Device and method for measuring roundness of underwater pressure-resistant structure

Abstract

The invention relates to a device and method for measuring the roundness of an underwater pressure-resistant structure. The device comprises a supporting structure unit. The guide rail adjusting unit comprises a linear guide rail and adjustable supporting rods, and the two ends of the linear guide rail are fixed through the adjustable supporting rods; the horizontal calibration unit comprises a laser instrument, and the laser instrument is used for verifying the levelness of the annular rib cylindrical shell and the rack and the levelness of a measurement center shaft formed by the linear guide rail and the adjustable supporting rod; and the roundness measuring unit comprises a roundness measuring device and a limiting stopper and is used for executing circumferential measurement and roundness fitting calculation. The device is compact and reasonable in structure and convenient to operate, and the problems of low precision, poor consistency, low efficiency and the like in a traditional roundness measurement technology are systematically solved through collaborative design of the device and the method. In the aspect of the device, high-precision positioning and automatic measurement are realized through the combination of a laser instrument and a limiting stopper; in the aspect of the method, the measurement precision and reproducibility are remarkably improved through a standardized measurement process and an error source control strategy.

Description

Technical Field

[0001] The present invention relates to the technical field of measurement methods, in particular to a device and method for measuring the roundness of an underwater pressure-resistant structure. Background Art

[0002] As the core load-bearing components of deep-sea equipment, the geometric accuracy of underwater pressure-resistant structures directly determines their structural safety and fluid dynamics performance. For typical structures such as ring-stiffened cylindrical shells and spherical shells, domestic submersible specifications (such as the "Submersible Structural Specifications") and national military standards (such as the GJB series of standards) explicitly require that the roundness error be controlled within millimeter-level accuracy to ensure structural stability in the high-pressure environments of the deep sea. However, existing internal diameter measurement technologies have significant drawbacks, making it difficult to meet the requirements of high-precision and high-efficiency inspection.

[0003] Traditional measurement methods rely primarily on the pole method, which relies on manually setting up a horizontal pole in a circular plane, using a cantilever gauge to approximately locate the measurement center, and reading the radial distance of the equally divided points using a string or tape measure. This method has the following prominent problems:

[0004] Low positioning accuracy of equal division points: Manual marking of equal division points is easily affected by operating experience. Especially for multi-rib structures, the rib plate spacing and the theoretical equal division angle are difficult to align, causing the distribution of measurement points to deviate from the true circumferential position and introduce systematic deviations.

[0005] Poor consistency between re-inspections and re-tests: The lack of a positioning reference requires re-marking for each measurement, and the previous measurement traces cannot be accurately reproduced, resulting in poor comparability between the re-inspection data and the initial results, making it difficult to assess the structural deformation trend.

[0006] Accumulation of measurement tool errors: The combination of a cable and tape measure is susceptible to fluctuations in ambient temperature and tension, and requires multiple levels of indirect measurement (such as center positioning errors added to radius measurements), resulting in single measurement errors of up to several millimeters.

[0007] Conflict between efficiency and cost: Although large-scale three-dimensional coordinate measuring machines can provide high precision, they are expensive, complex to operate, and require a constant temperature environment. They are not economical for small and medium-sized submersible manufacturers and cannot meet the needs of rapid on-site testing.

[0008] Further analysis reveals that the limitations of traditional methods have hindered industry development: Excessive roundness can lead to buckling failure during service due to localized stress concentrations; Measurement errors can also force designers to over-inflate safety factors, increasing material costs and fabrication difficulties. Furthermore, manual record-keeping and paper-based archiving methods result in insufficient data traceability, making it difficult to meet the demands of quality tracing and process improvement.

[0009] In response to the above problems, it is urgent to develop a roundness measurement technology that is both accurate, efficient and economical. Summary of the Invention

[0010] In response to the shortcomings of the above-mentioned existing production technology, the applicant provides a device and method for measuring the roundness of underwater pressure-resistant structures. Through the collaborative design of the device and method, the problems of low accuracy, poor consistency, and low efficiency in traditional roundness measurement technology are systematically solved.

[0011] The technical solutions adopted in the present invention are as follows:

[0012] A device for measuring the roundness of an underwater pressure-resistant structure, comprising:

[0013] The supporting structure unit includes a ring-stiffened cylindrical shell and a test stand. The ring-stiffened cylindrical shell is placed statically on the test stand and is used to support the pressure-resistant structure to be tested.

[0014] A guide rail adjustment unit, comprising a linear guide rail and an adjustable support rod, wherein both ends of the linear guide rail are fixed by the adjustable support rod, and the height of the adjustable support rod is adjustable to adapt to pressure-resistant structures of different outer diameters;

[0015] A horizontal calibration unit, comprising a laser instrument, wherein the laser instrument is used to verify the horizontality of the ring-stiffened cylindrical shell and the stand, and the horizontality of the measurement center axis composed of the linear guide rail and the adjustable support rod;

[0016] The roundness measurement unit includes a roundness measuring device and a limiter. The roundness measuring device can be movably mounted on a linear guide rail and axially limited by the limiter. The roundness measuring device has a built-in control display console, a laser ranging module, and a control and data processing module for performing circumferential measurement and roundness fitting calculation.

[0017] In one embodiment, the linear guide rail is equipped with balls and oil nozzles to reduce friction resistance when the roundness measuring device moves.

[0018] In one embodiment, the roundness measuring device includes a battery module, a motor and a driver, and a hollow rotating platform. The hollow rotating platform is connected to a laser ranging module to achieve multi-angle rotation measurement.

[0019] In one embodiment, the height adjustment range of the adjustable support rod is determined according to the formula b=a+R, where a is the height of the stand from the ground, and R is the outer diameter of the pressure-resistant structure to be measured.

[0020] In one embodiment, the laser instrument integrates the functions of a level meter and a plumb meter, the level meter is used to calibrate the horizontality of the linear guide rail, and the plumb meter is used to mark measurement points on the linear guide rail.

[0021] In one embodiment, a bolt locking structure is provided on the top of the limiter to achieve axial fixation of the roundness measuring device through friction.

[0022] A method for measuring the roundness of an underwater pressure-resistant structure, which uses the above-mentioned measuring device, comprises the following steps:

[0023] S1. Place the ring-ribbed cylindrical shell on a stand and adjust the adjustable support rod to keep the linear guide rail in a horizontal state;

[0024] S2. Select a certain measuring point, place the laser instrument 5 at the point, turn on the vertical meter function, mark on the linear guide rail 2, and mark multiple measuring points on the linear guide rail;

[0025] S3. Fix the roundness measuring device with a stopper and align it with the measuring point. Set the rotation angle and direction and start the laser distance measurement.

[0026] S4. Collect circumferential measurement data and perform fitting calculations, and output the roundness results according to the built-in calculation program.

[0027] In one embodiment, in S3, the operation is performed through the operation buttons and display screen of the roundness measuring device, and after setting the equal number / rotation angle and rotation direction, the laser ranging function is turned on to complete the circumferential measurement of the measuring points (1, 2, 3, ..., i, ..., n) and record and store the distance values.

[0028] The built-in calculation program in S4 takes the measurement of 16 equally divided points as an example:

[0029] According to the measured value, the roundness deviation W of each point can be obtained c =(R i -R), R i is the measured value, R is the theoretical value;

[0030] Get sinα according to the rotation angle i and cosα i , and get W c ·sinα i and W c ·cosα i ;

[0031] Calculate ΔR = ∑W c / 16, a1=∑(W c ·sinα i ) / 8, b1=∑(W c ·cosα i ) / 8;

[0032] The calculated roundness value W of each measuring point i =W c -a1·sinα i -b1·cosα i -ΔR.

[0033] The beneficial effects of the present invention are as follows:

[0034] The present invention has a compact and reasonable structure and is easy to operate. Through the collaborative design of the device and method, it systematically solves the problems of low precision, poor consistency, and low efficiency in traditional roundness measurement technology. At the device level, the combination of the laser instrument and the limiter realizes high-precision positioning and automated measurement, and the display and control console and the built-in calculation program improve the efficiency and reliability of data processing; at the method level, the standardized measurement process and error source control strategy significantly improve the measurement accuracy and reproducibility. The combination of the two not only simplifies the operation process and reduces the risk of manual intervention, but also provides strong support for quality traceability and process improvement through data closed-loop management. Specifically, the integrated design of the laser ranging module and the hollow rotating platform ensures the precise rotational positioning of the equally divided points; the coordination of the limiter and the linear guide realizes the axial limitation and precise alignment of the measuring device; the collaborative work of the display and control console and the built-in calculation program completes the automation of the entire process from data acquisition to result output. This innovative solution provides an efficient, accurate, and economical solution for the roundness measurement of underwater pressure-resistant structures, significantly improving the construction quality and safety of deep-sea equipment.

[0035] At the same time, the present invention also has the following advantages:

[0036] This device uses a laser to verify the horizontality of the measured object relative to the measurement axis, ensuring the installation accuracy of the linear guide and adjustable struts. A laser ranging module, combined with a hollow rotating platform, enables precise rotational positioning of the equidistant points, eliminating the systematic deviations associated with manually marking equidistant points in the traditional strut method. A stopper uses friction to provide axial positioning, ensuring precise alignment of the measuring device with the marked points, significantly improving the geometric accuracy of roundness measurements.

[0037] The roundness measurement device integrates a display and control console, a battery module, and control and data processing modules. It records and stores radial distance values at each measurement point in real time. A built-in calculation program automatically performs data fitting and roundness calculations, reducing manual calculation errors and providing data review and revalidation capabilities. This feature addresses the traceability issues inherent in traditional methods, resulting from manual record-keeping and paper archiving, providing a reliable basis for quality traceability and process improvement.

[0038] The device's simple structure allows only one or two people to complete measurement tasks, eliminating the need for complex pre-positioning and marking. Measurements can be initiated by simply entering the rotation angle and direction, with real-time pause and re-measurement support, significantly improving measurement efficiency. Compared to expensive large-scale coordinate measuring machines, this device is low-cost and suitable for the rapid on-site inspection needs of small and medium-sized submersible manufacturers.

[0039] This method uses a laser to verify the horizontality of a linear guide rail. Based on the measurement requirements, equally spaced points are marked on the rail to ensure consistent measurement datums. The roundness measurement device uses stoppers to align the marked points, standardizing the measurement process. This avoids the incomparable data from rechecks caused by the lack of a positioning datum in traditional methods, improving the repeatability and reliability of measurement results.

[0040] The method's built-in data processing capabilities rapidly provide on-site roundness measurement results, and data storage enables review, re-verification, and traceability. This feature provides data support for construction improvements, helping designers optimize safety factors, reduce material waste, and minimize processing difficulties. It also reduces the time and effort required for manual record-keeping and paper archiving, improving quality management efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the first step of adjusting the roundness measuring device for a pressure-resistant cylindrical shell;

[0042] Figure 2 This is a schematic diagram of the second step of adjusting the roundness measuring device of the pressure-resistant cylindrical shell;

[0043] Figure 3 This is a schematic diagram of the measurement device.

[0044] Figure 4 It is a layout diagram of the measuring device.

[0045] Figure 5 yes Figure 4 Bottom view of .

[0046] in:

[0047] 1. Ring-ribbed cylindrical shell; 2. Linear guide rail; 3. Roundness measuring device; 4. Adjustable support rod; 5. Laser instrument; 6. Test stand; 7. Limiter; 3.1. Display and control console; 3.2. Battery module; 3.3. Control and data processing module; 3.4. Motor and driver; 3.5. Hollow rotating platform; 3.6. Laser ranging module. DETAILED DESCRIPTION

[0048] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0049] Example 1

[0050] like Figure 1-Figure 5 As shown, in this embodiment, a device for measuring the roundness of an underwater pressure-resistant structure is disclosed, which mainly includes a support structure unit, a guide rail adjustment unit, a horizontal calibration unit and a roundness measurement unit.

[0051] like Figure 1 As shown, the device for measuring the roundness of an underwater pressure-resistant structure according to this embodiment includes:

[0052] The supporting structure unit includes a ring-stiffened cylindrical shell 1 and a stand 6. The ring-stiffened cylindrical shell 1 is placed statically on the stand 6 and is used to support the pressure-resistant structure to be tested;

[0053] The guide rail adjustment unit includes a linear guide rail 2 and an adjustable support rod 4. Both ends of the linear guide rail 2 are fixed by the adjustable support rod 4. The height of the adjustable support rod 4 can be adjusted to adapt to pressure-resistant structures with different outer diameters.

[0054] A horizontal calibration unit, comprising a laser instrument 5, which is used to verify the horizontality of the ring-stiffened cylindrical shell 1 and the stand 6, as well as the horizontality of the measurement center axis formed by the linear guide 2 and the adjustable support rod 4;

[0055] The roundness measurement unit includes a roundness measuring device 3 and a limiter 7. The roundness measuring device 3 is movably mounted on the linear guide 2 and axially limited by the limiter 7. The roundness measuring device 3 has a built-in control display console 3.1, a laser ranging module 3.6, and a control and data processing module 3.3 for performing circumferential measurement and roundness fitting calculations.

[0056] The linear guide rail 2 is equipped with balls and oil nozzles to reduce the friction resistance when the roundness measuring device 3 moves.

[0057] The roundness measuring device 3 includes a battery module 3.2, a motor and driver 3.4 and a hollow rotating platform 3.5. The hollow rotating platform 3.5 is connected to a laser ranging module 3.6 for realizing multi-angle rotation measurement.

[0058] The horizontality of the ring-stiffened cylindrical shell 1 and the gantry 6 is verified by a laser instrument 5, and the horizontality of the measurement center axis of the linear guide 2 and the adjustable strut 4 is verified by a laser instrument 5. The top bolt of the limiter 7 is tightened to limit the position through friction.

[0059] The roundness of the ring-stiffened cylindrical shell 1, the core structure of the object being measured, directly affects its underwater pressure resistance. The stable support of the test stand 6, combined with the horizontal calibration function of the laser instrument 5, ensures that the measured structure is in an ideal horizontal state during the measurement process. The coordinated design of the linear guide 2 and the adjustable strut 4 allows for dynamic adjustment of the measurement height based on the outer diameter of the pressure-resistant structure, adapting to cylindrical or spherical shells of different sizes. The limiter 7 uses a top bolt friction limiter to ensure axial positioning accuracy while avoiding mechanical damage to the measured surface. This is particularly suitable for testing finished products after high-precision welding.

[0060] In this embodiment, the laser instrument 5 performs dual functions, acting as both a level and a plumb line. Horizontal calibration ensures alignment of the measured structure with the measurement reference axis, while vertical calibration precisely calibrates the position of the measurement point. The combination of these two significantly improves overall measurement accuracy. The adaptive friction design of the stopper 7 ensures reliable fixation despite varying surface roughness, while avoiding structural deformation that can occur with traditional clamps. This design is particularly suitable for highly sensitive measurements of underwater pressure-resistant structures, balancing ease of operation with data reliability.

[0061] like Figure 4 and Figure 5 As shown, the roundness measuring device 3 is a core module that integrates display and control operation, data acquisition, motion control and laser ranging functions. The modular design reduces the complexity of the equipment and facilitates rapid on-site deployment and maintenance.

[0062] Specifically, the roundness measuring device 3 mainly includes a display and control console 3.1, a battery module 3.2, a control and data processing module 3.3, a motor and driver 3.4, a hollow rotating platform 3.5, a laser ranging module 3.6, and also includes supporting components of the linear guide 2 such as ball bearings and oil nozzles.

[0063] The roundness measuring device 3 in this embodiment performs roundness measurement by inputting a rotation angle and a rotation direction through the control display platform 3.1, and can pause and resume measurement in real time during the measurement process.

[0064] The display and control console 3.1 in this embodiment allows operators to intuitively set parameters such as equal fractions and rotation angles through input and real-time data display.

[0065] The battery module 3.2 also provides independent power for the entire system, eliminating the wiring constraints of an external power source and making it particularly suitable for docking or field operations. The hollow rotating platform 3.5 uses precision gear transmission to achieve 360° measurement without blind spots. Combined with the high-frequency sampling capability of the laser ranging module 3.6, it can capture micron-level roundness deviations.

[0066] The control and data processing module 3.3 includes a built-in calculation program that fits the recorded values to obtain roundness measurement results, ensuring repeatability and consistency. Furthermore, the combined use of ball bearings and grease nipples significantly reduces frictional resistance within the linear guide 2, enabling smoother movement of the measuring device and further minimizing operator error.

[0067] In summary, the device for measuring the roundness of underwater pressure-resistant structures of the present invention achieves high-precision and high-efficiency measurement of the roundness of underwater pressure-resistant structures through innovative structural design and intelligent measurement technology, and has significant technical advantages and practical value.

[0068] Example 2

[0069] This embodiment discloses a method for measuring the roundness of an underwater pressure-resistant structure, comprising the following steps:

[0070] S1, such as Figure 1 As shown, first place the ring-ribbed cylindrical shell 1 on the stand 6, and fix both ends of the linear guide rail 2 on the adjustable support rod 4. The support rod height b = a (the height of the stand 6 from the ground) + R (the outer diameter of the pressure-resistant structure). Set up a laser instrument 5 at a distance, turn on the level function, and verify the horizontality of the linear guide rail 2.

[0071] In this embodiment, step S1 establishes a measurement reference. The coordinated calibration of the gantry 6 and laser instrument 5 ensures precise spatial alignment between the measured structure and the measurement system. The dynamic height adjustment capability of the adjustable strut 4 enables rapid adaptation to pressure hulls of varying diameters without the need for hardware component replacement, significantly enhancing the device's versatility. The laser instrument 5's horizontal calibration function replaces traditional manual wire alignment, eliminating subjective errors and making it particularly suitable for measuring curved structures or complex welded joints.

[0072] S2, such as Figure 2 As shown, a certain measuring point is then selected according to the measurement requirements, the laser instrument 5 is placed at the point, the vertical meter function is turned on, and a mark is made on the linear guide rail 2. Then, the measurement mark is completed on the linear guide rail 2 according to the rib distance l or other measurement requirements.

[0073] Specifically, step S2 in this embodiment utilizes the plummet function to precisely calibrate the measurement points. The automated generation of laser marks avoids the cumulative errors associated with traditional manual marking, making it particularly suitable for high-density ribs or unevenly distributed pressure-resistant structures. Mark intervals can be flexibly set based on project requirements, supporting both equally divided measurements around the entire circumference and intensified sampling of key areas, providing a high-resolution foundation for subsequent data analysis.

[0074] S3. Place the roundness measuring device 3 on the linear guide rail 2, use the limiter 7 to limit the axial position to ensure alignment with the measurement mark point, operate the roundness measuring device 3 through the operation buttons and display screen 3.1, set the equal number / rotation angle and rotation direction, turn on the laser ranging function 3.6, complete the circumferential measurement of the measuring points (1, 2, 3, ..., i, ..., n) and record and store the distance values.

[0075] In this embodiment, step S3 is used for fully automatic data acquisition. The rapid positioning function of the stopper 7 enables the measuring device to accurately align each marked point without repeated adjustments. The non-contact measurement method of the laser ranging module 3.6 avoids physical contact damage to the measured surface, making it particularly suitable for high-precision inspection of coated or polished surfaces. The addition of data storage not only supports real-time viewing but also allows the export of complete data sets via USB or wireless transmission, providing a digital foundation for quality traceability and process optimization.

[0076] S4. According to the built-in calculation program, the recorded values are fitted and calculated to obtain the roundness measurement results.

[0077] The specific built-in calculation programs include, taking the measurement of 16 equally divided points as an example:

[0078] According to the measured value, the roundness deviation W of each point can be obtained c =(R i -R), R i is the measured value, R is the theoretical value;

[0079] Get sinα according to the rotation angle i and cosα i , and get W c ·sinα i and W c ·cosα i ;

[0080] Calculate ΔR = ∑W c / 16, a1=∑(W c ·sinα i ) / 8, b1=∑(W c ·cosα i ) / 8;

[0081] The calculated roundness value W of each measuring point i =W c -a1·sinα i -b1·cosα i -ΔR.

[0082] Specifically, step S4 in this embodiment implements intelligent data processing using the aforementioned built-in calculation algorithm. The calculation results visually display the maximum roundness error, localized concave or convex areas, and generate a standardized inspection report. This real-time analysis capability enables construction personnel to adjust welding or assembly processes on-site, significantly shortening the inspection-feedback-correction cycle and significantly improving production efficiency.

[0083] This invention patent takes into account the technical characteristics of roundness measurement and the feasibility of practical operation, and proposes a practical and efficient measurement technology and device. This invention can meet the technical requirements of roundness measurement and provide a data basis for the inspection of the construction quality of underwater platforms and construction improvements.

[0084] The present invention can be used to measure the roundness of pressure shell rings after welding, and has wide adaptability. The measurement technology of this invention is simple to operate, has good measurement accuracy, and is easy to implement. It does not require complicated pre-positioning and marking preparation, and can be performed by one or two people, achieving high measurement efficiency.

[0085] After completing the leveling and selecting the measuring points, the measurement is carried out through the measuring device to avoid errors caused by human factors as much as possible. It has its own data storage function to realize the review and re-inspection and traceability of the data, thus reducing the time cost of random inspections.

[0086] The built-in data processing function improves the efficiency of use and can quickly provide roundness measurement results on site, providing a basis for construction improvements. At the same time, it reduces the time cost and calculation pressure of data post-processing and reduces the probability of errors.

[0087] The above description is an explanation of the present invention, not a limitation of the present invention. The scope of the present invention is defined in the claims. Any modifications may be made within the scope of protection of the present invention.

Claims

1. A device for measuring the roundness of underwater pressure-resistant structures, characterized in that: include: The supporting structure unit includes a ring-stiffened cylindrical shell and a test stand. The ring-stiffened cylindrical shell is placed statically on the test stand and is used to support the pressure-resistant structure to be tested. A guide rail adjustment unit, comprising a linear guide rail and an adjustable support rod, wherein both ends of the linear guide rail are fixed by the adjustable support rod, and the height of the adjustable support rod is adjustable to adapt to pressure-resistant structures of different outer diameters; A horizontal calibration unit, comprising a laser instrument, wherein the laser instrument is used to verify the horizontality of the ring-stiffened cylindrical shell and the stand, and the horizontality of the measurement center axis composed of the linear guide rail and the adjustable support rod; The roundness measurement unit includes a roundness measuring device and a limiter. The roundness measuring device can be movably mounted on a linear guide rail and axially limited by the limiter. The roundness measuring device has a built-in control display console, a laser ranging module, and a control and data processing module for performing circumferential measurement and roundness fitting calculation.

2. The device for measuring the roundness of an underwater pressure-resistant structure according to claim 1, characterized in that: The linear guide rail is equipped with balls and oil nozzles to reduce friction resistance when the roundness measuring device moves.

3. The device for measuring the roundness of an underwater pressure-resistant structure according to claim 1, characterized in that: The roundness measuring device includes a battery module, a motor and a driver, and a hollow rotating platform. The hollow rotating platform is connected to a laser ranging module to achieve multi-angle rotation measurement.

4. The device for measuring the roundness of an underwater pressure-resistant structure according to claim 1, characterized in that: The height adjustment range of the adjustable support rod is determined according to the formula b=a+R, where a is the height of the stand from the ground, and R is the outer diameter of the pressure-resistant structure to be measured.

5. The device for measuring the roundness of an underwater pressure-resistant structure according to claim 1, characterized in that: The laser instrument integrates the functions of a level meter and a plumb meter. The level meter is used to calibrate the horizontality of the linear guide rail, and the plumb meter is used to mark measurement points on the linear guide rail.

6. The device for measuring the roundness of an underwater pressure-resistant structure according to claim 1, characterized in that: A bolt locking structure is provided on the top of the limiter to achieve axial fixation of the roundness measuring device through friction.

7. A method for measuring the roundness of an underwater pressure-resistant structure, which uses a device for measuring the roundness of an underwater pressure-resistant structure according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Place the ring-ribbed cylindrical shell on a stand and adjust the adjustable support rod to keep the linear guide rail in a horizontal state; S2. Select a certain measuring point, place the laser instrument 5 at the point, turn on the vertical meter function, mark on the linear guide rail 2, and mark multiple measuring points on the linear guide rail; S3. Fix the roundness measuring device with a stopper and align it with the measuring point. Set the rotation angle and direction and start the laser distance measurement. S4. Collect circumferential measurement data and perform fitting calculations, and output the roundness results according to the built-in calculation program.

8. The method for measuring the roundness of an underwater pressure-resistant structure according to claim 7, characterized in that: In S3, the roundness measuring device is operated through the operating buttons and display screen. After setting the equal number / rotation angle and rotation direction, the laser ranging function is turned on to complete the circumferential measurement of the measuring points (1, 2, 3, ..., i, ..., n) and record and store the distance values.

9. The method for measuring the roundness of an underwater pressure-resistant structure according to claim 7, wherein: The built-in calculation program in S4 takes the measurement of 16 equally divided points as an example: According to the measured value, the roundness deviation W of each point can be obtained c =(R i -R), R i is the measured value, R is the theoretical value; sinα is obtained according to the rotation angle i and cosα i , and get W c ·sinα i and W c ·cosα i ; Calculate ΔR = ∑W c / 16, a1=∑(W c ·sinα i ) / 8, b1=∑(W c ·cosα i ) / 8; The calculated roundness value W of each measuring point i =W c -a1·sinα i -b1·cosα i -ΔR.

Images