A method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade

Abstract

This invention discloses a method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrades. The dilution processing method includes the following steps: S1: Installing a lidar scanning system sequentially on the intelligent measurement point movement platform of the subgrade, initializing the lidar scanning system, and having the lidar scanning system scan the measurement points to collect lidar point cloud data; S2: Collecting the collected lidar point cloud data and constructing a lidar point cloud distribution map based on the lidar point cloud data collected by multiple sets of lidar scanning systems; S3: Obtaining the reflectivity and continuity parameters of the lidar point cloud, and calculating the distance between the corresponding lidar point cloud and the lidar scanning system. This invention can filter out the noise points collected by the lidar scanning system, effectively filter and dilute these noise points, thereby ensuring the accuracy of the data collected by intelligent measurement points for highway subgrades and avoiding large errors in the measurement results.

Description

Technical Field

[0001] This invention relates to the field of intelligent lidar measurement technology, and in particular to a method for noise reduction and dilution processing of intelligent measurement point clouds on highway subgrades. Background Technology

[0002] LiDAR is a general term for laser active detection sensor devices. Its working principle is that the LiDAR transmitter emits a laser beam. When the laser beam encounters an object, it undergoes diffuse reflection and returns to the laser receiver. The radar module calculates the distance between the transmitter and the object by multiplying the time interval between the transmitted and received signals by the speed of light and then dividing by 2. Depending on the number of laser beams, there are typically single-line LiDAR, 4-line LiDAR, 8 / 16 / 32 / 64-line LiDAR, etc. One or more laser beams are emitted vertically at different angles and scan horizontally to detect the three-dimensional contour of the target area. In recent years, with the continuous improvement and advancement of LiDAR scanning technology, its application in intelligent measurement of highway subgrades has become increasingly widespread.

[0003] Currently, when lidar scanning technology is applied to intelligent measurement of highway subgrade, in rainy, snowy, or foggy weather, due to the presence of water droplets of varying sizes in the air with a high density, when the laser beam shines on the water droplets, it generates reflected echoes, forming corresponding points in the point cloud. These points are not actual points on the target object and should therefore be considered noise. The distribution of these noise points seriously affects the measurement results of the lidar scanning system for intelligent measurement points of highway subgrade, leading to significant deviations in the measurement results. Therefore, it is necessary to design a noise reduction and dilution processing method for intelligent measurement point clouds of highway subgrade to solve the above problems. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the current intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a noise reduction and dilution method for intelligent measurement point clouds of highway subgrade. This method is applicable to solving the problem that in rainy, snowy, and foggy weather, due to the presence of water droplets of varying sizes with high density in the air, when a laser beam irradiates the water droplets, reflected echoes are generated, forming corresponding points in the point cloud. These points are not actual points on the target object and should therefore be considered noise. The distribution of these noise points seriously affects the measurement results of intelligent measurement points of highway subgrade by the lidar scanning system, leading to significant deviations in the measurement results.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for noise reduction and dilution processing of intelligent measurement point clouds of highway subgrade, the dilution processing method comprising the following steps:

[0008] S1: Install the lidar scanning system sequentially on the roadbed intelligent measurement point motion platform, initialize the lidar scanning system, and the lidar scanning system detects and scans the measurement points to collect lidar point cloud data;

[0009] S2: Collect the acquired laser point cloud data and construct a laser point cloud distribution map based on the laser point cloud data acquired by multiple sets of lidar scanning systems;

[0010] S3: Obtain the reflectivity and continuity parameters of the laser point cloud, calculate the distance between the corresponding laser point cloud and the lidar scanning system, and filter out the laser point clouds that belong to noise based on the calculated distance;

[0011] S4: Traverse the laser point cloud distribution map, calculate the dynamic threshold of each laser point cloud collected by the laser scanning radar, and filter out and dilute the laser point clouds that are not within the threshold range and belong to noise.

[0012] S5: Based on the initial calibration results of the lidar scanning system, the lidar point cloud data after noise reduction and dilution is converted into coordinates of the ranging system to construct a distribution map of intelligent measurement point cloud data of the roadbed.

[0013] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, in step S4, a pass-through filter is used to perform filtering and dilution processing on the early points.

[0014] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, the lidar scanning system includes:

[0015] The main unit includes a mounting base and a geared motor fixedly mounted on the mounting base. A laser radar scanner is fixedly connected to the top of the output shaft of the geared motor. A mounting groove is provided on the side wall of the laser radar scanner, and a laser emitting head is installed in the mounting groove.

[0016] The lens cleaning unit includes a wiping box located in a mounting slot and a wiping sponge fixedly installed on the side of the wiping box near the laser emitter head. A lead screw and a guide rod are rotatably connected to both sides of the mounting slot. A drive motor is fixedly installed on the lower side wall of the laser radar scanner. The output shaft of the drive motor is fixedly connected to the lower end of the lead screw, and the wiping box is threadedly connected to the lead screw. The wiping box is vertically slidably connected to the guide rod. Multiple sets of evenly distributed liquid inlet pipes are provided on the upper side wall of the wiping box.

[0017] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, the lidar scanning system further includes a water storage and replenishment unit, which comprises a water storage box fixedly installed on the top of the lidar scanner and a downpipe fixedly installed on the upper end of the water storage cover. A water receiving cover is fixedly connected to the upper opening of the downpipe, and a float is installed inside the water receiving cover. The inner wall of the water storage box is connected to the float via a connecting rope, and the diameter of the float is larger than the inner diameter of the downpipe. The side wall of the water storage box is fixedly connected to... There are multiple sets of evenly distributed replenishment tubes. A water-passing plate is fixedly installed inside each replenishment tube. A water-passing hole is opened on the water-passing plate. A fixed beam is fixedly connected to the inner wall of each replenishment tube. A sealing plate corresponding to the water-passing hole is fixedly connected to the lower side wall of the fixed beam through a telescopic column. A corresponding compression spring is sleeved on the telescopic column. A top tube is fixedly installed inside each inlet tube. The outer diameter of the top tube is smaller than the inner diameter of the water-passing hole. A symmetrically positioned side hole is opened at the upper end of the side wall of the top tube. A docking cover corresponding to the replenishment tube is fixedly installed on the outer side wall of the inlet tube.

[0018] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, the water storage and replenishment unit further includes a filter assembly, which includes a coarse filter, an activated carbon layer, and a fine filter installed sequentially in the water storage box. The coarse filter is located on the upper side of the activated carbon layer, and the activated carbon layer is located between the coarse filter and the fine filter.

[0019] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, the coarse filter, activated carbon layer and fine filter are wrapped with a fixing frame on the outside, and the fixing frame is sealed against the inner wall of the water storage box.

[0020] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, the connecting rope is made of lightweight nylon filaments, and the float has a hollow structure.

[0021] As a preferred embodiment of the intelligent measurement point cloud noise reduction and dilution processing method for highway subgrade described in this invention, a layer of uniformly thick sealing rubber ring is provided at the point where the downpipe and the float meet.

[0022] The beneficial effects of this invention are as follows: By collecting laser point cloud data acquired by the lidar scanning system, calculating the distance between the corresponding laser point cloud and the intelligent measurement point through the reflectivity and continuous parameters of the laser point cloud, the early points acquired by the lidar scanning system are screened out, and these noise points are effectively filtered out and diluted, thereby ensuring the accuracy of the data acquired by the intelligent measurement point of the highway subgrade and avoiding large errors in the measurement results.

[0023] When the laser emitter lens of a LiDAR scanner is exposed to the outside environment for a long time, dust and other impurities adhere to the lens. At this time, the drive motor is started to rotate the lead screw. The wiping box, which is threaded to the lead screw, is limited by the guide rod and can automatically wipe the laser emitter lens with the wiping sponge. When the wiping box rises to the top of the mounting slot, the top tube located in the liquid inlet pipe pushes upward into the liquid replenishment pipe, lifting the sealing plate. The telescopic column and the compression spring are squeezed, and the water in the liquid replenishment pipe enters the liquid inlet pipe through the side hole and water passage hole of the top tube, thereby automatically replenishing the wiping box and ensuring that the wiping box always maintains a good wiping effect. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0025] Figure 1 This is a schematic diagram illustrating the steps of a method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade proposed in this invention;

[0026] Figure 2 This is a schematic diagram of the cooperation structure of a lidar scanner, mounting base, and geared motor in a method for noise reduction and dilution of intelligent measurement point clouds for highway subgrade proposed in this invention.

[0027] Figure 3 This is a schematic diagram of the lens cleaning unit structure of a method for noise reduction and dilution of intelligent measurement point clouds of highway subgrade proposed in this invention.

[0028] Figure 4 This is a schematic diagram of the water storage and replenishment unit structure of a method for noise reduction and dilution of intelligent measurement point cloud on highway subgrade proposed in this invention.

[0029] Figure 5 This is a schematic diagram of the internal structure of the replenishment pipe in a method for noise reduction and dilution of intelligent measurement point clouds for highway subgrade proposed in this invention.

[0030] Figure 6This is a schematic diagram of the filter component structure of a method for noise reduction and dilution of intelligent measurement point clouds for highway subgrade proposed in this invention.

[0031] Figure Descriptions: 100 Main Unit, 101 Mounting Base, 102 Gear Motor, 103 LiDAR Scanner, 104 Laser Emitter, 200 Lens Cleaning Unit, 201 Wiping Box, 202 Drive Motor, 203 Lead Screw, 204 Guide Rod, 205 Wiping Sponge, 206 Liquid Inlet Pipe, 300 Water Storage and Replenishment Unit, 301 Water Storage Box, 302 Downpipe, 303 Water Receiving Cover, 304 Float Ball, 305 Connecting Rope, 306 Replenishment Pipe, 307 Water Passage Plate, 308 Sealing Plate, 309 Fixing Beam, 310 Telescopic Column, 311 Compression Spring, 312 Docking Cover, 313 Top Pipe, 314 Side Hole, 315a Filter Assembly, 3151 Fixing Frame, 3152 Coarse Filter Screen, 3153 Activated Carbon Layer, 3154 Fine Filter Screen. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0035] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0036] Example

[0037] Reference Figures 1-6 As an embodiment of the present invention, a method for noise reduction and dilution processing of intelligent measurement point clouds of highway subgrade is provided. The dilution processing method includes the following steps:

[0038] S1: Install the lidar scanning system sequentially on the roadbed intelligent measurement point motion platform, initialize the lidar scanning system, and the lidar scanning system detects and scans the measurement points to collect lidar point cloud data;

[0039] S2: Collect the acquired laser point cloud data and construct a laser point cloud distribution map based on the laser point cloud data acquired by multiple sets of lidar scanning systems;

[0040] S3: Obtain the reflectivity and continuity parameters of the laser point cloud, calculate the distance between the corresponding laser point cloud and the lidar scanning system, and filter out the laser point clouds that belong to noise based on the calculated distance;

[0041] S4: Traverse the laser point cloud distribution map, calculate the dynamic threshold of each laser point cloud collected by the laser scanning radar, and filter out and dilute the laser point clouds that are not within the threshold range and belong to noise.

[0042] S5: Based on the initial calibration results of the lidar scanning system, the laser point cloud data after noise reduction and dilution is converted into coordinates of the ranging system to construct a distribution map of intelligent measurement point cloud data for the roadbed. By collecting the laser point cloud data acquired by the lidar scanning system and calculating the distance between the corresponding laser point cloud and the intelligent measurement point through the reflectivity and continuous parameters of the laser point cloud, the early points acquired by the lidar scanning system are screened out, and these noise points are effectively filtered out and diluted, thereby ensuring the accuracy of the data acquired by the intelligent measurement points of the highway roadbed and avoiding large errors in the measurement results.

[0043] In step S4, a pass-through filter is used to filter and dilute the early point.

[0044] The lidar scanning system includes a main unit 100, a lens cleaning unit 200, and a water replenishment unit 300.

[0045] The main unit 100 includes a mounting base 101 and a geared motor 102 fixedly mounted on the mounting base 101. A laser radar scanner 103 is fixedly connected to the top of the output shaft of the geared motor 102. A mounting groove is provided on the side wall of the laser radar scanner 103, and a laser emitter 104 is installed in the mounting groove. The laser radar scanner 103 and the laser emitter 104 are widely used in actual measurement processes and are often used in real life. The working principle of the two is not described in detail in this invention.

[0046] The lens cleaning unit 200 includes a wiping box 201 located in the mounting slot and a wiping sponge 205 fixedly installed on the side of the wiping box 201 near the laser emitter 104. The side wall of the wiping box 201 has multiple sets of seepage holes corresponding to the wiping sponge 205. A lead screw 203 and a guide rod 204 are rotatably connected to both sides of the mounting slot. A drive motor 202 is fixedly installed on the lower side wall of the laser radar scanner 103. The output shaft of the drive motor 202 is fixedly connected to the lower end of the lead screw 203, and the wiping box 201 is threadedly connected to the lead screw 203. The wiping box 201 is vertically slidably connected to the guide rod 204. Multiple sets of evenly distributed liquid inlet pipes 206 are provided on the upper side wall of the wiping box 201.

[0047] The water storage and replenishment unit 300 includes a water storage box 301 fixedly installed on the top of the lidar scanner 103 and a downpipe 302 fixedly installed on the upper end of the water storage cover. A water receiving cover 303 is fixedly connected to the upper opening of the downpipe 302, and a float ball 304 is installed inside the water receiving cover 303. A layer of sealing rubber ring of uniform thickness is provided at the point where the downpipe 302 and the float ball 304 abut. The sealing rubber ring improves the sealing effect of the float ball 304 on the downpipe 302, thereby ensuring that the float ball 304 can block rainwater when there is no rainfall. Dust and large particles from the outside enter the water storage box 301 through the downpipe 302. The inner wall of the water storage box 301 is connected to the float 304 by a connecting rope 305. The connecting rope 305 is made of lightweight nylon yarn, and the float 304 has a hollow structure. The lightweight nylon yarn connecting rope 305 has little impact on the float 304 and can properly pull and limit the float 304, preventing the float 304 from falling out of the water collection cover 303. The hollow float 304 saves materials and ensures that rainwater can make the float 304 float normally.

[0048] Furthermore, the diameter of the float 304 is larger than the inner diameter of the drain pipe 302. Multiple sets of evenly distributed replenishment pipes 306 are fixedly connected to the side wall of the water storage box 301. A water-passing plate 307 is fixedly installed inside each replenishment pipe 306, with water-passing holes on the plate 307. A fixed beam 309 is fixedly connected to the inner wall of the replenishment pipe 306. A sealing plate 308 corresponding to the water-passing hole is fixedly connected to the lower side wall of the fixed beam 309 via a telescopic column 310. A corresponding compression spring 311 is fitted onto the telescopic column 310. The inlet pipe 206... A jacking pipe 313 is fixedly installed, and the outer diameter of the jacking pipe 313 is smaller than the inner diameter of the water passage hole. A symmetrically positioned side hole 314 is opened at the upper end of the side wall of the jacking pipe 313, and a docking cover 312 corresponding to the replenishment pipe 306 is fixedly installed on the outer wall of the liquid inlet pipe 206. With the setting of the water storage box 301, the drain pipe 302 and the float ball 304, rainwater and snow water in rainy and snowy weather can be collected to realize automatic replenishment of the wiping box 301 without the need for manual replenishment by staff, thus improving the utilization rate of water resources.

[0049] The water storage and replenishment unit 300 also includes a filter assembly 315a, which includes a coarse filter 3152, an activated carbon layer 3153, and a fine filter 3154 installed sequentially in the water storage box 301. The coarse filter 3152 is located on the upper side of the activated carbon layer 3153, and the activated carbon layer 3153 is located between the coarse filter 3152 and the fine filter 3154. The coarse filter 3152 and the fine filter 3154 can effectively filter large and small dust particles entering the water storage box 301. The activated carbon filter layer 3153 can adsorb particulate impurities mixed in the water, ensuring the purity of the water entering the replenishment pipe 306, which facilitates the subsequent cleaning of the laser emitter head 104 lens. The coarse filter 3152, the activated carbon layer 3153, and the fine filter 3154 are wrapped with a fixing frame 3151, which is sealed against the inner wall of the water storage box 301.

[0050] During use, when the lens of the laser emitter 104 of the LiDAR scanner 103 is exposed to the outside environment for a long time, dust and other impurities adhere to the lens of the laser emitter 104. At this time, the drive motor 202 is started to drive the lead screw 203 to rotate. The wiping box 201, which is threaded to the lead screw 203, can automatically wipe the lens of the laser emitter 104 under the limiting action of the guide rod 204. When the wiping box 201 rises to the top of the mounting groove, the top tube 313 located in the liquid inlet pipe 206 pushes upward into the liquid replenishment pipe 306, lifting the sealing plate 308. The telescopic column 310 and the compression spring 311 are squeezed, and the water in the liquid replenishment pipe 306 enters the liquid inlet pipe 206 through the side hole 314 and the water passage hole of the top tube 313, thereby automatically replenishing the wiping box 201 and ensuring that the wiping box 201 always maintains a good wiping effect.

[0051] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for noise reduction and dilution processing of intelligent measurement point clouds of highway subgrade, characterized in that, The dilution treatment method includes the following steps: S1: Install the lidar scanning system sequentially on the roadbed intelligent measurement point motion platform, initialize the lidar scanning system, and the lidar scanning system detects and scans the measurement points to collect lidar point cloud data; S2: Collect the acquired laser point cloud data and construct a laser point cloud distribution map based on the laser point cloud data acquired by multiple sets of lidar scanning systems; S3: Obtain the reflectivity and continuity parameters of the laser point cloud, calculate the distance between the corresponding laser point cloud and the lidar scanning system, and filter out the laser point clouds that belong to noise based on the calculated distance; S4: Traverse the laser point cloud distribution map, calculate the dynamic threshold of each laser point cloud collected by the laser scanning radar, and filter out and dilute the laser point clouds that are not within the threshold range and belong to noise. S5: Based on the initial calibration results of the lidar scanning system, the lidar point cloud data after noise reduction and dilution is converted into coordinates of the ranging system to construct a distribution map of intelligent measurement point cloud data of the roadbed; The lidar scanning system includes: The main unit (100) includes a mounting base (101) and a geared motor (102) fixedly mounted on the mounting base (101). A laser radar scanner (103) is fixedly connected to the top of the output shaft of the geared motor (102). A mounting groove is provided on the side wall of the laser radar scanner (103), and a laser emitter (104) is installed in the mounting groove. The lens cleaning unit (200) includes a wiping box (201) located in the mounting slot and a wiping sponge (205) fixedly installed on the side of the wiping box (201) near the laser emitter (104). A lead screw (203) and a guide rod (204) are rotatably connected to both sides of the mounting slot. A drive motor (202) is fixedly installed on the lower side wall of the laser radar scanner (103). The output shaft of the drive motor (202) is fixedly connected to the lower end of the lead screw (203), and the wiping box (201) is threadedly connected to the lead screw (203). The wiping box (201) is vertically slidably connected to the guide rod (204). Multiple sets of evenly distributed liquid inlet pipes (206) are opened on the upper side wall of the wiping box (201). A water storage and replenishment unit (300) includes a water storage box (301) fixedly installed on the top of a laser radar scanner (103) and a drain pipe (302) fixedly installed on the upper end of a water storage cover. A water receiving cover (303) is fixedly connected to the upper opening of the drain pipe (302), and a float (304) is installed inside the water receiving cover (303). The inner wall of the water storage box (301) is connected to the float (304) by a connecting rope (305), and the diameter of the float (304) is larger than the inner diameter of the drain pipe (302). Multiple sets of evenly distributed replenishment pipes (306) are fixedly connected to the side wall of the water storage box (301), and a water-passing plate (305) is fixedly installed inside the replenishment pipe (306). 7) A water passage hole is provided on the water passage plate (307). A fixed beam (309) is fixedly connected to the inner wall of the liquid replenishment pipe (306). A sealing plate (308) corresponding to the water passage hole is fixedly connected to the lower side wall of the fixed beam (309) through the telescopic column (310). A corresponding compression spring (311) is sleeved on the telescopic column (310). A top pipe (313) is fixedly installed inside the liquid inlet pipe (206). The outer diameter of the top pipe (313) is smaller than the inner diameter of the water passage hole. A side hole (314) with a symmetrical position is opened on the upper end of the side wall of the top pipe (313). A docking cover (312) corresponding to the liquid replenishment pipe (306) is fixedly installed on the outer side wall of the liquid inlet pipe (206).

2. The method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade according to claim 1, characterized in that: In step S4, a pass-through filter is used to filter and dilute the early point.

3. The method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade according to claim 1, characterized in that: The water storage and replenishment unit (300) also includes a filter assembly (315a), which includes a coarse filter (3152), an activated carbon layer (3153), and a fine filter (3154) installed sequentially in the water storage box (301). The coarse filter (3152) is located on the upper side of the activated carbon layer (3153), and the activated carbon layer (3153) is located between the coarse filter (3152) and the fine filter (3154).

4. The method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade according to claim 3, characterized in that: The coarse filter (3152), activated carbon layer (3153) and fine filter (3154) are wrapped with a fixing frame (3151), which is sealed against the inner wall of the water storage box (301).

5. The method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade according to claim 1, characterized in that: The connecting rope (305) is made of lightweight nylon yarn, and the float (304) has a hollow structure.

6. The method for noise reduction and dilution processing of intelligent measurement point clouds for highway subgrade according to claim 1, characterized in that: A layer of uniformly thick sealing rubber ring is provided at the point where the downpipe (302) and the float (304) meet.

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