Method for measuring coaxiality of large thin-wall box body

Abstract

The invention discloses a method for measuring the coaxiality of a large thin-wall box body. The method comprises the following steps: vertically placing a measured box body on a horizontal support ring; constructing an auxiliary reference cylinder by using a laser plumb aligner; establishing a ground horizontal cylindrical coordinate system; a self-leveling laser demarcation device is adopted to select section circles of different height values of a measured box body, and coordinate values of all measured points on the surface of the measured box body in a ground horizontal cylindrical coordinate system are calculated; fitting the circumference of the cross section by using the coordinate values of each measured point at the same height value to obtain the circle center, diameter and roundness of the cross section circle at each height value under the cylindrical coordinate system; and fitting a straight line by using the circle centers of the sections with the height values, wherein the straightness of the fitted straight line is the coaxiality of the measured box body. Compared with the prior art, on one hand, the limitation of the laser distance on the size of the box body to be measured is broken through, the coaxiality measurement requirement of the large-size thin-wall welding box body is met, and on the other hand, the climbing safety of personnel in the target ball placing process measured by the laser tracker is ensured.

Description

Technical Field

[0001] The invention belongs to the field of large-size coaxiality measurement, and in particular relates to a method for measuring the coaxiality of a large thin-wall box in a vertical state. Background Art

[0002] Coaxiality is a measurement index used to describe the amount of variation of the common central axis within an object or between different parts. In general, industrial production places high demands on the coaxiality of rotating parts to meet the accuracy and matching of assembly and to ensure the performance of equipment. For example, in the cold launch technology of weapons and equipment, it is required to have good coaxiality to meet the requirements of accurate loading and smooth ejection of products. Therefore, coaxiality is one of the important factors that determine the assembly quality and performance of rotating parts in the field of modern industrial manufacturing.

[0003] With the development of modern industrial technology, the demand for large workpieces in aerospace, aviation, ships, pipelines and large machinery is also increasing, especially for large thin-walled boxes. Whether the coaxiality of the workpiece can be accurately measured has a certain impact on the subsequent assembly and performance assurance. In response to the coaxiality measurement needs of large thin-walled boxes, laser trackers are currently used to measure the box in a horizontal position. Personnel place laser target balls on the surface of the box to collect data points. The instrument needs to be turned several times to cover the box. On the one hand, the measurement efficiency is low and the measurement time is long. Secondly, the safety of personnel climbing during the placement of the target ball must be considered. When a large-diameter thin-walled box is placed horizontally, the state of the box is affected by the support conditions and the self-weight deflection, and the coaxiality measurement result is more deviated from the true value. Limited by the linear propagation characteristics of lasers, the measurement coverage of the laser tracker depends on the laser emission and return light distance, and the measurement environment is required to be open and unobstructed. There are many disadvantages in the existing measurement methods, which greatly limit the scope of use of laser trackers and it is difficult to meet the coaxiality measurement needs of large thin-walled boxes. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the present invention proposes a method for measuring the coaxiality of a large thin-walled box to meet the coaxiality measurement requirements of a large-sized thin-walled welded box.

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

[0006] Step 1: Place the box to be tested vertically on a horizontal support ring;

[0007] Step 2: Use a laser plumb line to construct an auxiliary reference cylinder;

[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 of the same height value of the measured box, and measure the distance from the measured point of the same height value and different θ angles on the surface of the measured box to the corresponding point of the cross-sectional circle of the auxiliary reference cylinder;

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

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

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

[0013] Step 8. Use the center of each height value section to fit a straight line. The straightness of the fitted straight line is the coaxiality of the measured box.

[0014] Compared with the prior art, the present invention has the following positive effects:

[0015] The present invention adopts the auxiliary reference method to migrate the reference of the entire measurement system. Starting from the actual contour size of the measured box, the roundness and radius of the box end frame are expanded to construct an auxiliary reference cylinder, and then the circumference data of each height difference section of the box are unified to the same coordinate system. After subsequent data processing and fitting calculation, the coaxiality of the box is obtained. Compared with the commonly used laser tracker coaxiality measurement method at this stage, the present invention, on the one hand, breaks through the limitation of laser distance on the size of the measured box, meets the coaxiality measurement requirements of large-sized thin-walled welded boxes, and on the other hand, ensures the safety of personnel climbing during the laser tracker measurement of the target ball. The present invention measures large-sized boxes in a vertical state, which not only avoids the influence of the support state and self-weight deflection on the measurement results, but also its coaxiality data can better reflect the actual processing and use status, and reduces the difficulty of coaxiality measurement of large-sized boxes, while greatly improving the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 1 This is a diagram of the horizontal support ring and the tested box M placed vertically;

[0018] Figure 2 Schematic diagram of the cylindrical coordinate system G constructed for the auxiliary reference cylinder;

[0019] Figure 3 Schematic diagram of arranging and constructing auxiliary reference cylinder for laser plummet;

[0020] Figure 4 It is a top view of the laser plumb line, the auxiliary reference cylinder and the box to be measured;

[0021] Figure 5 It is a schematic diagram of measuring and calculating the distance of each point of the Z-value height section M from the auxiliary reference cylinder in the radial direction;

[0022] Reference numerals in the figures include:

[0023] 1 horizontal support ring, 2 self-aligning level, 3 reference horizontal line, 4 measured box, 5 lower end frame of measured box, 6 upper end frame of measured box, 7 section of measured box at Z value from lower end frame, 8 auxiliary reference cylinder, 9 cylindrical coordinate system, 10 center of auxiliary reference cylinder, 11 Z axis in cylindrical coordinate system, 12 X axis in cylindrical coordinate system, 13 laser vertical collimator, 14 vertical reference line, 15 section of auxiliary reference cylinder constructed by vertical reference line, 16 points on measured end frame, 17 radius R of each point on measured end frame i 、18 The distance between the auxiliary reference cylinder and the measured box is l、19 Self-leveling line projection instrument、20 The Z value height section circle selection auxiliary line、21 The minimum value L of the distance between the Zj value height section circle and the auxiliary reference cylinder in the radius direction izj , 22 Auxiliary reference cylinder radius R i +l, 23 The radial coordinate of the measuring point of the circular cross section of the measured box when the height is Zj is R=R i +lL izj . DETAILED DESCRIPTION

[0024] In order to avoid various influencing factors in the coaxiality measurement of a large-sized thin-walled welded box in a horizontal state, the present invention proposes to perform coaxiality measurement when the box is placed vertically. The tower is used to collect cross-sectional box data at different heights in the vertical state of the box to ensure the safety of the measurement personnel and the timeliness of the measurement.

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

[0026] In order to avoid collision between the vertically placed box and the tower and to reduce measurement errors caused by tilted support of the box, the horizontal support ring needs to be leveled before measurement.

[0027] step 1. Figure 1 As shown, before the measurement, the self-collimation level 2 is used to measure the levelness of the horizontal support ring 1, and the levelness is required to be maintained at ≤0.20mm / m. Figure 1 The apparatus comprises: a horizontal support ring 1, a self-aligning level 2, a reference horizontal line 3, a box to be measured 4, a lower end frame 5 of the box to be measured, an upper end frame 6 of the box to be measured, and a cross section of the box to be measured at a distance from the lower end frame to the Z value.

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

[0029] i. Filling the box: When the box is filled, the box end frame plane is required to be completely in contact with the upper end surface of the horizontal support ring 1 under the action of water pressure and gravity before measurement. The horizontal support ring levelness data will be referenced in subsequent calculations to establish the Z-axis reference plane of the geodetic horizontal cylindrical coordinate system G;

[0030] ii. Box without filling: When the product is not filled, it is necessary to consider the impact of the inclination error introduced by the flatness of the box end frame plane on the coaxiality measurement results.

[0031] Step 2: Acquisition of horizontal circular data in vertical state

[0032] Step 3. The end frames of large thin-walled boxes are mostly machined parts with good roundness and flatness. Generally, the end frames of the box to be measured are selected for measurement to obtain the end frame flatness data and the radius R at each point of the end frame outer diameter. i , used to construct auxiliary reference cylinder;

[0033] Step 4. Arrange N laser plummets 13 around the tested box, and N data collection points are 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). Debug the laser plummet 13 to emit a laser line perpendicular to the horizontal plane of the earth as the reference busbar 14, so that the horizontal distance between the reference busbar and the tested end frame surface of the box is l.

[0034] The reference lines emitted by multiple laser plummets are constructed into a diameter of (2R i +21) of the space cylinder, the measured box is included in it, and is used as an auxiliary reference cylinder 15 for measuring the coaxiality of the large-sized box. The auxiliary reference cylinder expands the actual outline size of the measured box, realizing the migration of the measurement reference of the measured box.

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

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

[0037] Step 7. Use a depth caliper to measure the minimum distance L between the measured point with the same height Z value and different θ angle on the surface of the measured box and the corresponding point of the auxiliary reference cylindrical section circle 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 16 on the end frame to be measured, and the radius R of each point on the end frame to be measured. i 17. The distance between the auxiliary reference cylinder and the measured box is l 18. Self-leveling line projection instrument 19. Z value height section circle selection auxiliary line 20; Among them: the radius of the auxiliary reference cylinder is R i +l, it can be known that the change of the measured point relative to the corresponding point of the auxiliary reference cylindrical section circle is Δ=lL i , the coordinate values ​​of the N evenly distributed measured points on the cross section in the cylindrical coordinate system 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, to obtain the spatial point data information of the circular cross section of the tested box when the height is Z value;

[0039] Step 3: Vertical cross-section data acquisition scheme

[0040] Step 9. Adjust the placement height of the self-leveling line projection instrument 19, and measure the cross-sectional circles at different heights Z of the measured box, which are recorded as Zj;

[0041] step 10 Repeat step 7 and step 8 in step 2, and use the depth caliper to measure the different heights Z of the surface of the box to be tested j The measured point with different θ angles is R corresponding to the auxiliary reference cylindrical section circle. i The minimum distance L iZj ;

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

[0043] i. Assign values ​​of θ in the coordinates of each measuring point according to the distribution of the laser plummet, which are 0, θ, 2θ...(N-1)θ respectively;

[0044] ii. Assign the coordinate Z value of each measuring point according to the height difference between each section and the horizontal support ring reference plane, recorded as Zj;

[0045] iii. According to the minimum value L of the radius direction of the auxiliary reference cylinder from the measured box surface izj Assign the coordinate R value of each measuring 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, the reference numerals in the figure include Zj value height section circle distance auxiliary reference cylinder radius direction minimum value L izj 21. Auxiliary reference cylinder radius R i +l 22. The box under test is at a height of Z j When the value is R, the radial coordinate of the measuring point of the circular cross section is R i +lL izj twenty three;

[0047] Step 4: Data processing and calculation of the coaxiality data of the tested box

[0048] Step 12. Import all measurement points into SA software for data calculation, and perform regression calculation on the coordinate values ​​of the measurement points with the same Z value to fit the cross-section 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 measured box is long and the coaxiality measurement of all sections of the measured box cannot be completed at one time due to the height of the tower, the box needs to be decomposed into sections for segmented measurement. After the segmented measurement, digital simulation docking is performed according to the actual docking status of each section to obtain the overall coaxiality measurement data.

Claims

1. A method for measuring the coaxiality of a large thin-walled box, characterized in that: The steps include: Step 1: Place the box to be tested vertically on a horizontal support ring; Step 2: Use a laser plumb line to construct an auxiliary reference cylinder; Step 3: Establish a geodetic horizontal cylindrical coordinate system; Step 4: Use a self-leveling laser line projector to select a cross-sectional circle of the same height value of the measured box, and measure the distance from the measured point of the same height value and different θ angles on the surface of the measured box to the corresponding point of the cross-sectional circle of the auxiliary reference cylinder; Step 5: Change the placement height of the self-leveling laser line projector and repeat step 4; Step 6: Calculate the coordinate values ​​of each measured point on the surface of the measured box in the geodetic horizontal cylindrical coordinate system; Step 7: Fit the cross-section circle using the coordinate values ​​of each measured point at the same height value to obtain the center, diameter and roundness of the cross-section circle in the cylindrical coordinate system at each height value; Step 8. Use the center of each height value section to fit a straight line. The straightness of the fitted straight line is the coaxiality of the measured box.

2. A method for measuring the 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. A method for measuring the coaxiality of a large thin-walled box according to claim 2, characterized in that: Use an autocollimation level to measure the levelness of the horizontal support ring.

4. A method for measuring the coaxiality of a large thin-walled box according to claim 1, characterized in that: The method of using a laser plumb line to construct an auxiliary reference cylinder described in step 2 is as follows: N laser plumb lines are arranged around the measured box, corresponding to N data collection points distributed on the same horizontal cross-section circle, and each laser plumb line is evenly distributed at an angle θ relative to the circumference of the measured box, where N*θ=360; the laser plumb line is debugged to emit a laser line perpendicular to the horizontal plane of the earth as a reference generatrix, so that the horizontal distance between the reference generatrix and the end frame surface of the measured box is l, thereby obtaining an auxiliary reference cylinder that includes the measured box.

5. A method for measuring the coaxiality of a large thin-walled box according to claim 1, characterized in that: The method for establishing the geodetic horizontal cylindrical coordinate system described in step three is: use the center of the auxiliary reference cylinder as the origin of the coordinate system, use the horizontality data of the horizontal support ring to establish the Z-axis reference plane, and use the position of any laser plumb line as the X-axis to establish the geodetic horizontal cylindrical coordinate system.

6. A method for measuring the coaxiality of a large thin-walled box according to claim 1, characterized in that: The method for calculating the coordinate values ​​of each measured point on the surface of the measured box in the geodetic horizontal cylindrical coordinate system described in step 6 is: The first step is to measure the same height Z on the surface of the box to be tested j The distance L between the measured point and the corresponding point of the auxiliary reference cylindrical section circle with different values ​​of θ iZj ; Step 2: L izj Perform data assignment processing and unify it in the (R, θ, Z) cylindrical coordinate system: 1) Assign a value of θ in the coordinate value of each measuring point according to the distribution of the laser plumb line, denoted as (i-1)θ, i = 1, 2, 3, ..., N, N is the number of laser plumb lines; 2) Assign the coordinate Z value of each measuring point according to the height difference between each measured section and the horizontal support ring reference plane, recorded as Zj; 3) According to the minimum value L of the radius direction of the auxiliary reference cylinder from the measured box surface izj Assign the coordinate R value of each measuring point, denoted as R i +lL izj , where: 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 between the auxiliary reference cylinder and the measured box; 4) Obtain the coordinate values ​​P of each point on the surface of the measured box in the cylindrical coordinate system ij for (R i +lL izj , (i-1)θ, Z j ).

7. A method for measuring the coaxiality of a large thin-walled box according to claim 6, characterized in that: The L iZj Use a depth caliper to measure the minimum distance from the measured point with the same height Zj value and different θ angles on the surface of the measured box to the corresponding point of the auxiliary reference cylindrical section circle.

8. A method for measuring the coaxiality of a large thin-walled box according to claim 1, characterized in that: When the box to be measured is long and the tower height cannot complete the coaxiality measurement of all sections of the box to be measured at one time, the box to be measured needs to be decomposed into sections for segmented measurement; after the segmented measurement, digital simulation docking is performed according to the actual docking status of each section to obtain the overall coaxiality measurement data.

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