Underwater acoustic positioning system

Abstract

To enable high-accuracy calibration, reduction of calibration time, and suppression of increases in power consumption, size, and mass of acoustic lighthouses even when a large number of acoustic lighthouses are installed in deep sea.SOLUTION: An offshore signal processing device 10 transmits and receives acoustic signals to and from a master lighthouse 20, acquires three-dimensional absolute coordinates of the master lighthouse 20 by acoustic positioning, and notifies the master lighthouse 20 of the three-dimensional absolute coordinates. The master lighthouse 20 transmits and receives acoustic signals to and from slave lighthouses 30a, 30b, acquires three-dimensional relative coordinates of the slave lighthouses 30a, 30b by acoustic positioning, and acquires three-dimensional absolute coordinates of the slave lighthouses 30a, 30b from the three-dimensional relative coordinates and its own three-dimensional absolute coordinates notified from the signal processing device 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an underwater acoustic positioning system. [Background technology]

[0002] Conventionally, underwater acoustic positioning systems that use underwater ultrasonic waves to measure the position of underwater moving objects such as underwater vehicles have three types: LBL (Long Base Line), SBL (Short Base Line), and SSBL (Super Short Base Line), which are determined by the distance between transducers or acoustic transponders on the underwater moving object that serve as the basis for determining the coordinate system. SSBL is also known as USBL (Ultra Short Base Line).

[0003] In an LBL acoustic positioning system, three or more acoustic transponders are installed underwater, and the direct distance (slant range ri (i=1, 2, 3...) between the transducer of the underwater vehicle and each acoustic transponder is measured to determine the position (x, y, z) of the transducer of the underwater vehicle relative to the coordinate system created by the transponders.

[0004] The advantage of the LBL method is that, compared to other methods such as the SBL and SSBL, it has a wide measurement range regardless of water depth, and can achieve high positioning accuracy over that wide range. However, the LBL method requires calibration to determine the relative positional relationship between acoustic transponders in advance, which takes a considerable amount of time (Patent Document 1). Note that hereinafter in this specification, acoustic transponders will be referred to as "acoustic lighthouses." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-257921 Summary of the Invention [Problem to be solved by the invention]

[0006] Calibration is performed using the LBL, SBL, or SSBL method from an offshore device. However, when an acoustic lighthouse is installed in the deep sea, for example, at a depth of about 3,000 m, the following problems (1) to (3) arise. (1) Errors caused by the motion of the offshore equipment, changes in the speed of sound due to changes in the thermal boundary layer and water temperature, and sound ray refraction are added, so even if sufficient integration (averaging) is performed on the time axis, the errors cannot be completely removed, making accurate measurements difficult. (2) When multiple acoustic lighthouses are installed, the offshore equipment must be moved to be positioned directly above each acoustic lighthouse in order to reduce the effects of sound ray refraction, which further increases the measurement time. (3) Since an acoustic lighthouse requires a high-power transmitter, the power consumption, size, and mass of the acoustic lighthouse increase.

[0007] The present invention has been made to solve these problems, and its purpose is to enable high-precision calibration, shorten calibration time, and suppress increases in power consumption, size, and mass of acoustic lighthouses, even when installing a large number of acoustic lighthouses in the deep sea. [Means for solving the problem]

[0008] The present invention provides an underwater acoustic positioning system having a plurality of acoustic lighthouses that constitute an underwater acoustic communication network and an above-water measuring device that holds its own three-dimensional absolute coordinates, The plurality of acoustic lighthouses comprises a master lighthouse and a slave lighthouse; The three-dimensional absolute coordinates of the master lighthouse are obtained by the on-water measurement device transmitting and receiving acoustic signals between the master lighthouse and the on-water measurement device, from the three-dimensional relative coordinates obtained by acoustic positioning and the three-dimensional absolute coordinates held by the device itself; The three-dimensional absolute coordinates of the slave lighthouse are obtained by the master lighthouse or the measuring device on the water by transmitting and receiving acoustic signals between the master lighthouse and the slave lighthouse, and from the three-dimensional relative coordinates of the slave lighthouse obtained by acoustic positioning and the three-dimensional absolute coordinates obtained by the measuring device on the water.This is an underwater acoustic positioning system. [Effects of the Invention]

[0009] According to the present invention, even when a large number of acoustic lighthouses are installed in the deep sea, it is possible to perform highly accurate calibration, shorten the calibration time, and suppress increases in the power consumption, size, and mass of the acoustic lighthouses. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a schematic configuration of an underwater acoustic positioning system according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing an outline of a flow from installation to positioning of an underwater acoustic positioning system according to an embodiment of the present invention. [Figure 3] FIG. 2 is a block diagram showing the configuration of the signal processing device in FIG. [Figure 4] FIG. 2 is a block diagram showing the configuration of the master lighthouse in FIG. 1. [Figure 5] FIG. 2 is a block diagram showing the configuration of a slave lighthouse in FIG. 1. [Figure 6] 2 is a block diagram showing the configuration of the underwater vehicle in FIG. 1. FIG. [Figure 7] 10 is a flowchart of a calibration process according to an embodiment of the present invention. [Figure 8] FIG. 1 is a diagram showing the amplitude and phase of the propagation distance or propagation time per wavelength of three ultrasonic waves with different frequencies. [Figure 9] FIG. 1 is a diagram showing the amplitude, phase, and phase difference of two ultrasonic waves having different frequencies over multiple wavelengths. [Figure 10] 10 is a graph showing the relationship between Δf and R of ultrasonic waves, and a graph showing the relationship between distance and phase when Δf is 1 kHz and 4 kHz. [Figure 11]FIG. 1 is a diagram for explaining distance measurement between a master lighthouse and a slave lighthouse using a two-wavelength CW phase difference ranging method. [Figure 12] FIG. 10 is a diagram showing an example of an operation in which a master lighthouse measures the distance to a slave lighthouse. [Figure 13] 13 is a flowchart showing a slave lighthouse distance measurement process in FIG. 12. [Figure 14] 13 is a diagram showing an example of a schematic structure of a packet of an acoustic signal transmitted and received in the operation shown in FIG. 12. FIG. [Figure 15] 10 is a flowchart showing the process of transmitting and receiving acoustic signals between the master lighthouse and the slave lighthouse. [Figure 16] FIG. 10 is a diagram illustrating non-contact synchronous control of a slave lighthouse by a master lighthouse. [Figure 17] FIG. 17 is a diagram showing the transmission and reception timing of the synchronization signal in FIG. [Figure 18] 1 is a diagram showing an overview of positioning of an underwater moving body using an underwater acoustic positioning system according to an embodiment of the present invention; [Figure 19] 19 is a diagram showing the timing of transmission and reception of the positioning acoustic signal in FIG. 18. FIG. [Figure 20] 19 is a flowchart showing the processing of the underwater moving body in FIG. 18. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. <Overview of the Underwater Acoustic Positioning System> FIG. 1 is a diagram showing a schematic configuration of an underwater acoustic positioning system according to an embodiment of the present invention.

[0012] An underwater acoustic positioning system according to an embodiment of the present invention includes a signal processing device 10 mounted on a ship 100 at sea, and three acoustic lighthouses installed underwater: a master lighthouse 20, a slave lighthouse 30a, and a slave lighthouse 30b. The acoustic lighthouse system consisting of the master lighthouse 20, the slave lighthouse 30a, and the slave lighthouse 30b constitutes an acoustic communication network.

[0013] The underwater vehicle 40 can acquire its own three-dimensional absolute coordinates by using this underwater acoustic positioning system. Although a configuration having three acoustic beacons has been exemplified here, the present invention can also be applied to a configuration having four or more acoustic beacons.

[0014] The signal processing device 10 is connected to a GNSS antenna 1 and has a function of receiving GNSS radio waves 201 transmitted from a GNSS satellite 101 and acquiring three-dimensional absolute coordinates (latitude, longitude, altitude) of the GNSS antenna 1. In this specification, three-dimensional absolute coordinates refer to positions (coordinate values) in a three-dimensional absolute coordinate system (GNSS coordinate system), and three-dimensional relative coordinates refer to positions (coordinate values) in a three-dimensional coordinate system other than the three-dimensional absolute coordinate system.

[0015] In addition, a wave transmitter 2 having the function of transmitting an acoustic signal, and a wave receiver 3 having the function of receiving an acoustic signal are connected to the signal processing device 10. The signal processing device 10, the wave transmitter 2, and the wave receiver 3 correspond to the on-water measuring device according to the present invention. Here, a case is shown in which an acoustic signal 301 is transmitted to a master lighthouse 20, and an acoustic signal 302 transmitted from the master lighthouse 20 is received.

[0016] The signal processing device 10 transmits an acoustic signal 301 to the master lighthouse 20, receives a response acoustic signal 302, and can acquire the three-dimensional relative coordinates of the master lighthouse 20, for example, by SBL acoustic positioning. Then, from the acquired three-dimensional relative coordinates of the master lighthouse 20 and its own three-dimensional absolute coordinates, the signal processing device 10 can acquire the three-dimensional absolute coordinates of the master lighthouse 20. Then, the signal processing device 10 can notify the master lighthouse 20 of the acquired three-dimensional absolute coordinates of the master lighthouse 20.

[0017] The master lighthouse 20 has the functions of transmitting and receiving acoustic signals. Here, the functions include transmitting an acoustic signal 302 to the signal processing device 10, transmitting and receiving an acoustic signal 303 to and from the slave lighthouse 30a (transmitting an acoustic signal 303a and receiving an acoustic signal 303b), transmitting and receiving an acoustic signal 305 to and from the slave lighthouse 30b (transmitting an acoustic signal 305a and receiving an acoustic signal 305b), and transmitting an acoustic signal 306 to the underwater vehicle 40. In this specification, a transmitted acoustic signal may be referred to as a "transmitted acoustic signal," and a response acoustic signal may be referred to as a "response acoustic signal" or "response signal."

[0018] The master lighthouse 20 transmits acoustic signals 303a and 305a to the slave lighthouses 30a and 30b, receives response acoustic signals 303b and 305b, and can acquire, by acoustic positioning, the three-dimensional relative coordinates of the slave lighthouses 30a and 30b based on its own three-dimensional relative coordinates. Details of this acoustic positioning will be described later. The master lighthouse 20 can also acquire the three-dimensional absolute coordinates of the slave lighthouses 30a and 30b from the acquired three-dimensional relative coordinates of the slave lighthouses 30a and 30b and its own three-dimensional absolute coordinates notified by the signal processing device 10. The reference of the three-dimensional relative coordinates means the origin (x=y=z=0) of the three-dimensional relative coordinate system.

[0019] The slave lighthouse 30a and the slave lighthouse 30b have functions for transmitting and receiving acoustic signals. Here, transmission and reception of acoustic signals 303 (303a, 303b) between the slave lighthouse 30a and the master lighthouse 20, transmission and reception of acoustic signals 305 (305a, 305b) between the slave lighthouse 30b and the master lighthouse 20, transmission and reception of acoustic signals 304 (304a, 304b) between the slave lighthouse 30a and the slave lighthouse 30b, and transmission of acoustic signals 307, 308 to the underwater vehicle 40 are shown.

[0020] Acoustic signals 306, 307, and 308 from the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b, which are used by the underwater vehicle 40 to measure its own three-dimensional absolute coordinates, are controlled by the master lighthouse 20 so that they are transmitted at the same timing. Details of this control will be described later.

[0021] The underwater vehicle 40 is an acoustic positioning device carried by a diver underwater, or an acoustic positioning device mounted on an AUV (Autonomous Underwater Vehicle), etc. The underwater vehicle 40 stores three-dimensional absolute coordinate data of the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b in advance, and can calculate and acquire its own three-dimensional absolute coordinates from these three-dimensional absolute coordinates and positioning acoustic signals 306, 307, and 308. The calculation method will be described in detail later.

[0022] <The process from installation of the underwater acoustic positioning system to positioning> 2 is a diagram showing an outline of the flow from installation to positioning of the underwater acoustic positioning system according to the embodiment of the present invention. The outline of the flow from installation to positioning of the underwater acoustic positioning system will be described with reference to this diagram and FIG.

[0023] First, a plurality of acoustic lighthouses are installed underwater (step S1). Here, it is assumed that a master lighthouse 20, a slave lighthouse 30a, and a slave 30b are installed.

[0024] Next, the coordinates of each acoustic lighthouse are acquired (calibration) (step S2). Here, the signal processing device 10 acquires the three-dimensional absolute coordinates of the master lighthouse 20, the slave lighthouse 30a, and the slave 30b. This calibration is a main process in the underwater acoustic positioning system according to the embodiment of the present invention. The details of this process will be described later.

[0025] Next, the coordinates of each acoustic lighthouse are stored in the underwater vehicle 40 (step S3). Here, the three-dimensional absolute coordinate data of the master lighthouse 20, slave lighthouse 30a, and slave 30b are written to the storage medium of the underwater vehicle 40 before it starts to be used. This writing is performed by the signal processing device 10 on the ship 100, for example.

[0026] Next, each acoustic lighthouse synchronously transmits a positioning acoustic signal (step S4). Here, the master lighthouse 20, the slave lighthouse 30a, and the slave 30b synchronously transmit positioning acoustic signals 306, 307, and 308, respectively. This synchronous transmission will also be described in detail later. In the following description, when there is no need to distinguish between the slave lighthouse 30a and the slave 30b, they will be referred to as the slave lighthouse 30.

[0027] Next, the underwater moving body receives the positioning acoustic signals (step S5), acquires its own coordinates (step S6), and ends the process. Here, the underwater moving body 40 receives the positioning acoustic signals 306, 307, and 308, respectively, and acquires its own three-dimensional absolute coordinates. This acquisition method will also be described in detail later.

[0028] <Configuration of signal processing device> FIG. 3 is a block diagram showing the configuration of the signal processing device appearing in FIG. The signal processing device 10 includes a control unit 11, a storage unit 12, an acoustic signal transmitting unit 13, an acoustic signal receiving unit 14, a GNSS signal receiving unit 15, and an external I / F (interface) 16.

[0029] The control unit 11 is equipped with a CPU, ROM, and RAM, and performs overall control of the signal processing device 10 and calculation processing, etc. by the CPU processing the programs and data stored in the ROM and memory unit 12 using the RAM as a work area.

[0030] The storage unit 12 is an SSD (Solid State Drive), HDD (Hard Disk Drive), flash memory, etc., and stores various programs and data necessary for operating the control unit 11, and data acquired by the control unit 11 operating each unit. Here, the data stored in the storage unit 12 are exemplified by its own three-dimensional absolute coordinate data 121, the three-dimensional absolute coordinate data of the master lighthouse 20, and the three-dimensional absolute coordinate data of the slave lighthouse 30.

[0031] The acoustic signal transmitting unit 13 has a function of generating a transmission signal and supplying it to the wave transmitter 2. The wave transmitter 2 has a function of converting the transmission signal supplied from the acoustic signal transmitting unit 13 into an acoustic signal (electrical / acoustic conversion) and sending it out into water. The wave receiver 3 has a function of receiving the acoustic signal, converting it into a received signal (acoustic / electrical conversion) and supplying it to the acoustic signal receiving unit 14. The acoustic signal receiving unit 14 has a function of supplying the received signal supplied from the wave receiver 3 to the control unit 11.

[0032] The GNSS signal receiving unit 15 acquires the three-dimensional absolute coordinates (latitude, longitude, and altitude) of the GNSS antenna 1 from the GNSS signal received by the GNSS antenna 1, and supplies them to the control unit 11. The external I / F 16 is a connection terminal for external control, monitor display, etc.

[0033] The wave transmitter 2 includes at least one ultrasonic transducer, and the wave receiver 3 includes at least three transducers.

[0034] <Master Lighthouse Configuration> FIG. 4 is a block diagram showing the configuration of the master lighthouse in FIG. The master lighthouse 20 includes a control unit 21 , a memory unit 22 , an acoustic signal transmitting unit 23 , an acoustic signal receiving unit 24 , a wave transmitter 25 , a wave receiver 26 , and a depth meter 27 .

[0035] The control unit 21 is equipped with a CPU, ROM, and RAM, and performs overall control and calculation processing of the master lighthouse 20 by the CPU processing the programs and data stored in the ROM and memory unit 22 using the RAM as a work area. Here, a slave lighthouse coordinate acquisition unit 211 and a slave lighthouse synchronization control unit 212 are illustrated as functional blocks realized by the control unit 21. Details of these functions will be described later.

[0036] The storage unit 22 is a flash memory, an SSD, or the like, and stores various programs and data necessary for operating the control unit 21, and data acquired by operating each unit by the control unit 21. Here, examples of data stored in the storage unit 22 include self coordinate data 221, slave lighthouse coordinate data 222, slave lighthouse ID 223, slave lighthouse synchronization control data 224, and inter-lighthouse distance data 225.

[0037] Here, the self coordinate data 221 is the three-dimensional absolute coordinate data of the master lighthouse 20 acquired and notified by the signal processing device 10. The slave lighthouse coordinate data 222 is three-dimensional absolute coordinate data of each slave lighthouse acquired by the slave lighthouse coordinate acquisition unit 211. The slave lighthouse ID 223 is, for example, a manufacturing number stored in the ROM of the slave lighthouse 30, and is written in the storage unit 22 in advance. The slave lighthouse synchronization control data 224 is data used by the slave lighthouse synchronization control unit 212 to control the master lighthouse 20 and the slave lighthouse 30 to transmit positioning acoustic signals simultaneously. The lighthouse distance data 225 is data that represents the distance between the master lighthouse 20 and the slave lighthouse 30, the distance between the master lighthouse 20 and the slave lighthouse 30b, and the distance between the slave lighthouse 30a and the slave lighthouse 30b. These data are calculated from the self coordinate data 221 and the slave lighthouse coordinate data 222.

[0038] The depth meter 27 is a sensor that measures the underwater depth where the master lighthouse 20 is installed. The functions of the acoustic signal transmitting unit 23 and the acoustic signal receiving unit 24 are similar to those of the acoustic signal transmitting unit 13 and the acoustic signal receiving unit 14 in the signal processing device 10, respectively, and the functions of the wave transmitter 25 and the wave receiver 26 are similar to those of the wave transmitter 2 and the wave receiver 3 connected to the signal processing device 10, respectively, so a description thereof will be omitted.

[0039] <Configuration of Slave Lighthouse> FIG. 5 is a block diagram showing the configuration of the slave lighthouse in FIG. The slave lighthouse 30 includes a control unit 31 , a memory unit 32 , an acoustic signal transmitting unit 33 , an acoustic signal receiving unit 34 , a wave transmitter 35 , a wave receiver 36 , and a depth meter 37 .

[0040] The control unit 31 is equipped with a CPU, ROM, and RAM, and performs overall control and calculation processing of the slave lighthouse 30 by the CPU processing the programs and data stored in the ROM and memory unit 32 using the RAM as a work area. The memory unit 32 is a flash memory, SSD, or the like, and stores various programs and data required to operate the control unit 31, as well as data acquired by the control unit 31 operating each unit.

[0041] The functions of the acoustic signal transmitting unit 33 and the acoustic signal receiving unit 34 are similar to those of the acoustic signal transmitting unit 13 and the acoustic signal receiving unit 14 in the signal processing device 10, respectively, the functions of the wave transmitter 35 and the wave receiver 36 are similar to those of the wave transmitter 2 and the wave receiver 3 connected to the signal processing device 10, respectively, and the function of the depth meter 37 is similar to that of the depth meter 27 in the master lighthouse 20, so a description thereof will be omitted. However, it is sufficient that the wave receiver 36 has at least one ultrasonic transducer.

[0042] <Configuration of underwater vehicle> FIG. 6 is a diagram showing the configuration of the underwater vehicle in FIG. The underwater vehicle 40 includes a control unit 41 , a memory unit 42 , an acoustic signal receiving unit 43 , a wave receiver 44 , and a depth meter 45 .

[0043] The control unit 41 is equipped with a CPU, a ROM, and a RAM, and the CPU processes the programs and data stored in the ROM and the storage unit 22 using the RAM as a work area, thereby performing overall control of the underwater vehicle 40 and arithmetic processing. Here, a positioning processing unit 411 is illustrated as a functional block realized by the control unit 41. Details of this function will be described later.

[0044] The storage unit 42 is an SSD, flash memory, or the like, and stores various programs and data necessary for operating the control unit 41, as well as data acquired by the control unit 41 operating each unit. Here, lighthouse coordinate data 421 is shown as an example of data stored in the storage unit 42. The lighthouse coordinate data 421 is three-dimensional absolute coordinate data of the master lighthouse 20 and the slave lighthouse 30, and is written by the signal processing device 10 on the ship 100, for example.

[0045] The function of the acoustic signal receiving unit 43 is the same as that of the acoustic signal receiving unit 14 in the signal processing device 10, the function of the wave receiver 44 is the same as that of the wave receiver 3 connected to the signal processing device 10, and the function of the depth meter 45 is the same as that of the depth meter 27 of the master lighthouse 20, so their explanations will be omitted. However, it is sufficient that the wave receiver 44 has at least one ultrasonic transducer.

[0046] <Calibration process> 7 is a flowchart of the calibration process according to the embodiment of the present invention, and the calibration process (step S2 in FIG. 2) will be described with reference to this figure and FIGS.

[0047] First, the signal processing device 10 on the ship 100 acquires its own coordinates by GNSS positioning (step S11). More specifically, the GNSS radio waves 201 transmitted from the GNSS satellites 101 are received by the GNSS antenna 1, the GNSS signal receiving unit 15 calculates the three-dimensional absolute coordinates (latitude, longitude, altitude) of the GNSS antenna 1, and the control unit 11 stores the calculated three-dimensional absolute coordinate data in the memory unit 12.

[0048] Next, the signal processing device 10 acquires the coordinates of the master lighthouse 20 by acoustic positioning (step S12). More specifically, the following steps (1) to (4) are executed between the signal processing device 10 and the master lighthouse 20.

[0049] (1) The signal processing device 10 transmits an acoustic signal 301 to the master lighthouse 20. (2) The master lighthouse 20 receives the acoustic signal 301 and transmits the acoustic signal 302 as a response signal. (3) The signal processing device 10 receives the acoustic signal 302 and acquires the three-dimensional relative coordinates of the master lighthouse 20 by SBL acoustic positioning. That is, the distance is measured based on the time from when the acoustic signal is transmitted by the transmitter 2 to when the response signal is received by the receiver 3, and the three-dimensional relative coordinates of the master lighthouse 20 are acquired by measuring the direction based on the difference in the reception times of the response signals from the three ultrasonic transducers included in the receiver 3. (4) The signal processing device 10 calculates the three-dimensional absolute coordinates of the master lighthouse 20 from the three-dimensional relative coordinates of the master lighthouse and its own three-dimensional absolute coordinates, and stores the calculated coordinates in the memory unit 12. The accuracy of the three-dimensional absolute coordinates of the master lighthouse 20 may be improved by having the master lighthouse 20 input the measurement value of the depth meter 27 into the acoustic signal 302 in the procedure (2) above.

[0050] Here, the reference for the three-dimensional relative coordinates of the master lighthouse 20 acquired in the above procedure (3) is the three-dimensional absolute coordinates of the GNSS antenna 1 stored in the memory unit 12, not the three-dimensional absolute coordinates of the receiver 3, and therefore includes an error due to the offset. However, this error is negligible compared to the error included in the measurement values ​​of the three-dimensional relative coordinates of the master lighthouse 20 (which would be several tens of meters if installed in the deep sea). Therefore, in the following embodiments of the present invention, the three-dimensional absolute coordinates of the GNSS antenna 1 will be described as the three-dimensional absolute coordinates of the receiver 3.

[0051] Next, the signal processing device notifies the master lighthouse of the three-dimensional absolute coordinates of the master lighthouse (step S13). More specifically, the signal processing device 10 transmits an acoustic signal 301 including the three-dimensional absolute coordinate data of the master lighthouse 20 stored in the memory unit 12 to the master lighthouse 20, and the master lighthouse 20 receives the acoustic signal 301 and stores it in the memory unit 22 as its own coordinate data 221.

[0052] Next, the master lighthouse acquires the coordinates of the slave lighthouses by acoustic positioning (step S14). In this step, the master lighthouse 20 executes the following steps (i) to (vii) under the control of the slave lighthouse coordinate acquisition unit 211 of the control unit 21 to acquire the three-dimensional absolute coordinates of the slave lighthouse 30a and the slave 30b. When executing this procedure, the slave lighthouse coordinate acquisition unit 211 and each unit of the master lighthouse 20 work together to function as acoustic signal transmitting means, response acoustic signal receiving means, distance calculation means, and coordinate acquisition means.

[0053] (i) First, the master lighthouse 20 acquires the three-dimensional relative coordinates of the slave lighthouse 30a by acoustic positioning. More specifically, the master lighthouse 20 transmits an acoustic signal 303a addressed to the slave lighthouse 30a and receives an acoustic signal 303b as a response signal. This response signal contains depth data measured by the depth meter 37 of the slave lighthouse 30a.

[0054] (ii) The master lighthouse 20 obtains the horizontal (x and y) direction of the slave lighthouse 30a relative to its own three-dimensional relative coordinates based on the difference in reception times of acoustic signals 303b from the two ultrasonic transducers in the receiver 26, and processes the acoustic signal 303b to calculate the distance to the slave lighthouse 30a, thereby obtaining the two-dimensional relative coordinates (x, y) of the slave lighthouse 30a. Then, by obtaining the z coordinate from the depth data, the three-dimensional relative coordinates (x, y, z) are obtained. Here, the distance calculation is performed using a two-wavelength CW phase difference ranging method (described in detail later).

[0055] (iii) The master lighthouse 20 obtains the three-dimensional absolute coordinates of the slave lighthouse 30a from the three-dimensional relative coordinates of the slave lighthouse 30a and its own three-dimensional absolute coordinates, and stores them in the memory unit 22 as slave lighthouse coordinate data 222.

[0056] (iv) The master lighthouse 20 transmits an acoustic signal 305a to the slave lighthouse 30b and receives a response signal 305b, which includes depth data measured by the depth gauge 37 of the slave lighthouse 30b.

[0057] (v) The master lighthouse 20 transmits an acoustic signal addressed to the slave lighthouse 30b via the slave lighthouse 30a, and receives a response signal from the slave lighthouse 30b via the slave lighthouse 30a.

[0058] (vi) The master lighthouse 20 calculates the distance from itself to the slave lighthouse 30b by processing the acoustic signal received directly from the slave lighthouse 30b, and calculates the distance from the slave lighthouse 30a to the slave lighthouse 30b by processing the acoustic signal received via the slave lighthouse 30a, and obtains the three-dimensional relative coordinates of the slave lighthouse 30b from the two distance data and the depth data. Note that in this specification, a slave lighthouse that has already obtained three-dimensional absolute coordinates, such as the slave lighthouse 30a, and that cooperates with the master lighthouse 20 when obtaining the three-dimensional relative coordinates of another slave lighthouse (here, the slave lighthouse 30b), and serves as the reference for distance measurement, is referred to as a reference slave lighthouse.

[0059] (vii) The master lighthouse 20 obtains the three-dimensional absolute coordinates of the slave lighthouse 30b from the three-dimensional relative coordinates of the slave lighthouse 30b and its own three-dimensional absolute coordinates, and stores them in the memory unit 22 as slave lighthouse coordinate data 222.

[0060] <2-wavelength CW phase difference ranging method> The distance between the master lighthouse 20 and the slave lighthouse 30 can be calculated by transmitting and receiving a rectangular pulse acoustic signal between the master lighthouse 20 and the slave lighthouse 30, and from the time difference between the time the acoustic signal is sent and the time the response signal is received at the master lighthouse 20 (the known response delay time within the slave lighthouse 30 is subtracted), and the speed of sound.

[0061] However, even if it were possible to transmit ultrasonic waves that could be considered to be perfectly square waves, it would be difficult to measure them with high accuracy. This is because the waveform of the ultrasonic waves changes on the path to the target due to the effects of attenuation and dispersion in the air, and this waveform change interferes with determining the time of reception.

[0062] Therefore, in this embodiment, two CW (continuous wave) acoustic signals with different wavelengths are transmitted and received between the master lighthouse 20 and the slave lighthouse 30, and the master lighthouse 20 calculates the distance between the master lighthouse 20 and the slave lighthouse 30 from the phase difference between the two CW acoustic signals received. The measurement principle will be explained below.

[0063] Figure 8 is a diagram showing the amplitude and phase versus propagation distance or propagation time per wavelength for three ultrasonic waves of different frequencies. In this figure, the upper graph (hereinafter referred to as the amplitude-per-wavelength graph) represents the amplitude per wavelength for ultrasonic waves with frequencies of 30 kHz, 31 kHz, and 40 kHz. The lower graph (hereinafter referred to as the phase-per-wavelength graph) represents the phase corresponding to the amplitude in the amplitude-per-wavelength graph. The horizontal axis in both graphs represents the propagation distance R in mm and the propagation time in ms relative to R / 1500.

[0064] Figure 9 shows the amplitude, phase, and phase difference of two ultrasonic waves of different frequencies over multiple wavelengths. Figure 9A shows the amplitude of multiple wavelengths of simultaneously transmitted frequencies f1 and f2 (f2 > f1). Figure 9B shows the phases φ(f1) and φ(f2) and phase difference Δφ corresponding to the amplitudes in Figure 9A. Figure 9C shows the propagation distance or time on the horizontal axis of Figure 9B multiplied by four.

[0065] It is known that the following equations [1] and [2] hold true (JP 2006-42201 A), where f1 and f2 are the frequencies of two simultaneously transmitted radio waves, c is the propagation speed, R is the distance from the transmitting position to the receiving position, and Δφ is the phase difference between the two radio waves at the receiving position. These equations also hold true for ultrasonic waves.

[0066] Δφ=(2πR / c)Δf …Equation [1] R = (cΔφ) / (2πΔf) ...Equation [2]

[0067] In equations [1] and [2], "-π≦Δφ≦π". Furthermore, equation [2] represents one period (2π) of the phase difference Δφ. Therefore, equation [2] represents the distance (hereinafter referred to as Rs) for one period of Δφ in Figure 9C. Rs is equal to one wavelength of Δf (=c / Δf), and is the longest distance that can be measured with one period of Δφ. From equation [2], we can see that Rs is inversely proportional to Δf.

[0068] Figure 10 is a graph showing the relationship between Δf and R of ultrasonic waves, and the relationship between distance and phase when Δf is 1 kHz and 4 kHz. From the graph showing the relationship between Δf and R in Figure 10, it can be seen that the larger Δf is, the higher the resolution at which short-distance measurements are possible, and the smaller Δf is, the lower the resolution at which long-distance measurements are possible.

[0069] For example, in equation [2], if Δf is 1 kHz (for example, f1 = 30 kHz, f2 = 31 kHz), Rs is one wavelength of Δf (hereinafter, λ Δf ), so Rs=λ Δf =c / Δf=(1500 / 1×10 3 ) = 1.5m (= 1500mm), and if the detection resolution of Δφ is 1°, the distance measurement resolution is 1500 / 360 ≒ 4.17 [mm]. Also, if Δf = 4kHz (for example, f1 = 30kHz, f2 = 34kHz), then Rs = λ Δf =c / Δf=(1500 / 4×10 3 ) = 375 mm, and if the detection resolution of Δφ is 1°, the distance measurement resolution is 375 / 360 ≒ 1.04 [mm].

[0070] Thus, measuring one period of Δφ (one wavelength of Δf) does not allow for measurement of long distances with high resolution. However, as can be seen from Figures 9B and 9C, the phase difference Δφ has a period of Δf. Therefore, in this embodiment, the number (hereinafter, ns) exceeding one period of Δφ (one wavelength of Δf) and the phase difference Δφ are measured, and the long distance can be calculated with high resolution using the following equation [3].

[0071] R=ns λ Δf +R'=(ns+Δφ)·c / Δf…Formula [3] Here, R' (= Δφ·c / Δf) is the distance calculated from the measured value of Δφ.

[0072] A method that enables long-distance measurement with high resolution will be described below. As mentioned above with reference to equation [2] and Figure 10, Δf and R are inversely proportional. In other words, decreasing Δf increases R, and conversely, increasing Δf decreases R. Each Δf has its own measurable range. Therefore, in the graph showing the relationship between Δf and R in Figure 10, Δf is appropriately selected so that the measurable range moves from the upper left to the lower right, and the frequency is chirped to narrow it down.

[0073] <Distance measurement from master lighthouse to slave lighthouse using two-wavelength CW phase difference ranging method> Next, we will provide additional information about the two-wavelength CW phase difference ranging method. Figure 11 is a diagram to explain how to measure the distance from the master lighthouse to the slave lighthouse using the two-wavelength CW phase difference ranging method.

[0074] As shown in the figure, the master lighthouse 20 simultaneously transmits acoustic signals of frequencies f1 and f2 to the slave lighthouse 30a. At this time, the master lighthouse 20 has already acquired the number of periods ns. The slave lighthouse 30a receives and stores the acoustic signals, and after a predetermined time, transmits a response signal to the master lighthouse 20. The master lighthouse 20 measures the phase difference Δφ between the frequency components f1 and f2 contained in the response signal, and can calculate the distance R using the previously acquired number of periods ns using the aforementioned equation [3].

[0075] Here, we will explain the phase difference Δφ between the f1 and f2 frequency components of the response signal received by the master lighthouse 20 and the phase difference between the f1 and f2 frequency components of the acoustic signal received by the slave lighthouse 30a. The slave lighthouse 30a simultaneously receives the two frequency components of the acoustic signal and simultaneously transmits them as a response signal after a predetermined time. Therefore, the phase difference Δφ between the two frequency components in the response signal received by the master lighthouse 20 is the same as the phase difference between the two frequency components of the acoustic signal received by the slave lighthouse 30a.

[0076] 11, the master lighthouse 20 transmits an acoustic signal including frequencies f1 and f2 to the slave lighthouse 30a, the slave lighthouse 30a delays the acoustic signal by a predetermined time and transmits a response signal to the master lighthouse 20, and the master lighthouse 20 measures the phase difference Δφ between the frequencies f1 and f2 of the response signal. In other words, the frequencies f1 and f2 are transmitted and received simultaneously, and the phase difference is measured.

[0077] The present invention is not limited to simultaneous transmission and reception, and can also measure the phase difference using sequential transmission and reception. This procedure is explained below. The master lighthouse 20 transmits an acoustic signal of frequency f1 to the slave lighthouse 30a. The slave lighthouse 30a receives the acoustic signal and, after a predetermined time, transmits a response signal of frequency f1 to the master lighthouse 20. The master lighthouse 20 compares the phase of the reference signal of frequency f1 with the phase of the received response signal of frequency f1 and stores the phase difference Δφ1. Next, the master lighthouse 20 and slave lighthouse 30a perform the same exchange for a signal of frequency f2. The master lighthouse 20 compares the phase of the reference signal of frequency f2 with the phase of the received response signal of frequency f2 and stores the phase difference Δφ2. Finally, the master lighthouse 20 calculates the difference between Δφ1 and Δφ2 to measure the phase difference Δφ between frequencies f1 and f2.

[0078] <Details of the process for obtaining distance information from the master lighthouse to the slave lighthouse> Fig. 12 is a diagram showing an example of the operation of the master lighthouse and the slave lighthouse in the two-wavelength CW phase difference positioning method according to the embodiment of the present invention, and is a flowchart showing the slave lighthouse ranging process in Fig. 12. With reference to these diagrams, the procedure by which the master lighthouse 20 measures the distances to the slave lighthouses 30a and 30b will be described.

[0079] Here, the master lighthouse 20 has already measured the distance to the slave lighthouse 30a, and the three-dimensional absolute coordinate data has also been stored in the memory unit 22 as slave lighthouse coordinate data 222. Below, we will explain a case where the master lighthouse 20 measures the distance to the slave lighthouse 30b by directly transmitting and receiving acoustic signals to and from the slave lighthouse 30b, and measures the distance between the slave lighthouse 30a and the slave lighthouse 30b by transmitting and receiving acoustic signals via the slave lighthouse 30a (which serves as a relay lighthouse) (slave lighthouse 30a is the reference slave lighthouse). The processing shown in Figure 12 is executed by the function of the slave lighthouse coordinate acquisition unit 211 in the control unit 21 of the master lighthouse 20.

[0080] As shown in FIG. 13, first, the master lighthouse 20 determines carrier frequencies f1 and f2 based on parameters such as the distance to the slave lighthouse 30b to be positioned and the required resolution (step S21).

[0081] Next, the master lighthouse 20 directly transmits an acoustic signal at carrier frequencies f1 and f2 to the slave lighthouse 30b, which is the target of positioning (step S22: acoustic signal 305a in Figure 12), and the slave lighthouse 30b directly receives the acoustic signal from the master lighthouse 20 (step S24: acoustic signal 305a in Figure 12).

[0082] Furthermore, acoustic signals are transmitted from the master lighthouse 20 to the slave lighthouse 30b, which is the positioning target, via the slave lighthouse 30a at carrier frequencies f1 and f2 (step S23: acoustic signals 303a and 304a in FIG. 12), and the slave lighthouse 30b receives the acoustic signals from the master lighthouse 20 via the slave lighthouse 30a (step S25: acoustic signals 303a and 304a in FIG. 12). At this time, the slave lighthouse 30a acts as a relay lighthouse (repeater).

[0083] For the sake of convenience, steps S22, S24 and steps S23, S25 are described as parallel processes, but in reality they are sequential processes. The same applies to the steps (S26, S28, S30) following step S24 and the steps (S27, S29, S31) following step S25.

[0084] Next, the slave lighthouse 30b transmits a response acoustic signal directly to the master and the lighthouse 20 (step S26: acoustic signal 305b in FIG. 12), and the master 20 receives a response acoustic signal directly from the slave lighthouse 30b (step S28: acoustic signal 305b in FIG. 12).

[0085] The slave lighthouse 30b also transmits a response acoustic signal to the master lighthouse 20 via the slave lighthouse 30a (step S27: acoustic signals 304b, 303b in Figure 12), and the master lighthouse 20 receives the response acoustic signal from the slave lighthouse 30b via the slave lighthouse 30a (step S29: acoustic signals 304b, 303b in Figure 12).

[0086] Finally, the master lighthouse 20 calculates the distance to the slave lighthouse 30b (step S30), and calculates the distance from the slave lighthouse 30a to the slave lighthouse 30b (step S31), and ends the processing shown in this figure.

[0087] Here, the distance calculation in step S30 is performed using the frequency chirp described above. The distance calculation in step S31 is performed using the following steps S311 to S313. As described above, the master lighthouse 20 has already measured the distance to the slave lighthouse 30a. Hereinafter, this distance will be referred to as R1, Δf at the time of measurement as Δf1, the phase difference as Δφ1, ns as ns1, and R' as R1'. That is, the following relationship holds for equations [1], [2], and [3].

[0088] Δφ1=(2πR1' / c)Δf1...Formula [1-1] R1'=(cΔφ1) / (2πΔf1) …Formula [2-1] R1=ns1·λ Δf1 +R1'=(ns1+Δφ1)·c / Δf1...Formula [3-1]

[0089] Step S311: The master lighthouse 20 acquires the value of ns for the distance from the master lighthouse 20 to the slave lighthouse 30b via the slave lighthouse 30a. This value is set as ns2.

[0090] Step S312: The master lighthouse 20 measures the phase difference of Δf in the acoustic signal 303b and obtains the measured value Δφ2. The acoustic signal 303b is obtained by delaying the acoustic signal 304b by a predetermined time, and the phase difference Δφ2 maintains the phase difference of Δf in the acoustic signal 304b.

[0091] Step S313: The master lighthouse 20 refers to the phase difference when measuring the distance to the slave lighthouse 30a. The subsequent processing differs depending on whether Δf1 and Δf (hereinafter referred to as Δf2) when step S312 is executed are the same (Δf1=Δf2) or different (Δf1≠Δf2).

[0092] If they are the same, the master lighthouse 20 calculates "Δφ2-Δφ1" and "ns2-ns1", and calculates the distance R2 between the slave lighthouse 30a and the slave lighthouse 30b based on the equation [3] (step S314).

[0093] If they are different, replace Δf1 with Δf2 in equation [1-1] to calculate "Δφ1' = (2πR1' / c)Δf2", and then solve equation [3-3] for ns1 to get "ns1 = (R1-R1') / λ Δf1 "λ Δf1 λ Δf2 Then, "Δφ2-Δφ1'" and "ns2-ns1'" are calculated, and the distance R2 between the slave lighthouse 30a and the slave lighthouse 30b is calculated based on the equation [3] (step S315).

[0094] As described above, the master lighthouse 20 obtains the three-dimensional relative position of the slave lighthouse 30b from the distance data from these two locations and the depth data included in the response acoustic signal. Then, the master lighthouse 20 obtains the three-dimensional absolute coordinates of the slave lighthouse 30b from this three-dimensional relative position data and its own three-dimensional absolute coordinates (its own coordinate data 221), and stores them in the memory unit 22 as slave lighthouse coordinate data 222.

[0095] <Example of a schematic structure of an audio signal packet> FIG. 14 is a diagram showing an example of a schematic structure of a packet of an acoustic signal transmitted and received in the operation shown in FIG.

[0096] As shown in FIG. 14A, the packet of the acoustic signal includes an area for storing a header as communication route information consisting of a source lighthouse ID, a destination lighthouse ID, and a relay lighthouse ID, and an area for storing a payload.

[0097] Figure 14B shows a packet of acoustic signal 305a sent directly from the master lighthouse 20 to the slave lighthouse 30b in Figure 12, with the source lighthouse ID being the master lighthouse 20, the destination lighthouse ID being the slave lighthouse 30b, there being no relay lighthouse ID, and the payload being a depth data request.

[0098] Also, Figure 14C shows a packet of acoustic signal 305b from slave lighthouse 30b in response to acoustic signal 305a in Figure 12, with the source lighthouse ID being slave lighthouse 30b, the destination lighthouse ID being master lighthouse 20, there being no relay lighthouse ID, and the payload being depth data.

[0099] 14D shows a packet of acoustic signal 303a transmitted from the master lighthouse 20 to the slave lighthouse 30b via the slave lighthouse 30a in FIG. 12, with the source lighthouse ID being the master lighthouse 20, the destination lighthouse ID being the slave lighthouse 30b, the relay lighthouse ID being the slave lighthouse 30a, and the payload being a depth data request. The slave lighthouse 30a receives the acoustic signal 303a and transmits an acoustic signal 304a to the slave lighthouse 30b.

[0100] 14E shows a packet of acoustic signal 304b transmitted from slave lighthouse 30b to master lighthouse 20 via slave lighthouse 30a in FIG. 12, where the source lighthouse ID is slave lighthouse 30b, the destination lighthouse ID is master lighthouse 20, the relay lighthouse ID is slave lighthouse 30a, and the payload is depth data. Slave lighthouse 30a receives acoustic signal 304b and transmits acoustic signal 303b to master lighthouse 20.

[0101] In addition, the IDs of the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b in Figure 14 are, for example, manufacturing numbers stored in their respective ROMs, and the IDs of the slave lighthouse 30a and slave 30b are stored in advance as slave lighthouse ID 223 in the memory unit 22 of the master lighthouse 20.

[0102] <Transmission and reception processing of acoustic signals between the master lighthouse and the slave lighthouse> FIG. 15 is a flowchart showing the transmission and reception process of acoustic signals between the master lighthouse and the slave lighthouse in FIG.

[0103] First, the master lighthouse selects an acoustic lighthouse to be measured and a communication route for the acoustic signal (step S41). In the case of Fig. 12, the acoustic lighthouse to be measured is the slave lighthouse 30b, and the communication routes are master lighthouse 20 → slave lighthouse 30b and master lighthouse 20 → slave lighthouse 30a → slave lighthouse 30b.

[0104] Next, the master lighthouse writes communication route information, including the identification information (ID) of the selected acoustic lighthouse, into the header of the transmitted acoustic signal (step S42). This step generates an acoustic signal including the packets shown in Figures 14B and 14D.

[0105] Next, the master lighthouse transmits an acoustic signal (step S43), the relay lighthouse receives the acoustic signal (step S44), and the relay lighthouse transmits an acoustic signal (step S45).

[0106] Steps S44 and S45 are repeatedly executed for the number of relay lighthouses. Therefore, the number of executions is 0 for the communication route "master lighthouse 20 → slave lighthouse 30b" in Fig. 12, and 1 for the communication route "master lighthouse 20 → slave lighthouse 30a → slave lighthouse 30b" in Fig. 12.

[0107] After steps S44 and S45 are repeated for the number of relay lighthouses, an acoustic signal is transmitted to the acoustic lighthouse to be measured, and the acoustic lighthouse to be measured receives the acoustic signal (step S46). The acoustic lighthouse to be measured transmits a response acoustic signal in response to receiving the acoustic signal (step S47).

[0108] The response acoustic signal is transmitted from the master lighthouse and reaches the master lighthouse via a communication route that is the reverse of the communication route of the acoustic signal received at the acoustic lighthouse to be measured. That is, after the reception of the response acoustic signal by the relay lighthouse (step S48) and the reception of the response acoustic signal by the relay lighthouse (step S49) are repeated the number of times equal to the number of relay lighthouses, the relay lighthouse transmits the response acoustic signal to the master lighthouse, and the master lighthouse receives the response acoustic signal (step S50).

[0109] <Added Slave Lighthouse> Here, a calibration process when a slave lighthouse is added to the underwater acoustic positioning system shown in FIG. 1 will be described.

[0110] A newly added slave lighthouse in Figure 1 is designated as 30c. The master lighthouse 20 has already acquired the distances to the slave lighthouses 30a and 30b, and as explained with reference to Figure 4, their three-dimensional absolute coordinates have also been stored in the memory unit 22 as slave lighthouse coordinate data 222. Then, using slave lighthouse 30b as the reference slave lighthouse, the three-dimensional absolute coordinates of slave lighthouse 30c are acquired. An example of an outline of this will be explained below.

[0111] The master lighthouse 20 transmits an acoustic signal directly to the slave lighthouse 30c, receives the response acoustic signal, and measures the distance from itself to the slave lighthouse 30c.

[0112] Furthermore, the master lighthouse 20 uses the slave lighthouse 30a as a relay lighthouse, transmits an acoustic signal to the slave lighthouse 30c, receives the response acoustic signal, and measures the distance from the slave lighthouse 30a to the slave lighthouse 30c. In this case, the slave lighthouse 30a is the reference slave lighthouse.

[0113] In addition, the master lighthouse 20 acquires the three-dimensional relative coordinates of the slave lighthouse 30c from the measured value of the distance from itself to the slave lighthouse 30c, the measured value of the distance from the slave lighthouse 30a to the slave lighthouse 30c, and the depth data of the slave lighthouse 30c contained in the response acoustic signal from the slave lighthouse 30c, and further acquires the three-dimensional absolute coordinates of the slave lighthouse 30c by referring to the three-dimensional absolute coordinates that it holds.

[0114] To add another slave lighthouse and designate it as slave lighthouse 30d, the master lighthouse 20 performs the following procedure, for example: Using slave lighthouse 30b as a relay lighthouse, it transmits an acoustic signal to slave lighthouse 30d, receives the corresponding acoustic response, and measures the distance from slave lighthouse 30b to slave lighthouse 30d. Using slave lighthouse 30c as a relay lighthouse, it transmits an acoustic signal to slave lighthouse 30d, receives the corresponding acoustic response, and measures the distance from slave lighthouse 30c to slave lighthouse 30d. Then, it obtains the three-dimensional relative coordinates of slave lighthouse 30d from the distance measurements and the depth data of slave lighthouse 30d contained in the corresponding acoustic response signal from slave lighthouse 30d. It then obtains the three-dimensional absolute coordinates of slave lighthouse 30d by referencing its own three-dimensional absolute coordinates. In this case, slave lighthouses 30b and 30c are the reference slave lighthouses.

[0115] To add another slave lighthouse and designate it as slave lighthouse 30e, the master lighthouse 20 performs the following procedure, for example: Using slave lighthouse 30b as a relay lighthouse, it transmits an acoustic signal to slave lighthouse 30e, receives the corresponding acoustic response, and measures the distance from slave lighthouse 30b to slave lighthouse 30e. Using slave lighthouse 30c as a relay lighthouse, it transmits an acoustic signal to slave lighthouse 30e, receives the corresponding acoustic response, and measures the distance from slave lighthouse 30c to slave lighthouse 30e. Then, it obtains the three-dimensional relative coordinates of slave lighthouse 30e from the distance measurements and the depth data of slave lighthouse 30e contained in the corresponding acoustic response signal from slave lighthouse 30e. It then obtains the three-dimensional absolute coordinates of slave lighthouse 30e by referencing its own three-dimensional absolute coordinates. In this case, slave lighthouses 30b and 30c are the reference slave lighthouses.

[0116] <Non-contact synchronous control of slave lighthouses by master lighthouse> In a system having multiple acoustic beacons, such as the underwater acoustic positioning system according to an embodiment of the present invention, no wiring is installed between the beacons, taking into consideration the installation, recovery, and safety of the acoustic beacons, and therefore it is necessary to perform non-contact synchronization control between the beacons. Fig. 16 is a diagram showing non-contact synchronization control of the slave beacons by the master beacon, and Fig. 17 is a diagram showing the timing of transmission and reception of the synchronization signal in Fig. 16.

[0117] This non-contact synchronization control controls the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b to transmit positioning acoustic signals at the same time, and is executed by the slave lighthouse synchronization control unit 212 of the control unit 21 of the master lighthouse 20 by referring to the slave lighthouse synchronization control data 224 stored in the memory unit 22.

[0118] As shown in FIG. 17, the master lighthouse 20 transmits a synchronization signal 305a1 to the slave lighthouse 30b at time t1, and transmits a synchronization signal 303a1 to the slave lighthouse 30a at time t2.

[0119] Then, the synchronization signal 305a1 is received by the slave lighthouse 30b at time t3 after the propagation time Tb has elapsed, and the synchronization signal 303a1 is received by the slave lighthouse 30a at time t3 after the propagation time Ta has elapsed.

[0120] Here, the propagation time Ta is the value obtained by dividing the distance between the master lighthouse 20 and the slave lighthouse 30a by the speed of sound, and the propagation time Tb is the value obtained by dividing the distance between the master lighthouse 20 and the slave lighthouse 30b by the speed of sound, and these are stored in the memory unit 22 as slave lighthouse synchronization control data 224.

[0121] In order to match the reception time of the synchronization signal 303a1 at the slave lighthouse 30a with the reception time of the synchronization signal 303a1 at the slave lighthouse 30b, the master lighthouse 20 delays the transmission time of the synchronization signal 303a1 by the difference in propagation time (Tb-Ta) from the transmission time of the synchronization signal 305a1.

[0122] After receiving synchronization signals 303a1 and 305a1, slave lighthouses 30a and 30b can transmit positioning acoustic signals 307 and 308 simultaneously with the positioning acoustic signal 306 of the master lighthouse 20 at a predetermined cycle starting at time t4 after a predetermined delay time Td. This delay time and cycle are known and are stored in memory unit 22 as slave lighthouse synchronization control data 224, so thereafter master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b can transmit positioning acoustic signals 306, 307, and 308 simultaneously at a predetermined cycle.

[0123] <Positioning using an underwater acoustic positioning system> The positioning of an underwater moving body using the above-described acoustic lighthouse system that performs non-contact synchronous control, that is, the underwater acoustic positioning system according to an embodiment of the present invention, will be described with reference to FIGS.

[0124] Figure 18 is a diagram showing an overview of positioning of an underwater moving body using an underwater acoustic positioning system according to an embodiment of the present invention, Figure 19 is a diagram showing the timing of transmitting and receiving positioning acoustic signals in Figure 18, and Figure 20 is a flowchart showing processing of the underwater moving body in Figure 18.

[0125] 18, the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b are installed at known three-dimensional absolute coordinates of (x1, y1, z1), (x2, y2, z2), and (x3, y3, z3) in the xyz Cartesian coordinate system, respectively. Data on these three-dimensional absolute coordinates is stored and held in advance in the memory unit 42 of the underwater vehicle 40 as lighthouse coordinate data 421.

[0126] The three-dimensional absolute coordinates (x, y, z) of the underwater vehicle 40 are unknown and are calculated by the positioning processing unit 411 of the control unit 41 after receiving positioning acoustic signals 306, 307, and 308 transmitted from the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b.

[0127] As shown in FIG. 19, the master lighthouse 20, the slave lighthouse 30a, and the slave lighthouse 30b simultaneously transmit positioning acoustic signals 306, 307, and 308 at time t10.

[0128] The positioning acoustic signals 306, 307, and 308 are received by the underwater vehicle 40 at times t11, t12, and t13 after the propagation times of the positioning acoustic signals from the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b, respectively, to the underwater vehicle 40. In this case, the master lighthouse 20 is the closest and the slave lighthouse 30b is the farthest from the underwater vehicle 40.

[0129] 20, the underwater vehicle 40 receives positioning acoustic signals from multiple acoustic beacons and stores the reception time data for each signal (step S61). Here, the reception times t11, t12, and t13 of the positioning acoustic signals 306, 307, and 308 from the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b are stored.

[0130] Here, two methods will be described for the underwater vehicle 40 to identify the positioning acoustic signals 306, 307, and 308. The first method is to set the frequencies of the positioning acoustic signals 306, 307, and 308 to different values, associate these frequencies with the lighthouse coordinate data 421, and store them in the memory unit 42. The second method is to set the IDs of the master lighthouse 20, slave lighthouse 30a, and slave lighthouse 30b in the headers of the packets of the positioning acoustic signals 306, 307, and 308, associate these IDs with the lighthouse coordinate data 421, and store them in the memory unit 42.

[0131] Returning to the explanation of Figure 20, next, the underwater vehicle 40 calculates the difference in distance from itself to each acoustic lighthouse from the difference in reception time and the speed of sound (step S62). Here, using the distance from itself to the master lighthouse 20 as a reference, the difference in distance to the slave lighthouse 30a and the difference in distance to the slave lighthouse 30b are calculated. That is, the difference in distance from itself to the master lighthouse 20 and the distance from itself to the slave lighthouse 30a is calculated from "reception time difference T1 × speed of sound" (hereinafter, the calculation result is referred to as L1), and the difference in distance from itself to the master lighthouse 20 and the distance from itself to the slave lighthouse 30b is calculated from "reception time difference T2 × speed of sound" (hereinafter, the calculation result is referred to as L2).

[0132] Finally, the underwater vehicle 40 calculates its own coordinates from the difference in distance between itself and each acoustic beacon and the coordinates of each acoustic beacon (step S63). Here, the three-dimensional absolute coordinates (x, y, z) are calculated from L1, L2, (x1, y1, z1), (x2, y2, z2), and (x3, y3, z3).

[0133] This calculation method utilizes the principle of hyperbolic navigation. 18, points where the difference L1 between the distance from the three-dimensional absolute coordinates of the master lighthouse 20 and the distance from the three-dimensional absolute coordinates of the slave lighthouse 30a is constant form a hyperboloid whose foci are the three-dimensional absolute coordinates of the master lighthouse 20 and the three-dimensional absolute coordinates of the slave lighthouse 30a. Similarly, points where the difference L2 between the distance from the three-dimensional absolute coordinates of the master lighthouse 20 and the three-dimensional absolute coordinates of the slave lighthouse 30b is constant form a hyperboloid whose foci are the three-dimensional absolute coordinates of the master lighthouse 20 and the three-dimensional absolute coordinates of the slave lighthouse 30b. Therefore, the three-dimensional absolute coordinates of the underwater vehicle 40 exist on the intersection of these two hyperboloids.

[0134] Therefore, the underwater vehicle 40 can calculate its own three-dimensional absolute coordinates (x, y, z) by calculating the intersection line of the two hyperboloids using the positioning processing unit 411 and then identifying its position on the intersection line by referring to the depth data from the depth meter. Note that if the acoustic beacon system is equipped with four or more acoustic beacons, the underwater vehicle 40 can calculate its own position as a point on the intersection line of three or more hyperboloids, making a depth meter unnecessary.

[0135] As explained above in detail, the underwater acoustic positioning system according to the embodiment of the present invention provides the following advantages (1) to (5). (1) Since the master lighthouse 20 and the slave lighthouse 30 are installed underwater at approximately the same depth, accurate calibration is possible with minimal errors caused by changes in sound speed due to changes in the thermal boundary layer and water temperature, sound ray refraction, etc. (2) Even when a large number of acoustic lighthouses are installed, the signal processing device 10 on the ocean does not need to be moved to be positioned directly above each acoustic lighthouse, thereby reducing the calibration time. (3) Since the slave lighthouses 30 do not require acoustic communication between themselves or with the master lighthouse 20, i.e., relatively long-distance acoustic communication with the offshore signal processing device 10, the increase in power consumption, size, and mass of the acoustic lighthouses can be reduced compared to conventional systems in which all acoustic lighthouses perform acoustic communication with offshore devices. (4) High-precision distance measurement is possible using the two-wavelength CW phase difference distance measurement method. (5) Non-contact synchronous control of the master lighthouse 20 allows the master lighthouse 20 and each slave lighthouse 30 to simultaneously transmit acoustic positioning signals.

[0136] [Variations] Next, modified examples of the embodiment of the present invention will be described. These modified examples and any possible combinations of the modified examples are also included in the present invention.

[0137] <Variation 1> (1) In Figure 1, the number of acoustic lighthouses shall be four or more (one master lighthouse and three or more slave lighthouses). (2) Calibration of the fourth and subsequent acoustic lighthouses is possible by measuring the distance from the three acoustic lighthouses whose positions are known. The fourth and subsequent slave lighthouses do not need depth meters. (3) The underwater vehicle 40 can also obtain its own three-dimensional absolute coordinates based on the positioning acoustic signals from the four acoustic lighthouses, so a depth meter is not necessary.

[0138] <Variation 2> In this embodiment, the master lighthouse 20 is notified of and stores its own three-dimensional absolute coordinates by the signal processing device 10 (FIG. 7: step S13). In addition, the master lighthouse 20 acquires the three-dimensional absolute coordinates of the slave lighthouse 30 from the three-dimensional relative coordinates of the slave lighthouse 30 acquired by acoustic positioning and its own three-dimensional absolute coordinates.

[0139] In this variant example 2, the signal processing device 10 does not notify the master lighthouse 20 of its three-dimensional absolute coordinates (step S13 in Figure 7 is not executed), and the master lighthouse 20 notifies the signal processing device 10 of the three-dimensional relative coordinates of the slave lighthouse 30 obtained by acoustic positioning, and the signal processing device 10 obtains the three-dimensional absolute coordinates of the slave lighthouse 30 from the three-dimensional absolute coordinates of the master lighthouse 20 and the notified three-dimensional relative coordinates of the slave lighthouse 30.

[0140] <Variation 3> The distance between the master lighthouse 20 and the slave lighthouse 30 is measured based on the propagation time of ultrasonic waves. Although the accuracy is lower than that of the two-wavelength CW phase difference ranging method, it enables quick measurement.

[0141] <Variation 4> The calculation of ns in two-wavelength CW phase difference ranging is performed using the results of ranging based on the propagation time of ultrasonic waves. In other words, the distance measured based on the propagation time is calculated based on the λ that can be measured with the desired resolution. Δf Calculate ns by dividing by .

[0142] <Variation 5> 16 and 17, the master lighthouse 20 sets the transmission times of the synchronization signals 303a1 at the slave lighthouse 30a and 305a1 at the slave lighthouse 30b so that the reception times of the synchronization signals 303a1 and 305a1 at the slave lighthouse 30a and 30b coincide. Then, the slave lighthouses 30a and 30b transmit positioning acoustic signals 307 and 308 after a delay time Td from the reception of the synchronization signals.

[0143] (2) In this modified example, the headers of the packets of the synchronization signals 303a1 and 305a1 are entered for the slave lighthouses 30a and 30b with setting data for the delay time Td from the time of reception of the synchronization signals 303a1 and 305a1 to the time of transmission of the positioning acoustic signals 307 and 308, depending on the difference in propagation time (Tb-Ta).This makes it possible for the master lighthouse 20 to simultaneously transmit the synchronization signals 303a1 and 305a1 and for the slave lighthouses 30a and 30b to simultaneously transmit the positioning acoustic signals 307 and 308, even if they receive the synchronization signals 303a1 and 305a1 at different times.

[0144] Variation 6 (1) The underwater vehicle 40 is configured to be able to notify the master lighthouse 20 of its own three-dimensional absolute coordinates determined by acoustic signals directly or via the slave lighthouse 30. (2) The master lighthouse 20 notifies the signal processing device 10 of the notified three-dimensional absolute coordinates of the underwater vehicle 40 . (3) When the three-dimensional absolute coordinates of multiple underwater moving bodies 40 are notified, the signal processing device 10 monitors to prevent interference. That is, for example, when two underwater moving bodies 40 are located at a predetermined distance from each other, an alarm signal is transmitted via a path reverse to the path along which the three-dimensional absolute coordinates were notified from the underwater moving body 40 to the signal processing device 10, and the underwater moving body 40 issues an alarm (audio output, light output, etc.). (4) When the signal processing device 10 is notified of the three-dimensional absolute coordinates of multiple underwater moving bodies 40, it transmits the three-dimensional absolute coordinates of the other underwater moving bodies 40 to each underwater moving body 40 via a route opposite to the route along which the three-dimensional absolute coordinates were notified from the underwater moving body 40 to the signal processing device 10, and each underwater moving body 40 displays its own three-dimensional absolute coordinates and the three-dimensional absolute coordinates of the other underwater moving bodies 40.

[0145] <Variation 7> Place a Master Lighthouse 20 and a Slave Lighthouse 30 in a lake or river. [Explanation of symbols]

[0146] 2, 25, 35...transmitter, 3, 26, 36, 44...receiver, 10...signal processing device, 11, 21...control unit, 12, 22, 32, 42...memory unit, 13, 23, 33...acoustic signal transmitting unit, 14, 24, 34, 43...acoustic signal receiving unit, 20...master lighthouse, 30a, 30b, 30c...slave lighthouse, 27, 37, 45...depth sensor, 40...underwater moving body, 211...slave lighthouse coordinate acquisition unit, 212...slave lighthouse synchronization control unit, 411...positioning processing unit.

Claims

1. An underwater acoustic positioning system having a plurality of acoustic lighthouses that constitute an acoustic communication network installed underwater, and a measuring device on the water that holds its own three-dimensional absolute coordinates, The plurality of acoustic lighthouses comprises a master lighthouse and a slave lighthouse; The three-dimensional absolute coordinates of the master lighthouse are obtained by the on-water measurement device transmitting and receiving acoustic signals between the master lighthouse and the on-water measurement device, from the three-dimensional relative coordinates obtained by acoustic positioning and the three-dimensional absolute coordinates held by the device itself; An underwater acoustic positioning system in which the three-dimensional absolute coordinates of the slave lighthouse are obtained by the master lighthouse or the measuring device on the water, by transmitting and receiving acoustic signals between the master lighthouse and the slave lighthouse, and the three-dimensional relative coordinates of the slave lighthouse obtained by acoustic positioning and the three-dimensional absolute coordinates obtained by the measuring device on the water.

2. 2. The underwater acoustic positioning system according to claim 1, The measuring device on the water notifies the master lighthouse of the three-dimensional absolute coordinates of the master lighthouse; An underwater acoustic positioning system in which the master lighthouse obtains the three-dimensional absolute coordinates of each slave lighthouse from the three-dimensional relative coordinates of each slave lighthouse obtained and its own three-dimensional absolute coordinates notified.

3. 2. The underwater acoustic positioning system according to claim 1, The master lighthouse notifies the measuring device on the water of the three-dimensional relative coordinates of each of the slave lighthouses; The underwater acoustic positioning system uses the above-water measuring device to obtain the three-dimensional absolute coordinates of each slave lighthouse from the obtained three-dimensional absolute coordinates of the master lighthouse and the notified three-dimensional relative coordinates of each slave lighthouse.

4. 3. The underwater acoustic positioning system according to claim 2, The Master Lighthouse an acoustic signal transmitting means for transmitting acoustic signals via multiple communication routes to a target slave lighthouse from which three-dimensional relative coordinates are to be acquired; a response acoustic signal receiving means for receiving a response acoustic signal returned from the target slave lighthouse via a communication route in the reverse direction of the plurality of communication routes in response to the acoustic signal transmitted by the acoustic signal transmitting means; a distance calculation means for calculating the distance between the target slave lighthouse and a plurality of slave lighthouses that have directly transmitted acoustic signals to and received response acoustic signals from the target slave lighthouse based on the response acoustic signals received by the response acoustic signal receiving means; a coordinate acquisition means for acquiring three-dimensional relative coordinates of the target slave lighthouse based on the two distance data calculated by the distance calculation means and the depth data of the target slave lighthouse included in the response acoustic signal when the acoustic signal transmission means has transmitted the acoustic signal via two communication routes, and for acquiring three-dimensional relative coordinates of the target slave lighthouse based on the three or more distance data calculated by the distance calculation means when the acoustic signal transmission means has transmitted the acoustic signal via three or more communication routes; An underwater acoustic positioning system having:

5. 5. The underwater acoustic positioning system according to claim 4, An underwater acoustic positioning system in which one of the communication routes is a communication route in which the master lighthouse directly transmits an acoustic signal to the target slave lighthouse, and the other communication routes are communication routes that pass through slave lighthouses whose three-dimensional absolute coordinates have already been obtained by the master lighthouse.

6. 5. The underwater acoustic positioning system according to claim 4, An underwater acoustic positioning system in which all of the communication routes are communication routes that pass through slave lighthouses whose three-dimensional absolute coordinates have already been acquired by the master lighthouse.

7. 5. The underwater acoustic positioning system according to claim 4, the acoustic signal transmitted by the acoustic signal transmitting means has two carrier waves with different frequencies, a response acoustic signal to the acoustic signal transmitted by the acoustic signal transmitting means is the acoustic signal delayed by a predetermined time, The distance calculation means of the underwater acoustic positioning system calculates the distance between the target slave lighthouse and multiple slave lighthouses that have directly transmitted acoustic signals and received response acoustic signals from the target slave lighthouse based on the phase difference between the two carrier waves in the response acoustic signal received by the response acoustic signal receiving means and the number of wavelengths of the frequency difference between the carrier frequencies.

8. 2. The underwater acoustic positioning system according to claim 1, The master lighthouse has a means for storing arrival time data representing the arrival time of an acoustic signal to each slave lighthouse, An underwater acoustic positioning system that transmits a synchronization signal to each slave lighthouse so that each slave lighthouse transmits a positioning acoustic signal at a predetermined timing based on the arrival time data.

9. 9. The underwater acoustic positioning system according to claim 8, An underwater acoustic positioning system in which the predetermined timing is the same timing common to each slave lighthouse.

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