Abstract:
A UAV recovery system is disclosed. In the illustrative embodiment for UAV recovery over water, the system includes ship-based elements and UAV-based elements. The UAV-based elements include a mass, such as ball, that is coupled to cord, which is in turn coupled to the tail of a UAV. The ship-based elements include a capture plate and a boom, wherein the boom is pivotably coupled to the deck of a ship. For use in recovery operations, the boom is rotated so that it extends over the side of the ship. A UAV is flown over the boom toward the capture plate at an altitude such that the mass that is attached to the tail of the UAV hangs lower than the capture plate. With continued forward motion, the cord that hangs from the UAV is captured by a grooves in the capture plate. The capture plate geometrically constrains the mass, thereby assuring positive capture of the UAV.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001]     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. N00014-03-C-0408 awarded by the U.S. Government. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to systems for retrieving unmanned aerial vehicles (“UAVs”).  
       BACKGROUND OF THE INVENTION  
       [0003]     The UAV is now widely used for reconnaissance. Characteristically small, inexpensive, and pilot-less (i.e., unmanned cockpit), the UAV is ideal for that purpose.  
         [0004]     Notwithstanding its,low cost, the UAV is not considered to be a disposable asset; recovery is at least attempted after each mission. Recovery is relatively straightforward when the UAV is operating over land. In such situations, the UAV is simply brought down on a makeshift landing field. Recovery is considerably more challenging, however, when the UAV is operating at sea. Due to the constant sway, roll, pitch, and yaw of a ship at sea, it is quite difficult to safely land a UAV on the deck of a ship. In fact, deck landings are rarely attempted.  
         [0005]     One alternative to the deck landing is the water “landing,” wherein a UAV is simply ditched in the sea. This technique has its own drawbacks, including a reasonable likelihood of damage to the UAV and some risk to the recovery crew.  
         [0006]     A second alternative to a deck landing is to capture the UAV while it&#39;s still in flight. U.S. Pat. No. 4,753,400 discloses a ship-mounted apparatus for this purpose. The system disclosed in that patent includes a recovery net that is attached to a parachute. The net is also coupled, via a tow line, to a winch that is located on the deck of a ship. In use, the parachute floats the recovery net to a desired altitude for mid-air capture of the UAV. After capture, the recovery net and ensnared UAV are winched down to the deck.  
         [0007]     The approach that is disclosed in U.S. Pat. No. 4,753,400 is not without drawbacks. In particular, one drawback is that the apparatus disadvantageously requires a substantial amount of deck area. A second drawback is that a relatively labor-intensive untangling operation is required to free the UAV from the net. Furthermore, the relatively abrupt stop of a UAV in the recovery net can damage its fragile wings.  
         [0008]     As a consequence, there is a need for a UAV recovery system that requires little deck space, enables rapid re-use of a UAV after recovery, and is less likely to damage a UAV than traditional recovery techniques.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a recovery system for a UAV. In the illustrative embodiment of the invention, the recovery system is adapted for recovering UAVs over water. In other embodiments, the UAV recovery system can be configured for use on land.  
         [0010]     A UAV recovery system in accordance with the present invention and adapted for recovery over water includes (1) ship-based elements and (2) UAV-based elements.  
         [0011]     The ship-based elements include a capture plate and a boom. In the illustrative embodiment, the boom has two degrees of freedom of movement; it is capable of pivoting or swiveling about a support point (i.e., in the manner of a door) and is also able to rotate about its long axis (i.e., in the manner of a rotisserie). In the illustrative embodiment, the boom is coupled to the deck of a ship. When stowed, the boom overlies the deck of a ship. In some other embodiments, the boom has three degrees of freedom of movement. In such embodiments, in addition to the two degrees mentioned above, the boom is telescoping; that is, it collapses in the manner of an antenna for stowage.  
         [0012]     The capture plate is coupled to the boom. In the illustrative embodiment, the capture plate includes a plurality of closely-spaced “teeth,” like a hair comb. The spaced teeth form a plurality of narrow grooves. The fingers and the grooves are oriented orthogonally to the long axis of the boom (akin to the relative spatial orientation of the “spine” of a hair comb and the teeth that depend from it).  
         [0013]     The individual teeth of the capture plate taper; in particular, they are relatively wider at their base than at their apex. As a consequence, the groove that is formed between adjacent fingers is v-shaped, being widest at its mouth (i.e., near the apex of adjacent fingers) and tapering to a pinch point at the base of the adjacent fingers.  
         [0014]     The UAV-based elements include a mass, such as ball, that is coupled to a cord. The cord, in turn, is coupled to the tail of a UAV. The cord, or, alternatively, a lanyard by which the cord is attached to the UAV, is elastic, resilient, or otherwise shock-absorbing.  
         [0015]     For use in recovery operations, the boom is rotated from its stowed position to an active position in which it extends over the side of the ship. To recover a UAV, the UAV is flown over the boom such that its direction of flight is substantially orthogonal to the boom and facing the mouth of the grooves in the capture plate. The UAV is flown at an altitude such that mass that is attached to the tail of the UAV is lower than the capture plate. With continued forward motion, the cord that hangs from the UAV is captured by one of the grooves in the capture plate. The UAV continues along a substantially level flight path until the mass/cord is seized at the pinch point of the groove. Since the mass is larger than the groove that is formed between adjacent teeth in the capture plate, a “geometrical” lock results, thereby assuring positive capture of the UAV.  
         [0016]     When the mass locks at the pinch point of the groove, the elastic/resilient cord or lanyard is placed in tension and stretched by the continued forward motion of the UAV. Stretching against tension, the cord/lanyard absorbs the energy of the in-flight UAV. Since the cord is attached to the tail of the UAV, the motion of the UAV during deceleration is quasi-linear. When the UAV decelerates to a velocity at which flight can no longer be sustained, it falls, swinging beneath the boom. The cord is appropriately sized to prevent contact between the UAV and the boom and or the UAV and the underlying water.  
         [0017]     The boom is rotated about its long axis to “reel-in” the hanging UAV. After the UAV is reeled in sufficiently to clear the deck, the boom is swiveled back to its original position above the deck of the ship for final retrieval and disengagement of the UAV.  
         [0018]     These and other features of a UAV recovery system in accordance with the illustrative embodiment, and variations thereof, are described further in the Detailed Description below and depicted in the accompanying Drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  depicts a bow-end view of a ship that incorporates elements of a UAV recovery system in accordance with the illustrative embodiment of the present invention.  
         [0020]      FIG. 2  depicts a top view of the ship of  FIG. 1 .  
         [0021]      FIG. 3  depicts further detail of the ship-based elements of a UAV recovery system in accordance with the illustrative embodiment of the present invention.  
         [0022]      FIGS. 4A-4C  depict detail of the UAV-based elements of a UAV recovery system in accordance with the illustrative embodiment of the present invention.  
         [0023]      FIGS. 5A-5C  depict various positions of the boom of the illustrative UAV recovery system.  
         [0024]      FIGS. 6A-6E  depict the manner in which the capture plate snares the cord and mass that hang from the UAV. 
     
    
     DETAILED DESCRIPTION  
       [0025]      FIGS. 1 and 2  depict, via respective bow and top views, ship  100 . Coupled to deck  102  of the ship are ship-based elements  104  of a UAV recovery system in accordance with the illustrative embodiment of the present invention.  
         [0026]      FIGS. 3A through 3C  depict further detail of ship-based elements  104  of the UAV recovery system. Referring now to  FIGS. 3A , ship-based elements  104  include support structure  306 , movable boom  308 , and capture plate  312 , which are mechanically interrelated as shown. In the embodiment depicted in  FIGS. 3A and 3B , support structure  306  comprises base  328  and upright member(s)  330 . In some embodiments, support structure  306  is disposed on an ISO module (not depicted).  
         [0027]     Support structure  306  supports boom  308 . As depicted by the arrows in  FIG. 3B , the boom is supported in such a way that it has two degrees of freedom. In particular, boom  308  is capable of being rotated about its horizontal long axis (the long axis is directed “into the page” in  FIG. 3B ) and it also pivots about a vertical axis that aligns with upright members  330 .  
         [0028]     The rotational and pivoting movement of boom  308  can be actuated by motors or manually, depending upon configuration. For embodiments that utilize manual actuation, to rotate boom  308  about its long axis, a hand crank (not depicted) can be coupled to the end of the boom. To manually pivot boom  308 , force can be applied directly against the side of boom. In embodiments that utilize automatic actuation, motors are appropriately coupled to boom  308  and base  328  (or upright members  330 ). Those skilled in the art will know how to configure support structure  306  and boom  308  for either case. This capability to rotate the boom about these two different axes is described in more detail later in this specification.  
         [0029]     Capture plate  312  is attached to boom  308  and extends to distal end  310  of the boom. In the illustrative embodiment, capture plate  312  is disposed on top of boom  308  (see, e.g.,  FIG. 1 ). In some alternative embodiments (not depicted), capture plate  312  is simply an extension of boom  308 ; that is, capture plate  312  begins where boom  308  ends.  
         [0030]      FIG. 3C  depicts further detail of comb-like capture plate  312 . The capture plate includes a plurality of teeth  316 , which depend from spine region  314 . The teeth are oriented orthogonally to the long axis of spine  314 . Adjacent teeth  316  are spaced apart from one another, such that groove  322  is defined between.  
         [0031]     Teeth  316  are wider at base  318 , where the teeth meet spine  314 , than at apex  320 . As a consequence, groove  322  is v-shaped, tapering inward from a widest point at mouth  326  to pinch point  324 .  
         [0032]     As described in more detail later in this specification, in operation, one of grooves  322  capture a cord that hangs from a UAV. As a consequence, mouth  326  of grooves  322  must be wide enough to readily accept the cord. Since the diameter of the cord will typically be about ⅜ to ½ inch, the mouth will be about ½ to ¾ inch. The edges of teeth  316  should be rounded or smoothed to avoid fraying the cord.  
         [0033]     For use at sea, ship-based elements  104  of the UAV recovery system are advantageously formed from a material(s) that is resistant to corrosion. Furthermore, since most UAVs are relatively lightweight and will have a relatively low net forward velocity at capture (about  20  knots), ship-based elements  104  can be formed from lightweight materials. For example, and without limitation, suitable materials of construction for support and capture elements (e.g., boom  308 , capture plate  312 , etc.) include composite materials and aluminum. It will be clear to those skilled in the art, after reading this specification, which materials are suitable for ship-based elements  104 .  
         [0034]     For most applications, capture plate  312  will be between about twelve to twenty feet in length, although it can be shorter or longer, as is appropriate for the size of the UAV and as is appropriate for the size of the ship with which the UAV recovery system is used.  
         [0035]      FIGS. 4A through 4C  depict UAV-based elements  450  of a UAV recovery system in accordance with the illustrative embodiment of the present invention. UAV-based element  450  include lanyard  452 , cord  454 , and mass  456 .  
         [0036]     As depicted in  FIG. 4A , UAV-based elements  450  are coupled to tail  442  of UAV  440 . More particularly, in the illustrative embodiment, lanyard  452  attaches to tail  442 , and cord  454  is attached to lanyard  452 , as depicted in  FIG. 4B . Lanyard  452  is attached to tail  442  near center of gravity axis A-A. In some embodiments, cord  454  is attached directly to tail  442  such that lanyard  452  is not used.  
         [0037]     At least one of either lanyard  452  and cord  454  are elastic, resilient, or otherwise adapted to absorb shock and energy. The reason for this is discussed later in conjunction with  FIGS. 6A through 6E . As an alternative to using a material to provide shock- and energy-absorbing capability, any of a variety of mechanical arrangements can be used to impart this property. For example, in some embodiments, cord  454  is coupled to tail  442  of UAV  440  by a spring or spring-like mechanism.  
         [0038]     With reference now to  FIG. 4C , mass  456 , which in the illustrative embodiment is a sphere, is attached to the free end of cord  454 . The mass functions as a “stop” that prevents a cord that has engaged a groove in capture plate  312  from slipping fully through the groove. To function adequately for this purpose, mass  456  must have a size and shape that ensures that it will not slip through grooves  322 . A semi-rigid sphere having a diameter of about 1 to 1½ inches is suitable for this purpose. Pyramidal-shaped masses, cubic-shaped masses, and other shapes would likewise be suitable.  
         [0039]     In some embodiments, cord  454  and mass  456  remain deployed during UAV operations. This avoids the complications that are typically associated with deployment systems (e.g., tail hook deployment systems, etc.). Since flight operations might be affected by a permanently deployed cord  454  and mass  456 , in some embodiments, the cord and mass are stowed beneath the body of the UAV in semi-coiled form and then released remotely at an appropriate time before a capture attempt.  
         [0040]      FIGS. 5A through 5C  and  6 A through  6 E depict the illustrative UAV recovery system in operation. More particularly,  FIGS. 5A through 5C  depict re-positioning of boom  308  from a stowed position to two different recovery positions.  FIGS. 6A through 6E  depict the approach and airborne capture of a UAV using a UAV recovery system in accordance with the present invention.  
         [0041]     Turning now to  FIG. 5A , ship-based elements  104  of the illustrative UAV recovery system are depicted in a stowed position, wherein boom  308  is positioned above deck  102  (i.e., not over the side of the deck). In preparation for recovery of a UAV, boom  308  is moved from the stowed positioned to a recovery position, such as to the positions depicted in  FIGS. 4B and 4C . Boom  308  can be pivoted manually or via a motorized system.  
         [0042]     In the recovery position that is depicted in  FIG. 5B , axis B-B of boom  308  is substantially orthogonal to the long axis of S-S of ship  100 . Furthermore, flight path C-C of a UAV on approach to the UAV recovery system is substantially parallel to axis S-S of ship  100 .  
         [0043]     In a second recovery position that is depicted in  FIG. 5C , axis A-A of boom  316  is not orthogonal to axis S-S; rather, it positioned at some offset from perpendicular, as measured by angle β. The purpose for orientating boom  308  at an offset, as depicted in  FIG. 5C , is to bring the UAV along flight path D-D that is not parallel to axis S-S of ship  100 . The reason for this is that if control of a UAV is lost on its approach to the ship, there is a reduced likelihood of crashing on the deck if the UAV follows flight path D-D as opposed to flight path C-C. In some embodiments, angle β is 14.1 degrees, which is the approach angle that is used for landing aircraft on aircraft carriers.  
         [0044]     Regarding  FIGS. 6A through 6E , it is to be understood that boom  308  is placed in a desired recovery position (e.g., see  FIGS. 5B and 5C ) to receive UAV  440 . For clarity of illustration, neither support structure  306  nor ship  100  is depicted in  FIGS. 6A-6E .  
         [0045]      FIG. 6A  depicts UAV  440  on approach to boom  308  and capture plate  312 . Mass  456  dangles from cord  454  off the tail of UAV  440 . In some embodiments, UAV  440  is remotely controlled by a pilot that is stationed on the deck of the ship (not depicted). In some other embodiments, UAV  440  is either partially or fully autonomously controlled via various video and electronic systems. For autonomous control, a video camera and a transmitter, which can be mounted on boom  308 , transmit a video signal to a processor that is located aboard ship. In some embodiments, the processor runs automated target recognition and automated target tracking software and receives altimeter information that is transmitted from UAV  440  by way of a transceiver. Additionally, the processor receives data about the ship&#39;s movement (e.g., speed, heading, etc.), such as from an inertial measurement unit (“IMU”) and other data that enables the processor to precisely determine the position (including height) of capture plate  312  and of UAV  440 .  
         [0046]     The transceiver transmits commands that originate from either ( 1 ) the remotely-located pilot or ( 2 ) the processor. Those commands cause UAV  440  to fly towards capture plate  312 . As depicted in  FIG. 6B , cord  454  is snagged within one of grooves  322  of capture plate  312 . Since little drag is associated with the initial capture, UAV  440  continues flying along a substantially level course.  
         [0047]     Referring now to  FIG. 6C , within moments after its initial capture, UAV  440  will have dragged cord  454  through groove  322  to the extent that mass  456 , which is located at the end of the cord, is jammed against the underside of capture plate  312  at the pinch point of the groove. Since mass  456  is too large to fit through groove  322 , and since pinch point  324  resists any further forward motion of the mass or cord  454 , capture plate  312  provides positive capture of UAV  440 .  
         [0048]     After positive capture, UAV  440  continues forward very briefly since cord  454  or lanyard  452  (or both) are elastic/resilient, etc. The cord/lanyard is stretched by the in-flight UAV. Stretching the cord/lanyard absorbs energy from the in-flight UAV, thereby decelerating it. Since cord  454  is attached to the tail of the UAV, the motion of UAV will be quasi linear during deceleration. When the UAV decelerates to the point at which flight cannot be sustained, it begins to fall.  
         [0049]     The allowable deceleration rate is dependent upon the fragility of the payload electronics, the height above water level of the system, and the mass of UAV  440 , among other factors.  
         [0050]     Regarding shock absorption during deceleration, in some embodiments, lanyard  452  is similar to “fall protection” lanyards (stitched strapping). This would absorb the energy of the UAV during deceleration, yet prevent a recoil effect that would be observed when using a bungee cord.  
         [0051]     Due to pendulum/pendular motion of the “mass on cord,” it is possible for mass  456  to wrap around capture plate  312  and then unwrap as the UAV travels past the capture plate. As it unwraps, mass  456  might exit out of the same groove  322  in which it entered. To prevent this from occurring, one or more of the following approaches can be taken: 
        Situate a catch at pinch point  324  or mouth  326  of grooves  322 , wherein the catch seizes cord  454  upon entry into the groove.     Use an appropriate cord length and tooth design such that the worst case “wrap ” prohibits mass  456  from unwrapping out of groove  322  due to a reduced effective cord length (i.e., UAV  440  has traveled forward and the pendulum length of the cord is shortening).     Use four capture plates  312 , which are oriented at 90 degrees with respect to each other about the circumference of boom  308 . This would enable a shorter teeth  316  to be used for the capture plates while increasing the points at which mass  456  will positively engage pinch point  324  of a groove  322 .        
 
         [0055]      FIG. 6D  depicts UAV  440  at rest, hanging from capture plate  312 . Cord  454  is sized so that UAV  440  will not contact the underlying water. Before boom  308  is pivoted back above the deck of the ship, the UAV must be drawn toward the boom (so that it can clear the side of the ship). In the illustrative embodiment, this is done by rotating the boom about its long axis, as depicted in  FIG. 6E . This “reels in” UAV  440 , such that cord  454  raps around capture plate  312 , drawing the UAV toward the boom. Once UAV  440  is drawn sufficiently close to boom  308 , the boom is pivoted back toward the ship so that the UAV is positioned above the deck for final retrieval.  
         [0056]     A particularly advantageous feature of the capture system described herein is the ability for a UAV to maintain a safe altitude above the capture system on approach. The length of cord  454  can be set to accommodate any vertical dither inherent in the UAV&#39;s flight due to general or environmental performance characteristics. For example, if the UAV is known to vary a maximum of five feet in altitude from a desired flight path, then cord  454  is designed to accommodate this. That is, it should be at least about six feet long to ensure that collision with the boom does not occur.  
         [0057]     It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiment of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other methods, materials, components, etc.  
         [0058]     Furthermore, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the illustrative embodiments. It is understood that the various embodiments shown in the Figures are illustrative, and are not necessarily drawn to scale. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the present invention, but not necessarily all embodiments. Consequently, the appearances of the phrase “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout the Specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.