Abstract:
A release device having a multi-segment split spool with a central bore adapted to axially restrain a tensioned member. A tensioned tape is overlappingly wound around the spool segments thereby preventing radial movement of the spool segments. The overlapping winding allows for a low profile housing for the release device. 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 release device 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. 
     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 split spool that minimizes the travel required of a spool element in order to affect a release of the captured member. 
     SUMMARY 
     A release device having a multi-segment split spool with a central bore adapted to axially restrain a tensioned member. A tensioned tape is overlappingly wound around the spool segments thereby preventing radial movement of the spool segments. The overlapping winding allows for a low profile housing for the release device. Overlapping design of flat tape provides predictable unwinding dynamics upon release. 
     The multiple segments require less radial motion for release of the tensioned member. Further, multiple segments spool reduces the potential of “Friction lock up” due to smaller contact angle between each segment with the captured member (almost 90 for 4-segment, almost 60 for a 6-segment, and almost 45 for a 8-segment spool). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of portions of a release device according to some embodiments of the present invention. 
         FIG. 1B  is a cutaway side view of a release device according to some embodiments of the present invention. 
         FIG. 2  is a perspective view of portions of a release device according to some embodiments of the present invention. 
         FIGS. 3A-B  are views of a two piece spool. 
         FIGS. 4A-B  are views of a six piece spool according to some embodiments of the present invention. 
         FIG. 5A  is a top view of portions of a release device according to some embodiments of the present invention. 
         FIG. 5B  is a cutaway view of portions of a release device according to some embodiments of the present invention. 
         FIG. 6  is a top view of portions of a release device according to some embodiments of the present invention. 
         FIGS. 7A-B  are a partial top view layout and cross-section of a release device illustrating anti-rotation pins according to some embodiments of the present invention. 
         FIG. 8  is a cutaway side view showing an inclined sliding surface according to some embodiments of the present invention. 
         FIGS. 9A-B  are cutaway side views showing pivoting bases for the spool segments according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In some embodiments of the present invention, as seen in  FIGS. 1A-B , a release apparatus  10  for controlling the deployment of a desired device by releasing a captured member  15  utilizes 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. 1B , 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. 
     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 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. 2  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 remained in plane and has released and unwound in an orderly fashion. 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. 
       FIGS. 3A-B  and  4 A-B illustrate a contrast between a two segment spool system  30  and a multi-piece spool system  40 . The two segment system  30  consists of two segments  31 ,  32  which define a central bore  39 . An interface surface  33  is adapted to interface with the expanded portion of a restrained member and to restrain its axial motion. The restrained member will typically be placed under tension. The tension along the axis of the bore of the spool will result in both axial and radial loading of the spool segments due to the conical profile of the interface surface  33  of the spool segments  31 ,  32 . The radial loading of the spool segments will be initially be countered by the wound tape as described above. Upon release of tension in the tape, there will no longer be a constraint on radial motion of the spool segments other than the friction of the bases of the spool segments against the adjacent surfaces. As will be discussed later, friction between surface  33  and expanded portion of the restrained member (typically a spherical surface) will have an effect on separation of spool segments. 
     The spool segments must move a distance  37  sufficient to allow for the outer diameter  34  of the expanded portion of the restrained member to pass through the bore in the axial direction. As the two segments  31 ,  32  begin to separate, the axial force, which in turn drives the separation of the segments, becomes concentrated on the comers  36  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. 
     Referring now to  FIGS. 4A-B , a six piece spool system  40  consists of six spool segments  41 ,  42 ,  43 ,  44 ,  45 ,  46 . Thus, the interface surface  47  is broken into six separate pieces. The spool segments must move a distance  49  sufficient to allow for the outer diameter  34  of the expanded portion of the restrained member to pass through the bore in the axial direction. As the segments  41 ,  42 ,  43 ,  44 ,  45 ,  46  begin to separate, the axial force, which in turn drives the separation of the segments, will be spread across the segments. The distance  49  that the segments  41 ,  42 ,  43 ,  44 ,  45 ,  46  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  51  in between the depth 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  52  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. 
       FIGS. 5A-B  illustrate a release system according to some embodiments of the present invention. A release apparatus  60  may control the deployment of a selected device by releasing a captured member  70 . A multi-piece split spool  67  consists of six segments  74  which define a central bore  75 . The central bore  75  is sized such that the expanded portion  71  of the captured member  70  is constrained from downward axial motion by the interface portion of the segments  74  of the spool  67 . 
     The segments  74  of the spool  67  are constrained from motion in the external radial direction by a wound restraining tape  63 . A first end  65  of the tape  63  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 tape  66  may be constrained by a fuse wire release device  69  or other means. The housing  61  is low profile due to the use of an overlapping tape as the spool restraint. The housing  61  may include a wall  72  adapted to separate the spool and tape from the electrical interface portion  68  of the system. The housing  61  may have a circular inner profile  64  adapted to reduce the likelihood that the tape, as it unwinds and expands radially during the release cycle, will hang up on any inner surfaces. Vertical members  76  may be in place to further separate the inner compartment. 
     The base  62  is of sufficient strength that it may withstand the axial force of the captured member. The base  62  may also provide the sliding surface upon which the spool segments move upon release of the tension in the tape. The base bore  73  is sized such that the expanded portion  71  of the captured member  70  may pass through the base bore upon release. The captured member  70  may be a rod with a threaded interface for connection into a larger system. As seen in  FIG. 5B , the surface  77  upon which the spool segments slide in this embodiment is a flat surface, as are the bottoms of the spool segments. The sliding surface and the bottoms of the spool segments may have different geometries is other embodiments. 
       FIG. 6  illustrates a release device  80  according to some embodiments of the present invention. A tape release lever  82  is mounted within the housing and rotates around a pin  88 . A first end  83  of the tape release lever  82  includes a tab  89  adapted to hold the wound tape  84  under tension. The tab  89  may be inserted into a hole in the tape. The tape release lever  82  is adapted to hold the tape 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  81  of the tape release lever  82  is adapted to be constrained by a fuse wire release system  86 , which may separated from the tape and spool by an interior wall  87 . The second end  81  of the tape release lever  82  may be significantly longer than the first end  83  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  81 . 
     In practice, the tape may be placed under tension by winding the tape around the spool with the bore in a horizontal position and the tape extended and under load. In some embodiments of the present invention, as seen in  FIGS. 7A-B , 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 tape  107 . The spool  100  is seen made up of four segments  101  in this embodiment. Anti-rotational pins  102  are located between the segments  101  and are affixed to the base plate  106  of the apparatus. The pins  102  are adapted to prevent rotation of the segments  101  yet do not interfere with the outward motion of the segments upon their release. 
     The tape may be anchored on a first end in a slot  103  in a spool segment  101  adapted to receive the tape  107 . The second end of the tape may anchored to a fuse link  105 , which may be attached to an insulator which is secured to the base plate of the housing in some embodiments. 
     In some embodiments of the present invention, as seen in  FIG. 8 , the geometry of the bottom of the spool segments, and of the surface upon which they slide during release, are altered in order to facilitate the release. The release apparatus  110  may have a spool whose segments  112  have an inclined bottom surface  111 . An advantage of this inclined surface is that the frictional component along the surface is lower than would be experienced with a perpendicular sliding surface, such as seen in  FIG. 5B . Also, the force  113  in the rod being released has a component along the incline, which facilitates the outward motion of the spool segments necessary for release. 
     In some embodiments of the present invention, as seen in  FIGS. 9A and 9B , another geometry of the bottom of the spool segments is used. As seen, the release apparatus  120  uses a pivoting motion as opposed to a sliding motion. The spool segments  121  may have a rounded bottom  122  which is adapted to pivot within a slot  123  upon release of the tension device constraining the spool. In some embodiments, the bottom of the spool segments may be circular as viewed from the top, in accord with the external periphery of the segments in the are where the tension device is wound. In some embodiments, the bottom of the spool segments may be linear, such that the pivot lies in a linear slot. In some embodiments, the spool segments may come to a rounded point. 
     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.