Abstract:
An underwater self adjusting displacement device includes a sealed housing having an exterior wall and an inner component area, the exterior wall having an opening formed therein. A sealing plug is slidably seated in the opening of the exterior wall, and an actuator mechanism selectively adjusts the sealing plug within the opening, thereby adjusting a total displacement of the sealed housing. The displacement device is incorporated into any substantially neutrally buoyant underwater deployable device such as an acoustic countermeasure device or an oceanographic sensor device. Further, the deployable devices may be deployed individually or as a field due. The displacement device requires less weight and weight within an overall deployed device, enabling large deployments and performance enhancements.

Description:
STATEMENT OF GOVERNMENT INTEREST  
       [0001] The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     
    
     
       CROSS REFERENCE TO OTHER PATENT APPLICATIONS  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    (1) Field of the Invention  
           [0004]    This invention generally relates to a self adjusting neutral buoyancy countermeasure and system for underwater devices.  
           [0005]    More particularly, the invention relates to a self adjusting neutral buoyancy mechanism which effects slight changes in an overall displacement of an underwater body, and thereby adjusts a buoyancy force of the body.  
           [0006]    (2) Description of the Prior Art  
           [0007]    The current art for devices required to maintain certain depths is known. These include military devices such as torpedo countermeasures and oceanographic survey devices. Acoustic countermeasures are particularly utilized to confuse hostile sonar systems and protect existing force assets. Typical countermeasures are launched from a submarine platform and use an active system to traverse to a predetermined depth, maintain a hovering depth, and begin operation. The known military devices utilize a propeller system or a variable pressure gasbag system to maintain a predetermined depth; however, these systems require active manipulation to maintain their position. In general the devices themselves are slightly negatively buoyant, thus requiring a means of providing additional upward force to maintain depth and prevent the device from free-falling to the ocean bottom.  
           [0008]    A propeller system for an acoustic countermeasure device  10  is shown by way of example in FIG. 1. In the case of FIG. 1, constant power is used to maintain the thrust that holds the device  10  at a predetermined depth D. The device  10  is comprised of a body tube  12  which houses power and electronics, a transducer section  14  which produces the acoustic power, and a hovering system  16  which provides thrust and keeps the device at the prescribed depth D in the underwater environment  18 . Thus, a problem exists in the art whereby the space and energy requirements for deploying and maintaining depth of one or more underwater devices, such as an acoustic countermeasure device, should be minimized.  
           [0009]    This invention describes a countermeasure as a single device and as a system which encompasses the traditional acoustic traits of countermeasures along with a novel hovering system and the use of multiple numbers of these countermeasure devices simultaneously. The invention disclosed here is designed to work on a body that is essentially neutrally buoyant by design, and requires only slight changes to effect depth control. Further, the invention herein utilizes a more passive device for maintaining a predetermined depth which takes less volume, weight and power than traditional methods. The savings in weight, volume and power should allow for a device design that is essentially neutrally buoyant on its own, thus requiring only small changes in buoyancy to effect depth change.  
           [0010]    The following patents, for example, disclose various types of depth adjusting devices, but do not disclose a novel hovering mechanism allowing a submerged device to adjust and to maintain a desired depth as does the present invention.  
           [0011]    U.S. Pat. No. 2,790,186 to Carapellotti;  
           [0012]    U.S. Pat. No. 4,286,539 to Pignone; and  
           [0013]    U.S. Pat. No. 4,364,325 to Bowditch.  
           [0014]    Specifically, Carapellotti discloses a buoy having an upper enclosed chamber housing a weight therein and a lower chamber joined to the upper chamber. The lower chamber has an open end remote from the upper chamber and a weight therein adapted to pass through the opening. A first removable closure member and a second closure member are provided for the opening, the second closure member being disposed in the lower chamber above the weight. Flexible means connect the weight and the second closure member, and orifices are provided in the lower chamber near the top thereof. When the first closure member is removed from the opening and the buoy is floated, the weight will pass through the opening and be suspended beneath the buoy by the flexible means, the second closure member will lodge on and seal the opening, and the lower chamber will become substantially filled with water.  
           [0015]    The patent to Pignone discloses a dual buoyancy device having two external dimensions, in the smaller of which, one end is closed by an elastic sheet undistended, and in the greater of which the sheet is distended from its normal position thereby increasing the external dimension of the device. The distention of the sheet is accomplished by a thruster member bearing on the sheet which thruster is impelled by a weight and lever system actuated by gravity, which causes the thruster to distend the sheet. When the sheet is distended, the overall volume increases causing the device to float. When the sheet is undistended, the overall volume decreases causing the device to sink. Distension of the sheet via the thruster only occurs when the device is inverted. Still further, there is no neutral buoyancy capability. The device either sinks or floats.  
           [0016]    Bowditch discloses a passive near neutral buoyancy platform including a structure housing a series of gas-filled cells, restrained in their maximum volume regardless of the internal charge pressure, and collapsible in character when external pressure exceeds the charge pressure. With this structure, once a cell having a predetermined initial internal charge pressure reaches a depth where the external pressure exceeds this initial value, that cell contracts, resulting in a net buoyancy change for the structure. Where this series of cells is attached integrally to a single structure, the cells form a pre-loaded compressibility compensation device matched to the external environment.  
           [0017]    It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a displacement mechanism for an underwater body in which the displacement mechanism changes the total displacement of the body and thereby a adjusts a buoyancy force of the body. This is done in the present invention on a substantially neutrally buoyant device and without the use of a known propeller system or a variable pressure gas bag system.  
         SUMMARY OF THE INVENTION  
         [0018]    Therefore it is an object of this invention to provide a self adjusting neutral buoyancy device.  
           [0019]    Another object of this invention is to provide a self adjusting neutral buoyancy device deployed as a system of devices.  
           [0020]    Still another object of this invention is to provide a self adjusting neutral buoyancy device having a mechanism for changing a sealed volume of the device and thereby adjusting a depth at which neutral buoyancy occurs.  
           [0021]    A still further object of the invention is to provide a self adjusting neutral buoyancy device which may be incorporated into any underwater neutrally buoyant device.  
           [0022]    Yet another object of this invention is to provide a self adjusting neutral buoyancy device which is less costly and requires less space than known devices.  
           [0023]    In accordance with one aspect of this invention, there is provided an underwater self adjusting displacement device including a sealed housing having an exterior wall and an inner component area, the exterior wall having an opening formed therein. A sealing plug is slidably seated in the opening of the exterior wall, and an actuator mechanism selectively adjusts the sealing plug within the opening, thereby adjusting a total displacement of the sealed housing. The displacement device is incorporated into any substantially neutrally buoyant underwater deployable device such as an acoustic countermeasure device or an oceanographic sensor device. Further, the deployable devices may be deployed individually or as a field. The displacement device requires less weight and weight within an overall deployed device, enabling large deployments and performance enhancements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which:  
         [0025]    [0025]FIG. 1 is a side view of an underwater acoustic countermeasure device according to the Prior Art;  
         [0026]    [0026]FIG. 2 is a side sectional view of a buoyancy displacement device according to a preferred embodiment of the present invention;  
         [0027]    [0027]FIG. 3 is a side sectional view of a buoyancy displacement device according to a further preferred embodiment of the present invention;  
         [0028]    [0028]FIG. 4 is a side sectional view of a generic underwater device for use with the preferred embodiments of the present invention;  
         [0029]    [0029]FIG. 5 is a side sectional view of an acoustic countermeasure device for use with the preferred embodiments of the present invention; and  
         [0030]    [0030]FIG. 6 is a side view of a field of countermeasure devices deployed simultaneously according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    In general, the present invention is directed to a mechanism which allows for a submerged device to adjust and maintain a certain depth. Examples of devices which are required to remain submerged at specific depths include military devices such as torpedo countermeasures and oceanographic devices which float submerged for long periods of time and map ocean currents. This invention accomplishes a volumetric displacement change in a submerged body which can alter and maintain floating at a certain depth.  
         [0032]    The invention is a mechanism to adjust and maintain depth for a submerged underwater device. It is designed to operate on a device which is essentially neutrally buoyant and requires only slight changes in its displacement/buoyancy to effect depth control. The variable density of seawater due to pressure as depth increases allows for bodies to float at a constant depth beneath the surface. Slight changes in the body&#39;s overall displacement can affect its buoyancy, and thereby its depth. This mechanism allows for changing the total displacement of a body and thereby an adjustment in buoyancy force.  
         [0033]    Turning now to FIG. 2, a first preferred embodiment of a displacement device  20  is shown. It will be understood from the following that the described displacement device  20  is applicable to a number of end uses such as the acoustic countermeasure device or oceanographic devices which float submerged for long periods of time and map ocean currents. These end uses are mentioned by way of example only and are not intended to limit the end uses of the present invention.  
         [0034]    The displacement device  20  includes a shell or body portion  22 , the body portion  22  being closed and sealed to provide a displacement of seawater and resulting buoyancy force. The body portion  22  has an outer surface  24  in contact with the sea water, and an inner wall surface  25  defining an inner chamber  26  for housing components of the displacement device  20 . An opening  28  is formed through the body portion  22 , the opening being defined by an inner wall surface  30 . A displacement mechanism  32  is provided in connection with and sealed against the opening  28  of the body portion  22 . The displacement mechanism  32  is sealed with the opening  28  so as to preserve the watertight integrity of the displacement device  20  as will be further described in the following.  
         [0035]    The displacement mechanism  32  particularly includes a plug member  34  having an outer peripheral shape corresponding to the shape of the inner wall surface  30 . The plug member  34  is sealed against the wall surface  30  with an O-ring seal  36  therearound. This seal  36  slides with the plug  34  to create a change in the overall displacement of the underwater device  20 .  
         [0036]    This sliding motion of the plug  34  and seal  36  is created by a linear actuator  38  mounted to the inner surface  25  of the body portion  22  by a bracket  40  and bolts  42 . An actuator shaft  44  is interconnected between the actuator  38  and the plug  34  and allows for controllable motion to be imparted from the actuator  38  to the plug  34 . The bracket  40  is shown as having a flange  40   b  extending radially from a central shaft type housing  40   a . The flange  40   b  is flush with the inner surface  25  of the body  22  adjacent the opening  28 . Although the bracket  40  having the housing  40   a  and flange  40   b  is illustrated, it should be appreciated that the bracket  40  may be of any suitable shape and attached in any known manner to the inner surface  25  of the body portion  22  of the device. Further, although the displacement device  20  is shown to utilize cylindrical parts for the plug  34  and the opening  28 , these shapes are not intended to limit the invention.  
         [0037]    Turning now to FIG. 3, an alternative displacement mechanism  46  is shown as another preferred embodiment. Like reference numbers refer to like parts throughout this specification. Accordingly, the body portion  22  having an opening  28  with an inner wall surface  30  formed therein remains the same as in FIG. 2. A displacement plug  48  is located concentrically within the opening  28  of the body  22  and includes an O-ring seal  50  formed therearound. The displacement plug  48  is formed to include an opening  52  on an inner surface thereof, the opening terminating in a cavity  54  within the plug  48  as shown.  
         [0038]    The displacement plug  48  along with its seal  50  slides within the wall surface  30  of the body portion  22  to create a change in the overall displacement of the underwater device  20 . This sliding motion of the plug  48  and seal  50  is created by a motor  56 , a drive gear  58 , and a power screw  60  engaged with drive gear  58 . The motor  56  is connected to the drive gear  58  with an intermediary shaft  62 . The power screw  60  includes an elongated shaft portion  60   a  having gear threads  60   b  at one end thereof and a plate  60   c  attached to the other end thereof. The plate portion  60   c  is seated within the cavity  54  of the displacement plug  48  such that the displacement plug  48  moves in response to movement of the plate portion  60   c . Rotation of the drive gear  58  translates to linear movement of the power screw  60  by engagement of the drive gear  58  with the threads  60   b  of the power screw  60 . Power screw  60  and plate portion  60   c  can rotate when moved by drive gear  58  without requiring rotation of plug  48  and seal  50 . These incremental linear movements of the power screw  60  generate a corresponding motion of the plug  48  and seal  50 . Other means of achieving the translation of the seal plug  48 , such as by use of a worm gear and rack or the like, may be affected by one of ordinary skill in the art and is intended to be included within the scope of the invention.  
         [0039]    Similar to the embodiment of FIG. 2, the assembly is fixed to the inner surface of the body  22  with a bracket  64 ,  66  and bolts  68 . The bracket assembly includes a substantially vertical bracket portion  64  and a substantially horizontal bracket portion  66 . The vertical bracket portion  64  supports the motor  56  of the displacement mechanism and the horizontal bracket portion  66  is flush with the inner surface  25  of the body for mounting thereto with the bolts  68 . At least a portion of the horizontal bracket  66  extends as an inner flange  66   a  to cover the opening  28  of the body portion  22 , such that the power screw  60  fits through an opening  66   c  thereof as shown. An outer flange portion  66   b  of the horizontal bracket  66  is used to attach the bracket to the inner surface  25  of the shell  22 .  
         [0040]    Adjustments of the plug  48  position in the opening  28  of the shell  22  changes the overall buoyancy of the device  20  since the displacement changes while the overall weight of the device remains constant.  
         [0041]    With the invention as described in FIGS. 2 and 3, there is achieved a controllable change in depth for an underwater floating device  20  through a small change in buoyancy. This is done in a manner to only consume very small quantities of energy to effect the change. Also, once the depth is attained, no further changes to the system are required to maintain near term depth and the system becomes truly passive. For extended time durations, movement of the device to water of different temperature or salinity may require further active adjustments.  
         [0042]    Referring now to FIG. 4, there is shown a generic underwater device  70  having a shell type body portion  72  as described in connection with FIGS. 2 and 3. The body portion  72  is assumed to be closed and sealed, providing a displacement of seawater and resulting buoyancy force. Positioned within the device  70  is a displacement mechanism  74  such as that described in connection with either of FIG. 2 or  3 . The displacement mechanism  74  is sealed against the shell  72  to preserve watertight integrity. Also located within the shell body  72  are a pressure sensor  76 , a salinity meter  78 , and a controller  80 . Other instrumentation such as accelerometers or motion detectors can also be provided and joined to controller  80 . By using the inputs of the pressure sensor  76  as a measure of depth and the salinity meter  78  as a measure of salt content (which affects buoyancy) the controller  80  can monitor the environmental variables and adjust the system through a commanded position for the displacement mechanism  74 .  
         [0043]    The displacement mechanism  74  functions in the same manner as described in either of FIG. 2 or  3 . The system  70  utilizes commercial components for depth pressure sensing and salinity measurements. A control algorithm developed to relate pressure, salinity, and position control of the displacement mechanism in order to achieve and maintain a prescribed depth can be implemented using a relatively simple control circuit. Power can be supplied through a battery, and likely would be supplied by whatever power source is energizing the device&#39;s other functions.  
         [0044]    Referring next to FIG. 5, there is illustrated an acoustic countermeasure device  82  utilizing a displacement mechanism  84  according to the present invention as described in either of FIG. 2 or  3 .  
         [0045]    The acoustic countermeasure  82  is utilized as a decoy and jammer in undersea warfare. Acoustic signals are transmitted which can confuse the sonar systems of hostile torpedoes and submarines. Similar to the previous figures, the acoustic countermeasure device  82  includes a shell type body  86  having an opening  88  therein for receiving the displacement mechanism  84 . The shell body  86  includes an interior chamber  90  for accommodating operating elements of the device  82 . As shown in the FIG. 5, transducers  92  are mounted on or in the walls of the shell body  86  and produce the acoustic signals. A battery power source  94  and signal electronics  96  are located within the chamber  90  and provide the power and signals for driving the transducers  92 . These systems are similar to current acoustic systems used in countermeasure devices.  
         [0046]    Similar to that of FIG. 4, the acoustic countermeasure device  82  includes a salinity meter  98  and a pressure sensor  100 . A controller  102  coordinates the information gathered from the salinity meter  98  and pressure sensor  100  in a manner identical to that described above for FIG. 4. This system incorporates the traditional acoustic transducers and electronics which supply the sound into the water which is the product of an acoustic countermeasure. The details will be eliminated herein for brevity.  
         [0047]    Referring now to FIG. 6, a field of acoustic countermeasure devices  82  is shown to be deployed as a substantially simultaneous event. Due to the volume saved by the novel buoyancy system, it is anticipated that multiple countermeasure devices can be launched using the volume previously required for a single device. As such, the application of simultaneously dispersed fields of countermeasures becomes an available option. These countermeasures can all be set to hover at different depths (D 1 , D 2 , D 3 ). Additionally, delays in launching while the launch platform is in motion will provide spatial separations (S 1 , S 2 ). The net effect is a series of acoustic sources at different depths and locations. This can cause a threat weapon or platform to rule out multiple sources as decoys rather than one. If the countermeasures  82  are employing different frequency bands in their transmissions, additional processing problems for the threat assets arise.  
         [0048]    Incorporated into each of the countermeasures  82  of FIG. 6 is the novel displacement mechanism of FIG. 2 or  3  to achieve and maintain a prescribed depth of the individual countermeasures which together make up the system. The variable density of seawater due to pressure as depth increases and changes in temperature allows for bodies to float at a constant depth beneath the surface. Slight changes in the body&#39;s overall displacement can affect its buoyancy, and thereby its depth. This system allows for changing the total displacement of a body and thereby an adjustment in buoyancy force to achieve and maintain a desired depth by an underwater device.  
         [0049]    The arrangement of FIG. 6 is advantageous in that it provides a multiple acoustic countermeasure system which presents multiple acoustic sources/frequencies to confuse incoming threats.  
         [0050]    Through an acoustic countermeasure system as described, the overall device may be made smaller than traditional devices due to the weight, volume, and power savings afforded by the novel depth control system. This may make available the option to package two devices into the launch apparatus currently used to deploy one device.  
         [0051]    The exact number of countermeasures used in the multiple countermeasure system can vary. The number available and mission specifics will affect launch numbers and individual depth/frequency assignments.  
         [0052]    The tolerance for depth accuracy and the time duration of the device mission can alter the control system components. If a short duration mission is required, and the area of the ocean known, then the need to measure and monitor salinity is reduced and this aspect of the control system could be omitted. Further, the specific mission of the countermeasure will influence the choice of transducers and the requisite power levels.  
         [0053]    In view of the above detailed description, it is anticipated that the invention herein will have far reaching applications other than those of underwater systems such as acoustic countermeasures and oceanographic devices.  
         [0054]    This invention has been disclosed in terms of certain embodiments. It will be apparent that many modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.