Mobile object guidance device and mobile object guidance system

Abstract

To provide a mobile object guidance device and mobile object guidance system that can accurately guide a moving object without using an inertial navigation device. [Solution] A mobile guidance device for guiding a predetermined target to a target position, comprising a media radiating means that radiates a first transmission wave whose frequency changes in a first frequency band and a second transmission wave whose frequency changes in a second frequency band different from the first frequency band into the surrounding environment.

Description

[Technical Field]

[0001] The present invention relates to a mobile object guidance device and a mobile object guidance system. [Background technology]

[0002] Non-patent document 1 below discloses a new strategy for seabed surveys using a convoy control of multiple AUVs. Submersible vehicles such as autonomous underwater vehicles (AUVs), whether manned or unmanned, navigate underwater by estimating their own position using an inertial navigation system (INS) because radio waves from systems such as the Global Navigation Satellite System (GNSS) cannot reach the seabed. As is well known, inertial navigation systems accumulate errors due to time integration, and the position error increases in proportion to the operating time.

[0003] Therefore, in the above background technology, a support vessel or an Autonomous Surface Vehicle (ASV) acquires its absolute position using a global positioning satellite system and determines the relative position of the submersible using acoustic relative positioning means. The support vessel or ASV then transmits these relative and absolute positions to the submersible using acoustic communication. The submersible then navigates underwater by sequentially correcting its own position (self-position) using the relative and absolute positions acquired from the support vessel or ASV. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A New Strategy for Seafloor Surveys Using Multiple AUV Platoon Control: Maritime Technology and Safety Research Report, Vol. 21, No. 4 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, inertial navigation systems installed in underwater vehicles (mobile bodies) such as autonomous underwater survey equipment are expensive devices. In other words, inertial navigation systems can be a factor that increases the cost of systems that guide mobile bodies underwater (mobile body guidance systems). In order to make mobile body guidance systems more widespread, it is important to develop technologies that can accurately guide mobile bodies without using inertial navigation systems.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a mobile body guidance device and a mobile body guidance system that can accurately guide a mobile body without using an inertial navigation device. [Means for solving the problem]

[0007] To achieve the above objective, the present invention employs a first solution relating to a mobile guidance device, which is a mobile guidance device for guiding a predetermined guidance target to a target position, and which includes a media radiating means that radiates into the surroundings a first transmission wave whose frequency changes in a first frequency band and a second transmission wave whose frequency changes in a second frequency band different from the first frequency band.

[0008] In the present invention, as a second solution relating to a mobile guidance device, the first solution described above is provided with a first main signal whose frequency changes linearly in the first frequency band, and the second main signal whose frequency changes linearly in the second frequency band.

[0009] In the present invention, as a third solution relating to a mobile guidance device, the second solution described above employs the following means: the first transmission wave includes a first synchronization signal in addition to the first main signal, and the second transmission wave includes a second synchronization signal that is at the same timing as the first synchronization signal in addition to the second main signal.

[0010] In the present invention, as a fourth solution relating to a mobile guidance device, the present invention adopts a method in which, in any of the first to third solutions described above, the medium radiating means comprises a plurality of transmitting transducers that individually radiate the first transmitting wave and the second transmitting wave.

[0011] In the present invention, as a fifth solution relating to a mobile guidance device, the fourth solution described above is provided with a pair of transmitting transducers arranged on the same plane and separated by a predetermined distance.

[0012] In the present invention, as a sixth solution relating to a mobile guidance device, the fifth solution described above is adopted by providing a third transmitting transducer located outside the same plane, in addition to the pair of transmitting transducers.

[0013] In the present invention, as a seventh solution relating to a mobile guidance device, the fourth solution described above is adopted, which includes four transmitting transducers, each positioned at four different coordinates in three-dimensional space.

[0014] In the present invention, as an eighth solution relating to a mobile guidance device, the present invention adopts a method in which, in any of the first to seventh solutions described above, the medium radiating means and the guided object are provided in water, and the first and second transmitted waves are ultrasonic waves.

[0015] Furthermore, in the present invention, as a first solution relating to a mobile guidance system, a means is adopted which comprises a mobile guidance device relating to any of the first to eight solutions described above, and a guided object, wherein the guided object is equipped with a course detection means for detecting a course toward the target position based on the received signals of the first and second transmitted waves.

[0016] Also, in the present invention, as a second solution means for the mobile body guidance system, in the above first solution means, the course detection means adopts a means of detecting the course based on the frequency difference between the first detection signal frequency related to the first transmission wave and the second detection signal frequency related to the second transmission wave.

Effect of the Invention

[0017] According to the present invention, it is possible to provide a mobile body guidance system capable of accurately guiding a mobile body without using an inertial navigation device.

Brief Description of the Drawings

[0018] [Figure 1] It is a block diagram showing the configuration of a mobile body guidance device and a mobile body guidance system according to a first embodiment of the present invention. [Figure 2] It is a waveform diagram showing first and second oscillation signals and received signals in a mobile body guidance device and a mobile body guidance system according to a first embodiment of the present invention. [Figure 3] It is a characteristic diagram showing the frequency changes of first and second transmission waves and received waves in a mobile body guidance device and a mobile body guidance system according to a first embodiment of the present invention. [Figure 4] It is a block diagram showing the configuration of a signal processing unit in a first embodiment of the present invention. [Figure 5] It is a characteristic diagram showing the frequency changes of a reference signal and a main signal detection signal in a first embodiment of the present invention. [Figure 6] It is a characteristic diagram showing the frequency spectra of a received signal, a reference signal, and a main signal detection signal in a first embodiment of the present invention. [Figure 7] It is a schematic diagram showing the arrangement of a transmission transducer in a mobile body guidance device and a mobile body guidance system according to a second embodiment of the present invention. [Figure 8] It is a characteristic diagram showing the frequency changes of first and second transmission waves and received waves in a second embodiment of the present invention. [Figure 9] It is a characteristic diagram showing the frequency changes of a reference signal and a main signal detection signal in a second embodiment of the present invention. [Figure 10] This is a schematic diagram showing the arrangement of transmitting transducers in a mobile guidance device and mobile guidance system according to the third embodiment of the present invention. [Figure 11] This is a schematic diagram showing the relationship between Doppler frequency and heading in a third embodiment of the present invention. [Modes for carrying out the invention]

[0019] One embodiment of the present invention will be described below with reference to the drawings. [First Embodiment] The mobile guidance system according to the first embodiment includes an acoustic marker A and an underwater unmanned vehicle B, as shown in Figure 1. This mobile guidance system is configured as an underwater system installed below the water surface, as shown in the figure.

[0020] In the first embodiment, the acoustic marker A corresponds to the mobile guidance device according to the present invention and guides the underwater unmanned vehicle B, which is the target of guidance, toward the target position. In addition, the underwater unmanned vehicle B in the first embodiment corresponds to the mobile body in the present invention and moves toward the acoustic marker A installed at the target position.

[0021] Acoustic marker A is fixedly positioned in the water and, as shown in the figure, comprises a pair of transmitting transducers 1a and 1b, a pair of oscillating circuits 2a and 2b, and a frequency control unit 3. On the other hand, underwater unmanned vehicle B navigates (moves) underwater toward a target position, and its position (navigation position) underwater may change. Such underwater unmanned vehicle B comprises a receiving transducer 4, a signal processing unit 5, a course calculation unit 6, and a propulsion / steering mechanism 7, as shown in the figure.

[0022] A pair of transmitting transducers 1a and 1b are connected to a pair of oscillation circuits 2a and 2b, respectively, forming an ultrasonic oscillator that emits ultrasonic waves of different frequency bands into water. Specifically, one transmitting transducer 1a is connected to one oscillation circuit 2a, and based on the first oscillation signal input from the oscillation circuit 2a, it emits ultrasonic waves of the first frequency band fa(t) as the first transmitted wave Sa into the water. Hereinafter, "t" is a variable representing time.

[0023] The other transmitting transducer 1b is connected to the other oscillation circuit 2b, and based on the second oscillation signal input from the other oscillation circuit 2b, it radiates ultrasonic waves in the second frequency band fb(t) as the second transmitting wave Sb into the water. The first transmitting wave Sa and the second transmitting wave Sb have a relationship in which their frequency bands differ by a predetermined frequency.

[0024] Such a pair of transmitting transducers 1a and 1b are arranged to be relatively close to each other. That is, the distance between the installation position of one transmitting transducer 1a and the installation position of the other transmitting transducer 1b at acoustic marker A is relatively short.

[0025] A pair of oscillator circuits 2a and 2b are connected to a pair of transmitting transducers 1a and 1b, respectively, and generate first and second oscillation signals in different frequency bands, which are output to the pair of transmitting transducers 1a and 1b, respectively. Specifically, one oscillator circuit 2a is connected to one transmitting transducer 1a and generates a first oscillation signal which is output to one transmitting transducer 1a. The other oscillator circuit 2b is connected to the other transmitting transducer 1b and generates a second oscillation signal in a different frequency band from the first oscillation signal which is output to the other transmitting transducer 1b.

[0026] The frequency control unit 3 is connected to the pair of oscillation circuits 2a and 2b, and outputs first and second control signals to the pair of oscillation circuits 2a and 2b, respectively. That is, the frequency control unit 3 outputs the first control signal to one oscillation circuit 2a and the second control signal to the other oscillation circuit 2b.

[0027] The first control signal is a control signal that instructs one oscillation circuit 2a on the oscillation timing and frequency of the first oscillation signal, and indirectly controls the first transmitted wave Sa radiated into the water by one transmitting transducer 1a. On the other hand, the second control signal is a control signal that instructs the other oscillation circuit 2b on the oscillation timing and frequency of the second oscillation signal, and indirectly controls the second transmitted wave Sb radiated into the water by the other transmitting transducer 1b.

[0028] Figure 2(a) is a waveform diagram showing examples of the waveforms of the first and second oscillation signals. As shown in Figure 2(a), the first and second oscillation signals consist of a synchronization signal and a main signal. Note that Figure 2(a) shows the first and second oscillation signals for two periods, so the waveforms show the synchronization signal and main signal arranged in time series.

[0029] As shown in the figure, the synchronization signal is a short burst signal that repeats at a predetermined time interval t0. In contrast, the main signal is a burst signal that rises after a period ta from the synchronization signal and continues for a period tm, as shown in the figure.

[0030] In other words, the first transmitted wave Sa is an ultrasonic wave comprising a first main signal in the first frequency band fa(t) and a first synchronization signal. In contrast, the second transmitted wave Sb is an ultrasonic wave comprising a second main signal in the second frequency band fb(t) and a second synchronization signal that is at the same timing as the first synchronization signal. Although the first transmitted wave Sa and the second transmitted wave Sb have the same signal form, the frequencies of their main signals are different.

[0031] Furthermore, as shown in Figure 3, the first main signal in the first transmission wave Sa maintains a constant frequency difference with respect to the second main signal in the second transmission wave Sb. In other words, the frequency of the first main signal in the first transmission wave Sa at any given time is in a relationship with the frequency difference (frequency difference) of the second main signal in the second transmission wave Sb at the same time, which is a predetermined constant value.

[0032] Here, the pair of transmitting transducers 1a, 1b, the pair of oscillating circuits 2a, 2b, and the frequency control unit 3 in the acoustic marker A constitute a medium radiating means that radiates a first transmitting wave Sa whose frequency changes in the first frequency band fa(t) and a second transmitting wave Sb whose frequency changes in the second frequency band fb(t) at a different frequency from the first frequency band fa(t) toward the underwater unmanned vehicle B (guided target, moving object).

[0033] The receiving transducer 4 is an ultrasonic receiver that receives the first and second transmitted waves Sa and Sb, and is connected to the signal processing unit 5. The receiving transducer 4 converts the received waves, which have arrived after the first and second transmitted waves Sa and Sb have propagated through the water, into an electrical signal (received signal) and outputs it to the signal processing unit 5.

[0034] Here, the ultrasonic waves (received waves) reaching the receiving transducer 4 include, as shown in Figure 1, a direct wave D that propagates directly from the pair of transmitting transducers 1a and 1b to the receiving transducer 4, as well as a first multipath wave M1 and a second multipath wave M2. The first multipath wave M1 is formed when the first and second transmitting waves Sa and Sb, radiated into the water from the pair of transmitting transducers 1a and 1b, are reflected at the water surface S and reach the receiving transducer 4.

[0035] The second multipath wave M2 is formed when the first and second transmitted waves Sa and Sb, radiated into the water from a pair of transmitting transducers 1a and 1b, are reflected off the seabed E and reach the receiving transducer 4. Since the propagation paths of these first and second multipath waves M1 and M2 in water are longer than those of the direct wave D, they arrive at the receiving transducer 4 with a time delay compared to the direct wave D, according to the path difference.

[0036] In other words, the receiving transducer 4 converts the direct wave D generated based on the first and second transmitted waves Sa and Sb, and the composite wave of the first multipath wave M1 and the second multipath wave M2 into a received signal and outputs it to the signal processing unit 5. The composite wave, or received signal, contains the frequency components of the first and second transmitted waves Sa and Sb, but it is a signal in which the first and second transmitted waves Sa and Sb cannot be separated on the time axis.

[0037] Figure 2(b) is a waveform diagram showing an example of a received signal waveform. As shown in the figure, the received signal is delayed by a delay time td relative to the first and second transmitted waves Sa and Sb. In addition, since the first multipath wave M1 and the second multipath wave M2 reach the receiving transducer 4 in addition to the direct wave D, the received signal comprises three time-shifted synchronization signals and a composite main signal formed by combining the second main signals of the first and second transmitted waves Sa and Sb based on the direct wave D, the first multipath wave M1 and the second multipath wave M2.

[0038] Figure 3 is a characteristic diagram showing the frequency changes of the first and second transmitted waves Sa and Sb radiated into the water by a pair of transmitting transducers 1a and 1b, and the frequency changes of the received waves reaching the receiving transducer 4. In Figure 3, Δf is the frequency difference between the direct wave D and the first and second multipath waves M1 and M2, assuming no error in the time change of the distance between the acoustic marker A and the underwater drone B, and no error in the synchronization time of the reference signal.

[0039] As shown in Figure 3(a), the first transmission wave Sa has a frequency of the first main signal set to the first frequency band fa(t) and a frequency change that increases linearly over time. Similarly, as shown in Figure 3(a), the second transmission wave Sb has a frequency of the second main signal set to the second frequency band fb(t) and a frequency change that increases linearly over time. The second frequency band fb(t) in the second transmission wave Sb is set to a different frequency that does not overlap at all with the first frequency band fa(t) in the first transmission wave Sa, as shown in the figure.

[0040] The received wave is a composite wave of the direct wave D, the first multipath wave M1, and the second multipath wave M2 related to the first and second transmitted waves Sa and Sb, respectively. As shown in Figure 3(b), it has a frequency change in which the direct wave D, the first multipath wave M1, and the second multipath wave M2 related to the synchronization signal and the main signal are shifted and superimposed on the time axis.

[0041] The signal processing unit 5 is connected to the receiving transducer 4 and the track calculation unit 6. This signal processing unit 5 performs signal processing on the received signal input from the receiving transducer 4 and outputs the result of the signal processing to the track calculation unit 6. As shown in Figure 4, this signal processing unit 5 includes a synchronization signal detection unit 8, a reference signal generation unit 9, a mixer 10, and an FFT unit 11.

[0042] The synchronization signal detection processing unit 8 is connected to the receiving transducer 4, the reference signal generation processing unit 9, and the mixer 10. This synchronization signal detection processing unit 8 extracts the synchronization signals included in the received signal input from the receiving transducer 4 and outputs them to the reference signal generation processing unit 9. As shown in Figure 2(b), the received signal includes multiple synchronization signals caused by the direct wave D, the first multipath wave M1, and the second multipath wave M2. The synchronization signal detection processing unit 8 detects all of these synchronization signals and outputs a timing signal indicating the generation time of each synchronization signal to the reference signal generation processing unit 9.

[0043] The reference signal generation processing unit 9 is connected to the synchronization signal detection processing unit 8 and the mixer 10. This reference signal generation processing unit 9 generates a reference signal based on the timing signal and outputs this reference signal to the mixer 10. This reference signal is a local signal for synchronous detection of the main signal of the received signal, which is separately input to the mixer 10 from the receiving transducer 4.

[0044] As shown in Figure 5(a), this reference signal is a burst signal in the third frequency band fm(t) whose frequency changes over time in synchronization with the synchronization signal of the received signal.

[0045] Mixer 10 is connected to the receiving transducer 4, the synchronization signal detection processing unit 8, the reference signal generation processing unit 9, and the FFT processing unit 11. Mixer 10 multiplies (mixes) the received signal input from the receiving transducer 4 and the reference signal input from the reference signal generation processing unit 9, and outputs the main signal detection signal generated by this multiplication to the FFT processing unit 11. The receiving transducer 4, the synchronization signal detection processing unit 8, the reference signal generation processing unit 9, and mixer 10 function as a synchronous detection circuit that synchronously detects the main signal contained in the received signal.

[0046] Figure 5(b) is a characteristic diagram showing the frequency variation of the main signal detection signal described above. As shown in the figure, the main signal detection signal includes detection signals for three main signals: the direct wave D, the first multipath wave M1, and the second multipath wave M2.

[0047] Figure 6(a) shows an example of the frequency spectrum of the main signal included in the received signal. Figure 6(b) shows an example of the frequency spectrum of the reference signal. Furthermore, Figure 6(c) shows the frequency spectrum of the main signal detection signal obtained by multiplying the main signal and the reference signal in this way.

[0048] As shown in Figure 6(c), the main signal detection signal includes the main signal of the first frequency fa(t) contained in the first transmission wave Sa, and three first detection signal frequencies resulting from the direct wave D, the first multipath wave M1, and the second multipath wave M2, as well as the main signal of the second frequency fb(t) contained in the second transmission wave Sb, and three second detection signal frequencies resulting from the direct wave D, the first multipath wave M1, and the second multipath wave M2.

[0049] The first detection signal frequency, caused by the first frequency fa(t) and the direct wave D, and the second detection signal frequency, caused by the second frequency fb(t) and the direct wave D, have a frequency difference Δfd. This frequency difference Δfd between the first and second detection signal frequencies of the direct wave D is a physical quantity that changes according to the relative speed between the fixed acoustic marker A and the navigable underwater unmanned vehicle B.

[0050] The FFT processing unit 11 is connected to the mixer 10 and the track calculation unit 6. The FFT processing unit 11 obtains the frequency spectrum of the main signal detection signal input from the mixer 10 by applying frequency analysis processing (FFT processing) to the main signal detection signal. The FFT processing unit 11 also calculates the frequency difference Δfd based on the frequency spectrum and outputs it to the track calculation unit 6.

[0051] In other words, the FFT processing unit 11 obtains the highest frequencies of the first detection signal frequency of the first transmission wave Sa and the second detection signal frequency of the second transmission wave Sb, respectively, included in the frequency spectrum of the main signal detection signal, and calculates the difference frequency between the first detection signal frequency and the second detection signal frequency of the direct wave D as the final frequency difference Δfd.

[0052] Here, acoustic marker A is fixed in place underwater, while the underwater drone B navigates (moves) underwater at a predetermined speed range. Therefore, the received signal described above undergoes a Doppler shift corresponding to the navigation speed of the underwater drone B. As will be explained in more detail later, the received signal contains Doppler frequencies as frequency components due to this Doppler shift.

[0053] The signal processing unit 5 obtains the first detection signal frequency originating from the first transmission wave Sa and the second detection signal frequency originating from the second transmission wave Sb based on the frequency spectrum of the main signal contained in the received signal, and obtains the frequency difference Δfd, which is the difference between the highest frequencies of the first and second detection signal frequencies. The signal processing unit 5 outputs this frequency difference Δfd to the course calculation unit 6 as a signal indicating its own direction of navigation (navigation direction detection signal).

[0054] The course calculation unit 6 is connected to the signal processing unit 5 and the propulsion / steering mechanism 7. Based on the navigation direction detection signal input from the signal processing unit 5, the course calculation unit 6 sets the direction of acoustic marker A (target position), that is, the course of the underwater unmanned vehicle B. The course calculation unit 6 outputs a course signal indicating the course of the underwater unmanned vehicle B to the propulsion / steering mechanism 7.

[0055] Here, the receiving transducer 4, signal processing unit 5, and heading calculation unit 6 in the underwater unmanned vehicle B constitute a heading detection means for detecting the heading of the underwater unmanned vehicle B toward acoustic marker A (target position) based on the received signals of the first transmitted wave Sa and the second transmitted wave Sb.

[0056] The propulsion and steering mechanism 7 is connected to the course calculation unit 6. Based on the course signal input from the course calculation unit 6, the propulsion and steering mechanism 7 operates the rudder so that the direction of navigation of the underwater unmanned vehicle B is towards the acoustic marker A. In other words, the direction of navigation of the underwater unmanned vehicle B is set based on the course signal input from the course calculation unit 6.

[0057] Next, the operation of the mobile guidance device (acoustic sign A) and the mobile guidance system according to the first embodiment will be described in detail.

[0058] As the underwater drone B navigates underwater, it receives received waves based on the first and second transmitted waves Sa and Sb emitted from the acoustic marker A using a course detection means. The course detection means then acquires a course toward the acoustic marker A (target position) based on the received waves, and the propulsion and steering mechanism 7 is controlled based on the course, causing the underwater drone B to navigate toward the acoustic marker A (target position).

[0059] Here, the underwater drone B, while navigating underwater, has a relative velocity with respect to the acoustic marker A. Therefore, the first main signal in the first frequency band fa(t) and the second main signal in the second frequency band fb(t) of the first and second transmitted waves Sb are frequency-shifted due to the Doppler effect, and the frequency-shifted received waves are received by the underwater drone B.

[0060] If fa0 is the first frequency band of the first transmitted wave Sa, fad is the first frequency band of the first main signal of the received wave related to the direct wave D, Vb is the relative velocity, and Vs is the speed of sound in water, then the following equations (1) and (2) hold. Note that the relative velocity Vb is considered positive when the underwater unmanned vehicle B approaches the acoustic marker A. fad = fa0·(Vs+Vb) / Vs (1) fbd = (fa0 + Δf)(Vs + Vb) / Vs (2)

[0061] Here, regarding the frequency difference Δfd between the first frequency band fad and the second frequency band fbd, the following equation (3) holds based on equations (1) and (2) above. That is, the frequency difference Δfd is the frequency with the Doppler shift caused by the relative velocity Vb between acoustic marker A and underwater drone B added.

[0062] Δfd = fbd - fad =(fa0+Δf)(Vs+Vb) / Vs-fa0(Vs+Vb / Vs =Δf(Vs+Vb) / Vs (3)

[0063] Here, if we denote the Doppler frequency as fd, this Doppler frequency fd can be expressed as the difference between the frequency difference Δfd and the frequency difference Δf, as shown in equation (4) below. fd = Δfd - Δf (4) Then, the relative velocity Vb of the underwater unmanned vehicle B (moving object) with respect to the acoustic marker A (fixed object) is given by equation (5) below, which is obtained by rearranging equation (3) above. Vb = Vs(Δfd / Δf-1) (5)

[0064] Furthermore, if there is an error in the synchronization time of the reference signal multiplied by the received signal in mixer 10 with respect to the received signal, an error will occur in the first frequency band fa0, and this error will be superimposed on the first frequency band fad and the second frequency band fbd. However, since the errors are canceled out in the frequency difference Δf, it does not affect the calculation of the frequency difference Δfd.

[0065] In equation (5) above, since the frequency difference Δf and the speed of sound Vs are constants (fixed values), it can be seen that the relative velocity Vb is proportional to the Doppler frequency Δfd. That is, when the underwater drone B (mobile object) is traveling at a predetermined speed, the Doppler frequency fd is largest when the course of the underwater drone B (mobile object) is set toward the acoustic marker A (target position).

[0066] In other words, the Doppler frequency fd is a course signal (course signal) for the underwater unmanned vehicle B (mobile body) navigating underwater with acoustic marker A as its target position. The underwater unmanned vehicle B (mobile body) navigates towards acoustic marker A (target position) by controlling its propulsion and steering mechanism 7 based on the course signal.

[0067] The acoustic marker A according to the first embodiment is a mobile guidance device that guides a predetermined underwater unmanned vehicle B (guided object, mobile body) to an acoustic marker A (target position), and includes a medium radiating means that radiates a first transmitting wave Sa whose frequency changes in a first frequency band fa(t) and a second transmitting wave Sb whose frequency changes in a second frequency band fb(t) different from the first frequency band fa(t) into the surroundings.

[0068] According to this first embodiment, since the medium radiating means radiates a first transmission wave Sa and a second transmission wave Sb toward the underwater unmanned vehicle B (target to be guided), it is possible to provide an acoustic marker A (mobile vehicle guidance device) that can accurately guide the underwater unmanned vehicle B (mobile vehicle) without using an inertial navigation device.

[0069] Furthermore, in the acoustic marker A according to the first embodiment, the first transmitting wave Sa is provided with a first main signal whose frequency changes linearly in the first frequency band fa(t), and the second transmitting wave Sb is provided with a second main signal whose frequency changes linearly in the second frequency band fb(t). According to the first embodiment, since the first transmitting wave Sa and the second transmitting wave Sb are radiated toward the underwater unmanned vehicle B (target to be guided), it is possible to guide the underwater unmanned vehicle B (moving object) more accurately.

[0070] Furthermore, in the acoustic marker A according to the first embodiment, the first transmitting wave Sa includes a first synchronization signal in addition to the first main signal, and the second transmitting wave Sb includes a second synchronization signal at the same timing as the first synchronization signal in addition to the second main signal. According to this first embodiment, it is possible to improve the synchronous detection accuracy of the first and second main signals in the underwater unmanned vehicle B (target of guidance). Therefore, according to the first embodiment, it is possible to guide the underwater unmanned vehicle B (moving object) more accurately.

[0071] Furthermore, in the acoustic marker A according to the first embodiment, the medium radiating means includes a pair of transmitting transducers 1a and 1b that individually radiate a first transmitting wave Sa and a second transmitting wave Sb. According to this first embodiment, since the first transmitting wave Sa and the second transmitting wave Sb are radiated toward the underwater unmanned vehicle B (target to be guided) by the individual transmitting transducers 1a and 1b, it is easy to ensure uniformity of the radiation intensity of the first transmitting wave Sa and the second transmitting wave Sb. Therefore, according to the first embodiment, it is possible to guide the underwater unmanned vehicle B (mobile object) more accurately.

[0072] Furthermore, in the acoustic marker A according to the first embodiment, the acoustic marker A (medium radiating means) and the acoustic marker A (guided target) are provided underwater, and the first transmitted wave Sa and the second transmitted wave Sb are ultrasonic waves. According to this first embodiment, it is possible to accurately guide the underwater unmanned vehicle B (mobile object) without using an inertial navigation system.

[0073] Furthermore, the mobile guidance system according to the first embodiment comprises an acoustic marker A (mobile guidance device) according to the first embodiment and an underwater unmanned vehicle B (target of guidance), and the underwater unmanned vehicle B (target of guidance) comprises a receiving transducer 4, a signal processing unit 5, and a heading calculation unit 6 (heading detection means) that detect a heading toward the acoustic marker A (target position) based on the received signals of the first transmitted wave Sa and the second transmitted wave Sb.

[0074] According to this first embodiment, since the acoustic marker A (mobile guidance device) radiates a first transmission wave Sa and a second transmission wave Sb toward the underwater unmanned vehicle B (target of guidance), it is possible to provide a mobile guidance system that can accurately guide the underwater unmanned vehicle B (mobile object) without using an inertial navigation system.

[0075] Furthermore, in the mobile guidance system according to the first embodiment, the heading detection means of the acoustic marker A detects the heading based on the frequency difference Δfd between the first Doppler frequency related to the first transmitted wave Sa and the second Doppler frequency related to the second transmitted wave Sb. According to this first embodiment, it is possible to accurately guide the underwater unmanned vehicle B (mobile body).

[0076] [Second Embodiment] Next, a second embodiment of the present invention will be described. The mobile guidance device and mobile guidance system according to the second embodiment have the same configuration as the mobile guidance device and mobile guidance system according to the first embodiment, but the arrangement of the pair of transmitting transducers 1a and 1b is different. In addition, the mobile guidance device and mobile guidance system according to the second embodiment include a third transmitting transducer 1c in addition to the pair of transmitting transducers 1a and 1b.

[0077] In the first embodiment, a pair of transmitting transducers 1a and 1b were placed in close proximity, but in the second embodiment, the pair of transmitting transducers 1a and 1b are deliberately placed further apart than in the first embodiment. Figure 7 is a schematic diagram showing the arrangement of the pair of transmitting transducers 1a and 1b and their positional relationship with the receiving transducer 4 in the second embodiment.

[0078] In the acoustic marker A (mobile guidance device) according to the second embodiment, as shown in the figure, a pair of transmitting transducers 1a and 1b are arranged horizontally on the same plane as the receiving transducer 4. In addition, in the acoustic marker A according to the second embodiment, the pair of transmitting transducers 1a and 1b are arranged to ensure a separation distance Sd.

[0079] In Figure 7, if we let dg be the amount of lateral displacement of the receiving transducer 4 from the line C-C' which is perpendicular to the line at point C in the center of the line connecting the pair of transmitting transducers 1a and 1b, and let R be the distance between point C and point C', then the following equations (6) and (7) hold true for the first distance d1 from one transmitting transducer 1a to the receiving transducer 4 and the second distance d2 from the other transmitting transducer 1b to the receiving transducer 4.

[0080] d1={(dg-Sd / 2) 2 +R 2} 1 / 2 (6) d2 = {(dg + Sd / 2)} 2 +R 2}1 / 2 (7) Here, on line C-C’, when dg = 0, the direction of one transmitting transducer 1a is +dg and the direction of the other transmitting transducer 1b is -dg, then at dg = 0, d1 = d2, when dg is positive, d1 < d2, and when dg is negative, d1 > d2.

[0081] FIG. 8 shows the frequency changes of the first and second transmission waves Sb radiated from the pair of transmitting transducers 1a and 1b in the second embodiment and the frequency change of the received wave received by the transmitting transducer 1b. In this FIG. 8, the first and second multipath waves are omitted. In the received wave of the receiving transducer 4, the direct wave Da related to the first transmission wave Sa and the direct wave Db related to the second transmission wave Sb have a time difference of Δtsd from the difference between the first distance d1 and the second distance d2.

[0082] FIG. 9 shows the frequency changes of the reference signal and the main signal detection signal in the signal processing unit 5 in the second embodiment. In this FIG. 9, similar to FIG. 8, the first and second multipath waves are omitted. In the main signal detection signal, similar to the first embodiment, the direct wave Da related to the first main signal in the first frequency band fa(t) and the direct wave Db related to the second main signal in the second frequency band fb(t) have a constant frequency, and the frequency difference is Δfsd.

[0083] At dg = 0, Δfsd = Δf, when the deviation amount dg is positive, Δfsd < Δf, and when the deviation amount dg is negative, Δfsd > Δf. From this, it is possible to detect the positive or negative of the deviation amount dg, that is, the left - right deviation of the receiving transducer 4, according to the magnitudes of the frequency difference Δfsd and the frequency difference Δf. Note that the frequency deviation Δfm and the period tm are set so that the frequency shift due to the Doppler effect and the frequency difference Δfsd are different frequencies.

[0084] According to this second embodiment, it is possible to achieve the same effects as the first embodiment. That is, according to the second embodiment, it is possible to provide an acoustic marker A (mobile body guidance device) and a mobile body guidance system that can accurately guide an underwater unmanned vehicle B (mobile body) without using an inertial navigation device.

[0085] Although the case described above involves a pair of transmitting transducers 1a and 1b and a receiving transducer 4 located on the same horizontal plane, it is also possible to consider placing the transmitting transducer 1c at a position vertically separated from the ultrasonic transducer 1a, that is, outside the same horizontal plane where the pair of transmitting transducers 1a and 1b are located, and radiating a transmission wave (ultrasound) with a constant frequency difference Δf' relative to the first frequency band fa(t) by changing its frequency.

[0086] In this case, the transmission time Δfm of the transmitted wave (ultrasound) radiated from the transmitting transducer 1c is the same as that of the pair of transmitting transducers 1a and 1b. The transmitted wave (ultrasound) radiated by the transmitting transducer 1c is received by the receiving transducer 4, and the amount of vertical deviation is detected by comparing the received wave with the transmission time Δfm of the direct wave for one of the transmitting transducers 1a.

[0087] By this method, the underwater drone B can detect the left-right and up-down directions, i.e., the heading, of the acoustic marker A as seen from itself, by radiating first to third transmission waves into the water from three spaced-apart transmitting transducers 1a to 1c.

[0088] In other words, according to the second embodiment, since it is equipped with three transmitting transducers 1a to 1c that individually radiate the first to third transmitting waves, it is possible to accurately guide the underwater unmanned vehicle B (mobile object) without using an inertial navigation system.

[0089] [Third Embodiment] Next, a third embodiment of the present invention will be described with reference to Figure 10. The mobile body guidance device and the mobile body guidance system according to the third embodiment are different from those of the first and second embodiments in the number and arrangement of a plurality of transmission transducers.

[0090] FIG. 10(a) shows the arrangement of four transmission transducers 12a to 12d in the mobile body guidance device according to the third embodiment. That is, the mobile body guidance device according to the third embodiment includes four transmission transducers 12a to 12d as a plurality of transmission transducers.

[0091] The four transmission transducers 12a to 12d are not in the same plane but are arranged at four different coordinates (Xa, Ya, Za), (Xb, Yb, Zb), (Xc, Yc, Zc), and (Xd, Yd, Zd) in the X-Y-Z orthogonal coordinate system (three-dimensional space).

[0092] That is, the first transmission transducer 12a is arranged at the first coordinate (Xa, Ya, Za), and the second transmission transducer 12b is arranged at the second coordinate (Xb, Yb, Zb). Also, the third transmission transducer 12c is arranged at the third coordinate (Xc, Yc, Zc), and the fourth transmission transducer 12d is arranged at the fourth coordinate (Xd, Yd, Zd).

[0093] Also, when the coordinates of the reception transducer 4 are taken as the fifth coordinate (Xt, Yt, Zt), the respective distances d1 to d4 between the four transmission transducers 12a to 12d and the reception transducer 4 can be expressed by the following equations (8) to (11).

[0094] d1 = { (Xt - Xa) 2 + (Yt - Ya) 2 + (Zt - Za) 2 )} 1 / 2 (8) d2 = { (Xt - Xb) 2 + (Yt - Yb) 2 + (Zt - Zb) 2 )} 1 / 2 (9) d3 = { (Xt - Xc) 2 + (Yt - Yc)2 +(Zt-Zc) 2 )} 1 / 2 (10) d4 = {(Xt - Xd)} 2 +(Yt-Yd) 2 +(Zt-Zd) 2 )} 1 / 2 (11)

[0095] Here, the frequency change of the main signal detection signal obtained by multiplying the received signals of the receiving transducer 4 with the transmitted waves (ultrasound) of the first and second transmitting transducers 12a and 12b by the reference signal in the signal processing unit 5 will be explained using Figures 8 and 9.

[0096] The difference between the frequency difference Δfsd and the distances d1 and d2 can be expressed by the following equation (12), where Vs (m / s) is the speed of sound in water. d1-d2=Vs·Δfsd / (Δf / tm) (12) Similarly, the difference between distance d1 and distance d3, and the difference between distance d1 and distance d4, can also be calculated from the respective frequency difference Δfsd, frequency difference Δf, and speed of sound Vs based on equation (12). That is, by solving the simultaneous equations (8) to (12), the fifth coordinate (Xt, Yt, Zt) of the receiving transducer 4 can be determined.

[0097] Figure 10(b) is a schematic diagram showing the relationship between the course and speed of an underwater drone B moving toward acoustic marker A. In Figure 10(b), it is assumed that the underwater drone B and acoustic marker A are on the same plane, there is no water current in the water, and the ground speed of the underwater drone B |Vg(→)| is constant.

[0098] When the heading of the underwater drone B and the azimuth angle (heading) of the acoustic marker A as seen from the underwater drone B are different, the relative velocity Vb (=|Vb(→)|) between the underwater drone B and the acoustic marker A is smaller than the ground velocity |Vg(→)|. In the first embodiment, the Doppler frequency fd generated due to the relative velocity Vb is expressed by equation (4) described above.

[0099] Figure 11 is a schematic diagram showing the relationship between the Doppler frequency fd and the course of the underwater drone B. Since the relationship between the Doppler frequency fd and the relative velocity Vb is given by equation (4) above, if the underwater drone B, which is traveling along course 1, maintains course 1, the relative velocity Vb will decrease until it passes the side of the acoustic marker A, and therefore the Doppler frequency fd will also decrease over time.

[0100] In contrast, on course 2 heading towards acoustic marker A, the relative velocity Vb is always constant and at its maximum. That is, by taking course 2, where the Doppler frequency fd is maximized, the underwater drone B can reliably navigate towards acoustic marker A.

[0101] Furthermore, if there is a water current underwater, the ground speed Vg(→) of the underwater drone B will be affected by the water current and will change depending on the course. However, the relative speed Vb will be maximum at the course where the Doppler frequency fd is maximum, and the underwater drone B can navigate towards the acoustic marker A.

[0102] In other words, the course calculation unit 6 controls the propulsion and steering mechanism 7 so that the Doppler frequency fd input from the signal processing unit 5 is maximized. Although Figure 11 was explained assuming that the underwater drone B and the acoustic marker A are on the same plane, by setting a course that maximizes the Doppler frequency fd even in the three-dimensional space underwater, the underwater drone B can reliably navigate towards the acoustic marker A (target position).

[0103] In the first and second embodiments, although the underwater drone B navigates toward the acoustic marker A (target position), it is unable to detect the distance to the acoustic marker A. Therefore, the approach distance of the underwater drone B to the acoustic marker A must be detected using the third embodiment or other distance detection means such as a separately provided sensor.

[0104] After approaching the acoustic marker A (target position) to a required distance, the underwater unmanned vehicle B operates the propulsion and steering mechanism 7 based on the Doppler frequency fd calculated by the signal processing unit 5 in order to ensure it navigates toward the acoustic marker A. For example, in the third embodiment, the underwater unmanned vehicle B can calculate the three-dimensional coordinates relative to the acoustic marker A using the course calculation unit 6, and based on this calculation result, it can approach the acoustic marker A (target position) even further.

[0105] According to this third embodiment, since four transmitting transducers 12a to 12d are arranged at four different coordinates (Xa, Ya, Za), (Xb, Yb, Zb), (Xc, Yc, Zc), and (Xd, Yd, Zd) in the XYZ Cartesian coordinate system (three-dimensional space), it is possible to provide an acoustic marker A (mobile vehicle guidance device) and a mobile vehicle guidance system that can accurately guide an underwater unmanned vehicle B (mobile vehicle) without using an inertial navigation device.

[0106] The present invention is not limited to the embodiments described above, and for example, the following modifications are possible. (1) In the above embodiment, guidance to the underwater unmanned vehicle B (target to be guided) in water was made possible by using ultrasound as the first transmission wave Sa and the second transmission wave Sb, but the present invention is not limited thereto. For example, the target to be guided may be guided to the target position by using light or radio waves instead of ultrasound as the first transmission wave Sa and the second transmission wave Sb.

[0107] Furthermore, since light and radio waves have poor propagation properties in water, when using light or radio waves as the first and second transmission waves Sa and Sb, it is preferable to guide the target in open air rather than in water. For example, in the atmosphere or exposed space, light and radio waves have good propagation properties, making it possible to guide the target effectively.

[0108] (2) In the above embodiment, a pair of transmitting transducers 1a and 1b are provided in the acoustic marker A, but the present invention is not limited thereto. That is, the number of transmitting transducers in the acoustic marker A is not limited to two.

[0109] For example, the first and second transmission waves Sb may be generated by using an oscillator circuit that generates a mixed signal by mixing the first and second oscillation signals generated by a pair of oscillator circuits 2a and 2b, and outputs a signal by superimposing the mixed signal onto a signal output from one of the oscillator circuits, and inputting this signal to a single transmitting transducer.

[0110] (3) In the above embodiment, the acoustic marker A was set at the target position, but the present invention is not limited thereto. For example, the target position may be a position displaced by a predetermined distance from the acoustic marker A that radiates the first transmission wave Sa and the second transmission wave Sb toward the guidance target. [Explanation of Symbols]

[0111] A, A1 sound sign B Underwater drone 1, 1a, 1b Transmitting transducers 2a, 2b Oscillator Circuit 3. Frequency Control Unit 4. Receiving transducer 5. Signal Processing Unit 6. Course Calculation Unit 7. Propulsion and Steering Mechanism 8. Synchronization signal detection processing unit 9. Reference signal generation processing unit 10 Mixer 11 FFT Processing Unit

Claims

1. A mobile object guidance device that guides a predetermined target object to a target position, A mobile guidance device characterized by comprising a media radiating means that radiates a first transmission wave whose frequency changes in a first frequency band and a second transmission wave whose frequency changes in a second frequency band different from the first frequency band into the surrounding environment.

2. The first transmission wave comprises a first main signal whose frequency changes linearly in the first frequency band, The mobile guidance device according to claim 1, characterized in that the second transmitting wave comprises a second main signal whose frequency changes linearly in the second frequency band.

3. The first transmission wave includes a first synchronization signal in addition to the first main signal. The mobile guidance device according to claim 2, characterized in that the second transmission wave includes a second synchronization signal that is at the same timing as the first synchronization signal, in addition to the second main signal.

4. The mobile guidance device according to claim 1 or 2, characterized in that the media radiating means comprises a plurality of transmitting transducers that individually radiate the first transmitting wave and the second transmitting wave.

5. The mobile guidance device according to claim 4, further comprising a pair of transmitting transducers arranged on the same plane and separated by a predetermined distance.

6. The mobile guidance device according to claim 5, further comprising a third transmitting transducer located outside the same plane, in addition to the pair of transmitting transducers.

7. The mobile guidance device according to claim 4, further comprising four transmitting transducers, each positioned at four different coordinates in three-dimensional space.

8. The media emitting means and the target of induction are provided in water. The mobile guidance device according to claim 1 or 2, characterized in that the first and second transmitted waves are ultrasonic waves.

9. A mobile guidance device according to claim 1 or 2, The system comprises the aforementioned induction target, The mobile guidance system is characterized in that the guided object includes a heading detection means for detecting a heading toward the target position based on the received signals of the first and second transmitted waves.

10. The mobile guidance system according to claim 9, characterized in that the heading detection means detects the heading based on the frequency difference between the first detection signal frequency for the first transmission wave and the second detection signal frequency for the second transmission wave.

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