Abstract:
A redundant release apparatus having a multi-segment split spool with a central bore adapted to axially restrain a tensioned member. Two tensioned tapes are overlappingly wound around the spool segments thereby preventing radial movement of the spool segments. Overlapping winding design of each of the tapes provide predictable unwinding dynamics upon release. The multiple segments require less radial motion for release of the tensioned member.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a redundant release apparatus which may to release such items as antennas, solar arrays, positioning mechanisms, and other devices. 
     2. Description of Related Art 
     A release apparatus, such as a separation spool device, is used to release a captured member which constrains the deployment of a spacecraft element, such as a solar array and/or reflectors, in the stowed position. In many prior art devices, the spacecraft element was restrained with a wire or a holddown rod system which was released using a pyrotechnic device. Typically, the pyrotechnic device would fire a blade against a base, with the wire or rod to be cut and released. Although useful in many applications, these devices imparted high shock loads into the units which they were to release, as well as the spacecraft itself. 
     A design that avoided the shocks associated with pyrotechnic release devices was the separation spool device, which used a fused element to release a captured member. U.S. Pat. No. 6,133,818, to Baghdasarian, discusses a release apparatus wherein two piece split spool with an annulus is used to capture a capture member larger in diameter than the annulus of the spool. The two pieces of the split spool are held together with a wire that is wrapped around the spool. A drawback of this design is that the wire, wrapped under tension around the outside of the spool, may have unpredictable dynamics in some cases when released. In some cases, there may be risk of the wire fouling upon itself when released, which may prevent the spool from spreading far enough apart to allow the captured member to pass through, and thus this may prevent the release device from releasing the stowed spacecraft element. Another drawback of this design is that a two piece spool design presents a geometry that requires significant radial movement of the spool pieces to affect the release. 
     Further, a two segment spool has geometric limitations as far as load carrying capacity and a phenomenon referred to as “Friction lock up” condition, a failure to release condition due to friction between the spool-to-captured member interface, and the fact that spherical (ball) end of the captured member leaves the segments contacting the two extreme points of each segment. These two points are almost 180 degrees apart for a 2-segment spool. A ball end could easily be prevented from release with very little friction between the ball and the spool interface. 
     An additional design feature sought out in high reliability areas is redundancy. Thus, a preferred release apparatus would have a design to allow it to release even in the case of a first mechanical failure. 
     What is called for is a capture spool release device that overcomes the potentially unstable dynamics of wire wrapped spool and the drawbacks of a two segment separation device. What is also called for is a release device with a mechanical redundancy that allows for release even in the case of a first failure. 
     SUMMARY 
     A redundant release apparatus having a multi-segment split spool with a central bore adapted to axially restrain a tensioned member. Two tensioned tapes are overlappingly wound around the spool segments thereby preventing radial movement of the spool segments. Overlapping winding design of each of the tapes provide predictable unwinding dynamics upon release. 
     The multi-segment spool requires less radial motion for release of the tensioned member. The spool is adapted to release a member with the release of either one of two wound tensioned tapes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of portions of a release apparatus according to some embodiments of the present invention. 
         FIG. 1B  is a cutaway side view of a release apparatus according to some embodiments of the present invention. 
         FIG. 1C  is a perspective view of portions of a release apparatus according to some embodiments of the present invention. 
         FIG. 2  is a cutaway side view of a stowed redundant release apparatus according to some embodiments of the present invention. 
         FIG. 3  is a cutaway side view of a redundant release apparatus according to some embodiments of the present invention. 
         FIGS. 4A-B  are views of a segmented spool according to some embodiments of the present invention. 
         FIG. 5  is a cutaway side view of a redundant release apparatus according to some embodiments of the present invention. 
         FIG. 6  is a cutaway side view of a redundant release apparatus according to some embodiments of the present invention. 
         FIGS. 7A-B  are top views of portions of a release apparatus according to some embodiments of the present invention. 
         FIGS. 8A-C  illustrate a spool wound with an upper and lower restraining tape with two fuse wires according to some embodiments of the present invention. 
         FIGS. 9A-B  illustrate a dual tape release system using a single fuse wire. 
         FIGS. 10A-B  are a top perspective view and partial view, respectively, of a dual tape release system according to some embodiments of the present invention. 
         FIGS. 11A-B  are a top and side cutaway view, respectively, of a dual tape release system according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A-C  illustrate a release apparatus  10  for controlling the deployment of a desired device by releasing a captured member  15  utilizing a multi-piece split spool  11  adapted to restrain the captured member  15 . The multi-piece spool  11  consists of three or more segments  50  which define a central bore  51  adapted to restrain a captured member  15 . In some embodiments, the spool  11  consists of six segments. In some embodiments, the spool consists of eight segments. As seen in cross-section in  FIG. 1A , the segments of the spool are adapted to fittingly receive and axially restrain an expanded portion  18  of the captured member  15  when the segments  50  are constrained together as a unit. The internal area of the spool  11  in the interface area of the spool  11  with the expanded portion  18  of the captured member  15  may be conical in some embodiments. In some embodiments, the internal area of the spool  11  in this region may be a cone or a partial cylinder (or a curved surface other than a cone) with an angle of 30 degrees off of the vertical axis of bore. In some embodiments, the external profile of the expanded portion  18  of the captured member  15  may also be conical. In some embodiments, the interface area may have a curved profile. In some embodiments, the internal area of the spool may be lubricated with a dry lubricant such as molybdenum disulfide. 
     The spool segments must move a distance sufficient to allow for the outer diameter of the expanded portion of the restrained member to pass through the bore in the axial direction. As the two segments begin to separate, the axial force, which in turn drives the separation of the segments, becomes concentrated on the corners of the segments. With just two segments, the force may be concentrated on just four points. With more force concentrated on each point, the possibility of galling and sticking at a single point, with a resulting failure to release the restrained member, is enhanced. In addition, the distance  37  that the segments must move is at a maximum. 
     A six piece spool system consists of six spool segments. Thus, the interface surface is broken into six separate pieces. The spool segments must move a distance sufficient to allow for the outer diameter of the expanded portion of the restrained member to pass through the bore in the axial direction. As the segments begin to separate, the axial force, which in turn drives the separation of the segments, will be spread across the segments. The distance that the segments must travel in order to allow the passage of the expanded portion of the restrained member is significantly less than with a two segment spool. The differential offset between the diameter of the segment bore and the diameter of the expanded portion of the restrained member in the multi-piece spool system is significantly smaller than the differential offset in the two piece spool system. This gives the multi-piece spool the distinct advantage of requiring less radial travel distance for each segment in order to release the captured member. The use of a full circumferential spool reduces the contact forces in the interface area of the spool segments and the expanded portion of the restrained member. 
     A tensioned tape  12  is wrapped around the external periphery of the spool  11 . The tape  12  is adapted to constrain the segment  50  of the spool  11  together. A first end of the tape  12  may be removably fastened to one of the segments  50  of the spool  11 . The fastening of the tape  12  to one of the segments provides tangential restraint such that the tape may be wound under tension around the outer periphery of the spool, and also will prevent the slipping of the tape around the spool once this tension has been placed in the tape. In some embodiments, the tape  12  may be a spring tempered stainless steel which is 0.2 inches wide and 0.005 inches thick. Once wound under tension, the second end  13  of the tape  12  may be secured under tension by a fuse wire locking device  14  or other restraint and release system. 
     Securing the second end  13  of the tape may be done to the tape itself or to an external support, not shown in this embodiment. Segments  50  of spool  11  may be prevented from rotation by use of anti-rotation pins between each segment, or by other means. 
     In some embodiments, the tape  12  is wound with its successive layers over each other in plane. This allows for a much more compact overall design, in the direction of the axis of the spool, of the release device compared to previous designs. Thus, the height of the housing  16  may be kept to a minimum.  FIG. 1C  illustrates the release apparatus with the tape  12  in relaxed, unwound position. This position is reached after the release of the second end  13  of the tape  12 . Typically, the captured member  15  is under tension axially. Thus, with the release of the second end  13  of the tape  12  and the removal of the constraint on outward motion of the spool segments, the axial pull by the captured member forces the segments of the spool outward in a radial direction. The tape  12  has released and unwound in an orderly fashion, and has remained in plane. The segments of the spool  11  are seen in a position further from the center axis of the constrained spool. 
     Another advantage of the overlaying tape is that the tape layers have friction between them, and thus the tension on the tape is reduced in the radially outward direction with each successive wrap. The tension, therefore, on the release mechanism may be significantly lower than the tension at the center of the tape. Thus, a release device, such as a fuse, with a low load capability may be used to release the tape. 
       FIG. 2  illustrates a redundant release apparatus in the stowed position, and  FIG. 3  illustrates a redundant release apparatus is a deployed position, according to some embodiments of the present invention. A redundant release apparatus  100  may control the deployment of a selected device by releasing a captured member  101 . A multi-piece split spool  102  consists of six segments  105  which define a central bore  103 . The central bore  103  is sized such that the expanded portion  104  of the captured member  101  is constrained from downward axial motion by the interface portion of the segments  105  of the spool  102 . 
     The segments  105  of the spool  102  are constrained from motion in the external radial direction by a wound upper restraining tape  111  and a wound lower restraining tape  110 . A first end of the tapes  110 ,  111  may be constrained from motion along the exterior of the spool by attachment to one of the segments of the spool. A second end of the tapes  110 ,  111  may be constrained by a fuse wire release device  112  or other means. As seen in  FIG. 4A , the segments  105  of the spool  102  may have openings  115 ,  116  in the upper and lower ends of the spool. The openings are adapted to allow for easier opening of the spool from either the top or the bottom, as when one of the tapes is released. 
     The apparatus housing may include a wall  123  adapted to separate the spool and tapes from the electrical interface portion of the system. The housing may have a circular inner profile adapted to reduce the likelihood that the tapes, as they unwind and expand radially during the release cycle, will hang up on any inner surfaces. Vertical members may be in place to further separate the inner compartment. 
     The spool segments  105  are adapted to reside upon a central support  113  which is attached to or integral with the base  120  of the housing  121  of the apparatus. The spool segments  105  are further adapted to allow for a variety of release modes. In a first release mode, the upper restraining tape  111  is released, resulting in a spreading of the upper portion of the spool  102 , as seen in  FIGS. 3 and 4B . In this first release mode, the segments  105  spread at their upper end in conjunction with the release of the upper restraining tape  111 . Although not constrained to a single type of motion, the segments  105  predominantly pivot off the top  114  of the central support in this release mode. The expanded portion  104  of the restrained member  101  provides radial force upon the spool segments  105 , allowing for the release of the restrained member. The release of the upper restraining tape  111  may be a selected mode of release in some embodiments. 
     In a second release mode, as seen in  FIG. 5 , the lower restraining tape  110  is released, resulting in a spreading of the lower portion of the spool  102 . In this second release mode, the segments  105  spread at their lower end in conjunction with the release of the lower restraining tape  110 . The bottom portions of the spool segments predominantly slide along their bottom surface  122  along the inclined top  114  of the central support  113 , although pivoting may also be involved. 
     In a third release mode, as seen in  FIG. 6 , both the upper restraining tape  111  and the lower restraining tape  110  may be released allowing for a spreading of both the lower portion and the upper portion of the spool. In this mode, the spool segments may pivot or slide, or a combination of the two, as the expanded portion of the restrained member forces the segments outward due to the tension in the member. 
       FIGS. 7A-B  illustrate the third release mode in a top view both prior to release and after release. The redundant release apparatus  100  is seen with an first internal cavity  130  adapted to minimize any potential interferences, and potential catch points, for the restraining tapes as they are released and expand radially, allowing the segments  105  of the spool  102  to expand. A first end of the restraining tapes may be captured within one of the spool segments  132 , which may have a slot or other means adapted to capture the end of the tape. 
     A second internal cavity  134  allows for the placement of a release device  135 . The release device  135  may be an electrically actuated fuse wire release device in some embodiments.  FIGS. 8A-C  and  9 A-B illustrate alternate configurations of the release device and fuse wire according to some embodiments of the present invention. As seen in  FIGS. 8A-C , a first fuse link  150  may be attached to the upper restraining tape, and a second fuse link  151  may be attached to the lower restraining tape. This configuration allows for the release of one or both of the restraining tapes as part of the initial release. The mechanical redundancy of the spool release modes allows for the failure of one of the fuse links while still achieving release. 
     As seen in  FIGS. 9A-B , a first fuse link  155  may be attached to both the upper and lower restraining tapes, and a second fuse link  156  may be similarly attached. This configuration allows for the release of both of the restraining tapes as part of the initial release. A failure of one of the fuse links thus does not preclude release of both the upper and lower restraining tapes. 
       FIGS. 10A ,  10 B,  11 A, and  11 B illustrate a release device  200  according to some embodiments of the present invention. A tape release lever  201  is mounted within the housing and rotates around a hinged joint  202 , which may be pinned. A first end  203  of the tape release lever  201  includes tabs  204  adapted to hold the wound tapes  205 ,  206  under tension. The tabs  204  may be inserted into a hole in the tapes. The tape release lever  201  is adapted to hold the tapes using the tab when the lever is in a first position, and to release the tape as the lever rotates to a second position. A second end  207  of the tape release lever  201  is adapted to be constrained by a fuse wire release system  208  or other similar device. An example of such a device is seen in U.S. Pat. No. 6,133,818, to Hsieh et al. The second end  207  of the tape release lever  201  may be significantly longer than the first end  203  to allow for the tension of the tape to be held with a lower force due to the longer lever arm of the second end  207 . 
     In practice, the tapes may be placed under tension by winding the tapes around the spool with the bore in a horizontal position and the tapes extended and under load. In some embodiments of the present invention, as seen in FIG.  11 A, a feature may be added to prevent rotation of the spool segments while under the torsional load that may be placed upon them by the wound tapes. The spool  220  is seen made up of six segments in this embodiment. Anti-rotational pins  221  are located between the segments and are affixed to the base plate of the apparatus. The pins  221  are adapted to prevent rotation of the segments yet do not interfere with the motion of the segments upon their release. 
     The tapes may be anchored on a first end in a slot  222  in a spool segment adapted to receive the tape. The second end of the tape may anchored to a fuse link, release lever, or other means for release. 
     As evident from the above description, a wide variety of embodiments may be configured from the description given herein and additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant&#39;s general invention.