Intelligent detection equipment for building wall crack detection

Abstract

The invention discloses intelligent detection equipment for building wall surface crack detection, and relates to the technical field of building detection, the intelligent detection equipment comprises a shell and an insertion rod, the insertion rod is fixedly mounted on one side of the shell, and the insertion rod is used for being inserted into a building gap; according to the device, an operator firstly aligns the front end of an insertion rod to a wall gap, tightly holds a shell handle and slowly inserts the insertion rod into the gap with stable and uniform force, in the insertion rod penetrating process, wall bodies on the two sides of the gap extrude a circular plate and a first air bag, air in the first air bag stably flows into a measuring cylinder through an air inlet pipe, and a piston is pushed to stably move upwards; as the first air bag and the measuring cylinder are equal in length and always equal in gas quantity, a stable foundation can be provided for accurate measurement and analysis of crack parameters, and the stable measurement mechanism can keep the performance of equipment stable even if being interfered by environmental factors such as wall materials and illumination in a complex construction site, and the measurement accuracy is greatly improved when a large number of wall cracks are continuously detected. Errors can be reduced, efficiency is improved, and accuracy and reliability of detection results are guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of building detection, and in particular to intelligent detection equipment for detecting cracks on building walls. Background Art

[0002] With the continuous development and progress of modern construction engineering technology, the requirements for building quality are becoming higher and higher. In particular, it is necessary to reduce harmful cracks in construction projects to avoid affecting the durability and applicability of the overall structure.

[0003] Existing detection equipment often focuses on detecting the surface features of cracks, such as crack width, length, and surface direction, but has a relatively weak detection capability for the key parameter of crack depth. Some equipment uses a simple optical measurement method to estimate the depth based on the reflection and refraction of light on the crack surface. However, this method is severely affected by factors such as wall material, surface roughness, and lighting conditions, resulting in large errors in the detection results and an inability to accurately reflect the true depth of the crack. Summary of the invention

[0004] The purpose of the present invention is to provide an intelligent detection device for detecting cracks in building walls to solve the problems raised in the above-mentioned background technology.

[0005] In order to solve the above technical problems, the present invention provides an intelligent detection device for detecting cracks on building walls, comprising a shell, a plug rod, which is fixedly installed on one side of the shell, and the plug rod is used to be inserted into the interior of the building gap; a first air bag, which is sleeved on the outer wall of the plug rod, and the front and rear ends of the plug rod are fixedly installed with circular plates, and the circular plate arranged at the rear end of the plug rod is fixedly installed on the shell, and the thickness of the circular plate at the rear end is greater than that of the front end; an air intake pipe, which is fixedly installed on one of the circular plates, and a measuring cylinder is installed on the other end, and a one-way valve is fixedly installed on the air intake pipe, and a rubber layer for preventing air leakage is provided at the part of the circular plate that contacts the plug rod; a measuring cylinder, which is fixedly installed on the inner bottom wall of the shell, and a scale is provided on the outer wall of the measuring cylinder; a piston, which is provided on the inner wall of the measuring cylinder; The air outlet pipe is fixedly installed between the first air bag and the measuring cylinder, and another one-way valve is fixedly installed on the air outlet pipe.

[0006] Furthermore, a first annular airbag is fixedly installed on the front end of the insertion rod, the first annular airbag is connected to a ventilation tube, a second annular airbag is fixedly installed on the other end of the ventilation tube, mounting plates are fixedly installed on both sides of the second annular airbag, a return spring is fixedly installed on one side of the mounting plate, a measuring plate is fixedly installed on the other end of the return spring, the measuring plate is abutted against the second annular airbag, and a measuring ruler is fixedly installed on the top of the outer shell.

[0007] Furthermore, a tension spring is fixedly installed between the two circular plates, and the tension spring is sleeved on the outside of the insertion rod. A contraction spring and a guide telescopic rod are fixedly installed between the piston and the inner top wall of the measuring cylinder, and the contraction spring is sleeved on the outside of the guide telescopic rod.

[0008] Furthermore, another guiding telescopic rod is fixedly installed between the mounting plate and the measuring plate, the reset spring is sleeved on the outside of the other guiding telescopic rod, and the measuring plate is arranged on one side of the measuring ruler.

[0009] Furthermore, a plurality of reset members are fixedly mounted on one side of the first annular airbag, the cross-section of the reset member is set to be S-shaped, and the reset member is evenly arranged in an annular shape inside the first annular airbag.

[0010] Furthermore, a reset rod is fixedly installed inside the first annular airbag, and the reset rod is composed of a sliding rod and a sleeve rod, and a telescopic spring is fixedly installed between the sliding rod and the sleeve rod.

[0011] Furthermore, a camera is fixedly mounted on a side of the housing opposite to the wall, and a micro display screen is arranged on the top of the housing.

[0012] Furthermore, a circular groove adapted to the first annular airbag is formed on the circular plate, and the first annular airbag is flush with the front side of the circular plate.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. In the present invention, when detecting cracks on building walls, the operator first aligns the front end of the insertion rod with the wall gap, holds the outer shell handle tightly, and slowly inserts the insertion rod into the gap with a steady and even force. During the insertion of the rod, the walls on both sides of the gap squeeze the circular plate and the first air bag, so that the gas in the first air bag flows steadily into the measuring cylinder through the air inlet pipe, pushing the piston to move steadily upward. Since the first air bag and the measuring cylinder are equal in length and the amount of gas is always the same, a stable basis can be provided for accurate measurement and analysis of crack parameters. In complex construction sites, even if disturbed by environmental factors such as wall material and light, the stable measurement mechanism can keep the performance of the equipment stable. When continuously detecting a large number of wall cracks, it can reduce errors, improve efficiency, and ensure the accuracy and reliability of the detection results.

[0014] 2. In the present invention, before detecting the width of the gap in the building wall, the initial diameter of the first airbag ring must be accurately recorded. When the rod is inserted into the gap, the wall exerts pressure on the first airbag ring, and the internal gas flows to the second airbag ring through the ventilation pipe. Since the gas volumes of the two are the same, the inflow of gas will cause the second airbag ring to expand and increase its diameter. By measuring the change in its diameter and based on the conversion relationship, the actual width of the gap can be calculated, thereby achieving efficient and accurate detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a schematic diagram of the internal structure of the present invention; Figure 3 It is a schematic diagram of the connection structure between the mounting plate and the return spring in the present invention; Figure 4 It is a schematic diagram of the connection structure between the first airbag and the mounting plate in the present invention; Figure 5 It is a schematic diagram of the connection structure between the first annular airbag and the resetting member in the present invention; Figure 6 It is a schematic diagram of the overall structure of the reset rod in the present invention.

[0016] In the figure: 1. shell; 2. plug rod; 3. first air bag; 4. air inlet pipe; 5. measuring cylinder; 6. piston; 7. air outlet pipe; 8. first annular air bag; 9. vent pipe; 10. second annular air bag; 11. mounting plate; 12. reset spring; 13. measuring plate; 14. measuring ruler; 15. reset member; 16. reset rod; 17. round plate; 18. contraction spring; 19. extension spring; 20. camera. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] See also Figure 1-Figure 6 , the present invention provides a technical solution: See also Figure 1-Figure 6 As shown, an intelligent detection device for detecting cracks on a building wall comprises a shell 1, a plug rod 2, which is fixedly mounted on one side of the shell 1, and the plug rod 2 is used to be inserted into the interior of a building gap; a first air bag 3, which is sleeved on the outer wall of the plug rod 2, and the front and rear ends of the plug rod 2 are fixedly mounted with circular plates 17, and the circular plate 17 arranged at the rear end of the plug rod 2 is fixedly mounted on the shell 1, and the thickness of the circular plate 17 at the rear end is greater than that of the front end; an air inlet pipe 4, which is fixedly mounted on one of the circular plates 17, and a measuring cylinder 5 is mounted on the other end, and a one-way valve is fixedly mounted on the air inlet pipe 4, and a rubber layer for preventing air leakage is arranged on the portion where the circular plate 17 contacts the plug rod 2; a measuring cylinder 5, which is fixedly mounted on the inner bottom wall of the shell 1, and a scale is arranged on the outer wall of the measuring cylinder 5; a piston 6, which is arranged on the inner wall of the measuring cylinder 5; an air outlet pipe 7, which is fixedly mounted between the first air bag 3 and the measuring cylinder 5, and another one-way valve is fixedly mounted on the air outlet pipe 7.

[0019] When inspecting cracks on building walls, the operator first needs to accurately align the front end of the insertion rod 2 with the gap to be inspected on the building wall. Then, the operator holds the handle on the shell 1 tightly, and with a stable and uniform force, uses the shell 1 as a support for applying force to slowly push the insertion rod 2 into the depth of the gap. During this process, the insertion rod 2 will gradually penetrate into the interior of the building gap. Since the walls on both sides of the gap form an extrusion effect on the circular plate 17 and the first airbag 3 installed thereon, the gas originally contained in the first airbag 3 will be driven by the pressure and flow into the internal space of the measuring cylinder 5 through the air inlet pipe 4 connected thereto in a stable airflow form. As the gas continues to flow in, the piston 6 inside the measuring cylinder 5 will be subjected to the thrust of the gas, and then steadily move upward along its axial direction inside the measuring cylinder 5. It is worth noting that the first airbag 3 and the measuring cylinder 5 have a specific consistency in design, that is, the lengths of the two are completely equal, which is It ensures that when the first airbag 3 is squeezed and compressed, its compressed length can be precisely consistent with the length of the piston 6 moving in the measuring cylinder 5, and from the perspective of gas volume, the amount of gas contained in the first airbag 3 and the amount of gas received in the measuring cylinder 5 are always kept the same, thereby providing a reliable and stable basic condition for the subsequent accurate measurement and analysis of crack-related parameters based on gas volume changes. In complex construction sites, environmental factors may interfere with the detection equipment. This stable and reliable measurement mechanism enables the equipment to maintain relatively stable measurement performance under different environmental conditions, such as temperature changes, slight vibrations, wall materials, light and other factors that interfere with depth measurement. This is very important for ensuring the accuracy and reliability of the detection results, especially when a large number of wall cracks need to be continuously detected. The stable measurement mechanism can reduce measurement errors and improve detection efficiency.

[0020] It should be noted that the measuring cylinder 5 is made of transparent material, the one-way valve on the air inlet pipe 4 can only take in air, and the other one-way valve on the air outlet pipe 7 is equipped with a switch. When the next measurement is required, it is necessary to press the switch to release the gas in the measuring cylinder 5, and the released gas flows back to the inside of the first airbag 3 through the air outlet pipe 7.

[0021] See also Figure 2 A first annular airbag 8 is fixedly installed at the front end of the insertion rod 2, and the first annular airbag 8 is connected to a ventilation pipe 9. A second annular airbag 10 is fixedly installed at the other end of the ventilation pipe 9. Mounting plates 11 are fixedly installed on both sides of the second annular airbag 10. A return spring 12 is fixedly installed on one side of the mounting plate 11, and a measuring plate 13 is fixedly installed on the other end of the return spring 12. The measuring plate 13 is against the second annular airbag 10, and a measuring ruler 14 is fixedly installed on the top of the outer shell 1.

[0022] Before carrying out the inspection of the width of the gap in the building wall, it is necessary to first carefully observe and accurately record the initial value of the diameter of the first annular airbag 8, which will be used as a basic data reference for subsequent measurement and calculation. When the insertion rod 2 gradually penetrates into the wall gap, the wall structure on both sides of the gap will exert pressure on the first annular airbag 8, causing the gas inside it to be driven by the pressure difference and transmitted to the second annular airbag 10 through the ventilation pipe 9 connected thereto. Given that the first annular airbag 8 and the second annular airbag 10 are designed to have completely identical gas volumes, when the gas in the first annular airbag 8 is squeezed into the second annular airbag 10, the second annular airbag 10 will expand due to the injection of gas, and its diameter will increase accordingly. At this time, by accurately measuring and observing the change in the diameter of the second annular airbag 10, the actual width of the wall gap can be accurately calculated based on the pre-set conversion relationship, thereby achieving efficient and accurate detection of the width of the building wall gap.

[0023] See also Figure 4 A tension spring 19 is fixedly installed between the two circular plates 17, and the tension spring 19 is sleeved on the outside of the insertion rod 2. A contraction spring 18 and a guide telescopic rod are fixedly installed between the piston 6 and the inner top wall of the measuring cylinder 5, and the contraction spring 18 is sleeved on the outside of the guide telescopic rod.

[0024] When the detection operation is completed, the insertion rod 2 is smoothly pulled out of the building gap, so that the extrusion force on the circular plate 17 and the first airbag 3 disappears instantly. At this time, the tension spring 19, relying on its own stored elastic potential energy, quickly releases the elastic force, accurately pushes the front circular plate 17 to move to the initial position, and then drives the front end part of the first airbag 3 connected thereto to start the reset action. At the same time, the contraction spring 18, under the action of the elastic force, forcefully pushes the piston 6 downward along the inner wall of the measuring cylinder 5, thereby squeezing out the air in the measuring cylinder 5. Under the action of the pressure difference, the gas inside the measuring cylinder 5 flows smoothly to the internal space of the first airbag 3, prompting the first airbag 3 to gradually return to its original state before being squeezed, thereby making full preparations for the next measurement operation, ensuring that the equipment can efficiently and stably perform multiple continuous tests, greatly improving the overall efficiency and convenience of the detection work.

[0025] See also Figure 3 Another guide telescopic rod is fixedly installed between the mounting plate 11 and the measuring plate 13 , the reset spring 12 is sleeved on the outside of the other guide telescopic rod, and the measuring plate 13 is arranged on one side of the measuring ruler 14 .

[0026] The guide telescopic rod arranged between the mounting plate 11 and the measuring plate 13 provides a precise guide path for the movement of the measuring plate 13. During the detection process, when the measuring plate 13 is subjected to external force, the guide telescopic rod restricts it to move only along a predetermined straight line direction, thereby avoiding measurement errors caused by shaking, offset or twisting of the measuring plate 13. At the same time, the reset spring 12 is sleeved on the outside of the guide telescopic rod. When the external force causes the measuring plate 13 to deviate from the initial position, the reset spring 12 will produce corresponding elastic deformation, and its elastic force will prompt the measuring plate 13 to quickly return to the initial position after the force disappears, thereby ensuring that the starting state of each measurement is consistent, thereby improving the repeatability and accuracy of the measurement. For example, when measuring the width of a crack on a wall, the measuring plate 13 needs to fit closely to the edge of the crack. Without the stable support of the guide telescopic rod and the reset function of the reset spring 12, the measuring plate 13 may not be accurately aligned with the edge of the crack, resulting in deviations in the measurement results.

[0027] See also Figure 5 A plurality of reset members 15 are fixedly mounted on one side of the first annular airbag 8 . The cross section of the reset member 15 is set to an S shape. The reset member 15 is evenly arranged in an annular shape inside the first annular airbag 8 .

[0028] When the first annular airbag 8 is squeezed or expanded, the pressure and distribution of the gas inside it will change. The existence of the S-shaped reset member 15 can guide the flow direction of the gas to a certain extent, so that the gas is more evenly distributed in the annular airbag. For example, in the process of gas flowing from the first annular airbag 8 to the second annular airbag 10, if there is such a gas transmission mechanism, the reset member 15 can prevent the gas from gathering in a local area or forming turbulence, ensuring that the gas can be transmitted smoothly and stably, thereby ensuring that the crack measurement principle based on gas pressure or volume changes can function accurately.

[0029] During the long-term detection process, the first annular airbag 8 will be frequently subjected to the cycle of squeezing and recovery, which can easily lead to material fatigue and reduce its performance and life. The elastic buffering effect of the reset member 15 can effectively reduce the stress concentration on the first annular airbag 8 and disperse the influence of external force on the airbag material. In each cycle, the reset member 15 absorbs and releases part of the energy, reducing the deformation degree of the first annular airbag 8 itself and the stress change amplitude inside the material, thereby reducing the accumulation rate of fatigue damage and extending the service life of the first annular airbag 8.

[0030] See also Figure 6 A reset rod 16 is fixedly installed inside the first annular airbag 8. The reset rod 16 is composed of a slide rod and a sleeve rod. A telescopic spring is fixedly installed between the slide rod and the sleeve rod.

[0031] When the first annular airbag 8 is deformed by external force, the sliding rod in the reset rod 16 will move relative to the sleeve rod, causing the telescopic spring to be compressed or stretched, thereby storing elastic potential energy. Once the external force disappears, the telescopic spring will push the sliding rod back to its initial position by virtue of its characteristic of restoring its original state, thereby driving the first annular airbag 8 to return to its original shape and position. For example, when detecting cracks in the wall, the first annular airbag 8 may be deformed due to contact and squeezing with the edge of the crack. At this time, the telescopic spring of the reset rod 16 will come into play to ensure that after the detection is completed, the first annular airbag 8 can quickly and accurately return to its initial state, providing consistent starting conditions for the next detection, thereby ensuring the repeatability and accuracy of the measurement.

[0032] In the detection of cracks on building walls, it may be necessary to perform multiple measurements on multiple cracks or different parts of the same crack. The precise resetting function of the resetting rod 16 enables the device to be in the same initial state before each measurement, thus avoiding measurement errors caused by inconsistent initial states of the device. This can provide more reliable data for scenarios requiring high-precision detection, such as monitoring of cracks on building walls, and provide strong support for protecting the structural safety of buildings. At the same time, precise resetting also helps to improve detection efficiency and reduce time wasted on equipment adjustments.

[0033] See also Figure 1-2 A camera 20 is fixedly mounted on the side of the housing 1 opposite to the wall, and a micro display screen is arranged on the top of the housing 1.

[0034] The camera 20 can capture the image information of the wall in real time and transmit it to the micro display screen on the top of the shell 1. When the operator is detecting wall cracks, there is no need to use additional observation equipment or complicated operations to view the wall condition. Only by looking directly at the micro display screen, the operator can intuitively see the wall area photographed by the camera 20. This real-time visual detection method allows the operator to quickly and accurately locate the crack position and conveniently adjust the position and angle of the detection equipment according to the image information on the display screen to ensure comprehensive and detailed detection of the cracks. For example, when detecting high or difficult to directly observe wall areas, the operator can clearly see the picture taken by the camera 20 through the micro display screen and easily find cracks without the need to look up or use other climbing tools for close observation, which greatly improves the convenience and efficiency of detection.

[0035] At construction sites, especially in the detection of wall cracks in large buildings or high-rise buildings, inspectors may need to inspect walls of different heights and positions in a complex environment. At this time, the combination of camera 20 and micro display screen enables inspectors to quickly and accurately scan the wall in a relatively safe and comfortable position, avoiding the safety risks and time waste caused by frequent climbing and moving. At the same time, for some professional inspection work that requires precise measurement and recording of crack conditions, operators can clearly see the detailed features of the cracks on the display screen, such as the direction of the cracks, width changes, etc., so that they can more conveniently use relevant measurement tools for precise measurements and record the data in real time, thereby improving the accuracy and professionalism of the inspection work.

[0036] See also Figure 4 A circular groove matched with the first annular airbag 8 is opened on the circular plate 17, and the first annular airbag 8 is arranged on the circular groove, and the first annular airbag 8 is flush with the front side of the circular plate 17.

[0037] When the first annular airbag 8 and the insertion rod 2 enter the gap, the circular plate 17 and the first airbag 3 are squeezed synchronously. A circular groove adapted to the first annular airbag 8 is provided on the circular plate 17, and the first annular airbag 8 is made flush with the front side of the circular plate 17. In this way, when the insertion rod 2 drives the circular plate 17 and the first annular airbag 8 to enter the wall gap, the circular plate 17 and the first airbag 3 can be squeezed uniformly synchronously. Since the force conditions of the first annular airbag 8 and the first airbag 3 can truly reflect the pressure applied by the walls on both sides of the gap, the measurement data based on the changes in the gas in the airbag, such as the gas volume and pressure changes, can more accurately correspond to the actual situation of the gap. For example, when the squeezing force applied by the walls on both sides of the gap is evenly distributed on the circular plate 17 and the airbag, the gas in the airbag is stably compressed and transmitted to the corresponding measuring components such as the measuring cylinder 5, so that the measurement results can more accurately reflect the parameters such as the width and depth of the gap, avoiding measurement errors caused by uneven force.

[0038] In the detection of cracks on building walls, accurate measurement of crack size is crucial, especially when detecting some old buildings, high-rise buildings or buildings with high structural safety requirements. Small measurement errors may affect the assessment of the stability of the building structure. This design ensures the accuracy of the detection equipment during the measurement process, provides reliable data support for the subsequent building maintenance and repair plan formulation, and helps to take targeted measures to ensure the safe use of the building. At the same time, it also reduces the cost waste caused by unnecessary repair work due to misjudgment.

Claims

1. An intelligent detection device for detecting cracks on a building wall, comprising a housing (1), characterized in that: An insertion rod (2) is fixedly mounted on one side of the housing (1), and the insertion rod (2) is used to be inserted into a gap in a building; The first airbag (3) is sleeved on the outer wall of the insertion rod (2), and the front and rear ends of the insertion rod (2) are fixedly mounted with circular plates (17), the circular plate (17) arranged at the rear end of the insertion rod (2) is fixedly mounted on the housing (1), and the thickness of the circular plate (17) at the rear end is greater than that at the front end; An air intake pipe (4) is fixedly mounted on one of the circular plates (17), and a measuring cylinder (5) is mounted on the other end. A one-way valve is fixedly mounted on the air intake pipe (4), and a rubber layer for preventing air leakage is provided at the portion of the circular plate (17) that contacts the insertion rod (2); A measuring cylinder (5), the measuring cylinder (5) being fixedly mounted on the inner bottom wall of the housing (1), and a scale being arranged on the outer wall of the measuring cylinder (5); A piston (6) is arranged on the inner wall of the measuring cylinder (5); An air outlet pipe (7) is fixedly mounted between the first air bag (3) and the measuring cylinder (5), and another one-way valve is fixedly mounted on the air outlet pipe (7).

2. The intelligent detection device for detecting cracks in building walls according to claim 1, characterized in that: A first annular airbag (8) is fixedly mounted on the front end of the insertion rod (2), the first annular airbag (8) is connected to a ventilation tube (9), a second annular airbag (10) is fixedly mounted on the other end of the ventilation tube (9), mounting plates (11) are fixedly mounted on both sides of the second annular airbag (10), a return spring (12) is fixedly mounted on one side of the mounting plate (11), a measuring plate (13) is fixedly mounted on the other end of the return spring (12), the measuring plate (13) abuts against the second annular airbag (10), and a measuring ruler (14) is fixedly mounted on the top of the housing (1).

3. The intelligent detection device for detecting cracks in building walls according to claim 2, characterized in that: A tension spring (19) is fixedly mounted between the two circular plates (17), and the tension spring (19) is sleeved on the outside of the insertion rod (2). A contraction spring (18) and a guide telescopic rod are fixedly mounted between the piston (6) and the inner top wall of the measuring cylinder (5), and the contraction spring (18) is sleeved on the outside of the guide telescopic rod.

4. The intelligent detection device for detecting cracks in building walls as claimed in claim 3, characterized in that: Another guide telescopic rod is fixedly mounted between the mounting plate (11) and the measuring plate (13), the return spring (12) is sleeved on the outside of the other guide telescopic rod, and the measuring plate (13) is arranged on one side of the measuring ruler (14).

5. The intelligent detection device for detecting cracks in building walls as claimed in claim 4, characterized in that: A plurality of reset members (15) are fixedly mounted on one side of the first annular airbag (8); the cross-section of the reset members (15) is arranged in an S shape; the reset members (15) are evenly arranged in an annular shape inside the first annular airbag (8).

6. The intelligent detection device for detecting cracks in building walls as claimed in claim 5, characterized in that: A reset rod (16) is fixedly installed inside the first annular airbag (8), and the reset rod (16) is composed of a sliding rod and a sleeve rod, and a telescopic spring is fixedly installed between the sliding rod and the sleeve rod.

7. The intelligent detection device for detecting cracks in building walls according to claim 6, characterized in that: A camera (20) is fixedly mounted on a side of the housing (1) opposite to the wall, and a micro display screen is arranged on the top of the housing (1).

8. The intelligent detection device for detecting cracks in building walls according to claim 7, characterized in that: The circular plate (17) is provided with a circular groove adapted to fit the first annular airbag (8), and the first annular airbag (8) is flush with the front side of the circular plate (17).

Images