A semi-trailer main frame

Abstract

The application discloses a semitrailer main frame, a side plate comprising a lower plate body, an upper plate body and an intermediate plate body, the height of the intermediate plate body relative to the lower plate body is adjusted through a first height adjusting mechanism to realize the overall height adjustment of the side plate, the fixing device comprises a lifting column, a second height adjusting mechanism and a limiting sleeve, after the height adjustment of the side plate, the height of the limiting sleeve is adjusted through the second height adjusting mechanism to realize the height adjustment of the limiting sleeve, so that the height of the limiting sleeve can be adapted to the height of the folding corner of the upper plate body to realize the sleeving fixation; meanwhile, during the use of the side plate, the two folding corners at the top of the upper plate body are respectively limited through the limiting sleeves of the two fixing devices, at this time, the first height adjusting mechanism can drive the small-amplitude lifting of the upper plate body to realize the connection and disconnection of the upper plate body and the two limiting sleeves; in addition, the lifting column and the limiting sleeve are connected at the folding corner of the upper plate body, the side plate can be reinforced, and the structural stability of the whole side plate is improved.

Description

Technical Field

[0001] This invention relates to the field of semi-trailer technology, and in particular to a semi-trailer main frame. Background Technology

[0002] A semi-trailer consists of a frame, main connecting base, towing pin, suspension system, running gear, and support devices. The main connecting base is mounted on the frame and allows for cargo stacking. A typical main connecting base structure includes a floor plate mounted on the frame (using methods such as fixed connection or hydraulic cylinder rotation connection), a front baffle at the front end of the floor plate, a rear baffle at the rear end of the floor plate, and side baffles on both sides of the floor plate. The side baffles include multiple uprights mounted on the floor plate, multiple side plates hinged to the floor plate and located between two uprights, and multiple fixing devices between the side plates and uprights for fixing or unlocking the side plates.

[0003] During the transportation of goods, some goods are taller and require higher side guards, while others are shorter and only require lower side guards. However, the height of the side guards on the existing vehicle connecting base is usually fixed and cannot be adjusted to a suitable height for different goods. Summary of the Invention

[0004] The purpose of this invention is to provide a semi-trailer main frame that enables adjustment of the side guard height.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a semi-trailer main frame, including a floor plate, a front guard disposed at the front end of the floor plate, a rear guard disposed at the rear end of the floor plate, and side guards disposed on both sides of the floor plate. The side guards include multiple columns disposed on the floor plate, multiple side plates hinged to the floor plate and respectively located between two columns, and multiple fixing devices disposed between the side plates and columns to fix or unlock the side plates. The side plates include a lower plate body hinged to the floor plate, an upper plate body, an intermediate plate body disposed at the bottom of the upper plate body and telescopically disposed on the lower plate body, and a first height adjustment mechanism disposed between the lower plate body and the intermediate plate body to adjust the height of the intermediate plate body relative to the lower plate body. The fixing devices include a lifting column disposed on the columns, a second height adjustment mechanism disposed between the columns and the lifting column to adjust the height of the lifting column, and a limiting sleeve disposed at the upper end of the lifting column and sleeved at the corner of the adjacent upper plate body during the upward movement of the upper plate body. The fixing device located at the end has one limiting sleeve, and the fixing device located in the middle has two limiting sleeves respectively corresponding to the corners of two adjacent upper plates.

[0006] By adopting the above technical solution, the side panel includes a lower panel, an upper panel, and a middle panel. The height of the middle panel relative to the lower panel is adjusted by a first height adjustment mechanism to achieve overall height adjustment of the side panel. The fixing device includes a lifting column, a second height adjustment mechanism, and a limiting sleeve. After the height of the side panel is adjusted, the height of the lifting column is adjusted by the second height adjustment mechanism to adjust the height of the limiting sleeve so that the height of the limiting sleeve can be adapted to the height of the corner of the upper panel for fixing. At the same time, during the use of the side panel, since the two corners at the top of the upper panel are limited by the limiting sleeves of the two fixing devices, the upper panel can be slightly raised and lowered by the first height adjustment mechanism to connect and disconnect the upper panel and the two limiting sleeves. In addition, the lifting column and the limiting sleeve are connected at the corners of the upper panel to reinforce the side panel and improve the structural stability of the entire side panel.

[0007] A further feature of the present invention is that: the top of the intermediate plate is provided with a plurality of telescopic shafts that are telescopically mounted on the upper plate and have an anti-detachment function; a first compression spring is sleeved on the telescopic shaft and abuts between the upper plate and the intermediate plate; a handle is provided on the outer side of the upper plate; when the handle is pulled down to make the upper plate move downward against the elastic force of the first compression spring, the corner of the upper plate gradually disengages from the limiting sleeve.

[0008] By adopting the above technical solution, since the first height adjustment mechanism drives the upper plate to move up and down slightly, it is inconvenient to connect and disconnect the upper plate and the two limiting sleeves. At this time, through the setting of telescopic shaft, first compression spring and handle, when the handle is pulled down so that the upper plate moves down against the elastic force of the first compression spring, the corner of the upper plate gradually separates from the limiting sleeve, so that the side plate can be opened. Similarly, when the handle is released, the upper plate can be embedded in the limiting sleeve for limiting under the reset action of the first compression spring, so that the side plate can be fixed.

[0009] A further feature of the present invention is that: a limiting groove extending vertically is provided at the position of the column near the side plate; limiting shafts that are telescopically provided on both sides of the top of the intermediate plate are used to embed into the limiting groove; a second compression spring is provided between the intermediate plate and the limiting shafts to drive the limiting shafts to move away from the limiting grooves; and a linkage mechanism is provided between the upper plate, the intermediate plate, and the two limiting shafts to cause the limiting shafts to disengage from the limiting grooves during the downward movement of the upper plate and to gradually embed the limiting shafts into the limiting grooves during the upward movement of the upper plate.

[0010] By adopting the above technical solution, since the connection between the side plate and the column is only between the upper plate and the limiting sleeve, the connection stability between the two is relatively poor. At this time, the linkage mechanism is set so that when the upper plate is connected to the limiting sleeve at the corner, the limiting shaft can be embedded in the limiting groove for reinforcement. When the upper plate moves downward and separates from the limiting groove, the limiting shaft also separates from the limiting groove, thus improving the connection stability between the side plate and the column.

[0011] A further configuration of the present invention is as follows: the linkage mechanism includes a connecting base disposed in the middle of the bottom of the upper plate, a first wedge block disposed on both sides of the connecting base, and a second wedge block disposed at the end of the limiting shaft and abutting against the first wedge block. When the first wedge block moves downward, the second wedge block moves toward the direction closer to the connecting base.

[0012] By adopting the above technical solution, during the downward movement of the upper plate, the contact surface of the first wedge block and the second wedge block changes, so that the second wedge block, the limiting shaft, and the second compression spring move towards the connecting base under the action of the second wedge block, the limiting shaft gradually disengages from the limiting groove to open the side plate. Conversely, it does not affect the installation and fixation of the side plate when it is fixed.

[0013] A further feature of the present invention is that: the two columns are provided with guide slopes that drive the limiting shaft to overcome the force of the second compression spring and gradually retract into the middle plate body, and during the extension and retraction of the middle plate body, the limiting shaft is within the range of the guide slopes.

[0014] By adopting the above technical solution, when closing the side panel, the side panel is rotated upward by the handle. During the rotation of the side panel, the guide slope is set, and under the elastic force of the second compression spring, the limiting shaft can be gradually retracted into the middle plate. At this time, the second wedge block also applies pressure to the first wedge block. Under the elastic force of the first compression spring, the upper plate moves downward, thus facilitating the closing of the side panel without having to apply a downward pulling force to the handle when closing.

[0015] A further feature of the present invention is that the handle is hinged to the upper plate, and a hook is provided on the second wedge block. When the upper plate moves downward against the elastic force of the first compression spring to disengage from the limiting sleeve, the handle can be inserted into the hook after rotation and is pressed against the first compression spring under the reset action. In this state, the upper plate does not interfere with the limiting sleeve during rotation.

[0016] By adopting the above technical solution, after the side panel is opened, the handle is connected to two hooks to prevent the first compression spring from fully resetting. This eliminates the need to pull the handle down to move the upper panel downwards when closing the side panel, thus improving ease of operation. At the same time, the handle can improve the connection stability between the upper panel and the middle panel when the side panel hangs down naturally after opening.

[0017] A further provision of the present invention is that a plurality of first height adjustment mechanisms are arranged between the lower plate and the middle plate. The first height adjustment mechanism includes a first threaded rod disposed on the lower plate, a second threaded rod disposed on the upper plate, and a threaded tube having threaded ends with opposite thread directions at both ends. The two ends of the threaded tube are respectively connected to the first threaded rod and the second threaded rod, and the threaded tube has a rotating end in the shape of a regular polygon on its periphery.

[0018] By adopting the above technical solution, when adjusting the height of the intermediate plate, by simultaneously rotating multiple threaded tubes, the corresponding first threaded rod and second threaded rod can be moved closer or further apart, thereby driving the intermediate plate to rise and fall, so as to adjust the height of the intermediate plate.

[0019] A further feature of the present invention is that the lower end of the lifting column is provided with a threaded shaft extending through the bottom of the column, and the second height adjustment mechanism includes a limiting ring disposed on the lifting column and not affecting the fastening of the limiting sleeve and the upper plate, a third compression spring sleeved on the lifting column and pressing against the limiting ring and the column, and an adjustment handwheel threadedly connected to the threaded shaft and pressing against the bottom of the column.

[0020] By adopting the above technical solution, when adjusting the height of the lifting column after adjusting the side plate height, the position of the threaded connection between the adjusting handwheel and the threaded shaft is changed by rotating the adjusting handwheel, thereby adjusting the height of the lifting column protruding from the upright column. Furthermore, after the lifting column height is adjusted, the third compression spring prevents the lifting column from moving downwards. Simultaneously, when covering the main connecting base with a tarpaulin and securing it with ropes, the lower end of the threaded shaft can serve as a securing connection point. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0022] Figure 1 This is a schematic diagram of the structure of Example 1; Figure 2 This is a partial structural schematic diagram of Example 1; Figure 3 yes Figure 2 A magnified view of the area located at point A; Figure 4 This is a partial front view of the structure in Embodiment 2; Figure 5 This is a partial structural schematic diagram of Example 3.

[0023] In the diagram: 1. Base plate; 2. Front guard; 3. Rear guard; 4. Side guard; 41. Column; 411. Limiting groove; 412. Guide slope; 42. Side plate; 421. Lower plate; 422. Upper plate; 4221. Waist-shaped hole; 4222. Handle; 423. Middle plate; 4231. Telescopic shaft; 4232. Limiting bolt; 4233. Limiting shaft; 4234. Second compression spring; 424. First height adjustment mechanism; 425. First compression spring; 4251. First threaded rod ; 4252, Second threaded rod; 4253, Threaded tube; 426, Linkage mechanism; 4261, Connecting base; 4262, First wedge block; 4263, Second wedge block; 427, Hook; 43, Fixing device; 431, Lifting column; 4311, Threaded shaft; 432, Second height adjustment mechanism; 4321, Limiting ring; 4322, Third compression spring; 4323, Adjusting handwheel; 433, Limiting sleeve. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1: A semi-trailer main frame, such as Figure 1 As shown, the system includes a base plate 1, a front stop 2 located at the front end of the base plate 1, a rear stop 3 located at the rear end of the base plate 1, and side stops 4 located on both sides of the base plate 1. The side stops 4 include multiple uprights 41 mounted on the base plate 1, multiple side plates 42 hinged to the base plate 1 and located between two uprights 41 respectively, and multiple fixing devices 43 located between the side plates 42 and the uprights 41 to fix or unlock the side plates 42.

[0026] like Figure 1 and Figure 2 As shown, the side plate 42 includes a lower plate 421 hinged to the base plate 1, an upper plate 422, an intermediate plate 423 disposed at the bottom of the upper plate 422 and telescopically disposed on the lower plate 421, and a first height adjustment mechanism 424 disposed between the lower plate 421 and the intermediate plate 423 and realizing the adjustment of the height of the intermediate plate 423 relative to the lower plate 421.

[0027] like Figure 2 and Figure 3 As shown, multiple first height adjustment mechanisms 424 are arranged between the lower plate 421 and the middle plate 423. Each first height adjustment mechanism 424 includes a first threaded rod 4251 on the lower plate 421, a second threaded rod 4252 on the upper plate 422, and a threaded tube 4253 with threaded ends having opposite thread directions at both ends. The two ends of the threaded tube 4253 are respectively connected to the first threaded rod 4251 and the second threaded rod 4252. A rotating end in the shape of a regular polygon is provided around the periphery of the threaded tube 4253. Multiple telescopic shafts 4231, which are telescopically mounted on the upper plate 422 and have an anti-fall-off function, are provided on the top of the middle plate 423. An oblong hole 4221 is provided on the upper plate 422, and a limiting bolt 4232 located within the oblong hole 4221 is threaded to the upper end of each telescopic shaft 4231. A first compression spring 425 is sleeved on the telescopic shaft 4231, which abuts against the upper plate 422 and the middle plate 423. A handle 4222 is provided on the outside of the upper plate 422. When the handle 4222 is pulled down so that the upper plate 422 moves downward against the elastic force of the first compression spring 425, the corner of the upper plate 422 gradually disengages from the limiting sleeve 433.

[0028] like Figure 1 and Figure 2 As shown, the fixing device 43 includes a lifting column 431 that is lifted and lowered on the column 41, a second height adjustment mechanism 432 that is disposed between the column 41 and the lifting column 431 and realizes the height adjustment of the lifting column 431, and a limiting sleeve 433 disposed at the upper end of the lifting column 431 and realized by fitting at the corner of the adjacent upper plate 422 during the upward movement of the upper plate 422. The fixing device 43 located at the end has one limiting sleeve 433, and the fixing device 43 located in the middle has two limiting sleeves 433 that correspond to the corners of two adjacent upper plates 422 respectively. The lower end of the lifting column 431 is provided with a threaded shaft 4311 that passes through the bottom of the column 41. The second height adjustment mechanism 432 includes a limiting ring 4321 that is provided on the lifting column 431 and does not affect the fastening of the limiting sleeve 433 and the upper plate 422, a third compression spring 4322 that is sleeved on the lifting column 431 and abuts against the limiting ring 4321 and the column 41, and an adjustment handwheel 4323 that is threadedly connected to the threaded shaft 4311 and abuts against the bottom of the column 41.

[0029] Implementation effect: The side panel 42 includes a lower panel 421, an upper panel 422, and a middle panel 423. The height of the middle panel 423 relative to the lower panel 421 is adjusted by the first height adjustment mechanism 424 to achieve overall height adjustment of the side panel 42. The fixing device 43 includes a lifting column 431, a second height adjustment mechanism 432, and a limiting sleeve 433. After the height of the side panel 42 is adjusted, the height of the lifting column 431 is adjusted by the second height adjustment mechanism 432 to adjust the height of the limiting sleeve 433, ensuring that the height of the limiting sleeve 433 is suitable for... The height of the corner of the upper plate 422 is used to achieve the fixed installation; at the same time, during the use of the side plate 42, since the two corners at the top of the upper plate 422 are limited by the limiting sleeves 433 of the two fixing devices 43, the upper plate 422 can be raised and lowered slightly by the first height adjustment mechanism 424 to achieve the connection and disconnection of the upper plate 422 and the two limiting sleeves 433; in addition, the lifting column 431 and the limiting sleeves 433 are connected to the corner of the upper plate 422 to reinforce the side plate 42 and improve the structural stability of the entire side plate 4. Because the first height adjustment mechanism 424 drives the upper plate 422 to rise and fall slightly, it is inconvenient to connect and disconnect the upper plate 422 and the two limiting sleeves 433. At this time, through the setting of the telescopic shaft 4231, the first compression spring 425 and the handle 4222, when the handle 4222 is pulled down so that the upper plate 422 moves downward against the elastic force of the first compression spring 425, the corner of the upper plate 422 gradually separates from the limiting sleeve 433, so that the side plate 42 can be opened. Similarly, when the handle 4222 is released, the upper plate 422 can be embedded in the limiting sleeve 433 for limiting under the reset action of the first compression spring 425, so that the side plate 42 can be fixed.

[0030] Example 2: A semi-trailer main frame, such as Figures 1 to 4 As shown, the difference from Embodiment 1 is that: a limiting groove 411 extending vertically is provided on the column 41 near the side plate 42; limiting shafts 4233 are telescopically provided on both sides of the top of the middle plate 423 to be embedded in the limiting groove 411; a second compression spring 4234 is provided between the middle plate 423 and the limiting shafts 4233 to drive the limiting shafts 4233 to move away from the limiting groove 411; and a linkage mechanism 426 is provided between the upper plate 422, the middle plate 423 and the two limiting shafts 4233 to separate the limiting shafts 4233 from the limiting groove 411 during the downward movement of the upper plate 422 and to gradually embed the limiting shafts 4233 into the limiting groove 411 during the upward movement of the upper plate 422.

[0031] like Figure 4As shown, the linkage mechanism 426 includes a connecting base 4261 located at the bottom center of the upper plate 422, first wedge blocks 4262 symmetrically arranged on both sides of the connecting base 4261, and a second wedge block 4263 located at the end of the limiting shaft 4233 and abutting against the first wedge block 4262. When the first wedge block 4262 moves downward, the second wedge block 4263 moves towards the connecting base 4261. At the same time, the two columns 41 are provided with guide slopes 412 that drive the limiting shaft 4233 to overcome the force of the second compression spring 4234 and gradually retract into the middle plate 423. During the extension and retraction of the middle plate 423, the limiting shaft 4233 is always within the range of the guide slopes 412.

[0032] Implementation effect: Since the connection between the side plate 42 and the column 41 is only between the upper plate 422 and the limiting sleeve 433, the connection stability between the two is relatively poor. At this time, the linkage mechanism 426 is set so that when the upper plate 422 is connected to the limiting sleeve 433 at the corner, the limiting shaft 4233 can be embedded in the limiting groove 411 for reinforcement. When the upper plate 422 moves downward and separates from the limiting groove 411, the limiting shaft 4233 also separates from the limiting groove 411, thus improving the connection stability between the side plate 42 and the column 41. During the downward movement of the upper plate 422, the contact surfaces of the first wedge block 4262 and the second wedge block 4263 change, so that the second wedge block 4263, the limiting shaft 4233, and the second compression spring 4234 move toward the connecting base 4261 under the action of the second wedge block 4263, the limiting shaft 4233, and the second compression spring 4234, so that the limiting shaft 4233 gradually disengages from the limiting groove 411 to open the side plate 42. Conversely, when the side plate 42 is fixed, it does not affect the installation and fixation of the side plate 42.

[0033] Example 3: A semi-trailer main frame, such as Figure 4 and Figure 5 As shown, the difference from Embodiment 2 is that the guide ramp 412 is not provided, but the handle 4222 is hinged to the upper plate 422. The second wedge block 4263 is provided with a hook 427. When the upper plate 422 moves downward against the elastic force of the first compression spring 425 to achieve the process of disengaging from the limiting sleeve 433, the handle 4222 can be embedded in the hook 427 after rotation and is pressed against the first compression spring 425 under the reset action. In this state, the upper plate 422 does not interfere with the limiting sleeve 433 during rotation.

[0034] Implementation effect: After the side panel 42 is opened, the handle 4222 is connected to the two hooks 427 to prevent the first compression spring 425 from fully resetting. Therefore, when closing the side panel 42, there is no need to pull the handle 4222 downward to make the upper panel 422 move downward, which improves the convenience of operation. At the same time, when the side panel 42 hangs down naturally after being opened, the handle 4222 can improve the connection stability between the upper panel 422 and the middle panel 423.

Claims

1. A semi-trailer main frame, comprising a floor plate (1), a front guard (2) disposed at the front end of the floor plate (1), a rear guard (3) disposed at the rear end of the floor plate (1), and side guards (4) disposed on both sides of the floor plate (1), wherein the side guards (4) comprise a plurality of uprights (41) disposed on the floor plate (1), a plurality of side plates (42) hinged to the floor plate (1) and respectively located between two uprights (41), and a plurality of fixing devices (43) disposed between the side plates (42) and the uprights (41) and realizing the movement of fixing or unlocking the side plates (42), characterized in that: The side plate (42) includes a lower plate (421) hinged to the base plate (1), an upper plate (422), an intermediate plate (423) disposed at the bottom of the upper plate (422) and telescopically disposed on the lower plate (421), and a first height adjustment mechanism (424) disposed between the lower plate (421) and the intermediate plate (423) to adjust the height of the intermediate plate (423) relative to the lower plate (421); the fixing device (43) includes a lifting column (431) that is lifted and lowered on the column (41), and a fixing device (431) that is disposed on the column (41). 41) and the second height adjustment mechanism (432) between the lifting column (431) and the lifting column (431) to adjust the height of the lifting column (431), the limiting sleeve (433) provided at the upper end of the lifting column (431) and implemented at the corner of the adjacent upper plate (422) during the upward movement of the upper plate (422), the fixing device (43) at the end has a limiting sleeve (433), and the fixing device (43) in the middle has two limiting sleeves (433) respectively corresponding to the corners of two adjacent upper plates (422). The top of the intermediate plate (423) is provided with a plurality of telescopic shafts (4231) that are telescopically mounted on the upper plate (422) and have an anti-fall-off function. A first compression spring (425) is sleeved on the telescopic shaft (4231) and abuts against the upper plate (422) and the intermediate plate (423). A handle (4222) is provided on the outside of the upper plate (422). When the handle (4222) is pulled down so that the upper plate (422) moves down against the elastic force of the first compression spring (425), the corner of the upper plate (422) gradually separates from the limiting sleeve (433). The column (41) is provided with a limiting groove (411) extending vertically near the side plate (42). The top two sides of the middle plate (423) are provided with limiting shafts (4233) that can be embedded in the limiting grooves (411). A second compression spring (4234) is provided between the middle plate (423) and the limiting shafts (4233) to drive the limiting shafts (4233) to move away from the limiting grooves (411). A linkage mechanism (426) is provided between the upper plate (422), the middle plate (423) and the two limiting shafts (4233) to separate the limiting shafts (4233) from the limiting grooves (411) during the downward movement of the upper plate (422) and to gradually embed the limiting shafts (4233) into the limiting grooves (411) during the upward movement of the upper plate (422).

2. The semi-trailer main frame according to claim 1, characterized in that: The linkage mechanism (426) includes a connecting base (4261) disposed in the middle of the bottom of the upper plate (422), a first wedge block (4262) symmetrically disposed on both sides of the connecting base (4261), and a second wedge block (4263) disposed at the end of the limiting shaft (4233) and abutting against the first wedge block (4262). When the first wedge block (4262) moves downward, the second wedge block (4263) moves toward the connecting base (4261).

3. A semi-trailer main frame according to claim 2, characterized in that: The two columns (41) are provided with a guide slope (412) that drives the limiting shaft (4233) to overcome the force of the second compression spring (4234) and gradually retract into the middle plate (423). During the extension and retraction of the middle plate (423), the limiting shaft (4233) is within the range of the guide slope (412).

4. A semi-trailer main frame according to claim 3, characterized in that: The handle (4222) is hinged to the upper plate (422), and the second wedge block (4263) is provided with a hook (427). When the upper plate (422) moves downward against the elastic force of the first compression spring (425) to achieve the process of disengaging from the limiting sleeve (433), the handle (4222) can be embedded in the hook (427) after rotation and is pressed against the first compression spring (425) under the reset action. In this state, the upper plate (422) does not interfere with the limiting sleeve (433) during rotation.

5. A semi-trailer main frame according to claim 1, characterized in that: Multiple first height adjustment mechanisms (424) are arranged between the lower plate (421) and the middle plate (423). The first height adjustment mechanism (424) includes a first threaded rod (4251) on the lower plate (421), a second threaded rod (4252) on the upper plate (422), and a threaded tube (4253) with threaded ends having opposite thread directions at both ends. The two ends of the threaded tube (4253) are respectively connected to the first threaded rod (4251) and the second threaded rod (4252). The threaded tube (4253) has a rotating end in the shape of a regular polygon on its periphery.

6. A semi-trailer main frame according to claim 1, characterized in that: The lower end of the lifting column (431) is provided with a threaded shaft (4311) that passes through the bottom of the column (41). The second height adjustment mechanism (432) includes a limiting ring (4321) that is provided on the lifting column (431) and does not affect the fastening of the limiting sleeve (433) and the upper plate (422), a third compression spring (4322) that is sleeved on the lifting column (431) and abuts against the limiting ring (4321) and the column (41), and an adjustment handwheel (4323) that is threadedly connected to the threaded shaft (4311) and abuts against the bottom of the column (41).

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