A coaxiality measurement method for a large thin-walled box

Abstract

This invention discloses a method for measuring the coaxiality of a large thin-walled box. The box to be measured is placed vertically on a horizontal support ring. An auxiliary reference cylinder is constructed using a laser plumb line. A geodetic horizontal cylindrical coordinate system is established. A self-leveling laser line projector is used to select cross-sectional circles at different heights of the box, and the coordinates of each measured point on the surface of the box in the geodetic horizontal cylindrical coordinate system are calculated. The coordinates of each measured point at the same height are used to fit the circumference of the cross-section, obtaining the center, diameter, and roundness of the cross-section circle at each height in the cylindrical coordinate system. A straight line is fitted using the center of the cross-section at each height, and the straightness of the fitted line is the coaxiality of the box. Compared with existing technologies, this invention overcomes the limitation of laser distance on the size of the box, meeting the coaxiality measurement requirements of large-size thin-walled welded boxes. Furthermore, it ensures the safety of personnel climbing to heights during the laser tracker measurement of the target ball placement process.

Description

Technical Field

[0001] This invention belongs to the field of large-size coaxiality measurement, specifically relating to a method for measuring the coaxiality of large thin-walled boxes in a vertical state. Background Technology

[0002] Coaxiality is a measurement index used to describe the amount of variation in the common central axis between internal parts or different parts of an object. In general industrial production, high requirements are placed on the coaxiality of rotating parts to ensure assembly precision, compatibility, and equipment performance. For example, in the cold-launch technology of weaponry, good coaxiality is essential to meet the requirements of accurate loading and successful ejection. Therefore, coaxiality is one of the important factors determining the assembly quality and performance of rotating parts in modern industrial manufacturing.

[0003] With the development of modern industrial technology, the demand for large workpieces in aerospace, aviation, shipbuilding, pipeline, and large machinery fields is increasing, especially for large thin-walled boxes. Accurate measurement of the coaxiality of these workpieces has a significant impact on subsequent assembly and performance assurance. Currently, for coaxiality measurement of large thin-walled boxes, laser trackers are often used in a horizontally placed box. Personnel place a laser target ball on the box surface to collect data points. The instrument needs to be moved multiple times to cover the box, resulting in low measurement efficiency, long measurement time, and safety concerns regarding personnel climbing to heights during target ball placement. When large-diameter thin-walled boxes are placed horizontally, the box's condition is affected by support conditions and its own weight deflection, leading to a significant deviation between the measured coaxiality and the true value. Limited by the linear propagation characteristics of lasers, the measurement coverage of laser trackers depends on the laser emission and return distance, and requires an open, unobstructed measurement environment. Existing measurement methods have many drawbacks, greatly limiting the application range of laser trackers and making it difficult to meet the coaxiality measurement requirements of large thin-walled boxes. Summary of the Invention

[0004] To overcome the aforementioned shortcomings of the prior art, this invention proposes a method for measuring the coaxiality of large thin-walled boxes, in order to meet the coaxiality measurement requirements of large-size thin-walled welded boxes.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for measuring the coaxiality of a large thin-walled box, comprising the following steps:

[0006] Step 1: Place the test chamber vertically on the horizontal support ring;

[0007] Step 2: Construct an auxiliary reference cylinder using a laser plumb line;

[0008] Step 3: Establish a geodetic horizontal cylindrical coordinate system;

[0009] Step 4: Use a self-leveling laser line projector to select a cross-sectional circle with the same height value of the box being measured, and measure the distance from the measured point with the same height value but different θ angles on the surface of the box being measured to the corresponding point of the auxiliary reference cylindrical cross-sectional circle;

[0010] Step 5: Change the placement height of the self-leveling laser line projector and repeat step 4;

[0011] Step 6: Calculate the coordinates of each measured point on the surface of the measured box in the geodetic horizontal cylindrical coordinate system;

[0012] Step 7: Fit the cross-sectional circle using the coordinate values ​​of each measured point at the same height value to obtain the center, diameter, and roundness of the cross-sectional circle in the cylindrical coordinate system at each height value;

[0013] Step 8: Fit a straight line using the center of the circle at each height value section. The straightness of the fitted line is the coaxiality of the measured box.

[0014] Compared with the prior art, the positive effects of the present invention are:

[0015] This invention employs an auxiliary reference method to perform reference transfer for the entire measurement system. Starting from the actual contour dimensions of the box being measured, the roundness and radius of the box's end frame are expanded outwards to construct an auxiliary reference cylinder. This unifies the circumferential data of each height difference section of the box into the same coordinate system. Subsequent data processing and fitting calculations yield the coaxiality of the box. Compared to the commonly used laser tracker method for measuring coaxiality, this invention overcomes the limitation of laser distance on the size of the box being measured, meeting the coaxiality measurement requirements of large-sized thin-walled welded boxes. Furthermore, it ensures the safety of personnel climbing to heights during the laser tracker measurement of the target ball placement process. This invention measures large-sized boxes in a vertical state, avoiding the influence of support conditions and self-weight deflection on the measurement results. Its coaxiality data better reflects the actual processing and usage conditions, and significantly improves measurement efficiency while reducing the difficulty of coaxiality measurement for large-sized boxes. Attached Figure Description

[0016] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0017] Figure 1 Diagram showing the horizontal support ring and the tested box M in a vertically placed state;

[0018] Figure 2 A schematic diagram of the cylindrical coordinate system G constructed to assist the reference cylinder;

[0019] Figure 3 A schematic diagram showing the setup and construction of the auxiliary reference cylinder for the laser plumb line;

[0020] Figure 4 Top view of the laser plumb line, auxiliary reference cylinder, and the box under test;

[0021] Figure 5 A schematic diagram showing the measurement and calculation of the distance from each point on the Z-value height section M to the radius of the auxiliary reference cylinder;

[0022] The reference numerals in the figure include:

[0023] 1. Horizontal support ring; 2. Autocollimating level; 3. Baseline level; 4. Measured box; 5. Lower frame of the measured box; 6. Upper frame of the measured box; 7. Section of the measured box at the Z-value distance from the lower frame; 8. Auxiliary reference cylinder; 9. Cylindrical coordinate system; 10. Center of the auxiliary reference cylinder; 11. Z-axis in the cylindrical coordinate system; 12. X-axis in the cylindrical coordinate system; 13. Laser plumb line; 14. Vertical baseline; 15. Section of the auxiliary reference cylinder constructed by the vertical baseline; 16. Points on the measured end frame; 17. Radius R of each point on the measured end frame. i 18. Distance l between auxiliary reference cylinder and the measured box; 19. Self-leveling projection instrument; 20. Selection of auxiliary line for Z-value height section circle; 21. Minimum value L in the direction of the radius of Zj-value height section circle from the auxiliary reference cylinder. izj 22. Auxiliary reference cylinder radius R i +l、23 When the height of the measured box is Zj, the radius direction coordinate of the measurement point on the circumferential cross-section is R=R i +lL izj . Detailed Implementation

[0024] To mitigate various influencing factors in coaxiality measurement of large, thin-walled welded boxes placed horizontally, this invention proposes performing coaxiality measurements while the boxes are placed vertically. A tower is used to collect cross-sectional data of the boxes at different heights when placed vertically, ensuring the safety of the measurement personnel and the timeliness of the measurement.

[0025] Step 1: Leveling to reduce tilt error in vertical position

[0026] To avoid collisions between the vertically placed test box and the tower, and to reduce measurement errors caused by the tilting of the support, the horizontal support ring must be leveled before measurement.

[0027] Step 1. As Figure 1 As shown, before measurement, the horizontal support ring 1 is measured using an autocollimating level 2, and its horizontality is required to be ≤0.20mm / m. Figure 1 The system includes: 1. Horizontal support ring; 2. Autocollimating level; 3. Baseline level; 4. Test box; 5. Lower frame of the test box; 6. Upper frame of the test box; and 7. Cross-section of the test box at the Z-value of the distance from the lower frame.

[0028] Step 2. Place the test chamber 4 vertically on the horizontal support ring 1:

[0029] i. Box filling: Under the box filling state, the box end frame plane is required to be completely in contact with the upper end face of the horizontal support ring 1 under the action of water pressure and gravity before measurement. The horizontality data of the horizontal support ring will be used to establish the Z-axis reference plane of the geodetic horizontal cylindrical coordinate system G in subsequent calculations.

[0030] ii. Unfilled box: When the product is unfilled, the impact of tilt error introduced by the flatness of the box end frame on the coaxiality measurement results needs to be considered.

[0031] Step 2: Scheme for Obtaining Horizontal Circumferential Data in Vertical Position

[0032] Step 3. The end frames of large, thin-walled enclosures are mostly machined parts, possessing good roundness and flatness. Measurements are typically taken at the end frame of the enclosure being measured to obtain the flatness data and the radius R at various points on the outer diameter of the end frame. i Used to construct an auxiliary reference cylinder;

[0033] Step 4. Arrange N laser plumb bobs 13 around the box to be tested. The N plumb bobs correspond to N data acquisition points distributed on the same horizontal cross-section circle, so that they are evenly distributed at an angle θ relative to the circumference of the box (N*θ=360). Adjust the laser plumb bob 13 to emit a laser line perpendicular to the horizontal plane of the ground as a reference generatrix 14, and make the horizontal distance between the reference generatrix and the frame surface of the box to be tested l.

[0034] The reference generatrices emitted by multiple laser plumb bobs are configured to form a diameter of (2R) i A spatial cylinder (+2l) is included within the box to be measured, serving as an auxiliary reference cylinder 15 for measuring the coaxiality of large-size boxes. This auxiliary reference cylinder extends the actual contour dimensions of the box to be measured, thus realizing the transfer of the measurement reference for the box to be measured.

[0035] Step 5. Using the center of the auxiliary reference cylinder as the origin of the coordinate system, establish the Z-axis reference plane using the horizontal support ring levelness data, and establish a geodetic horizontal cylindrical coordinate system using any laser plumb line position as the X-axis, as follows. Figure 2 As shown, it includes an auxiliary reference cylinder 8, a cylindrical coordinate system 9, the center of the auxiliary reference cylinder 10, the Z-axis 11 in the cylindrical coordinate system, and the X-axis 12 in the cylindrical coordinate system;

[0036] Step 6. Use the self-leveling laser line projector 19 to draw the Z-value cross-section circle of the measured box at the same height and select the auxiliary line 20;

[0037] Step 7. Use depth calipers to measure the minimum distance L from the corresponding point on the auxiliary reference cylindrical section circle at the same height Z value but different θ angles on the surface of the box being measured. i (Minimum distance to ensure all measurements are centripetal);

[0038] Step 8. Figure 3 and Figure 4 As shown, it includes: a laser plumb line 13, a vertical reference line 14, an auxiliary reference cylindrical section 15 constructed by the vertical reference line, points on the end frame to be measured 16, and radii R of each point on the end frame to be measured. i 17. Distance l between the auxiliary reference cylinder and the measured box; 18. Self-leveling projection instrument; 19. Auxiliary line selection for the Z-value height section circle; 20. Wherein: the radius of the auxiliary reference cylinder is R. i +l, we can know that the change of the measured point relative to the corresponding point on the auxiliary reference cylindrical cross-section circle is Δ=lL i In cylindrical coordinates, the coordinates of the N uniformly distributed measured points on this cross section are (R1+l-L1, 0, Z), (R2+l-L2, θ, Z), (R3+l-L3, 2θ, Z), ... (R i +lL i ,(i-1)θ,Z),……(R) N +lL N ,(N-1)θ,Z), that is, the spatial point data of the circumferential cross-section of the measured box at a height of Z is obtained;

[0039] Step 3: Scheme for Obtaining Longitudinal Section Data in Vertical State

[0040] Step 9. Adjust the placement height of the self-leveling projection instrument 19, measure the cross-sectional circle at different heights of the box being measured (Z value), and record it as Zj;

[0041] Step 10: Repeat steps 7 and 8 in step two, and use a depth caliper to measure different heights Z on the surface of the box being measured. j The measured point R at different θ angles corresponds to the auxiliary reference cylindrical cross-section circle. i minimum distance L iZj ;

[0042] Step 11. For the obtained distance L izj The numerical values ​​are processed and unified in the (R, θ, Z) cylindrical coordinate system G:

[0043] i. Assign values ​​to θ in the coordinates of each measurement point according to the distribution of the laser plumb line, namely 0, θ, 2θ...(N-1)θ;

[0044] ii. Assign Z-values ​​to the coordinates of each measurement point based on the height difference between each cross section and the reference plane of the horizontal support ring, and denote them as Zj;

[0045] iii. Based on the minimum value L in the direction of the radius of the auxiliary reference cylinder from the surface of the tested box. izj Assign values ​​R to the coordinates of each measurement point, denoted as R. i+lL izj ;

[0046] iv. Obtain the coordinate values ​​P of each point on the surface of the measured box in the cylindrical coordinate system G. ij For (R) i +lL izj ,(i-1)θ,Zj), such as Figure 5 As shown in the figure, the reference numerals include the minimum value L in the direction of the distance from the height section circle of the Zj value to the radius of the auxiliary reference cylinder. izj 21. Radius R of the auxiliary reference cylinder i +l 22, the tested box is at a height of Z j When the value is measured, the radial direction coordinates of the measurement point of the circumferential cross-section are R = R i +lL izj twenty three;

[0047] Step 4: Data Processing and Calculation of Coaxiality Data of the Test Box

[0048] Step 12. Import all measurement points into SA software for data calculation. Perform regression calculation on the coordinate values ​​of measurement points with the same Z value to fit the cross-sectional circumference and obtain the relative center deviation, diameter and roundness in the cylindrical coordinate system G.

[0049] Step 13. Select the center of each Z-value section to construct a fitting straight line. The straightness of the fitting straight line is used to replace the coaxiality of the measured box.

[0050] Step 14. When the test enclosure is long and the coaxiality measurement of all sections cannot be completed in one go due to the height limitation of the tower, the enclosure needs to be decomposed into sections for segmented measurement. After segmented measurement, digital simulation docking is performed based on the actual docking status of each section to obtain the overall coaxiality measurement data.

Claims

1. A method of measuring the coaxiality of a large thin-walled box, characterized by: It comprises the following steps: Step one, place the measured box vertically on the horizontal support ring; Step two, constructing an auxiliary reference cylinder by using laser plummet, the method of constructing an auxiliary reference cylinder by using laser plummet is: arranging N laser plummets around the measured box, corresponding to N data collection points distributed on the same horizontal section circle respectively, each laser plummet is uniformly distributed at θ angle relative to the circumference of the measured box, wherein N θ=360; adjusting the laser plummet to emit a laser line perpendicular to the horizontal plane of the earth as the reference generatrix, making the horizontal distance between the reference generatrix and the end frame surface of the measured box be l, thereby obtaining an auxiliary reference cylinder in which the measured box is included; Step three, establish a horizontal cylindrical coordinate system of the earth; Step four, select the cross-section circle of the same height value of the measured box by using the self-levelling laser line projector, and measure the distance from the measured point of the same height value and different θ angle on the surface of the measured box to the corresponding point of the auxiliary reference cylindrical cross-section circle; Step five, change the placement height of the self-levelling laser line projector and repeat step four; Step six, according to the geometric parameters of the auxiliary reference cylinder in step two and the distance from each measured point to the corresponding point of the auxiliary reference cylindrical cross-section circle in step four, calculate the coordinate values of each measured point on the surface of the measured box in the horizontal cylindrical coordinate system of the earth; Step seven, fit the cross-sectional circle with the coordinate values of each measured point at the same height value to obtain the center, diameter and roundness of the cross-sectional circle at each height value in the cylindrical coordinate system; Step eight, fit a straight line with the centers of each height value cross section, and the straightness of the fitted straight line is the coaxiality of the measured box.

2. The method for measuring coaxiality of a large thin-walled box according to claim 1, characterized in that: The levelness of the horizontal support ring is ≤0.20mm / m.

3. The method of measuring the coaxiality of a large thin-walled box according to claim 2, characterized in that: The horizontal support ring is measured for levelness by using a self-collimating level.

4. The method of claim 1, wherein: The method for establishing the horizontal cylindrical coordinate system of the earth in step three is: taking the center of the auxiliary reference cylinder as the origin of the coordinate system, establishing the Z-axis reference plane with the levelness data of the horizontal support ring, and establishing the horizontal cylindrical coordinate system of the earth with the position of any laser plummet as the X-axis.

5. The method of measuring the coaxiality of a large thin-walled box according to claim 4, characterized in that: The method for calculating the coordinate values of each measured point on the surface of the measured box in the horizontal cylindrical coordinate system of the earth in step six is: First step, measure the same height Z of the surface of the measured box j The distance L of the measured point with different angle θ to the corresponding point of the auxiliary reference cylindrical section circle iZj ; Second step, data assignment processing is carried out to L izj is unified in (R, θ, Z) cylindrical coordinate system: 1) Assign values to θ in the coordinate values of each measurement point according to the distribution of the laser plummets, denoted as (i-1)θ, i=1,2,3,...,N, N is the number of laser plummets; 2) According to the difference between the measured section and the reference plane of the horizontal support ring, the coordinate Z value of each measuring point is assigned, denoted as Z j ; 3) The minimum value L of the auxiliary reference cylinder radius direction from the measured box surface izj The coordinate R value of each measurement point is assigned, denoted as R i + l-L izj , wherein: R i is the radius of the measured point corresponding to different θ angles on the end frame of the measured box, and l is the distance from the auxiliary reference cylinder to the measured box. 4) get the coordinate value P of each point on the surface of the measured box in the cylindrical coordinate system ij for (R i + l-L izj , (i-1)θ, Z j ).

6. The method of measuring the coaxiality of a large thin-walled box according to claim 5, characterized in that: The L iZj The same height Z of the measured box surface is measured by a depth gauge j The minimum distance of the measured point with different θ angle to the corresponding point of the auxiliary reference cylindrical section circle.

7. The method of measuring the coaxiality of a large thin-walled box according to claim 1, characterized in that: When the measured box is long and the tower height cannot complete the coaxiality measurement of all sections of the measured box at one time, the measured box needs to be sectioned and measured. After the segmented measurement, the actual butt joint state of each section is simulated digitally to obtain the overall coaxiality measurement data.

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