JP7523760B2 - Explosion-proof unmanned aerial vehicle - Google Patents

Description

This disclosure relates to an explosion-proof unmanned aerial vehicle that flies in explosion-proof areas where flammable gases may be present.

Patent Document 1 discloses technology relating to an unmanned aerial vehicle for inspecting equipment installed in a monitored area. In this technology, the unmanned aerial vehicle flies along a preset flight route to inspect the equipment. When a sensor mounted on the unmanned aerial vehicle detects a leak of explosive gas, the unmanned aerial vehicle determines a dangerous area where flying is dangerous and sets a new flight route that avoids the dangerous area.

JP 2019-202682 A

Unmanned aerial vehicles may deviate from their flight route due to malfunctions during flight or external disturbances. For this reason, even if a new flight route is set to avoid dangerous areas, as with the unmanned aerial vehicle in Patent Document 1, there is a risk that the vehicle may unintentionally enter the dangerous area and crash or be damaged. In this case, there is a risk that the aircraft may become a source of ignition for flammable gases in the dangerous area.

This disclosure was made in consideration of the above-mentioned problems, and aims to provide an explosion-proof unmanned aerial vehicle that can prevent the aircraft from becoming a source of ignition in explosion-proof areas where flammable gases may be present.

In order to solve the above problems, the first disclosure is applied to an explosion-proof unmanned aerial vehicle. The explosion-proof unmanned aerial vehicle includes a body that houses electric devices inside, a cylindrical fixed pipe that is inserted into a through hole provided in the body so as to communicate with the inside and outside of the body and is fixed in a state where it protrudes from the inside and outside of the body , a propeller that generates thrust, a hollow tubular arm pipe that supports the propeller and through which a cable of the propeller is passed, and a sealing structure that is provided inside the cylindrical fixed pipe and seals communication between the inside and outside of the body. The arm pipe is configured to be fixed in a state where it is inserted into the fixed pipe.

The second disclosure further has the following features in addition to the first disclosure.
The body has a thick-walled portion in a predetermined area surrounding the fixed pipe, the thickness of which is greater than the thickness of other areas.

The third disclosure is the first or second disclosure, further comprising the following features.
The sealing structure includes a fixed joint formed by hardening a resin filled inside the fixed pipe.

The fourth disclosure is any one of the first to third disclosures, further having the following features.
The cable is configured to be pulled into the interior of the body from the fixed pipe. The sealing structure holds the cable inside the fixed pipe and includes a cable clamp bonded to an inner wall of the fixed pipe.

The fifth disclosure is any one of the first to fourth disclosures, further having the following features.
The fixed pipe is configured to be joined to the body by welding, and the arm pipe is configured to be joined to the fixed pipe by adhesive with resin.

The sixth disclosure is any one of the first to fifth disclosures, further comprising the following features.
The explosion-proof unmanned aerial vehicle further includes a protective layer including a polyurea resin applied to the surfaces of the body and the fixed pipe.

The seventh disclosure is the sixth disclosure and further has the following features.
The arm pipe is configured so that no protective layer containing polyurea resin is applied to the surface.

The eighth disclosure is the sixth or seventh disclosure further having the following features.
The explosion-proof unmanned aerial vehicle further comprises a conductive coating applied over the protective layer.

According to the first disclosure, the inside of the tube of the fixed pipe fixed to the body is sealed by a sealing structure. Therefore, even if the arm pipe fixed to the fixed pipe receives an impact and is damaged, the pressure-resistant explosion-proof structure of the body is maintained by the sealing structure inside the tube of the fixed pipe. This makes it possible to prevent electrical equipment inside the body from becoming a source of ignition, even if the arm pipe is damaged in an explosion-proof area.

According to the second disclosure, the fixing strength between the body and the fixed pipe is increased by the thick portion. This makes it possible to prevent cracks and the like from occurring between the body and the fixed pipe. Furthermore, by increasing the fixing strength of the fixed pipe, when the propeller or arm pipe receives an impact, the arm pipe is more likely to break than the fixed pipe. As a result, the pressure-resistant explosion-proof structure of the body is maintained by the sealed structure inside the tube of the fixed pipe.

According to the third disclosure, the inside of the fixed pipe is filled with a fixed joint formed by hardening of the filled resin. This makes it possible to reliably seal the inside of the fixed pipe even when a cable is passed through the inside of the body.

According to the fourth disclosure, the inside of the fixed pipe can be sealed more firmly while holding the cable by the cable clamp. In addition, unlike hardened resin, the cable clamp has stable dimensions, making it easier to manage the dimensions of the sealing structure.

According to the fifth aspect of the invention, the fixed pipe is firmly joined to the body by welding, while the arm pipe is joined to the fixed pipe by adhesive with resin. With this configuration, when an impact is applied to the arm pipe, the adhesive of the arm pipe is more likely to break before a crack occurs in the weld of the fixed pipe. This makes it possible to prevent any further load from acting on the weld of the fixed pipe.

According to the sixth disclosure, a protective layer containing a polyurea resin is applied to the surfaces of the body and the fixed pipe. This configuration increases the bonding strength of the fixed pipe to the body, preventing cracks from occurring at the bond between the fixed pipe and the body when an impact is applied to the arm pipe.

According to the seventh disclosure, the surface of the arm pipe is not coated with a protective layer containing polyurea resin. With this configuration, stresses that occur in the fixed pipe due to breakage of the fixed pipe when an impact is applied to the arm pipe are mitigated. This makes it possible to prevent cracks from occurring at the joint between the fixed pipe and the body.

According to the eighth disclosure, a conductive coating is applied to the surface of the protective layer containing a polyurea resin. This configuration makes it possible to prevent the protective layer from being charged with static electricity, thereby reducing the risk of static electricity in explosion-proof areas.

1 is a perspective view showing the general structure of an unmanned aerial vehicle according to an embodiment of the present invention; FIG. 2 is a top view of the unmanned aerial vehicle shown in FIG. 1 . FIG. 2 is a front view of the unmanned aerial vehicle shown in FIG. 1 . 2 is a perspective side view of the internal structure of the unmanned aerial vehicle shown in FIG. 1. 1 is an oblique view of an unmanned aerial vehicle according to an embodiment, viewed from below. 2 is a diagram showing part of a cross section of the arm pipe taken along a plane passing through the center axis of the arm pipe and parallel to the front-rear direction. FIG. 1 is a diagram for explaining the surface treatment applied to an unmanned aerial vehicle of an embodiment. 1 is a schematic diagram of an analytical model of an unmanned aerial vehicle according to an embodiment of the present invention. FIG. 1 is a diagram showing an outline of a test device for an impact test. FIG. 11 is a cross-sectional view for explaining the configuration of a test arm pipe. FIG. 1 is a diagram showing an outline of a drop test. FIG. 2 is a diagram showing locations at which the surface resistance value of an unmanned aerial vehicle is measured.

Below, the embodiments of the present disclosure will be described with reference to the drawings. However, when the numbers, quantities, amounts, ranges, etc. of each element are mentioned in the embodiments shown below, this disclosure is not limited to the mentioned numbers unless specifically stated or clearly specified in principle to that number. Furthermore, the structures, etc. described in the embodiments shown below are not necessarily essential to this disclosure unless specifically stated or clearly specified in principle to that number.

Embodiment
1. Schematic structure of the unmanned aerial vehicle Fig. 1 is a perspective view showing a schematic structure of an unmanned aerial vehicle according to an embodiment. Fig. 2 is a top view of the unmanned aerial vehicle shown in Fig. 1. Fig. 3 is a front view of the unmanned aerial vehicle shown in Fig. 1. Fig. 4 is a side view showing the internal structure of the unmanned aerial vehicle shown in Fig. 1. In the following description, the longitudinal direction of the body of the aircraft is defined as the "front-rear direction", the width direction of the aircraft is defined as the "left-right direction", and the height direction of the aircraft is defined as the "up-down direction".

The unmanned aerial vehicle 10 is a small unmanned aerial vehicle with longitudinal and lateral dimensions of, for example, approximately 600-700 mm each. The unmanned aerial vehicle 10 can fly by moving up and down, horizontally, and in the yaw direction, as well as by combinations of these, while grasping the attitude and position of the aircraft according to commands from a command terminal (not shown). The unmanned aerial vehicle 10 mainly comprises a body 12, multiple propellers 14, an arm pipe 16, and a propeller guard 18.

The body 12 forms the outer shell of the unmanned aerial vehicle 10. The body 12 is made of a metal such as an aluminum alloy. Inside the body 12, multiple electrical devices such as a camera device, LEDs, and sensors are housed. A first camera lens 20 for protecting the camera, multiple second camera lenses 22, and an LED lens 24 for protecting the LEDs are attached to the front side of the body 12. A sensor lens 26 for protecting the distance sensor is attached to the underside of the body 12. These lenses 20, 22, 24, and 26 are made of, for example, reinforced glass or a resin such as acrylic.

A head rear 28 that constitutes the outer shell of the unmanned aerial vehicle 10 is removably attached to the rear side of the body 12. The head rear 28 is made of a metal such as an aluminum alloy. By removing the head rear 28, it is possible to access the components stored inside the body 12.

The propellers 14 are components that convert the rotational force of the motor into thrust. Typically, the propellers 14 are made of lightweight, high-strength resin such as carbon fiber reinforced plastic (CFRP) or glass fiber reinforced plastic (GFRP). The unmanned aerial vehicle 10 of this embodiment is equipped with four propellers 14. Each propeller 14 is supported by an arm pipe 16 with its rotation axis oriented vertically.

The arm pipes 16 are holding parts for holding each propeller 14 and motor to the body 12. Typically, the arm pipes 16 are hollow tubular parts made of resin such as CFRP or GFRP, or metal such as aluminum alloy. The unmanned aerial vehicle 10 of this embodiment has four arm pipes 16 corresponding to the four propellers 14.

The base end of the arm pipe 16 is fixed to a fixed pipe 8 joined to the side of the body 12. The fixing structure of the base end of the arm pipe 16 is a characteristic feature of the unmanned aerial vehicle 10 of this embodiment, and will be described in detail below. A motor with a propeller 14 attached is attached to the tip of the arm pipe 16. The motor is covered by a motor case 30 made of a metal such as an aluminum alloy. The motor cable passes through the tube of the arm pipe 16 and is pulled into the inside of the body 12.

The propeller guard 18 is a protective member for protecting the propeller 14. Typically, the propeller guard 18 is made of resin such as CFRP or GFRP, and is sized to extend outward beyond the rotational area of the propeller 14. With this configuration, the propeller guard 18 can prevent the propeller 14 from coming into contact with obstacles such as people or buildings.

Attached to the body 12 are two antennas 32 for communicating with the GPS and the command terminal, and body guides 34 that serve as the landing gear of the unmanned aerial vehicle 10. The body guides 34 are made of resins such as CFRP, GFRP, and nylon, or metals such as aluminum alloys, and are attached to the front and rear of the underside of the body 12.

In addition to the electrical components described above, the body 12 also contains components such as a battery 36, a battery case 38, and a flight controller 40. The battery 36 is the power source for the unmanned aerial vehicle 10. The battery 36 is contained in a battery case 38 inside the body 12. The battery case 38 is made of a resin such as CFRP or GFRP, or a metal such as an aluminum alloy.

The flight controller 40 controls the flight of the unmanned aerial vehicle 10 according to commands input from the command terminal. For example, the flight controller 40 controls the position and attitude of the unmanned aerial vehicle 10 so that the unmanned aerial vehicle 10 flies autonomously according to a flight route instructed from the command terminal. Alternatively, the flight controller 40 may search for an object instructed from the command terminal, calculate a target flight route, and fly autonomously up to above the object according to the calculated target flight route. There are no limitations to the flight control of the unmanned aerial vehicle 10. In other words, various methods for flight control of unmanned aerial vehicles have already been proposed in many documents. The unmanned aerial vehicle 10 of this embodiment can adopt well-known flight control as appropriate.

2. Pressure-resistant and explosion-proof structure of the unmanned aerial vehicle The unmanned aerial vehicle 10 of this embodiment is designed to fly in an explosion-proof area where flammable gas may be present, such as a chemical plant. Specifically, the unmanned aerial vehicle 10 is an explosion-proof unmanned aerial vehicle designed in accordance with the pressure-resistant and explosion-proof structure (IEC60079-1) of the IEC standard. FIG. 5 is a perspective view of the unmanned aerial vehicle according to the embodiment, seen from the bottom side. Note that the propeller guard 18 on the left side of the aircraft is omitted in FIG. 5. Below, the main pressure-resistant and explosion-proof structure of the unmanned aerial vehicle 10 will be described in more detail with reference to FIG. 5.

The rear side of the body 12 functions as an outlet for removing the battery 36 and other items stored inside. For this reason, the head rear 28 is detachably screwed to the rear side of the body 12, thereby realizing a pressure-resistant explosion-proof structure.

2-2. Pressure-resistant and explosion-proof structure around the lens The first camera lens 20 is joined to the first lens cover 202 by filling the outer periphery with resin to form a fixed joint 204. The first lens cover 202 is screwed to the front part of the body 12. This realizes a pressure-resistant and explosion-proof structure around the first camera lens 20 and the first lens cover 202.

The second camera lens 22 is joined to the second lens cover 222 by filling the outer periphery with resin to form a fixed joint (not shown). The second lens cover 222 is joined to the front part of the body 12 by filling the outer periphery and the threaded part of the body 12 with resin to form a fixed joint (not shown). Furthermore, the LED lens 24 and the sensor lens 26 are joined to the body 12 by filling the outer periphery of each lens with resin to form fixed joints 242, 262. This realizes a pressure-resistant explosion-proof structure around the second camera lens 22, the second lens cover 222, the LED lens 24, and the sensor lens 26.

2-3. Pressure-resistant explosion-proof structure around the antenna A fixed joint is formed by filling resin around the portion where the antenna 32 is taken out from inside the body 12. This realizes a pressure-resistant explosion-proof structure around the antenna 32.

2-4. Pressure-resistant explosion-proof structure of the arm pipe base end Fig. 6 is a diagram showing part of a cross section of the arm pipe taken along a plane passing through the central axis of the arm pipe and parallel to the front-rear direction. The fixed pipe 8 is a cylindrical part for fixing the base end of the arm pipe 16 to the body 12. Typically, the fixed pipe 8 is made of a metal such as an aluminum alloy, and is joined by welding while inserted into a through hole 6 provided in the body 12. In other words, the fixed pipe 8 is fixed so that it communicates with the inside and outside of the body 12. A welded part 82 is formed around the entire circumference of the joint between the fixed pipe 8 and the body 12. The inner diameter of the fixed pipe 8 is larger than the outer diameter of the arm pipe 16. The arm pipe 16 is joined by adhesive (resin) while inserted into the tip end 8a of the fixed pipe 8. An adhesive part 84 is formed around the entire circumference of the joint between the fixed pipe 8 and the arm pipe.

In the present embodiment, the unmanned aerial vehicle 10 has a basic thickness of the body 12 set to t = 2 mm in order to reduce weight. Therefore, when force is applied to the tip of the arm pipe 16, stress is concentrated at the base end of the arm pipe 16, which may cause cracks in the welded portion of the fixed pipe 8.

Therefore, the unmanned aerial vehicle 10 of this embodiment is provided with a thick-walled portion 4 that is thicker than the basic thickness of the body 12 in a predetermined area surrounding the fixed pipe 8. Typically, the thick-walled portion 4 is thickened by applying a rectangular padding to the surface of the body 12. The body thickness of the thick-walled portion 4 is set to t = 10 mm, including the basic thickness of 2 mm, for example. With this configuration, the stress of the force applied to the tip of the arm pipe 16 is concentrated at the boundary between the thick-walled portion 4 at t = 10 mm and the body 12 at t = 2 mm, reducing the load on the welded portion 82 of the fixed pipe 8. This makes it possible to prevent cracks from occurring in the welded portion 82 of the fixed pipe 8 while minimizing the increase in the weight of the unmanned aerial vehicle 10.

In addition, the motor cable 42 is pulled into the body 12 through the arm pipe 16 and the inside of the fixed pipe 8. Therefore, if the arm pipe 16 is damaged by impact, the inside of the body 12 will be connected to the outside atmosphere, and the pressure-resistant explosion-proof structure will not be able to be maintained.

Therefore, in the unmanned aerial vehicle 10 of this embodiment, in order to realize a pressure-resistant explosion-proof structure, a sealing structure for sealing the communication between the inside and outside of the body 12 is provided inside the tube of the fixed pipe 8. Typically, the sealing structure includes a fixed joint 44 in which resin is filled and hardened in the middle part 8b between the tip end 8a and the base end 8c of the fixed pipe 8. The sealing structure also includes a cable clamp 46 attached to the base end 8c of the fixed pipe 8. The cable clamp 46 is for holding the cable 42 in a clamped state, and is made of a metal such as an aluminum alloy or a resin such as nylon. The cable clamp 46 fills the gap between the inner wall of the base end 8c and the fixed joint 44 with resin and hardens it, thereby sealing the inside of the fixed pipe 8 more firmly. With this sealing structure, the pressure-resistant explosion-proof structure of the body 12 of the unmanned aerial vehicle 10 is maintained even if the arm pipe 16 is damaged. This prevents the unmanned aerial vehicle 10 from becoming a source of ignition even if the arm pipe 16 of the unmanned aerial vehicle 10 is damaged in an explosion-proof area.

In particular, in the unmanned aerial vehicle 10 of this embodiment, the arm pipe 16 is joined to the fixed pipe 8 with an adhesive. In other words, the joining strength of the arm pipe 16 to the fixed pipe 8 is weaker than the joining strength of the fixed pipe 8 to the body 12. For this reason, when a load is applied to the arm pipe 16, the adhesive portion 84 of the arm pipe 16 breaks and comes off before cracks occur in the welded portion 82 of the fixed pipe 8. This makes it possible to prevent cracks from occurring in the welded portion 82 of the fixed pipe 8, thereby maintaining the pressure-resistant and explosion-proof structure of the body 12.

2-5. Surface Treatment of Unmanned Aerial Vehicle The unmanned aerial vehicle 10 of this embodiment is subjected to a surface treatment in which a polyurethane resin, which is an elastic body having impact resistance, is applied to the surface of the aircraft. Polyurea resin is a resin whose main component is polyurethane, and is a compound mainly composed of bonds formed by a chemical reaction between isocyanate and amine groups. FIG. 7 is a diagram for explaining the surface treatment applied to the unmanned aerial vehicle of this embodiment. As shown in this figure, the unmanned aerial vehicle 10 of this embodiment has a protective layer 2 of polyurethane resin applied to the surface of the body 12 including the thick portion 4 and the fixed pipe 8. In FIG. 8, the area where the protective layer 2 is applied is shown by hatching. For example, LINE-X (registered trademark (LINE-X LLC)) can be used as the polyurea resin. The applied thickness of the protective layer 2 is, for example, 1.5 mm or more. However, if the applied thickness of the protective layer 2 exceeds 4.0 mm, it becomes difficult to maintain the uniformity of the applied thickness, and the flight time is shortened due to excessive weight. For this reason, it is preferable to set the coating thickness of the protective layer 2 to 1.5 mm or more and 4.0 mm or less. With this configuration, it is possible to realize a pressure-resistant and explosion-proof structure that further improves the impact resistance of the unmanned aerial vehicle 10.

In addition, the protective layer 2 is not applied to the arm pipe 16, propeller guard 18, body guide 34, or head rear 28. With this configuration, if a load is applied to the arm pipe 16 or propeller guard 18, these parts will break first, preventing cracks in the welds of the fixed pipe 8. Also, by limiting the areas where the protective layer 2 needs to be applied, the increase in aircraft weight can be kept to a minimum.

The protective layer 2 made of polyurea resin may become charged with static electricity. If static electricity discharge occurs in an explosion-proof area, it may become a source of ignition. Therefore, in the unmanned aerial vehicle 10 of this embodiment, a conductive paint is applied to the surface of the protective layer 2. Typical examples of the conductive paint include polyester urethane-based silver-copper conductive paint and carbon-based conductive paint. Here, the conductive paint is applied so that the surface resistance of the aircraft is 1.0×10 ⁹ Ω or less. With this configuration, a conductive coating film is formed on the surface of the protective layer 2, making it possible to reduce the risk of static electricity charging in the explosion-proof area.

The inventors of the present application conducted tests to verify the effectiveness of the pressure-resistant and explosion-proof structure of the unmanned aerial vehicle 10 of the present embodiment. These tests and the results of their consideration will be described below.

4-1. Strength Analysis Test 4-1-1. Overview An analytical model was used to analyze the load stress generated at the base end of the arm pipe when a downward load is applied to the tip end of the arm pipe of the unmanned aerial vehicle of this embodiment. The design parameters to be compared were the presence or absence of a fixed pipe, the thickness of the body, and the thickness of the thick portion. The analytical values calculated were the load stress at the weld between the fixed pipe and the thick portion, and the load stress at the joint between the fixed pipe and the arm pipe.

4-1-2. Configuration of the strength analysis model Figure 8 is a schematic diagram of the analysis model of the unmanned aerial vehicle of this embodiment. As shown in this figure, the analysis model is configured to include a body, thick-walled portion, fixed pipe, and arm pipe that are equivalent in structure to the unmanned aerial vehicle 10 of this embodiment. The analysis parameters of the analysis model were set as follows:

[Analysis software]
Femap With NX Nastran
[Analysis parameters]
Body: Material A5056, thickness is 2, 4, 10, 15 (mm) Fixed pipe: Material A5056, thickness is 2mm
Arm pipe: Material: A5056, thickness: 2mm

[Mechanical properties of material A5056 (aluminum alloy)]
Modulus of elasticity: 70.6 kN/ ^mm2
Poisson's ratio: 0.34
[Analysis conditions]
Load: Applied downward to the tip of the arm pipe. Restraint conditions: Fully restrain the end of the body.

4-1-3. Strength analysis results The strength analysis results are shown in Table 1. Note that, because the analysis was performed under the same analysis conditions for all models, the analysis values (stress values) were calculated as the average values for each model. In addition, the analysis values (stress values) are listed as comparative values when the maximum stress value among all models is set to 1.

4-1-4. Consideration of strength analysis results When the body thickness was 4 mm without the fixed pipe (No. 2), the load on the welded part was reduced to about 44% compared to the 2 mm body thickness, but the weight increased by about 1.61 times. On the other hand, when the body thickness was 2 mm, the thick part was 2 mm thick, and the fixed pipe was included (No. 7), the load on the welded part was reduced to about 25%, and the weight increased by only about 1.11 times. This confirmed that adding the fixed pipe is a structure that reduces the load on the welded part while suppressing the increase in weight.

Furthermore, it was confirmed that the load on the welded part is gradually reduced as the thickness of the thicker part increases, and when the thickness of the thicker part is 2 mm or more, the load is greater at the fixed pipe-arm pipe joint than at the welded part.

The above strength analysis results confirmed that the load on the welded parts can be reduced by welding the fixed pipe to the body rather than directly welding the arm pipe to the body, locally increasing the body thickness around the welded parts, and joining the arm pipe and fixed pipe with adhesive.

4-2. Impact Test 4-2-1. Overview A test arm pipe (test specimen) simulating the mounting structure of arm pipe 16 of unmanned aerial vehicle 10 of this embodiment was set horizontally, and a weight was dropped vertically onto the tip of the arm pipe to apply an impact. The weight drop height, the presence or absence of a fixed pipe, and the thickness of the body + thick part were changed to check for the presence or absence of cracks in the welded part of the arm pipe.

4-2-2. Testing Equipment Figure 9 is a diagram showing an outline of the testing equipment for the shock test. The testing equipment 100 comprises a main body 102, a guide 106, and a weight 104. An arm pipe for testing is fixed to the lower part of the main body. The testing equipment 100 is configured so that the weight 104 passes through the inside of the guide 106 and falls onto the tip of the arm pipe.

Figure 10 is a cross-sectional view for explaining the configuration of the test arm pipe. As shown in this figure, the test arm pipe is composed of a test arm pipe, fixed pipe, and body + thick section, simulating the configuration of the arm pipe 16, fixed pipe 8, body 12, and thick section 4 of the unmanned aerial vehicle 10. The fixed pipe is welded to the body + thick section, and a welded section is formed at the joint. The arm pipe is glued to the fixed pipe, and an adhesive section is formed at the joint. For the impact test, seven types of test specimens were prepared, differing in the thickness (A) of the body + thick section and the presence or absence of a fixed pipe.

The test conditions for this impact test are as follows:
Weight: 1.0 kg
Weight falling height: 100mm to 2000mm
Arm pipe: Material: A5056, diameter: φ14mm, thickness: t1.0mm
Fixed pipe: Material A5056, diameter φ20mm, thickness t2.0mm

4-2-3. Impact test results The impact test results are shown in Table 2. Note that the "drone drop height" in the table corresponds to the height at which the unmanned aerial vehicle 10 was dropped. In this test, the impact force applied to the tip of the arm pipe 16 when the unmanned aerial vehicle 10 was dropped was calculated using the following formula (1) (see Table 3). Then, the drop height of the weight equivalent to the calculated impact force was calculated (see Table 4).

F=m・V/(t・g)...(1)
F: Impact force [kgf]
m: Speed just before deceleration [m/s]
g: Gravitational acceleration 9.81 [m/s ² ]

4-2-4. Consideration of impact test results When comparing the presence and absence of a fixed pipe when the body + thick part thickness is 4 mm (No. 2 and No. 4), it was confirmed that the one with the fixed pipe had better impact resistance at the welded part.
The body + thick part thickness of 15 mm without a fixed pipe (No. 3) and the 5 mm thickness with a fixed pipe (No. 5) had the same impact resistance. When comparing the weights shown in Table 4, the 15 mm thickness weighs 3,160 g, while the 5 mm thickness with a fixed pipe weighs 665 g, which means that the same impact resistance is achieved with about 20% of the weight of the 15 mm thickness.
No. 4 could not withstand 0.9 m (drone drop height: 10 m), but No. 5 and onwards were confirmed to be able to withstand 1.35 m (drone drop height: 15 m).

These results confirm that if the fixed pipes are welded and the body + thickened parts are a total of 5 mm or more, it is possible to withstand a drop height of 15 m while minimizing weight increase. It was also confirmed that by locally thickening only the area around the weld, it is possible to reduce the load on the weld while suppressing weight increase compared to thickening the entire body.

4-3. Drop Test 4-3-1. Overview A drop test was conducted to confirm the effect of applying protective layer 2 of polyurethane resin to unmanned aerial vehicle 10 of the present embodiment. Figure 11 is a diagram showing an overview of the drop test. In the drop test, unmanned aerial vehicle 10 was dropped from a specified drop height, and then the breakage and peeling state of the polyurethane resin was confirmed.

4-3-2. Test conditions The test conditions for this drop test are as follows:
[Polyurea resin used]
Product name: LINE-X (registered trademark) (LINE-X LLC)
Product number: XS-350
Composition: Polyisocyanate 50wt%, Polyamine 50wt%
Description: 100% polyurea elastomer made by heating and mixing agent A (curing agent) of an isocyanate mixture and agent B (resin) which is a polyol/aromatic diamine mixture. [Test conditions]
Polyurea resin coating thickness: 1.0 mm, 1.5 mm, 2.0 mm
Landing floor: Concrete Fall height: 1m, 10m, 15m, 20m
Number of tests: 1 Criteria: Meet IPX7 (JIS C 0920 Protection class for the outer shell of electrical equipment)
IPX7 test conditions: The bottom end of the test specimen is submerged 1 m below the water surface for 30 minutes.

4-3-3. Drop test results The drop test results are shown in Table 5.

4-3-4. Consideration of drop test results When no polyurethane resin was applied (No. 1), a crack occurred in the weld at the base end of the arm pipe. As a result of the IPX7 test, water was confirmed to have entered the interior.
In the case where the polyurea resin was applied (No. 2), if the thickness was 1.5 mm or more, no breakage of the polyurea resin was observed visually when dropped from a maximum height of 20 m. In addition, as a result of the IPX7 test, no water intrusion was observed inside.
Regarding the coating thickness of the polyurea resin, if the thickness exceeds 4.0 mm, it is difficult to maintain uniformity of the coating thickness due to the complex shape of the unmanned aerial vehicle 10. In addition, since there is a concern that the weight will be too heavy and the flight time will be shortened, the coating thickness is preferably 4.0 mm or less.
As a result of carrying out the drop test, it was confirmed that the impact resistance of the structure No. 5, which could not withstand a 20 m drop in the impact test shown in Table 5, was significantly improved by applying a polyurethane resin having a thickness of 1.5 mm or more to the structure No. 5, and that the structure could withstand a 20 m drop.

4-4. Conductivity Test 4-4-1. Overview A conductive paint was applied to the unmanned aerial vehicle 10 coated with the protective layer 2 of polyurea resin, and then the surface resistance was measured.

4-4-2. Test conditions
[Conductive paint used]
Product name: Polycalm (Pluscoat Co., Ltd.)
Product number: PCS-1201S
Ingredients: As shown in Table 6 [Resistance meter]
Product name: Digital multimeter (HIOKI E.E. CORPORATION)
Product number: DT4282
[Test condition]
Polycalm was applied to the surface of a protective layer of polyurea resin (LINE-X (registered trademark)), and the surface resistance was measured after drying for 12 hours. Figure 12 shows the locations where the surface resistance of an unmanned aerial vehicle was measured. In this test, the surface resistance was measured between A-B, A-C, A-D, B-C, B-D, and C-D shown in the figure.

4-4-3. Conductivity test results The conductivity test results are shown in Table 7.

4-4-4. Consideration of the electrical conductivity test results It was confirmed that the electrical conductivity was 1.0 x 10 ⁹ Ω or less at all measurement points. From these results, it was confirmed that the application of the conductive paint can reduce the risk of static electricity buildup.

5. Modifications The explosion-proof structure applied to the unmanned aerial vehicle 10 of this embodiment may adopt the following modified forms.

The configuration of the cable clamp 46 as a sealing structure is not essential. That is, the cable clamp 46 may be configured as a fixed joint that is filled with resin and hardened, similar to the fixed joint 44. The configuration of the thick-walled portion 4 is also not essential.

There is no limitation on the type of polyurea resin used in the protective layer 2. Similarly, there is no limitation on the type of conductive paint as long as it satisfies the standard that the surface resistance value is 1.0×10 ⁹ Ω or less.

There are no limitations to the pressure-resistant explosion-proof structure of the head rear 28, the pressure-resistant explosion-proof structure around the lenses 20, 22, 24, and 26, and the pressure-resistant explosion-proof structure around the antenna 32. These pressure-resistant explosion-proof structures can be appropriately applied using pressure-resistant explosion-proof structures that are already publicly known.

2 Protective layer 4 Thick portion 6 Through hole 8 Fixed pipe 8a Tip portion 8b Middle portion 8c Base portion 10 Unmanned aerial vehicle 12 Body 14 Propeller 16 Arm pipe 18 Propeller guard 20 First camera lens 22 Second camera lens 24 LED lens 26 Sensor lens 28 Head rear 30 Motor case 32 Antenna 34 Body guide 36 Battery 38 Battery case 40 Flight controller 42 Cable 44 Fixed joint 46 Cable clamp 82 Welded portion 84 Adhesive portion 100 Test device 102 Main body 104 Weight 106 Guide 202 First lens cover 204 Fixed joint 222 Second lens cover 242, 262 Fixed joint

Claims (8)

A body that houses electrical equipment inside,
a cylindrical fixed pipe that is inserted into a through hole provided in the body so as to communicate with the inside and outside of the body and is fixed in a state protruding from the inside and outside of the body ;
A propeller that generates thrust;
a hollow tubular arm pipe that supports the propeller and through which a cable of the propeller is passed;
a sealing structure provided inside the fixed pipe and configured to seal communication between the inside and the outside of the body,
The explosion-proof unmanned aerial vehicle is characterized in that the arm pipe is configured to be fixed in a state where it is inserted into the fixed pipe. The explosion-proof unmanned aerial vehicle according to claim 1, characterized in that the body has a thick-walled portion in a predetermined area surrounding the fixed pipe, the thickness of which is configured to be thicker than the thickness of other areas. The sealing structure includes:
3. The explosion-proof unmanned aerial vehicle according to claim 1 or 2, characterized in that it is configured to include a fixed joint portion formed by hardening a resin filled inside the fixed pipe. The cable is configured to be drawn from the fixed pipe into the inside of the body,
The explosion-proof unmanned aerial vehicle described in any one of claims 1 to 3, characterized in that the sealing structure includes a cable clamp that holds the cable inside the fixed pipe and is adhered to the inner wall of the fixed pipe. The fixed pipe is joined to the body by welding,
The explosion-proof unmanned aerial vehicle according to any one of claims 1 to 4, characterized in that the arm pipe is configured to be joined to the fixed pipe by adhesive using a resin. The explosion-proof unmanned aerial vehicle according to any one of claims 1 to 5, further comprising a protective layer containing a polyurea resin applied to the surface of the body and the fixed pipe. The explosion-proof unmanned aerial vehicle according to claim 6, characterized in that the arm pipe is configured so that the protective layer containing the polyurea resin is not applied to the surface. The explosion-proof unmanned aerial vehicle according to claim 6 or 7, further comprising a conductive coating applied onto the protective layer.

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