Abstract:
Redundant fuse wire apparatus and redundant release devices, such as those used to release deployable appendages, such as solar array and reflectors disposed on satellites, and the like. An exemplary redundant release device comprises a restraint release mechanism having one or more restraint release arms, a redundant release device comprising a segmented spool having a plurality of segments that are constrained from separating by spring restraint tape releasably secured to the restraint release arms, a redundant fuse wire assembly comprising primary and redundant positive contacts, a common negative contact, primary and redundant fuse wires respectively connected between the primary positive and common negative contacts and the redundant positive and common negative contacts that respectively wrap around the opposed positive contact and the restraint release arms, and an electrical power source for heating and severing the fuse wires.

Description:
BACKGROUND 
     The present invention relates generally to release devices, and more particularly, to a redundant fuse wire release device and redundant fuse apparatus that may be used to stow or release items such as solar arrays, antenna positioning mechanisms, reflectors, and the like, found on satellites, space stations, and spacecraft, for example. 
     Conventional prior art non-explosive release apparatus, such as a separation spool device, for example, is used to stow or release a captured member that constrains deployment of a spacecraft element, for example, such as a solar array, in a stowed position. In such apparatus, a single fuse wire acts as a locking member that fastens a tensioned member wrapped in tension around a split spool. When the tensioned member is under tension, the split spool is clamped to a portion of the device to be deployed (the captured member) which prevents deployment of the captured member, such as a solar array. Once the release device is actuated, the fuse wire unlocks by self-destructing, thereby releasing the tensioned member to unclamp the captured member and allow deployment. 
     However, such a single fuse wire locking member is subject to self-unlocking resulting from mechanical failure. The single locking member (fuse wire) can fail due to mechanical stress and cause premature release of the device. An electrical failure can also prevent the device from releasing if inadequate current flows to melt the fuse wire upon actuation. 
     To overcome the limitations of this conventional single fuse wire locking member, a redundant fuse for use with in a split spool device was developed by the assignee of the present invention is disclosed in U.S. Pat. No. 6,133,818, issued to Hseih, et al., and is an example of a redundant fuse wire design for an application similar to that of the present invention. 
     The redundant fuse wire design disclosed in U.S. Pat. No. 6,133,818 uses three individual fuses configured in a triangular shape preventing a round disk from release. It requires cutting two of three fuses to release the disk, and it prevents premature release if one fuse is accidentally cut, thus, it is single point fault tolerant. 
     The shortcoming of this redundant fuse wire design is that third fuse does not always get cut upon actuation, and thus it could potentially cause release hang up. 
     Also, with three fuses rigidly connected to three contacts, depending upon the accuracy of fuse wrapping tension, the load may not be equally shared by all there fuses, therefore it is possible for one or two fuses to be overloaded while the other is not loaded at all, resulting in a potential for fuse overload 
     In view of the above, it would be desirable to have a improved redundant fuse wire release device and redundant fuse apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawing figures, wherein like reference numerals designate like structural element, and in which: 
         FIG. 1  illustrates exemplary redundant fuse wire release device; 
         FIG. 2  illustrates a bottom view of the redundant fuse wire release device; 
         FIG. 3  illustrates an enlarged view of a redundant fuse wire assembly that may be used in the redundant fuse wire release device; 
         FIG. 4  illustrates an enlarged plan view of the redundant fuse wire assembly; 
         FIG. 5  illustrates an enlarged side view of the redundant fuse wire release device; 
         FIG. 6   a - 6   c  show engagement and disengagement of the restraint tapes with the release arms; and 
         FIGS. 7   a  and  7   b  illustrate the sequence of events performed when actuating the redundant fuse wire release device. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawing figures,  FIG. 1  illustrates exemplary redundant fuse wire release device  10 .  FIG. 2  illustrates a bottom view of the redundant fuse wire release device  10 .  FIG. 3  illustrates an enlarged view of a redundant fuse wire assembly  30  that may be used in the redundant fuse wire release device  10 .  FIG. 4  illustrates an enlarged plan view of the redundant fuse wire assembly  10 .  FIG. 5  illustrates an enlarged side view of the redundant fuse wire release device  10 .  FIG. 6  shows engagement and disengagement of restraint tapes from release arms.  FIGS. 7   a  and  7   b  illustrate the sequence of events performed when actuating the redundant fuse wire release device  10 . 
     The redundant fuse wire release device  10  is a fully redundant low shock release device actuated using a redundant fuse wire assembly  30 . More particularly, and referring to  FIGS. 1 and 5 , the redundant fuse wire release device  10  comprises a housing  11  or fuse block  11  ( FIG. 1 ), a restraint release mechanism  21  ( FIG. 1 ), a redundant fuse wire assembly  30  ( FIG. 1 ), a redundant release device  40  ( FIG. 5 ), and an electrical power source  41 ,  42  ( FIGS. 4 ,  7   a ,  7   b ). 
     The redundant fuse wire assembly  30  comprises a primary positive contact  31 , a redundant positive contact  32 , a common negative contact  33 , and primary and redundant fuse wires  34 ,  35 . Each of the contacts  31 ,  32 ,  33  are housed in the housing  11  or fuse block  11 . Electrical wires  36  connect between the electrical power source  41 ,  42  and respective contacts  31 ,  32 ,  33 . 
     The primary fuse wire  34  is connected between the primary positive contact  31  and the common negative contact  33  and wraps around the redundant positive contact  32  and rotatable restraint release arms  24 ,  25 . The redundant fuse wire  35  is connected between the redundant positive contact  32  and the common negative contact  33  and wraps around the primary positive contact  31  and the rotatable restraint release arms  24 ,  25 . 
     More particularly, the restraint release mechanism  21  comprises a top restraint pin  22 , a bottom restraint pin  23 , a top rotatable restraint release arm  24 , and a bottom rotatable restraint release arm  25 . The restraint release arms  24 ,  25  are preferably made of dielectric material to prevent electrical shorting to ground. The restraint release arms  24 ,  25  are free to rotate around a hinge  13 . The restraint release arms  24 ,  25  are held in place under tension from tightly wound stainless steel spring restraint tapes  39  ( FIG. 5 ) by the primary and redundant fuse wires  34 ,  35 . 
     Referring to  FIG. 5 , the redundant release device  40  comprises a segmented spool  37  assembled on a cylindrical base  43 . The segments of the segmented spool  37  are prevented from separating by tightly wound stainless steel spring restraint tapes  39 . The restraint release arms  24 ,  25  are held in tension by the restraint tapes  39  that engages the top and bottom restraint pins  22 ,  23  of the restraint release arms  24 ,  25 . The restraint tape  39  are wrapped around the segmented spool  37 . 
       FIGS. 6   a - 6   c  show engagement and disengagement of the restraint tapes  39  from the release arms  24 ,  25 . As shown, once both fuse wires  34 ,  35  are cut, both release arms  24 ,  25  are free to rotate and allow the restraint tapes  39  to disengage from the arms  24 ,  25  under tension provided by wound spring tapes  39 , acting as a clock spring trying to unwind. 
     A nut  38  and rod assembly (not shown) that is held in place by the segmented spool  37  is prevented from retracting unless the segments of the segmented spool  37  are separated. Release of either or both restraint tapes  39  allow separation of segments of the segmented spool  37  and release of nut and rod assembly. The restraint tapes  39  unwind once disengaged from the restraint release arms  24 ,  25 , which are restrained from rotation by the electrically actuated redundant fuse wires  34 ,  35 . The redundant fuse wire device  10  is electrically and mechanically redundant to avoid single point failure while providing simultaneous release capability. 
     The redundant fuse wire release device  10  provides a release function upon electrical command while offering single fault tolerant redundancy with maximum current split between the two fuses  34 ,  35 . The redundant fuse wire release device  10  is used in the release device  10  as a release initiation element actuated by the electrical power source  41 ,  42 . 
     Thus, the design of the redundant fuse wire device  10  includes two redundant fuses  34 ,  35 . Both fuses  34 ,  35  are cut (heated and severed) upon actuation of electrical power from power supplies  41 ,  42 , thus there is no uncut fuse after actuation to pose a release hang up. Further, unlike the conventional redundant fuse wire design discussed in the Background section, where each of the three fuses may be loaded with different tension, the disclosed redundant fuse wire device  10  equalizes the tension in both fuses  34 ,  35  due to flexibility of the common negative contact  33 , and thus one fuse  34 ,  35  does not get overloaded. 
     The redundant fuse wire device  10  may be preferably configured to provide maximum current to burn both fuses  34 ,  35  one at a time. The redundant fuse wire device  10  is configured as a combination of parallel and series circuitry with different fuse wire lengths to maximize the resistance difference between two parallel circuits in order to minimize the power requirement for firing both fuses  34 ,  35  from a given power source  41 ,  42 . 
     The redundant fuse wire device  10  comprises two positive contacts  31 ,  32  and one common negative contact  33 . Each fuse  34 ,  35  starts from a positive contact  31 ,  32  and ends at the common negative contact  33  while passing over the other positive contact  32 ,  31 . This arrangement provides redundancy in firing from either positive contact while providing redundancy against single fuse failure to release the restraint release arms  24 ,  25 . This provides a single fault fail-safe design against premature failure of either fuse. 
     The redundant fuse wire assembly  30  is electrically and mechanically redundant to prevent premature release while providing simultaneous release capability. Either primary or secondary circuits fire both fuses  34 ,  35  at the same time. It should be noted that the time required to burn the fuse wires  34 ,  35  is in milliseconds, and that a shorter fuse wire  34 ,  35  is burnt milliseconds sooner than a longer fuse wire  34 ,  35 . However, for practical purposes, both fuse wires  34 ,  35  are cut substantially simultaneously. The redundant fuse wire assembly  30  is preferably wired to release both top and bottom restraints  24 ,  25  simultaneously, although it may be wired to release each restraint  24 ,  25  individually. 
     The redundant fuse wire assembly has two independent fuses  34 ,  35  in an overlapping configuration. Both fuses  34 ,  35  must be severed in order to release the device  10 . A single fuse  34 ,  35  is configured to provide at least a one-hundred percent strength margin against failure. The redundant fuse wire assembly  30  allows fuse tension balancing to eliminate possible assembly slack. The fuse block  11  provides electrical isolation for the contacts  31 ,  32 ,  33  and structural support for the restraint release arms  24 ,  25 . 
     With regard to redundancy, the redundant fuse wire assembly  30  thus has two substantially identical circuits with a common negative contact  33 . The redundant fuse wire assembly  30  has two independent positive contacts and one common negative contact  33 . Actuation of either circuit fires both fuses  34 ,  35 . 
     Referring to  FIGS. 7   a  and  7   b , they illustrate an exemplary sequence of events performed when actuating the redundant fuse wire release device  10 . Power may be applied to the primary circuit, and more current flows to the redundant fuse  35  (because the fuse wire is shorter than the primary fuse,) thus redundant fuse  35  gets cut or severed first, then full current flows to primary fuse  34  and it is cut or severed second. Motion of both release arms  24 ,  25  initiate simultaneously as soon as the second fuse wire  35  is cut. However, it is to be understood that either the primary circuit or the secondary circuit may be configured to fire other fuse configurations not described herein, to enable motion of top or bottom release arms  24 ,  25  separately to allow separate release of the top or bottom restraint release arms  24 ,  25 . 
     Thus, improved redundant release devices and redundant fuse apparatus have been disclosed that may be used to stow or release items such as solar arrays, antenna positioning mechanisms, reflectors, and the like, found on satellites, space stations, and spacecraft, for example. It is to be understood that the above-described embodiment is merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.