Foundation settlement visual monitoring device

Abstract

The application relates to the technical field of foundation settlement detection, and discloses a foundation settlement visual monitoring device which comprises a detection disc fixed to the settlement position of a foundation pit and a hollow box body fixed to the top central position of the detection disc, a plurality of measuring mechanisms for detecting the settlement height of the foundation pit are arranged in the hollow box body, the plurality of measuring mechanisms are symmetrically arranged, the measuring mechanism comprises a threaded straight rod rotatably arranged in the hollow box body and a measuring square column vertically penetrating the top surface of the hollow box body, the measuring square column is threadedly connected to the circumferential side of the top of the threaded straight rod, a scale ruler for height measurement is vertically fixed to the side wall of the measuring square column, and a driving mechanism for driving the threaded straight rod to rotate during the settlement of the foundation pit is arranged in the hollow box body. The application has the effect of improving the foundation settlement detection process and the difficulty in detecting the inclination of the foundation settlement.

Description

Technical Field

[0001] This invention relates to the technical field of foundation settlement detection, and in particular to a foundation settlement visualization monitoring device. Background Technology

[0002] The foundation already contains self-weight stress caused by the soil's own weight. The building load is transferred to the foundation through the bottom of the embankment, changing the original stress state of the natural soil layers. Under the action of the additional triaxial stress components, vertical, lateral, and shear deformations occur in the foundation, leading to vertical and lateral displacements at various points. With the booming development of the construction industry, the foundation settlement of buildings and their ancillary structures is increasingly attracting the attention of designers. For underground structures with numerous and complex underground facilities, such as communication, water, electricity, and gas pipelines, this is especially true.

[0003] For example, Chinese utility model patent CN215832707U discloses a foundation settlement detection device, including a fixing device and a settlement device, with the settlement device positioned to one side of the fixing device. The fixing device includes a fixing rod with several scale lines on its peripheral surface and a groove on its right surface. A slider is connected to the left end of the connecting rod of the settlement device, and the slider slides in conjunction with the groove. A first pointer and a second pointer are fixed to the front and rear surfaces of the slider, respectively, and both pointers align with the scale lines. A settlement rod is located at the right end of the connecting rod, and a settlement base is fixed to the lower end of the settlement rod.

[0004] Regarding the aforementioned related technologies, the inventors believe that the foundation settlement detection device is placed on the settlement location of the foundation using a settlement base, and then the changes in the first and second pointers and the scale lines around the fixed rod are observed to determine the height of the foundation settlement. However, foundation settlement measurement involves not only measuring the height of the foundation settlement but also detecting the inclination of the foundation settlement. Summary of the Invention

[0005] To address the difficulty in detecting the tilt of foundation settlement during the foundation settlement detection process, this application provides a foundation settlement visualization monitoring device.

[0006] This application provides a foundation settlement visualization monitoring device, which adopts the following technical solution:

[0007] A foundation settlement visualization monitoring device includes a detection disc fixed at the settlement position of a foundation pit and a hollow box fixed at the center of the top surface of the detection disc. The hollow box contains several measuring mechanisms for detecting the settlement height of the foundation pit, arranged symmetrically. Each measuring mechanism includes a threaded rod vertically rotatably mounted inside the hollow box and a measuring square column vertically passing through the top surface of the hollow box. The measuring square column is threaded to the periphery of the top of the threaded rod, and a graduated ruler is vertically fixed to the side wall of the measuring square column. The hollow box contains a driving mechanism for rotating the threaded rod when the foundation pit settles.

[0008] By adopting the above technical solution, when the foundation inside the pit settles, a height difference is formed between the foundation inside the pit and the reference ground. The drive mechanism drives the threaded rod to rotate, and the relative movement between the threaded rod and the measuring column causes the measuring column to slide vertically upwards. The data center then determines the settlement height of the foundation inside the pit. The data center can determine the inclination of the foundation inside the pit after settlement by using the differences in data from several measuring columns.

[0009] Optionally, the driving mechanism includes a helical rod horizontally rotatably mounted inside the hollow box, a driving block slidably disposed inside the hollow box along the length of the helical rod, and a pushing component disposed on the outside of the hollow box for moving the driving block during pit settlement. The helical rod is a straight rod structure with several helical strips evenly spaced around its own axis. The driving block has helical through holes that cooperate with several helical strips on the outer circumference of the helical rod. The driving block is helically engaged with the helical rod through the helical through holes. Bevel gears are coaxially fixed at positions close to the threaded rod and the helical rod, and two bevel gears are meshed together.

[0010] By adopting the above technical solution, when the foundation inside the pit settles, a height difference is formed between the foundation inside the pit and the reference ground. The pushing component pushes the guide rod to move towards the interior of the hollow box. The guide rod pushes the driving block to slide along the length of the spiral rod. The driving block drives the spiral rod to rotate through the spiral through hole. The spiral rod drives the threaded rod to rotate through the meshing relationship of two bevel gears. In this way, the pushing component drives the threaded rod to rotate.

[0011] Optionally, the pushing component includes a reference block installed on the top edge of the pit, a stranded steel wire fixed to the side wall of the reference block near the hollow box, a guide rod hinged to the side wall of the driving block away from the reference block, a support rod vertically fixed to the top surface of the detection disc, and a prying rod horizontally hinged to the support rod. The end of the guide rod away from the driving block extends out of the hollow box, one end of the prying rod is hinged to the end of the guide rod away from the driving block, and the other end of the prying rod is hinged to the end of the stranded steel wire away from the reference block.

[0012] By adopting the above technical solution, when the foundation inside the pit settles, a height difference is formed between the foundation inside the pit and the reference ground. The steel wire strand fixed to the reference block pulls one end of the pry bar, causing it to tilt upwards. The other end of the pry bar pushes the guide bar to move towards the interior of the hollow box. The guide bar then pushes the drive block to slide along the length of the spiral bar, thereby achieving the effect of using the height difference after settlement to drive the drive block to slide along the length of the spiral bar.

[0013] Optionally, a camera for monitoring the scale changes of the ruler is rotatably mounted on the top surface of the hollow box, and a protective mechanism for protecting the camera lens is provided on the top surface of the hollow box.

[0014] By adopting the above technical solution, the camera detects the scale changes of the ruler on the surface of the two measuring columns by rotating it. The camera feeds the data back to the data center to determine the settlement height of the foundation inside the pit.

[0015] Optionally, the protective mechanism includes two vertically fixed sliding rails on the top surface of the hollow box, a protective cover vertically slidable between the two sliding rails, and a wiping ball rotatably mounted on the bottom of the protective cover for wiping the camera lens. The top of the hollow box is provided with a synchronization mechanism for driving the camera and the protective cover to move synchronously.

[0016] By adopting the above technical solution, when the camera rotates to a vertical position, the protective cover slides vertically downward through the synchronization mechanism, and the wiping ball inside the protective cover covers and can wipe the camera lens, thereby achieving the protection of the camera lens by the protective cover.

[0017] Optionally, the synchronization mechanism includes a drive cylinder fixed to the top of the hollow housing, a drive rack fixed to the output shaft of the drive cylinder, an adjustment gear coaxially fixed to the tail end of the camera, and a drive component disposed on the top of the hollow housing for driving the protective cover to slide vertically. The drive rack passes through the top surface of the hollow housing and meshes with the adjustment gear.

[0018] By adopting the above technical solution, the drive cylinder pushes two drive racks to move vertically upward through the synchronous straight rod, and the drive racks drive the camera to rotate through the control gear, thereby adjusting the detection angle of the camera.

[0019] Optionally, the drive component includes a transmission gear rotatably mounted on the top of the hollow housing, a rotating disk coaxially fixed to the side wall of the transmission gear away from the camera, and a support cylinder fixed to the surface of the rotating disk away from the camera and near its own outer peripheral edge. A connecting rod is hinged between the side wall of the protective cover and the end of the support cylinder away from the rotating disk.

[0020] By adopting the above technical solution, when the camera rotates to a vertical position, the drive rack drives the rotating disk to rotate through the transmission gear. The rotating disk drives the protective cover to slide vertically downward through the connecting rod until the wiping ball inside the protective cover covers and wipes the camera lens.

[0021] Optionally, the hollow housing is provided with a limiting mechanism to minimize the rotational retraction of the threaded rod. The limiting mechanism includes a ratchet gear ring coaxially sleeved around the threaded rod, a limiting sleeve fixed to the bottom of the threaded rod, a limiting wedge block passing through the limiting sleeve, and a compression spring fixedly connected between the limiting wedge block and the sidewalls of the threaded rod that are close to each other. The ratchet gear ring is fixed to the bottom surface of the hollow housing, and the end of the limiting wedge block is inclined, with the inclined surface of the limiting wedge block engaging with the inclined surface of the ratchet teeth of the ratchet gear ring.

[0022] By adopting the above technical solution, the problem of wire strand breakage during the testing process, causing the threaded rod to rotate back and requiring the testing device to restart, is addressed. The limiting mechanism is designed to minimize the problem of the threaded rod retraction; even if the rope suddenly breaks, the measuring column will stop at the currently displayed scale position.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. When the foundation inside the excavation pit settles, a height difference is formed between the foundation inside the pit and the reference ground. The drive mechanism drives the threaded rod to rotate, and the threaded rod moves relative to the measuring column, causing the measuring column to slide vertically upward. The data center then determines the settlement height of the foundation inside the excavation pit. The data center can determine the inclination of the foundation inside the excavation pit after settlement by using the differences in data from several measuring columns.

[0025] 2. When the foundation inside the pit settles, a height difference is formed between the foundation inside the pit and the reference ground. The pushing component pushes the guide rod to move towards the interior of the hollow box. The guide rod pushes the driving block to slide. The driving block drives the spiral rod to rotate through the spiral through hole. The spiral rod drives the threaded rod to rotate through the meshing relationship of two bevel gears. In this way, the pushing component drives the threaded rod to rotate.

[0026] 3. When the camera rotates to a vertical position, the protective cover slides vertically downwards through the action of the synchronization mechanism. The wiping ball inside the protective cover covers and wipes the camera lens, thereby protecting the camera lens. Attached Figure Description

[0027] Figure 1 This is a structural schematic diagram of an embodiment of this application.

[0028] Figure 2 This is a cross-sectional schematic diagram of the hollow box and measuring cylinder according to an embodiment of this application.

[0029] Figure 3 This is a schematic diagram of the inner structure of the ratchet gear ring according to an embodiment of this application.

[0030] Figure 4 This is a schematic diagram of the internal structure of the measuring cylinder according to an embodiment of this application.

[0031] Reference numerals: 11. Detection disc; 12. Disc through hole; 13. Hollow box; 14. Detection structure; 15. Rotating groove; 16. Box through groove; 17. Threaded straight rod; 18. Measuring square column; 19. Threaded through hole; 20. Scale ruler; 21. Ratchet gear ring; 22. Limiting ring; 23. Limiting sleeve; 24. Limiting wedge block; 25. Compression spring; 26. Assembly groove; 27. Helical straight rod; 28. Bevel gear; 29. ​​Drive block; 30. Helical through hole; 31. Guide straight rod; 32. Guide through groove; 33. Reference block; 3 4. Steel wire strand; 35. Support rod; 36. Prying rod; 37. Cylindrical through hole; 38. Measuring cylinder; 39. Supporting plate; 40. Camera; 41. Adjusting rod; 42. Adjusting gear; 43. Transmission rod; 44. Transmission gear; 45. Rotating disc; 46. Drive cylinder; 47. Synchronizing rod; 48. Drive rack; 49. Slide rail rod; 50. Slide rail groove; 51. Protective cover; 52. Supporting cylinder; 53. Connecting rod; 54. Cover groove; 55. Wiping rod; 56. Wiping ball; 57. Protective rod. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0033] This application discloses a visual monitoring device for foundation settlement. (Refer to...) Figure 1 The foundation settlement visualization monitoring device includes a detection disc 11 installed at the settlement location of the foundation pit. Four through holes 12 are axially formed on the top surface of the detection disc 11. Ground nails are inserted through these through holes 12 into the settlement location of the foundation pit, thus fixing the detection disc 11 to the settlement location. A hollow box 13 is fixed at the center of the top surface of the detection disc 11. Inside the hollow box 13 are two detection structures 14 for detecting the settlement height of the foundation pit, symmetrically arranged.

[0034] Reference Figure 1-3 The hollow box 13 has two rotating circular grooves 15 along its length on its inner bottom surface, and each rotating circular groove 15 has a circular cross-section. The top surface of the hollow box 13 has two box-through grooves 16 along its length, and each box-through groove 16 has a rectangular cross-section. The detection structure 14 includes a threaded straight rod 17 vertically positioned on the inner bottom surface of the hollow box 13 via the rotating circular grooves 15, and a measuring square column 18 passing through the box-through grooves 16 on the top surface of the hollow box 13. A bearing is installed between the outer circumferential surface of the threaded straight rod 17 and the inner circumferential surface of the rotating circular grooves 15, thereby enabling the threaded straight rod 17 to be rotatably mounted inside the hollow box 13. The bottom surface of the measuring square column 18 has a threaded through hole 19 along its length. The measuring square column 18 is threadedly connected to the periphery of the top of the threaded straight rod 17 through the threaded through hole 19. A graduated ruler 20 for measurement is fixed to the front side of the measuring square column 18 along its length.

[0035] Reference Figure 1-3 A ratchet ring 21 is coaxially fitted around the periphery of the threaded straight rod 17. The ratchet ring 21 is fixed to the bottom surface of the hollow housing 13. The inner diameter of the ratchet ring 21 is larger than the diameter of the threaded straight rod 17. The ratchet ring 21 is a circular structure with a ring of ratchet teeth on its inner circumference. A limiting ring 22 is coaxially fixed around the bottom periphery of the threaded straight rod 17. A limiting sleeve 23 is fixed to the outer circumference of the limiting ring 22. A limiting wedge 24 passes through the end of the limiting sleeve 23 away from the limiting ring 22. A compression spring 25 is fixedly connected between the limiting wedge 24 and the side wall of the limiting ring 22. The end of the limiting wedge 24 near the inner circumference of the ratchet ring 21 is inclined, and the inclined surface of the limiting wedge 24 fits against the inclined surface of the ratchet teeth of the ratchet ring 21.

[0036] Reference Figure 1-3The hollow housing 13 has assembly grooves 26 on both its left and right inner sidewalls. A helical rod 27 is horizontally mounted on the inner sidewall of the hollow housing 13 through the assembly grooves 26. The helical rod 27 is a straight rod structure with four helical strips evenly spaced around its own axis. Bearings are installed between the inner circumferential surface of the assembly grooves 26 and the outer circumferential surface of the helical rod 27, allowing the helical rod 27 to rotate and be mounted inside the hollow housing 13 via the bearings. Bevel gears 28 are coaxially fixed to the end of the helical rod 27 near the threaded rod 17 and to the periphery of the helical rod 27, and the two bevel gears 28 are meshed together. Inside the hollow housing 13, a drive block 29 is slidably disposed along the length of the spiral rod 27. The drive block 29 has a spiral through hole 30 that matches the spiral strip on the outer circumference of the spiral rod 27 along the length of the spiral rod 27, so that the drive block 29 is spirally engaged with the spiral rod 27 through the spiral through hole 30.

[0037] Reference Figure 1-3 A guide rod 31 is hinged to the side wall of the drive block 29 away from the bevel gear 28. A guide slot 32, penetrating the left and right side walls, is provided in the hollow box 13. The guide slot 32 has a rectangular longitudinal section. The end of the guide rod 31 away from the drive block 29 passes through the guide slot 32 and exits the hollow box 13. Two reference blocks 33 are fixed at the edge of the top of the pit, facing each other. A steel wire strand 34 is fixedly installed on the side wall of the reference blocks 33 near the hollow box 13. A support rod 35 is vertically fixed to the top surface of the detection disc 11. A prying rod 36 is horizontally hinged to the top of the support rod 35. One end of the prying rod 36 is hinged to the end of the guide rod 31 away from the drive block 29, and the other end is hinged to the end of the steel wire strand 34 away from the reference block 33.

[0038] Reference Figure 2 and Figure 4 A cylindrical through-hole 37 is provided on the top surface of the hollow box 13. A measuring cylinder 38 is fixed to the top surface of the hollow box 13 through the cylindrical through-hole 37. Two supporting straight plates 39 are vertically fixed to the top surface of the measuring cylinder 38, and the two supporting straight plates 39 are arranged opposite each other. A camera 40 for monitoring the scale changes of the scale ruler 20 is installed between the two supporting straight plates 39. An adjusting rod 41 passes through both supporting straight plates 39, and the tail end of the camera 40 is fixed to the periphery of the adjusting rod 41. Both ends of the adjusting rod 41 pass through the supporting straight plates 39 and are coaxially fixed with adjusting gears 42. A transmission rod 43 passes through the opposite sidewalls of the two supporting straight plates 39. A transmission gear 44 is coaxially fixed to the end of the transmission gear 44 away from the supporting straight plate 39, and a rotating disk 45 is coaxially fixed to the sidewall of the transmission gear 44 away from the supporting straight plate 39.

[0039] Reference Figure 2 and Figure 4A drive cylinder 46 is vertically fixed to the bottom surface of the measuring cylinder 38. A synchronous straight rod 47 is horizontally fixed to the top of the output shaft of the drive cylinder 46. A drive rack 48 is vertically fixed to the top surface of both ends of the synchronous straight rod 47. Both drive racks 48 pass through the top surface of the measuring cylinder 38 and correspond one-to-one with two support plates 39. The adjusting gear 42 and the transmission gear 44 on the same support plate 39 are meshed with the corresponding drive rack 48. A slide rail straight rod 49 is vertically fixed to the top surface of the support plate 39, and the two slide rail straight rods 49 are arranged opposite each other. The side walls of the two slide rail straight rods 49 that are close to each other are vertically provided with slide rail through grooves 50. A protective cover 51 is vertically slidably installed between two slide rail rods 49. Protective rods 57 are fixed on the opposite side walls of the protective cover 51. The two protective rods 57 correspond one-to-one with the two slide rail rods 49. The protective rods 57 pass through the slide rail through slots 50 and slide rail rods 49, thereby enabling the protective cover 51 to slide along the length of the slide rail rods 49.

[0040] Reference Figure 2 and Figure 4 A supporting cylinder 52 is fixed to the rotating disk 45 near its outer edge, away from the surface of the supporting plate 39. Two sliding rods correspond one-to-one with the two supporting cylinders 52. The end of the protective rod 57 away from the protective cover 51 and the end of the corresponding supporting cylinder 52 away from the rotating disk 45 are hinged together by a connecting rod 53. The bottom surface of the protective cover 51 has a cover groove 54 that runs through its left and right sides. A wiping rod 55 is fixed to the protective cover 51 along its width direction through the cover groove 54. Wiping balls 56 are inserted around the wiping rod 55. The wiping balls 56 are spherical structures made of sponge.

[0041] The implementation principle of the foundation settlement visualization monitoring device in this application embodiment is as follows: When the foundation inside the foundation pit settles, a height difference is formed between the foundation inside the foundation pit and the reference ground. The steel wire strand 34 fixed by the reference block 33 pulls one end of the prying rod 36 to tilt upwards, and the other end of the prying rod 36 pushes the guide rod 31 to move towards the interior of the hollow box 13. The guide rod 31 pushes the driving block 29 to slide along the length direction of the spiral rod 27. The driving block 29 drives the spiral rod 27 to rotate through the spiral through hole 30. The spiral rod 27 drives the threaded rod 17 to rotate through the meshing relationship of two bevel gears 28. The threaded rod 17 and the measuring column 18 generate relative motion, causing the measuring column 18 to slide vertically upwards.

[0042] The drive cylinder 46 pushes two drive racks 48 vertically upward via a synchronous straight rod 47. The drive racks 48 drive the camera 40 to rotate via a regulating gear 42. The camera 40 detects the scale changes of the graduated rulers 20 on the surfaces of the two measuring columns 18 by rotating. The camera 40 feeds the data back to the data center to determine the settlement height of the foundation inside the pit. The data center can determine the inclination of the foundation inside the pit after settlement by the difference in data between the two measuring columns 18. When the camera 40 rotates to a vertical position, the drive racks 48 drive the rotating disk 45 to rotate via a transmission gear 44. The rotating disk 45 drives the protective cover 51 to slide vertically downward via a connecting straight rod 53 until the wiping ball 56 inside the protective cover 51 covers and wipes the lens of the camera 40, thereby protecting the lens of the camera 40 with the protective cover 51.

[0043] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A foundation settlement visualization monitoring device, comprising a detection disc (11) fixedly installed at the settlement position of a foundation pit and a hollow box (13) fixedly installed at the center of the top surface of the detection disc (11), wherein the hollow box (13) is provided with a plurality of measuring mechanisms for detecting the settlement height of the foundation pit, and the plurality of measuring mechanisms are symmetrically arranged, characterized in that: The measuring mechanism includes a threaded rod (17) that is vertically rotatably installed inside the hollow box (13) and a measuring square column (18) that is vertically inserted through the top surface of the hollow box (13). The measuring square column (18) is threaded to the periphery of the top of the threaded rod (17). A graduated ruler (20) is vertically fixed on the side wall of the measuring square column (18). The hollow box (13) is provided with a driving mechanism for driving the threaded rod (17) to rotate when the foundation pit settles. The driving mechanism includes a helical rod (27) horizontally rotatably installed inside the hollow box (13), a driving block (29) sliding along the length of the helical rod (27) inside the hollow box (13), and a pushing component located on the outside of the hollow box (13) for moving the driving block (29) during pit settlement. The helical rod (27) is a straight rod structure with several helical strips fixed around its circumference at equal intervals around its own axis. The driving block (29) has a helical through hole (30) that cooperates with several helical strips on the outer circumference of the helical rod (27). The driving block (29) is helically engaged with the helical rod (27) through the helical through hole (30). The threaded rod (17) and the helical rod (27) are coaxially fixed with bevel gears (28) at positions close to each other. The two bevel gears (28) are meshed together. The pushing component includes a reference block (33) installed on the top edge of the pit, a steel wire strand (34) fixed to the side wall of the reference block (33) near the hollow box (13), a guide rod (31) hinged to the side wall of the driving block (29) away from the reference block (33), a support rod (35) vertically fixed to the top surface of the detection disc (11), and a prying rod (36) horizontally hinged to the support rod (35). The end of the guide rod (31) away from the driving block (29) extends out of the hollow box (13), one end of the prying rod (36) is hinged to the end of the guide rod (31) away from the driving block (29), and the other end of the prying rod (36) is hinged to the end of the steel wire strand (34) away from the reference block (33).

2. The foundation settlement visualization monitoring device according to claim 1, characterized in that: A camera (40) for monitoring the scale changes of the scale ruler (20) is rotatably mounted on the top surface of the hollow box (13), and a protective mechanism for protecting the lens of the camera (40) is provided on the top surface of the hollow box (13).

3. The foundation settlement visualization monitoring device according to claim 2, characterized in that: The protective mechanism includes two vertically fixed sliding rail rods (49) on the top surface of the hollow box (13), a protective cover (51) vertically slidably disposed between the two sliding rail rods (49), and a wiping ball (56) rotatably mounted on the bottom of the protective cover (51) for wiping the lens of the camera (40). The top of the hollow box (13) is provided with a synchronization mechanism for driving the camera (40) and the protective cover (51) to move synchronously.

4. The foundation settlement visualization monitoring device according to claim 3, characterized in that: The synchronization mechanism includes a drive cylinder (46) fixed to the top of the hollow box (13), a drive rack (48) fixed to the output shaft of the drive cylinder (46), an adjustment gear (42) coaxially fixed to the tail end of the camera (40), and a drive component set on the top of the hollow box (13) for driving the protective cover (51) to slide vertically. The drive rack (48) passes through the top surface of the hollow box (13) and meshes with the adjustment gear (42).

5. The foundation settlement visualization monitoring device according to claim 4, characterized in that: The driving component includes a transmission gear (44) rotatably mounted on the top of the hollow housing (13), a rotating disk (45) coaxially fixed to the side wall of the transmission gear (44) away from the camera (40), and a supporting cylinder (52) fixed to the surface of the rotating disk (45) away from the camera (40) near its own outer peripheral edge. A connecting rod (53) is hinged between the side wall of the protective cover (51) and the end of the supporting cylinder (52) away from the rotating disk (45).

6. The foundation settlement visualization monitoring device according to claim 1, characterized in that: The hollow box (13) is provided with a limiting mechanism to prevent the threaded rod (17) from rotating back. The limiting mechanism includes a ratchet ring (21) coaxially sleeved on the periphery of the threaded rod (17), a limiting sleeve (23) fixed on the periphery of the bottom of the threaded rod (17), a limiting wedge (24) passing through the inside of the limiting sleeve (23), and a compression spring (25) fixedly connected between the limiting wedge (24) and the side wall of the threaded rod (17) that are close to each other. The ratchet ring (21) is fixed on the inner bottom surface of the hollow box (13). The end of the limiting wedge (24) is inclined and the inclined surface of the limiting wedge (24) is in contact with the ratchet inclined surface of the ratchet ring (21).

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