Abstract:
A system for communicating with a remotely operated underwater vehicle (ROV) includes an ROV coupled to a surface buoy by a tether. A controller is coupled to a first wireless transceiver and a second wireless transceiver is attached to the surface buoy. Control signals are transmitted from the controller through the first wireless transceiver the second wireless transceiver on the surface buoy. The control signals are then transmitted through the tether to the ROV. Feedback and sensor signals are transmitted from the ROV through the wireless transceivers to the controller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/155,658, REMOTELY OPERATED UNDERWATER VEHICLE, filed on Feb. 26, 2009 which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    With reference to  FIG. 1 , remotely operated underwater vehicles (ROV&#39;s)  101  are, widely used by industry and science for unmanned undersea work tasks. The ROV  101  requires an electromechanical cable connection (tether)  105  to the surface for communications and power which are typically located on a boat  109 . The tether cable  105  presents serious constraints and difficulties in use. For example, the tether  105  can restrict the mobility of the ROV  101  due to its short length. Therefore it would be an advantage to be able to dispense with the tether that is coupled to the control station. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed towards a control system for operating a remotely operated underwater vehicle (ROV). The ROV has a propulsion system and directional controls that allow an operator to control the speed and direction of the ROV through a body of water. The ROV can also have sensors and feedback devices that can provide information that is transmitted back to the operator or any other receiver. 
         [0004]    In order to eliminate the restrictions due to the traditional tethered submersible systems, a floating buoy can be coupled to the ROV with a tether and a wireless transceiver can be mounted on the buoy. A remotely located controller can be coupled to another wireless transceiver so the operator can transmit and receive data from the ROV. For example, the controller transmits control signals from a first wireless transceiver to the second wireless transceiver on the buoy. These control signals are then transmitted through the tether to the ROV and the ROV performs the actions of the control signals. The sensors and feedback signals produced by the ROV are transmitted back through the tether to the buoy. The sensors and feedback signals then sent from the second wireless transceiver on the buoy to the first wireless transceiver and the controller. The wireless communications allow the buoy to travel very far from the controller while remaining under the control of the operator. The wireless signals cannot be transmitted through water, so the tether provides a high speed communications link between the buoy and the ROV. 
         [0005]    The diving depth of the ROV can be limited by the length of the tether. The tether can have various lengths in diameters. A larger diameter tether will be stronger but will also result in more drag forces as the ROV moves through the water. A ⅜ inch tether cable can have sufficient room for a conductive wire cable and may be suitable for tether lengths up to 500 feet. A ⅛ inch diameter cable can have a length of up to about 1,000 feet and can have sufficient room for an optical data fiber. The system solves the problem of remotely controlling ROVs in a manner that allows the ROV to travel through any body of water while being in full high speed data communications with a controller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates a prior art ROV with support boat; 
           [0007]      FIG. 2  illustrates a ROV coupled to a buoy with a tether and wireless transceivers; 
           [0008]      FIG. 3  illustrate a view of the ROV with the tether and the external forces applied to the ROV; and 
           [0009]      FIG. 4  illustrates an embodiment of the surface buoy. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    In order to dispense with the tether, an alternate means for powering the ROV is required and an alternate means of remote control communication with the ROV are needed. Various energy systems can be employed to provide on board power for the ROV. In a preferred embodiment, the invention&#39;s power is provided by lithium ion batteries as used on Hawkes designed manned submersibles. In addition to the power supply, wireless communications are also required. Wireless communications are the most difficult problem and the system and method for providing wireless communications is a significant part of this invention. 
         [0011]    The difficulty in providing a suitable means of communication is a problem with free swimming ROVs when human intervention and a control are needed at a high enough level to require a high band width. The ROV may be controlled by using acoustic control signals that are transmitted between the support boat and the ROV through the ambient water. This means of communications can utilize an acoustic transmitters and receivers for data transmissions between the ROV and a remote control unit. The speed of communication is limited by the speed of sound through water about 1,500 meters/second and the physical distance between the ROV and the remote control unit. An example of a high bandwidth communications is a closed circuit television that requires data transfer rate of about 1-12 Mega Bytes per second (MBps). Based upon the data transfer rate limitations of acoustic systems, high bandwidth data cannot be easily transmitted through water. 
         [0012]    In order to provide a wireless system for the ROV, the communications are broken up into a two stage communication method. With reference to  FIG. 2 , the present invention uses a first stage that includes an ROV  201  that is permanently attached to a towed surface buoy  211  by a communications tether  205  that enables high bandwidth communications between the ROV  201  and the surface buoy  211 . The second stage includes radio communications link between the surface buoy  211  and a surface control station  215 . Each stage utilizes different communication mechanisms and operates in very different manners. 
         [0013]    The first stage include a communications tether  205  includes an optical fiber and/or an electrically conductive wire. The communications between the optical fiber require an optical transmitter that transmits data signals in the form of light through the optical fiber to an optical receiver. For electrical signals, the data is transmitted as electrical signals through the conductor(s) from a transmitter to a receiver. For two way communications, the ROV  201  and surface buoy  211  will each have a receiver and transmitter. Control instructions for movement will be transmitted from the control station  215  to the ROV  201  while data such as video, photographs, etc will be transmitted from the ROV  201  to the control station  215 . 
         [0014]    As the ROV  201  moves, the communications tether  205  is pulled in tension and the surface buoy  211  is towed across the surface of the water  219 . Vertical movement of the ROV  201  will not cause the buoy to move. However, as the ROV  201  moves horizontally away from the buoy  211 , the tether  205  will be tensioned and the ROV  205  will pull the buoy across the water  219 . Thus, the ROV  201  is free to move anywhere horizontally through the water and the depth of the ROV  201  movement will only be restricted by the length of the tether  205 . 
         [0015]    The second stage is a radio communications link from the surface buoy  211  to the surface support control station  215 . The control station  215  may be a portable unit aboard a boat  221 , ship, oil rig, or land based that is typically above sea level. The radio signals travel through air between an antenna  213  coupled to a RF transceiver on the surface buoy  211  and a RF transceiver coupled to the control station  215 . By using a two stage communications link, the control station  215  can remotely control the ROV  201  and receive high bandwidth data from the ROV  201 . 
         [0016]    In some cases, a plurality of wireless communication bases  215  can be used in series. For example, a land based control station  215  can transmit data to a support ship  221  which then transmits the data as wireless signals to the surface buoy  213  which transmits the data through the tether  205  coupled to the ROV  201 . Similarly, the ROV  201  can transmit signals through the tether  205  to the buoy  211  which can then transmit the wireless signals to the support ship  221  control station  215  which are forwarded to the land based control station  215 . Since the buoy  211  will always remain on the water surface, the ROV can travel anywhere that is within the communications range of the surface support control station. The only restriction on travel would be that the ROV travel depth cannot exceed the length of the cable. 
         [0017]    In an embodiment the maximum length of the cable tether will depend upon the type of cable being used and the drag generated by the tether. A wider tether will cause more drag and will need to be shorter in length than a thinner tether. As discussed, the tether can contain an electrical conductor or an optical fiber. The tether containing a conductive wire cable will tend to be wider in diameter. For example, a ⅜ inch diameter cable may be required to contain a copper wire can only have a maximum length of approximately 500 feet. In contrast a ⅛ inch diameter armored cable that contains a thin optical fiber can be up to about 1,000 ft in length. The hydrodynamic drag can also be reduced by using a fairing around the tether. If a hydrodynamic fairing is used, the drag is significantly reduced in comparison to a circular cross section tether. The drag coefficient C d  used to predict the drag forces can be reduced from about 1.2 for a circular cross section to about 0.3 for a tether with fairing having a minimum thickness that is equal to the diameter of cross section. Thus, an ⅛ inch wide armored cable that has a fairing can be up to about 2,000 feet in length and produce less drag than a much shorter circular cross section cable. 
         [0018]    In an embodiment, the operator can select the most appropriate tether having a fixed length. Since the operator will typically know the required dive depth prior to releasing the ROV, a suitable length communications cable can be attached between the ROV and buoy. During the dive, the operator can control the ROV so that it does not exceed the maximum depth. 
         [0019]    In other embodiments, the tether can be retracted into the buoy or the ROV. The tether can be stored on a storage spool can be mounted on the buoy to store long cables. The spool can be rotated to release the stored tether as additional length is needed. As the ROV returns to the surface the tether can also be retracted. This feature can be useful in simplifying the deployment and retrieval of the ROV, since the cable tether can be retracted and would not have to be retrieved separately from the ROV and buoy. Also, by only exposing the required length of the tether, the hydrodynamic drag of the cable is also minimized. 
         [0020]    In order for the ROV to tow the cable connected to the surface buoy, the ROV will need sufficient power to overcome the drag forces of the tether cable and the buoy. The drag forces will act on the ROV by the tension in the tether. Thus, a high tension will be caused by a high drag force. The tether tension will typically pull the ROV back and up at the angle of the tether to the ROV. The drag forces and tether tension will increase with the velocity of the tether and buoy through the water. Since the ROV may be used to explore fixed objects on the sea floor, the cable may also be subjected to sea water current. In addition to the drag from the cable movement through the water, various other forces will be applied to the cable including wind and wave forces against the surface buoy and the hydrodynamic drag against the buoy movement through the water. Thus, the ROV must provide enough propulsion force to overcome the sum of the drag on the tow cable can include the cable drag and current, wind and wave forces on the surface buoy. Hence in order for the vehicle to move as commanded, it will need to at all times be able to generate the counter forces and vector to the tension, direction and rotational moments inflicted by the tension in the tow cable and its angle and place of action(s) on the vehicle. 
         [0021]    The ability of the ROV to physically move as commanded and remain under control and counter all tow forces and moments coupled to a support ship with a cable has been impractical to date, even using a minimum diameter and streamlined drag armored fiber optic link. As the ROV moves, the cable tension pulls the ROV up and prevents accurate movement control. In order to overcome this problem, a winged submersible is required, such as the Hawkes Ocean Technologies (HOT), U.S. Pat. No. 7,131,389 which is hereby incorporated by reference. The wings, rudders and elevators of the ROV produce strong directional forces that are able to resist the uncontrolled disruptive physical vertical pull and turning moments caused by the tow cable. The cable and buoy forces that result from movement of the ROV are instantly controlled by controllable winged surfaces of the ROV. In order to minimize the effects of the buoy, the connection point can be at the center of hydrodynamic effort of the winged submersible ROV. Thus, any vertical forces applied to the ROV by the tether will not alter the pitch of the ROV. The tether can also be connected to an elevated surface such as a fin, so that it is kept away from any moving components such as the propellers to avoid entanglement. 
         [0022]    The remotely controlled ROV uses winged surfaces with single or multiple thrusters providing forward thrust and speed. The winged ROV uses the movement or flow of the water over the wings to provide forces perpendicular to the wings. Thus, a winged ROV that is traveling horizontally through the water will produce a substantial vertical force that is substantially greater than any vertical forces caused by the cable drag or buoy buoyancy. The relationship between thrust and lift can by estimated and quantified by the lift/drag ratio. In an embodiment the lift to drag ratio of the winged ROV may be about 10:1. Thus, an upward pull of the tow cable of say 100 lbs can be resisted by a downward lift from a wing of 100 lbs for a forward thrust penalty of only 10 lbs. In contrast, a non-winged ROV will require a downward thrust of 100 lbs. just to counteract the cable drag. 
         [0023]    With reference to  FIG. 3 , the wing force is instantly controllable by actuators, via manual control or autopilot to quickly act as needed to counter the disruptive tow forces and moments. For example, the autopilot of the winged ROV can include force sensors that monitor the drag tension and direction on the cable. If a variation in the cable tension is detected, the system can automatically increase or decrease the thrust or wings to counteract the change in cable tension. Thrust can be used to counteract the horizontal component of the cable tension and the wing angles can be changed to altered to counteract the vertical component of the cable tension. 
         [0024]    For example, the forces applied to the winged ROV can be estimated by the equations: 
         [0000]        Fv=T ×SIN θ 
         [0000]        Fh=T ×COS θ+ L/D×Fv    
         [0025]    Where:
       Fv=vertical force   Fh=horizontal force   T=tension   Θ=angle of cable to the ROV   L/D=lift/drag ratio       
 
         [0031]    Self-powered craft, especially battery-powered craft, are energy-limited. And thus the leverage and efficiency of a fully controllable (Pitch, Roll, yaw) winged body, able to hold large vertical loads and moments and able to manage the large tow forces with a smaller amount of additional forwards thrust, is a great advantage in making the concept work for a self-powered craft requiring minimum power. 
         [0032]    The present invention has been described as having a rechargeable lithium battery which can limit the duration of the ROV operations. In an alternative embodiment, the surface buoy can have the energy source such as an electrical power supply, electrical generator, solar cells, fuel cells, etc. In this embodiment, the cable can include electrical conductors that provide a low resistance transmission of electrical power through tethered tow cable to the ROV. Since the power source is exposed to air, the source of power in the buoy can be an air-breathing gas powered electrical generator to provide longer duration operations. 
         [0033]    The winged ROV can also have three axis sensors so the vehicle will be flown through the water manually with the wings level to a heading or have auto pilot controlling the ROV on three axis of movement. Because the wing surfaces of the ROV are substantially greater than the drag forces, the cable can move with the applied forces and the vehicle will stay on course. 
         [0034]    In an embodiment, a Global Positioning System (GPS) unit can be mounted to the buoy so that a position of the ROV can be accurately determined. Based upon the buoy position, the system can estimate the position of the ROV by adding the length of the tether in the direction of the tether from the buoy. The system can then use a pressure transducer signal from the ROV to determine its depth. Based upon these calculations, the system can accurately determine the position of the ROV. 
         [0035]    With reference to  FIG. 4 , in an embodiment the buoy  211  may include a weighted keel  229  which provides roll stability to the vertically oriented antenna  213 . The buoy  211  can be an elongated structure that provides buoyancy and pitch stability. The tether  205  can be coupled directly to the buoy  211  or to the keel  229 . In addition to the keel, the buoy  211  may include a rudder  231  which provides yaw stability as the buoy  211  is towed through the water. The drag on the tether  205  can also pull down on the buoy  211 . The buoy  211  may have a positive buoyant force of 1,000 pounds or more to overcome any potential downward forces applied by the tether  205 . 
         [0036]    As discussed, the hydrodynamic drag on tether resists the movement of the ROV  201 . The drag will be increased if the tether  205  runs into growth such as kelp. The kelp can wrap around the tether  205  and substantially increase the drag. If the drag due to kelp becomes problematic, a kelp cutter can be used to remove the kelp from the tether  205 . In an embodiment, the kelp cutter  235  can include a cutting surface that moves along the tether to remove any attached kelp. 
         [0037]    While the invention has been described herein with reference to certain preferred embodiments, these embodiments have been presented by way of example only, and not to limit the scope of the invention. Accordingly, the scope of the invention should be defined only in accordance with the claims that follow.