Shield tunnel measuring device

Abstract

The invention relates to a shield tunnel measuring device, and belongs to the technical field of tunnel measurement, the shield tunnel measuring device comprises a mounting assembly and measuring units, the mounting assembly is mounted at the tail end of a shield tunneling machine, the measuring units are mounted on the mounting assembly, the mounting assembly comprises a fixed seat and a rotating arm, the fixed seat is mounted on the shield tunneling machine, the rotating arm is hinged to the fixed seat, and the measuring units are mounted on the rotating arm. A torsion spring used for enabling the fixing base and the rotating arm to be located on the same straight line is arranged on a hinge shaft between the rotating arm and the fixing base, an abutting piece used for abutting against the inner wall of the shield tunnel is arranged on the rotating arm, the measuring unit comprises a displayer, a measuring element and a target, and the target is installed on a fixing piece arm and electrically connected with the displayer. The measuring unit is installed on the rotating arm and can emit laser towards the target. The method has the effect of saving time to improve the measurement efficiency.

Description

Technical Field

[0001] The present application relates to the field of tunnel measurement, and in particular to a shield tunnel measurement device. Background Art

[0002] Shield tunnel is a general term for underground tunnels built using shield machines, among which subway tunnel is one of the common shield tunnels. During the construction of subway tunnels, the hydraulic system on the shield machine will push the shield machine to excavate in the direction of the tunnel extension, and at the same time, the prefabricated support plate inside the shield machine will be pushed out to support the tunnel excavated by the shield machine. However, since the shield tunnel is opened underground, the underground soil layer will squeeze the outer wall of the shield tunnel constructed by the shield machine. Therefore, it is necessary to measure the shield tunnel constructed by the shield machine in real time, so as to timely understand the deformation of the shield tunnel caused by the squeezing of the soil on the surface.

[0003] At present, measurement in shield tunnels mainly relies on total stations. After the shield tunnel is completed, the total station selects a unit measurement length in the shield tunnel for measurement to understand the deformation inside the subway shield tunnel. However, with the extension of the shield tunnel, the points that need to be measured are gradually increasing, which requires the use of total stations for measurement in shield tunnels multiple times. However, each time the total station is used, it needs to be adjusted, which takes a lot of time and has low efficiency. Summary of the invention

[0004] In order to reduce the number of total stations, thereby saving the time spent on adjusting the total stations and improving measurement efficiency, the present application provides a shield tunnel measurement device.

[0005] The present application provides a shield tunnel measurement device that adopts the following technical solution: It includes a mounting assembly and a measuring unit. The mounting assembly is mounted at the rear end of the shield machine. The measuring units are respectively mounted on the mounting assembly. The mounting assembly includes a fixed seat and a rotating arm. The fixed seat is mounted on the shield machine. The rotating arm is hinged on the fixed seat. A torsion spring for making the fixed seat and the rotating arm in the same straight line is arranged on the hinge shaft between the rotating arm and the fixed seat. An abutment piece for abutting against the inner wall of the shield tunnel is arranged on the rotating arm. The measuring unit includes a display, a measuring element and a target. The target is mounted on the fixed arm and electrically connected to the display. The measuring unit is mounted on the rotating arm and can emit laser toward the target.

[0006] By adopting the above technical solution, when the front end of the shield machine is in the tunneling process, the rear end of the shield machine is in a static state. At this time, the fixed seat and the rotating arm are in a straight line state. The measuring element on the mounting assembly emits laser towards the target, and the abutting member on the mounting assembly abuts against the inner wall of the already built shield tunnel. When the tunnel has not deformed, the abutting member only abuts against the inner wall of the shield tunnel, and the laser of the measuring element irradiates the central area of the target. If the shield tunnel has deformed, the abutting member will drive the rotating arm to rotate around the hinge axis on the fixed seat under the push of the inner wall of the shield tunnel, so that the position where the measuring element irradiates on the target is shifted. The electrical connection between the target and the display enables the staff to view the deviation degree of the laser on the target through the display inside the shield machine, so as to understand the deformation situation of the tunnel. Since the mounting assembly will move forward with the advancement of the shield machine, when the tunnel excavation is completed, the measurement of the tunnel is initially completed, and there is no need to set up multiple points in the tunnel for measurement after the excavation is completed, saving the time spent on adjusting the total station multiple times and achieving the effect of improving the construction efficiency.

[0007] Optionally, the rotating arm includes a first rotating arm and a second rotating arm. The first rotating arm is hinged to the fixed seat, and the axis of the hinge axis between the first rotating arm and the fixed seat is perpendicular to the ground. The second rotating arm is sleeved on the first rotating arm and can slide on the first rotating arm. The measuring element and the abutting member are both arranged on the second rotating arm.

[0008] By adopting the above technical solution, the rotating arm includes a first rotating arm and a second rotating arm. The second rotating arm is sleeved on the first rotating arm and can slide along the first rotating arm, which enables the distance between the measuring element and the target to be adjusted, thereby adjusting the length of the measuring section and having a wider applicable range.

[0009] Optionally, a sliding groove is arranged on the first rotating arm, and the depth of the sliding groove gradually decreases from the direction close to the fixed seat to the direction away from the fixed seat. A limiting member is arranged at the position corresponding to the sliding groove on the rotating arm. The limiting member is connected to the second rotating arm by means of thread fit, and the limiting member can abut against the sliding groove after passing through the second rotating arm.

[0010] By adopting the above technical solution, when the limiting member is not tightened, one end of the limiting member is located in the sliding groove, so that when the second rotating arm slides on the first rotating arm, it will not come out of the first rotating arm. The depth of the sliding groove gradually decreases from the direction close to the fixed seat to the direction away from the fixed seat, so that after the limiting member is tightened, the limiting member can be tightly abutted in the limiting groove, thereby fixing the sliding position of the second rotating arm on the first rotating arm.

[0011] Optionally, the fixed seat is hinged to the shield machine. The axis of the hinge shaft between the fixed seat and the shield machine is perpendicular to the axis of the hinge shaft between the first rotating arm and the fixed seat. An extensible support rod is arranged on the second rotating arm. One end of the extensible support rod away from the second rotating arm is detachably connected to the shield machine. The extensible support rod is used to support the second rotating arm so that the second rotating arm can maintain a horizontal state.

[0012] By adopting the above technical solution, the fixed seat is hinged to the shield machine, so that the fixed seat can rotate around the axis of the hinge shaft on the shield machine. Thus, when not in use, the fixed seat and the rotating arm can be stored as the fixed seat rotates, thereby reducing the occupied space of the fixed seat and the rotating arm when not in use. The extensible support rod plays a supporting role for the rotating arm when the fixed seat and the rotating arm need to be used.

[0013] Optionally, one end of the extensible support rod is connected to the second rotating arm by means of a spherical hinge. The other end of the support rod is connected with a plug-in member by means of a spherical hinge. A plug-in part is arranged on the shield machine. The plug-in member and the plug-in part are connected by means of plug-in cooperation.

[0014] By adopting the above technical solution, one end of the extensible support rod is connected to the second rotating arm by means of a spherical hinge, and the other end of the extensible support rod is connected with a plug-in member by means of a spherical hinge. When the plug-in member is connected to the plug-in part on the shield machine, while the extensible support rod plays a supporting role for the second rotating arm, when the rotating arm rotates around the axis of the hinge shaft between the rotating arm and the fixed seat, the extensible support rod can deflect as the rotating arm rotates.

[0015] Optionally, the abutting member includes a first telescopic rod, a second telescopic rod, a spring and a rolling bead. One end of the first telescopic rod is connected to the second rotating arm. The other end of the first telescopic rod is sleeved on the second telescopic rod. The second telescopic rod can slide on the first telescopic rod. The rolling bead is installed at the end of the second telescopic rod away from the first telescopic rod by means of a spherical hinge. The spring is located inside the first telescopic rod and is connected to the second telescopic rod. The elastic coefficient of the spring is less than that of the torsion spring.

[0016] By adopting the above technical solution, when the shield machine is in the process of moving forward, the rolling bead is always in contact with the outer wall of the shield tunnel, so as to move along the shield tunnel. When the rolling bead contacts an uneven place on the inner wall of the shield tunnel, the spring inside the first telescopic rod plays a role in compensating for the displacement. The spring enables the rolling bead to always be in contact with the inner wall of the shield tunnel when passing through an uneven place on the inner wall of the shield tunnel. The fact that the elastic coefficient of the spring is less than that of the torsion spring further enables the spring to undergo elastic deformation prior to the torsion spring when the rolling bead passes through an uneven place on the inner wall of the shield tunnel with bumps and depressions, and the rotating arm will not rotate before the spring is compressed to the limit, reducing the probability of measurement errors caused by the uneven inner wall of the shield tunnel.

[0017] Optionally, a sensor is provided on the first telescopic rod. The sensor is electrically connected to the display. An induction block for the sensor to sense is provided on the second telescopic rod.

[0018] By adopting the above technical solution, the sensor is electrically connected to the display, and an induction block for the sensor to sense is provided on the second telescopic rod, enabling the staff to read the distance between the induction block and the sensor through the display, thereby understanding the compressed state of the spring at this time.

[0019] Optionally, a sliding portion is provided on the induction block. The sliding portion is sleeved on the second telescopic rod, and a fixing member is inserted through the sliding portion for fixing the position of the sliding portion on the second telescopic rod.

[0020] By adopting the above technical solution, a sliding portion is provided on the induction block, enabling the position of the induction block on the first telescopic rod to be adjusted, thereby adjusting the induction distance between the inductor and the induction block. After the position of the induction block is adjusted, the position of the induction block on the second telescopic rod can be fixed by the fixing member.

[0021] In summary, the present application includes at least the following beneficial technical effects: 1. By providing a fixed seat installed on the shield machine, a rotating arm hinged to the fixed seat, a target installed on the fixed seat, a measuring element installed on the rotating arm, and an abutting member installed on the rotating arm and capable of abutting against the inner wall of the shield tunnel, when the shield machine advances, the target and the measuring element will also advance together. Therefore, when the tunnel excavation is completed, the measurement of the tunnel deformation amount is initially completed, eliminating the need to set multiple points in the tunnel for measurement after excavation, saving the time spent on repeatedly adjusting the total station, and achieving the effect of improving construction efficiency; 2. By setting the rotating arm as the first rotating arm and the second rotating arm that can slide on the first rotating arm, the distance between the measuring element and the target can be adjusted, achieving the effect of adjusting the measuring distance between the measuring element and the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a three-dimensional schematic diagram of a shield tunnel measuring device of the present application; Figure 2 is Figure 1 a cross-sectional view of the rotating arm in Figure 3 is Figure 2 an enlarged schematic view of part A in Figure 4 is Figure 1 a structural schematic diagram of the abutting member in

[0023] Description of reference numerals: 1. Installation component; 2. Measuring unit; 3. Shield machine; 4. Fixed seat; 5. Rotating arm; 6. Torsion spring; 7. Contact member; 8. Measuring element; 9. Display; 10. Target; 11. First rotating arm; 12. Second rotating arm; 13. Telescopic support rod; 14. Insertion part; 15. Connector; 16. Sliding groove; 17. Limiting member; 18. First telescopic rod; 19. Second telescopic rod; 20. Spring; 21. Rolling bead; 22. Sensor; 23. Induction block; 24. Sliding part; 25. Fixing member. Detailed implementation manners

[0024] The following further describes the present application in detail with reference to the Figures 1-4 accompanying drawings.

[0025] An embodiment of the present application discloses a shield tunnel measuring device. Referring to Figure 1 , it includes two sets of installation components 1 and two sets of measuring units 2. The two sets of measuring units 2 are respectively installed on the two sets of installation components 1. The two sets of installation components 1 are respectively installed at the tail end of the shield machine 3 and are symmetrically distributed on both sides of the tail end of the shield machine 3 with respect to the central axis of the shield machine 3. A contact member 7 that can contact the inner wall of the shield tunnel is provided on the side wall of the end of the installation component 1 away from the shield machine 3.

[0026] Referring to Figure 1 , Figure 2 and Figure 3 , the installation component 1 includes a fixed seat 4 and a rotating arm 5. The rotating arm 5 includes a first rotating arm 11 and a second rotating arm 12. The first rotating arm 11 is hinged to the fixed seat 4. The axis of the hinge shaft between the first rotating arm 11 and the fixed seat 4 is perpendicular to the ground. And a torsion spring 6 is provided on the hinge shaft between the first rotating arm 11 and the fixed seat 4. The torsion spring 6 enables the rotating arm 5 and the fixed seat 4 to maintain a straight state without external force.

[0027] When the soil in the ground exerts a horizontal extrusion on the outer wall of the shield tunnel constructed by the shield machine 3, the inner wall of the shield tunnel will press against the contact member 7, and then the contact member 7 drives the first rotating arm 11 to rotate around the axis of the hinge shaft on the fixed seat 4 towards a position closer to the central axis of the shield tunnel.

[0028] Further, a fixed seat 4, a first rotating arm 11 and a second rotating arm 12 (not shown in the figure) can also be provided above the tail end of the shield machine. At this time, the axis of the hinge shaft between the first rotating arm 11 and the fixed seat 4 is parallel to the ground, and the contact member 7 provided on the second rotating arm 12 contacts the inner wall of the shield tunnel in the vertical direction, so as to measure the deformation of the shield tunnel in the vertical direction.

[0029] The second rotating arm 12 is sleeved on the other end of the first rotating arm 11 and can slide along the length direction of the first rotating arm 11, which enables the extending distance of the second rotating arm 12 on the first rotating arm 11 to be adjusted. To prevent the second rotating arm 12 from disengaging from the first rotating arm 11, a sliding groove 16 with an extending direction consistent with the length direction of the first rotating arm 11 is provided on the outer wall of the first rotating arm 11, and the depth of the sliding groove 16 gradually decreases from the side close to the fixed seat 4 towards the side away from the fixed seat 4. On the outer wall of the second rotating arm 12 corresponding to the sliding groove 16, a limiting member 17 is provided by means of threaded engagement. The limiting member 17 can be an ordinary bolt, and the axis of the limiting member 17 is perpendicular to the bottom surface of the sliding groove 16. This makes it so that when the limiting member 17 is not tightened, as long as one end of the limiting member 17 is located within the sliding groove 16, the second rotating arm 12 will not easily disengage from the first rotating arm 11. When the limiting member 17 is tightened, the extending position of the second rotating arm 12 on the first rotating arm 11 can be fixed.

[0030] The measuring unit 2 includes a measuring element 8, a target 10, and a display 9. The measuring unit 2 is installed on the second rotating arm 12, and the target 10 is installed on the fixed seat. This enables the distance between the measuring element 8 and the target 10 to change accordingly when the length of the second rotating arm 12 on the first rotating arm 11 is adjusted, thereby realizing the change of the measuring spacing when measuring the shield tunnel. The measuring element 8 can be a laser emitter, and the target 10 is made of a photosensitive material. The target 10 is electrically connected to the display 9. Among them, the measuring element 8 is installed on the rotating arm 5, and the target 10 is installed on the fixed seat 4. When the laser of the measuring element 8 irradiates on the target 10, the target 10 displays the position where the laser is irradiated on the display 9 by receiving the laser, and the display 9 is installed inside the shield machine 3, facilitating the staff to view the display 9.

[0031] Refer to Figure 1 and Figure 4, the abutting member 7 includes a first telescopic rod 18, a second telescopic rod 19, rolling beads 21 and a spring 20. Among them, the first telescopic rod 18 is vertically fixed on the side of the second rotating arm 12 close to the inner wall of the shield tunnel, and the other end of the first telescopic rod 18 is sleeved on the second telescopic rod 19. The spring 20 is located inside the first telescopic rod 18 and can push the second telescopic rod 19 to slide inside the first telescopic rod 18. The rolling beads 21 are installed at the end of the second telescopic rod 19 far from the first telescopic rod 18 by means of ball hinge. Under the action of the spring 20, the rolling beads 21 on the second telescopic rod 19 can always abut against the inner wall of the shield tunnel and roll relative to the inner wall of the shield tunnel on the second telescopic rod 19. Moreover, since the elastic coefficient of the spring 20 is smaller than that of the torsion spring 6, even when there are unevenness on the inner wall of the shield tunnel, the spring 20 can, under the action of its own elastic force, make the rolling beads 21 on the second telescopic rod 19 abut against the inner wall of the shield tunnel, thereby reducing the rotation of the first rotating arm 11 and the second rotating arm 12 caused by the unevenness of the inner wall of the shield tunnel, and thus preventing the situation that the light spot irradiated by the measuring element 8 at the center of the target 10 is deflected, playing a role in reducing the measurement error.

[0032] Furthermore, a sensor 22 is provided on the first telescopic rod 18. The sensor 22 can be a laser rangefinder. The sensor 22 is electrically connected to the display 9. An induction block 23 is provided on the second telescopic rod 19. A sliding part 24 that can be sleeved on the second telescopic rod 19 is provided on the induction block 23. The sliding part 24 can slide along the axis of the second telescopic rod 19 on the second telescopic rod 19, which enables the distance between the sensor 22 and the induction block 23 to be adjusted. The sensor 22 senses the distance from the induction block 23 and then displays the induction signal on the display 9 in digital form, so that the staff can read the value on the display 9 and compare it with the value within the set allowable error range, further reducing the measurement error caused by the unevenness of the inner wall of the shield tunnel.

[0033] A fixing member 25 is further provided on the sliding part 24. The fixing member 25 can be an ordinary bolt. After passing through the sliding part 24, the fixing member 25 fixes the position of the sliding part 24 on the second telescopic rod 19 by pressing against the outer wall of the second telescopic rod 19.

[0034] Refer to Figure 1 and Figure 2The end of the fixed seat 4 away from the rotating arm 11 is hinged on the shield machine 3, and the axis of the hinge shaft between the fixed seat 4 and the shield machine 3 is parallel to the ground and perpendicular to the axis of the hinge shaft between the rotating arm 11 and the fixed seat 4. This allows the rotating arm 11 and the rotating arm 2 12 to be stored by rotating the fixed seat 4 around the axis of the hinge shaft with the shield machine 3 when measurement is not required, thereby reducing the space occupied by the rotating arm 11 and the rotating arm 2 12.

[0035] Furthermore, a telescopic support rod 13 is connected to the lower surface of the rotating arm 12 by a ball hinge, and a spring 20 is built in the telescopic support rod 13. The end of the telescopic support rod 13 away from the rotating arm 12 is installed with a connector 15 by a ball hinge, and a plug-in portion 14 is provided on the shield machine 3 for the connector 15 to be plugged in and matched with. This allows the connector 15 on the telescopic support rod 13 to be connected by plugging and matching with the plug-in portion 14, so that the fixed seat 4, the rotating arm 11 and the rotating arm 2 12 can maintain a horizontal state when in use, and when not in use, the plug-in block on the telescopic support rod 13 can be removed from the plug-in portion 14, and then connected to the rotating arm 11 block for storage.

[0036] The implementation principle of the embodiment of the present application is: when the front end of the shield machine 3 is excavating, the rear end of the shield machine 3 is in a stationary state. At this time, the fixed seat 4, the rotating arm 11 and the rotating arm 2 12 are rotated out from the rear end of the shield, and at the same time, one end of the telescopic support rod 13 is set to be rotated out from the rotating arm 2 12, and the plug-in block on the telescopic support rod 13 is plugged into the plug-in part 14 at the rear end of the shield machine 3, so that the fixed seat 4, the rotating arm 11 and the rotating arm 2 12 are in a horizontal state, and at the same time, the distance of the rotating arm 2 12 on the rotating arm 1 11 is adjusted, and the measuring element 8 on the rotating arm 2 12 is started, so that the laser emitted by the measuring element 8 is irradiated on the central area of ​​the target 10, and at this time, the rolling ball 21 on the telescopic rod 2 19 is in contact with the inner wall of the shield tunnel.

[0037] When the excavation work at the front end of the shield machine 3 and the work of constructing the shield tunnel are completed, the shield machine 3 moves forward, and the rear end of the shield machine 3 will move forward together. At this time, under the premise of straight-line advancement, if the shield tunnel is deformed, the inner wall of the prefabricated tunnel will be squeezed toward the abutment 7, so that the sensor 22 on the telescopic rod 18 is in a sensing state. At the same time, the rotating arm 12 will drive the rotating arm 11 and the fixed seat 4 to rotate, thereby causing the position of the light spot of the measuring element 8 on the target 10 to shift. The staff can understand the offset of the light spot of the measuring element 8 according to the display of the display 9 inside the shield machine 3, thereby realizing the measurement of the deformation amount of the shield tunnel in the horizontal direction.

[0038] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A shield tunnel measurement device, characterized in that: The invention comprises a mounting assembly (1) and a measuring unit (2), wherein the mounting assembly (1) is mounted at the rear end of a shield machine (3), and the measuring unit (2) is mounted on the mounting assembly (1). The mounting assembly (1) comprises a fixed seat (4) and a rotating arm (5), wherein the fixed seat (4) is mounted on the shield machine (3), and the rotating arm (5) is hinged on the fixed seat (4). A torsion spring (6) is arranged on the hinge shaft between the rotating arm (5) and the fixed seat (4) for making the fixed seat (4) and the rotating arm (5) be in the same straight line, and an abutment member (7) is arranged on the rotating arm (5) for abutting against the inner wall of the shield tunnel. The measuring unit (2) comprises a display (9), a measuring element (8) and a target (10), wherein the target (10) is mounted on the fixed seat (4) and electrically connected to the display (9), and the measuring element (8) is mounted on the rotating arm (5) and can emit laser light toward the target (10).

2. A shield tunnel measurement device according to claim 1, characterized in that: The rotating arm (5) comprises a rotating arm 1 (11) and a rotating arm 2 (12); the rotating arm 1 (11) is hinged to the fixed seat (4); the rotating arm 2 (12) is sleeved on the rotating arm 1 (11) and can slide on the rotating arm 1 (11); the measuring element (8) and the abutment member (7) are both arranged on the rotating arm 2 (12).

3. A shield tunnel measurement device according to claim 2, characterized in that: The first rotating arm (11) is provided with a sliding groove (16), the depth of which gradually decreases from close to the fixed seat (4) towards away from the fixed seat (4), and the second rotating arm (12) is provided with a limiting member (17) at a position corresponding to the sliding groove (16), the limiting member (17) is connected to the second rotating arm (12) by means of threaded fitting, and the limiting member (17) can abut against the sliding groove (16) after passing through the second rotating arm (12).

4. A shield tunnel measurement device according to claim 2, characterized in that: The fixed seat (4) is hinged on the shield machine (3); the axis of the hinge shaft between the fixed seat (4) and the shield machine (3) is perpendicular to the axis of the hinge shaft between the rotating arm 1 (11) and the fixed seat (4); a telescopic support rod (13) is provided on the rotating arm 2 (12); one end of the telescopic support rod (13) away from the rotating arm 2 (12) can be connected to the shield machine (3) in a detachable manner; the telescopic support rod (13) is used to support the rotating arm 2 (12) so that the rotating arm 2 (12) maintains a horizontal state.

5. A shield tunnel measurement device according to claim 4, characterized in that: One end of the telescopic support rod (13) is connected to the second rotating arm (12) by means of a ball hinge, and the other end of the telescopic support rod (13) is connected to a plug-in connector (15) by means of a ball hinge. A plug-in connector (14) is provided on the shield machine (3), and the plug-in connector (15) is connected to the plug-in connector (14) by means of a plug-in fit.

6. A shield tunnel measurement device according to claim 2, characterized in that: The abutment member (7) comprises a telescopic rod 1 (18), a telescopic rod 2 (19), a spring (20) and a rolling ball (21); one end of the telescopic rod 1 (18) is connected to the rotating arm 2 (12); the other end of the telescopic rod 1 (18) is sleeved on the telescopic rod 2 (19); the telescopic rod 2 (19) can slide on the telescopic rod 1 (18); the rolling ball (21) is installed at one end of the telescopic rod 2 (19) away from the telescopic rod 1 (18) in a ball-hinged manner; the spring (20) is located in the telescopic rod 1 (18) and connected to the telescopic rod 2 (19); the elastic coefficient of the spring (20) is smaller than the elastic coefficient of the torsion spring (6).

7. A shield tunnel measurement device according to claim 6, characterized in that: The telescopic rod (18) is provided with a sensor (22), the sensor (22) is electrically connected to the display (9), and the telescopic rod (19) is provided with a sensing block (23) for sensing by the sensor (22).

8. A shield tunnel measurement device according to claim 7, characterized in that: The sensing block (23) is provided with a sliding part (24), the sliding part (24) is sleeved on the second telescopic rod (19), a fixing piece (25) is passed through the sliding part (24), and the fixing piece (25) is used to fix the position of the sliding part (24) on the second telescopic rod (19).

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