System for navigating hull cleaning robot by using ultrasonic positioning signal and method therefor

Abstract

The purpose of the present invention is to provide a system for navigating a hull cleaning robot and a method therefor, wherein underwater acoustic positioning signals based on underwater ultrasonic waves are used in an auxiliary manner such that same can be applied even to a condition in which multiple hull cleaning robots simultaneously clean a hull, and in an environment in which acoustic waves are diffracted or reflected waves exist, distortion of ultrasonic positioning signals is corrected, thereby using same as navigation assist signals. In order to accomplish the above purpose, a system for navigating a hull cleaning robot by using ultrasonic positioning signals according to the present invention comprises: a hull cleaning robot to be positioned, the hull cleaning robot comprising a first acoustic communication unit which is triggered by an external signal, or which generates an acoustic signal at a predetermined interval; ultrashort baselines (USBLs) each comprising a second acoustic communication unit installed on a buoy so as to position the hull cleaning robot, two sets of USBLs being disposed on the prow and stern of a ship to be cleaned, respectively; reference sound source devices installed on the portside and starboard of the hull center, respectively, each reference sound source device being equipped with a third acoustic communication unit and a GPS unit; a signal processing unit for analyzing positioning signals of the hull cleaning robot and the reference sound source devices received by the second acoustic communication unit, thereby identifying distorted positioning signals caused by hull obstacles, and correcting the distorted positioning signals; and a navigation system for determining outliers with regard to corrected positioning signals, and using positioning signals from which outliers are removed as auxiliary signals for underwater three-dimensional position estimation.

Description

Navigation system and method for a hull cleaning robot using ultrasonic positioning signals

[0001] The present invention relates to a navigation system and method for a hull cleaning robot using ultrasonic positioning signals, and more particularly, to a navigation system and method for a hull cleaning robot using ultrasonic positioning signals for correcting errors in the inertial navigation system of a hull cleaning robot that cleans a ship underwater, such as a ship docked at a port quay or a ship moored in a port, by using ultrasonic positioning signals as navigation assistance signals.

[0002]

[0003] Since ships are generally operated with the lower part of the hull submerged in seawater, biofouling may occur on the hull surface located underwater.

[0004] Here, biofouling refers to the attachment and growth of aquatic organisms to the submerged parts of a ship.

[0005] These aquatic organisms can be attached to various aquatic organisms such as sphagnum moss, barnacles, sea squirts, and seaweed.

[0006] These aquatic organisms have the problem of increasing surface friction drag during ship operation, which reduces the fuel efficiency of the ship.

[0007] For example, foreign substances attached to the hull act as resistance when the hull is operating, reducing the speed and increasing fuel consumption accordingly. This not only increases the operating cost of the ship due to increased fuel consumption, but also increases exhaust gases such as CO₂, SOx, or NOx.

[0008] Additionally, biofouling is pointed out as a major cause of ecosystem disruption due to the movement and invasion of alien aquatic organisms, as the aquatic organisms attached to the vessel move along with the vessel's operation.

[0009] Biofouling not only reduces the energy efficiency of operating vessels, but also requires its removal to prevent the introduction of invasive alien species.

[0010] In this way, various foreign substances and aquatic organisms attached to the hull not only disrupt the marine ecosystem, but also act as resistance when the ship is sailing, which reduces the ship's speed and significantly increases the ship's fuel consumption. Therefore, it is very important to periodically clean various foreign substances and aquatic organisms attached to the hull.

[0011] In the past, cleaning the surface of the bottom or side of a ship was usually done by having divers go in and clean foreign substances and aquatic organisms attached to the surface. However, the working environment was poor and physically demanding, making it difficult and time-consuming to clean the exterior of the hull, and there was the problem that cleaning was impossible in areas with heavy currents.

[0012] Additionally, there have been reports of fatal accidents involving divers involved in hull cleaning operations.

[0013]

[0014] Recently, with the advancement of robotics technology, underwater robots for hull cleaning have emerged, and operators on board remotely control these underwater robots to clean the hull.

[0015] To improve the work efficiency of hull cleaning underwater robots, technology is being developed to measure the robot's three-dimensional underwater position and automatically perform cleaning tasks along the cleaning path.

[0016] To achieve these goals, a navigation system is needed to accurately measure the position, attitude, and velocity of the hull cleaning underwater robot.

[0017] Additionally, thanks to advancements in artificial intelligence and robotics technology, research is being conducted in each country to enhance the functionality of hull cleaning robots.

[0018] Autonomous cleaning using robots, fast and accurate eco-friendly cleaning is required, and to achieve this, accurately measuring the position of the hull cleaning robot is key.

[0019] Development of specialized positioning technology for underwater cleaning robots is required to enable them to clean crevices that current robots cannot.

[0020] Additionally, there is a need to deploy multiple underwater robots simultaneously to quickly remove biofouling during loading and unloading of ships entering the port.

[0021] In order to deploy multiple underwater robots simultaneously, the development of a navigation system for multiple underwater cleaning robots is required.

[0022] The navigation system of a hull cleaning robot is configured to measure the moving position of the robot by integrating the rotation speed of the driving device based on the three-dimensional posture of the robot body, or an inertial sensor-based underwater robot navigation system is configured using an inertial measurement unit (IMU) and a Doppler velocity log (DVL).

[0023] Inertial sensor-based navigation systems have the disadvantage of positional errors drifting over time, so a method of correcting the position using external signals is required.

[0024] External signals used include depth sensors, GPS signals obtained through periodic surface surfacing, attachment of identifier markers to designated underwater locations, welding line tracking, underwater ultrasonic distance information to known locations, and short base line (SBL), long base line (LBL), and ultra short base line (USBL) acoustic positioning devices.

[0025] If there is an obstacle in the path of the underwater acoustic wave, i.e., if there is a ship hull between the acoustic signal transmission location and the hull cleaning robot, an acoustic shadow zone exists, and the acoustic signal is blocked, reflected, diffracted, or scattered, making it difficult to measure the position normally.

[0026] In particular, hull cleaning robots that perform cleaning work by closely contacting the hull surface of large ships docked at a dock often disappear from the acoustic line of sight (LOS) of the acoustic reference point.

[0027] In such cases, acoustic waves may be diffracted along the hull surface due to obstacles in the ship, or acoustic waves reflected from the walls or bottom may be transmitted to the hull cleaning robot.

[0028]

[0029] These abnormal acoustic signals severely distort the position information obtained from the ultrasonic positioning system.

[0030] Additionally, in areas where acoustic signals cannot be transmitted, acoustic positioning signals cannot be obtained for a long period of time.

[0031] The present invention relates to an underwater composite navigation system for a hull cleaning robot that uses a position signal of a USBL acoustic positioning system as an auxiliary signal for a navigation system of the hull cleaning robot.

[0032] A method is provided for deciphering cases where acoustic distortion occurs due to a hull, converting positioning signals distorted by acoustic diffraction and acoustic reflection into valid information, and identifying and filtering outliers by considering the error characteristics of USBL.

[0033]

[0034] The purpose of the present invention to solve the above-mentioned conventional problems is to provide a navigation system and method for a hull cleaning robot that can be applied even under conditions where multiple hull cleaning robots simultaneously clean a hull by utilizing underwater acoustic positioning signals using underwater ultrasonic waves as assistance, and that corrects distortion of the ultrasonic positioning signals in an environment where diffraction or reflection of acoustic waves exists and uses them as navigation assistance signals.

[0035]

[0036] In order to achieve the above object, a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention is characterized by including: a hull cleaning robot that requires positioning, including a first acoustic communication unit that is triggered by an external signal or generates an acoustic signal at regular intervals; two USBL (Ultra Short Base Line) buoys that are installed on buoys and include a second acoustic communication unit that measures the position of the hull cleaning robot, and are respectively positioned at the front and rear of the hull; two acoustic reference units (RSU: Reference Sound Units) that each include a third acoustic communication unit at the port and starboard centers of the hull; and a signal processing unit that analyzes the positioning signal received by the second acoustic communication unit to estimate an underwater three-dimensional position.

[0037] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the USBL buoy includes a GPS and an attitude sensor for measuring position and attitude, and is characterized in that the GPS is installed in pairs for measuring azimuth.

[0038] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the hull cleaning robot is characterized in that it is equipped with a 6-axis inertial sensor (IMU, Inertial Measurement Unit), a 3-axis Doppler Velocity Log (DVL, Doppler Velocity Log), and a depth sensor.

[0039] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the USBL buoys are respectively placed at the front center of the bow and the rear center of the stern of the ship, and when the ship is berthed at the quay wall, the USBL buoys are anchored to prevent drifting, and when the ship is moored in the inner harbor, the USBLs are tied with ropes to the bow and the stern of the ship, respectively. The heading angle of the hull is measured from the difference in the positions of GPS signals mounted on the front and rear USBL buoys.

[0040] In addition, the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention is characterized in that two acoustic reference units (RSUs) are installed on the left and right outer walls of the center of the hull of the ship using magnets, respectively, and a third acoustic communication unit is included for correcting the distorted positioning between the hull cleaning robot and the USBL due to interference by the ship.

[0041] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the relative position of the hull cleaning robot measured by the USBL is characterized in that the coordinates are converted to the relative position of the hull cleaning robot in the hull fixed coordinate system by correcting the position change of the ship and the USBL.

[0042] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the USBL is characterized in that it measures the three-dimensional position using the transmission delay time of the underwater sound wave and the azimuth and inclination angle of the received signal.

[0043] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, the measurement distortion between the hull cleaning robot and the USBL is characterized in that it varies depending on the shape of the hull and the relative position of the second acoustic communication unit of the hull cleaning robot and the USBL.

[0044] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, when diffraction of the sound wave signal occurs, the positioning of the USBL is measured from the incident angle of the sound wave and the transmission delay time, and is measured to exist in a different direction and position than the actual one, but since the difference in the measured values ​​of the distance and direction of the acoustic reference device RSU on the left and right sides of the center of the hull is equal to the distance in the direction of the hull bow between the RSU and the hull cleaning robot, this difference is characterized in that it is replaced with the distance from the center of the hull side.

[0045] To explain this more specifically, in the navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention, when the acoustic field of view LOS is not secured (diffraction occurs), the x-direction position of the hull cleaning robot on the hull plane is characterized by correcting the distorted USBL positioning signal to the longitudinal position on the hull side wall in an area where diffraction occurs by a reference sound source difference method in which the difference between the position of the hull cleaning robot measured by the USBL and the position of the reference sound source by the third acoustic communication unit is equal to the difference between the position of the hull cleaning robot located on the hull wall and the position of the reference sound source.

[0046] Furthermore, in the navigation system of a hull cleaning robot using ultrasonic positioning signals according to the present invention, when the vessel docks in a port, the positioning of the hull cleaning robot may exhibit random position measurement results due to the influence of reflected waves. It is common to determine and remove the positioning data of the USBL obtained from the reflected signal of the port as an outlier.

[0047] In the present invention, when the USBL receives a reflected wave signal and projects the measured distance onto the side wall of the hull, the longitudinal position of the hull remains unchanged, so it is converted into a longitudinal (x-direction) position measurement value at the position projected onto the hull wall without being removed as an outlier. At this time, the error covariance of the projected USBL positioning signal increases in proportion to the sine function of the incident angle of the reflected wave acoustic signal and the distance.

[0048] The USBL positioning distortion due to bottom reflection is projected onto the hull bottom in the same way as the distortion due to wall reflection, and the x and y positions on the projection plane remain the same as the position values ​​measured from the USBL. The error covariance in the USBL range direction increases in proportion to the sine function of the reflected wave incidence angle and the distance.

[0049] In addition, in a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention, a box-shaped hull shape function having a size slightly larger than the hull size is defined to determine whether the position of the underwater robot measured by USBL is obtained from a distorted acoustic wave signal. A box-shaped filter having a first thickness predetermined for each of the bow, stern, and side of the ship is applied, and a positioning signal that deviates from the box-shaped shape is interpreted as having acoustic distortion.

[0050] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, considering that the measurement error of the normal positioning signal of the USBL is proportional to the distance, a triangular filter having a second predetermined thickness corresponding to the error of the USBL at the center of the hull is additionally applied to the box-shaped filter, and a positioning signal that deviates from the box-shaped shape including the triangular shape is judged as having occurred acoustic distortion.

[0051] In addition, the present invention is characterized in that it determines an outlier based on the Mahalanobis distance for a normal or distortion-corrected USBL positioning signal. Since the range direction distance measurement error and the slant angle & bearing angle measurement error vary and the principal component axis changes depending on the distance and bearing between the USBL buoy reference position and the hull cleaning robot, the principal component axis is obtained through principal component analysis for the error component between the estimated position obtained from the hull cleaning robot navigation system and the USBL measured position, and whether it is an outlier is determined through Mahalanobis distance calculation. If it is determined to be an outlier, the USBL positioning signal is ignored, and the navigation system is operated using only the speed signal, depth signal, and attitude signal. If it is determined to be a normal signal, the USBL measurement value is used as an innovation signal of the navigation system, and the error covariance is decorated to apply the Kalman filter of the navigation system.

[0052] In addition, in a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention, when the positioning signal of the third acoustic communication unit is poor while the LOS of the USBL is not secured, the USBL positioning signal is replaced with a positioning signal by projecting it to the hull side position, and the distance error in the bow direction is characterized in that the error covariance is modulated according to the position of the hull cleaning robot with respect to an increase in distance.

[0053] In addition, in the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, when a change in ballast occurs due to a change in the draft caused by cargo unloading or loading of the ship, a depth sensor is installed in the third acoustic communication unit to compensate for the change in the draft.

[0054] Meanwhile, in order to achieve the above object, the method for operating a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention comprises the steps of: mounting a first acoustic communication unit on the hull cleaning robot; arranging a second acoustic communication unit on the bow and stern of the ship, respectively, and mounting a third acoustic communication unit on the port and starboard centers of the hull; receiving a signal generated by the second acoustic communication unit by the first and third acoustic communication units; and applying a box-shaped shape function having a first thickness predetermined for the ship and determining that a positioning signal deviating from the box-shaped shape has USBL positioning distortion.

[0055]

[0056] Specific details of other embodiments are included in the “Specific Details for Carrying Out the Invention” and the attached “Drawings.”

[0057] The advantages and / or features of the present invention and the methods for achieving them will become clear with reference to the various embodiments described in detail below together with the accompanying drawings.

[0058] However, the present invention is not limited to the configuration of each embodiment disclosed below, but may be implemented in various different forms, and each embodiment disclosed in this specification is provided only to ensure that the disclosure of the present invention is complete and to fully inform a person having ordinary skill in the art to which the present invention pertains of the scope of the present invention, and it should be understood that the present invention is defined only by the scope of each claim of the claims.

[0059]

[0060] According to the present invention, by utilizing underwater acoustic positioning signals using underwater ultrasonic waves as an auxiliary, it is effective in being applicable even under conditions where multiple hull cleaning robots simultaneously clean a hull, has the effect of deciphering cases where acoustic distortion occurs due to the hull and converting positioning signals by acoustic diffraction and acoustic reflection into valid information, and has the effect of identifying and filtering outliers by considering the error characteristics of USBL.

[0061]

[0062] Figure 1 is a conceptual diagram illustrating the concept of an integrated navigation system for a multi-hull cleaning robot.

[0063] Figure 2 is a schematic diagram showing the configuration of a USBL-supported integrated navigation system for a multi-hull cleaning robot.

[0064] Figure 3 is a schematic diagram showing the system configuration of a USBL buoy.

[0065] Figure 4 is a schematic diagram showing the navigation system configuration of a hull cleaning robot.

[0066] Figure 5 is a diagram showing a process for identifying whether a USBL positioning signal is distorted due to hull interference, correcting for the effects of diffraction and reflection of acoustic waves, and determining outliers.

[0067] Figure 6 is a drawing showing the coordinates of the integrated navigation system of the hull cleaning robot on the hull.

[0068] Figure 7 is a graph showing the characteristics of USBL measurement errors in Euclidean space (left column) and Mahalanobis distance for principal component axes (right column).

[0069] Figure 8 is a diagram showing distorted range measurements through USBL positioning of a hull cleaning robot on a hull due to acoustic diffraction.

[0070] Figure 9 is a drawing showing the distorted position of the hull cleaning robot on an ideal hull due to diffraction of sound waves in the case of USBL measurement.

[0071] Figure 10 is a drawing showing the range measurement error of the USBL for the hull cleaning robot for an ideal hull, with the position of the USBL being (150:2:250, -30:2:30) m.

[0072] Figure 11 is a diagram showing USBL measurements due to reflections between a harbor quay wall and an anchored vessel.

[0073] Figure 12 is a conceptual diagram of positioning by wall reflection for a vessel moored at a pier.

[0074] Figure 13 is a diagram showing positioning signals by diffracted waves and seabed reflection waves when measuring the position of an underwater robot cleaning a ship.

[0075] Figure 14 is a diagram of a hull shape function showing criteria for determining anomalies in USBL measurements due to reflection of acoustic signals.

[0076] Figure 15 is a diagram showing specific errors unique to USBL according to location.

[0077] Figure 16 is a diagram showing an integrated navigation system supporting USBL of multiple hull cleaning robots.

[0078] Figure 17 is a flow chart showing the operation method of a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention.

[0079]

[0080] A navigation system for a hull cleaning robot using an ultrasonic positioning signal according to the present invention is characterized by including: a hull cleaning robot that requires positioning, including a first acoustic communication unit that is triggered by an external signal or generates an acoustic signal at regular intervals; two USBL (Ultra Short Base Line) buoys that are installed on buoys and include a second acoustic communication unit that measures the position of the hull cleaning robot, and are respectively positioned at the front and rear of the hull; two acoustic reference units (RSUs: Reference Sound Units) that each include a third acoustic communication unit at the port and starboard centers of the hull; and a signal processing unit that analyzes the positioning signal received by the second acoustic communication unit to estimate an underwater three-dimensional position.

[0081]

[0082] Before describing the present invention in detail, it should be understood that the terms or words used in this specification should not be interpreted as being unconditionally limited to their usual or dictionary meanings, and that the inventor of the present invention may appropriately define and use the concepts of various terms in order to explain his or her invention in the best possible manner, and further, that these terms or words should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention.

[0083] That is, it should be noted that the terms used in this specification are only used to describe preferred embodiments of the present invention, and are not intended to specifically limit the contents of the present invention, and that these terms are defined in consideration of various possibilities of the present invention.

[0084] Additionally, it should be noted that in this specification, singular expressions may include plural expressions unless the context clearly indicates a different meaning, and similarly, even if expressed in plural, may include a singular meaning.

[0085] Throughout this specification, whenever a component is described as "including" another component, it may mean that the component may further include any other component, rather than excluding any other component, unless specifically stated otherwise.

[0086] Furthermore, when a component is described as being "inside or connected to" another component, it should be understood that the component may be installed in direct connection with or in contact with the other component, may be installed spaced apart from the other component by a certain distance, and if installed spaced apart from the other component by a certain distance, there may be a third component or means for fixing or connecting the component to the other component, and the description of this third component or means may be omitted.

[0087] On the other hand, if a component is described as being "directly connected" or "directly connected" to another component, it should be understood that no third component or means exists.

[0088] Likewise, other expressions that describe the relationship between components, such as "between" and "directly between", or "adjacent to" and "directly adjacent to", should be interpreted as having the same meaning.

[0089] Additionally, it should be noted that the terms “one side,” “the other side,” “one side,” “the other side,” “first,” “second,” etc. in this specification, if used, are used to clearly distinguish one component from another component, and that the meaning of the component is not limited by such terms.

[0090] In addition, terms related to position, such as “upper,” “lower,” “left,” and “right,” etc., in this specification, if used, should be understood to indicate relative positions of the corresponding components in the corresponding drawings, and unless absolute positions are specified for these positions, these position-related terms should not be understood to refer to absolute positions.

[0091] In addition, in this specification, when specifying the drawing numbers for each component of each drawing, the same component has the same drawing number even if the component is shown in a different drawing, that is, the same reference number indicates the same component throughout the specification.

[0092] In the drawings attached to this specification, the size, position, connection relationship, etc. of each component constituting the present invention may be described with some exaggeration, reduction, or omission in order to sufficiently clearly convey the idea of ​​the present invention or for convenience of explanation, and therefore the proportions or scales may not be strict.

[0093] In addition, in the following description of the present invention, a detailed description of a configuration that is judged to unnecessarily obscure the gist of the present invention, for example, a known technology including a prior art, may be omitted.

[0094]

[0095] Hereinafter, embodiments of the present invention will be described in detail with reference to the relevant drawings.

[0096]

[0097] - Navigation system design for a multi-hull cleaning robot (HCR)

[0098] - Conceptual design of requirements, constraints, and navigation systems

[0099] Hull underwater cleaning is performed on vessels moored at docks, but should also be able to be performed on moored vessels in the harbor.

[0100] Multiple hull cleaning robots are deployed for rapid cleaning.

[0101] In this embodiment, four hull cleaning robots are used as an example for ease of explanation, but the present invention is not limited thereto, and multiple hull cleaning robots may be deployed for rapid cleaning.

[0102] The navigation system must be mounted on the hull cleaning robot, and sensors that require external installation must be installed on the hull's outer wall or outside without boarding the ship.

[0103] Additionally, the time required to install the navigation system must be minimized.

[0104] Accordingly, the present invention implements a hull cleaning robot navigation system based on an inertial sensor and utilizing USBL (Ultra Short Base Line) ultrasonic positioning.

[0105]

[0106] Figure 1 is a conceptual diagram illustrating the concept of an integrated navigation system for a multi-hull cleaning robot.

[0107] Figure 1 illustrates the concept of a hull cleaning robot navigation system that uses USBL positioning information as an auxiliary signal.

[0108] A navigation system (1000) of a hull cleaning robot using an ultrasonic positioning signal according to the present invention includes a hull cleaning robot (100), a USBL (Ultra Short Base Line: 200), and a signal processing unit (300).

[0109] The hull cleaning robot (100) includes a first acoustic communication unit (110) that is triggered by an external signal or generates an acoustic signal at regular intervals, and positioning is required.

[0110] Here, the hull cleaning robot (100) is equipped with a 6-axis inertial sensor (IMU: Inertial Measurement Unit), a 3-axis DVL (Doppler Velocity Log), and a depth sensor.

[0111] In addition, the first acoustic communication unit (110) is mounted on the hull cleaning robot (100) that wants to measure the position and is triggered by an external signal or transmits sound waves at regular intervals.

[0112] In this embodiment, for the sake of ease of explanation, the first acoustic communication unit (110) is described as an Ultra Short Base Line (USBL) transponder as an example, but is not limited thereto, and any device that can be triggered by an external signal or generate an acoustic signal at regular intervals can be used.

[0113] In this way, the USBL transponder mounted on the hull cleaning robot (100) transmits a transmission signal for positioning after receiving a trigger signal.

[0114] In addition, the USBL transponder is a separate type in which the sensor and driving circuit are separated to facilitate installation on the hull cleaning robot (100), and power is supplied and communication is performed via the hull cleaning robot (100).

[0115] The USBL (200) is installed on a buoy and includes a second acoustic communication unit (210) that measures the position of the hull cleaning robot (100).

[0116] These two USBL transceivers are installed at the front and rear of the ship respectively to measure the positions of two front hull cleaning robots (100) and two rear hull cleaning robots (100).

[0117] USBL (200) is installed on the buoy and placed at the front center of the bow and the rear center of the stern, respectively.

[0118] When a vessel is docked at a quay, the USBL (200) is anchored to prevent it from drifting, and when it is moored in an inner port, the USBL (200) is tied to the bow and stern with ropes to allow it to drift together with the hull.

[0119] To measure the position and attitude of USBL (200), GPS (220) and attitude sensor are used, and azimuth measurement is calculated using two GPS (220).

[0120] The power supply for driving USBL (200) is built into the buoy body, and transmits a positioning signal to the signal processing unit (300) via LTE.

[0121] The signal processing unit (300) analyzes the positioning signal received by the second acoustic communication unit (210) to estimate the underwater three-dimensional position.

[0122] This signal processing unit (300) displays the underwater position of the hull cleaning robot (100) in real time, estimates the position of the hull cleaning robot (100) using distance / angle information, considers the diffraction phenomenon and change in sound speed in the shaded area, and corrects the position using a reference sound source.

[0123] In other words, USBL (200) is formed in a buoy shape, and GPS (220) is installed at each end of the frame located at the top to measure position and heading, and attitude is measured using an attitude control sensor (AHRS).

[0124] Additionally, the relative position is measured using the USBL transceiver, which is the second acoustic communication unit (210).

[0125] The top of the buoy body is equipped with an RF modem for wireless communication, and a battery is built into it for operation.

[0126] In addition, the position and heading angle of the target vessel to be cleaned can be measured by using the difference in the positions of the two USBL (200) buoys placed at the center of the bow and stern.

[0127] Figure 4 shows a system configuration diagram of a USBL buoy.

[0128] USBL (200) has a distorted position measurement when it cannot secure LOS (Line Of Sight) due to interference from a ship between the hull cleaning robot (100) and the USBL transceiver.

[0129] Accordingly, the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention includes an acoustic reference device installed on the left and right sides of the center of the hull of the ship using a magnet, and a third acoustic communication unit (400) for correcting the distorted positioning between the hull cleaning robot (100) and the USBL (200) due to interference from the ship.

[0130] These acoustic communication units are installed by hanging from the acoustic reference device under their own weight so that they can be submerged more than 2 m underwater.

[0131] In this embodiment, for the sake of ease of explanation, the third acoustic communication unit (400) is described as an example of a USBL (Ultra Short Base Line) transponder, but is not limited thereto, and any device that can be triggered by an external signal or generate an acoustic signal at regular intervals can be used.

[0132] That is, in order to correct the above distortion, in the present invention, two acoustic reference transponders are installed on the left and right side walls of the center of the hull using magnets.

[0133] These USBL transponders are installed in pairs on the left and right sides of the hull to estimate the ship's position and heading, are fixed using magnets, and are equipped with GPS for absolute coordinate correction.

[0134] Additionally, the USBL transponder is equipped with an LTE modem for wireless communication and is battery-operated.

[0135] In addition, in the case of a moored vessel, since the vessel is drifting, GPS (220) is installed in the air of each of the two acoustic reference devices for real-time location measurement, and location information is transmitted to the signal processing unit (300) via LTE.

[0136] The measurement characteristics of the navigation system of the hull cleaning robot using the ultrasonic positioning signal according to the present invention, which is an ultrasonic positioning system, are as follows: ① the presence of step-like jumps or spike-shaped outliers in the measured distance due to underwater multipath; ② the presence of a time zone of poor signal acquisition when the underwater noise level fluctuates; and ③ the presence of diffraction of sound waves or blackout of signals in the hull shadow area.

[0137] The requirements for a hull-mounted non-acoustic sensor for navigation of a hull cleaning robot (100) for removing organisms attached to the hull are ① the ability to move in narrow spaces, ② the configuration of an inertial navigation system using a high-precision IMU by examining the navigation error limit when applying a small, low-precision IMU used in existing cleaning robots, and ③ the avoidance of using DVL or the use of DVL installed in a narrow gap.

[0138] In addition, the navigation system of the hull cleaning robot (100) needs to be implemented as a navigation system that is robust to the motion disturbance of the hull, which is the object to be cleaned.

[0139] For this purpose, absolute position error compensation according to hull movement is required, and a design that minimizes the effects of waves and wind is required.

[0140] In the present invention, the navigation system of the hull cleaning robot (100) has the following features.

[0141] By using ultrasonic positioning signals as navigation assistance signals, navigation errors caused by bias signals of inertial sensors are prevented from increasing.

[0142] The Doppler velocity and depth information of the hull cleaning robot (100) are used as navigation assistance signals.

[0143] Figure 5 shows a configuration diagram of the navigation system of the hull cleaning robot.

[0144] Outlier filtering is performed using the drift error characteristics of an inertial sensor-based navigation system and the statistical characteristics of the hull shape.

[0145] The signal processing process of the inertial sensor-based navigation system of a hull cleaning robot (100) using an ultrasonic positioning system as an auxiliary sensor includes the following.

[0146] - Hull shape function for reading distorted USBL signals caused by diffraction, reflection, etc. of acoustic waves

[0147] - Selective outlier determination through principal component analysis based on USBL's unique distance and direction error measurement characteristics and location.

[0148] - To implement this, outliers are determined based on the Mahalanobis distance.

[0149] - High-dimensional navigation algorithm that takes into account the drift error of high-precision inertial sensors.

[0150] - Low-precision inertial sensor-based dead-navigation algorithm and ultrasonic positioning-assisted navigation algorithm

[0151]

[0152] - Navigation system configuration of a multi-hull cleaning robot

[0153] Figure 2 is a schematic diagram showing the configuration of a USBL-supported integrated navigation system for a multi-hull cleaning robot.

[0154] Figures 2 and 4 show the navigation system configuration of a multi-hull cleaning robot (100).

[0155] Each hull cleaning robot (100) is equipped with an inertial sensor (IMU) and a Doppler velocity sensor (DVL), and a USBL transponder is installed on top.

[0156] USBL #1 alternately acquires the positions of hull cleaning robot #1 and hull cleaning robot #2, and USBL #2 alternately acquires the positions of hull cleaning robot #3 and hull cleaning robot #4.

[0157] Position measurements of the acoustic reference device transponder alternate between USBL #1 and USBL #2 at one order of magnitude lower frequency.

[0158] The measured position signal is collected by the signal processing unit (300) via LTE and transmitted to each hull cleaning robot.

[0159] Each hull cleaning robot converts the relative position information of the measured USBL (200) into coordinates, checks the soundness of the signal, discards outliers, and inputs only normal signals into the navigation system to be used for updating the navigation system.

[0160] Figure 5 distinguishes that if the measured USBL position is within the hull shape function range, it is a normal signal, and if it is outside the range, acoustic distortion has occurred.

[0161] The positioning signal due to acoustic wave distortion is converted to coordinates by projecting the difference in distance from the acoustic reference device to the distance of the hull side wall.

[0162] Additionally, in the case of seafloor reflection or pier wall reflection, the position projected onto the hull wall by USBL (200) positioning is converted into a USBL (200) positioning signal.

[0163] Outlier determination of USBL (200) is performed at the estimated position of the hull cleaning robot (100) for a normal or converted USBL (200) signal.

[0164] The error characteristics of the distance direction and heading angle direction of USBL (200) are calculated for the estimated position of the navigation system, and the error characteristics are projected by considering the heading angle and inclination angle, and if the difference between the estimated position and the measured position of USBL (200) does not exist within the specified error range, it is determined as an outlier.

[0165]

[0166] - Coordinate system

[0167] Figure 6 is a drawing showing the coordinates of the integrated navigation system of the hull cleaning robot on the hull.

[0168] Figure 6 shows the coordinate system of the ship and USBL (200).

[0169] The spatial coordinate system in which the hull cleaning robot (100) moves uses the ship-fixed coordinate system, with the center of the hull as the origin, the bow direction as the X axis, the starboard direction as the Y axis, and the downward direction as the Z axis.

[0170] The body coordinate system of the hull cleaning robot (100) sets the forward direction as x, the starboard direction as y, and the downward direction toward the hull wall as z.

[0171] The ship and USBL (200) use the Earth-fixed NED (North East Downward) coordinate system.

[0172] USBL (200) floating on the water is moved by marine disturbances such as waves, wind and currents.

[0173] Also, moored vessels move slowly due to maritime disturbances (vessels at berth also move slightly).

[0174] Therefore, the relative position of the hull cleaning robot (100) measured by the USBL (200) is converted into coordinates to the relative position of the hull cleaning robot (100) in the hull-fixed coordinate system by correcting the positional change of the ship and the USBL (200), and is used as a positioning innovation of the navigation system.

[0175]

[0176] - Error response of the hull cleaning robot navigation system -

[0177] - USBL positioning error and outlier signals

[0178] Figure 7 is a graph showing the characteristics of USBL measurement errors in Euclidean space (left column) and principal component axis (right column).

[0179] USBL (200) measures three-dimensional position using the propagation delay time of underwater sound waves and the azimuth and inclination angles of the received signal.

[0180] The distance error of USBL(200) is constant regardless of the distance, but the angular direction error increases in proportion to the measurement distance because the angular error is constant.

[0181] The left column of Figure 7 shows the statistical positioning error distribution at a distance of 50 to 250 m when the distance error rms is 0.1 m and the angle error rms is 1°.

[0182] Looking at Table 1 below, the angular position error rms increases linearly with increasing distance, and at distances greater than 28.6 m, the USBL (200) alone shows an error of more than 0.5 m for the navigation system.

[0183]

[0184] [Table 1]

[0185]

[0186]

[0187] Since a large ship has a length of up to 400 m, the navigation system of the hull cleaning robot according to the present invention places USBLs (200) at the bow and stern respectively to limit the maximum measurement distance to about 250 m.

[0188] This arrangement maintains the longitudinal range error of the ship within 0.1 m and is configured to be integrated with the inertial navigation system.

[0189] In addition, USBL (200) is sensitive to noise because it measures the reception angle by the phase difference of the received sound wave.

[0190] By modeling the unique error of USBL(200) as an uncorrelated error covariance, applying a Kalman filter, and introducing the Mahalanobis distance, outliers that frequently occur in USBL(200) can be appropriately removed.

[0191] The right column of Fig. 7 shows examples of positioning signals expressed in terms of Mahalanobis distances, and the concentric circles represent Mahalanobis equidistant MD, 2MD, and 3MD corresponding to 1-σ, 2-σ, and 3-σ.

[0192] For reference, in the present invention, the position measurement error of the USBL (200) is modeled based on the position measurement error characteristics of the USBL (200) that vary depending on the distance and azimuth of the underwater vehicle, and the hull cleaning robot (100) uses this to remove outliers and improve navigation performance.

[0193] Specifically, when the position of the hull cleaning robot (100) is tracked by USBL (200), the horizontal measurement position of the hull cleaning robot (100) shows an elliptical shape distribution in which the position measurement error is proportionally distorted as the distance from the water reference point increases.

[0194] Accordingly, in the embodiment of the present invention, the measurement error of the USBL (200) is modeled by considering the position measurement error characteristics of the USBL (200) that vary depending on the distance and azimuth of the hull cleaning robot (100), and the position measurement error characteristics in the x and y directions are modeled as uncorrelated errors using the Mahalanobis distance and principal component analysis (PCA).

[0195]

[0196] - Diffraction of underwater acoustic waves by the hull

[0197] FIG. 8 is a drawing showing a distorted range measurement through USBL positioning of a hull cleaning robot on a hull due to acoustic wave diffraction, and FIG. 7 is a drawing showing a distorted position of a hull cleaning robot on an ideal hull due to acoustic wave diffraction in the case of USBL measurement.

[0198] When underwater sound waves encounter an obstacle, some signals are reflected and some are rotated.

[0199] Figure 8 is a conceptual diagram showing the actual and estimated positions of the hull cleaning robots when USBL #1 and USBL #2 are placed at the stern and bow, four hull cleaning robots (100) are operated, and reflection from the seabed or diffraction in the direction of the bottom of the ship is ignored.

[0200] In Fig. 8, the solid line indicates the propagation path of underwater sound, and the dotted line indicates the location measured by USBL (200).

[0201] Figure 9 is an example of distortion of the positioning of USBL (200) due to diffraction of sound waves for HCR located on the central port side of a simplified hull.

[0202] The actual position (0.0, 15.0) m of the hull cleaning robot (100) is measured differently as (1.11, 29.83) m.

[0203] Measurement distortion depends on the hull shape, the relative positions of the hull cleaning robot (100) and the USBL transceiver.

[0204] When the measurement location is projected onto the side of the hull, the x-direction position error becomes 1.11 m.

[0205] When the measurement position is rotated around USBL (200) and the y-position is aligned with the side of the hull (y = 15 m), the x-direction position error becomes -0.56 m.

[0206] Therefore, when diffraction of sound waves occurs, it is advantageous to rotate the USBL (200) positioning to match the side of the hull rather than projecting it onto the side of the hull.

[0207] However, errors still exist.

[0208] For a simplified ship (L × W = 300 × 30 m) shown in Fig. 9, a hull cleaning robot (100) is positioned at 10, 20, …, 70 m from the center of the starboard side in the bow direction, and a positioning error is simulated for a method of rotating around the USBL (200) so that the positioning signal is positioned at the side of the hull when acoustic wave diffraction occurs.

[0209] Fig. 10 is a drawing showing that the position of USBL (200) is (150:2:250, -30:2:30) m due to the range measurement error of USBL for a hull cleaning robot for an ideal hull.

[0210] Figure 10 shows the error size according to the change in USBL (200) position (150:2:250, -30:2:30) m.

[0211] Therefore, when LOS is not secured, the rotation method toward the side of the hull of the USBL (200) positioning keeps the error to the smallest when the USBL transceiver is located on the longitudinal axis of the hull (y = 0), and the error becomes smaller as the distance increases.

[0212] However, when cleaning a moored vessel, it is difficult to always position the USBL transceiver on the longitudinal axis, and the angular positioning error increases as the distance from the USBL (200) reference point increases.

[0213] Meanwhile, installing acoustic reference transponders on the left and right sides of the center of the hull can be utilized to correct USBL (200) positioning errors due to horizontal plane diffraction of underwater acoustic waves.

[0214] As shown in Fig. 8, if a reference sound source is installed at the center of the starboard side, the positioning of the hull cleaning robot #4 measured at USBL #2 and reference sound source positioning The difference is the x-direction position of the hull cleaning robot #4 on the starboard wall. and the x-direction position of the reference sound source It is the same as the difference between

[0215] Since the reference sound source is located at the center of the starboard side, when LOS is not secured (diffraction occurs), the x-direction position of the hull cleaning robot (100) is defined as the difference in distance s from the reference sound source, and the y-direction position can be designated as being located on the starboard side.

[0216] The method provided in the present invention is defined as a reference sound source difference method.

[0217] The reference sound source difference method can correct longitudinal position errors due to diffraction.

[0218] Meanwhile, since the diffraction path of sound waves changes as the water depth of the hull cleaning robot (100) changes, the error increases as the difference from the water depth of the reference sound source increases, so it is necessary to adjust the allowable range of measurement error.

[0219]

[0220] - Multipath reflections from ship berthing and seafloor

[0221] Figure 11 is a diagram showing USBL measurements due to reflections between a harbor quay wall and an anchored vessel.

[0222] The positioning of a hull cleaning robot (100) on a ship docked at a port must take into account the influence of reflected waves.

[0223] Fig. 11 is a simulation result of position measurement of USBL (200) measured as a signal reflected from the hull wall for two hull cleaning robots (100) located at different positions.

[0224] Here, Case II can be considered by replacing it with a reference sound source.

[0225] Unlike the positioning distortion caused by diffraction of underwater sound, it is common to judge the positioning data of USBL (200) obtained from the reflected signal as an outlier and remove it.

[0226] If the hull cleaning robot (100) is attached to the side wall of the hull, the position of the hull cleaning robot (100) in the transverse direction of the hull is designated as the hull wall, and the hull longitudinal position, i.e., the x-direction position, can be replaced with the position projected by the USBL (200) positioning signal onto the hull wall.

[0227] This relationship can be confirmed in Figure 11.

[0228] For a hull cleaning robot (100) that cleans the land side of a ship docked at a pier, the reflected acoustic wave signal has a characteristic similar to the positioning distortion caused by diffracted acoustic waves due to the narrow gap between the wall and the hull.

[0229] Figure 12 shows a conceptual diagram of positioning by wall reflection for a vessel moored at a pier.

[0230] Therefore, the hull cleaning robot (100) cleaning the vertical surface of the hull on the pier side of a ship at a pier is required to use the reference sound source difference method.

[0231] Since the positioning error range of the reference sound source and the hull cleaning robot (100) increases due to the influence of reflected waves, it is necessary to significantly adjust the error covariance of the USBL (200) measurement at this location.

[0232] Position measurement distortion due to seafloor reflection also has similar characteristics to wall reflection.

[0233] Figure 13 shows the positioning signals of diffraction waves and seabed reflections when measuring the position of a hull cleaning robot cleaning a ship's bottom.

[0234] The reference source difference method, which uses the difference in distance between the diffracted wave and the reference source diffracted wave at the ship's bottom, cannot be applied as is because the sound wave diffraction paths are different.

[0235] Therefore, the ship's bottom diffraction wave is configured to rotate the measurement distance to the ship's bottom, transform the coordinates, and greatly adjust the error range to lower the weight in the navigation system.

[0236] In the case of a seafloor reflection wave, the USBL (200) positioning signal can be projected to the water depth of the hull cleaning robot and the x-direction and y-direction positions can be maintained as is.

[0237] It is necessary to identify whether the USBL(200) positioning is due to diffraction or reflection signals.

[0238] Figure 14 is a diagram showing criteria for identifying whether there is distortion in USBL measurements due to diffraction or reflection of an acoustic signal.

[0239] In the present invention, the APS hull shape filter shown in Fig. 14 is provided as a criterion for identifying distortion due to underwater acoustic wave diffraction or reflection.

[0240]

[0241] A method of defining a larger box-shaped shape filter with a thickness h for a ship having a size of L × W × D, and identifying a positioning signal outside this shape as a distorted signal.

[0242] Since the positioning error of USBL(200) increases in proportion to the distance, the thickness corresponding to the 3-σ error of USBL(200) at the center of the hull Add a triangle shape.

[0243] The bow and stern sections, which are less affected by underwater sound reflection or diffraction, have a shape filter thickness , You can also specify a negative value, replace the box shape with a cone shape, or specify a representative line based on linear data.

[0244] If the positioning signal of the reference sound source transponder is poor in the LOS unsecured state of USBL (200), the reference sound source difference method described above cannot be applied.

[0245] In this case, the USBL (200) positioning is rotated to the hull side position to calculate the positioning signal.

[0246] At this time, the distance error in the direction of the player increases, so the navigation gain is adjusted by adaptively modulating the error covariance according to the position of the hull cleaning robot (100).

[0247] Figure 15 is a diagram showing specific errors unique to USBL according to location.

[0248] Fig. 15 shows a conceptual diagram in which error covariance is adjusted according to the position (A to D of Fig. 7) of the hull cleaning robot (100).

[0249]

[0250] - Effect of position change due to ballast change and ship movement

[0251] The draft changes due to changes in ballast caused by loading or unloading cargo on a ship, and thus the positioning reference position of the underwater hull cleaning robot (100) changes.

[0252] To compensate for this, it is necessary to equip the acoustic reference transponder with a depth sensor to compensate for changes in draft.

[0253] Additionally, when cleaning the mooring line, the reference sound source installed at the center of the hull may shake due to disturbance from the marine environment, which may cause additional positional errors.

[0254] In this case, the error covariance is adjusted to vary depending on the sea state.

[0255] FIG. 16 is a diagram illustrating a USBL-supported integrated navigation system for multiple hull cleaning robots working in acoustic wave shadow zones by correcting the acoustic wave distortion described above.

[0256]

[0257] Figure 17 is a flow chart showing the operation method of a navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention.

[0258] In the method of operating the navigation system of a hull cleaning robot using an ultrasonic positioning signal according to the present invention, the description of the same components as those of the navigation system of a hull cleaning robot using the ultrasonic positioning signal described above is omitted.

[0259] Referring to FIG. 17, the operation method of the navigation system of the hull cleaning robot (100) using the ultrasonic positioning signal according to the present invention includes four steps.

[0260] In the first step (S100), a first acoustic communication unit (110) is mounted on the hull cleaning robot (100).

[0261] The first acoustic communication unit (110) is mounted on the hull cleaning robot (100) for which position measurement is desired as described above, and is triggered by an external signal or transmits sound waves at regular intervals.

[0262] In the second stage (S200), a second acoustic communication unit (210) is installed by placing USBL buoys at the front center of the ship and the rear center of the stern, respectively, and a third acoustic communication unit (400) is installed by attaching a reference sound source device to the port and starboard centers of the hull.

[0263] In this embodiment, for the sake of ease of explanation, the second acoustic communication unit (210) is described as a USBL (Ultra Short Base Line) transceiver as described above, but it is not limited thereto, and any device capable of receiving an acoustic signal generated from the acoustic wave generating unit (10) can be used.

[0264] In addition, in this embodiment, for the sake of ease of explanation, the third acoustic communication unit (400) is described as an example of a USBL (Ultra Short Base Line) transponder as described above, but is not limited thereto, and any device that can be triggered by an external signal or generate an acoustic signal at regular intervals can be used.

[0265] This third acoustic communication unit (400) is mounted on the reference sound source device and is installed on the left and right sides of the center of the ship's hull using magnets, and is used to correct the positioning distorted by acoustic wave diffraction between the hull cleaning robot (100) and the USBL (200) due to interference from the ship.

[0266] In the third step (S300), the first acoustic communication unit (110) and the third acoustic communication unit (400) receive and respond to the signal generated by the second acoustic communication unit (210) to measure the positions of the hull cleaning robot (100) and the reference sound source device.

[0267] USBL (200) measures the three-dimensional position of the hull cleaning robot (100) and the reference sound source in the Earth coordinate system by using the propagation delay time of underwater sound waves and the azimuth and inclination angles of the received signal.

[0268] Here, the relative position of the hull cleaning robot (100) measured by the USBL (200) is converted into the relative position of the hull cleaning robot (100) in the hull-fixed coordinate system by compensating for the change in position of the ship and the USBL (200).

[0269] Meanwhile, the ship's heading angle is calculated and the hull shape function is defined using the GPS signals of the USBL buoys installed at the bow and stern.

[0270] In the fourth step (S400), a hull shape function is determined based on the measured heading angle and position of the ship, a box-shaped filter having a predetermined first thickness is applied, and a positioning signal that deviates from the box-shaped shape is identified as a distorted signal.

[0271] In the fifth step (S500), the USBL distortion signal is converted into a longitudinal position of the hull at the hull side wall using the reference sound source difference method and then converted into a projected position of the hull bottom.

[0272] In step 6 (S600), the difference between the estimated position of the hull cleaning robot and the positioning signal of the USBL buoy corrected from the positioning signal of the distorted USBL buoy is calculated.

[0273] In step 7 (S700), outliers are identified and removed based on principal component analysis and Mahalanobis distance at the estimated location.

[0274] The measurement distortion between the hull cleaning robot (100) and the USBL (200) varies depending on the hull shape and the relative positions of the second acoustic communication unit (210) of the hull cleaning robot (100) and the USBL (200).

[0275] When LOS is not secured (diffraction occurs), the x-direction position of the hull cleaning robot (100) on the plane is converted into a distance from the center side wall of the hull using a reference sound source difference method in which the difference between the position of the hull cleaning robot (100) measured by the USBL (200) and the position of the reference sound source by the third acoustic communication unit (400) is equal to the difference between the position of the hull cleaning robot (100) located on the hull wall and the position of the reference sound source.

[0276] When a ship is docked at a port pier, the positioning of the hull cleaning robot (100) is converted into the positioning data of the USBL (200) obtained from the reflected signal of the pier liner wall by taking into account the influence of reflected waves, and into the position of the hull side wall by using the reference acoustic difference method.

[0277] Additionally, a box-shaped filter having a predetermined first thickness is applied to the ship, and a positioning signal that deviates from the box-shaped shape is identified as a USBL distortion signal.

[0278] Considering that the inherent positioning error of USBL (200) is proportional to the distance, a triangular filter having a predetermined second thickness corresponding to the error of USBL (200) at the center of the hull is applied in addition to a box-shaped filter, and a positioning signal that deviates from the triangular or box-shaped shape is identified as a USBL distortion signal.

[0279] When the positioning signal of the third acoustic communication unit (400) is poor while the LOS of the USBL (200) is not secured, the positioning signal is calculated by rotating the USBL (200) positioning to the side position of the hull, and the navigation gain is adjusted by modulating the error covariance according to the position of the hull cleaning robot (100) in response to an increase in the distance error in the direction of the bow.

[0280] When a change in ballast occurs due to a change in the draft of a ship due to cargo unloading or loading, a depth sensor is installed in the third acoustic communication unit (400) to compensate for the change in draft.

[0281]

[0282] In other words, the present invention provides and designs an underwater navigation system for a multi-underwater cleaning robot (100) using a USBL (200) as an auxiliary sensor.

[0283] In order for multiple hull cleaning robots (100) to have a minimum positional error at any location on the ship, two sets of USBL transceivers are placed at the bow and stern.

[0284] To compensate for the position measurement distortion error of USBL (200) caused by diffraction sound waves, an acoustic reference transponder is additionally installed on the center side wall of the ship.

[0285] A hull shape filter is provided to identify USBL positioning distortion caused by reflected waves and multipath between the quay wall and the seabed of a ship at a pier.

[0286]

[0287] In this way, according to the present invention, by utilizing an underwater acoustic positioning signal using underwater ultrasonic waves as an auxiliary, there is an effect that can be applied even under conditions where an acoustic wave shadow zone exists and a plurality of hull cleaning robots clean the hull simultaneously.

[0288]

[0289] Above, although some examples have been given and various preferred embodiments of the present invention have been described, the description of the various embodiments described in the “Specific Details for Carrying Out the Invention” section is merely exemplary, and those skilled in the art to which the present invention pertains will readily understand that they can carry out various modifications of the present invention or carry out equivalent implementations of the present invention based on the above description.

[0290] In addition, since the present invention can be implemented in various other forms, the present invention is not limited by the above description, and the above description is provided only to make the disclosure of the present invention complete and to fully inform a person having ordinary skill in the art to which the present invention belongs of the scope of the present invention, and it should be understood that the present invention is defined only by each claim of the claims.

[0291]

[0292] The present invention has the effect of being applicable even under conditions where multiple hull cleaning robots clean a hull simultaneously by utilizing underwater acoustic positioning signals using underwater ultrasonic waves as an auxiliary, has the effect of deciphering cases where acoustic distortion occurs due to the hull and converting positioning signals by acoustic diffraction and acoustic reflection into valid information, and has the effect of identifying and filtering outliers by considering the error characteristics of USBL.

Claims

1. A hull cleaning robot comprising a first acoustic communication unit that is triggered by an external signal or generates an acoustic signal at regular intervals, and for which positioning is required; USBL (Ultra Short Base Line) installed on a buoy and including a second acoustic communication unit for measuring the position of the hull cleaning robot; A signal processing unit that analyzes the positioning signal received by the second acoustic communication unit to estimate the underwater three-dimensional position; and A reference sound source device comprising a third sound communication unit and a GPS; characterized in that it includes; Navigation system for a hull cleaning robot using ultrasonic positioning signals.

2. In paragraph 1, The above hull cleaning robot, It includes a navigation system equipped with a 6-axis inertial measurement sensor (IMU), a 3-axis Doppler velocity sensor (DVL), a depth sensor and a first acoustic communication unit, and is based on the inertial measurement sensor. USBL buoys with USBL installed, Equipped with the above second acoustic communication unit, two GPS units, and an attitude sensor (AHRS), Two sets of USBL buoys are placed at the center of the bow front and center of the stern rear of the vessel to be cleaned. Characterized in that the two sets of the above standard sound source devices are attached to the port and starboard sides of the ship respectively with magnets. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

3. In paragraph 2, The above USBL includes GPS and attitude sensors for position and attitude measurement, and the GPS is installed in pairs for azimuth measurement. When the above vessel is berthed, the USBL is anchored to prevent it from drifting. When the above vessel is moored in the inner port, the USBL buoy is tied to the bow and stern of the vessel with ropes and moves together with the vessel. The relative position of the hull cleaning robot measured by the USBL is converted into the relative position of the hull cleaning robot in the hull-fixed coordinate system by compensating for the change in position between the ship and the USBL, Using the GPS location of the USBL placed at the center of the front of the ship and the center of the rear of the stern, and using the distance measured between the reference sound source device and the USBL, the heading angle and position of the ship to be cleaned are measured. The third acoustic communication unit is installed on the left and right sides of the center of the ship's hull using magnets, and corrects the distorted positioning between the hull cleaning robot and the USBL due to interference from the ship. A method of compensating for changes in draft by installing a depth sensor in the third acoustic communication section of the reference sound source device attached to the port and starboard sides of the ship when a change in ballast occurs due to unloading or loading cargo on the ship. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

4. In paragraph 1, Regarding the phenomenon in which acoustic waves are diffracted or reflected and transmitted abnormally due to interference of a ship between the hull cleaning robot and the USBL, the measurement signal of the USBL distorted due to the abnormal acoustic wave transmission is corrected using the hull shape function. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

5. In paragraph 4, A hull shape function is determined based on the measured bow angle and position of the ship, a box-shaped filter having a predetermined first thickness is applied, and a positioning signal out of the box-shaped shape is identified as a positioning distortion of USBL. Considering that the positioning error of the USBL is proportional to the distance, a triangular filter having a predetermined second thickness corresponding to the error of the USBL at the center of the hull is additionally applied to the box-shaped filter, and a positioning signal deviating from the triangular shape or the box-shaped shape is identified as a positioning distortion of the USBL. When LOS is not secured (diffraction occurs), the x-direction position of the hull cleaning robot on the plane is The longitudinal position error due to diffraction is corrected by the reference sound source difference method, in which the difference between the position of the hull cleaning robot measured by the USBL and the position of the reference sound source by the third acoustic communication unit is equal to the difference between the position of the hull cleaning robot located on the hull wall and the position of the reference sound source. When the above vessel is docked at a port pier, the positioning of the hull cleaning robot is converted into the positioning data of the USBL obtained from the reflection signal of the pier lining by considering the influence of the reflected wave, and into the position of the hull side wall by using the reference acoustic difference method. For the hull cleaning robot cleaning the hull bottom, the hull bottom diffraction wave rotates the measurement distance to the hull bottom surface to transform the coordinates and adjust the error range. In a case where the positioning signal of the third acoustic communication unit is poor while the LOS of the USBL is not secured, the positioning of the USBL is rotated to the side of the hull to convert the positioning signal. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

6. In paragraph 5, In the estimated position of the hull cleaning robot for the conversion position of a normal USBL signal or a distorted USBL signal, if the difference between the estimated position and the measured position of the USBL exceeds a standard, it is determined as an outlier. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

7. In paragraph 6, The error characteristics of the distance direction and heading angle direction of the USBL are calculated from the estimated position obtained from the navigation system of the above hull cleaning robot, Considering the direction and inclination angle of USBL, the error characteristics are converted into the object coordinate system of the hull cleaning robot and the error covariance of the principal component axes is calculated through principal component analysis. The Mahalanobis distance is calculated for the difference value between the estimated position of the above hull cleaning robot and the positioning of the USBL, and if it is within a set error range, it is used as an innovation in the navigation system. Characterized in that the positioning signal of USBL is judged as an outlier when the error range is exceeded. Navigation system for a hull cleaning robot using ultrasonic positioning signals.

8. Step of mounting a first acoustic communication unit on the hull cleaning robot; Step of installing a second acoustic communication unit on a USBL buoy, placing two USBL buoys respectively in the forward center part of the ship's bow and the rear center part of the stern, and installing a third acoustic communication unit by attaching a reference sound source device to the port and starboard centers of the hull; A step for measuring the positions of the hull cleaning robot and the reference sound source device by receiving and responding to a signal generated by the second sound communication unit by the first sound communication unit and the third sound communication unit; A step of determining a hull shape function based on the measured bow angle and position of the vessel, applying a box-shaped filter having a predetermined first thickness, and identifying a positioning signal out of the box-shaped shape as a positioning distortion of USBL; A step of converting the distortion signal of the above USBL into the longitudinal position of the hull on the hull side wall using the reference sound source difference method and converting it into the projection position of the bottom surface; A step of calculating the difference between the estimated position of the hull cleaning robot and the positioning signal of the USBL corrected from the positioning signal of the above-mentioned distorted USBL; and A step of determining and removing outliers based on principal component analysis and Mahalanobis distance at the estimated location; characterized in that it includes; Method for operating a navigation system of a hull cleaning robot using ultrasonic positioning signals.

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