to drop more gradually as the restraining wire  28  unwinds around the spools. It was previously felt that while such direct release was quite advantageous compared to mechanical advantage devices, direct release required a spool that could withstand far greater force than the plastic spools typically used in such mechanical advantage devices. Metal spools were difficult to use because it was felt that any current transmitted through the fuse wire  42  may ground on the metal spool, preventing actuation and risking damage to other parts of the release vehicle. Additionally, attempts to add insulation add weight to the device and provide additional material that can become debris after actuation, interfering with moving parts and causing failure of the release mechanism. For instance, the G &amp; H 8014 device insulates the entire fuse wire. The present invention utilizes the insulator hub  34  to isolate the frangible actuator  12 , which because of its size and the fact that it is permanently attached to the loop-shaped release end  32  of the restraining wire  28 , simply travels with the unwinding restraining wire  28 . 
     The present invention can be front or rear loaded, that is the load can be pushing against the spool from the top, or being pulled from the bottom. 
     Another embodiment of the present invention provides a device useful for rear entry applications, in which a rod is employed having two flat sides. Once inserted it may be turned 90 degrees to lock in position, as shown by FIG.  8 . Comparing FIG. 8 with FIGS. 5-7, first restraining pin  22  and second restraining pin  24  have been replaced with first restraining channel  22 -a and second restraining channel  24 - a , which are both stationary with respect to the upper surface  26  and base portion  14 . First and second restraining channels  22 - a ,  22 - b  each have a groove, such as groove  30 . Release pin  76  has been replaced with modified release pin  76 - a , which is generally identical to release pin  76  except that in modified release pin  76 - a , restraining head portion  86  has two flattened sides to form flattened restraining head portion  106  (only one flat side  108  is shown). A modified first half-spool  16 - a  and modified second half-spool  18 - a  are also provided. The modified half-spools  16 - a  &amp;  18 - a  are identical to the previously described half-spools  16  &amp;  18 , except that pin recess  94  and pin recess  96  are absent in the modified half-spools, and the modified half-spools each represent a reduced arc to allow them to surround first restraining channel  22 - a  and second restraining channel  24 - a  and still approximate a circle. The modified half-spools  16 - a  and  18 - a  still include the shaft aperture  92  and cut-outs  102  &amp;  98 . Each groove  30  is sized to receive the flattened restraining head portion  106  only in an orientation such that each flat side  108  forms a plane passing through the two grooves  30 . In operation, the modified release pin  76 - a  may be inserted through the base portion  14  in an orientation such that the flat side  108  travels within the grooves  30 . Once the flat side of the flattened restraining head portion  106  is above the restraining channels  22 - a  &amp;  22 - b , the modified release pin  76 - a  is turned ninety degrees and then allowed to pass back into and abut the interior surface  70 , just as with the other described embodiment. The weight of the load prevents the flattened restraining head portion  106  from migrating above the restraining channels  22 - a  &amp;  22 - b . This allows the load to be attached to the release pin  76  before insertion and further permits the rear loading discussed above. With the load in place, this embodiment functions identically to the earlier described embodiment. 
     Having now described the invention in accordance with the requirements of the patent statutes, those skilled in the art will understand how to make changes and modifications in the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.