Abstract:
A propulsion system is provided for an underwater vehicle such as a Remote Operated Vehicle (ROV). Two propellers are independently driven by motors, while the orientation of the propellers is simultaneously controlled by a third motor. A means is provided for reprogramming the control electronics that can be disabled when the vehicle is underwater. The control electronics also provides that all signals including video are transmitted to a base station without requiring coaxial cable.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 60/710,552 filed Aug. 23, 2005, which is incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is directed to a method of propulsion for underwater vehicle, and more particularly to a propulsion and steering mechanism for an underwater vehicle such as a Remote Operated Vehicle (ROV). 
       BACKGROUND OF THE INVENTION 
       [0003]    Inspection class Remote Operated Vehicles (ROVs) are typically used to position a video camera underwater. The ROV usually contains electronics that are connected to a base station by a wire tether. Motor driven propellers called thrusters are used to move the ROV. 
         [0004]    Current ROVs, for example as described in U.S. Pat. No. 6,662,742, generally use separate thrusters to control motion in the horizontal and vertical planes. For example, a pair of thrusters mounted horizontally on the sides of the ROV can move the ROV forwards, backwards and control azimuth, while another thruster mounted vertically can move the ROV up and down. 
         [0005]    Since motors are generally heavy, this configuration is not optimally efficient. When the ROV is moving in the horizontal plane, the vertical thruster is essentially dead weight, so that the power to weight ratio is diminished. The situation is typically worse when moving vertically because the multiple horizontal thrusters that are idle reduce the efficiency even further. 
         [0006]    Another problem with ROVs relates to the electronics. Control circuitry, which is generally not waterproof, is often housed in a watertight box. This allows for access to perform reprogramming of the electronics, but causes a problem because opening and resealing the watertight enclosure may be time consuming. 
         [0007]    A solution to this problem may be to run the reprogramming signals through the tether, but this has the disadvantage of adding to the size, weight and cost of the tether. 
         [0008]    Also, it may be desirable to encapsulate the electronics in epoxy, eliminating the need for a watertight enclosure for the electronics. This solution has not typically been employed in past ROVs because once encapsulated, either the electronics cannot be reprogrammed, or as mentioned above the reprogramming wires must be run through the tether. 
         [0009]    Another problem with existing ROVs is that in general an expensive tether is required. This is because the tether typically contains power wires, control wires and video cable. Since video is usually a coaxial cable and the power and control signals are not, the tether must contain both standard unshielded wires for power and control and shielded coaxial cable for the composite video. 
         [0010]    A standard solution is to use a custom cable for the tether, but this adds to the cost of the ROV. Another solution heretofore employed is to put batteries in the ROV eliminating the need to run power through the tether. This allows a single coaxial cable to be used for the tether, carrying modulated video and control signals. The problem with this method is that the batteries add weight to the ROV and the modulation circuitry can be expensive. 
         [0011]    A need therefore exists for a propulsion system for an ROV that improves the power to weight ratio while allowing motion in both the horizontal and vertical planes. The electronics should be reprogrammable without requiring a watertight box or additional reprogramming wires in the tether, and the tether should supply video to the base station without requiring coaxial wires. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    This invention is directed to a method of propulsion for an underwater vehicle. Two propellers are independently driven by motors, while the orientation of the propellers is simultaneously controlled by a third motor. A means is provided for reprogramming the control electronics that can be disabled when the vehicle is underwater. The control electronics also provides that all signals including video are transmitted to a base station without requiring coaxial cable. 
         [0013]    This invention uses two horizontally opposed propellers, which can be rotated into the horizontal or vertical planes, to drive the ROV. The control electronics includes an electrically isolatable programming port that allows the electronics to be reprogrammed. All signal including video are run through standard category 5 network cable (Cat5 cable), reducing weight and cost. 
         [0014]    For the preferred embodiment, a separate motor drives each propeller and a single servo motor controls the orientation (horizontal, vertical or in between) of the propellers. To move in the horizontal plane, the motors can drive the ROV forward and backward by changing the direction of rotation of the propellers. Turning can be accomplished by varying the relative speed of the motors, and rotation about a point can be accomplished by running the propellers so as to create thrust in opposite directions. 
         [0015]    To move the ROV up and down, the servo rotates the propellers to the vertical orientation. The direction of the propellers then controls whether the ROV moves up or down, and the relative speed of the propellers controls the roll of the ROV. In addition, the servo motor can position the propellers in between the horizontal and vertical planes, to provide a motion that combines both horizontal and vertical components. When operating in this manner, the floatation at the top of the ROV provides stability and reduces any tendency for unwanted roll. 
         [0016]    The electronics provides a programming port that is exposed to the water. Two pins on the port are used to electrically isolate the port from the programming bus. In this manner, when being operated in the water, the pins can be shorted together by a shorting block and the programming port will be unaffected by any conductive effect of the water. 
         [0017]    However, when the unit is on dry land and reprogramming is desired, the shorting block can be removed and the electronics can be connected to a reprogramming device by the programming port. 
         [0018]    The camera is connected to the tether through a video balun, which converts the 75-ohm composite video, ordinarily requiring coaxial cable, to 100 ohm balanced signal compatible with standard low cost Cat5 cable. Additional pairs of the Cat5 cable are used for power, ground and control signals. In the base station, a second balun can be used to convert the video signal back into composite video if desired for recording, display or digitizing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is an illustration of the system. 
           [0020]      FIG. 2  is a right side perspective view of the underwater vehicle of  FIG. 1 . 
           [0021]      FIG. 3  is a left side perspective of  FIG. 2 . 
           [0022]      FIG. 4  is a simplified horizontal cross section of the drive and propulsion system. 
           [0023]      FIG. 5  is a simplified schematic view of the rotation mechanism. 
           [0024]      FIG. 6  is a schematic view of the electrical circuit. 
           [0025]      FIG. 7  is a detailed schematic of the programming port. 
           [0026]      FIGS. 8A to 8C  are perspective views of  FIG. 2  showing the propellers in three orientations: horizontal, vertical, and degrees. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  shows an illustration of the system, including Remote Operated Vehicle ROV  10  connected to base station  80  by tether  14 . The output of ROV video camera  12  is displayed in real time on the screen of the laptop  82 , and the joystick  84  is used to control the movement of the ROV  10 . 
         [0028]      FIG. 2  shows a perspective view of the right side of ROV  10 . The main components of ROV  10  are video camera  12 , a right side thruster consisting of a drive motor  20  linked to propeller  46  through rotatable arm  40 , a left side thruster consisting of drive motor  50  linked to propeller  66  through rotatable arm  60 , and servo  70  to simultaneously rotate the arms  40  and  60 . 
         [0029]    Case  16  provides the attachment points for camera  12 , drive motors  20  and  50 , drive arms  40  and  60 , servo  70 , floatation  90  and control electronics  100 . Floatation  90  counterbalances the weight of the ROV to provide approximately neutral buoyancy. For shallow operation, a block of closed cell foam can be used. For deeper operation, the foam can be covered in a solid outer shell such as fiberglass, or a sealed container or other hard buoyant object can be used for floatation. 
         [0030]    Right arm gear  42  is connected to right arm  40 , and the corresponding left arm gear  62  is connected to left arm  60 . Servo gear  72  is connected to servo  70 , and drives right idler gear  44 , which also connects to rotation shaft  74 . Shaft  74  also connects to left idler gear  64 , shown in left perspective view  FIG. 3 . When servo  70  turns servo gear  72 , right idler gear  44  rotates right arm  40  and also rotates rotation shaft  74  and left idler gear  64 , which rotates left arm  60 . In this fashion servo  70  controls the orientation of both right arm  40  and left arm  60  simultaneously. 
         [0031]      FIG. 4  shows a cutaway view of the motor drive system. Drive motor  20  is offset from case  16  centerline  18  in order to avoid interference between right motor bevel gear  24  and left drive bevel gear  26 . Similarly, drive motor  50  is offset from centerline  18  in order to avoid interference between left motor bevel gear  24  and right drive bevel gear  26 . The offset is exaggerated in  FIG. 4  for the sake of clarity. 
         [0032]    In the preferred embodiment, drive motor  20  is housed in a watertight housing and protected from water ingress by shaft seal  22 . Shaft seal  22  can be a simple lip seal for shallow water operation, or a higher performance seal for deep water use. Alternatively, a magnetic coupling could be used to isolate the motor from the seawater. Locating drive motor  20  in a watertight housing has some of advantages. First, there is no need to make case  16  waterproof because the gearing and shafts it contains can be made from materials compatible with submersible use. Second, the motor then becomes an easily replaceable part, allowing for standard motors to be replaced with higher performance motors for greater operating speed or operation at a greater depth. 
         [0033]    In the preferred embodiment, drive motor  20  connects to motor bevel gear  24  that drives right drive bevel gear  26 . Right drive bevel gear  26  connects to right drive shaft  30 , which is supported by right shaft bearings  38 . Drive shaft  30  is concentric with right arm  40 . This allows right propeller  46  to be turned by motor  20  independently of the rotation of right arm  40 . Drive shaft  30  is supported by sleeve bearing  38 , which may for example be a flange mounted sleeve bearing. 
         [0034]    The distal end of right drive shaft  30  connects to right end bevel gear  32  that drives right propeller bevel gear  34 . Right propeller bevel gear  34  connects to right propeller shaft  36  and drives right propeller  46 . The left side drive system is symmetrical to the right side drive system, with drive motor  50  connected to motor bevel gear  24  which drives left drive bevel gear  26 . Left drive bevel gear  26  connects to left drive shaft  30 , which is supported by left shaft bearings  38 . For the preferred embodiment, right propeller  46  is a right hand propeller and left propeller  66  is a left hand propeller, i.e. right propeller  46  provides forward thrust when turning clockwise, and the left propeller  66  provides forward thrust when turning counterclockwise. This provides a balancing effect and prevents the direction of rotation of the propellers from inducing a rotational force to the ROV  10 . 
         [0035]      FIG. 5  is a cutaway view of the servo driven rotation mechanism. For the preferred embodiment, servo  70  is a servo motor housed in a watertight housing. Since servo  70  typically moves with a range of plus or minus 90 degrees from the neutral horizontal position, a rotating shaft seal is not required and a low cost latex bellows can be used to seal the gear to the housing. 
         [0036]    When servo  70  is driven clockwise when viewed from the right, it drives servo gear  72  clockwise. Servo gear  72  drives both idler gears by directly driving right idler gear  44  and indirectly driving left idler gear  64  which is connected to right idler gear  44  by rotation shaft  74 . The rotation of the idler gears will be opposite that of the servo, so that when the servo is driven clockwise, both idler gears will turn counterclockwise. 
         [0037]    Each idler gear in turn drives the associated arm gear; right idler gear  44  drives right arm gear  42 , and left idler gear  64  drives left arm gear  62 . Counterclockwise motion of the idler gears causes clockwise motion of the arm gears, with the net effect being that when the servo  70  moves clockwise both arms move clockwise. 
         [0038]      FIG. 6  shows a block diagram of the electrical connections of the system. There are two major electrical components: base station  80  and control electronics  100  located in ROV  10 . Base station  80  consists of a processing unit such as laptop PC  82 , power supply  88 , and joystick  84  to control the motion of ROV  10 . 
         [0039]    Control electronics  100  contains microprocessor  104 , which is typically a low cost 8-bit microprocessor. Sensors  108  are connected to microprocessor  104 . A variety of sensors can be used, typically consisting of an accelerometer to provide roll and pitch, an electronic compass to provide heading, and a depth sensor. Microprocessor  104  is also connected to pulse width modulator (PWM) circuits  106  for drive motors  20  and  50 . PWM circuits  106  are used to independently control the speed and direction of each drive motor. 
         [0040]    In the preferred embodiment, all signals between base station  80  and the control electronics  100  are run through 100 feet of standard Cat5 cable, which contains four twisted pairs of 24 gauge wire. Two pairs are used to carry power from base station  80  to ROV  10 . Another pair of wires is allocated to the control signals, with one wire for transmit and one wire for receive. Any appropriate electrical interface may be used for the control signals; in the preferred embodiment, RS-232 serial interface is used to send data to and from the ROV. The final pair of wires in tether  14  is used to carry video. 
         [0041]    In base station  80 , the two pairs dedicated to power are connected to power supply  88 . For example, power supply  88  may generate 24 volts DC. One pair of wires is connected to +24 volts and one pair of wires is connected to ground. The pair of wires allocated to control signal is connected to the serial port of laptop  82 . The pair of wires for video is connected to balun  86 . 
         [0042]    In control electronics  100  in ROV  10 , the pair of wires for power is connected directly to PWM circuits  106 , and is also used to supply power to the rest of the circuitry in control electronics  100  and to camera  12 . In the preferred embodiment, control circuitry  100  requires 3.3 volts, and camera  12  requires 12 volts, so voltage regulators are used to convert the 24 volts from power supply  88  into the appropriated level as required. The control electronics may also contain a programming port connected to microprocessor  104  through an analog switch  110 . The switch can be disabled by shorting together two pins on programming connector  112 , allowing the connector to be isolated from the microprocessor. 
         [0043]      FIG. 7  shows a detailed schematic of the programming port. In the preferred embodiment, programming connector  112  is a 10 pin connector used to connect to the JTAG programming port on microprocessor  104 . Programming connector  112  is positioned on the outside of ROV  10 , where it will come in contact with sea water which has conductive properties. Analog switch  110  is connected in between microprocessor  104  and programming connector  112 . Pin  9  of programming connector  112  is used to enable or disable the programming port. When pin  9  is unconnected, resistor  114  pulls up the enable input of analog switch  110 , enabling the switch and allowing microprocessor  104  to be reprogrammed. When pin  9  is connected to pin  10 , for example by a shorting block, jumper, or similar connection, the enable input of analog switch  110  will be a zero potential disabling the programming port. With the jumper in place, programming connector  112  is effectively disconnected from microprocessor  104 . 
         [0044]    During normal operation, output of camera  12  is shown in real time on screen of laptop  82 . Laptop  82  also displays output of sensors  108  (for example roll, pitch, and yaw) and may also display any other pertinent local information such as time, date and GPS coordinates. Laptop  82  may also save video, sensor and local data on its hard drive, CD or DVD storage. In addition, video may also be saved on an external VCR or other recording device, not shown. 
         [0045]    The base station uses a command structure to encode the desired speed and direction for the drive motors  20  and  50 , and the desired rotation for servo motor  90 . Base station  80  also periodically polls the ROV  10  to determine the current status of sensors  108 . Since output of the sensors may be relevant information used in piloting the ROV  10 , base station  80  may poll sensor  108  status many times a second, so that base station  80  can display current sensor data in real time. 
         [0046]    Joystick  84  is used to pilot the ROV  10  so as to position ROV  10  in order to capture the desired information on video. For the preferred embodiment, a 3D joystick is used. Forward and backward motion of the joystick  84  is used to control the angle of rotation of the propellers, with the neutral position of joystick  84  corresponding to a horizontal orientation of the propellers. Depth of the ROV  10  is controlled as follows: pushing the joystick forward will cause the ROV  10  to descend, and pulling the joystick back causes the ROV  10  to move toward the surface. 
         [0047]      FIGS. 8A to 8C  show the propeller position corresponding to the position of joystick  84 .  FIG. 8A  corresponds to the neutral position of joystick  84 , and ROV  10  will move forward horizontally when thrust is applied.  FIG. 8B  corresponds to joystick  84  being pushed forward approximately 50%; this will cause ROV  10  to descend at about a 45 degree angle when forward thrust is applied.  FIG. 8C  corresponds to joystick  84  being pushed all the way forward and ROV  10  will descend vertically when thrust is applied. 
         [0048]    Joystick  84  also has a throttle lever, which moves between off (no thrust) and on (full thrust). Laptop  82  in turn sends commands to ROV  10  to control the voltage applied to the drive motors  20  and  50  using the PWM controllers in the ROV control electronics  100 . 
         [0049]    Azimuth of the ROV  10  is controlled by joystick  84  in two ways: when throttle is on, relative power to the drive motors is modified according to the side to side position of joystick  84 . The neutral (centered) position corresponds to equal power to the drive motors; joystick  84  moved to the right corresponds to increased power to the left drive motor  50 , and joystick  84  moved to the left corresponds to increased power to right drive motor  20 . In this manner the operator may move joystick  84  right to go right and move joystick  84  left to go left. 
         [0050]    Another way to control azimuth by joystick  84  is by twisting the joystick. When laptop  82  detects clockwise twist of joystick  84 , forward thrust is generated on left drive motor  50  and reverse thrust is generated with right drive motor  20 . This caused the ROV  10  to pivot in place, allowing camera  12  to be panned to the right. The speed of the motion is proportional to the amount of rotation of joystick  84 . A symmetrical but opposite motion is generated when joystick  84  is twisted to the left; i.e. camera  12  is panned to the left. 
         [0051]    One potential limitation of the preferred embodiment may be the cost of laptop  82 . This could be ameliorated by using a custom display to show output of camera  12  and additional custom electronics in the base station to replace the functionality of the laptop in interfacing joystick  84  to tether  14 . 
         [0052]    Regarding attachment of drive motor  20  and  50  to case  16 , the drive motors could be attached perpendicular to centerline  18 . This would allow motor bevel gears  24  to be replaced with pinion gears, and drive bevel gears to be replaced with spur gears, potentially providing a wider range of available gear ratios and lower cost. 
         [0053]    Regarding the placement of the motor shaft seals  22 , case  16  could be made waterproof and motor shaft seals  22  could be moved into the drive arms. This would allow the servo  70  and control electronics  100  to be moved inside case  16 , and would reduce the size of floatation  90  by reducing the submerged weight of case  16 . 
         [0054]    Power supply  88  is describes as a 24 volt supply for the preferred embodiment. However, other voltages could be used and may be advantageous in certain circumstances. For example, if tether  14  were longer that the 100 feet of the preferred embodiment, it may be desirable to used a higher voltage to reduce the necessary current and thus lower the voltage drop across the cable. 
         [0055]    While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be afforded the full scope of the claims so as to embrace any and all equivalent apparatus and articles.