Abstract:
Embodiments described herein provide a highly reliable UUV recovery systems and methods that utilize multiple independent release mechanisms that can detach a load and allow the UUV to float to the surface of the water. One embodiment is a recovery system for a UUV. The recovery system includes a detachable load that renders the UUV neutrally buoyant in water. The recovery system further includes a plurality of release mechanisms that detach the load to render the UUV positively buoyant in the water. The release mechanisms include a first, second, and third release mechanism. The first release mechanism detaches the load in response to a command signal. The second release mechanism detaches the load in response to the UUV being submerged in the water beyond a threshold time. The third release mechanism detaches the load in response to the UUV exceeding a maximum depth in the water.

Description:
FIELD 
     This disclosure relates to the field of recovery of Unmanned Underwater Vehicles (UUVs). 
     BACKGROUND 
     UUVs may be irretrievably lost during underwater operation and be unable to return to the surface for a number of reasons. The UUV may inadvertently travel below a design depth, may be caught by debris or mud, may lose power and be unable to return to the surface, etc. By design, UUVs are often neutrally buoyant, which may require the UUV to utilize a propulsion system to return to the surface. However, propulsion may not be available when power is lost or the UUV incurs software and/or computer failures. The result is that the UUV may drift under water, making recovery nearly impossible. 
     SUMMARY 
     Embodiments described herein provide UUV recovery systems and methods that utilize multiple independent release mechanisms that can detach a load and allow the UUV to float to the surface of the water. The independent release mechanisms are each capable of releasing the load from the UUV utilizing different release criteria, thereby rendering the UUV positively buoyant when various conditions are met. 
     One embodiment is a recovery system for a UUV. The recovery system includes a detachable load that renders the UUV neutrally buoyant in water. The recovery system further includes a plurality of release mechanisms that are configured to detach the load to render the UUV positively buoyant in the water. The release mechanisms include a first, second, and third release mechanism. The first release mechanism is configured to detach the load in response to a command signal. The second release mechanism is configured to detach the load in response to the UUV being submerged in the water beyond a threshold time. The third release mechanism is configured to detach the load in response to the UUV exceeding a maximum depth in the water. 
     Another embodiment is a recovery system for a UUV. The recovery system includes a detachable load, a first release mechanism, a second release mechanism, and a third release mechanism. The load is configured to render the UUV positively buoyant in water upon release. The first release mechanism is configured to detach the load in response to a command signal. The second release mechanism is configured to detach the load in response to the UUV being submerged in the water beyond a threshold time. The third release mechanism is configured to detach the load in response to the UUV exceeding a maximum depth in the water. 
     Another embodiment is a method for operating a recovery system for an Unmanned Underwater Vehicle (UUV). The method comprises affixing a detachable load that renders the UUV neutrally buoyant in water. The method further comprises detaching the load in response to a command signal to render the UUV positively buoyant in the water. The method further comprises detaching the load in response to the UUV being submerged in the water beyond a threshold time to render the UUV positively buoyant in the water. The method further comprises detaching the load in response to the UUV exceeding a maximum depth in the water to render the UUV positively buoyant in the water. 
     The above summary provides a basic understanding of some aspects of the specification. This summary is not an extensive overview of the specification. It is intended to neither identify key or critical elements of the specification nor delineate any scope of the particular embodiments of the specification, or any scope of the claims. Its sole purpose is to present some concepts of the specification in a simplified form as a prelude to the more detailed description that is presented later. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings 
         FIG. 1  illustrates a vehicle that utilizes a recovery system in an exemplary embodiment. 
         FIG. 2  is a block diagram of a recovery system for the vehicle of  FIG. 1  in an exemplary embodiment. 
         FIG. 3  is an isometric view of another recovery system for the vehicle of  FIG. 1  in an exemplary embodiment. 
         FIG. 4  is an isometric view of a plurality of release mechanisms for the recovery system of  FIG. 3  in an exemplary embodiment. 
         FIG. 5  is an isometric view of a cable and disk assembly for the recovery system of  FIG. 3  in an exemplary embodiment. 
         FIGS. 6-8  illustrate a release scenario for detaching a load in an exemplary embodiment. 
         FIG. 9  is a flow chart of a method of operating the recovery systems of  FIGS. 2-3  in an exemplary embodiment. 
     
    
    
     DESCRIPTION 
     The figures and the following description illustrate specific exemplary embodiments. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the embodiments and are included within the scope of the embodiments. Furthermore, any examples described herein are intended to aid in understanding the principles of the embodiments, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the inventive concept(s) is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 1  illustrates a submersible vehicle  100  that utilizes a recovery system in an exemplary embodiment. In this embodiment, vehicle  100  is depicted as an Unmanned Underwater Vehicle (UUV), although in other embodiments, vehicle  100  may be any type of vehicle that is able to submerge under water and utilize a recovery system to ensure that vehicle  100  may be recovered at the surface when various recovery criteria are met. For instance, vehicle  100  may inadvertently dive past a pre-determined depth, which triggers the recovery system to return vehicle  100  to the surface. Vehicle  100  may exceed a pre-determined amount of time under water, which triggers the recovery system to return vehicle  100  to the surface. Vehicle  100 , or some other entity, may generate a command signal which triggers the recovery system to return vehicle  100  to the surface. 
       FIG. 2  is a block diagram of a recovery system  200  for vehicle  100  of  FIG. 1  in an exemplary embodiment. In this embodiment, recovery system  200  includes a plurality of release mechanisms  202 - 204  that are mechanically coupled to a detachable load  206 . Load  206  may include a portion of vehicle  100  and/or a drop weight that is able to be detached from vehicle  100  in some embodiments. In this embodiment, load  206  renders vehicle  100  substantially neutrally buoyant in water, and renders vehicle  100  positively buoyant in water when load  206  is released from vehicle  100 . When load  206  is released, vehicle  100  is able to float to the surface of the water and be recovered. 
     Release mechanisms  202 - 204  operate substantially independently to ensure that load  206  is detached from vehicle  100  when certain conditions are met. This ensures vehicle  100  may be recovered. Release mechanism  202  in this embodiment comprises any component, system, or device that is able to detach load  206  in response to a command signal. The command signal may be generated by vehicle  100  and/or by another entity, such as a support vessel. For instance, vehicle  100  may generate a command signal to detach load  206  if vehicle  100  becomes stuck and is unable to surface (e.g., stuck in mud, ensnared in fishing gear, etc.). 
     Release mechanism  203  in this embodiment comprises any component, system, or device that is able to detach load  206  in response to vehicle  100  being submerged in the water beyond a pre-determined time. For instance, if vehicle  100  loses power and drifts under water beyond a pre-determined amount time, then release mechanism  203  acts to detach load  206  and cause vehicle  100  to float to the surface of the water. 
     Release mechanism  204  in this embodiment comprises any component, system, or device that is able to detach load  206  in response to vehicle  100  exceeding a maximum depth in the water. For instance, if vehicle  100  loses power or becomes negatively buoyant, then vehicle  100  may sink below a pre-determined depth in the water. In this case, release mechanism  204  acts to detach load  206  and cause vehicle  100  to float to the surface of the water. 
     Because release mechanisms  202 - 204  act substantially independently of each other to detach load  206  and render vehicle  100  positively buoyant, vehicle  100  is more likely to be recovered on the surface of the water in response to a variety of possible failures that may otherwise cause vehicle  100  to be lost. 
       FIG. 3  is an isometric view of another recovery system  300  for vehicle  100  in an exemplary embodiment. In this embodiment, recovery system  300  includes a plurality of release mechanisms (not visible in this view) which are surrounded by a housing  306 . Housing  306  of recovery system  300  is fixed to a shell  304 , which surrounds a detachable load  302 . In this embodiment, load  302  is a drop weight, although in other embodiments load  302  may include portion(s) of vehicle  100 . For instance, load  302  may be an instrument package for vehicle  100 , may be external lights for vehicle  100 , etc. Thus, it is not intended that load  302  in this embodiment be limited to only drop weights. 
     In this embodiment, load  302  is able to slide within shell  304  and detach from recovery system  300  when certain conditions are met. While load  302  remains connected to recovery system  300  (which is part of or is mounted to vehicle  100 ), vehicle  100  is approximately neutrally buoyant. This allows vehicle  100  to operate under water without incurring a buoyancy penalty (e.g., either positively or negatively) when utilizing recovery system  300 . However, when load  302  is dropped, released, detached, etcetera, from recovery system  300  (and consequentially also from vehicle  100 ), vehicle  100  becomes positively buoyant. With positive buoyancy, vehicle  100  floats to the surface of the water, which allows for the recovery of vehicle  100 . 
       FIG. 4  is an isometric view of release mechanisms  402 - 404  for recovery system  300  of  FIG. 3  in an exemplary embodiment. In this view, housing  306  (see  FIG. 3 ) has been removed to allow for the visibility of release mechanisms  402 - 404 . In this embodiment each of release mechanisms  402 - 404  are capable of operating independently to detach load  302  from recovery system  300 . Release mechanisms  402 - 404  are detachably coupled to a disk  405 , which is mounted to load  302 . However, in other embodiments, release mechanisms  402 - 404  may be detachably coupled to load  302  in any number of ways as a matter of design choice. Further, although disk  405  is depicted as substantially round, disk  405  may include other shapes as well. For instance, disk  405  may oblong, rectangular, triangular, etc. Disk  405  may be referred to as a weigh distribution plate in some embodiments. 
     Release mechanism  402  in this embodiment is an active release, and is able to detach load  302  from recovery system  300  in response to receiving a command signal. For instance, vehicle  100  may generate a command signal to detach load  302  from recovery system  300 . Release mechanism  402  includes a pair of redundant actuator coils  414  which are used to release load  302 , although in other embodiments only one coil  414  may be used. Vehicle  100 , or some other entity such as a ship or an operator, may generate the command signal to release load  302  in cases where vehicle  100  is unable to return to the surface. For example, if a propulsion system for vehicle  100  fails, then vehicle  100  may generate the command signal actuating coils  414 . Coils  414  are mechanically coupled to a fixed arm  406  (which may be bonded to housing  306 ) and hold a movable arm  408  in place until coils  414  are actuated. Movable arm  408  is rotatably coupled to fixed arm  406  by a pin  407 . Upon actuation, movable arm  408  rotates out of position along a pin  407  coupled to fixed arm  408 , which causes movable arm  408  to decouple from disk  405  and release load  302  from shell  304 . This imparts positive buoyancy to vehicle  100  and allows vehicle  100  to float to the surface of the water for recovery. 
     Release mechanism  403  in this embodiment is a passive release, and is able to detach load  302  from recovery system  300  in response to how long recovery system (and consequentially vehicle  100 ) is in and/or under the water. Release mechanism  403  may include a breakable link  410 , which corrodes in salt water at a known rate. When link  410  breaks, movable arm  408  rotates with respect to fixed arm  406  (which may be bonded to housing  306 ) along pin  407 , which causes movable arm  408  to decouple from disk  405  and allows load  302  to be released from shell  304 . For example, if vehicle  100  loses power or becomes entangled or trapped under water, link  410  eventually corrodes until link  410  breaks, which detaches load  302  from recovery system  300 . This imparts positive buoyancy to vehicle  100 , which is able to float to the surface and be recovered. 
     Release mechanism  404  in this embodiment is another passive release, and is able to detach load  302  from recovery system  300  in response to recovery system  300  (and consequentially vehicle  100 ), exceeding a maximum depth. Release mechanism  404  may include a burst plug  412  or some other device which actuates in response to a pressure setting. For instance, if vehicle  100  sinks below a pre-determined depth in the water, burst plug  412  ruptures and causes load  302  to be released from recovery system  300 . This imparts positive buoyancy to vehicle  100  and allows vehicle  100  to float to the surface of the water and be recovered. The particulars of how release mechanism  404  may operate will be discussed with respect to  FIG. 5 . 
       FIG. 5  is an isometric view of a cable  502  and disk  405  assembly for the recovery system of  FIG. 3  in an exemplary embodiment. In this view, the relationship between disk  405  and movable arms  408  is more clearly shown. Movable arms  408  include a hooked portion which allows disk  405  to be held or captured in place until any of movable arms  408  rotate out of position. Load  402  in this view is coupled to disk  405  utilizing a linkage and/or cable  502 . This allows load  402  to hang by cable  502  and remain part of recovery system  300  until disk  405  is dropped or titled out of position between movable arms  408 . Although  FIG. 5  illustrates that each of movable arms  408  are located approximately equidistant around disk  405 , other configurations may exist. Referring again to release mechanism  404 , burst plug  412  couples movable arm  408  to fixed arm  406  (which may be bonded to housing  306 ) until burst plug  412  ruptures. In response to burst plug  412  rupturing, movable arm  408  rotates out of position with respect to fixed arm  406  along pin  407 , which causes movable arm  408  to decouple from disk  405  and allows load  302  to be released from shell  304 . 
       FIGS. 6-8  illustrate a release scenario for detaching load  302  in an exemplary embodiment. Although  FIGS. 6-8  illustrate the actuation of release mechanism  403 , which is based on the amount of time vehicle  100  is in and/or under the water, any of the other release mechanisms  404 - 405  may operate in a similar manner to allow disk  405  to rotate out of position and release load  302  from recovery system  300 . 
     In  FIG. 6 , link  410  is illustrated as releasing movable arm  408 , which pivots movable arm  408  toward the left in  FIG. 6  along pin  407 . As movable arm  408  rotates, the capture of disk  405  is lost. Disk  405  begins to tilt, as illustrated in  FIG. 7 . As disk  405  tilts and capture is lost (see  FIG. 8 ), disk  405  becomes unstable and is able to slide out of position between movable arms  408  for each of release mechanisms  402 - 404 . As disk  405  is mechanically coupled to load  302  via cable  502 , load  302  is able to drop away from recovery system  300 , which then imparts positive buoyancy to vehicle  100 . Vehicle  100  is then able to float to the surface of the water for recovery. 
     One advantage of recovery system  300  is that it includes a plurality of independent release mechanisms  402 - 404 , each of which are capable of releasing load  302  and allowing vehicle  100  to float to the surface.  FIG. 9  is a flow chart of a method  900  of operating the recovery system of  FIGS. 2-8  in an exemplary embodiment. The steps of method  900  will be described with respect to recovery system  200 ; although one skilled in the art will understand that method  900  may be performed by other devices or systems not shown. The steps of method  900  are not all inclusive and may include other steps not shown. Further, the steps may be performed in an alternate order. 
     In step  902 , a detachable load (e.g., load  206 ) is affixed to a UUV (e.g., vehicle  100 ). The load may be part of the UUV and/or a drop weight, or some combination thereof. In step  904 , if a command signal has been received, then the load is detached from the UUV in step  910  and the UUV floats to the surface. If a command signal has not been received, then step  906  is performed. In step  906 , if the UUV has been submerged under water beyond a time limit, then the load is detached in step  910  and the UUV floats to the surface. If the UUV has not been submerged beyond the time limit, then step  908  is performed. In step  908 , if the UUV has sunk below a pre-determined depth under the water, then the load is detached in step  910  and the UUV floats to the surface. Each of steps  904 - 908  may be performed nearly simultaneously. If none of the previous conditions for detaching the load occurs, then the load may not be detached from the UUV. 
     Although specific embodiments were described herein, the scope is not limited to those specific embodiments. Rather, the scope is defined by the following claims and any equivalents thereof.