JP7724496B2 - Non-contact acoustic detection system, unmanned aerial vehicle - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Published on August 1, 2020, for the 75th Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, 2020. Published in the Lecture Abstracts (DVD-ROM) of the 75th Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, 2020.

Article 30, paragraph 2 of the Patent Act is applicable. Published on August 26, 2020, for the 2020 Autumn Research Presentation of the Acoustical Society of Japan, Proceedings of the 2020 Autumn Research Presentation of the Acoustical Society of Japan, pages 543-544.

Application of Article 30, Paragraph 2 of the Patent Act Announced at the IEEE International Ultrasonics Symposium 2020 held from September 6th to 11th, 2020

Article 30, paragraph 2 of the Patent Act is applicable. Published on October 28, 2020, for the 2020 Autumn Lecture Meeting of the Japanese Society for Non-Destructive Inspection, in the Lecture Abstracts for the 2020 Autumn Lecture Meeting of the Japanese Society for Non-Destructive Inspection, pages 3-4.

Application of Article 30, Paragraph 2 of the Patent Act Announced at the Symposium on UltraSonic Electronics (USE2020) held from November 25th to 27th, 2020

Article 30, Paragraph 2 of the Patent Act was applied. Presented at the 143rd (Autumn 2020) Academic Conference of the Japan Society of Exploration Geophysicists held from November 25th to 27th, 2020.

Article 30, Paragraph 2 of the Patent Act was applied. A presentation titled "Research on noncontact acoustic inspection method using aerial emission, sound wave, and laser Doppler vibrometer" was given at the Toin International Symposium on Medical Engineering 2020, held on November 28, 2020.

Patent Law Article 30, Paragraph 2 applied. Presented at the Toin International Symposium on Medical Engineering 2020 held on November 28, 2020, entitled "Study on Buried Object Exploration in Shallow Underground Using Sound Waves."

Article 30, paragraph 2 of the Patent Act is applicable. Published on February 24, 2021, for the 2021 Spring Meeting of the Acoustical Society of Japan, Proceedings of the 2021 Spring Meeting of the Acoustical Society of Japan, pages 583-584.

Application of Article 30, Paragraph 2 of the Patent Act. Presented at the Defense Construction Association Annual Forum 2021 held on April 19, 2021.

Article 30, Paragraph 2 of the Patent Act applies. Published on April 30, 2021 at https://iopscience.iop.org/article/10.35848/1347-4065/abf515

Article 30, paragraph 2 of the Patent Act applies. Published in Toin Ronso No. 44, pages 123-128, published on June 15, 2021.

Article 30, paragraph 2 of the Patent Act applies. Published in Toin Ronso No. 44, pages 129-133, published on June 15, 2021.

The present invention relates to a non-contact acoustic detection system and an unmanned aerial vehicle used in the non-contact acoustic detection system.

Various technologies have been proposed for irradiating objects with sound waves in order to analyze and explore them non-contact. For example, the inventors previously invented the technology disclosed in Patent Document 1 below.

Patent Document 1 discloses a system in which a vertical surface such as a wall surface is measured, sound waves are emitted from an acoustic source mounted on an unmanned aerial vehicle (UAV) to the vertical surface to vibrate the vertical surface, the vibration velocity of the vibrated vertical surface is measured using a laser Doppler vibrometer, and the measurement results are analyzed.
This system mounts the acoustic source on an unmanned aerial vehicle and moves it around, so there is no need to set up temporary scaffolding even if the object to be measured is in a dangerous location such as a high place, making it advantageous in terms of cost and work safety.

Japanese Patent Application Laid-Open No. 2019-196973

Patent Document 1 describes irradiating sound waves from an acoustic source onto a vertical plane while the unmanned aerial vehicle is flying. When operating an unmanned aerial vehicle using this method, the more locations there are to be measured, the longer the unmanned aerial vehicle must hover near the measurement targets, which quickly consumes the battery of the unmanned aerial vehicle.

Incidentally, when the measurement target is a horizontal surface such as the ground, the vibration velocity of the horizontal surface can be measured by irradiating sound waves from an acoustic source after the unmanned aerial vehicle has landed, thereby improving the problem of battery consumption mentioned above.
However, when an unmanned aerial vehicle is operated using the above-mentioned method, vibrations generated when the acoustic source emits sound waves propagate through the landing unmanned aerial vehicle and are transmitted to the horizontal surface of the measurement target. In a system that uses sound waves to vibrate a measurement target, such propagated vibrations cause local disturbances (noise) in the measurement target, which reduces measurement accuracy.

The present invention has been developed in consideration of the above-mentioned problems, and provides a non-contact acoustic inspection system that reduces noise propagating to a measurement target when sound waves are irradiated onto the measurement target from an acoustic source mounted on the unmanned aerial vehicle, as well as an unmanned aerial vehicle used in the system.

According to the present invention, a non-contact acoustic exploration system is provided in which, after an unmanned aerial vehicle flies and lands at a measurement location, an acoustic source mounted on the unmanned aerial vehicle emits sound waves downward to vibrate the measurement location, and the measurement results of the vibration velocity at the excited measurement location are analyzed to explore the measurement location. The unmanned aerial vehicle is equipped with the acoustic source, legs that are in contact with the measurement location when the vehicle has landed, and a vibration isolation mechanism that is located on a path along which vibrations generated in the acoustic source when the acoustic source emits sound waves propagate to the measurement location via the legs and that isolates the propagation of the vibrations.

The present invention also provides an unmanned aerial vehicle for use in a non-contact acoustic exploration system that vibrates a measurement position by irradiating it with sound waves, measures the vibration velocity of the vibrated measurement position, and analyzes the results to explore the measurement position. The unmanned aerial vehicle has an acoustic source that irradiates sound waves downward to vibrate the measurement position when it has landed, legs that are in contact with the measurement position when it has landed, and a vibration isolation mechanism that is provided on a path along which vibrations generated in the acoustic source when it irradiates sound waves propagate to the measurement position via the legs and that isolates the propagation of the vibrations.

According to the above invention, when the unmanned aircraft is in a landing state, vibrations propagating from the acoustic source through the legs of the unmanned aircraft are blocked by the vibration blocking mechanism, thereby reducing noise propagating to the object being measured.

The present invention provides a non-contact acoustic inspection system that reduces noise transmitted to a measurement target when sound waves are irradiated onto the measurement target from an acoustic source mounted on the unmanned aerial vehicle, and an unmanned aerial vehicle used in the system.

1 is a configuration diagram showing the configuration of a non-contact acoustic inspection system according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing three proposed blocking methods that were considered. FIG. 10 is a diagram showing a single-degree-of-freedom system model used to calculate the amount of blocking. FIG. 10 is a diagram showing the amount of interruption calculated based on actual measurements. FIG. FIG. FIG. 10 is a side view of the vibration isolation mechanism during measurement. FIG. 10 is a side view of the vibration isolation mechanism during storage. 10A and 10B are diagrams illustrating the oscillation modes of an acoustic source in a vibration isolation mechanism.

Embodiments of the present invention will be described below with reference to the drawings. Note that in all drawings, similar components will be designated by the same reference numerals, and descriptions will be omitted where appropriate.

<Configuration of the non-contact acoustic inspection system according to the present invention>
Fig. 1 is a diagram showing the configuration of a non-contact acoustic exploration system (hereinafter abbreviated as "exploration system") 100 according to an embodiment of the present invention. Fig. 1(a) shows a state in which an unmanned aerial vehicle 10 is flying, and Fig. 1(b) shows a state in which the unmanned aerial vehicle 10 has landed and is irradiating a measurement position with sound waves.

The exploration system 100 is a system that, after the unmanned aerial vehicle 10 flies and lands at a measurement location, emits sound waves downward from an acoustic source 14 mounted on the unmanned aerial vehicle 10 to vibrate the measurement location, and then analyzes the results of measuring the vibration velocity of the vibrated measurement location to explore the measurement location.
Here, "probing the measurement position" does not only mean probing the surface (ground surface) of the measurement position where vibration is applied, but also includes probing the layer below the measurement position (underground). For example, Figure 1 shows a state in which the presence of a buried object BP buried below the measurement position is being probed.

The exploration system 100 includes an unmanned aerial vehicle 10, a laser Doppler vibrometer 20, a computer 30, and an arbitrary waveform generator 40.
Each configuration will be explained below.

The unmanned aerial vehicle 10 has a main body 11, a propeller 12, legs 13, and an acoustic emission source 14.
The main body 11 is the main component of the unmanned aerial vehicle 10 and is connected to the propeller 12 via an arm. The main body 11 may store a receiver, flight controller, battery, camera, gimbal, sensor, etc. (not shown). Note that the main body 11 does not necessarily need to store all of the components exemplified here, and may store components other than those exemplified.
The propeller 12 rotates to provide lift to the unmanned aerial vehicle 10, and is controlled by a motor that is driven based on a control signal from a flight controller (not shown). It is preferable to stop the rotation of the propeller 12 while the acoustic source 14 is irradiating the measurement position with sound waves and vibrating the measurement position. This is because the wind generated by the rotation of the propeller 12 may move sand, pebbles, etc. on the ground surface, which may reduce the accuracy of measurements by the laser Doppler vibrometer 20.
The legs 13 are landing gear for the unmanned aerial vehicle 10, and are configured to touch down at the measurement position when the unmanned aerial vehicle 10 has landed. The legs 13 serve to absorb shocks during landing, and also to ensure a certain distance between the acoustic emission source 14 and the measurement position (ground surface) when the unmanned aerial vehicle 10 has landed.
The acoustic source 14 is a device that emits sound waves downward in a landed state to vibrate the measurement position, and uses a flat speaker that outputs plane sound waves that vibrate the measurement position in a planar manner.
In this embodiment, for the sake of convenience, the main body 11 and the leg 13 are described as being separate components, but the components that perform their respective roles may be an inseparable, integrated unit.

The laser Doppler vibrometer 20 measures the vibration velocity at a measurement position that has been vibrated by irradiating sound waves from the acoustic source 14. The laser Doppler vibrometer 20 is preferably installed in a stable location (a location where the influence of vibrations due to sound wave irradiation and other disturbance factors is small) and is installed at a location away from the measurement position.
It should be noted that the measuring device used in implementing the present invention does not necessarily have to be a laser Doppler vibrometer; it is sufficient if it can measure the vibration velocity at the measurement position in a non-contact manner (from a certain distance). For example, it is also conceivable to use a laser displacement meter depending on the measurement environment and conditions.

The arbitrary waveform generator 40 is a device that causes the acoustic emission source 14 to output sound waves of a desired frequency. The arbitrary waveform generator 40 also serves to provide a trigger signal to the computer 30 and cause the computer 30 to control the laser Doppler vibrometer 20 so that measurements are performed by the laser Doppler vibrometer 20 in synchronization with the trigger signal. The arbitrary waveform generator 40 is capable of wireless communication with the acoustic emission source 14, and can control the time when the acoustic emission source 14 outputs sound waves and the frequency of the sound waves output from the acoustic emission source 14.
The arbitrary waveform generator 40 according to this embodiment is realized by combining a so-called function generator and an FM transmitter.

The computer 30 is a device that controls the arbitrary waveform generator 40 and also a device that analyzes the measurement position based on the measurement results obtained by the laser Doppler vibrometer 20 .
The method by which the computer 30 controls the arbitrary waveform generator 40 (the form of the sound waves output by the acoustic source 14) and the method by which the computer 30 analyzes the measurement results obtained by the laser Doppler vibrometer 20 can be modified as appropriate within the scope of achieving the object of the present invention.

When a measurement position is probed using the probe system 100 shown in FIG. 1 , as already explained as a problem of the present invention, vibrations generated when the acoustic source 14 irradiates sound waves may propagate to the measurement position via the legs 13, which may result in a decrease in the measurement accuracy of the laser Doppler vibrometer 20.
As a countermeasure, a vibration isolation mechanism that blocks the transmission of the vibrations is provided in the transmission path of the vibrations in the unmanned aerial vehicle 10.
The technical concept of the vibration isolation mechanism will be described in detail below.

<Target amount of blocking>
First, the amount of vibration blocking from the legs 13 of the unmanned aerial vehicle 10 to the measurement position was examined, and the target was set at -40 dB at 50 Hz.
50 Hz is the practical lower limit of the low frequency radiation characteristics of the acoustic source 14, and is the frequency at which noise reduction is most necessary because the volume that can be output is limited and it is difficult to ensure a satisfactory signal-to-noise ratio.
-40 dB is equivalent to a 100-fold reduction in noise, which is a target of sufficient order for the purposes of the present invention.

<Optimal shutoff method>
Next, we investigated the optimal shutoff method.
One method of isolating vibrations is to increase the mass of the unmanned aerial vehicle 10, but this was ruled out from the perspective of the flight performance of the unmanned aerial vehicle 10.
Therefore, we considered a concrete proposal for a method of blocking vibrations by providing an elastic body in the vibration propagation path.

FIG. 2 is a schematic diagram showing three proposed blocking methods that were investigated.
The proposal shown in Figure 2(a) is a proposal in which the acoustic source 14 is suspended from the main body 11 of the unmanned aerial vehicle 10 by an elastic body E1 (e.g., a spring), and vibrations are blocked at a position close to the acoustic source 14, which is the source of vibration.
The proposal shown in Figure 2(b) is a proposal in which an elastic body E2 (e.g., a spring) is inserted midway along the leg 13 of the unmanned aerial vehicle 10 to block vibrations propagating in the axial direction of the leg 13.
The proposal shown in Figure 2(c) is to provide an elastic body E3 (e.g., a sponge) at the lower end of the leg 13 of the unmanned aerial vehicle 10 to block vibrations propagating from the leg 13 to the contact surface of the leg 13.

The proposals shown in Figures 2(b) and 2(c) are not optimal methods, as there are concerns about the legs 13 bending, the unmanned aircraft 10 wobbling when landing, and mud adhering to the elastic body, which can cause a deterioration in elastic force.
On the other hand, the plan shown in FIG. 2(a) has the potential to be realized more effectively and compactly than the other plans, and so we decided to focus on this plan for the design.

<Calculation of the amount of interruption>
In order to realize the scheme shown in FIG. 2(a), the blocking capacity required for the elastic body E1 was calculated.
In calculating the above-mentioned blocking amount, the vibration generated in the acoustic source 14 was assumed to be in the vertical direction, and the excitation force was assumed to be F ₀ (N). Furthermore, the acoustic source 14 was assumed to be a lumped mass, and its mass was assumed to be M (kg).
The acoustic source 14 was assumed to be suspended by springs at the four corners, and the sum of the stiffness of the parallel springs at the four corners was taken as k (N/mm), and calculations were carried out using a simple one-degree-of-freedom system model.

FIG. 3 is a diagram showing a single-degree-of-freedom model used to calculate the amount of interruption.
If the vertical coordinate of the vibration direction is x, then equation (1) holds true due to the balance of forces.

Here, if only the steady-state solution is found, it becomes equation (2).

Since the transmission force _F1 is k×x, the interruption amount Trans is calculated as F1/F0, as shown in equation (3).

FIG. 4 is a diagram showing the amount of interruption calculated based on actual measurements.
Specifically, when the mass M of the acoustic source 14 actually used is set to 2 (kg), the values shown by the solid line in FIG. 4 represent the calculation results of the blocking amount when the spring constant k is set to 2 (N/mm), and the values shown by the dashed line in FIG. 4 represent the calculation results of the blocking amount when the spring constant k is set to 0.72 (N/mm).
As shown in FIG. 4, the former provides a cutoff of −40 dB at 50 Hz, and the latter provides a cutoff of −49 dB at 50 Hz.

Here, if we use the familiar rubber band as an example of the spring constant, the spring constant of one rubber band is 0.02 (N/mm), so in order to achieve a spring constant of 2 (N/mm), the four corners of the acoustic source 14 would need to be suspended by 100 rubber bands, meaning 25 rubber bands per corner.
Furthermore, to achieve a spring constant of 0.72 (N/mm), the four corners of the acoustic source 14 must be suspended by 36 rubber bands, meaning that nine rubber bands are required per corner.

<Configuration of vibration isolation mechanism 50>
Based on the design concept described above, a prototype was created and experiments using the prototype were repeated to prevent and deal with any problems. The configuration of the vibration isolation mechanism 50 that was ultimately arrived at as a result of this trial and error is shown in Figures 5 to 8.
Fig. 5 is a perspective view of the vibration isolating mechanism 50. Fig. 6 is a top view of the vibration isolating mechanism 50. Fig. 7 is a side view of the vibration isolating mechanism 50 during measurement. Fig. 8 is a side view of the vibration isolating mechanism 50 during storage.

The vibration isolation mechanism 50 is a device attached to the underside of the main body 11 of the unmanned aerial vehicle 10, and suspends the acoustic source 14 at each of the four corners by springs 551 to 554.
In this embodiment, a configuration is adopted in which the acoustic source 14 itself is processed so that the springs 551 to 554 can directly suspend the acoustic source 14. However, if it is difficult to process the acoustic source 14, a configuration may be adopted in which a mechanism for holding the acoustic source 14 (for convenience, this mechanism will be referred to as a holding portion) is manufactured, and the four corners of the holding portion are suspended by the springs 551 to 554, thereby indirectly storing the acoustic source 14 in the vibration isolation mechanism 50.
In the following description, the structural features described for the acoustic source 14 may be replaced with features relating to the holder that holds the acoustic source 14, as long as the object of the present invention is achieved.

The vibration isolation mechanism 50 has a frame body consisting of a first member 51, a second member 52, a third member 53, and a fourth member 54 (hereinafter, the frame body consisting of these four members may be collectively referred to as the frame portion).
Springs 551 and 554 are attached to both ends of the first member 51, and springs 552 and 553 are attached to both ends of the second member 52, and as described above, each suspends a corner of the acoustic emission source 14.
The third member 53 and the fourth member 54 are members provided between the first member 51 and the second member 52, and each has a screw hole on its upper surface for screwing to the lower surface of the main body 11. The third member 53 and the fourth member 54 also have a plurality of holes drilled therein to reduce weight.
In this embodiment, a frame portion as described above is provided between the underside of the unmanned aerial vehicle 10 (main body portion 11) and the acoustic emission source 14, and springs 551 to 554 suspend the acoustic emission source 14 from the frame portion, but the springs 551 to 554 may also suspend the acoustic emission source 14 directly from the underside of the unmanned aerial vehicle 10 (main body portion 11).

Springs 551-554 can be substituted with rubber as long as the elastic material achieves the spring constant described in the <Calculating the shutoff amount> section. However, considering durability that can withstand long-term use and storage, it is preferable to use stainless steel springs (SUS type).

As explained in the section <Calculation of the Blocking Amount>, the use of springs with a low spring constant results in a greater amount of noise blocking for springs 551 to 554. However, there is a concern that springs with a low spring constant may undergo plastic deformation, so it is desirable that no load is applied to springs 551 to 554 (no load) during storage (when not being used for measurement).
To address this issue, in order to reduce the load on the springs 551 to 554 during storage, the acoustic emission source 14 is joined to the frame portion (first member 51) as shown in Fig. 8. Specifically, screw receiving portions 581 and 582 are provided on the first member 51, and two similar screw receiving portions (not shown) are provided on the second member 52. During storage, the acoustic emission source 14 can be joined to the first member 51 and the second member 52 by screwing them into the respective screw receiving portions with thumb screws (Fig. 8 shows thumb screw 591 inserted into screw receiving portion 581 and thumb screw 592 inserted into screw receiving portion 582). In the following description, for convenience, the configuration consisting of the screw receiving portions and thumb screws will be referred to as the joining mechanism.

7 and 8, the length of springs 551 and 554 during measurement is shorter than the length of springs 551 and 554 during storage. This occurs because the joining mechanism prevents the load from acoustic source 14 from being applied to springs 551 and 554. This phenomenon also occurs in the lengths of springs 552 and 553, which are not shown in FIGS. 7 and 8.
Naturally, from the viewpoint of preventing plastic deformation, which is the purpose of providing a joining mechanism, it is preferable that the length of springs 551 to 554 during storage (when the acoustic emission source 14 is joined to the frame portion) be closer to its natural length than the length of springs 551 to 554 during measurement (when the acoustic emission source 14 is not joined to the frame portion).

As shown in Figure 8, during measurement, the acoustic source 14 hangs down from the frame. Therefore, the acoustic source 14 swings like a swing during flight and landing of the unmanned aerial vehicle 10. If the swing amplitude of the acoustic source 14 becomes large, there is a concern that it may interfere with surrounding components (e.g., the legs 13).
To address this issue, the springs 551 to 554 that support the four corners of the sound emitting source 14 are inclined (hereinafter, support by these inclined springs 551 to 554 will be referred to as inclined support). The inclined support prevents the sound emitting source 14 from swinging horizontally. The effect of the inclined support will be described in detail later.

Furthermore, in addition to the tilt support, the vibration isolation mechanism 50 is provided with a restriction mechanism that restricts the oscillation width of the sound emission source 14 to a predetermined dimension or less in order to restrict the oscillation width. Specifically, a hole 571 is provided in the first member 51, a hole 572 is provided in the second member 52, and a columnar member 561 and a columnar member 562 are inserted into the hole 571 and the second member 52, respectively. The columnar member 561 and the columnar member 562 are each fixed to the sound emission source 14, and horizontal movement of the sound emission source 14 that exceeds the diameter of the hole 571 and the hole 572 is restricted. That is, in this embodiment, the restriction mechanism is realized by the columnar member 561 and the hole 571, and the columnar member 562 and the hole 572.
By providing the above-described restricting mechanism, the swing (horizontal movement) of the large sound source 14, which cannot be suppressed by the inclined support provided by the springs 551 to 554, can be restricted to a predetermined dimension or less.

<Effect of tilt support>
As described above, a structure (inclined support) is adopted in which the springs 551 to 554 supporting the sound source 14 are inclined in order to suppress the oscillation of the sound source 14. The effect of the inclined support will be described in detail below.
To quantitatively and precisely express the effect of tilt support, the phenomenon involves large displacements, is nonlinear, and is a transient phenomenon, which necessitates a numerical solution using a computer, which is a high hurdle. Therefore, as an alternative, we considered the mechanism of oscillation suppression from two mutually complementary perspectives, a mechanical interpretation and an interpretation as vibration, based on a simple experimental model.

First, for the purpose of mechanical consideration, the acoustic source 14 is actually supported at its four corners, and its swinging motion will be considered two-dimensionally as viewed from the front or side.
9 is a diagram showing the oscillation mode of the sound emitting source 14 in the vibration isolation mechanism 50, using a so-called "four-bar link mechanism," in which the upper end of the vibration isolation mechanism 50 (the underside of the main body 11 of the unmanned aerial vehicle 10) is designated as stationary link L1, the sound emitting source 14 provided at the lower end of the vibration isolation mechanism 50 is designated as link L3, and the members supporting the sound emitting source 14 (corresponding to springs 551 to 554) are designated as links L2 and L4. Note that in FIG. 9, link L3 represents the sound emitting source 14 at rest, and link L3' represents the sound emitting source 14 when it is at its maximum oscillation amplitude.

Figure 9(a) shows a link mechanism in which the sound emitting source 14 is suspended vertically, while Figures 9(b) and 9(c) show link mechanisms in which the sound emitting source 14 is suspended at an angle. Figure 9(b) shows a link mechanism in which the length of link L1 is shorter than that of link L3, and in the following explanation, this link mechanism will be referred to as a V-shaped suspension. Figure 9(c) shows a link mechanism in which the length of link L1 is longer than that of link L3, and in the following explanation, this link mechanism will be referred to as an inverted V-shaped suspension.

Arrow A1 shown in FIG. 9(a), arrow A2 shown in FIG. 9(b), and arrow A3 shown in FIG. 9(c) indicate the magnitude of the horizontal swing amount of the link mechanism that each indicates.
As can be seen by comparing the link mechanisms shown in Figures 9(b) and 9(c) with the link mechanism shown in Figure 9(a), the amount of swing of the sound emitting source 14 is reduced by adding rotation (turning) to the horizontal translational movement.
The magnitude relationship of the amount of swing is vertical hanging > V-shaped hanging > inverted V-shaped hanging, and it can be seen that the inverted V-shaped hanging is the most appropriate structure from the viewpoint of reducing the amount of swing.

Next, in order to consider vibration, actual models of each link mechanism shown in Figures 9(a) to 9(c) were created and their movements were observed by hitting (striking) them horizontally.
As a result, it was found that with vertical suspension, only horizontal and vertical translation occurs, whereas with inclined suspension, translation and rotation (turning) occur immediately after a horizontal impact. In other words, with inclined suspension, translation and rotation become strongly coupled vibration modes, and the energy of the impact applied in the horizontal direction is dispersed and injected into both translation and rotation modes.
Therefore, from a vibration perspective, the effect of inclined suspension on vibration (horizontal translation) can be interpreted as being due to the rotational mode bearing the impact energy, resulting in a reduction in the amount of energy injected into the translational mode compared to vertical suspension.

Based on the above considerations, the springs 551 to 554 in the vibration isolation mechanism 50 in this embodiment are attached so that they are inclined downward toward the inside of the vibration isolation mechanism 50 when stationary, so as to form an inverted V-shaped hanging configuration.
Here, "inside the vibration isolation mechanism 50" refers to a direction closer to the center of the vibration isolation mechanism 50 when viewed from above (when viewed from the viewpoint shown in FIG. 8). Also, "sloping downward toward the inside of the vibration isolation mechanism 50" refers to the fact that the lower end of each spring (the portion attached to the acoustic source 14) is closer to the center of the vibration isolation mechanism 50 than the upper end of each spring (the portion attached to the first member 51 and the second member 52).
As shown in Figure 8, in this embodiment, the springs 551 to 554 are inclined downward toward the inside of the vibration-isolating mechanism 50 in both the extension direction of the first member 51 and the second member 52 (horizontal direction in Figure 8) and the extension direction of the third member 53 and the fourth member 54 (vertical direction in Figure 8), so that they form an inverted V-shaped suspension when viewed from any direction, front, back, left, or right.
This reduces the vibration of the acoustic source 14 in all horizontal directions.

<Modification>
As described above, the present invention has been described by showing specific embodiments, but the present invention is not limited to the above-described embodiments and includes various modifications, improvements, and other aspects as long as the object of the present invention is achieved.
Below, we will explain some modifications that have not yet been mentioned.

The non-contact acoustic inspection system according to the present invention may be realized by adding a different component to the configuration described using Figure 1, or by replacing part of that configuration with a different component.

In the above embodiment, the vibration isolation mechanism was described as having a joining mechanism (thumb screw and screw receiver) and a regulating mechanism (columnar member and hole), but the present invention may also be implemented in a form that omits one or both of these.

In the above embodiment, it has been explained that the vibration isolation mechanism has each spring supporting the acoustic source at an angle, so that each spring serves to suspend the acoustic source and also serves to suppress horizontal oscillation of the acoustic source. However, the present invention may also be implemented by a configuration in which the former and latter roles are performed by different springs.
However, this modified example requires more springs than the described embodiment, resulting in a more complex configuration and increasing the risk of failure of the vibration isolation mechanism, so it can be said that the configuration described in the above-mentioned embodiment is a more desirable form.

The present embodiment encompasses the following technical ideas.
(1) A non-contact acoustic exploration system that, after an unmanned aerial vehicle flies and lands at a measurement location, emits sound waves downward from an acoustic source mounted on the unmanned aerial vehicle to vibrate the measurement location, and then analyzes the results of measuring the vibration velocity of the vibrated measurement location to explore the measurement location, wherein the unmanned aerial vehicle is equipped with the acoustic source, legs that are grounded at the measurement location when landed, and a vibration isolation mechanism that is provided on a path along which vibrations generated in the acoustic source when the acoustic source emits sound waves propagate to the measurement location via the legs and that blocks the propagation of the vibrations.
(2) The non-contact acoustic exploration system described in (1) is characterized in that the vibration isolation mechanism has an elastic body that suspends the acoustic source or a holding part that holds the acoustic source from the underside of the main body part of the unmanned aerial vehicle or a frame part provided on the underside.
(3) A non-contact acoustic inspection system as described in (2), characterized in that the elastic body is inclined when in a stationary state.
(4) A non-contact acoustic inspection system as described in (3), characterized in that the elastic body is inclined downward toward the inside of the vibration isolation mechanism when in a stationary state.
(5) A non-contact acoustic exploration system described in any one of (2) to (4), characterized in that the vibration isolation mechanism has a joining mechanism that joins the acoustic source or the holding part to the frame part, and the elastic body that is stationary when the acoustic source or the holding part is joined to the frame part is closer to its natural length than the elastic body that is stationary when the acoustic source or the holding part is not joined to the frame part.
(6) A non-contact acoustic exploration system described in any one of (1) to (5), characterized in that the vibration isolation mechanism has a regulating mechanism that regulates the width of horizontal oscillation of the acoustic source to a predetermined dimension or less.
(7) An unmanned aerial vehicle used in a non-contact acoustic exploration system that vibrates a measurement position by irradiating sound waves, measures the vibration velocity of the vibrated measurement position, and analyzes the results to explore the measurement position, the unmanned aerial vehicle having an acoustic source that irradiates sound waves downward to vibrate the measurement position when landed, legs that are grounded to the measurement position when landed, and a vibration isolation mechanism that is provided on a path along which vibrations generated in the acoustic source when the acoustic source irradiates sound waves are transmitted to the measurement position via the legs and that blocks the propagation of the vibrations.

100 Exploration system 10 Unmanned aerial vehicle 11 Main body 12 Propeller 13 Leg 14 Acoustic source 20 Laser Doppler vibrometer 30 Computer 40 Arbitrary waveform generator 50 Vibration isolation mechanism 51 First member 52 Second member 53 Third member 54 Fourth member 551, 552, 553, 554 Springs 561, 562 Pillar members 571, 572 Hole portions 581, 582 Screw receiving portions 591, 592 Thumb screws

Claims (7)

A non-contact acoustic exploration system that, after an unmanned aerial vehicle flies and lands at a measurement position, irradiates sound waves downward from an acoustic source mounted on the unmanned aerial vehicle to vibrate the measurement position, and analyzes the results of measuring the vibration velocity of the vibrated measurement position to explore the measurement position,
The unmanned aerial vehicle comprises:
the acoustic source;
a leg that is brought into contact with the measurement position in a landed state;
a vibration isolation mechanism that is provided on a path along which vibrations generated in the acoustic source when the acoustic source irradiates sound waves propagate to the measurement position via the legs and that isolates the propagation of the vibrations;
A non-contact acoustic inspection system. the vibration isolation mechanism has an elastic body that suspends the acoustic source or a holder that holds the acoustic source from the underside of a main body of the unmanned aerial vehicle or a frame portion provided on the underside;
2. The non-contact acoustic inspection system according to claim 1. The elastic body is inclined in a resting state.
3. The non-contact acoustic inspection system according to claim 2. The elastic body is inclined downward toward the inside of the vibration isolation mechanism when in a stationary state.
4. The non-contact acoustic inspection system according to claim 3. the vibration isolation mechanism has a joining mechanism that joins the sound source or the holding part to the frame part,
the elastic body at rest in a state where the acoustic source or the holding unit is joined to the frame unit has a length closer to a natural length than the elastic body at rest in a state where the acoustic source or the holding unit is not joined to the frame unit;
5. The non-contact acoustic inspection system according to claim 2, wherein the non-contact acoustic inspection system is a non-contact acoustic inspection system. The vibration isolation mechanism has a restriction mechanism that restricts the width of horizontal oscillation of the sound source to a predetermined dimension or less.
6. The non-contact acoustic inspection system according to claim 2 , wherein the non-contact acoustic inspection system is a non-contact acoustic inspection system. An unmanned aerial vehicle used in a non-contact acoustic exploration system that vibrates a measurement position by irradiating it with sound waves, measures the vibration velocity of the vibrated measurement position, analyzes the results, and explores the measurement position,
an acoustic source that emits sound waves downward in a landed state to vibrate the measurement position;
a leg that is brought into contact with the measurement position in a landed state;
a vibration isolation mechanism that is provided on a path along which vibrations generated in the acoustic source when the acoustic source irradiates sound waves propagate to the measurement position via the legs, and that isolates the propagation of the vibrations;
An unmanned aerial vehicle having: