Rotary-wing aircraft

Abstract

It is small and lightweight, and can detect flying objects regardless of field of view. [Solution] A rotary-wing aircraft equipped with a propeller that rotates to generate thrust, comprising a microphone for acquiring ambient mixed sound, and a control unit, wherein the control unit performs modulation frequency analysis on the acquired mixed sound to calculate the mixed sound analysis result, acquires vibration information of the rotary-wing aircraft or control signals of the propeller, estimates the self-modulation frequency which is the modulation frequency corresponding to the operating sound of the rotary-wing aircraft based on the vibration information of the rotary-wing aircraft or the control signals of the propeller, and removes the self-modulation frequency component from the mixed sound analysis result.

Description

[Technical Field]

[0001] This disclosure relates to rotary-wing aircraft. [Background technology]

[0002] In recent years, the use of unmanned aerial vehicles, including drones, has been attracting attention due to factors such as the declining workforce. Drones generally fly at low altitudes to avoid collisions with passenger planes and other aircraft, but commercial helicopters, including air ambulances, also fly at low altitudes for about half of their total flight time. In other words, drones and commercial helicopters sometimes fly in the same airspace, which carries the risk of collision. Drones are difficult for helicopter pilots to see, and drones are more maneuverable, so it is necessary for the drone to detect aircraft like helicopters and avoid collisions.

[0003] For example, Patent Document 1 discloses a system that uses the position information of an aircraft to issue a warning when the aircraft approaches another aircraft. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-147583 [Overview of the project] [Problems that the invention aims to solve]

[0005] Methods like the one described in Patent Document 1 may not function correctly if there is an error in the acquired position information for any reason. Furthermore, with aircraft detection methods using only cameras, it is difficult for the camera to accurately grasp the surrounding situation when flying in poor visibility conditions such as at night or in bad weather. While aircraft detection methods using radar can detect the position of aircraft even in poor visibility conditions, the sensors become larger and heavier, and consequently the batteries also become larger and heavier, making it difficult to mount them on small drones and negatively impacting the drone's continuous flight time.

[0006] The purpose of this disclosure is to provide a rotary-wing aircraft that is small, lightweight, and capable of accurately detecting flying objects regardless of the field of view. [Means for solving the problem]

[0007] A rotary-wing aircraft as a first aspect of this disclosure is (1) It is a rotary-wing aircraft equipped with a propeller that rotates to generate thrust. A microphone that captures ambient sounds, and Control unit and Equipped with, The control unit, Modulation frequency analysis is performed on the acquired mixed sound to calculate the mixed sound analysis results. The vibration information of the rotor blade or the control signal of the propeller is acquired. Based on the vibration information of the rotorcraft or the control signal of the propeller, the self-modulation frequency, which is the modulation frequency corresponding to the operating sound of the rotorcraft, is estimated. This is a rotary-wing aircraft that removes the component of the aircraft's own modulation frequency from the mixed sound analysis results.

[0008] A rotary-wing aircraft as one embodiment of the present disclosure is (2) The operating sound of the rotorcraft is the operating sound of the propeller. The rotary-wing aircraft described in (1) above.

[0009] A rotary wing aircraft according to one embodiment of the present disclosure is (3) further comprising a vibrometer that measures vibration of the propeller, wherein the control unit estimates the self-modulation frequency based on the vibration measured by the vibrometer, which is the rotary wing aircraft according to (1) above.

[0010] A rotary wing aircraft according to one embodiment of the present disclosure is (4) wherein the control unit estimates rotation speed information of the propeller based on a control signal for the propeller, which is the rotary wing aircraft according to (2) above.

[0011] A rotary wing aircraft according to one embodiment of the present disclosure is (5) wherein the control unit determines whether the mixed sound includes an operation sound from another aircraft based on a mixed sound analysis result from which a component of the self-modulation frequency has been removed, which is the rotary wing aircraft according to any one of (1) to (4) above.

[0012] A rotary wing aircraft according to one embodiment of the present disclosure is (6) wherein the self-modulation frequency is a modulation frequency corresponding to a primary component or a harmonic component of vibration of the rotary wing aircraft, which is the rotary wing aircraft according to any one of (1) to (5) above.

[0013] A rotary wing aircraft according to one embodiment of the present disclosure is (7) wherein the self-modulation frequency is a value obtained by multiplying a modulation frequency corresponding to a primary component or a harmonic component of vibration of the rotary wing aircraft by the number of blades of the propeller, which is the rotary wing aircraft according to any one of (1) to (6) above.

[0014] A rotary wing aircraft according to one embodiment of the present disclosure is (8) One or more microphones are attached, It is a rotary-wing aircraft as described in any one of the above (1) to (7).

[0015] A rotary-wing aircraft as one embodiment of the present disclosure is (9) The one or more microphones constitute a microphone array, and the microphone array is mounted on, It is a rotary-wing aircraft as described in any one of the above (1) to (8). [Effects of the Invention]

[0016] The rotary-wing aircraft described herein is small and lightweight, and can accurately detect flying objects regardless of the field of view. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing an example of how a rotary-wing aircraft is used according to one embodiment of the present disclosure. [Figure 2] Figure 1 is a block diagram showing the configuration of a rotary-wing aircraft. [Figure 3] This graph shows the results of a modulation frequency analysis performed on the propeller vibration. [Figure 4] This graph shows the results of the mixed sound analysis calculated by the control unit of a rotary-wing aircraft. [Figure 5] This graph shows the results of removing the component of the instrument's own modulation frequency from the mixed sound analysis results. [Figure 6] This flowchart shows an example of the operation of a rotary-wing aircraft according to one embodiment of the present disclosure. [Figure 7] This graph shows the results of a modulation frequency analysis performed on the propeller vibration. [Figure 8] This graph shows the results of the mixed sound analysis calculated by the control unit of a rotary-wing aircraft. [Figure 9] This graph shows the results of removing the component of the instrument's own modulation frequency from the mixed sound analysis results. [Modes for carrying out the invention]

[0018] The embodiments of this disclosure will be described below with reference to the drawings.

[0019] Figure 1 is a schematic diagram showing an example of how a rotary-wing aircraft 1 according to one embodiment of the present disclosure is used. Figure 2 is a block diagram showing the configuration of an aircraft detection device 5 provided by the rotary-wing aircraft 1.

[0020] A rotary-wing aircraft 1 is an aircraft that flies by obtaining thrust from a propeller 2 that rotates around a rotation axis A. Rotary-wing aircraft 1 includes unmanned aerial vehicles (UAVs), such as drones, and helicopters.

[0021] The rotary-wing aircraft 1 is equipped with one or more microphones 3, a vibrometer 4, and an aircraft detection device 5.

[0022] Microphone 3 acquires mixed sound, which is the sound around the rotorcraft 1, and creates sound data. Microphone 3 outputs the created sound data to the control unit 11 (see Figure 2) of the aircraft detection device 5. Referring to Figure 1, one or more microphones 3 may be attached to the rotorcraft 1. For example, microphone 3 may be mounted on the aircraft detection device 5. Mixed sound includes the operating sounds of the rotorcraft 1, the operating sounds of other aircraft 100, etc. Other aircraft 100 include helicopters, drones and other unmanned aerial vehicles.

[0023] Microphone 3 is a condenser microphone or the like. Microphone 3 may also be a microphone array composed of two or more microphones. The microphone array may be assembled from two or more microphones. The microphone array may have a structure in which two or more microphones are installed at equal intervals in a straight line. In the microphone array, the distance between adjacent microphones is, for example, 5 cm. The microphone array may be attached to the rotorcraft 1. The microphone array may be separate from the rotorcraft 1.

[0024] The vibration meter 4 measures vibrations caused by the rotation of the propeller 2 and generates vibration information. The vibration meter 4 outputs the generated vibration information to the control unit 11 of the aircraft detection device 5. The vibration meter 4 is, for example, an accelerometer. Referring to Figure 1, the vibration meter 4 may be installed on the mounting part of the propeller 2. The vibration meter 4 may, for example, measure vibrations in a direction perpendicular to the rotation axis A of the propeller 2 (generally the horizontal direction).

[0025] The vibration meter 4 is not necessarily required for the rotorcraft 1. For example, the control unit 11 may acquire the control signal of the propeller 2 and estimate the rotational speed information of the rotorcraft 1 based on the control signal. The control signal may be, for example, the applied voltage to the motor that drives the propeller 2, the drive signal given to the controller of the motor, the tachometer pulse generated by the motor driver, or the signal emitted from the resolver. The control unit 11 may further estimate the vibration of the propeller based on the estimated rotational speed information of the propeller 2.

[0026] The aircraft detection device 5 can detect aircraft 100 other than the rotary-wing aircraft 1 on which the aircraft detection device 5 is installed. The other aircraft 100 is, for example, a helicopter.

[0027] The aircraft detection device 5 comprises a control unit 11 and a memory unit 12. Referring to Figure 1, the aircraft detection device 5 may be installed on the upper part of the main body of the rotary-wing aircraft 1.

[0028] The control unit 11 performs various processes related to the operation of the aircraft detection device 5 and controls each part of the aircraft detection device 5. The control unit 11 includes at least one processor, at least one dedicated circuit, or a combination thereof. The processor is a general-purpose processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), or a dedicated processor specialized for a specific process. The control unit 11 may realize its control function by executing a program stored in the memory unit 12.

[0029] The storage unit 12 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or a combination thereof. The storage unit 12 functions, for example, as a main memory, an auxiliary memory, or a cache memory. The storage unit 12 stores, for example, programs and data used for the operation of the aircraft detection device 5, and data obtained by the operation of the aircraft detection device 5.

[0030] Next, we will explain the operation of the rotary-wing aircraft 1.

[0031] Microphone 3 collects mixed sound, which is the ambient noise around the rotorcraft 1 equipped with the aircraft detection device 5. Vibration meter 4 measures the vibration of the rotorcraft 1 and creates vibration information. In this embodiment, vibration meter 4 measures the vibration of the four propellers 2 as the vibration of the rotorcraft 1. The collection of mixed sound and the measurement of the propeller 2 vibrations are performed, for example, while the rotorcraft 1 is hovering.

[0032] Here, the operating sound of a rotary-wing aircraft propeller is generally called "blade slap noise." Blade slap noise is an amplitude-modulated sound generated when a subsequent blade strikes air compressed by the rotation of a blade. The technology disclosed here focuses particularly on the modulation frequency characteristics of this amplitude-modulated sound. Modulation frequency characteristics have advantages such as being less susceptible to noise from ambient sounds and being less affected by distance attenuation than carrier frequency characteristics.

[0033] The sound pressure P(t) of the blade slap is given by the following prediction equation (1) (see Liang Yu et al., Passive sound detection of the helicopter in the far-field with a spectral coherence decomposition method, Mechanical Systems and Signal Processing, Vol.185, 2023). The first term of equation (1) is the sound due to shaft rotation, the second term is the sound due to blade rotation, and the third term is broadband noise with amplitude modulation. Here, fSRF This indicates the shaft rotation frequency (SRF), and f BPF indicates the blade rotation frequency (BPF) (BPF = SPF × number of blades), i indicates the number of rotational order components, and A i This indicates the amplitude of SRF, and B i This indicates the amplitude of the BPF.

number

[0034] The third term of equation (1) In TIFF2026144787000003.tif14146, the modulation frequency is f SRF and f BPF This is the part. f BPF is f SRF Since it is a multiple of , the first-order vibration of the rotational speed (the value not multiplied by the number of blades, the first-order component of the vibration) may be treated as the self-modulation frequency.

[0035] (Modulation frequency analysis for mixed noise and rotorcraft vibrations) The following describes the modulation frequency analysis for mixed noise and rotorcraft vibrations. Alternatively, instead of rotorcraft vibrations, propeller rotation speed information obtained from control signals of propeller 2, such as the voltage sent to the motor, can be used. For example, rotation speed can be calculated by dividing the number of pulses per second sent from the controller to the motor by the number of pulses per revolution, depending on the type of motor used. The aircraft's modulation frequency can be estimated from the rotation speed information. Specifically, the aircraft's modulation frequency can be calculated by multiplying the rotation speed by the number of blades on propeller 2.

[0036] FIG. 3 is a graph showing the result of performing modulation frequency analysis on the vibrations of four propellers 2. Propeller vibrations 1 to 4 respectively indicate the vibrations of the front right, front left, rear right and rear left propellers 2. FIG. 4 is a graph showing the mixed sound analysis result calculated by the control unit 11 of the rotorcraft 1. Hereinafter, an example of a method in which the control unit 11 calculates the magnitude of amplitude modulation at each modulation frequency for the vibration and mixed sound of the rotorcraft 1 as shown in FIGS. 3 and 4, and generates the mixed sound analysis result will be described. Although a method using calculation of spectral correlation density is described here, the analysis method is not limited thereto. Spectral correlation density S for modulation frequency a and frequency f x is calculated by double Fourier transform of the autocorrelation function. The control unit 11 Fourier-transforms the autocorrelation coefficient with respect to time t according to the following formula (2). In the following formula (1), x * represents the complex conjugate of a signal.

Math

[0037] Subsequently, the control unit 11 further Fourier-transforms the periodic autocorrelation coefficient Rx(a,τ) calculated by Fourier transform of the autocorrelation coefficient with respect to τ according to the following formula (3).

Math

[0038] The spectral correlation density Sx(a,f) calculated by double Fourier transform of the autocorrelation coefficient is averaged in the frequency f direction, and converted into a function of only the modulation frequency a. In the following formula (4), X is a signal vector, N is an overlap size, W is a window size, f max represents the maximum frequency.

Math

[0039] The control unit 11 estimates the operating sounds of other aircraft 100 based on the modulation frequency analysis results of the vibration of the propeller 2 and the mixed sound. The inventors conducted thorough research and found that the value obtained by multiplying the modulation frequency corresponding to the first-order component of the vibration of the four propellers 2 (circled in Figure 3) by the number of blades on the propeller 2 (two in this embodiment) is included in the modulation frequency at the peak position of the first-order component of the mixed sound (circled in Figure 4). In Figure 3, the values ​​obtained by multiplying the modulation frequency corresponding to the first-order component of the vibration of the four propellers 2 by the number of blades on the propeller 2 (2) were 220Hz, 234Hz, 191Hz, and 203Hz for the front right, front left, rear right, and rear left propellers, respectively. The modulation frequencies at the peak position of the first-order component of the mixed sound were also 220Hz, 234Hz, 191Hz, and 203Hz. Therefore, the value obtained by multiplying the modulation frequency corresponding to the first-order component of the vibration of the four propellers by the number of blades of propeller 2 is considered to be the modulation frequency (self-modulation frequency) corresponding to the operating sound of the rotary-wing aircraft 1.

[0040] Next, the control unit 11 removes the component of the aircraft's modulation frequency from the mixed sound analysis results as shown in Figure 4. The control unit 11 may also remove components within a predetermined range from the aircraft's modulation frequency from the mixed sound analysis results. In the example shown here, as shown in Figure 5, components of frequencies corresponding to the harmonic components of the aircraft's modulation frequency are also removed. More specifically, the control unit 11 removes from the mixed sound analysis results the value obtained by multiplying the first harmonic component of the vibration of the four propellers by 2, which is the number of blades of propeller 2 (shown as a dotted line in Figure 4), and the value obtained by multiplying its second harmonic component by 2, which is the number of blades of propeller 2 (shown as a dashed line in Figure 4). The control unit 11 may also remove from the mixed sound analysis results the value obtained by multiplying other harmonic components, such as the third harmonic component, by 2, which is the number of blades of propeller 2.

[0041] Furthermore, the rotary-wing aircraft 1 disclosed herein can detect other aircraft 100 even if the rotary-wing aircraft 1 and other aircraft 100 are of the same type and under the same flight conditions. Even when the rotary-wing aircraft 1 and other aircraft 100 are of the same type and under the same flight conditions, they do not always maintain the same propeller rotation speed while flying; rather, the propeller rotation speed fluctuates somewhat during flight. As a result, by performing modulation frequency analysis sequentially (for example, every 3 seconds), the estimated modulation frequency of the aircraft itself will differ somewhat from the modulation frequency corresponding to the operating sound of the other aircraft 100. Therefore, the rotary-wing aircraft 1 is capable of detecting other aircraft 100 of the same type and under similar flight conditions.

[0042] The following describes an example of the control process for the rotary-wing aircraft 1 according to this embodiment, which has the above configuration, with reference to Figure 6. Figure 6 is a flowchart illustrating the process.

[0043] The control unit 11 acquires sound data based on the mixed sound collected by the microphone 3 (step S101). The control unit 11 performs modulation frequency analysis on the sound data and creates a mixed sound analysis result (step S102). The control unit 11 acquires vibration information of the rotor blade machine 1 (e.g., the propeller 2) or control signals of the propeller 2, for example, measured by the vibrometer 4 (step S103). Based on the vibration information of the rotor blade machine 1, the control unit 11 estimates the self-modulation frequency, which is the modulation frequency corresponding to the operating sound of the rotor blade machine 1 (e.g., the propeller 2) (step S104). The control unit 11 removes the self-modulation frequency component from the mixed sound analysis result (step S105).

[0044] Steps S101 and S102 may be performed during or after steps S103 and S104.

[0045] After step S105, the control unit 11 may determine whether the mixed sound contains the operating sounds of other aircraft 100, based on the results of the mixed sound analysis, which are the results of removing the aircraft's operating sounds, after removing the component of the aircraft's own modulation frequency.

[0046] (First embodiment) The experimental results of the first embodiment of the aircraft detection method for the rotary-wing aircraft 1 according to this embodiment will be described. In the first embodiment, the other aircraft 100 is a different aircraft from the rotary-wing aircraft 1.

[0047] The detection process for aircraft 100 was carried out using the following procedure. First, in an anechoic chamber, a large drone corresponding to rotary-wing aircraft 1 and a small drone corresponding to other aircraft 100 were hovered, and mixed sound was measured using microphone 3. That is, the flight conditions for rotary-wing aircraft 1 and other aircraft 100 were the same. Microphone 3 was placed directly above each propeller of rotary-wing aircraft 1 at approximately the same distance. Simultaneously with the measurement of mixed sound, the vibration of each propeller was measured using vibrometer 4. The measurement time was 30 seconds.

[0048] Subsequently, the control processing of the rotary-wing aircraft 1 according to the present invention was applied to the measured mixed noise and the measured propeller vibration to create the analysis results of the propeller 2 vibration shown in Figure 3, the mixed noise analysis results shown in Figure 4, and the results of removing the aircraft's own operating noise shown in Figure 5. In the results of removing the aircraft's own operating noise, the modulation frequency corresponding to the operating noise of the rotary-wing aircraft 1 disappears from the measured mixed noise, and the modulation frequency corresponding to the operating noise of other aircraft 100 becomes prominent. From these results, it can be said that the rotary-wing aircraft 1 is capable of detecting other aircraft 100.

[0049] (Second example) The experimental results of a second embodiment of the aircraft detection method for the rotary-wing aircraft 1 according to this embodiment will be described. In the second embodiment, the other aircraft 100 are of the same type as the rotary-wing aircraft 1.

[0050] The detection process for aircraft 100 was carried out using the following procedure. First, in an anechoic chamber, a large drone equivalent to rotary-wing aircraft 1 and another large drone equivalent to aircraft 100 were hovered, and mixed sound was measured using microphone 3. That is, the flight conditions for rotary-wing aircraft 1 and the other aircraft 100 were the same. Microphone 3 was placed directly above each propeller of rotary-wing aircraft 1 at approximately the same distance. Simultaneously with the measurement of mixed sound, the vibration of each propeller was measured using vibrometer 4. The measurement time was 30 seconds.

[0051] Subsequently, the control processing of the rotary-wing aircraft 1 according to the present invention was applied to the measured mixed noise and the measured vibration of the propeller 2 to create the analysis results of the propeller 2 vibration shown in Figure 7, the mixed noise analysis results shown in Figure 8, and the results of removing the aircraft's own operating noise shown in Figure 9. In the results of removing the aircraft's own operating noise, the modulation frequency corresponding to the operating noise of the rotary-wing aircraft 1 disappears from the measured mixed noise, and the modulation frequency corresponding to the operating noise of other aircraft 100 of the same type and under similar flight conditions becomes prominent. From these results, it can be said that the rotary-wing aircraft 1 is capable of detecting other aircraft 100 of the same type and under similar flight conditions.

[0052] As described above, by employing the aircraft detection method according to this disclosure, other aircraft 100 at a distance can be detected. In the aircraft detection method according to this disclosure, the only sensors used may be a microphone 3 and a vibrometer 4, and the vibrometer 4 can be omitted. Therefore, both the sensors and battery are small and lightweight, and a rotary-wing aircraft 1 can be constructed that has a collision avoidance method that is not affected by the field of view.

[0053] This disclosure is not limited to the embodiments described above. For example, multiple blocks described in the block diagram may be combined, or a single block may be divided. Instead of executing multiple steps described in the flowchart in chronological order as described, they may be executed in parallel or in a different order, depending on the processing capacity of the device performing each step, or as necessary. Other modifications are possible without departing from the spirit of this disclosure.

[0054] For example, in the above-described embodiment, the control unit 11 and / or storage unit 12 of the rotorcraft 1 may not be mounted on the rotorcraft 1, but rather be a general-purpose computer such as a WS (Work Station) or PC (Personal Computer) installed in a facility such as a data center. In this case, the control unit 11 and / or storage unit 12 may be connected to the aircraft detection device 5 of the rotorcraft 1 via a network. [Explanation of symbols]

[0055] 1. Rotary-wing aircraft 2 propellers 3 Microphone 4 Vibration meter 5 Aircraft detection device 11 Control Unit 12 Storage section 100 Other flying objects

Claims

1. It is a rotary-wing aircraft equipped with a propeller that rotates to generate thrust. One or more microphones to capture ambient sounds, Control unit and Equipped with, The control unit, Modulation frequency analysis is performed on the acquired mixed sound to calculate the mixed sound analysis results. The vibration information of the rotor blade or the control signal of the propeller is acquired. Based on the vibration information of the rotorcraft or the control signal of the propeller, the self-modulation frequency, which is the modulation frequency corresponding to the operating sound of the rotorcraft, is estimated. From the mixed sound analysis results, remove the component of the self-modulated frequency. Rotary-wing aircraft.

2. The rotary-wing aircraft according to claim 1, wherein the operating sound of the rotary-wing aircraft is the operating sound of the propeller.

3. The system further includes a vibration meter for measuring the vibration of the propeller, The control unit estimates the self-modulation frequency based on the vibration measured by the vibration meter. The rotary-wing aircraft according to claim 1.

4. The rotary-wing aircraft according to claim 2, wherein the control unit estimates the rotational speed information of the propeller based on the control signal of the propeller.

5. The rotary-wing aircraft according to any one of claims 1 to 4, wherein the control unit determines whether the mixed sound contains the operating sounds of other aircraft based on the mixed sound analysis results obtained by removing the component of the self-modulated frequency.

6. The rotary-wing aircraft according to any one of claims 1 to 4, wherein the self-modulation frequency is a modulation frequency corresponding to the first or harmonic component of the vibration of the rotary-wing aircraft.

7. The rotary-wing aircraft according to any one of claims 1 to 4, wherein the self-modulation frequency is the value obtained by multiplying the modulation frequency corresponding to the first or harmonic component of the vibration of the rotary-wing aircraft by the number of propeller blades.

8. The rotary-wing aircraft according to any one of claims 1 to 4, wherein one or more microphones are attached.

9. The rotary-wing aircraft according to any one of claims 1 to 4, wherein one or more microphones constitute a microphone array, and the microphone array is mounted.

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