Road base material thickness laser detection device for municipal engineering

Abstract

The invention relates to the field of road construction detection, and discloses a municipal engineering road base material thickness laser detection device which comprises a shell, a first protection assembly is arranged at the lower end of the interior of the shell, a second protection assembly is arranged on the periphery of the first protection assembly, and the second protection assembly is arranged at the lower end of the interior of the shell. A mounting frame is arranged at the upper end of the interior of the shell, a laser sensor is arranged at the lower end of the mounting frame, a support assembly is arranged at the upper end of the shell, and balancing mechanisms are rotationally arranged at the positions, located at the lower end of the support assembly, of the periphery of the shell. The road base material thickness laser detection device for municipal engineering provided by the invention has the functions of integrated active safety, modular drop resistance, self-cleaning and anti-interference stability, laser is blocked through a gravity sensing deflection physical layer, modular parts absorb energy and can be replaced at low cost during dropping, and pulse blowing and magnetic attraction locking are adopted, so that the detection efficiency is improved. And safety, precision and durability are ensured.

Description

Technical Field

[0001] This invention relates to the field of road construction inspection technology, specifically to a laser detection device for the thickness of road substrates used in municipal engineering. Background Technology

[0002] In the construction and quality acceptance of municipal road engineering, the paving thickness of road substrates (such as asphalt mixtures and water-stabilized crushed stone layers) is one of the key indicators for measuring project quality. Traditional thickness detection methods mainly rely on manual core drilling, which is inefficient, destructive, and can only obtain data from discrete points, making it difficult to comprehensively reflect the thickness uniformity of the entire work surface. To overcome these limitations, laser detection technology has been introduced into the field of road thickness detection in recent years. Existing technologies include some laser detection devices integrated into pavers or rollers, such as: In the patent application with application publication number CN221276262U, it includes a main frame, a feeder, a spiral paver, a vibrator, a paving plate, a laser rangefinder, an adjusting screw, and an LED display screen;

[0005] The feeder is provided on the main frame, and the spiral paver is provided at the front of the main frame. Asphalt is paved by the spiral paver through the feeder;

[0006] The vibrator is also provided at the front of the main frame. The vibrator is used to vibrate the asphalt;

[0007] The paving plate is also provided at the front end of the main frame. The paving plate is connected to the main frame through the adjusting screw. The adjusting screw is used to adjust the paving thickness of the asphalt. The laser rangefinder is provided on the paving plate. The laser rangefinder is used to detect the paving thickness of the asphalt. The LED display screen is provided on the adjusting screw. The LED display screen is used to display the paving thickness of the asphalt. The advantages include: a main frame, a feeder, an auger paver, a vibrator, a slab, a laser rangefinder, an adjusting screw, and an LED display screen. The feeder and auger paver are located at the bottom of the main frame. Asphalt concrete is poured into the paver and fed to the auger paver via the feeder. After being vibrated by the vibrator, the asphalt concrete is spread into shape by the slab. Before paving, the paving thickness can be adjusted using the laser rangefinder and the adjusting screw, and the paving thickness is displayed on the LED display screen. Through the above configuration, this disclosure provides a paver capable of real-time monitoring of paving quality.

[0003] Even in the prior art, including the aforementioned patents, some defects still exist. Safety concerns exist: the laser emitter of this device is exposed to the construction environment, and the lens surface is easily contaminated, leading to a sharp decrease in laser scattering and measurement accuracy. More importantly, this device and similar integrated designs lack any active safety management mechanism for the laser beam itself. When the equipment is moving, turning, or not in operation, the laser beam may accidentally shine into the eyes of personnel or construction monitoring equipment, posing a safety hazard. Although some patents propose cleaning solutions for the optical lens, their purpose is limited to dust prevention and does not address attitude-based safety locking functionality. The measurement benchmark is singular and lacks adaptability; the measurement benchmark depends on the installation plane of the paver screed; when working on sloping sections, or when the equipment tilts due to its own posture, the emission direction of the laser beam cannot be kept consistent with the direction of the slope normal, so the measured distance is actually the slope distance, not the true vertical thickness, thus introducing a fundamental error and making it difficult to guarantee the reliability of the data. Existing technologies are fragmented and piecemeal, failing to provide integrated solutions. Most existing solutions address dustproofing, impact resistance, and thickness measurement functions in isolation; for example, some patents focus on separate sensor installations, others on high-precision dust removal, and still others on adaptive optical collimation. However, no solution organically integrates these functions, particularly active safety protection and dynamic measurement benchmark calibration, making the overall equipment ill-suited for complex and ever-changing real-world construction conditions. Summary of the Invention

[0004] The problem this invention aims to solve is to achieve a balance between proactive personal safety protection and dynamic terrain adaptation in laser detection of paving thickness under complex construction environments.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a laser detection device for road substrate thickness in municipal engineering, comprising a housing, a protective component one disposed at the lower end of the housing, a protective component two disposed around the protective component one, the protective component two disposed at the lower end of the housing, a mounting frame disposed at the upper end of the housing, a laser sensor disposed at the lower end of the mounting frame, a support assembly disposed at the upper end of the housing, and a balancing mechanism rotatably disposed around the lower end of the support assembly on the periphery of the housing; The protective component mainly includes a housing, a mounting ball, a lens, and a magnet. The mounting ball is located inside the housing, a lens is located in the center of the mounting ball, and magnets are located around the mounting ball. The housing contains a transparent lubricant.

[0006] Preferably, there are two housings. Each housing consists of a transparent arc-shaped plate and a metal flange. The gaps inside the housing are filled with transparent lubricant. The mounting ball is slidably connected to the housing. The mounting ball is a sphere with an offset center of gravity. Both ends of the lens are slidably connected to the housing. There are four magnets. One end of each magnet is slidably connected to the housing. The magnets can be attracted to one side of the housing flange.

[0007] Preferably, the second protective component includes an electric actuator, which is fixedly installed inside the housing. Four electric actuators are arranged around the center of the housing. An installation ring is provided at the upper end of the electric actuator. The installation ring is concentric with the housing. A square groove is provided below the installation ring through the housing. Four square grooves are also arranged around the center of the housing.

[0008] Preferably, a piston rod is fixedly provided at the lower end of the mounting ring, the piston rod is slidably connected to the square groove, and a valve disc is provided in the middle of the piston rod.

[0009] Preferably, a sealing strip is provided below the piston rod inside the square groove. The sealing strip is slidably connected to the square groove via a connecting rod. A pair of magnets are provided at the lower end of the connecting rod above the sealing strip and inside the square groove. The magnets repel each other. A gas guide groove is fixedly provided at the lower end of the housing. The gas guide groove is connected to the square groove and blows towards the outer shell.

[0010] Preferably, the upper end of the mounting bracket is provided with a battery pack for powering the laser sensor and the electric actuator, and the upper end of the mounting bracket is provided with a control unit for controlling the electric actuator and receiving signals from the laser sensor.

[0011] Preferably, the support assembly mainly includes a cover plate, which is disposed at the upper end of the housing. An air storage chamber is disposed at the upper end of the inner part of the cover plate. A piston cylinder is disposed at the upper end of the cover plate. The lower end of the piston cylinder is connected to the air storage chamber. A magnet is disposed at the upper end of the piston cylinder. The piston cylinder and the magnet are rotatably connected.

[0012] Preferably, sixteen magnets are evenly arranged around the center of the outer cover plate of the piston cylinder, and the magnets are connected to the piston cylinder through the base, and the magnets are rotatably connected to the base.

[0013] Preferably, the balancing mechanism includes a rotating ring, on one side of which a mounting beam is rotatably mounted. The mounting beam is I-shaped, and a square hole is provided at the connection between the mounting beam and the rotating ring, which is fixed by a square strip. Several limiting blocks are fixedly mounted on one side of the mounting beam, and the limiting blocks are cylindrical.

[0014] Preferably, a magnetic base is fixedly installed at one end of the rotating ring opposite to the mounting beam. A counterweight is installed inside the magnetic base, and insert rods are fixedly installed at both ends of the counterweight. The insert rods can be attracted by the magnetic base. Limiting rings are provided at the upper and lower ends of the counterweight. The limiting rings are connected by connecting rods. The connecting rods between the limiting rings are slidably connected to the counterweight. The counterweight can cooperate with the limiting blocks. The weight of the counterweight, insert rods and limiting rings is the same as the weight of the mounting beam.

[0015] Compared with the prior art, the technical solution of the present invention has the following advantages: (1) Integrating active safety protection, intelligent cleaning and anti-interference stabilization functions into one; This invention realizes active laser safety management based on gravity sensing through the "center of gravity offset mounting ball-lens" structure: When the tilt angle of the equipment exceeds the safety threshold, the mounting ball automatically deflects under the action of gravity, physically blocking the laser path, fundamentally preventing accidental irradiation of the human eye and equipment; while within the normal tilt angle range of the equipment, this structure can ensure that the laser passes through normally, and through additional components, it can also prevent direct damage to the laser sensor when it falls. Through modular design, only the corresponding parts need to be replaced, thereby reducing the cost of use to a certain extent; at the same time, the built-in pulse blowing cleaning system can automatically remove dust from the lens surface, and the magnetic attraction stabilization mechanism in the first protective component can quickly lock the optical component when the equipment shakes, integrating the three functions of active safety, environmental self-cleaning and dynamic anti-interference stabilization, ensuring the long-term measurement accuracy and operational safety of the equipment under harsh working conditions; (2) It realizes dynamic terrain adaptation and benchmark maintenance; through the collaborative leveling system consisting of leveling mechanism, support assembly and magnetic base, the device can actively adapt to different slopes; whether on flat ground or steep slope, it can be automatically or manually adjusted to ensure that the laser sensor housing is always perpendicular to the horizontal plane, thereby ensuring the accuracy and data reliability of thickness measurement benchmark under any terrain, and overcoming the defect of inaccurate measurement when traditional equipment is used on slopes. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the present invention; Figure 2 This is a schematic cross-sectional view of the overall structure of the present invention; Figure 3 This is a schematic diagram of the support assembly structure of the present invention; Figure 4 For the present invention Figure 3 Enlarged structural diagram at point A in the middle; Figure 5 This is a schematic diagram of the housing and laser sensor structure of the present invention; Figure 6 This is a schematic diagram of the internal protective component two of the housing of the present invention; Figure 7 This is a schematic diagram of the internal structure of the housing of the present invention; Figure 8 This is a top view of the internal structure of the housing of the present invention; Figure 9 This is a schematic diagram of the air guide groove structure of the present invention; Figure 10 This is a schematic diagram of the balancing mechanism of the present invention; Figure 11 This is a schematic diagram of the mounting bracket and laser sensor structure of the present invention; Figure 12 This is a schematic diagram of the mounting ring and piston rod structure of the present invention. Figure 13 This is a schematic diagram of the internal structure of the protective component of the present invention.

[0017] In the diagram: 1. Housing; 2. Protective Component 1; 201. Outer shell; 202. Mounting ball; 203. Lens; 204. Magnet; 3. Protective Component 2; 301. Electric actuator; 302. Mounting ring; 303. Square groove; 304. Piston rod; 305. Sealing strip; 306. Air guide groove; 4. Mounting bracket; 5. Laser sensor; 6. Bracket assembly; 601. Cover plate; 602. Air storage chamber; 603. Piston cylinder; 604. Magnet; 7. Balancing mechanism; 701. Rotating ring; 702. Mounting beam; 703. Limiting block; 704. Magnetic base; 705. Counterweight; 706. Insert rod; 707. Limiting ring. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0019] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "comprising" or "including," and similar terms used in this disclosure, mean that an element or object preceding the term encompasses the elements or objects listed following the term and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but may also include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0020] like Figures 1 to 13 As shown, the present invention provides a laser detection device for road substrate thickness in municipal engineering, comprising a housing 1, characterized in that: a protective component 1 2 is provided at the lower end of the interior of the housing 1, a protective component 2 3 is provided around the protective component 1 2, the protective component 2 3 is provided at the lower end of the interior of the housing 1, a mounting frame 4 is provided at the upper end of the interior of the housing 1, a laser sensor 5 is provided at the lower end of the mounting frame 4, a support assembly 6 is provided at the upper end of the housing 1, and a balancing mechanism 7 is rotatably provided around the lower end of the support assembly 6 around the housing 1. The protective component 2 mainly includes a housing 201, a mounting ball 202, a lens 203, and a magnet 204. The mounting ball 202 is located inside the housing 201. The lens 203 is located in the center of the mounting ball 202. The magnet 204 is located around the mounting ball 202. The housing 201 contains a transparent lubricant.

[0021] There are two housings 201. Each housing 201 consists of a transparent arc-shaped plate and a metal flange. The gaps inside the housing 201 are filled with transparent lubricant. The mounting ball 202 is slidably connected to the housing 201. The mounting ball 202 is a sphere with an offset center of gravity. Both ends of the lens 203 are slidably connected to the housing 201. There are four magnets 204. One end of each magnet 204 is slidably connected to the housing 201. The magnets 204 can be attracted to one side of the flange of the housing 201.

[0022] The second protective component 3 includes an electric actuator 301, which is fixedly installed inside the housing 1. Four electric actuators 301 are arranged around the center of the housing 1. An installation ring 302 is provided at the upper end of the electric actuator 301. The installation ring 302 is concentric with the housing 1. A square groove 303 is provided below the installation ring 302 through the housing 1. Four square grooves 303 are also arranged around the center of the housing 1.

[0023] A piston rod 304 is fixedly installed at the lower end of the mounting ring 302. The piston rod 304 is slidably connected to the square groove 303, and a valve disc is provided in the middle of the piston rod 304.

[0024] A sealing strip 305 is provided below the piston rod 304 inside the square groove 303. The sealing strip 305 is slidably connected to the square groove 303 through a connecting rod. A pair of magnets are provided at the lower end of the connecting rod above the sealing strip 305 and inside the square groove 303. The magnets repel each other. A gas guide groove 306 is fixedly provided at the lower end of the housing 1. The gas guide groove 306 is connected to the square groove 303 and blows towards the outer shell 201.

[0025] The upper end of the mounting bracket 4 is provided with a battery pack for powering the laser sensor 5 and the electric actuator 301, and the upper end of the mounting bracket 4 is provided with a control unit for controlling the electric actuator 301 and receiving signals from the laser sensor 5.

[0026] The bracket assembly 6 mainly includes a cover plate 601, which is located at the upper end of the housing 1. An air storage chamber 602 is located at the upper end of the cover plate 601. A piston cylinder 603 is located at the upper end of the cover plate 601. The lower end of the piston cylinder 603 is connected to the air storage chamber 602. A magnet 604 is located at the upper end of the piston cylinder 603. The piston cylinder 603 and the magnet 604 are rotatably connected.

[0027] Sixteen magnets are evenly arranged around the center of the outer cover plate 601 of the piston cylinder 603. The magnet 604 is connected to the piston cylinder 603 through the base, and the magnet 604 is rotatably connected to the base.

[0028] The balancing mechanism 7 includes a rotating ring 701. A mounting beam 702 is rotatably mounted on one side of the rotating ring 701. The mounting beam 702 is I-shaped. A square hole is provided at the connection between the mounting beam 702 and the rotating ring 701 and it is fixed by a square bar. Several limiting blocks 703 are fixedly mounted on one side of the mounting beam 702. The limiting blocks 703 are cylindrical.

[0029] A magnetic base 704 is fixedly installed at one end of the rotating ring 701 opposite to the mounting beam 702. A counterweight 705 is installed inside the magnetic base 704. Insert rods 706 are fixedly installed at both ends of the counterweight 705. The insert rods 706 can be attracted by the magnetic base 704. Limiting rings 707 are provided at the upper and lower ends of the counterweight 705. The limiting rings 707 are connected by connecting rods. The connecting rods between the limiting rings 707 are slidably connected to the counterweight 705. The counterweight 705 can cooperate with the limiting block 703. The weight of the counterweight 705, the insert rods 706 and the limiting rings 707 is the same as the weight of the mounting beam 702.

[0030] Working principle and usage process of this invention: Installation requirements: When measuring the thickness of road substrate paving, the device body must first be installed on the front and rear sides of the paving equipment or at the lower end of other supporting equipment; the following conditions must be met during installation: At least two devices must be used for each installation, and the two devices must be aligned in a straight line. After determining the installation location, the height of the installation point must be measured to ensure that the lower ends of the two devices are on the same plane. Installation height adjustment: If the height difference between the two devices is within one-third of the total stroke of the piston cylinder 603, the overall height of the devices can be raised or lowered by adjusting the air pressure in the air storage chamber 602; if the height difference exceeds one-third of the total stroke of the piston cylinder 603, an additional bracket must be installed to fix the devices in the selected position. Vertical fixing and adjustment of the housing: After the height adjustment is completed, simply attach the magnet 604 to the designated installation position. If the magnet 604 is not parallel to the ground, the housing 1 will be forcibly pulled to a vertical state under the action of gravity after attachment. When the housing 1 is subjected to external force, under the action of the air pressure in the air storage chamber 602, the piston cylinder 603 in the same direction as the force will shorten, and the piston cylinder in the opposite direction will lengthen accordingly, thereby ensuring that the housing 1 is always perpendicular to the ground. Ramp scene adaptation adjustment: If the road surface is a slope, gravity alone cannot make the shell 1 perpendicular to the ground. The balancing mechanism 7 needs to be adjusted according to the slope angle, which can be divided into two cases: When the slope angle is small: remove the counterweight 705, rotate the mounting beam 702 to make it perpendicular to the shell 1, and force the shell 1 to tilt by changing the overall center of gravity of the device, so that the shell 1 is perpendicular to the ground. When the ramp angle is large: install the counterweight 705 onto the mounting beam 702, and select the appropriate limiting block 703 according to the ramp angle for fixing; after the above operations are completed, the mounting beam 702 needs to be rotated and adjusted to ensure that it is always parallel to the ground; Detection working principle: During measurement, two paired devices collect thickness data of the road surface before and after paving, respectively. By calculating the difference between the two sets of data, the actual paving thickness of the road substrate can be obtained. Laser safety protection device: When the device is powered on, if the tilt angle is too large, the lens 203 will shift under the action of the mounting ball 202. At this time, the laser cannot pass through the mounting ball 202, which can effectively prevent the laser from directly shining on the human eye or camera and other devices. If the device has a tilt angle but the angle is small, the laser can pass through the lens 203 normally to complete the measurement; when there is no need to disassemble the device for inspection, the device can be directly inverted after powering off without affecting subsequent use; When the equipment shakes, in order to avoid frequent refraction of the laser under the action of lens 203, it can be attracted to the vicinity of housing 201 under the action of magnet 204, thereby fixing the mounting ball 202 and ensuring measurement stability. After the dust cleaning function is turned on, the electric push rod 301 starts and drives the piston rod 304 to move repeatedly: first, the air in the square groove 303 is compressed, and when the piston rod moves to the bottom, it will press down the sealing strip 305, generating a pulse airflow to blow away the dust at the bottom of the outer shell 201, ensuring the laser transmission channel is clean and guaranteeing measurement accuracy.

[0031] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A laser detection device for road substrate thickness in municipal engineering, comprising a housing (1), characterized in that: The lower interior of the housing (1) is provided with a protective component one (2), and a protective component two (3) is provided around the protective component one (2). The protective component two (3) is located at the lower interior of the housing (1). The upper interior of the housing (1) is provided with a mounting bracket (4), and a laser sensor (5) is provided at the lower end of the mounting bracket (4). The upper end of the housing (1) is provided with a support assembly (6), and a balancing mechanism (7) is rotatably provided around the housing (1) at the lower end of the support assembly (6). The protective component 1 (2) mainly includes a housing (201), a mounting ball (202), a lens (203) and a magnet (204). The mounting ball (202) is disposed inside the housing (201). A lens (203) is disposed in the middle of the mounting ball (202). A magnet (204) is disposed around the mounting ball (202). A transparent lubricant is disposed inside the housing (201).

2. The laser detection device for road substrate thickness in municipal engineering according to claim 1, characterized in that: There are two housings (201). Each housing (201) consists of a transparent arc-shaped plate and a metal flange. The gaps inside the housing (201) are filled with transparent lubricant. The mounting ball (202) is slidably connected to the housing (201). The mounting ball (202) is a sphere with an offset center of gravity. Both ends of the lens (203) are slidably connected to the housing (201). There are four magnets (204). One end of each magnet (204) is slidably connected to the housing (201). The magnets (204) can be attracted to one side of the flange of the housing (201).

3. The laser detection device for road substrate thickness in municipal engineering according to claim 1, characterized in that: The second protective component (3) includes an electric actuator (301), which is fixedly installed inside the housing (1). Four electric actuators (301) are arranged around the center of the housing (1). An installation ring (302) is provided at the upper end of the electric actuator (301). The installation ring (302) is concentric with the housing (1). A square groove (303) is provided below the installation ring (302) through the housing (1). Four square grooves (303) are also arranged around the center of the housing (1).

4. The laser detection device for road substrate thickness in municipal engineering according to claim 3, characterized in that: A piston rod (304) is fixedly provided at the lower end of the mounting ring (302). The piston rod (304) is slidably connected to the square groove (303). A valve disc is provided in the middle of the piston rod (304).

5. The laser detection device for road substrate thickness in municipal engineering according to claim 4, characterized in that: A sealing strip (305) is provided below the piston rod (304) inside the square groove (303). The sealing strip (305) and the square groove (303) are slidably connected by a connecting rod. A pair of magnets are provided at the lower end of the connecting rod above the sealing strip (305) and inside the square groove (303). The magnets repel each other. A gas guide groove (306) is fixedly provided at the lower end of the housing (1). The gas guide groove (306) is connected to the square groove (303). The gas guide groove (306) blows towards the outer shell (201).

6. The laser detection device for road substrate thickness in municipal engineering according to claim 1, characterized in that: The upper end of the mounting bracket (4) is provided with a battery pack for powering the laser sensor (5) and the electric actuator (301), and the upper end of the mounting bracket (4) is provided with a control unit for controlling the electric actuator (301) and receiving signals from the laser sensor (5).

7. The laser detection device for road substrate thickness in municipal engineering according to claim 1, characterized in that: The bracket assembly (6) mainly includes a cover plate (601), which is located at the upper end of the housing (1). An air storage chamber (602) is provided at the upper end of the cover plate (601). A piston cylinder (603) is provided at the upper end of the cover plate (601). The lower end of the piston cylinder (603) is connected to the air storage chamber (602). A magnet (604) is provided at the upper end of the piston cylinder (603). The piston cylinder (603) and the magnet (604) are rotatably connected.

8. The laser detection device for road substrate thickness in municipal engineering according to claim 7, characterized in that: The piston cylinder (603) has sixteen magnets evenly arranged around the center of the outer cover plate (601). The magnet (604) is connected to the piston cylinder (603) through the base, and the magnet (604) is rotatably connected to the base.

9. The laser detection device for road substrate thickness in municipal engineering according to claim 1, characterized in that: The balancing mechanism (7) includes a rotating ring (701), on one side of which a mounting beam (702) is rotatably provided. The mounting beam (702) is I-shaped. A square hole is provided at the connection between the mounting beam (702) and the rotating ring (701) and it is fixed by a square bar. Several limiting blocks (703) are fixedly provided on one side of the mounting beam (702). The limiting blocks (703) are cylindrical.

10. A laser detection device for road substrate thickness in municipal engineering according to claim 9, characterized in that: The rotating ring (701) is fixedly provided with a magnetic base (704) at one end opposite to the mounting beam (702). A counterweight (705) is provided inside the magnetic base (704). Insert rods (706) are fixedly provided at both ends of the counterweight (705). The insert rods (706) can be attracted by the magnetic base (704). Limiting rings (707) are provided at the upper and lower ends of the counterweight (705). The limiting rings (707) are connected by connecting rods. The connecting rods between the limiting rings (707) are slidably connected to the counterweight (705). The counterweight (705) can cooperate with the limiting block (703). The weight of the counterweight (705), insert rods (706) and limiting rings (707) is the same as the weight of the mounting beam (702).

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