Sucker rod detection device with straightening function

Abstract

The utility model discloses a sucker rod detection device with a straightening function, which comprises a base, the top of the base is fixedly connected with two U-shaped blocks, a support roller is rotatably connected between the front inner wall and the rear inner wall of each U-shaped block, the front side of the U-shaped block on the right side is fixedly provided with a driving motor, and the rear side of the U-shaped block on the right side is fixedly provided with a straightening device. An output shaft of the driving motor is fixedly connected with the front end of the supporting roller on the right side, and the same sucker rod is movably contacted with the middles of the tops of the two supporting rollers. By arranging a series of structures, the bending detection of the sucker rod is facilitated, the sucker rod is conveniently driven to rotate, and the sucker rod is conveniently pressed and compressed at the upper part in a pressure-controlled manner, so that the bending convex part of the sucker rod is downwards pressed to be straight, and the purpose of automatically extruding and straightening the sucker rod in a pressure-controlled manner is achieved; and other independent straightening equipment does not need to be taken out for straightening work, so that the moving time is saved, time and labor are saved, the integration and the use convenience are improved, and the working efficiency is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of sucker rod bending detection, in particular to a sucker rod detection device with a straightening function. Background Art

[0002] The sucker rod is a slender rod of the pumping well. It is connected to the bare rod at the top and the oil pump at the bottom, and plays the role of transmitting power. After the sucker rod is manufactured, it is necessary to perform bending detection and treatment on the sucker rod itself to ensure that it is vertical and prevent the normal operation from being affected by the bending of the sucker rod.

[0003] There are a variety of detection methods for sucker rod bending detection in the prior art, such as circular runout detection using multiple dial indicators. In addition, the existing straightening work is often performed manually using straightening equipment after detection. Currently, there is a lack of integrated detection equipment for sucker rod bending detection and straightening, which requires personnel to move the sucker rod back and forth for straightening, which is time-consuming and labor-intensive, and undoubtedly wastes a lot of time for moving and replacing equipment. In view of this, we propose a sucker rod detection device with straightening function to solve the above problems. Utility Model Content

[0004] The utility model aims to provide a sucker rod detection device with a straightening function to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the utility model provides the following technical solutions: a sucker rod detection device with a straightening function, comprising a base, two U-shaped blocks are fixedly connected to the top of the base, a support roller is rotatably connected between the front inner wall and the rear inner wall of the U-shaped block, a drive motor is fixedly installed on the front side of the U-shaped block on the right side, the output shaft of the drive motor is fixedly connected to the front end of the support roller on the right side, a sucker rod is movably contacted in the middle of the tops of the two support rollers, the sucker rod is supported by the two support rollers, and the drive motor is used to drive the support roller on the right side to rotate, so as to drive the sucker rod to rotate;

[0006] The top of the base is rectangular and fixedly connected to four support rods, the tops of the four support rods are fixedly connected to the same circular top plate, the four support rods are slidably sleeved with the same lifting plate, and the top right side of the circular top plate is fixedly connected to a control pressure display component;

[0007] A lifting pressure control and clamping assembly electrically connected to the pressure control and display assembly is fixedly installed on the left side of the top of the circular top plate. The lifting pressure control and clamping assembly is embedded and fixed on the left side of the top of the lifting plate. Two straightening rollers are rotatably installed at the bottom of the lifting plate. Both straightening rollers are located above the sucker rod and cooperate with the sucker rod. The lifting pressure control and clamping assembly is used to be controlled by the pressure control and display assembly to drive the lifting plate and the straightening roller to lift and lower to control the pressure, press and straighten the sucker rod;

[0008] The top of the lifting plate is fixedly connected with a pressure measuring detection component which is electrically connected to the control pressure display component. The bottom of the pressure measuring detection component extends to the bottom of the lifting plate and is rotatably installed with a measuring roller. The bottom of the measuring roller is in movably contact with the top of the sucker rod. The pressure measuring detection component is used to perform pressure bending detection on the rotating sucker rod and transmit the pressure to the control pressure display component for display.

[0009] Preferably, the control and pressure display component includes a PLC controller fixedly connected to the top right side of the circular top plate, and a pressure display is fixed and electrically connected to the top of the PLC controller; the PLC controller and the pressure display are set to cooperate, and the PLC controller is used to receive pressure and control the closing and control of the pressure display to display pressure changes through a preset pressure value.

[0010] Preferably, the lifting and lowering pressure-controlled clamping assembly includes an electric push rod fixedly installed on the left side of the top of the circular top plate, the protruding end of the electric push rod extends to the bottom of the circular top plate and is fixedly connected to a first pressure sensor, the first pressure sensor is embedded and fixed on the left side of the top of the lifting plate, and the first pressure sensor and the electric push rod are both electrically connected to the PLC controller; the set electric push rod and the first pressure sensor cooperate, and the electric push rod is controlled by the PLC controller to control the lifting and lowering of the lifting plate, and the downward movement of the lifting plate drives the two straightening rollers to press the sucker rod downward, and the first pressure sensor is used to detect the extrusion force during the descent and transmit it to the PLC controller. When the preset pressure value is reached, the PLC controller controls the electric push rod to automatically close, so as to realize the pressure-controlled, compacting and straightening of the sucker rod. The principle of compaction and straightening is that when the sucker rod rotates, its curved protruding part will rotate and squeeze with the straightening roller, and under the relative extrusion force, the curved protruding part will be straightened to achieve the squeezing and straightening effect of the sucker rod.

[0011] Preferably, the pressure measuring and detecting assembly comprises a fixed box fixedly connected to the top of the lifting plate, the bottom of the fixed box is set to be an opening, a sliding sleeve is provided in the fixed box, a rectangular rod is fixedly connected to the bottom of the sliding block, the bottom end of the rectangular rod slides and extends to the bottom of the lifting plate, the measuring roller is rotatably installed at the bottom end of the rectangular rod, a second pressure sensor is fixedly installed on the top inner wall of the fixed box, and a spring is fixedly connected between the bottom of the second pressure sensor and the top of the sliding block, and the second pressure sensor is electrically connected to the PLC controller; the fixed box, the sliding block, the rectangular rod, the second pressure sensor and the spring are arranged to cooperate, when the measuring roller is in contact with the top of the sucker rod, when the sucker rod rotates, its curved protruding part rotates to the upper side, which squeezes the measuring roller to move upward, the measuring roller drives the sliding block upward to compress the spring through the rectangular rod, and the spring in the compressed state increases the squeezing force on the second pressure sensor, the second pressure sensor detects the squeezing force in real time and transmits it to the PLC controller, the PLC controller controls the pressure display to display the pressure, and the personnel observe the pressure change displayed on the pressure display, which can be judged as the bending state, so as to achieve the purpose of bending detection, and then the electric push rod can be controlled to start forward to perform the squeezing and straightening work.

[0012] Preferably, the outer adhesive sleeve of the support roller is provided with an anti-slip rubber sleeve.

[0013] Preferably, a U-shaped rod is fixedly connected to the bottom of the rectangular rod, and pins are fixedly connected to the front and rear sides of the measuring roller. Circular holes are provided on the front inner wall and the rear inner wall of the U-shaped rod, and a first bearing is fixedly sleeved in the circular hole, and the inner ring of the first bearing is fixedly sleeved with the outer side of the corresponding pin.

[0014] Preferably, a rectangular guide hole is provided on the top of the lifting plate and is in sliding contact with the outer side of the rectangular rod, and the fixing box is located in the circular top plate and is not in contact with the inner wall of the circular top plate.

[0015] Compared with the prior art, the beneficial effects of the utility model are:

[0016] 1. This sucker rod detection device with straightening function can drive the sucker rod to rotate by cooperating with the support roller, drive motor, U-shaped block, pressure detection assembly, measuring roller and control pressure display assembly, and measures and displays the squeezing force by squeezing the measuring roller by the curved convex part of the sucker rod when it rotates. By observing the change of squeezing force, it is convenient for personnel to accurately judge whether the sucker rod is bent, so as to realize the bending detection of the sucker rod;

[0017] 2. The sucker rod inspection device with a straightening function can drive two straightening rollers to respectively control the pressure and squeeze the top two sides of the sucker rod through the cooperation of the set circular top plate, lifting plate, straightening roller, control and display pressure component, support rod and lifting and controlling pressure clamping component, so that when the sucker rod rotates, the two straightening rollers can be used to press the curved protruding part of the sucker rod downward to achieve the effect of automatic pressure-controlled extrusion and straightening of the sucker rod, and the method of integrated pressure-controlled straightening after inspection, without taking out and using other separate straightening equipment for straightening work, thereby improving the integration and convenience of use and improving work efficiency.

[0018] The utility model is provided with a series of structures, which is convenient for detecting the bending of the sucker rod, and is convenient for driving the sucker rod to rotate and controlling the pressure on the upper part to press it tightly, so as to press the bent convex part downward to straighten it, thereby realizing the purpose of automatically controlling the pressure and squeezing and straightening the sucker rod. Moreover, by performing the pressure control and straightening in one piece after the detection, there is no need to take out and use other separate straightening equipment for straightening work, thus saving moving time, saving time and effort, improving the integration and convenience of use, and improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the utility model;

[0020] Figure 2 It is a schematic diagram of the main cross-sectional structure of the utility model.

[0021] In the figure: 1. base; 2. U-shaped block; 3. support roller; 4. drive motor; 5. support rod; 6. circular top plate; 7. lifting plate; 8. PLC controller; 9. pressure display; 10. straightening roller; 11. first pressure sensor; 12. electric push rod; 13. fixing box; 14. second pressure sensor; 15. spring; 16. rectangular rod; 17. measuring roller; 18. anti-slip rubber sleeve. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0023] like Figure 1 to Figure 2As shown, a sucker rod detection device with a straightening function proposed in this embodiment includes a base 1, two U-shaped blocks 2 are fixedly connected to the top of the base 1, a support roller 3 is rotatably connected between the front inner wall and the rear inner wall of the U-shaped block 2, a drive motor 4 is fixedly installed on the front side of the U-shaped block 2 on the right, and the output shaft of the drive motor 4 is fixedly connected to the front end of the support roller 3 on the right, wherein the front and rear ends of the support roller 3 on the left and the rear end of the support roller 3 on the right are fixedly connected to the support shaft, and rotation holes are opened on the front inner wall and the rear inner wall of the U-shaped block 2, and the two rotation holes on the left and the rotation hole on the right rear are fixedly connected to the support shaft. The second bearing is fixedly sleeved, and the inner ring of the second bearing is fixedly sleeved with the outer side of the corresponding support shaft. The support shaft and the second bearing are used to realize the effect of rotating and installing the corresponding support roller 3. The middle of the top of the two support rollers 3 is in active contact with the same sucker rod. The outer adhesive sleeve of the support roller 3 is provided with an anti-skid rubber sleeve 18. The anti-skid rubber sleeve 18 is used to increase the friction between the support roller 3 and the sucker rod, so as to facilitate the effect of stable friction driving the sucker rod to rotate when the support roller 3 rotates. The two support rollers 3 are used to support the sucker rod, and the drive motor 4 is used to drive the right support roller 3 to rotate, so as to realize the drive of the sucker rod to rotate;

[0024] The top of the base 1 is rectangular and fixedly connected with four support rods 5, and the tops of the four support rods 5 are fixedly connected with the same circular top plate 6. The four support rods 5 are slidably sleeved with the same lifting plate 7, wherein the top of the lifting plate 7 is rectangular and has four vertical guide holes that are respectively in sliding contact with the outer sides of the corresponding support rods 5. The lifting plate 7 is slidably sleeved on the four support rods 5 through the four vertical guide holes, which play the effect of guiding the vertical sliding of the lifting plate 7, and a control pressure display component is fixedly connected to the top right side of the circular top plate 6; a lifting and lowering pressure control and clamping component electrically connected to the control pressure display component is fixedly installed on the top left side of the circular top plate 6, and the lifting and lowering pressure control and clamping component is embedded and fixed on the top left side of the lifting plate 7, and two straightening rollers 10 are rotatably installed on the bottom of the lifting plate 7, wherein the bottom of the lifting plate 7 is fixedly connected with two U-shaped seats, and the front and rear ends of the straightening rollers 10 are fixedly connected with round shafts, and the front inner wall and rear end of the U-shaped seat The inner wall of the side is provided with a circular through-hole, and a third bearing is fixedly sleeved in the circular through-hole. The inner ring of the third bearing is fixedly sleeved with the outer side of the corresponding circular shaft. The straightening roller 10 is rotatably mounted on the bottom of the lifting plate 7 through two circular shafts, two third bearings and a U-shaped seat, which plays the effect of rotatably mounting the straightening roller 10. The two straightening rollers 10 are both located above the sucker rod and cooperate with the sucker rod. The lifting and lowering pressure control and clamping assembly is used to be controlled by the control pressure display assembly to drive the lifting plate 7 and the straightening roller 10 to lift and lower the sucker rod to control the pressure, tighten and straighten the sucker rod; the top of the lifting plate 7 is fixedly connected with a pressure measuring detection assembly electrically connected to the control pressure display assembly, the bottom of the pressure measuring detection assembly extends to the bottom of the lifting plate 7 and is rotatably mounted with a measuring roller 17, the bottom of the measuring roller 17 is in active contact with the top of the sucker rod, and the pressure measuring detection assembly is used to perform pressure measurement and bending detection on the rotating sucker rod and transmit the displayed pressure to the control pressure display assembly.

[0025] Specifically, the control and pressure display component includes a PLC controller 8 fixedly connected to the top right side of the circular top plate 6, and a pressure display 9 is fixed and electrically connected to the top of the PLC controller 8; the PLC controller 8 and the pressure display 9 are set to cooperate, and the PLC controller 8 receives the pressure and controls the closing and control of the pressure display 9 to display the pressure change through a preset pressure value.

[0026] Furthermore, the lifting and lowering pressure-controlling clamping assembly includes an electric push rod 12 fixedly mounted on the left side of the top of the circular top plate 6, the protruding end of the electric push rod 12 extends to the bottom of the circular top plate 6 and is fixedly connected to a first pressure sensor 11, the first pressure sensor 11 is embedded and fixed on the left side of the top of the lifting plate 7, wherein the left side of the top of the lifting plate 7 is provided with an embedding groove fixedly connected to the outer side of the first pressure sensor 11, the first pressure sensor 11 is embedded and fixed on the left side of the top of the lifting plate 7 through the embedding groove, the top of the first pressure sensor 11 is the detection end, the first pressure sensor 11 and the electric push rod 12 are both electrically connected to the PLC controller 8; the electric push rod 12 is arranged The push rod 12 and the first pressure sensor 11 cooperate with each other. The electric push rod 12 is controlled by the PLC controller 8 to control the lifting and lowering of the lifting plate 7. The downward movement of the lifting plate 7 drives the two straightening rollers 10 to press the sucker rod downward. The first pressure sensor 11 is used to detect the extrusion force during the descent and transmit it to the PLC controller 8. When the preset pressure value is reached, the PLC controller 8 controls the electric push rod 12 to automatically close, thereby realizing the pressure control, compression and straightening of the sucker rod. The principle of compression and straightening is that when the sucker rod rotates, its curved protruding part will rotate and squeeze with the straightening roller 10. Under the relative extrusion pressure, the curved protruding part will be straightened to achieve the squeezing and straightening effect of the sucker rod.

[0027] Furthermore, the pressure measuring and detecting assembly includes a fixed box 13 fixedly connected to the top of the lifting plate 7, the bottom of the fixed box 13 is set to be an opening, a sliding sleeve is provided in the fixed box 13, and a rectangular rod 16 is fixedly connected to the bottom of the slider, and the bottom of the rectangular rod 16 slides and extends to the bottom of the lifting plate 7, wherein the top of the lifting plate 7 is provided with a rectangular guide hole that slides in contact with the outer side of the rectangular rod 16, the fixed box 13 is located in the circular top plate 6 and does not contact the inner wall of the circular top plate 6, so as to guide the vertical sliding of the rectangular rod 16, and the measuring roller 17 is rotatably installed at the bottom end of the rectangular rod 16, wherein the bottom of the rectangular rod 16 is fixedly connected to a U-shaped rod, and the front and rear sides of the measuring roller 17 are fixedly connected with pins, and circular holes are provided on the front inner wall and the rear inner wall of the U-shaped rod, and a first bearing is fixedly provided in the circular hole, and the inner ring of the first bearing is fixedly fitted on the outer side of the corresponding pin, so as to rotatably install the measuring roller 17, and a second pressure The force sensor 14, the bottom of the second pressure sensor 14 is the detection end, and a spring 15 is fixedly connected to the top of the slider, and the second pressure sensor 14 is electrically connected to the PLC controller 8; the fixed box 13, the slider, the rectangular rod 16, the second pressure sensor 14 and the spring 15 are arranged to cooperate, when the measuring roller 17 is in contact with the top of the sucker rod, when the sucker rod rotates, its curved protruding part rotates to the upper side and squeezes the measuring roller 17 to move upward, and the measuring roller 17 drives the slider upward through the rectangular rod 16 to compress the spring 15, and the spring 15 in the compressed state increases the squeezing force on the second pressure sensor 14, and the second pressure sensor 14 detects the squeezing force in real time and transmits it to the PLC controller 8, and the PLC controller 8 controls the pressure display 9 to display the pressure, and the personnel observe the change in the pressure displayed on the pressure display 9, and can judge that it is in a state of bending and not straight, so as to achieve the purpose of bending detection, and can control the electric push rod 12 to start forward to perform the extrusion straightening work.

[0028] The method of using this embodiment is as follows: during detection, the sucker rod is first placed in the middle position of the top of the two support rollers 3 from front to back, and then the electric push rod 12 is started in the positive direction to drive the lifting plate 7 to move downward through the first pressure sensor 11. When the lifting plate 7 drives the measuring roller 17 downward to contact the top of the sucker rod through the rectangular rod 16, the personnel closes the electric push rod 12, and then the driving motor 4 is started to drive the right support roller 3 to rotate. The right support roller 3 drives the sucker rod to rotate through the corresponding anti-slip rubber sleeve 18 friction, and the sucker rod friction drives the left support roller 3 to rotate. When the sucker rod is bent, when the bent protruding part of the sucker rod rotates to the upper side, it will squeeze the measuring roller 17 to move upward. The measuring roller 17 drives the slider upward through the rectangular rod 16 to compress the spring 15. The spring 15 in the compressed state increases the squeezing force on the second pressure sensor 14. The second pressure sensor 14 detects the squeezing force in real time and transmits it to the PLC controller 8. The PLC controller 8 controls the pressure display 9 to display the pressure. The personnel observe the pressure change displayed on the pressure display 9, which can be judged as a bending state, thereby achieving the purpose of bending detection.

[0029] When a bending state occurs and straightening work is required, the automatic closing pressure of the electric push rod 12 is preset by the PLC controller 8 according to the required extrusion straightening pressure, and the electric push rod 12 is started forward again to drive the lifting plate 7 to slide downward on the four support rods 5 through the first pressure sensor 11. The lifting plate 7 drives the second pressure sensor 14 downward to compress the spring 15 through the fixing box 13. At the same time, the lifting plate 7 drives the two straightening rollers 10 downward to press against the top two sides of the sucker rod respectively. The first pressure sensor 11 detects the extrusion force during downward movement and transmits it to the PLC controller 8 pressure value. When the preset pressure value is reached , the PLC controller 8 controls the electric push rod 12 to automatically close, and controls the two straightening rollers 10 to automatically control the pressure and tighten the sucker rod, and starts the drive motor 4 to make the sucker rod rotate again. At this time, the curved protruding part of the sucker rod will be rotated and squeezed with the two straightening rollers 10. Under the rotational squeezing force, the curved protruding part can be pressed downward to be straightened, and the pressure-controlled squeezing and tightening method can be used to achieve the effect of automatic pressure-controlled squeezing and straightening of the sucker rod. In addition, the pressure-controlled straightening method after detection is used, and there is no need to take out other separate straightening equipment for straightening work, which saves time and effort, improves the integration and convenience of use, and improves work efficiency.

[0030] Finally, it should be noted that the above description is only a preferred embodiment of the utility model and is not intended to limit the utility model. Although the utility model is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions recorded in the above embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A sucker rod detection device with a straightening function, comprising a base (1), characterized in that: Two U-shaped blocks (2) are fixedly connected to the top of the base (1); a support roller (3) is rotatably connected between the front inner wall and the rear inner wall of the U-shaped block (2); a drive motor (4) is fixedly installed on the front side of the U-shaped block (2) on the right; the output shaft of the drive motor (4) is fixedly connected to the front end of the support roller (3) on the right; and a sucker rod is movably contacted in the middle of the top of the two support rollers (3); The top of the base (1) is rectangular and fixedly connected to four support rods (5), the tops of the four support rods (5) are fixedly connected to the same circular top plate (6), the four support rods (5) are slidably sleeved with the same lifting plate (7), and the top right side of the circular top plate (6) is fixedly connected to a control pressure display component; A lifting and lowering pressure control and clamping assembly electrically connected to the pressure control and display assembly is fixedly installed on the left side of the top of the circular top plate (6); the lifting and lowering pressure control and clamping assembly is embedded and fixed on the left side of the top of the lifting plate (7); two straightening pressure rollers (10) are rotatably installed on the bottom of the lifting plate (7); the two straightening pressure rollers (10) are both located above the sucker rod and cooperate with the sucker rod; The top of the lifting plate (7) is fixedly connected with a pressure measuring and detecting assembly electrically connected to the control pressure display assembly. The bottom of the pressure measuring and detecting assembly extends to the bottom of the lifting plate (7) and is rotatably mounted with a measuring roller (17). The bottom of the measuring roller (17) is in active contact with the top of the sucker rod.

2. The sucker rod detection device with straightening function according to claim 1, characterized in that: The control and pressure display component comprises a PLC controller (8) fixedly connected to the top right side of the circular top plate (6), and a pressure display (9) is fixed and electrically connected to the top of the PLC controller (8).

3. The sucker rod detection device with straightening function according to claim 2, characterized in that: The lifting and lowering pressure-controlling clamping assembly comprises an electric push rod (12) fixedly mounted on the left side of the top of the circular top plate (6); the protruding end of the electric push rod (12) extends to the bottom of the circular top plate (6) and is fixedly connected to a first pressure sensor (11); the first pressure sensor (11) is embedded and fixed on the left side of the top of the lifting plate (7); the first pressure sensor (11) and the electric push rod (12) are both electrically connected to a PLC controller (8).

4. The sucker rod detection device with straightening function according to claim 2, characterized in that: The pressure measuring and detecting assembly comprises a fixed box (13) fixedly connected to the top of the lifting plate (7), the bottom of the fixed box (13) is set to be an opening, a sliding block is slidably sleeved in the fixed box (13), a rectangular rod (16) is fixedly connected to the bottom of the sliding block, the bottom end of the rectangular rod (16) slides and extends to the bottom of the lifting plate (7), a measuring roller (17) is rotatably mounted on the bottom end of the rectangular rod (16), a second pressure sensor (14) is fixedly mounted on the top inner wall of the fixed box (13), and a spring (15) is fixedly connected between the bottom of the second pressure sensor (14) and the top of the sliding block, and the second pressure sensor (14) is electrically connected to the PLC controller (8).

5. The sucker rod detection device with straightening function according to claim 1, characterized in that: The outer adhesive sleeve of the support roller (3) is provided with an anti-slip rubber sleeve (18).

6. The sucker rod detection device with straightening function according to claim 4, characterized in that: The bottom of the rectangular rod (16) is fixedly connected to a U-shaped rod, the front and rear sides of the measuring roller (17) are fixedly connected to pins, circular holes are opened on the front inner wall and the rear inner wall of the U-shaped rod, and a first bearing is fixedly sleeved in the circular hole, and the inner ring of the first bearing is fixedly sleeved with the outer side of the corresponding pin.

7. The sucker rod detection device with straightening function according to claim 4, characterized in that: A rectangular guide hole is provided on the top of the lifting plate (7) for sliding contact with the outer side of the rectangular rod (16); the fixing box (13) is located inside the circular top plate (6) and does not contact the inner wall of the circular top plate (6).

Images