REMOTELY OPERATED UNDERWATER VEHICLE

Abstract

A system for communicating with a remotely operated underwater vehicle (ROV) includes a winged ROV coupled to a surface buoy by a tether. A controller on a support ship is coupled to the tether and 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. The wings of the ROV produce negative lift which is greater than the buoyant force of the ROV and the vertical tension forces on the tether.

Description

BACKGROUND

With reference to FIG. 1, remotely operated underwater vehicles (ROV'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

The present invention is directed towards a control system for operating a remotely operated winged underwater vehicle (ROV). The winged ROV has a propulsion system and directional controls that allow an operator to control the speed and direction of the winged ROV through a body of water. The winged ROV can also have sensors and feedback devices that can provide information that is transmitted back to the operator or any other receiver.

A ship can be coupled to the winged ROV with an optical tether. A remotely located controller can be coupled to an optical transceiver so the operator can transmit and receive data from the winged ROV. For example, the controller transmits control signals through the tether to the winged ROV and the winged ROV performs the actions of the control signals. The sensors and feedback signals produced by the winged ROV are transmitted back through the tether to the controller on the ship.

The diving depth of the winged ROV can be limited by the length of the tether. The tether can have various lengths and diameters. A larger diameter tether will be stronger but will also result in more drag forces as the winged 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 in the cable cross section for an optical data fiber. The system solves the problem of remotely controlling winged ROVs in a manner that allows the winged ROV to travel through any body of water while being in full high speed data communications with a controller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art ROV with support boat;

FIG. 2 illustrates a ROV coupled to a support boat with a tether;

FIG. 3 illustrates a view of the ROV with the tether and the external forces applied to the ROV;

FIGS. 4 and 5 illustrate cross sections of the tether with a hydrodynamic fairing; and

FIG. 6 illustrates a cross section of a spool holding the tether with a hydrodynamic fairing.

DETAILED DESCRIPTION

In order to drive the winged ROV, an alternate means for power is required. Various energy systems can be employed to provide on board power for the ROV. In a preferred embodiment, the invention's power is provided by lithium ion batteries as used on Hawkes designed manned submersibles. In addition to the power supply, an optical communications system is also required. The data transfer rate for high bandwidth communications sufficient to support a closed circuit television may require data transfer rate of about 1-12 Mega Bytes per second (MBps).

With reference to FIG. 2, the present invention includes an ROV 201 that is permanently attached to a communications tether 205 that enables high bandwidth communications between the winged ROV 201 and the support ship 221. The 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 support ship 221 will each have a receiver and transmitter. Control instructions for movement will be transmitted from a controller on the support ship 221 to the ROV 201 while data such as video, photographs, etc will be transmitted from the ROV 201 to the control station 215.

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. As the ROV 201 moves horizontally away from the support ship 221, the tether 205 will be tensioned and additional tether 205 can be released from the support ship 221 or the support ship 221 will follow the ROV 205. 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 fully extended length of the tether 205.

In some cases, the described system can be used with other communications systems that would like to receive data from the ROV 201 or transmit data to the support ship 221 or the ROV 201. For example, a land based control station 215 can transmit data to a support ship 221 which then 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 support ship 221 and then the support ship 221 can transmit information to the land based control station 215. Since the support ship 221 will always remain on the water surface, the ROV 201 can travel anywhere.

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. The ROV will have to have sufficient power to overcome the buoyant forces of the ROV and the forces applied to the ROV by the tether. A wider cross section tether will cause more drag as it moves through the water and therefore a wider tether may need to be shorter in length for the ROV to overcome the drag forces than a thinner cross section 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.

In some embodiments, the system can use different cables depending upon the dive that can be connected to the control ship and the ROV by optical fiber connectors. An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so that light can pass. Most optical fiber connectors are spring-loaded so the fiber endfaces of the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic contact, avoiding any glass to air or plastic to air interfaces, which would result in higher connector losses. A variety of optical fiber connectors are available. The main differences among types of connectors are dimensions and methods of mechanical coupling.

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. With reference to FIGS. 4 and 5, two examples of hydrodynamic fairings that surround the optical fiber cable 811 are illustrated. With reference to FIG. 4, the fairing includes a leading section 801 and a trailing section 803. The leading edge section 801 includes a rounded edge 805 and a trailing section 803 includes tapered surfaces that form a sharp trailing edge 809. With reference to FIG. 5, the fairing only includes a trailing section 813 that has tapered surfaces that form a sharp trailing edge 819. The rounded surface of the optical fiber cable 811 is used as the front edge 815. In an embodiment, the fairings are formed in an extrusion process where the optical cable 811 is passed through a die having the desired fairing cross section with a heated thermoplastic material. The liquid thermoplastic will cool and solidify around the optical cable forming the fairing.

The optical fiber cable includes an optical fiber that that is surrounded by a cladding of plastic layers that are coated around the outer diameter of the optical fiber. The cladding can be coated with a tough resin buffer layer, which may be further surrounded by a jacket layer which can be made of a plastic material. These layers add strength to the fiber but do not contribute to its optical wave guide properties. The jacketed fiber can be enclosed, with a bundle of high strength flexible fibrous polymer members like aramid materials. Each end of the cable may be terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from the ROV and communications equipment on the ship.

In an embodiment, the operator can select the most appropriate tether 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. The system may also contain warning mechanisms that inform the operator when ROV is reaching the maximum depth for the cable being used.

In other embodiments, the tether can be retracted into the support ship 221 or a spool module that is placed in the water adjacent to the support ship 221. With reference to FIG. 6, the tether can be stored on a storage spool 901. The spool 901 can be rotated to release the stored tether 205 as additional length is needed or rotated to retract the tether 205 as the ROV returns to the surface and moves closer to the support ship 221. 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. An alignment mechanism 905 can be used to properly align the tether 205 with the spool 901. In an embodiment, the alignment mechanism 905 aligns the tether 205 with a rounded leading edge facing the center of the spool 901 and the trailing edge facing away from the center of the spool 901.

With reference to FIG. 2, in order for the ROV to tow the cable connected to the surface buoy, the ROV 201 will need sufficient power to overcome the drag forces of the tether cable 205 moving through the water and against any water movement due to currents 291. The drag forces will act on the ROV 201 by the tension in the tether 205. Thus, a high tension will be caused by a high drag and lift force. The tether tension will typically pull the ROV 201 back and up at the angle of the tether to the ROV 201. The drag forces and tether tension will increase with increases in the velocity of the tether 205 through the water. Since the ROV 201 may be used to explore fixed objects on the sea floor, the tether 205 may also be subjected to sea water current 291. Thus, the ROV must provide enough propulsion force to overcome the sum of the drag on the tether 205 can include the cable drag due to ROV velocity and water current.

The forces acting on the ROV also include vertical forces. The wings of the ROV must be able to provide sufficient vertical forces to overcome both the buoyant forces of the ROV and the lift forces from the tension on the cable. 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.

The ability of the ROV to physically move as commanded and remain under control and counter all tether 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), US 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. Alternatively, the connection point can be slightly forward of 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. When the tension on the tether pulls the ROV sideways, the ROV can roll so that the tether is vertically aligned with the ROV. This allows the wings to provide both a down ward vertical force and a horizontal side force to resist the tension in the cable.

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.

This negative lift of the ROV can be altered by changing the area of the wings. A larger wing will be able to produce more negative lift for a ROV velocity. Thus, if there is going to be a large tension force on the cable and the cable is positioned at a high vertical angle relative to the ROV and the ROV has a large buoyant force and must travel at slow horizontal speeds, larger wings may be necessary. A drawback of the larger wing is increased drag. Thus, more thrust is required to move an ROV having larger wings through the water. Conversely, if the tension is low and the ROV has a low buoyant force and must travel fast, smaller wings will reduce the drag and allow for more energy efficiency. In an embodiment, the ROV may have replaceable wings that allow for multiple negative lift forces. Alternatively, the ROV may have wings that are adjustable in size.

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 211 can include force sensors that monitor the drag tension and direction on the cable 205. If a variation in the cable tension is detected, the system can automatically increase or decrease the thrust or angle of the 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. For example, the forces applied to the winged ROV can be estimated by the equations:

Fv=T×SIN θ

Fh=T×COS θ+D/L×Fv

Where:

Fv=vertical force

Fh=horizontal force

T=tension

η=angle of cable to the ROV

L/D=lift/drag ratio

In addition to the tether forces, the buoyant force will lift the ROV. In order to overcome the buoyant vertical forces negative lift provided by the wings and must be greater than the Fv and buoyant force Fb. As discussed, the lift to drag ratio can be about 10:1, thus a thrust force Ft of 1 pound in the horizontal direction will result in 10 pounds of vertical force. The thrust must also overcome the horizontal forces. Thus, the required thrust of the ROV can be estimated based upon the equation:

Ft>D/L×(Fv+Fb)+Fh

Where:

Fb=buoyant force

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.

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 support ship 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 support ship can be an air-breathing gas powered electrical generator to provide longer duration operations.

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.

In an embodiment, the system can estimate the position of the ROV by adding the length of the tether in the direction of the tether from the support ship. 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.

With reference to FIG. 2, as discussed above, 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.

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.

Claims

1. An apparatus comprising: a remotely operated underwater vehicle having a propulsion mechanism, wings that provide downward lift and directional controls; anda tether coupled between the remotely operated underwater vehicle and a control vessel, the tether including a communications cable;wherein control data is transmitted from the control vessel to the remotely operated underwater vehicle to control the operation of the remotely operated underwater vehicle.

2. The apparatus of claim 1 wherein the communications cable includes an optical fiber.

3. The apparatus of claim 2 wherein the communications cable is less than ⅛ inch in width.

4. The apparatus of claim 1 wherein the remotely operated underwater vehicle includes sensors and sensor data is transmitted at a data transfer rate of about 1-12 mbps from the remotely operated underwater vehicle through the communications cable and the second wireless transceiver to the first wireless transceiver.

5. The apparatus of claim 1 wherein the tether includes a power cable and the surface buoy has a power supply which transmits electrical power through the power cable to the remotely operated underwater vehicle.

6. The apparatus of claim 1 wherein the tether has a fairing that has a rounded front surface and a sharp back surface.

7. The apparatus of claim 6 wherein a portion of the tether is stored on a spool.

8. The apparatus of claim 7 wherein a portion of the tether is stored on the spool with the rounded front surface facing the center of the spool.

9. The apparatus of claim 1 wherein the downward lift of the wings is greater the buoyancy of the remotely operated underwater vehicle and an upward pull of the tether.

10. The apparatus of claim 1 the tether has a diameter that is less than about ⅛ inch and a length greater than about 1,000 feet.

11. A method for operating a comprising: placing a remotely operated underwater vehicle having a propulsion mechanism, wings that provide downward lift and directional controls in a body of water;transmitting control data from a control vessel through an optical fiber communications cable to the remotely operated underwater vehicle to control the operation of the remotely operated underwater vehicle.

12. The method of claim 11 wherein the remotely operated underwater vehicle includes sensors and sensor data is transmitted at a data transfer rate of about 1-12 mbps from the remotely operated underwater vehicle through the optical fiber communications cable to the control vessel.

13. The method of claim 11 wherein the sensors include video cameras and the sensor data includes video images.

14. The method of claim 11 further comprising: moving the remotely operated underwater vehicle horizontally through the body of water;

15. The method of claim 11 further comprising: storing a portion of the tether on the control vessel; andreleasing the portion of the tether from the control vessel as the remotely operated underwater vehicle travels deeper into the body of water.

16. The method of claim 15 further comprising: retracting the portion of the tether into the control vessel as the remotely operated underwater vehicle travels towards the surface of the body of water.

17. The method of claim 11 further comprising: storing a portion of the tether on a spool;

18. The method of claim 17 further comprising: retracting the portion of the tether into the remotely operated underwater vehicle as the remotely operated underwater vehicle travels towards the surface of the body of water.

19. The method of claim 18 further comprising: rotating the spool; andmoving the tether through a guide that causes the rounded front surface of the tether to face the center of the spool.

20. The method of claim 11 wherein the downward lift of the wings is greater the buoyancy of the remotely operated underwater vehicle and an upward pull of the tether.