MARKIII cargo containment system cargo hold size measurement method

Abstract

A MARKIII cargo containment system cargo hold size measuring method comprises the steps that a cargo hold is divided into 10 faces and 16 angular points in total, laser trackers are arranged at the centers of the bow face and the stern face, a plurality of target balls are arranged in the three faces corresponding to each angular point, the laser trackers are used for detecting the target points in the three faces corresponding to the angular points, and after detection is finished, the cargo hold size is measured through the target balls. According to the method, the planes can be created in polyworks software, after the three planes corresponding to the angular points are created, coordinates of intersection points formed by intersection of the three planes are three-dimensional coordinates of the current angular points, and three-dimensional coordinates of the 16 angular points are obtained through measurement in sequence. And inputting the three-dimensional coordinates of the angular points into EXCEL to directly obtain the lengths of line segments and diagonals of the cargo hold. According to the method disclosed by the invention, the number of times of measurement is reduced from original 64 times to 16 times and is reduced by 75%. And the labor hour is reduced, 20 persons are required to measure for 2 days in the original method, 5 persons are required to measure for 1 day in the method, and the labor hour is reduced by 87.5%. The measurement precision is improved, and calculation errors are avoided.

Description

Technical Field

[0001] This invention belongs to the field of marine ship construction and design, and specifically relates to a method for measuring the dimensions of the cargo hold in the MARKⅢ cargo containment system. Background Technology

[0002] The MARK III type cargo containment system (hereinafter referred to as cargo containment) for LNG carriers has octagonal prism-shaped cargo holds, each with 10 faces: A, B, C, D, E, F, G, H, J, and K. (See attached diagram.) Figure 1 .

[0003] One of the most important materials used in cargo containment construction is insulating panels, which are fixed to the cargo hold bulkhead using nuts, studs, and resin adhesive. The studs are pre-welded to the bulkhead. To ensure accurate stud positioning and that the insulating panels are installed within tolerances, grid lines are drawn on each bulkhead, and the insulating panels are installed within these grid lines.

[0004] To ensure the accurate placement of the grid lines, two baseline lines, one horizontal and one vertical, need to be drawn in advance on each deck. The grid lines are drawn using the baseline lines as a reference to avoid cumulative errors.

[0005] The main bulkhead of the MARK III cargo containment system is made of stainless steel corrugated sheet. To ensure the airtightness of the main bulkhead, the corrugations must be continuous, and the corrugations must also be continuous on adjacent surfaces. Therefore, the lines marked on the corrugated sheet must also be continuous on adjacent surfaces. Since the corrugated sheet is welded to the insulation board, and the corrugated sheet lines are obtained by reflecting the grid lines of the insulation board, the dimensions of the entire hold must be measured before marking the baseline on the insulation board. By considering the overall structure, the continuity of the lines marked on adjacent surfaces must be ensured.

[0006] According to process requirements, before marking the cargo hold lines, it is necessary to measure the lengths of the 24 sides and 40 diagonals of the cargo hold (see...). Figure 2 , 3 ).

[0007] The conventional method for measuring the side length is to use a laser rangefinder to measure the length of each of the 24 sides one by one.

[0008] For diagonals, conventional measurement methods require the use of specialized diagonal dimension measuring fixtures (see...). Figure 4The fixtures are fan-shaped, with angles matching the bulkhead angles. Conventional LNG carrier cargo holds have four angles: 90°, 135°, 108.4°, and 161.6°. Each set of fixtures consists of two parts: one with a box for holding a laser rangefinder (the rangefinder can move on the fixture), and the other a diagonal target fixture. The distance 'a' between the rangefinder and the center of the fixture, and the radius 'b' of the target fixture, are fixed values. During measurement, the two fan-shaped fixtures are placed diagonally, ensuring that the fixture is in contact with three surfaces simultaneously. The distance 'c' between the rangefinder and the target fixture is measured; the diagonal length is then a + b + c. This process is repeated to measure the lengths of all 40 diagonals.

[0009] The disadvantages of conventional cargo hold size measurement are as follows: (1) Too many measurements are required, with 64 measurements needed per compartment, which requires a long time and manpower.

[0010] (2) The rangefinder has a large tolerance at longer distances. Based on field experience, it was found that the deviation of the rangefinder measurement can reach more than 10mm when the measurement range is 50m (the total length of the cargo hold is about 50m). Moreover, the laser spot emitted by the rangefinder is blurry when measuring long distances, making it difficult to determine the accuracy of the measurement position.

[0011] (3) The diagonal measurement method has a large error. During diagonal measurement, the accuracy of the tooling has a certain error, and the tooling cannot be tightly attached to the bulkhead due to deformation, which also produces a certain error. The accumulation of multiple errors makes this method have a large systematic error.

[0012] (4) Difficulty in measuring the C-face diagonal. The support legs of the installation platform (scaffolding required for cargo enclosure construction) inside the cargo hold are located on the C-face. Due to the large number of support legs, they will block the laser, making it difficult to measure the C-face diagonal using a laser rangefinder. Summary of the Invention

[0013] To address the aforementioned problems, this invention provides a method for measuring cargo hold dimensions in the MARKⅢ cargo containment system, aiming to reduce the number of measurements while ensuring accurate measurement data. The technical solution adopted is as follows: A method for measuring the dimensions of the cargo hold in a MARKⅢ cargo containment system. The cargo hold has 10 faces: bow, stern, port, starboard, top, bottom, upper left, upper right, lower left, and lower right. Three adjacent faces form a corner point, for a total of 16 corner points.

[0014] S1: Fix the laser tracker at the center of the bow or stern of the cargo hold, and set multiple target balls in the three planes corresponding to each corner point. The target balls are close to the adjacent corner points, and the multiple target balls are scattered and staggered.

[0015] S2: Use a laser pointer at the laser tracker positions on the bow and stern to simultaneously illuminate the target balls on the port and starboard sides. Observe whether the laser can detect all the target balls on the port and starboard sides at the same time. If a target ball cannot be detected at a certain position, it needs to be moved to ensure that the target balls on the port and starboard sides can be illuminated by the laser pointers at both positions at the same time.

[0016] S3: Input the actual diameter of the target ball into the Polyworks software. Use the laser tracker to perform the first detection on the target point in the three planes corresponding to the current corner point. After the first detection, lift the target ball and perform the second detection. After the second detection, a plane can be created in the Polyworks software. After the three planes corresponding to the current corner point are created, the coordinates of the intersection point formed by the intersection of the three planes are the three-dimensional coordinates of the current corner point.

[0017] The three-dimensional coordinates of the 16 corner points were measured sequentially using the method in step S3.

[0018] S4: Calculate the side lengths and diagonals Input the 3D coordinates of the 16 corner points into an Excel spreadsheet, and use the formula: Distance between two points = Obtain the side length or diagonal dimension corresponding to each corner point.

[0019] Where X1 and X2 are the X coordinates of the two corner points.

[0020] Y1 and Y2 are the Y coordinates of the two corner points.

[0021] Z1 and Z2 are the Z coordinates of the two corner points.

[0022] Finally, the dimensions of the cargo hold's 24 sides and 40 diagonals are output in an Excel spreadsheet.

[0023] S5: Verify the results by comparing the calculated side lengths and diagonal dimensions with the theoretical dimensions to check for any deviations. If some data deviates too much, remeasure the data by directly measuring with a measuring tape or rangefinder and compare the deviation with the data measured by the laser tracker. If the deviation is within the specified range, the data measured by the laser tracker can be accepted.

[0024] Furthermore, in the aforementioned method for measuring cargo hold dimensions using the MARKⅢ cargo containment system, a square frame is created at the center of the bow or stern of the cargo hold using masking tape, and the laser tracker base is fixed to the bulkhead within the square frame.

[0025] Furthermore, in the aforementioned method for measuring cargo hold dimensions of the MARKⅢ cargo containment system, the target ball base is fixed to the bulkhead using hot melt adhesive.

[0026] Furthermore, in the aforementioned method for measuring cargo hold dimensions of the MARKⅢ cargo containment system, the distance between the target ball and the adjacent corner point is between 100mm and 300mm.

[0027] Furthermore, in the aforementioned method for measuring cargo hold dimensions of the MARKⅢ cargo containment system, the laser tracker is fixed to the bulkhead via a base, and the base thickness plus the laser tracker height is less than the distance from the boundary of each layer of the installation platform to the bulkhead.

[0028] Furthermore, in step S3, the above-mentioned method for measuring the cargo hold dimensions of the MARKⅢ cargo containment system involves first measuring eight corner points on one of the bow or stern faces, and then measuring eight corner points on the other face.

[0029] Furthermore, to ensure that the data measured before and after the laser tracker shifts are consistent within a single coordinate system, after measuring eight corner points on one surface, a leapfrog operation needs to be performed in PolyWorks software to measure eight corner points on another surface.

[0030] The beneficial effects of this invention are: 1. The number of measurements was reduced from 64 to 16, a reduction of 75%.

[0031] 2. Reduced manpower hours: The original method required 20 people to measure for 2 days, while this method requires 5 people to measure for 1 day, reducing manpower hours by 87.5%.

[0032] 3. High measurement accuracy: When measuring long distances (up to about 60m) inside the cargo hold, the rangefinder's measurement error is >10mm, while the laser tracker's error is <1mm, improving accuracy by 90%.

[0033] 4. This method uses computer recording and calculation throughout the process, avoiding errors caused by manual transcription.

[0034] 5. Calculations can be performed by entering formulas in an Excel worksheet, allowing for one-time input and multiple uses while avoiding calculation errors. Attached Figure Description

[0035] Figure 1 This is a diagram showing the distribution of the 10 sides of the cargo hold.

[0036] Figure 2 This is a diagram showing the diagonal lines that need to be measured in the cargo hold. Figure 1 .

[0037] Figure 3 This is a diagram showing the diagonal lines that need to be measured in the cargo hold. Figure 2 .

[0038] Figure 4This is a schematic diagram of the existing measuring device.

[0039] Figure 5 This is a schematic diagram of a laser tracker and a target ball.

[0040] Figure 6 It refers to the three planes adjacent to the corner point being detected.

[0041] Figure 7 This means unchecking the targets with the largest deviations.

[0042] Figure 8 This is a diagram illustrating the calculation of side lengths using an Excel spreadsheet. Detailed Implementation

[0043] The present invention will be described in detail with reference to specific embodiments.

[0044] like Figure 6 The diagram illustrates a method for measuring cargo hold dimensions in the MARKⅢ cargo containment system. The laser tracker is a portable, high-precision three-dimensional coordinate measuring device. It uses laser as the measurement method and is equipped with a laser emitting mechanism rotating around two axes and a reflecting target sphere (hereinafter referred to as the target sphere). See [link to diagram]. Figure 5 During measurement, the laser tracker emits a laser beam to the center of the target sphere. The target sphere contains three mirrors that reflect the laser beam back to the laser tracker. The distance is determined by the laser reflection velocity, and the laser emission angle is determined by an angle encoder within the device. Combining these two methods, the three-dimensional coordinates of the target's location can be determined. The specific steps are as follows: S1: Attach the laser tracker to the D-side of the cargo hold using the laser tracker base. The laser tracker base is mainly composed of a ring frame, a cross structure, laser tracker connectors, and a magnet assembly. The thickness of the base should not be too large, and the base thickness plus the laser tracker height should be less than the distance from the boundary of each layer of the installation platform to the bulkhead.

[0045] The installation platform is a scaffold for construction inside the cargo hold. Each layer of the installation platform has a certain distance between its boundary and the bulkhead, which is the space required for the cargo enclosure construction.

[0046] S2: Use masking tape to create a square frame near the center of the bow and stern (i.e., D and B sides) of the cargo hold. Attach the laser tracker base to the bulkhead inside the square frame on the D side of the cargo hold using the magnetic assembly. Then, fix the laser tracker to the laser tracker base using the equipment connector.

[0047] Determine the position of the target ball base. The target ball base is the base that supports the target ball. It consists of a cylindrical shell and a magnet. There is a spherical groove on the top surface of the cylindrical shell. The groove matches the size of the target ball. When in use, the target ball base is attracted to the cabin wall by the magnet. The target ball is placed in the groove of the cylindrical shell. The magnet can ensure that the target ball is fixed.

[0048] Place some target ball bases on both planes F and J. The target ball bases should be distributed and staggered vertically. These serve as reference points for the laser tracker's relocation, ensuring that the points measured by the laser tracker before and after movement are within the same coordinate system.

[0049] Use a laser pointer next to the laser tracker on side D to observe whether the laser can detect the target ball bases on sides F and J without being blocked by the mounting platform columns. If a target ball base cannot be detected, it needs to be moved. Simultaneously use a laser pointer to illuminate the box position on side B to ensure that all fixed target bases can be detected by laser pointers in both positions at the same time.

[0050] After determining the position of the target ball base, use hot melt adhesive to further secure it to the bulkhead to prevent displacement caused by ship vibration. Magnetic attachment is convenient for installation, but it cannot be fixed permanently. Ship vibration or the placement of the target ball can cause the target ball base to shift, affecting accuracy. Therefore, hot melt adhesive is needed for fixation.

[0051] The laser tracker is powered on and probed according to the equipment operation procedure. The laser tracker is then turned on and its accuracy is calibrated. In the equipment operation software, this invention uses PolyWorks software, where the target sphere diameter is set to match the actual target sphere diameter.

[0052] S3: Taking the measurement of corner point CDK as an example: In PolyWorks software, select "Create Plane" and choose "Probe" as the creation method. For each of the three faces corresponding to the corner point of face D, set 5 target ball placement points, as follows: Figure 6 As shown, the distance between these points and the corner points is between 100 and 300 mm. The target ball is placed close to the bulkhead and probes sequentially. After each probe, the target ball is lifted and probed again. The probed plane will then correspond to surface D. Surfaces C and K are probed using this method. Five target balls are set up and measured on each surface to complete the measurement of corner points CDK.

[0053] The naming convention for the edges inside the cargo hold is: "edge" + the two faces on which the edge is located, such as the edges on face D being named: edge DA, edge DE, edge DF, etc.; the naming convention for corner points is: "corner point" + the three faces on which the corner point is located, such as the corner points on face D being named: corner point ADE, corner point CDK, etc.

[0054] In PolyWorks software, select the detected surfaces D, C, and K, create points by intersecting the three planes, and you can obtain the three-dimensional coordinates of the corner point CDK.

[0055] Using the method described in step S3, the eight corner points of surface D were detected sequentially, resulting in a total of 24 small planes and 120 points being measured. The three-dimensional coordinates of these eight corner points were obtained, extracted, and output using PolyWorks software.

[0056] Because there are welds and arc plates at the intersection of the three sides of the cargo hold, and the target ball itself is large, it is impossible to directly detect the three-dimensional coordinates of the corner point. It is necessary to indirectly detect the three-dimensional coordinates of the corner point by detecting the three adjacent sides and then their intersection.

[0057] "Leapfrog" operation, also known as laser tracker hopping, refers to the process of ensuring that the data measured by a laser tracker before and after displacement are consistent within a single coordinate system. In the cargo hold of an LNG ship, due to obstructions from the installation platform structure, it is impossible to detect the coordinates of all corner points at a single location; therefore, leapfrog operation is necessary.

[0058] In the PolyWorks software, select the target position of the device to be measured, and place the target ball on the target ball base placed on the F and J surfaces in step 2 in sequence. Detect the coordinates of the target ball base one by one, which will serve as the reference point for the unified coordinate system before and after the laser tracker is moved.

[0059] After measuring all corner points on plane D, in PolyWorks software, select the mobile device and move the laser tracker within the box on plane B. Use the target spheres to re-probe the coordinates of all target sphere bases. In PolyWorks software, uncheck targets with large deviations; retain at least three targets, as many as possible. Figure 7 As shown.

[0060] S4: Detect the corner points of surface B. Following the method in step S3, detect and output the three-dimensional coordinates of the eight corner points of surface B.

[0061] Calculate the side length and diagonal In three-dimensional space, the distance between the two target balls = To reduce computational workload, enter the above formula into an Excel spreadsheet, along with the coordinates of 16 corner points. This will generate the corresponding side length or diagonal dimension at another location, such as... Figure 8 As shown.

[0062] like Figure 8 As shown, in the Excel spreadsheet, B3, C3, and D3 are the X, Y, and Z coordinates of corner point ABE, and B13, C13, and D13 are the X, Y, and Z coordinates of corner point HBA. The formula for the distance between the two (that is, the side length BA) is "=((B3-B13)^2+(C3-C13)^2+(D3-D13)^2)^0.5".

[0063] The three-dimensional coordinates of corner point ABE are (-24722.5, -10411.9, 17242.5), and the three-dimensional coordinates of corner point HBA are (-24722.5, 10411.9, 17242.5). Therefore, the distance between them is = =20823.8.

[0064] Following the method in step S4, enter the calculation formulas for the 24 side lengths and 40 diagonals of the cargo hold into the Excel worksheet to calculate all side lengths and diagonal dimensions.

[0065] S5: Compare the calculated side lengths and diagonal dimensions with the theoretical dimensions to check if they exceed the tolerance. If some data exceed the tolerance by a large margin, remeasure the data by directly measuring with a measuring tape or rangefinder and compare the deviation with the measurement data of the laser tracker. If the deviation is within a certain range, the measurement data of the laser tracker can be accepted.

Claims

1. A method for measuring cargo hold dimensions in a MARKⅢ cargo containment system, characterized in that, The cargo hold has 10 faces: bow, stern, port, starboard, top, bottom, upper port, upper starboard, lower port, and lower starboard. Three adjacent faces form a corner, for a total of 16 corners. S1: Fix the laser tracker at the center of the bow or stern of the cargo hold, and set multiple target balls in the three planes corresponding to each corner point. The target balls are close to the adjacent corner points, and the multiple target balls are scattered and staggered in the upper and lower parts. S2: Use a laser pointer to simultaneously illuminate the target balls on the port and starboard sides at the laser tracker positions on the bow and stern sides. Observe whether the laser can detect all the target balls on the port and starboard sides at the same time. If a target ball cannot be detected at a certain position, it needs to be moved to ensure that the target balls on the port and starboard sides can be illuminated by the laser pointers at both positions at the same time. S3: Input the actual diameter of the target ball into the Polyworks software. Use the laser tracker to perform the first detection on the target point in the three planes corresponding to the current corner point. After the first detection, lift the target ball and perform the second detection. After the second detection, a plane can be created in the Polyworks software. After the three planes corresponding to the current corner point are created, the coordinates of the intersection point formed by the intersection of the three planes are the three-dimensional coordinates of the current corner point. The three-dimensional coordinates of the 16 corner points were measured sequentially using the method in step S3. S4: Calculate the side lengths and diagonals Input the 3D coordinates of the 16 corner points into an Excel spreadsheet, and use the formula: Distance between two points = Obtain the side length or diagonal dimension corresponding to each corner point; Where X1 and X2 are the X coordinates of the two corner points; Y1 and Y2 are the Y coordinates of the two corner points; Z1 and Z2 are the Z coordinates of the two corner points; Finally, output the dimensions of the cargo hold's 24 sides and 40 diagonals in an Excel spreadsheet; S5: Verify the results by comparing the calculated side lengths and diagonal dimensions with the theoretical dimensions to check for any deviations. If some data deviates too much, remeasure the data by directly measuring with a measuring tape or rangefinder and compare the deviation with the data measured by the laser tracker. If the deviation is within the specified range, the data measured by the laser tracker can be accepted.

2. The method for measuring cargo hold dimensions of the MARKⅢ cargo containment system according to claim 1, characterized in that, Use masking tape to create a square frame at the center of the bow or stern of the cargo hold, and then fix the laser tracker base to the bulkhead inside the square frame.

3. The method for measuring cargo hold dimensions of the MARKⅢ cargo containment system according to claim 1, characterized in that, The target ball base is fixed to the bulkhead with hot melt adhesive.

4. The method for measuring cargo hold dimensions of the MARKⅢ cargo containment system according to claim 1, characterized in that, The distance between the target ball and the adjacent corner point is between 100mm and 300mm.

5. The method for measuring cargo hold dimensions of the MARKⅢ cargo containment system according to claim 1, characterized in that, The laser tracker is fixed to the bulkhead via a base. The thickness of the base plus the height of the laser tracker is less than the distance from the boundary of each layer of the installation platform to the bulkhead.

6. The method for measuring cargo hold dimensions of the MARKⅢ cargo containment system according to claim 1, characterized in that, Regarding step S3, first measure the 8 corner points on one of the bow or stern faces. After the measurement is completed, measure the 8 corner points on the other face.

7. A method for measuring cargo hold dimensions of a MARKⅢ cargo containment system according to claim 1, characterized in that, To ensure that the data measured before and after the laser tracker is moved are consistent within a single coordinate system, after measuring the eight corner points on one surface, a leapfrog operation needs to be performed in the Polyworks software to measure the eight corner points on another surface.

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