Method for determining the position of a marine vessel relative to a fixed location

A method is provided by which a position of a marine vessel can be determined relative to a stationary object, such as a dock. Two position sensors are attached to a marine vessel and a microprocessor, onboard the marine vessel, computes various distances and angular relationships between the position sensors on the marine vessel and stationary transponders attached to the fixed device, such as a dock. The various dimensions and angular relationships allow a complete determination regarding the location and attitude of a marine vessel relative to the dock. This information can then be used by a maneuvering program to cause the marine vessel to be berthed at a position proximate the dock.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method for determining a position of a marine vessel and, more particularly, to a method by which devices on a marine vessel can obtain information, in cooperation with fixed devices on shore, to allow a determination of the relative position and attitude of the marine vessel relative to a fixed location, such as a dock.

2. Description of the Related Art

Many different types of navigation and docking systems are known to those skilled in the art.

U.S. Pat. No. 3,690,767, which issued to Missio et al. on Sep. 12, 1972, describes an optical tanker docking system. The docking system is intended for large ocean going vessels. It comprises a laser pulse range radar system having a laser transmitter and receiver, a retroreflector, and receiving and transmitting optics. Two such systems are disposed on a dock. The retroreflectors are disposed at the bow and stern of a vessel. The laser systems share a time interval meter, a computer, and a display panel. The lasers track the retroreflectors as the ship approaches the dock and the time interval between the transmitted and received pulses is measured. Computations are made in the velocity of the approaching vessel, its distance from the dock, and the vessel position with reference to the dock are continually displayed. The information is then transmitted to the ship's captain.

U.S. Pat. No. 3,707,717, which issued to Frielinghaus on Dec. 26, 1972, describes a boat berthing monitor incorporating sonar and Doppler radar techniques. The system generates correction command signals relative to the berthing velocity profile of a vehicle in approach of a docking station. A Doppler radar system includes a radar transceiver. It projects signals between the docking position and the vehicle and respondingly generates Doppler shift frequency signals indicative of the velocity of the vehicle and the relative displacement thereof. A radar counter has preset initial counts stored therein which are indicative of anticipated initial berthing conditions and responds to the frequency shift signals by counting down from the initial counts in accordance with the Doppler shift.

U.S. Pat. No. 5,274,378, which issued to O'Conner on Dec. 28, 1993, describes a docking velocity indicator system. A relative velocity indicator system for assistance in the docking of vessels uses a radar sensor providing a relative velocity signal indicative of the relative velocity between a ship and a reference, such as a dock. A wireless transmitter associated with the radar sensor receives the relative velocity signal and transmits a signal indicative of the relative velocity signal. A portable receiver and indicator unit carried by the captain of the vessel has a receiver for receiving the transmitted signal and an indicator arranged to receive, from the receiver, a receiver signal indicative of the transmitted signal and, thereby, of the relative velocity signal for indicating the relative velocity between the ship and the reference.

U.S. Pat. No. 5,933,110, which issued to Tang et al. on Aug. 3, 1999, describes a vessel attitude determination system and method. A portable attitude determination apparatus and method are disclosed that can be used with a ship docking system. At least two receivers on a vessel receive global positioning system (GPS) satellite data. GPS carrier phase measurements are used to determine attitude of a moving platform. The phase measurements are processed to determine a precise vector from one receiver phase center to the other. The azimuth and elevation of a baseline vector is then computed.

U.S. Pat. No. 6,268,829, which issued to Weckstrom on Jul. 31, 2001, describes a Doppler direction finder and method of location using Doppler direction finder. It comprises at least one antenna spaced from a location point. The antenna is arranged in use to be rotated about the rotation point. The antenna is arranged to provide a first output signal comprising a signal received by the antenna combined with the Doppler shift component. There are means for providing a second output signal comprising the received signal without the Doppler shift component. Processing means process the first and second signals to obtain the Doppler shift component. Determining means determine from the Doppler shift component the direction from which the received signal is received.

U.S. Pat. No. 6,492,933, which issued to McEwan on Dec. 10, 2002, describes an SSB pulse Doppler sensor and active reflector system. A dual channel microwave sensor employs single sideband Doppler techniques in innumerable vibration, motion, and displacement applications. When combined with an active reflector, the sensor provides accurate range and material thickness measurements even in cluttered environments.

U.S. patent application Ser. No. 11/248,482, which was filed on Oct. 12, 1995 by Bradley et al., discloses a marine vessel maneuvering system. The vessel is maneuvered by independently rotating first and second marine propulsion devices about their respective steering axes in response to commands received from a manually operable control device, such as a joystick. The marine propulsion devices are aligned with their thrust vectors intersecting at a point on a centerline of the marine vessel and, when no rotational movement is commanded, at the center of gravity of the marine vessel. Internal combustion engines are provided to drive the marine propulsion devices. The steering axes of the two marine propulsion devices are generally vertical and parallel to each other. The two steering axes extend through a bottom surface of the hull of the marine vessel.

U.S. patent application Ser. No. 11/248,483, which was filed on Oct. 12, 2005 by Bradley et al., discloses a vessel positioning system that maneuvers a marine vessel in such a way that the vessel maintains its global position and heading in accordance with a desired position and heading selected by the operator of the marine vessel. When used in conjunction with a joystick, the operator of the marine vessel can place the system in a station keeping enabled mode and the system then maintains the desired position obtained upon the initial change of the joystick from an active mode to an inactive mode. In this way, the operator can selectively maneuver the marine vessel manually and, when the joystick is released, the vessel will maintain the position in which it was at the instant the operator stopped maneuvering it with the joystick.

A paper, titled “Direction Finding System” by Harry Lythall describes a roof mounted direction finding system which uses eight antennae for direction finding purposes. Appropriate circuitry is also described in the paper.

A product description pamphlet by the Banner Company describes a particular type of ultrasonic sensor which is available in commercial quantities and identified as the U-GAGE T30 series with analog and discreet outputs. Signals provided by these ultrasonic sensors allow a determination to be made regarding the distance between the sensor and an object that reflects signals transmitted by the sensors.

SUMMARY OF THE INVENTION

A method for determining the position of a marine vessel relative to a fixed structure, in a preferred embodiment, comprises the steps of providing first and second position sensors which are attached to the marine vessel and providing first and second fixed reference devices which are attached to the fixed structure and are stationary. The method further comprises the steps of determining first and second relative positions between the first sensor and the first and second fixed reference devices and between the second sensor and the first and second fixed reference devices. The method further comprises the step of determining a position of the marine vessel relative to the first and second fixed reference devices as a function of the first and second relative positions.

The first and second position sensors can be radio frequency (RF) transceivers. The method of a preferred embodiment of the present invention can further comprise the steps of transmitting an initiation signal from the first position sensor to the first fixed reference device, transmitting a response signal from the first fixed reference device back to the first position sensor in response to receiving the initiation signal, receiving the response signal by the first position sensor, and computing a distance between the first position sensor and the first fixed reference device as a function of the elapsed time between the initiation transmitting step and the response signal receiving step. The step of computing the distance between the first position sensor and the first fixed reference device as a function of the elapsed time between the initiation transmitting step and the response signal receiving step is performed by a microprocessor disposed on the marine vessel and connected in signal communication with the first position sensor.

In certain embodiments of the present invention, the first and second position sensors can be Doppler direction finders. The method can further comprise the steps of transmitting an initiation signal from the first position sensor to the first fixed reference device, transmitting a direction signal from the first fixed reference device to the first position sensor in response to receiving the initiation signal, receiving the direction signal by the first position sensor, and computing an angle between the first position sensor and the first fixed reference device as a function of frequency differences of the direction signal at a plurality of reception positions created by the first position sensor. The step of computing an angle between the first position sensor and the first fixed reference device as a function of frequency differences of the direction signal at a plurality of reception positions created by the first position sensor is performed by a microprocessor disposed on the marine vessel and connected in signal communication with the first position sensor in a preferred embodiment of the present invention. The method can further comprise the step of determining a first angular relationship between lines which extend from the first position sensor to the first and second fixed reference devices and determining a second angular relationship between lines which extend from the second position sensor to the first and second fixed reference devices. The first and second fixed reference devices can be radio frequency transponders.

The method of a preferred embodiment of the present invention can further comprise the step of determining an angular relationship between a first line which extends between the first and second position sensors and a second line which extends between the first and second fixed reference devices. It can further comprise the steps of determining a first distance between the first position sensor and the first fixed reference device and determining a second distance between the second position sensor and the second fixed reference device. The preferred embodiment of the present invention can further comprise the step of calculating an effective distance between the marine vessel and a stationary point as a function of the first and second distances. The first and second fixed reference devices can be attached to a dock.

In a particularly preferred embodiment of the present invention, the method can further comprise the step of maneuvering the marine vessel as a function of the position of the marine vessel relative to the first and second fixed reference devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a schematic representation showing a marine vessel10at a position relative to a fixed structure, such as a dock12. The position of the marine vessel10, represented by solid lines, is intentionally shown displaced from a desired mooring position of the marine vessel10which is represented by dashed lines inFIG. 1. The present invention is intended to provide a system by which information can be determined and then provided to appropriate equipment on the marine vessel10which allows the vessel to be properly maneuvered from the position of the vessel shown by solid lines inFIG. 1to the berthed position represented by dashed lines inFIG. 1. Two fixed reference devices are also shown inFIG. 1. These are identified by reference numerals16and18and will be described in greater detail below.

In a particularly preferred embodiment of the present invention, shown inFIG. 2, the method of the present invention begins with the transmission of an initiation signal20from a first position sensor attached to the marine vessel10.FIG. 2also shows a second position sensor22attached to the marine vessel10. The operation of the second position sensor22will be described in greater detail below.

With continued reference toFIG. 2, the initiation signal20is transmitted from the first position sensor21toward the first fixed reference device16. It is transmitted in a first frequency to which the first fixed reference device16is configured to be responsive. In alternate embodiments of the present invention, the first position sensor21can be a radio frequency (RF) transceiver or a Doppler direction finder. Both embodiments will be described below.

If the first position sensor21is a radio frequency transceiver, the initiation signal20is responded to, by the first fixed reference device16, with a response signal. The response signal is received by the first position sensor21. As will be described in greater detail below, the elapsed time between the transmission of the initiation signal20and the receipt of the response signal allows the calculation of the linear distance between the first position sensor21and the first fixed reference device16.

With continued reference toFIG. 2, it should be understood that the procedure described above, in conjunction with the initiation signal20and the response signal transmitted by the first fixed reference device16, can be repeated in conjunction with the first position sensor21and the second fixed reference device18. This allows the linear distance between the second fixed reference device18and the first position sensor21to be calculated as a function of the time it takes for the initiation signal to travel to the second fixed reference device18and be responded to with a transmission from the second fixed reference device18. In both instances, a known latency period which occurs between the receipt of the initiation signals by the fixed reference devices,16and18, and the retransmission of a response signal by those devices is considered in the calculation of the distance between the first position sensor21and the two fixed reference devices,16and18. For purposes of simplicity,FIG. 2does not show representations of the other initiation signals. It should also be understood that a similar process is performed with regard to the second position sensor22and the two fixed reference devices,16and18. The purposes of these calculations will be described in greater detail below.

FIG. 3is a schematic representation of the marine vessel10with the first and second position sensors,21and22, mounted to the marine vessel at known locations. A microprocessor26is connected in signal communication with the first and second position sensors.

FIG. 4shows the marine vessel10, the dock12, and several dashed lines that represent distances between various points. For example, dimension X is the distance between the first and second fixed reference devices,16and18. For purposes of clarity, the points at which these fixed reference devices are located are identified as F and G inFIG. 4. Similarly, the positions at which the first and second position sensors,21and22, are attached to the marine vessel10are identified as points M and N. In the description ofFIG. 2, the methodology for determining the distances between the two position sensors,21and22, and the two fixed reference devices,16and18, was described. Dimension A inFIG. 4represents the distance between the first position sensor21at point M and the first fixed reference device16at point F. Similarly, line B represents the distance between the first position sensor21at point M and the second fixed reference device18at point G.

With continued reference toFIG. 4, dashed line L represents the linear distance between the first and second position sensors,21and22, which are identified as points M and N. The distances represented by lines A and B can be determined as described above by transmitting a signal from the first position sensor21, receiving that signal by the first fixed reference device16, responding by transmitting a signal from the first fixed reference device16back to the first position sensor21, and receiving that response signal by the first position sensor21. The microprocessor26, described above in conjunction withFIG. 3, can then determine the total elapsed time for the signal to travel in both directions, including an empirically derived latency time. It can then calculate the distance A by subtracting the latency time from the total elapsed time, dividing by two, and mathematically calculating the distance A because the signal is known to travel at the speed of light. Distance B can be determined in the same way, but a preferred embodiment of the present invention would use a signal of a different frequency so that the microprocessor26, in conjunction with the first position sensor21, can discriminate between the signals received from the first and second fixed reference devices,16and18.

The methodology described immediately above to determine the lengths of lines A and B would typically use a radio frequency transceiver as both the first and second position sensors,21and22. In alternative embodiments of the present invention, the first and second positions sensors,21and22, could be alternatively Doppler direction finders.FIG. 5illustrates how a Doppler direction finder can be used to provide the necessary information to determine the position of the marine vessel10.

InFIG. 5, a response signal30, comprising pulses of a known frequency, are transmitted by the fixed reference devices,16and18. In a manner that is generally known to those skilled in the art, a Doppler direction finder used as the first position sensor21can determine the direction of the shortest distance between the Doppler direction finder and the source of the signal30. The descriptive article identified above, published by Harry Lythall on the Internet, discloses this technique and exemplary circuitry used to process the signals. In addition, Doppler direction finders can be obtained from many other sources. In effect, a Doppler direction finder provides information relating to the magnitude of angle θ at point M between lines A and L. With reference toFIGS. 4 and 5, the Doppler direction finder can also easily provide information relating to the angle at point M between lines B and L. For convenience, the response signal30from the two fixed reference devices,16and18, are different frequencies so that the Doppler direction finder used as the first position sensor21can discriminate between signals received from those two fixed reference devices.

FIG. 6is a graphical representation showing the specific methodology used by the present invention to determine the distance, represented by line A inFIG. 4, between a first position sensor21and a first fixed reference device16. It should be understood, however, that a similar technique would be used to determine the distances between either the first or second position sensors,21or22, and the two fixed reference devices,16and18. The exchange of signals inFIG. 6is, therefore, exemplary for any of these determinations. With reference toFIGS. 4 and 6and with specific reference to the determination of the length of line A, a first initiation signal41is transmitted by the first position sensor21. The first initiation signal is of a known frequency that the first fixed reference device16is configured to recognize. That initiation signal41is transmitted at a time represented by dashed line51. As represented by arrow60, the first initiation signal41is received by the first fixed reference device16at a time which is a function of the distance A and the speed of a radio frequency signal. The received signal is identified by reference numeral42and is received at a time which is represented by dashed line52. Between dashed lines51and52is the elapsed time for the initiation signal to travel from the first position sensor21on the marine vessel10to the shore based first fixed reference device16. After receipt of the signal42by the first fixed reference device16, a latency period occurs during which the signal42is recognized and the appropriate response is prepared. This latency period exists between dashed lines52and53. A response signal43is then transmitted by the first fixed reference device16. This signal is a radio frequency signal that travels at the speed of light and is received, at dashed line54, by the first position sensor21mounted on the marine vessel10. This received signal is identified by reference numeral44. The graphical representation inFIG. 6illustrates that the travel time of the initiation in response signals, identified by arrows60and61, is represented by the time between dashed lines51and52added to the time between dashed lines53and54. Since the speed of the signal is known, the distance A between the first position sensor21at point M and the first fixed reference device16at point F can be calculated.

FIG. 7shows the marine vessel10at the position discussed above in conjunction withFIGS. 1,2and4along with numerous dimensional lines identifying the distances between various points. The length of lines X and L are easily determined because they represent the distances between devices that are either the fixed reference devices,16and18, or the first and second position sensors,21and22, which are attached to the marine vessel10. The distances A, B, C and D can be determined in one of two ways, depending on the particular embodiment of the present invention which is used. If, for example, the first and second position sensors are radio frequency transceivers, the distances identified by reference letters A, B, C and D can be calculated according to the technique described above in conjunction withFIG. 6. If the length of the dashed lines shown inFIG. 7are initially calculated in the manner described above in conjunction withFIG. 6, the various angles between dashed lines at points F, G, M and N can be determined by the law of cosines since the lengths of all of the sides of the relevant triangles are known. In an embodiment of the present invention which uses a Doppler direction finder to determine the angles between lines A and L, B and L, C and L, and D and L, the magnitudes of the dashed lines inFIG. 7can be determined by the law of sines because lengths X and L are known in addition to the measured angles provided by the Doppler direction finder described above in conjunction withFIG. 5.

InFIG. 7, lines X and L are intentionally shown as being in non-parallel association with each other. To assist in maneuvering the marine vessel10in relation to the dock12, it is important to know the angular relationship between lines X and L. As can be seen fromFIG. 7and the discussion regarding the known dimensions and angles, it can be seen that simple geometric calculations can determine all of the angles between line L and lines A and B. In addition, all of the angles between line X and lines A and C can be easily calculated. Since the length of line A is also known, the magnitude of angle Φ can be calculated. This allows the microprocessor26, described above in conjunction withFIG. 3, to determine the degree of parallelism between lines X and L. If the goal is to maneuver the marine vessel toward a parallel relationship between lines X and L and move the marine vessel toward the dock12, the magnitude of angle Φ can be very useful. Alternatively, the marine vessel10can be maneuvered until the dimensions of lines A and D are generally equal to each other prior to moving the marine vessel, in a sidle movement, toward the dock12as the magnitudes of lines A and D are decreased in a coordinated fashion. The specific maneuvering techniques used to perform this function can include the techniques described in U.S. patent application Ser. Nos. 11/248,482 and 11/248,483, which are described above. The primary purpose of the present invention is to determine the position of the marine vessel10and communicate this information, by the microprocessor26, to software whose function is to cause movement of the marine vessel10in response to differences between an actual position and a desired position, as represented by the solid and dashed line versions of the marine vessel10inFIG. 1. The movement of the marine vessel10is represented generally by the two arrows inFIG. 1.

FIG. 8illustrates an additional technique that can be used in conjunction with the method of the present invention. It employs a plurality of ultrasonic sensors, such as those described above in conjunction with the information relating to the Banner Corporation and its commercially available products. When the marine vessel10is maneuvered to a position within a certain preselected range of the dock12, the ultrasonic sensors70can be activated to more accurately measure the precise distances between various locations of the marine vessel70and the dock12. These sensors would transmit a generally conical ultrasonic signal, such as that represented by dashed lines74, in a direction from the marine vessel10toward the dock12. An echo signal would be received by the device and the distance76would be determined for each transmitting ultrasonic sensor that receives an echo signal. The ultrasonic sensors70could be connected in signal communication with the microprocessor26to determine the closest distance between a stationary object, such as the dock12, and the marine vessel10. It should be understood that the system described above in conjunction withFIG. 7would be the primary position determination tool implemented under the scope of the present invention but, for purposes of accuracy, the ultrasonic sensors70could be used when the marine vessel10is in close proximity with the stationary object, such as the dock12. This would be done because the ultrasonic sensors are capable of providing increased accuracy, in comparison to the radio frequency devices and Doppler direction finding devices described above, particularly when the marine vessel10is close to the dock12.

With reference toFIGS. 1-8, the method for determining the position of a marine vessel10relative to a fixed structure, such as the dock12, in a preferred embodiment of the present invention comprises the steps of providing a first position transceiver21and a second position transceiver22which are both attached to the marine vessel10. It further comprises the steps of providing first and second fixed reference transponders,16and18, which are attached to a stationary object such as the dock12. The present invention further comprises the step of determining a first relative position between the first position transceiver21and the first and second fixed reference transponders,16and18. It also comprises the step of determining a second relative position between the second position transceiver22and the first and second fixed reference transponders,16and18. A preferred embodiment of the present invention further comprises the step of determining a position of the marine vessel10relative to the first and second fixed reference transponders,16and18, as a function of the first and second relative positions. In a preferred embodiment of the present invention, the first and second relative positions include the magnitudes of lines A, B, C and D.

A preferred embodiment of the present invention can further comprise the steps of determining first and second angular relationships between lines A and B, which extend from the first position transceiver21to the first and second fixed reference transponders,16and18. It also comprises the step of determining a second angular relationship between lines C and D which extend from the second position transceiver22to the first and second fixed reference transponders,16and18. It can comprise the additional step of determining an angular relationship between a first line L which extends between the first and second position transceivers,21and22, and a second line X which extends between the first and second fixed reference transponders,16and18. This angular relationship is identified as angle Φ inFIG. 7.

The method of the present invention can further comprise the step of determining a first distance A between the first position transceiver21and the first fixed reference transponder16and the step of determining a second distance D between the second position transceiver22and the second fixed reference transponder18.

The method of the present invention can further comprise the steps of transmitting an initiation signal20from the first position transceiver21to the first fixed reference transponder16and transmitting a response signal from the first fixed reference transponder16to the first position transceiver21in response to receiving the initiation signal. Furthermore, it can comprise the step of receiving the response signal by the first position transceiver21and computing a distance A between the first position transceiver21and the first fixed reference transponder16as a function of the elapsed time between the initiation transmitting step and the response signal receiving step. A preferred embodiment can further comprise the step of calculating an effective distance between the marine vessel10and a stationary point, such as a midpoint between the first and second fixed reference transponders,16and18, as a function of the first and second distances. In a preferred embodiment of the present invention, it can further comprise the step of maneuvering the marine vessel10as a function of the position of the marine vessel relative to the first and second reference transponders,16and18. This maneuvering can be accomplished by performing selective portions of the methods disclosed in U.S. patent application Ser. Nos. 11/248,482 and 11/248,483. These maneuvering steps can be accomplished according to the teachings of these two patent applications identified immediately above in situations where the marine vessel10is provided with two independently steerable marine propulsion devices.

Although the present invention has been described in considerable detail and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.