Telescopic centering device in circular tube and measuring method using telescopic centering device

Abstract

The invention discloses a telescopic centering device in a circular tube, which comprises a disc structure placed in the circular tube, a mounting seat for positioning a prism is arranged at the central position of the disc structure, and a group of telescopic structures which can extend out along the radial direction of the disc to prop against the inner wall of the circular tube for positioning are arranged in the disc structure. The measurement method comprises the following steps of: selecting the prism part to be mounted on the mounting seat; rotating the rotating part: selecting a proper depth in the to-be-detected pipe body, rotating the rotating sleeve, extending the rotating blade until the rubber anti-sliding columns abut against the inner wall of the to-be-detected pipe body, and checking and adjusting the side edges of one group of rubber anti-sliding columns to be in a clinging state with the inner wall of the to-be-detected pipe body so as to ensure that the whole device is vertical to the bus of the to-be-detected pipe body; locking by a locking bolt: rotating a locking nut to lock the rotating blade and the rotating sleeve until the anti-sliding column is tightly attached to the inner wall and does not relatively slide; after the telescopic centering device is self-held in the pipe wall, a total station is erected to directly measure the center of the prism, and then the circle center coordinate of the pipe body to be measured can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of total station measurement, in particular to a telescopic centering device in a circular tube and a use and measurement method thereof. Background Art

[0002] At present, the circular pipe installation and construction process of the project often involves the verification of the circular pipe installation position, installation angle, and verticality (such as pre-embedded foundation bolts of pad stone supports, pre-embedded cable ducts of cable-stayed bridges, etc.). This type of installation work places high demands on installation accuracy.

[0003] Most traditional circular pipe measurement methods involve measuring multiple points (no less than 3) evenly on the edge of the pipe at both ends to indirectly calculate the center of the circle, which is labor-intensive. Alternatively, a customized matching circular plate with a center mark is installed for measurement. Circular plates of different sizes need to be customized for different pipe diameters, which is inconvenient to use. It is difficult to measure the center of a certain depth inside the pipe body, and the center position of a certain depth inside the hollow pipe body cannot be directly measured.

[0004] In the field of construction, the position can be determined by measuring with a prism and a total station; the prism requires a base or a bracket for positioning, and the existing structural scheme cannot be applied to circular pipes of different sizes; for example, a prism bracket disclosed in patent CN216621167U includes a bracket body, which also includes: a connecting component, which is arranged at one end of the bracket body, and the connecting component is used to connect to a vertical rod; a mounting member, which is arranged at one end of the bracket body away from the connecting component; and when the connecting component is connected to the vertical rod, the center line of the mounting member is parallel to the center line of the vertical rod; the bracket body is an L-shaped rod; it cannot be applied to positioning inside a circular tube. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a retractable centering device in a circular tube and a method for using the same, which can accurately and quickly find the center of the tube body and is easy to operate.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A telescopic centering device in a circular tube comprises a disc structure for placement in the circular tube, a mounting seat for prism positioning is arranged at the center of the disc structure, and a group of telescopic structures are arranged in the disc structure which can be extended radially along the disc to support the inner wall of the circular tube for positioning.

[0008] The mounting seat is a rotatable rotating seat, and a thread structure for replacing the prism part is arranged inside the rotating seat.

[0009] The disc structure is a hollow structure, and a driving structure for driving a group of telescopic structures to telescope is arranged inside the hollow structure.

[0010] The telescopic structure is a telescopic arm, and a rubber column for anti-slip is arranged at the outer end of the telescopic arm.

[0011] The disc structure includes a base and a cover plate. A rotating shaft is provided at the center of the base. A mounting seat is installed on the rotating shaft. A through hole is provided on the cover plate corresponding to the mounting seat. The telescopic structure is located between the base and the cover plate.

[0012] The driving structure is a rotating part, which includes a rotating sleeve and a group of rotating plates. The rotating sleeve is sleeved on the rotating shaft, and the inner end of the rotating plate is fixedly connected to the outer edge of the rotating sleeve. The telescopic structure is a telescopic arm, and the inner end of the telescopic arm is hingedly connected to the outer end of the rotating plate. The base and the inner side of the cover plate are provided with an arc guide groove for guiding the inner end of the telescopic arm.

[0013] The cover plate is provided with an arc-shaped locking bolt notch, a locking bolt passing through the locking bolt notch is provided at a hinged portion of the outer end of the rotating plate, and a locking nut is provided at the end of the locking bolt.

[0014] The outer end notch of the arc-shaped guide groove is provided with a retracting notch for accommodating the outer end of the telescopic arm.

[0015] The rotating plate is a rotating clamping plate, the telescopic arm is a rotating blade, the inner end of the rotating blade is located between the outer ends of the rotating clamping plate, and the inner end of the rotating blade and the outer end of the rotating clamping plate are both semicircular chamfered structures.

[0016] A method for using and measuring the retractable centering device in a circular tube comprises the following steps:

[0017] S1. Select the prism part and install it on the mounting base;

[0018] S2. Rotation of the rotating part: Select a suitable depth inside the tube to be tested, rotate the rotating sleeve, extend the rotating blade until the rubber anti-slip column is in close contact with the inner wall of the tube to be tested, check and adjust a set of side edges of the rubber anti-slip column to be in close contact with the inner wall of the tube to be tested to ensure that the device as a whole is perpendicular to the generatrix of the tube to be tested;

[0019] S3, locking bolt locking: turn the locking nut to lock the rotating blade and the rotating sleeve until the anti-slip column is close to the inner wall without relative sliding;

[0020] S4. Measure coordinates: After the telescopic centering device is self-supporting in the pipe wall, set up a total station to directly measure the center of the prism to obtain the coordinates of the center of the pipe to be measured.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The retractable centering device in a circular tube and the measurement method for its use are reasonably designed. By evenly and stably converting the rotation of the rotating part into the elongation of the three rotating blades, the synchronous elongation enables the invention to have a high marking accuracy for the center of the installed tube body, which can meet the positioning accuracy of the tube body; the function of accurately and quickly finding the center of the tube body can be achieved, and the center position of a certain depth in the tube body can be directly collected, and the measurement is simple, efficient and accurate; compared with conventional methods, the invention can effectively reduce the number of on-site installation personnel, reduce the personnel cost during the project construction process, and increase revenue and reduce expenditure for the continuous advancement of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following is a brief description of the contents and symbols in the drawings of this specification:

[0024] Figure 1 Schematic diagram of various states of the centering device of the present invention.

[0025] Figure 2 It is the bottom view of the top cover of the present invention.

[0026] Figure 3 It is a schematic diagram of the replaceable prism functional part of the present invention.

[0027] Figure 4 It is a schematic diagram of the functional part of the replaceable centering rod placement device of the present invention.

[0028] Figure 5 It is a schematic diagram of the replaceable prism rod of the present invention.

[0029] Figure 6 It is a schematic diagram of the rotating part of the present invention.

[0030] Figure 7 This is a schematic diagram of the locking bolt structure of the present invention.

[0031] Figure 8 It is a schematic diagram of the structure and connection of the anti-slip column and the rotating blade of the present invention.

[0032] Fig. 9 It is a schematic diagram of the base structure of the present invention.

[0033] Fig.10 This is a schematic diagram of the working analysis of the present invention.

[0034] Fig.11 This is a schematic diagram of the installation process of replacing a replaceable functional part of the present invention.

[0035] Fig.12 and Fig.13 This is a working scene diagram of the prism version of the present invention.

[0036] Fig.14 and Fig.15 This is a working scene diagram of the centering rod installer of the present invention.

[0037] Fig.16 and Fig.17 This is a working scene diagram of the replaceable prism rod version of the present invention. DETAILED DESCRIPTION

[0038] The specific implementation modes of the present invention will be further explained in detail below through the description of embodiments with reference to the accompanying drawings.

[0039] The telescopic centering device in a circular tube comprises a disc structure for being placed in the circular tube, a mounting seat for prism positioning is arranged at the center of the disc structure, and a group of telescopic structures are arranged in the disc structure which can be extended radially along the disc to support the inner wall of the circular tube for positioning.

[0040] The mounting seat is a rotatable rotating seat, and a thread structure for replacing the prism part is arranged inside the rotating seat, so as to facilitate the installation of various types of prisms.

[0041] The disc structure includes a base and a cover plate, a rotating shaft is arranged at the center of the base, a mounting seat is mounted on the rotating shaft, a through hole is arranged on the cover plate corresponding to the mounting seat, and the telescopic structure is located between the base and the cover plate. The telescopic structure is a telescopic arm, and a rubber column for anti-slip is arranged at the outer end of the telescopic arm.

[0042] The disc structure is a hollow structure, and a driving structure for driving a group of telescopic structures to extend and retract is arranged inside the hollow structure; a group of telescopic structures is a group of telescopic arms, and the driving structure can adopt a group of electric push rods, which drive the telescopic arms to extend and retract, and the outer ends of a group of telescopic arms are against the inner wall of the circular tube for positioning.

[0043] Or the driving structure adopts a manual structure, preferably; the driving structure is a rotating part, the rotating part includes a rotating sleeve and a group of rotating plates, the rotating sleeve is sleeved on the rotating shaft, the inner end of the rotating plate is fixedly connected to the outer edge of the rotating sleeve, the telescopic structure is a telescopic arm, the inner end of the telescopic arm is hingedly connected to the outer end of the rotating plate, and the base and the inner side of the cover plate are provided with an arc guide groove for guiding the inner end of the telescopic arm.

[0044] The cover plate is provided with an arc-shaped locking bolt notch, and a locking bolt passing through the locking bolt notch is provided at the hinge of the outer end of the rotating plate. A locking nut is provided at the end of the locking bolt, and the telescopic arm is locked by the locking structure after being extended. The rotating plate is a rotating splint, and the telescopic arm is a rotating blade. The inner end of the rotating blade is located between the outer ends of the rotating splint. The inner end of the rotating blade and the outer end of the rotating splint are both semi-circular chamfered structures, which are conducive to guiding, and the inner end of the rotating blade is located at the hinge of the outer end of the rotating splint corresponding to the locking bolt. The rotating blade can be extended and retracted by the locking bolt, which is easy to operate.

[0045] A retracting notch for receiving the outer end of the telescopic arm is arranged at the outer end notch of the arc-shaped guide groove. When the telescopic arm is retracted, the rubber column is located in the retracting notch, and the structure is compact.

[0046] The measuring method using the retractable centering device in the round tube comprises the following steps:

[0047] S1. Select the prism part and install it on the mounting base;

[0048] S2. Rotation of the rotating part: Select a suitable depth inside the tube to be tested, rotate the rotating sleeve, extend the rotating blade until the rubber anti-slip column is in close contact with the inner wall of the tube to be tested, check and adjust a set of side edges of the rubber anti-slip column to be in close contact with the inner wall of the tube to be tested to ensure that the device as a whole is perpendicular to the generatrix of the tube to be tested;

[0049] S3, locking bolt locking: turn the locking nut to lock the rotating blade and the rotating sleeve until the anti-slip column is close to the inner wall without relative sliding;

[0050] S4. Measure coordinates: After the telescopic centering device is self-supporting in the pipe wall, set up a total station to directly measure the center of the prism to obtain the coordinates of the center of the pipe to be measured.

[0051] The retractable centering device in a circular tube of the present invention and the method for measuring its use are reasonably designed. By evenly and stably converting the rotation amount of the rotating part into the elongation amount of the three rotating blades, the synchronous elongation enables the invention to have a high marking accuracy for the center of the installed tube body, and can meet the positioning accuracy of the tube body; the function of accurately and quickly finding the center of the tube body can be achieved, and the center position of a certain depth in the tube body can be directly collected, and the measurement is simple, efficient and accurate; compared with conventional methods, the invention can effectively reduce the number of on-site installation personnel, reduce the personnel cost during the project construction process, and increase revenue and reduce expenditure for the continuous advancement of the project.

[0052] like Figures 1 to 17 As shown, preferred embodiments of the present invention are:

[0053] The retractable centering device in a circular tube comprises a top cover, a replaceable functional part, a rotating part and a base;

[0054] 1. Top cover

[0055] like Figure 2 As shown, the top cover includes four parts: a top cover limiting boss, a locking bolt notch, a top cover cover plate, and a replaceable part working window, which can be made of lightweight plastic by 3D printing. The top cover limiting boss and the top cover cover plate provide a sealed connection area for the combination of the top cover and the base, enhance the rigidity of the entire device, and provide effective support for the entire device; through the mutual engagement of the top limiting boss and the bottom notch, dust and other debris can be effectively prevented from entering the device from the side, ensuring the accuracy and reliability of the device. The locking bolt notch reserves a working channel for the anchoring of the entire device and the locking of the rotating part in the appropriate working position. The replaceable part working window provides an effective working space for the operation of the rotating part and the observation of the replaceable part.

[0056] 2. Replaceable functional parts

[0057] like Figures 3 to 5 As shown, one end of this part is a base connection bolt, which is connected to the base with a threaded hole. There are three types of the other end; the first type of port is a top cone-shaped opening with a bottom inverted cone-shaped opening, which can be used with the prism centering rod of the total station to obtain the center point of the measured tube body when the measured tube body is in a vertical state; the second type of port is an opening inlaid with a small prism, which can be used with the total station to obtain the center point of the measured tube body in an inclined state; the third type is composed of a lower support boss and an upper prism connecting rod, and the prism can be directly installed on the top of the prism connecting rod to adjust the prism angle and then measured with the total station. The end point center of the replaceable centering rod mounter, the geometric center of the replaceable prism part, and the bottom center of the support boss should be on the same axis as the axis of the rotating shaft and located on the rotation axis of the rotating blade.

[0058] 3. Rotating part

[0059] like Figures 6 to 8As shown, the rotating part includes five parts: a rotating sleeve, a locking bolt, a rotating splint, a rotating blade, and an anti-slip column. As the core component of the device, the rotating part can linearly control the synchronous extension and contraction of the three rotating blades by converting the angle change of the rotating sleeve into the elongation of the rotating blade and the anti-slip column along the radius of the device through the fulcrum of the limiting notch of the base. As the main force-bearing part of the device after self-sustaining work, the rotating sleeve is made of stainless steel cutting, and the cutting length is the height difference from the top of the top cover plate to the top surface of the rotating splint notch of the base. The rotating splint and the rotating blade are made of stainless steel sheets, wherein the thickness of the rotating blade is preferably twice the thickness of a single rotating splint to increase the stability of the rotating splint and the rotating blade. The top of each two identical rotating splints is chamfered with a semicircular arc, and holes are opened at the rotating axis of the rotating splint and the rotating blade to facilitate the installation of the rotating blade and the locking bolt in a pin-connected manner. The rotating splint and the rotating sleeve are connected by welding. Cut six equal-length rotating splints and divide them into three groups of two. The three groups of rotating splints are arranged along the radial direction of the rotating sleeve. The angles between the axes of the three groups of rotating splints along the radial direction of the rotating sleeve are in the same plane and are 120 degrees to each other. The locking bolt is made of stainless steel by turning. A bottom gasket is turned at the bottom of the locking bolt. The part above the bottom gasket that pins the rotating splint and the rotating blade is a smooth round rod. The part above the round rod needs to be threaded. The nut is installed to lock the device in the working state. A small hole with a radius of 3 mm is opened at the end of the rotating blade away from the axis, and the hole is given a thread by tapping to install the anti-slip column. The center of the anti-slip column is composed of two rubber cylindrical blocks with a radius of 1 cm connected by a 3 mm radius bolt. After the center bolt is tightened at the opening position of the rotating blade, another rubber cylindrical block is tightened again to complete the installation of the entire anti-slip column. The total length of the anti-slip column does not exceed the thickness of the device. When the three anti-slip columns of the device are pressed against the inner wall of the tube to be tested at the same time, there are three rubber lines in close contact with the inner wall of the tube to be tested, which can ensure that the invention is always in an orthogonal state with the tube to be tested. Subsequently, by tightening the locking bolt and clamping the rotating clamp by squeezing, the telescopic angle of the rotating blade is fixed, so that the device can be self-sustaining inside the tube.

[0060] 4. Base

[0061] like Fig. 9 and Fig.10As shown, the base consists of seven parts: bottom cover plate, rotating shaft, limiting boss, replaceable functional part mounting seat, blade notch, rotating splint notch, and anti-skid column retraction notch. The bottom cover plate is the basic load-bearing part of the entire base component. It is cut and formed from hard plastic as a whole. The cutting thickness is the height of the rotating shaft. The remaining base components are sequentially turned to ensure that the various parts of the base are firmly and tightly connected. The rotating shaft part is turned from the outermost side of the top in a circular motion toward the axis. The rotating shaft also serves as the supporting part of the rotating sleeve and the connecting part of the replaceable functional part mounting seat. The lower end is drilled and tapped to open the bolt connection hole of the replaceable functional part mounting seat. The function of the device is expanded by tightening the replaceable functional part. After turning out the rotating shaft, the tool feed is controlled to turn out the base limiting boss. The turning height of the base limiting boss is the sum of the thickness of the bottom gasket of the rotating part locking bolt plus the combined thickness of the rotating clamp and the rotating blade. The base limiting boss is engaged with the top cover plate to limit the height of the blade notch to prevent the rotating blade from shaking inside the device. At the same time, the outer edge of the base limiting boss can provide a fulcrum for the blade to come out, that is, when the rotating part comes out in a clockwise direction, the edge of the rotating blade will first press against the outer edge of the base limiting boss, making it a blade fulcrum, and the fulcrum will center The amount of rotation driven by the rotating shaft is linearly converted into the elongation of the rotating blade along the outer radius of the device, making the entire blade-out process more linear and smooth; from the design principle of the rotating part mentioned above, it can be seen that the distance from the three base limiting boss fulcrums to the axis of the rotating shaft is the same. From the geometric relationship, it can be seen that when the rotating part rotates, the three groups of rotating splints with equal angles and lengths have the same rotation speed at the ends of the principle axis. Under the condition of ensuring that the rotating blade and each group of rotating splints are connected at the same position, the elongation of the three rotating blades at the base limiting boss fulcrum is equal and synchronous, and its sealing effect is the same as that of the top cover limiting boss. Continue to adjust the tool feed depth to turn out the bottom rotating splint slot, the depth of which should be one more than the bottom surface of the bottom rotating splint piece. The rotating splint slot plays a role in limiting and supporting the rotation of the rotating splint, leaving rotation space for the activity of the rotating splint. After the turning of the rotating splint groove is completed, the anti-skid column retraction groove is carved at the end of the cutting groove. The carving depth is 3 mm more than the actual size of the anti-skid column. The groove provides space for the storage and protection of the rubber anti-skid column.

[0062] The corresponding test method:

[0063] like Figures 11 to 13As shown, method of use one: ① Installation of replaceable functional parts: First, select the replaceable prism part and install it tightly in the connecting hole of the base of the centering device, and then assemble the various parts of the device in order. ② Rotation of the rotating part: Select the appropriate depth inside the tube to be measured, rotate the rotating sleeve, extend the rotating blade until the rubber anti-skid column is close to the inner wall of the tube to be measured, check and adjust the three rubber anti-skid column side edges and the inner wall of the tube to be measured to ensure that the device as a whole is perpendicular to the generatrix of the tube to be measured. ③ Locking bolt locking: Turn the three locking nuts to lock the rotating blade and the rotating sleeve until the anti-skid column is close to the inner wall without relative sliding. ④ Measure coordinates: After the telescopic centering device is self-supporting in the tube wall, set up the total station to directly measure the center of the prism to obtain the coordinates of the center of the tube to be measured. Taking the installation of the replaceable prism part as an example, the installation process of the device is demonstrated: first, select and install the replaceable prism part according to the inclination degree of the measured tube body; after the installation of the replaceable functional part is completed, first remove the top locking nut of the locking bolt, and then install the rotating part; install the top cover according to the axis system relationship and the opening of the slot and hole positions; after the top cover is installed, install the locking nut removed in the second step, and reset the rotating part to complete the installation of the telescopic centering device.

[0064] like Fig.14 and Fig.15 As shown, the second method of use is: ① Installation of replaceable functional parts: First, select the centering rod placement type replaceable functional part and install it tightly in the connection hole of the centering device base, and then assemble the various parts of the device in order. ② Rotation of the rotating part: Select the appropriate depth inside the pipe to be tested, rotate the rotating sleeve, extend the rotating blade until the anti-slip column is close to the inner wall of the pipe to be tested, check and adjust the three rubber anti-slip column side edges and the inner wall of the pipe to be tested to ensure that the device as a whole is perpendicular to the generatrix of the pipe to be tested. ③ Locking bolt locking: Turn the three locking bolts to lock the rotating blade and the rotating sleeve until the anti-slip column is close to the inner wall of the pipe body without relative sliding. ④ Measure coordinates: After the telescopic centering device is self-supporting in the pipe wall, place the prism centering rod in the centering device of the finder plate, adjust the bubble of the prism rod to the center position, and directly measure the center of the prism to obtain the coordinates of the center of the pipe to be tested.

[0065] like Fig.16 and Fig.17As shown, the third method of use is: ① Installation of the replaceable functional part: First, select the prism rod type replaceable functional part and install it tightly in the connection hole of the base of the centering device, and then assemble the various parts of the device in order. ② Rotation of the rotating part: Select the appropriate depth inside the tube to be measured, rotate the rotating sleeve, extend the rotating blade until the anti-slip column is close to the inner wall of the tube to be measured, check and adjust the three rubber anti-slip column side edges and the inner wall of the tube to be measured to ensure that the device as a whole is perpendicular to the generatrix of the tube to be measured. ③ Locking bolt locking: Turn the three locking bolts to lock the rotating blade and the rotating sleeve until the anti-slip column is close to the inner wall of the tube without relative sliding. ④ Measure coordinates: After the telescopic centering device is self-supporting in the tube wall, place the prism centering rod at the top of the prism connector. After adjusting the prism rotation angle, directly measure the center of the prism to obtain the coordinates of the center of the tube to be measured.

[0066] The invention has ingenious conception, reasonable design, low processing and manufacturing cost, flexible and convenient use, strong versatility and economy, and can double the pipe body installation measurement efficiency, which is beneficial to the compatibility of the pipe body installation measurement environment and the improvement of measurement accuracy, and has good prospects for promotion and application.

[0067] The above is only an explanation of the preferred embodiments of the present invention, and the above technical features can be arbitrarily combined to form multiple embodiments of the present invention.

[0068] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A retractable centering device in a circular tube, characterized in that: It comprises a disc structure for being placed in a circular tube, wherein a mounting seat for positioning a prism is arranged at the center of the disc structure, and a group of telescopic structures which can be extended radially along the disc to support the inner wall of the circular tube for positioning are arranged in the disc structure.

2. The retractable centering device in a circular tube as claimed in claim 1, characterized in that: The mounting seat is a rotatable rotating seat, and a thread structure for replacing the prism part is arranged inside the rotating seat.

3. The retractable centering device in a circular tube as claimed in claim 1, characterized in that: The disc structure is a hollow structure, and a driving structure for driving a group of telescopic structures to telescope is arranged inside the hollow structure.

4. The retractable centering device in a circular tube as claimed in claim 1, characterized in that: The telescopic structure is a telescopic arm, and a rubber column for anti-slip is arranged at the outer end of the telescopic arm.

5. The retractable centering device in a circular tube as claimed in claim 3, characterized in that: The disc structure includes a base and a cover plate. A rotating shaft is provided at the center of the base. A mounting seat is installed on the rotating shaft. A through hole is provided on the cover plate corresponding to the mounting seat. The telescopic structure is located between the base and the cover plate.

6. The retractable centering device in a circular tube as claimed in claim 5, characterized in that: The driving structure is a rotating part, which includes a rotating sleeve and a group of rotating plates. The rotating sleeve is sleeved on the rotating shaft, and the inner end of the rotating plate is fixedly connected to the outer edge of the rotating sleeve. The telescopic structure is a telescopic arm, and the inner end of the telescopic arm is hingedly connected to the outer end of the rotating plate. The base and the inner side of the cover plate are provided with an arc guide groove for guiding the inner end of the telescopic arm.

7. The retractable centering device in a circular tube as claimed in claim 6, characterized in that: The cover plate is provided with an arc-shaped locking bolt notch, a locking bolt passing through the locking bolt notch is provided at a hinged portion of the outer end of the rotating plate, and a locking nut is provided at the end of the locking bolt.

8. The retractable centering device in a circular tube as claimed in claim 6, characterized in that: The outer end notch of the arc-shaped guide groove is provided with a retracting notch for accommodating the outer end of the telescopic arm.

9. The retractable centering device in a circular tube as claimed in claim 6, characterized in that: The rotating plate is a rotating clamping plate, the telescopic arm is a rotating blade, the inner end of the rotating blade is located between the outer ends of the rotating clamping plate, and the inner end of the rotating blade and the outer end of the rotating clamping plate are both semicircular chamfered structures.

10. A method for measuring using the retractable centering device in a circular tube as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Select the prism part and install it on the mounting base; S2. Rotation of the rotating part: Select a suitable depth inside the tube to be tested, rotate the rotating sleeve, extend the rotating blade until the rubber anti-slip column is in close contact with the inner wall of the tube to be tested, check and adjust a set of side edges of the rubber anti-slip column to be in close contact with the inner wall of the tube to be tested to ensure that the device as a whole is perpendicular to the generatrix of the tube to be tested; S3, locking bolt locking: turn the locking nut to lock the rotating blade and the rotating sleeve until the anti-slip column is close to the inner wall without relative sliding; S4. Measure coordinates: After the telescopic centering device is self-supporting in the pipe wall, set up a total station to directly measure the center of the prism to obtain the coordinates of the center of the pipe to be measured.

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