Abstract:
A system for enhancing control of an underwater vehicle, and providing a quick change modular payload section includes a motor configured to rotate an internally threaded member threadingly engaged with a threaded rod. Rotating the member creates linear motion of the threaded rod. A control rod connected to the threaded rod provides movement of a rudder or fin. The threaded rod and member are configured with threads having a fine pitch which maintains a stable position of the fins without needing to supply power to the motor for adjustments. The modular payload arrangement includes a bulkhead ring having L-shaped recesses that receive fasteners disposed on a central body section. The payload section may be fastened to the vehicle by pressing the payload section onto the central body such that the fasteners align with the recesses and turning the payload section to secure the payload section.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to control and payload systems for small underwater vehicles, and more particularly to an improved system for controlling position of a small underwater vehicle and for a modular payload system for a small underwater vehicle. 
     BACKGROUND OF THE INVENTION 
     A-size underwater vehicles (i.e., those having a size of about 4⅞″ diameter×36″ long) are often used as simulators for testing a variety of Navy shipboard systems. For example, such vehicles can be outfitted with systems that simulate the noise of a submarine or other water-borne vehicle or device, and are used to teach other systems to detect and recognize such noises as being associated with that specific device. 
     Currently there are no A-size underwater vehicles that employ stable, energy efficient, linear controls. At present, these small underwater vehicles have directional controls that are either binary (i.e., on-off) controls or which use linear motors that must be constantly electronically actuated to hold the vehicle on a desired position or course. Binary controls, which apply either full left rudder or full right rudder, cause the vehicle to swim erratically, while linear motors use too much power, since they employ a solenoid that must be constantly “on” in order to hold the rudder/elevator at a particular position. Thus, there is a need for an improved control system for an underwater vehicle that is stable, and that requires less power than existing systems. 
     Furthermore, current A-size underwater vehicles employ fixed payload sections which, as previously noted, may contain devices such as noisemakers for simulating the noise signature of a particular water-borne vehicle or device. Having a fixed payload section, however, limits use of the vehicle to specific applications and thus a larger number of such vehicles must be kept on hand to address a typical array of testing requirements. Thus, there is a need for an improved underwater vehicle having a simple modular payload arrangement that allows a variety of payloads to be simply and efficiently interchangeable with a single vehicle body. 
     SUMMARY OF THE INVENTION 
     A system is disclosed for controlling an underwater vehicle. The system may comprise a linear control assembly having a motor and a threaded rod. The motor may be engaged with an internally threaded member that is threadably engaged with the threaded rod. A control rod is connected to the threaded rod and a fin assembly is connected to the control rod. Thus arranged, actuation of the motor rotates the internally threaded member, thereby causing a linear movement of the threaded rod, the control rod, and the fin assembly. 
     A modular payload system is also disclosed for an underwater vehicle having a payload section and a central body section. The system includes a payload section having a bulkhead section, and a central body section. The central body section may have a circumferential lip portion and a plurality of fasteners circumferentially disposed on the lip portion. The bulkhead section may further include a plurality of L-shaped recesses positioned to receive the plurality of fasteners, each of the L-shaped recesses having an axially-disposed opening and a transversely disposed locking section. The central body section is engageable with the bulkhead section by aligning the plurality of fasteners with the axially-disposed openings of the recesses, pressing the bulkhead section toward the central body portion, and twisting the bulkhead portion with respect to the central body portion to engage the plurality of fasteners with the transversely disposed locking sections of the plurality of recesses. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The details of the invention, both as to its structure and operation, may be obtained by a review of the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
         FIG. 1  is a side view of an A-size underwater vehicle; 
         FIG. 2  is a schematic of the interrelation of the components of the vehicle of  FIG. 1 , taken along line  2 - 2 ; 
         FIG. 3  is an isometric view of the vehicle of  FIG. 1 , showing the positioning of a communications antenna; and 
         FIG. 4  is an isometric view of the disclosed control system for use in the vehicle of  FIG. 1 ; 
         FIG. 4A  is a side view of an exemplary linear actuator for use in the vehicle of  FIG. 1 ; 
         FIG. 5  is an isometric view of the control system of  FIG. 4  fitted in the tail section of the vehicle of  FIG. 1 ; 
         FIG. 6  is a side view of the control system and tail section of  FIG. 5 ; 
         FIG. 7  is a top view of the control system and tail section of  FIG. 5 ; and 
         FIGS. 8-11  are isometric views of the connection arrangement between the body section and the payload section of the vehicle of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the accompanying drawings, like items are indicated by like reference numerals. This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. 
     The disclosed system comprises an underwater vehicle having directional controls including screw-type linear actuators and position feedback controls. The screw-type linear actuators hold fin position using a fine pitched thread, which requires no continuous external electric power to maintain position. The disclosed system provides increased accuracy and control of the underwater vehicle as compared to current systems. The screw-type linear actuator also minimizes noise and power consumption, since the incline of the screw holds its position under load, without the need for external electrical power. 
     The disclosed system also includes a modular payload arrangement in which a quick connect bulkhead section enables quick connection/disconnection of the payload section from the rest of the vehicle via a single faster and a plurality of retaining pins. With this arrangement the user can simply loosen one fastener and twists the payload section to detach the section from the vehicle. A single user can manipulate and deploy the vehicle in minutes on the deck of a ship or rubber inflatable boat (RIB). The disclosed design is self contained and makes swapping out payloads a clean and simple transition. 
     Referring to  FIGS. 1 and 2 , an underwater vehicle  1  is shown having a forward payload section  2 , a central body section  4 , and an aft propulsion section  6 . The payload section  2  may comprise a tapered nose  8  for reducing drag, while the central body section  4  may have a generally cylindrical shape and may contain the vehicle&#39;s battery assembly  10 , guidance, navigation and communications components. The propulsion section  6  may include a tapered aft portion  14  ending in a propulsion and steering assembly  16 . 
     The payload section  2  houses the vehicle&#39;s payload, which may include any of a variety of communications, sensing or ordnance devices, including, without limitation, sound simulation equipment, a camera, a Doppler velocity log, up-looking sonar, a conductivity-temperature-density measuring device, and the like. The payload section  2  may also include a standalone payload processor  18  for communicating with and/or controlling the payload. Where the payload is a sensor  19 , the payload processor  18  may receive and process data from the sensor. A signal conditioner  21  may be provided in communication with the sensor  19  to condition signals from sensor prior to their transmission to the payload processor  18 . The payload processor  18  may be in communication with a main processor  20  for the vehicle  1 , and may function to reduce the processing load on the main processor. This is an advantage over prior designs in which the main vehicle processor  20  runs all controls and sensors in the vehicle. In one embodiment, the payload processor communicates with the main processor  20  and tells it what the sensor is sensing. For example, if the payload sensor senses a mine near the vehicle, the payload processor  18  may send a signal to the main processor  20  to instruct it to control the vehicle to perform a desired action (e.g., stay, go). In one embodiment, the payload processor  18  is disposed on the forward side of a quick disconnect bulkhead  68  (see  FIG. 8 ) inside the payload section  2 . It can communicate via a network cable to the main processor  20  via a single connection. 
     The main processor  20  may be connected to a data logger  23  to enable continuous storage of sensor and/or mission data received by and/or processed by the main processor  20 . The main processor  20  may also be in communication with a plurality of vehicle sensors  27  such as depth sensors or the like. A signal conditioner  31  may be provided to condition signals from the vehicle sensors  27  sensor prior to their transmission to the main processor  20 . 
     The payload section  2  may be connected to the central body section  4  using a quick connect/disconnect arrangement, which will be described in greater detail later. As previously noted, the central body section  4  may house the vehicle&#39;s battery  10 , which may be a rechargeable or replaceable battery. In one embodiment, the battery  10  is fixed within the central body section  4  and is provided with a power interface to allow recharging by plugging the battery into a power source on board a host vessel. In another embodiment, the battery  10  is removable from the central body section  4  so that, when depleted, the battery can be unplugged and replaced with a fully charged battery to enable quick redeployment of the vehicle  1 . 
     As noted, the central body section  4  may also include guidance, navigation and communications components. In one embodiment, these components include a series of printed wire boards (PWBs) in communication with the battery  10 . These PWBs may control the navigation, guidance and control functions of the vehicle  1 . The main processor  20  may be included on one of the PWB&#39;s, or it may be part of a separate board or card. Regardless of the physical arrangement, the main processor  20  communicates with, and controls the operation of, the PWBs. One of the PWB&#39;s may be a navigation board  24 , which can include, or connect to, a compass or Inertial Measuring Unit (IMU) and a global positioning system (GPS)  25 . Another of the PWB&#39;s may be a guidance board  26 , which may include a control loop that accepts, for example, depth sensing information and vehicle heading information and controls the vehicle to turn, dive or surface. Another of the PWB&#39;s may be a communications board  28 , which may include a WiFi connection  29 , a satellite modem, and/or a control and mission algorithm to enable a ship-based or land-based user to communicate with the vehicle&#39;s main processor  20  or payload processor  18  while the vehicle is in the water or on the deck of a host ship. In one embodiment, the communications board  28  enables a user to locally program the main processor  20  and/or the payload processor  18  using a laptop computer or handheld device. The user may program a mission or run-plan for the vehicle  1  via the vehicle&#39;s wireless link. Alternatively, the wireless link may enable user to download data collected by the vehicle during its run. As shown in  FIG. 3 , the vehicle may be provided with an antenna  30  to facilitate modem operations. The antenna  30  may be embedded in the vehicle fin, mounted flush on the hull, or it may be retractable and/or optional depending on the vehicle&#39;s particular mission application. 
     The modem may also enable the payload processor  18  and/or the main processor  20  to communicate with other unmanned vehicles or with a local buoy, which can then transmit data collected by the vehicle (or vehicles) to a satellite transmission system and/or a nearby vessel. In one embodiment, the vehicle may collect data, surface, and call a host ship. The host ship may then retrieve the vehicle and download the vehicle&#39;s collected data to a shipboard computer. 
     The battery  10  may be connected to a DC/DC converter  11  for powering the PWB&#39;s  24 ,  26 ,  28 . In addition, battery power may be used, either directly, or via the DC/DC converter  11 , to power some payloads. 
     The propulsion section  6  is positioned immediately aft of the central body section  4  and may be attached thereto by a permanent or removable connection. As shown in  FIG. 2 , the propulsion section  6  may include a linear actuator control  32 , a propulsion motor  34 , linear actuators  36   a, b  and a steering assembly  16 . The steering assembly  16  may include a pair of rudders  38 , and a pair of elevators  40 . The linear actuator control  32  is in communication with one or more of the PWB&#39;s  24 ,  26 ,  28  for receiving control commands from the main processor  20  and to instruct the linear actuators to start and stop. 
     Referring to  FIGS. 4-7 , the linear actuators  36   a, b  are shown, along with connections to the associated rudders  38  and elevators  40 . Each of the linear actuators  36   a, b  includes a linkage rod  42   a, b  that connects to a central linkage  44   a, b  of the associated rudders  38  and elevators  40  to move the rudders/elevators via corresponding movement of the actuators. As can be seen, the individual rudders  38  are connected together via central linkage  44   a , while the individual elevators  40  are connected together via central linkage  44   b . The rudders  38  and elevators  40  further each include an extension rod  46 ,  48  that rotatably connects the rudder/elevator to an inner surface of the propeller shroud  50  ( FIGS. 2 ,  5 ) so that when linear actuator  36   a  moves the central linkage  44   a , the rudders  38  rotate together about the extension rod  46  to change their angle of inclination with respect to the vehicle. Likewise, when linear actuator  36   b  moves the central linkage  44   b , the elevators  40  rotate together about the extension rod  48  to change their angle of inclination with respect to the vehicle. 
       FIG. 5  shows the linear actuators  36   a, b  positioned within the aft structure of the propulsion assembly  6 . In this embodiment, the actuators are mounted on an intermediate bulkhead  52  so that they straddle the opening  54  that houses the vehicle&#39;s propulsion shaft bearing and seal (not shown). 
     Referring to  FIG. 4A , each of the linear actuators  36   a, b  may comprise an actuator element  56 , a threaded rod  58 , a position sensor  60  and a spring compensator  62 . A coupling  64  is provided at an aft end of the actuator  36   a, b  for engaging an associated extension rod  42   a, b . The actuator element  56  may comprise a motor that spins a threaded nut  57 , which in turn, engages the threaded rod  58  to more forward. Actuation of the motor in a second direction causes the threaded rod  58  to move aft. When coupled to an extension rod  42   a, b , rotation of the motor controls the angular position of the rudders  38  and elevators  40 . 
     In one embodiment, the position sensor  60  comprises a slide rheostat which changes resistance with a change in rod position. As the threaded rod  58  moves, the rheostat provides feedback to a control loop to inform the linear actuator control  32  that the elevators (or rudders) are positioned at, for example 10-degrees. The control system, in turn, can order a change in position by controlling the motor to spin the nut  57 , thereby moving the threaded rod, and actuating the associated elevators/rudders to achieve the desired movement of the vehicle. 
     Self locking of the threaded rod  58  is obtained whenever the coefficient of friction is equal to or greater than the tangent of the thread angle. This is a function of pitch and friction. Thus, a fine thread per inch will produce this self-locking condition due to small thread angle and increased coefficient of friction. 
     The spring compensator  62  may be a coil spring calibrated to compensate for the forces of seawater pressure on the linear actuator  36   a, b . As will be understood, sea pressures at increased depths can counteract the force of the linear actuators  36   a, b , hindering or preventing them from moving the linkage rods  42   a, b . This is because the linkage rods are subject to full sea pressure, while the linear actuators  36   a, b  are subject only to the pressures associated with the interior of the vehicle (the dividing line is shown in the figures as the intermediate bulkhead  52 ). To counteract the forces of sea pressure on the linkage rods, the spring compensator  62  provides a pre-load on the threaded rod  58  that acts in direction opposite to the load applied by the sea. 
     Thus arranged, the rudders  38  and elevators  40  can be adjusted simply by rotating the threaded nut and translating the associated threaded rod by a desired amount. Once a desired position of the elevators and/or rudders has been achieved, the actuator element  56  is turned off and the position of the rod (and the elevators or rudders) is held constant without the need for further operation of the actuators  36   a, b . As previously noted, this fixed positioning feature results from the use of a fine thread pitch on the nut and threaded rod. Fine thread pitches are exceptionally resistant to rotation when subjected to large axial forces, such as the force of sea pressure and the forces applied to the rudders and elevators as the vehicle moves through the water. 
     Referring now to  FIGS. 8-11 , the disclosed modular connection arrangement between the payload section  2  and the central body section  4  will be described in greater detail. As previously noted, providing a quick connect/disconnect arrangement facilitates quick change-out of vehicle payloads and batteries, resulting in a highly versatile vehicle. 
       FIG. 8  shows the payload section  2  and central body section  4  connected via a quick disconnect bulkhead  68 . The quick disconnect bulkhead  68  may be a cylindrical ring that approximates the outer diameter of the payload section  2  and the central body section  4  to provide a smooth and uninterrupted exterior surface between the sections. As shown in  FIG. 11 , the quick disconnect bulkhead  68  is sized so that its inner surface  70  fits over, and engages, a circumferential lip portion  72  of the central body section  4 . An opposite side of the quick disconnect bulkhead  68  may be fixed to the payload section  2  by fasteners, welding or other appropriate connection arrangement. The quick disconnect bulkhead  68  may be sealed to the circumferential lip portion  72  of the central body section  4  via an o-ring seal. 
     The circumferential lip portion  72  of the central body section  4  may carry first and second fasteners  74 ,  76  configured to mate with corresponding first and second recesses  78 ,  80  in the quick disconnect bulkhead  68 . In the illustrated embodiment, the first fastener  74  may be a screw-type fastener having an increased diameter head  82  and a threaded body  84  ( FIG. 11 ). The first fastener  74  may be sized to engage the first recess  78  in the bulkhead  68 . In the illustrated embodiment, the first recess  78  is an L-shaped recess having an axially-oriented open mouth section  78   a  and a transversely-oriented locking section  78   b . The locking section  78   b  may have a bevel that matches a corresponding bevel of the head  82  of the first fastener  74  such that when the first fastener is engaged with the locking section  78   b  of the first recess  78  and the fastener is tightened, the head  82  of the fastener engages the locking section  78   b  to lock the bulkhead  68  to the central body section  4 . 
     A plurality of second fasteners  76  may be provided at spaced intervals around the circumference of the circumferential lip portion  72 . Likewise, a plurality second recesses  80  may be correspondingly spaced around the circumference of the quick disconnect bulkhead  68 . In the illustrated embodiment, the second fasteners  76  are cylindrical pins, and the second recesses  80  are L-shaped recesses having an axially-oriented open mouth section  80   a  and a transversely oriented locking section  80   b . In contrast to the first fasteners, the second fasteners do not have an increased diameter head portion, and thus they do not lock down onto quick disconnect bulkhead. Rather, they serve as retention pins, preventing axial movement of the payload section (and bulkhead section) with respect to the central body section when received within the locking section  80   b  of the associated recess. 
     It will be appreciated that, although the second fasteners  76  have been described as being pins, they (as well as the second recesses  80 ) could instead be of the same design as that of the first fasteners  74  and the first recesses  78 . Further, although the illustrated embodiment contemplates a total of four fasteners and four recesses, fewer or greater numbers of fasteners and recesses could be provided as desired. It will also be appreciated that it is not critical to provide a separate bulkhead element, and thus the locking features described in relation to the bulkhead could instead be implemented directly in the payload section  2 , or the bulkhead could be an integral part of the payload section or the central body section. Moreover, although the bulkhead is described as fitting over a portion of the central body section, an opposite arrangement could be provided, with fasteners provided on the bulkhead and corresponding recesses provided in the central body section. 
     Referring again to  FIG. 8 , the quick connect bulkhead  68  is shown locked in place, with the first and second fasteners  74 ,  76  residing in the transversely oriented locking sections  78   b ,  80   b  of their respective recesses  78 ,  80 . To disconnect the payload section  2  from the central body section  4 , the first fastener  74  is loosened as shown in  FIG. 9 , so that the fastener head  82  disengages from the locking section  78   b  of the first recess  78 . As shown in  FIG. 10 , the payload section  2  (and bulkhead  68 ) are then twisted in the direction of arrow “A” so that the first and second fasteners  74 ,  76  align with the axially oriented open mouth sections  78   a ,  80   a  of the associated recesses  78 ,  80 . Since the second fasteners  76  do not tighten down onto the surface of the bulkhead  68 , there is no need to loosen these fasteners in order to twist the bulkhead. The payload section  2  and bulkhead  68  are then moved axially in the direction of arrow “B” to disconnect them from the central body section  4 . One connector may be provided that carries all wires (e.g., power, digital, analog, network) that provide communications between the payload section  2  and the central body section  4 . 
     In this manner the payload section  2  can be quickly disassembled from the central body section  4  simply by loosening a single fastener, and twisting the two apart. The user can then quickly install another payload section with the central body section  4  and send the vehicle back out on another run. Alternatively, the user can reattach the payload section  2  to another central body section  4  having a fully charged battery  10 . In another case, the user can simply remove a depleted battery  10  from the central body section, install a fully charged battery, reinstall the payload section  2  and send the recharged vehicle back out on another run. 
     Although the system has been described in relation to A-sized vehicles it will be appreciated that the arrangements disclosed herein could find application in any of a variety of vehicles of different sizes and configurations. 
     Further, although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.