Abstract:
Apparatus for providing a stable platform for equipment to be employed in  underwater environment includes a fin assembly for preventing uncontrolled azimuthal motion of the equipment when the fin assembly is suspended in the underwater environment to a level at which a current is present. The equipment is joined to a mounting which is rotatably positioned upon the fin assembly, and is oriented to a selected azimuth by the rotatable mounting in response to control signals received thereby, the fin assembly remaining at a fixed azimuthal orientation determined by the direction of the current as the mounting azimuthally displaces the equipment.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     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. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention disclosed and claimed herein pertains generally to systems which include a platform suspended in an underwater environment to resist angular or other motion as equipment which is joined to the platform is controllably displaced in various degrees of motion. Even more particularly, the invention pertains to such systems wherein the platform interacts with a current present in the underwater environment in order to remain immobile as the equipment joined thereto is controllably displaced. 
     Certain equipments intended for operation in an underwater environment, such as an ocean body, must be selectively displaceable in one or more degrees of freedom or motion in order to accomplish desired tasks. For example, a hydrophone placed in an underwater environment to track or monitor a submarine may have to be rotatable in both a horizontal plane (azimuthal motion) and in a vertical plane (elevational motion) in order to follow a submarine as it moves through the environment. It will be readily apparent that if such equipments are not stabilized in some manner, controlled motion thereof will generate motion which is not controlled. For example, if the above hydrophone is suspended from a cable, the cable may be twisted as the hydrophone is turned through an azimuth. The twisting of the cable stores a potential energy which, upon release, will cause the hydrophone to be shifted from a desired position, if stability is not in some way provided thereto. 
     In a prior art system for resisting uncontrolled azimuthal motion of equipment suspended in an underwater environment, the equipment is mounted on a structure which includes an elevation trunnion and an azimuth gimbal. A servo motor is mounted on a stabilizing unit which has fins thrust outwardly into the environment. As the servo motor turns a shaft joined to the equipment, the equipment is rotated through an azimuth, while the fins resist azimuthal motion of the stabilizing unit in the water. However, such a prior art system generally requires a special winch for deployment and recovery so that its use is limited to specially equipped vessels, or else a suitable winch must be provided as part of the system. In addition, the system is deployed by suspending it from a single cable, which also includes power conductors for conveying electric power to the servo motor. As the servo motor rotates the shaft, there is sufficient azimuthal drift of the stabilizing unit that the cable is twisted enough to store a disruptive amount of potential energy. Also, slip rings are required to couple the power conductors of the cable to the servo motor as the cable is twisted. As a further disadvantage, such prior art system does not provide for controlled elevational displacement of equipment employed therewith, due to the use of a trunnion for mounting the equipment. 
     In a stabilizing system which improves over the above prior art, the need for comparatively expensive slip rings should be eliminated. Also, the azimuthal drift of a stabilizing platform included in the system should be eliminated or sufficiently reduced to prevent storage of potential energy in a cable from which the system is suspended. Such improved system should also provide stability for elevational or vertical displacements of equipment, as well as for azimuthal displacements thereof. 
     SUMMARY OF THE INVENTION 
     The present invention provides apparatus for enabling equipment to be controllably moved or displaced in an underwater environment. The apparatus includes a fin assembly means which makes use of the forces of a current present at a selected level in the underwater environment to prevent uncontrolled angular motion of the equipment when the fin assembly means is suspended in the environment to the selected level. The apparatus further includes movable mounting means joined to the equipment and to the fin assembly means for receiving control signals, and for selectively orienting the equipment in response to the control signals. 
     Preferably, the fin assembly means comprises means for maintaining a fixed azimuthal orientation in the underwater environment, even if only a current of negligible velocity is flowing against it, the fixed orientation of the fin assembly being determined by the direction of current flow. Preferably also, the movable mounting means comprises means for controllably displacing the equipment in each of a selected number of degrees of motion without displacing the fin assembly means from the fixed azimuthal orientation. For example, the mounting means usefully comprises means for displacing the equipment to provide it with both a selected azimuthal orientation and a selected elevational orientation. 
     In a preferred embodiment, the equipment comprises equipment having a central axis, such as a sonar transducer, and is deployed in an ocean environment or other natural body of water. The movable mounting means is rotatable joined to the fin assembly, and includes sensor means for providing equipment displacement signals which indicate the azimuthal displacement of the central axis, from the direction of magnetic north, and the elevational displacement of the central axis, from a vertical reference axis. The mounting means further includes a first servo motor, capable of turning the central axis of the transducer through several complete revolutions in a horizontal plane without displacing the fin assembly from its fixed azimuthal orientation, and a second servo motor, capable of turning the central axis through a complete revolution in a vertical plane without displacing the fin assembly. In such preferred embodiment the equipment, fin assembly and movable mounting means are suspended from a supporting cable to the selected level from a remotely located support platform, and an electric cable is provided for containing electric data paths. The data paths convey equipment displacement signals from the sensor means to the support platform, and control signals from the support platform to the servo motors, a plurality of coils of the electric cable being formed about the suspension cable to prevent twisting of the electric cable as the mounting means is turned through a number of revolutions. 
     Alternatively, the invention discloses apparatus which interacts with a current present at a selected level in an underwater environment to provide a stabilized platform for equipment to be employed in the environment. Such apparatus includes a facing panel having a forward side, a rearward side, two side edges and an upper end edge, the dimensions of the side edges being greater than the dimensions of the upper end edge. Such apparatus further includes a spacing panel having an upper end edge, and forward and rearward side edges which are in parallel relationship and are spaced a selected distance from each other, the forward side edge of the spacing panel being joined to the rearward side of the facing panel so that the spacing panel and the facing panel are in fixed perpendicular relationship. First and second angled panels, which are symmetrical, are also provided, each of the angled panels having a forward side edge, and upper and lower end edges, the dimensions of the forward side edges of the angled panels being greater than the dimensions of the upper and lower end edges thereof, the forward side edge of each of the angled panels being immovably joined to the rearward side edge of the spacing panel so that the upper end edges of the first and second angled panels, and also the lower end edges of the first and second angled panels, form a selected angle. Such combination of facing panel, spacing panel and angled panels cooperate to form a fin assembly for maintaining the forward side of the facing panel in perpendicular relationship with the direction of the above current when the fin assembly is positioned in the underwater environment at the level of the current. The equipment is joined to the fin assembly by mounting means which are movable in relation to the fin assembly. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide simplified and inexpensive apparatus for reducing or eliminating uncontrolled motion of equipment which is deployed in an underwater environment, and which must be controllably displaced or moved through various degrees of motion therein. 
     Another object is to provide a stabilizing platform for deploying equipment in an underwater environment which must be controllably oriented in a horizontal plane, a vertical plane, and rotated about a central axis passing through the equipment, without being affected by forces generated in response to controlled motion required for such orientations. 
     Another object is to provide a stabilizing fin assembly which employs the forces of a current flowing in an underwater environment to maintain a constant or fixed azimuthal orientation in relation to the direction of current flow. 
     Another object is to provide a stabilized platform in an underwater environment for equipment to be employed in the environment wherein the platform and equipment are deployable from a vessel equipped only with a standard deck capstan, whereby the need for a specialized winch or other deployment and recovery system is eliminated. 
     Another object is to avoid the need for electrically conductive slip rings in such stabilized platform systems. 
     These and other objects of the invention will become more readily apparent from the ensuing specification when taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an embodiment of the invention deployed in an underwater environment. 
     FIG. 2 is a perspective view showing the embodiment of FIG. 1 in greater detail. 
     FIG. 3 is a perspective view showing the embodiment of FIG. 1 subjected to roll. 
     FIG. 4 is a perspective view showing further details of the embodiment of FIG. 1. 
     FIG. 5 is a frontal view of the embodiment of FIG. 1. 
     FIG. 6 is a side view of the embodiment of FIG. 1. 
     FIG. 7 is a cross-sectional view of the fin assembly of the embodiment of FIG. 1 taken along lines 7--7 of FIG. 5. 
     FIG. 8 is a schematic view of a cross-section of the fin assembly means of the embodiment of FIG. 1 to illustrate the operation thereof in response to an underwater current. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a fin assembly 10 suspended into an underwater environment 12 from a surface vessel or other support platform 14 by means of a supporting cable 16. Cable 16 usefully comprises a 1/4&#34; nylon line. Fin assembly 10 is a configuration of planar members or panels 18 and weights 20, described hereinafter in greater detail, which is suspended in underwater environment 12 to a level at which at least a negligible current 22 is flowing. Fin assembly 10 is structured so that if current 22 is in the approximate range 1/4-5 knots, the forward planar surface, or side, of a facing panel 18a will be held in a perpendicular relationship with the direction of current flow. Consequently, fin assembly 10 is maintained in a fixed azimuth, regardless of the motion of other structure attached thereto. It is anticipated that current 22 will virtually always be present to enable effective operation of fin assembly 10. For example, the required minimum quarter knot current could be provided if vessel 14 was drifting in response to a moderate wind. 
     Referring further to FIG. 1, there is shown fin assembly 10 and supporting cable 16 joined together by means of a tubular mounting 24, mounting 24 being movably joined to the fin assembly so that it is rotatable in relation thereto. Equipment to be employed in environment 12 which must be controllably displaced, such as sonar transducers or hydrophones 26a and 26b, are joined to tubular mounting 24, and are movable in various degrees of freedom or motion, in response to electric control signals coupled to mounting 24 through electric cable 28. Assembly 10 and mounting 24 together comprises a stabilizing platform. 
     To deploy the stabilizing platform and transducers 26 in environment 12, supporting cable 16 is reeved through a block 30, which is supported by boom 32, and an end of cable 16 is affixed to capstan 34. Because of the comparatively small combined weight of the platform and transducers 26, they may be readily lowered and raised in environment 12 by a capstan as small as the capstan carried aboard a tug-size vessel. Consequently, the need to provide a specialized winch which can be interfaced with the power supply of a particular vessel is eliminated. 
     As the platform and transducers are lowered into environment 12, personnel aboard vessel 14 join support cable 16 and electric cable 28 together at intervals by means of ties 36. FIG. 1 shows a readily transportable basket 38 aboard vessel 14 in which cable 28 may be stored in a figure-8 pattern, and from which cable 28 can readily be removed for deployment in environment 12. FIG. 1 also shows a transportable shelter 40 receiving cable 28, and housing controls by means of which an operator, stationed in shelter 40, can generate control signals coupled through cable 28. 
     Referring to FIG. 2, there is shown cable 16 joined to mounting 24 by means of a lifting bridle 42. FIG. 2 also shows electric cable 28 forming several loose coils about cable 16 in proximity to mounting 24. Consequently, slip rings or other rotatable devices are not required in mounting 24 to allow the passage of electric power and signals, and to prevent twisting of cable 28, as hydrophones 26 are turned through an azimuth of up to several revolutions, or 1440°. Electric cable 28 usefully comprises a fluid-filled cable containing discrete electric conductors, the end of cable 28 being joined to a pressure equalized connector 44. Connector 44 maintains a constant fluid pressure in cable 28, regardless of the ambient pressure of the environment 12 proximate to cable 28. 
     Referring further to FIG. 2, there is shown tubular mounting 24 comprising upper and lower housings 24a and 24b, respectively. Housing 24a protectably houses several electric conductor junctions and sensor devices employed to monitor the azimuthal and elevational displacements of mounting 24. Lower housing 24b is employed to protectably house servo motors used to pan and tilt transducers 26a and 26b in response to control signals received through electric cable 28, cable 28 also including paths for the electric power which energizes the servo motors. 
     Transducer 26a usefully comprises a device for tracking or &#34;locking on&#34; to a target moving through environment 12, while transducer 26b usefully comprises a device for receiving sonar data from a sonar source toward which the central axis of transducer 26b is oriented. Transducers 26a and 26b are respectively joined, in perpendicular relationship, to a shaft 46 so that the central axes of transducers 26a and 26b remain parallel, and therefore always have the same azimuths and elevation angles with respect to horizontal and vertical references. Consequently, transducers 26a and 26b cooperate to track and gather data from a target generating sonar data as the target moves through environment 12. Received sonar data is coupled to data storage or display apparatus housed in shelter 40 through conductive paths contained in electric cables 28, 52a and 52b. 
     Referring again to FIG. 2, there is shown a standard device 48 comprising a combination pendulus potentiometer and pressure transducer joined to transducer 26b by means of a bracket 50b. Device 48 indicates both the depth of transducers 26a and 26b in environment 12 and the pitch thereof. Pitch is the angle between the central axes of transducers 26a and 26b and vertical reference axes. Electric transducer displacement signals generated by device 48, which respectively represent the depth and pitch of the transducers, are coupled to display apparatus in shelter 40 through electric cables 52 and 28. 
     Fin assembly 10, in addition to facing panel 18a, comprises a spacing panel 18b, and angled panels 18c and 18d, panel 18d not being shown in FIG. 2. A base panel 54 is joined to the respective upper edges of panels 18a-d to provide a firm base upon which mounting 24 is rotatably joined. Each panel is formed from a flat sheet of aluminum or other lightweight material, and weights 20 usefully are formed from stainless steel and weigh on the order of 180 pounds. 
     By forming panels 18a-d of light material, and by joining weights 20 to the lower portions thereof, a corrective moment is applied to fin assembly 10 and mounting 24 which urges the axis of mounting 24 to a true vertical orientation. Such moment is necessary to counteract the force of current 22 against facing panel 18a and angled panels 18c and d when current 22 is on the order of 5-7 knots. Such current, as shown by FIG. 3, tends to roll assembly 10 and tubular mounting 24 so that the axis M a  of mounting 24 is displaced from a vertical reference axis V ra  by an angle θ r . θ r  is on the order of 3°-5° when current 22 is on the order of 5-7 knots. 
     It has been found that fin assembly 10 is capable of maintaining a fixed azimuth even when θ r  is in the range 3°-5°. However, it will be readily apparent that the pitch of transducers 26a and b, the angles between their respective central axes and vertical reference axes, is varied by displacement of axis M a  of mounting 24 from axis V ra . Referring once more to FIG. 2, and also to FIG. 4, there are shown roll servo motors 56a and 56b which are respectively joined to transducers 26a and 26b. Servos 56a and b are provided to selectively rotate the transducers about their respective central axes to compensate for disorientation of the transducers due to rolling of mounting 24. Servos 56a and b are operated by electric power and control signals coupled thereto by an operator in shelter 40 through cables 28 and 52a and b. 
     Referring further to FIG. 4, there is shown shaft 46 passing through lower housing 24b in transverse relationship thereto. Shaft 46 is rotated by a pitch servo motor 58 contained in lower housing 24b to elevationally displace the central axes of transducers 26b and a by pitch angles θ p , in relation to vertical reference angles V ra  &#39; and V ra  &#34;, respectively. Pitch servo 58 is operated by electric power and control signals coupled thereto from shelter 40 through electric cable 28. FIG. 4 also shows shafts 60a and 60b transversally joined to the ends of shaft 46 by means of brackets 50a and 50b respectively, and respectively joining transducer 26a and roll servo 56a and transducer 26b and roll servo 56b. 
     Referring to FIG. 5, there is shown lower housing 24b containing pitch servo 58 and also containing an azimuth servo motor 62. Servo 62 turns a shaft 64 which has an end fixably joined to fin assembly 10, so that tubular mounting 24 is rotated about its central axis, fin assembly 10 maintaining a fixed azimuth in response to current 22. Transducers 26a and b may thereby be directed to a selected azimuth by selectively coupling power and control signals to servo 62 through electric conductors 64 and cable 28. Servos 58 and 62 of lower housing 24b, together with conventional bearings and linkages contained therein, usefully comprises a standard pan and tilt apparatus. 
     Referring further to FIG. 5, there is shown upper housing 24a containing a magnetic compass 66, and an pendulus potentiometer 68. Compass 66 is joined to housing 24a in such a relation to the central axes of transducers 26 that, as the central axes are turned through a horizontal plane, compass 66 generates a signal representing the angular displacement of the central axes from the direction of magnetic north. Such displacement signal, representing the azimuth of transducers 26, is coupled through an electric conductor 64 and cable 28 to a display apparatus in shelter 40. In like manner, pendulus potentiometer 68 couples a signal representing roll angle θ r  through cable 28 to a display in shelter 40. It is to be noted that an operator, by observing displayed signals representing the azimuth and pitch of transducers 26 and the roll angle of mounting 24, is enabled to send control signals to servo motors 56a, 56b, 58 and 62 to selectively orient the transducers. 
     Referring to FIGS. 6 and 7, there are shown a side view of mounting 24, transducers 26 and fin assembly 10, and a cross-sectional view of FIG. 6 taken along lines 7--7 thereof, respectively. FIGS. 6 and 7 show facing panel 18a having a forward side 70a, a rearward side 70b, two side edges 70c and 70d, respectively, and an upper end edge 70e. Spacing panel 18b has an upper end edge 72a and forward and rearward side edges 72b and c respectively, which are in parallel relationship and spaced a selected distance from each other. Forward side edge 72b is joined to rearward side 70b of facing panel 18a midway between side edges 70c and 70d, so that spacing panel 18b and facing panel 18a are in fixed perpendicular relationship. Angled panels 18c and 18d are symmetrical, each having a forward side edge 74a and upper and lower end edges 74b and c, respectively. The forward side edge 74a of each angled panel is immovably joined to rearward side edge 72c of spacing panel 18b so that upper end edges 74b of angled panels 18c and 18d together form a 90° angle, lower end edges 74c of angled panels 18c and 18d also forming a 90° angle. Angled panels 18c and 18d each forms an angle with spacing panel 18b which is on the order of 135°. FIG. 7 further shows a bracing member 76 joined between angled panels 18c and d to maintain them in rigid relationship with each other. 
     Facing panel 18a usefully has an area on the order of 8 sq. ft., and side edges 70c and d thereof are 4 ft. The spacing between side edges 72b and 72c is 1 ft., and the areas of angled panels 18c and d are on the order of 11.5 sq ft. While the above dimensions for fin assembly 10 may be varied to accommodate transducers or other equipments of varying size, the ratios or relationships therebetween should remain relatively constant. 
     Referring to FIG. 8, there is shown fin assembly 10, assembly 10 initially receiving current 22. When facing panel 18a is not in perpendicular relationship with the direction of current flow, a region R 1  is formed which has a very low pressure in comparison with the pressure adjacent to forward side 70a of panel 18a. Region R 1  is bounded by spacing panel 18b, facing panel 18a, angled panel 18c, and a line extended between facing panel 18a and angled panel 18c in perpendicular relation with panel 18a. A region R 2  is also formed which is bounded by facing panel 18a, spacing panel 18b, angled panel 18d, and a line extending between angled panel 18d and facing panel 18a, and in perpendicular relationship therewith. However, region R 2  contains turbulence, and the pressure therein is comparatively higher than the pressure within region R 1 . Consequently, a substantial pressure differential is created between current 22 and region R 1  so that a moment M is applied to fin assembly 10, whereby fin assembly 10 is turned until facing panel 18a is in perpendicular relationship to the direction of flow of current 22. If the current velocity is at least 1/4 knot, facing plate 18a will be maintained in perpendicular relationship with the direction of current flow despite motion of transducers 26 in response to control signals coupled servo motors. 
     It will be apparent that additional transducers or other equipment requiring selctive displacement in environment 12 may be readily emplaced upon the mounting 24 without requiring more than negligible alteration of the above embodiment. Such equipments may be operated by means of electric cables in addition to cable 28, which may be readily joined to support cable 16 and mounting 24 in the manner illustrated for cable 28. 
     Obviously, many modifications and variations of the present invention are possible in the light of the above teachings, and, it is therefore understood that within the scope of the disclosed inventive concept, the invention may be practiced otherwise than specifically described.