A standard block-based double-line laser calibration method and calibration device

Abstract

The application discloses a double-line laser calibration method and device based on a standard block, and comprises the following steps: 1, transforming the local coordinate system of the double-line laser to the same local coordinate system; 2, transforming the local coordinate system to a virtual coordinate system; wherein, the coordinate system transformation step comprises an angle transformation step and a position transformation step, and the angle and position calibration of the double-line laser measuring instrument is completed through the angle transformation step and the position transformation step. The angle and position calibration of the double-line laser measuring instrument can be completed after one-time scanning of the standard block.

Description

Technical Field

[0001] This invention belongs to the field of laser measurement and calibration technology, specifically relating to a dual-line laser calibration method and calibration device based on a standard block. Background Technology

[0002] Among various aerospace propulsion technologies, liquid rocket engines dominate aerospace engineering applications due to their high performance and reliability, good mission adaptability, and many other advantages. The injection system, often referred to as the throat of a liquid rocket engine, primarily functions to introduce liquid propellant into the combustion chamber at a specific mass flow rate and to atomize it uniformly. Pairs of angled injection holes are machined into the nozzles of the injection system to atomize and mix the fuel and oxidizer. The machining quality of these injection holes determines key technical indicators of the engine, such as fuel atomization performance, combustion efficiency, specific impulse, and combustion stability.

[0003] Before welding the mutual impact injection disc, it is necessary to check whether the dimensions, impact height, and spatial misalignment of the injection holes meet the requirements. Currently, most methods use contact-based inspection, which employs specialized tooling, height gauges, dial indicators, and other traditional measuring instruments to measure the conformity of design parameters. This method suffers from low inspection efficiency, low accuracy, and human error. To address this engineering problem, the proposed solution is to use a dual-line laser scanning instrument mounted in opposite directions to acquire point cloud data of the surfaces on both sides of the injection hole. The data from the dual-line laser scanner are then stitched together and fitted to obtain the coordinates of the center points of the two holes. This allows for the calculation of the axis equation of the injection hole, yielding parameters such as the impact height and spatial misalignment of the paired injection holes.

[0004] When using a dual-line laser measuring instrument, several installation errors exist, as the collected data reside in the local coordinate systems of the two instruments and are independent of each other. To accurately stitch together the data collected by the dual-line laser measuring instruments and accurately measure the various geometric parameters of the injection orifice, calibration of the two line laser measuring instruments is necessary. Currently, there is no satisfactory solution for calibrating opposing line laser measuring instruments. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a dual-line laser calibration method and calibration device based on a standard block. This method can complete the calibration of the angle and position of the dual-line laser measuring instrument after one scan of the standard block.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A dual-line laser calibration method based on a standard block includes the following steps;

[0008] Step 1: Transform the dual-line laser local coordinate system to the same local coordinate system;

[0009] Step 2: Transform the local coordinate system to the virtual coordinate system;

[0010] The coordinate system transformation steps include angle transformation and position transformation steps. Through these steps, the angle and position of the dual-line laser measuring instrument are calibrated.

[0011] Step 1 specifically involves transforming the dual-line laser local coordinate system to the same local coordinate system:

[0012] Angle transformation steps: Place the standard block between two opposing line laser measuring instruments A and B. The thickness of the standard block is D, and the major axis is at a certain angle θ with the scanning direction, so that the two sets of adjacent planes of the standard block are within the scanning range of the two line laser measuring instruments.

[0013] The point cloud data of two adjacent surfaces of the standard block were acquired by line laser measuring instrument A and line laser measuring instrument B, respectively.

[0014] First, the collected point cloud data is preprocessed, including curvature downsampling to simplify the data, and statistical filtering and radius filtering to remove a large amount of noise from the point cloud;

[0015] The point cloud data of the line laser measuring instrument B is mirrored along the XY plane so that the local coordinate system of the dual-line laser measuring instrument has the same direction.

[0016] The point cloud data of the two adjacent surfaces is divided into planes, the angle between the normal vectors of the larger relative planes in the two sets of data is obtained, and the rotation matrix is ​​calculated to make the normal vectors of the two larger planes parallel, that is, the two larger planes in the point cloud data are parallel. The rotation matrix is ​​then applied to the point cloud data of the line laser measuring instrument B.

[0017] Calculate the normal vector of the smaller plane in the point cloud data acquired by the line laser measuring instrument A and the point cloud data of the line laser measuring instrument B after applying the rotation matrix. Find the angle between the two normal vectors, calculate the rotation matrix to make the normal vectors of the two smaller planes parallel, and apply the rotation matrix to the point cloud data of the line laser measuring instrument B to complete the angle transformation from the local coordinate system of the two line lasers to the same coordinate system. Obtain the point cloud data of the standard block with two relatively parallel planes in the local coordinate system of the line laser measuring instrument A and the rotation matrix of the angle transformation of the two point cloud data in the point cloud data acquired by the line laser measuring instrument A and the line laser measuring instrument B.

[0018] Position transformation steps: Process the point cloud data collected from two adjacent surfaces after angle transformation. Fit the larger plane in each of the two scanned point clouds and find the center point of that plane. Calculate the center point coordinates of the standard block using the coordinates of the plane's center point, the plane's normal vector, and the thickness of the standard block. Calculate the difference between the fitted center points of the point cloud data from line laser measuring instruments A and B to obtain the position transformation parameters for the dual-line laser, completing the position transformation of the opposing dual-line laser measurement. Obtain the point cloud data collected from line laser measuring instruments A and B in the local coordinate system of line laser measuring instrument A, the point cloud data after stitching together the standard block, and a vector matrix representing the position transformation of the point cloud data.

[0019] Step 2 specifically involves:

[0020] Transformation from local coordinate system to virtual coordinate system: The transformation process is the same as the steps for transforming the dual-line laser local coordinate system to the same local coordinate system;

[0021] Angle transformation steps: Calculate the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument A and the normal vector of the corresponding larger plane in the virtual coordinate system, calculate the rotation matrix to make the two larger planes parallel, and apply the rotation matrix to the point cloud data collected by the line laser measuring instrument A.

[0022] Similarly, calculate the normal vector of the smaller plane in the point cloud data of the line laser measuring instrument A and the normal vector of the corresponding smaller plane in the virtual coordinate system, calculate the rotation matrix to make the two smaller planes parallel, and apply the rotation matrix to the point cloud data acquired by the line laser measuring instrument A.

[0023] Obtain the angle transformation matrix from the local coordinate system to the virtual coordinate system of the line laser measuring instrument A.

[0024] Position transformation steps: Calculate the coordinates of the center point of the standard block in the virtual coordinate system and the coordinates of the center point of the standard block in the point cloud data of the line laser measuring instrument A after the angle transformation. Calculate the difference between the coordinates of the center point of the standard block in the virtual coordinate system and the coordinates of the center point of the standard block in the point cloud of the line laser measuring instrument A after the angle transformation. Obtain the position transformation vector matrix from the local coordinate system to the virtual coordinate system.

[0025] The point cloud data of the line laser measuring instrument A in the local coordinate system is transformed into the virtual coordinate system by angle transformation and position transformation, thus completing the calibration of the dual-line laser measuring instrument.

[0026] Step 1 further includes:

[0027] Place a standard block between two opposing line laser measuring instruments. The standard block can be a grade 0 gauge block with a thickness of D. The major axis of the standard block forms a certain angle θ with the scanning direction, so that the two sets of opposite planes of the standard block are within the scanning range of the line laser measuring instruments.

[0028] The two adjacent surfaces of the standard block are scanned by line laser measuring instrument A and line laser measuring instrument B to obtain point cloud data of the two adjacent surfaces of the standard block. Since the two adjacent planes of the block are orthogonal, there is a pair of orthogonal planes in each of the two sets of point cloud data collected.

[0029] The local coordinate systems of the line laser measuring instrument A and the line laser measuring instrument B are S1 and S2, respectively;

[0030] Assume that the virtual coordinate system S0 of the system is located between the two line laser measuring instruments, and the origin of the virtual coordinate system S0 is a corner point of the standard block.

[0031] Angle transformation steps:

[0032] The scanning data of the line laser measuring instrument B is mirrored along the XY plane so that its local coordinate system is in the same direction as the local coordinate system of the line laser measuring instrument A. That is, transformation matrix B1 is applied to the scanning data of the line laser measuring instrument B.

[0033]

[0034] The point cloud data collected from the two sets of adjacent surfaces are preprocessed; firstly, curvature downsampling is performed to simplify the data, and statistical filtering and radius filtering are used to remove a large amount of noise from the point cloud.

[0035] The Ransac algorithm was used to fit and segment the four planes in the two sets of adjacent surface point cloud data. The larger plane in the point cloud data collected by line laser measuring instrument A was P1, and the smaller plane was P2; the larger plane in the point cloud data collected by line laser measuring instrument B was P3.

[0036] Calculate the normal vectors of the larger planes P1 and P3 in the segmented point cloud data, and define the direction of the normal vectors. The normal vector of the larger plane of the line laser measuring instrument A is n. a1 =(x a1 y a1 , z a1 The larger plane normal vector of the line laser measuring instrument B is n. b1 =(x b1 y b1 , z b1 ).

[0037] Calculate the included angle, rotation axis, and rotation angle of the two larger plane normal vectors to make the two normal vectors parallel, and construct the rotation matrix R1 using the formula R1·n. b1 The direction and n a1 They are in the same direction.

[0038] The formula for constructing the rotation matrix is ​​as follows:

[0039] A ab =n a1 ×n b1

[0040]

[0041] α1 = arccos(cos(α1))

[0042]

[0043] In the formula, n a1 The normal vector of the larger plane in the point cloud data acquired by the line laser measuring instrument A; n b1 For the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument B, A ab Let α1 be the rotation axis, α2 be the rotation angle, and R1 be the rotation matrix.

[0044] The rotation matrix R1 is applied to the data collected by the line laser measuring instrument B to make the two larger planes in the collected point cloud data parallel.

[0045] The point cloud data with the applied rotation matrix line R1 is segmented using Ransac fitting to obtain the smaller plane P4 in the point cloud data.

[0046] Calculate the normal vectors of the smaller planes P2 and P4 in the segmented point cloud data, and define the direction of the normal vectors. The normal vector of the smaller plane of the line laser measuring instrument A is n. a2 =(x a2 y a2 , z a2 The larger plane normal vector of the line laser measuring instrument B is n. b2 =(x b2 y b2 , z b2 ).

[0047] Using the formula (1), calculate the included angle, rotation axis, and rotation angle of the two smaller plane normal vectors to make the two normal vectors parallel, and construct the rotation matrix R2 using the formula, i.e., R2·n b2 The direction and n a2 The directions are the same, thus completing the angle transformation.

[0048] The rotation matrix R1·R2 of the dual-line laser measuring instrument's local coordinate system is obtained, which transforms the local coordinate system to the same local coordinate system S1. The point cloud data collected by the dual-line laser measuring instrument is transformed into the same local coordinate system S1, and the larger and smaller planes are parallel to each other.

[0049] The position transformation steps are as follows:

[0050] The point cloud data of the two adjacent surfaces that have completed angle calibration are processed separately. The planes of the two sets of data are segmented by the Dbscan density clustering algorithm and the segmentation results are saved to obtain the point cloud data of the two larger relative planes of the standard block.

[0051] Calculate the corner coordinates of the two larger opposing planes, and calculate the center coordinates of the point cloud plane. Assume the center coordinates of the larger plane in line laser measuring instrument A are C. a1 = (x1, y1, z1), the coordinates of the center point of the larger plane in line laser measuring instrument B are C. b1 = (x2, y2, z2);

[0052] Using the thickness D of the standard block and the coordinates C of the center point of the plane. a1 C b1 and the plane normal vector n calculated in the angle calibration step a1 n b1 The coordinates C of the center point of the standard block in the two sets of scan data were calculated using a formula. a2 = (x3, y3, z3), C b2 = (x4, y4, z4).

[0053] The formula for calculating the coordinates of the center point is as follows:

[0054]

[0055] C a2 =C a1 +v1 (2)

[0056] Using the above formula, calculate C. b2 This will give you the coordinates of the center points of the two sets of standard block data;

[0057] Calculate the difference in the coordinates of the center point of the standard block data in the x, y, and z directions to obtain the translation vector of the position transformation, T1 = (△x1, △y1, △z1).

[0058] △x1=x3-x4

[0059] △y1=y3-y4

[0060] △z1=z3-z4 (3)

[0061] In the formula, △x represents the translation in the x direction; △y represents the translation in the y direction; and △z represents the translation in the z direction.

[0062] The obtained translation vector is applied to the measurement data of the line laser measuring instrument B, which completes the position transformation from the dual-line laser local coordinate system to the same local coordinate system S1.

[0063] The position transformation vector T1 of the dual-line laser measuring instrument is obtained by transforming the local coordinate system to the same local coordinate system S1, and the stitched data of the standard block point cloud under the local coordinate system S1 is obtained.

[0064] By performing angle and position transformations, the transformation matrix M1 is obtained, which transforms the dual-line laser local coordinate system to the same local coordinate system S1:

[0065]

[0066] Step 2 also includes:

[0067] The process of converting the standard block data in the local coordinate system S1 to the virtual coordinate system S0 and calculating the transformation matrix is ​​the same as the process of converting the dual-line laser local coordinate system to the same local coordinate system S1.

[0068] During measurement, the angle between the major axis of the standard block and the scanning direction is θ, and the normal vectors of the larger and smaller planes of the standard block in the virtual coordinate system are n and n respectively. a0 =(0,-sin(θ),cos(θ)),n b0 = (0, cos(θ), sin(θ));

[0069] Calculate the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument A and the normal vector of the corresponding plane in the virtual coordinate system, and use the formula (1) to calculate the rotation matrix R3;

[0070] The rotation matrix R3 is applied to the point cloud data collected by the line laser measuring instrument A, and the rotation matrix R4 of the smaller plane normal vector is calculated according to the formula (1);

[0071] The rotation matrix R4 is applied to the point cloud data of the line laser measuring instrument A to complete the angle transformation from the local coordinate system S1 to the virtual coordinate system S0.

[0072] Calculate the coordinates of the center point of the larger plane in the point cloud data of the measuring instrument A after the angle transformation is completed, and use the formula (2) to calculate the coordinates of the center point of the point cloud data;

[0073] Assuming the standard block has a length of L, a height of H, and a thickness of D, the coordinates of the center point of the standard block are:

[0074]

[0075] According to the formula (3), the position transformation vector from the local coordinate system to the virtual coordinate system can be calculated, T2=(△x2,△y2,△z2);

[0076] By performing angle and position transformations, the transformation matrix M2 is obtained to transform the point cloud data in the local coordinate system S1 to the virtual coordinate system S0:

[0077]

[0078] The local coordinate system of the dual-line laser is transformed to the local coordinate system S1 of the line laser measuring instrument A, and then the local coordinate system is transformed to the virtual coordinate system S0 to complete the calibration of the dual-line laser.

[0079] The calibration transformation matrix M2 of the line laser measuring instrument A and the calibration transformation matrix M1·M2 of the line laser measuring instrument B are obtained. The point cloud data collected by the line laser measuring instruments A and B in the local coordinate system are transformed to the virtual coordinate system to complete the point cloud data stitching and coordinate transformation of the standard block.

[0080] The calibration device includes: a line laser measuring instrument bracket, a line laser measuring instrument, a connecting plate, a standard block, a wedge-type expansion clamp, a line laser measuring instrument, a three-axis fine-tuning platform, and a precision linear module;

[0081] The line laser measuring instrument and the line laser measuring instrument are mounted opposite each other on the breadboard via brackets. The brackets are machined with multiple grooves to adjust the position of the line laser measuring instrument and the line laser measuring instrument. The precision linear module is placed in the middle of the line laser measuring instrument and the line laser measuring instrument. A three-axis fine adjustment platform is fixed on the precision module. A connecting plate is installed on the three-axis fine adjustment platform. Two wedge-type expansion clamps are fixed on the connecting plate for fixing the standard block.

[0082] The fine-tuning platform adjusts the angle and position of the standard block between the dual-line laser measuring instrument to ensure that the two sets of adjacent surfaces of the standard block are within the measurement range.

[0083] The beneficial effects of this invention are:

[0084] This invention only requires a single scan of the standard block to complete angle and position transformations, thus realizing the process of converting the local coordinate system of the dual-line laser measuring instrument to the virtual coordinate system.

[0085] The dual-line laser calibration method and calibration device based on standard blocks proposed in this invention have been tested and found to be convenient and accurate, meeting the accuracy requirements of existing dual-line laser opposing installation measurements. Attached Figure Description

[0086] Figure 1 The flowchart of the dual-line laser calibration method provided by the present invention is shown.

[0087] Figure 2 This is a schematic diagram showing the placement of the standard block before dual-line laser calibration provided by the present invention.

[0088] Figure 3 This is a schematic diagram of the dual-line laser local coordinate system and virtual coordinate system provided by the present invention.

[0089] Figure 4 This is a schematic diagram of angle calibration for the dual-line laser calibration method provided by the present invention.

[0090] Figure 5 The flowchart shows the angle calibration process of the dual-line laser calibration method provided by the present invention.

[0091] Figure 6 This is a schematic diagram of the position calibration method for the dual-line laser calibration method provided by the present invention.

[0092] Figure 7 The flowchart of the position calibration process of the dual-line laser calibration method provided by the present invention is shown.

[0093] Figure 8 This is a schematic diagram of the dual-line laser calibration device provided by the present invention. Detailed Implementation

[0094] The present invention will now be described in further detail with reference to the accompanying drawings.

[0095] This invention provides a calibration method for a dual-line laser measuring instrument, which can complete the calibration of the angle and position of the dual-line laser measuring instrument after a single scan of a standard block.

[0096] The calibration of a dual-line laser measuring instrument involves establishing the relationship between the relative positions and included angles of the two line laser devices. This method is simple and convenient to operate, and offers high calibration accuracy.

[0097] Reference Figure 1 The dual-line laser calibration process includes: installing the dual-line laser measuring instruments opposite each other, constructing local coordinate systems S1 and S2 for line laser measuring instrument A and line laser measuring instrument B respectively, and a virtual coordinate system S0 for the measuring system; placing the standard block on a special fixture and initializing the relevant system parameters; acquiring point cloud data of two sets of adjacent surfaces of the standard block from line laser measuring instruments A and B, with a pair of mutually orthogonal standard planes in each set of acquired data.

[0098] The dual-line laser calibration process also includes two steps: transforming the local coordinate system of the dual-line laser measuring instrument to the same local coordinate system S1 and transforming the local coordinate system S1 to the virtual coordinate system S0; the coordinate system transformation process in both steps includes an angle transformation step and a position transformation step.

[0099] After completing the calibration processes in steps 1 and 2, the point cloud data acquired by the dual-line laser local coordinate system can be converted to the virtual coordinate system, thus completing the calibration of the dual-line laser system.

[0100] Reference Figure 2 The dual-line laser measuring instrument is installed in a reciprocating manner, and is fixed to the breadboard by the measuring instrument bracket to ensure that the absolute position of the line laser measuring instrument will not deviate during calibration and measurement.

[0101] Reference Figure 2 The process involves scanning a standard block once, placing the standard block between two opposing line laser measuring instruments. The standard block has a thickness of D, and its major axis forms a certain angle θ with the scanning direction. By adjusting the positions and angles of the line laser measuring instruments A and B and the standard block, both sets of adjacent surfaces of the standard block are within the scanning range of the line laser measuring instruments. The standard block is supported by a standard block clamp, which is fixedly connected to a precision linear module, allowing the standard block to move linearly within the middle region of the dual-line laser measuring instruments.

[0102] The standard blocks are machined to a high precision, and different thicknesses can be selected based on the line laser measurement parameters. During measurement, the dual-line laser measuring instrument can be adjusted appropriately to ensure that the two adjacent planes of the standard block are within the measurement range of the two line laser measuring instruments. Generally, standard blocks from well-known domestic brands, such as Harbin Measuring & Cutting Tool Group (HMT) or Chengdu Measuring & Cutting Tool Group (CMT), with an accuracy grade of 0, can be selected to improve data processing speed and calibration accuracy. After use, the standard blocks should be wiped clean and oiled promptly, and stored in a dedicated box in a dry environment.

[0103] When the line laser measuring instrument acquires data from the standard block, it collects point clouds of the fixture portion of the standard block. This acquisition process generates significant noise, which can be easily processed. By performing pass-through filtering based on the local coordinate systems of the line laser measuring instrument (A and B), invalid point clouds can be filtered out, improving data processing speed and calibration accuracy.

[0104] Reference Figure 3 The local coordinate systems of the line laser measuring instrument A and the line laser measuring instrument B are S1 and S2, respectively. The virtual coordinate system S0 is located between the two line laser measuring instruments, and the origin of the virtual coordinate system S0 is a corner point of the standard block. The point cloud collected by the line laser measuring instruments A and B is data under the local coordinate systems S1 and S2, and the collected data are independent of each other.

[0105] Reference Figure 4Point cloud data of two adjacent surfaces of the standard block were acquired by two line laser measuring instruments A and B respectively. Since the two adjacent planes of the standard block are orthogonal, there is a pair of mutually orthogonal standard planes in each set of data.

[0106] Reference Figure 5 The angle calibration step in step 1 includes: preprocessing the collected point cloud data: curvature downsampling simplifies the data, retaining more point cloud data in areas with greater curvature. Statistical filtering and radius filtering remove a large amount of noise from the point cloud.

[0107] The local coordinate system S2 of the line laser measuring instrument B is mirrored along the XY plane, so that the direction of the local coordinate system S2 is the same as that of the local coordinate system S1.

[0108] Reference Figure 4 , 5 The angle calibration step in step 1 further includes: using the Ransac algorithm to segment four planes in two sets of adjacent surface point cloud data; the larger plane in the point cloud data acquired by line laser measuring instrument A is designated as P1, and the smaller plane as P2; the larger plane in the point cloud data acquired by line laser measuring instrument B is designated as P3. The normal vectors of the two larger planes after segmentation are calculated respectively, and the directions of the normal vectors are set. The normal vector of the larger plane of line laser measuring instrument A is n. a1 =(x a1 y a1 , z a1 The larger plane normal vector of the line laser measuring instrument B is n. b1 =(x b1 y b1 , z b1 ).

[0109] Calculate the angle between the two larger plane normal vectors, the rotation axis, and the rotation angle, and construct the rotation matrix R1 using the formula, such that R1·n b1 The direction and n a1 They are in the same direction.

[0110] The formula used is formula (1) above, which is used to calculate the rotation matrix.

[0111] Reference Figure 5 The angle calibration step in step 1 further includes: applying the rotation matrix R1 to the data collected by the line laser measuring instrument B, so that the larger plane in the two sets of data is parallel.

[0112] Calculate the normal vector n of the smaller plane in the data collected by the line laser measuring instrument A. a2 =(x a1 x a2 x a3), and the normal vector n of the smaller plane P2 in the data collected by the transformed line laser measuring instrument B. b2 =(x b1 x b2 x b3 Using the above formula (1), the rotation matrix is ​​calculated to make the normal vectors of the two smaller planes parallel, and the rotation matrix R2 is applied to the measurement data of the line laser measuring instrument B, so that R2·n b2 The direction and n a2 The directions are the same, meaning that the two smaller planes in the data collected by the line laser measuring instruments A and B are parallel.

[0113] The rotation matrix R1·R2 from the local coordinate system S2 to the local coordinate system S1 is obtained, thus completing the angle transformation.

[0114] Reference Figure 6 The position transformation step in step 1 includes: processing the data after angle transformation, performing plane segmentation on the point cloud data after angle transformation using the Ransac algorithm, and obtaining the point cloud data of two larger relative planes of the standard block.

[0115] Reference Figure 6 , 7 The position transformation step in step 1 further includes: calculating the normal vectors and corner coordinates of the two larger opposing planes, and calculating the coordinates of the center point of the planes. The coordinates of the center point of the larger plane in the line laser measuring instrument A are C. a1 = (x1, y1, z1), the coordinates of the center point of the larger plane in line laser measuring instrument B are C. b1 = (x2, y2, z2);

[0116] Using the thickness D of the standard block and the coordinates C of the center point of the plane. a1 C b1 And the normal vector of the larger plane, the coordinates C of the center point of the standard block in the two sets of scan data are calculated by formula (2). a2 = (x3, y3, z3), C b2 = (x4, y4, z4).

[0117] The difference between the center point coordinates of the standard block data in the x, y, and z directions is calculated by formula (3) to obtain the translation vector of the position transformation, T1 = (△x1, △y1, △z1).

[0118] The obtained translation vector is applied to the measurement data of the line laser measuring instrument B, which completes the position transformation from the dual-line laser local coordinate system to the same local coordinate system S1.

[0119] The position transformation vector T1 of the dual-line laser measuring instrument is obtained by transforming the local coordinate system to the same local coordinate system S1, and the stitched data of the standard block point cloud under the local coordinate system S1 is obtained.

[0120] Reference Figure 7 The calculation of corner coordinates includes: fitting the parametric equations of each edge line using the least squares method, calculating the coordinates of the four corner points of the four edges of the plane, and using the average of the coordinates of the two center points calculated from the two diagonals as the coordinates of the center point of the plane. Through angle transformation and position transformation steps, the transformation matrix M1 of the point cloud data in the local coordinate system S2 to the local coordinate system S1 can be obtained.

[0121] Reference Figure 1 The angle transformation and position transformation steps in step 2 are the same as those in the transformation from the local coordinate system S2 to the local coordinate system S1 of the line laser. Using the normal vectors of the two planes in the virtual coordinate system and the coordinates of the center point of the standard block, the point cloud in the local coordinate system S1 is transformed to the virtual coordinate system, completing the calibration of the dual-line laser measuring instrument. The normal vectors of the larger and smaller planes of the standard block in the virtual coordinate system are n... a0 =(0,-sin(θ),cos(θ)),n b0 = (0, cos(θ), sin(θ)).

[0122] The larger plane normal vector n in the point cloud acquired by the line laser measuring instrument A is calculated using the formula (1). a1 =(x a1 y a1 , z a1 ) and the larger plane normal vector n in the virtual coordinate system a0 = (0, -sin(θ), cos(θ)) and the rotation matrix R3.

[0123] The rotation matrix R3 is applied to the point cloud data collected by the line laser measuring instrument A, and then the rotation matrix R4 of the smaller plane normal vector is calculated according to the formula (1).

[0124] The rotation matrix is ​​applied to the point cloud data collected by the line laser measuring instrument A to obtain the rotation matrix R3·R4 from the local coordinate system S1 to the virtual coordinate system S0, thus completing the angle transformation.

[0125] Calculate the coordinates of the point cloud data center points of the line laser measuring instrument A and the coordinates of the center point of the standard block in the virtual coordinate system. According to the formula (3), the position transformation vector from the local coordinate system to the virtual coordinate system can be calculated, T2=(△x2,△y2,△z2).

[0126] By transforming the angle and position, the transformation matrix M2 can be obtained to transform the point cloud data in the local coordinate system S1 to the virtual coordinate system S0.

[0127] Reference Figure 1 By performing two transformations in steps 1 and 2, we can obtain the transformation matrix M2 from the local coordinate system of line laser measuring instrument A to the virtual coordinate system, and the transformation matrix M1·M2 from the local coordinate system of line laser measuring instrument B to the virtual coordinate system. The point cloud data collected by line laser measuring instruments A and B in their local coordinate systems are then transformed to the virtual coordinate system, completing the point cloud data stitching and coordinate transformation of the standard block.

[0128] The present invention also provides a calibration device for dual-line laser measurement.

[0129] Reference Figure 8 The calibration device includes: a line laser measuring instrument bracket 1, a line laser measuring instrument 2, a connecting plate 3, a standard block 4, a wedge-type expansion clamp 5, a line laser measuring instrument 6, a three-axis fine-tuning platform 7, and a precision linear module 8.

[0130] Line laser measuring instruments 2 and 6 are mounted opposite each other on a breadboard via bracket 1. Multiple grooves are machined on bracket 1 to adjust the position of line laser measuring instruments 2 and 6. The precision linear module 8 is placed in the middle of line laser measuring instruments 2 and 5. A three-axis fine-tuning platform 7 is fixed on the precision module 8. A connecting plate 3 is installed on the three-axis fine-tuning platform 7. Two wedge-type expansion clamps 5 are fixed on the connecting plate 3 for fixing the standard block 4.

[0131] The fine-tuning platform 6 adjusts the angle and position of the standard block 4 between the dual-line laser measuring instrument to ensure that the two sets of adjacent surfaces of the standard block are within the measurement range.

Claims

1. A dual-line laser calibration method based on a standard block, characterized in that, The process includes the following steps: Step 1: Transform the dual-line laser local coordinate system to the same local coordinate system; Step 2: Transform the local coordinate system to the virtual coordinate system; The coordinate system transformation steps include: angle transformation steps and position transformation steps. Through the angle transformation steps and position transformation steps, the angle and position calibration of the dual-line laser measuring instrument is completed. In step 1, the angle transformation step is as follows: the standard block is placed between two opposing line laser measuring instruments A and B. The thickness of the standard block is D, and the major axis direction forms a certain angle θ with the scanning direction, so that the two sets of adjacent planes of the standard block are within the scanning range of the two line laser measuring instruments. The point cloud data of two adjacent surfaces of the standard block were acquired by line laser measuring instrument A and line laser measuring instrument B, respectively. First, the collected point cloud data is preprocessed, including curvature downsampling to simplify the data, and statistical filtering and radius filtering to remove a large amount of noise from the point cloud; The point cloud data of the line laser measuring instrument B is mirrored along the XY plane so that the local coordinate system of the dual-line laser measuring instrument has the same direction. The point cloud data of the two adjacent surfaces is divided into planes, the angle between the normal vectors of the larger relative planes in the two sets of data is obtained, and the rotation matrix is ​​calculated to make the normal vectors of the two larger planes parallel, that is, the two larger planes in the point cloud data are parallel. The rotation matrix is ​​then applied to the point cloud data of the line laser measuring instrument B. Calculate the normal vector of the smaller plane in the point cloud data acquired by the line laser measuring instrument A and the point cloud data of the line laser measuring instrument B after applying the rotation matrix. Find the angle between the two normal vectors, calculate the rotation matrix to make the normal vectors of the two smaller planes parallel, and apply the rotation matrix to the point cloud data of the line laser measuring instrument B to complete the angle transformation from the local coordinate system of the two line lasers to the same coordinate system. Obtain the point cloud data of the standard block with two relatively parallel planes in the local coordinate system of the line laser measuring instrument A and the rotation matrix of the angle transformation of the two point cloud data in the point cloud data acquired by the line laser measuring instrument A and the line laser measuring instrument B. Position transformation steps: Process the point cloud data collected from the two adjacent surfaces after angle transformation. Fit the larger plane in each of the two scanned point clouds and find the center point of the plane. Calculate the center point coordinates of the standard block using the coordinates of the plane's center point, the plane's normal vector, and the thickness of the standard block. Calculate the difference between the fitted center points of the point cloud data from line laser measuring instruments A and B to obtain the position transformation parameters of the dual-line laser, thus completing the position transformation of the opposing dual-line laser measurement. Obtain the point cloud data collected from line laser measuring instruments A and B in the local coordinate system of line laser measuring instrument A, the point cloud data after stitching together the standard block, and a vector matrix representing the position transformation of the point cloud data. In step 2, the local coordinate system is transformed into a virtual coordinate system: the transformation process is the same as the step of transforming the dual-line laser local coordinate system into the same local coordinate system. Angle transformation steps: Calculate the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument A and the normal vector of the corresponding larger plane in the virtual coordinate system, calculate the rotation matrix to make the two larger planes parallel, and apply the rotation matrix to the point cloud data collected by the line laser measuring instrument A. Similarly, calculate the normal vector of the smaller plane in the point cloud data of the line laser measuring instrument A and the normal vector of the corresponding smaller plane in the virtual coordinate system, calculate the rotation matrix to make the two smaller planes parallel, and apply the rotation matrix to the point cloud data acquired by the line laser measuring instrument A. Obtain the angle transformation matrix from the local coordinate system to the virtual coordinate system of the line laser measuring instrument A; Position transformation steps: Calculate the coordinates of the center point of the standard block in the virtual coordinate system and the coordinates of the center point of the standard block in the point cloud data of the line laser measuring instrument A after the angle transformation. Calculate the difference between the coordinates of the center point of the standard block in the virtual coordinate system and the coordinates of the center point of the standard block in the point cloud of the line laser measuring instrument A after the angle transformation. Obtain the position transformation vector matrix from the local coordinate system to the virtual coordinate system. The point cloud data of the line laser measuring instrument A in the local coordinate system is transformed into the virtual coordinate system by angle transformation and position transformation, thus completing the calibration of the dual-line laser measuring instrument.

2. The dual-line laser calibration method based on a standard block according to claim 1, characterized in that, Step 1 further includes: Place a standard block between two opposing line laser measuring instruments. The standard block can be a grade 0 gauge block with a thickness of D. The major axis of the standard block forms a certain angle θ with the scanning direction, so that the two sets of opposite planes of the standard block are within the scanning range of the line laser measuring instruments. The two adjacent surfaces of the standard block are scanned by line laser measuring instrument A and line laser measuring instrument B to obtain point cloud data of the two adjacent surfaces of the standard block. Since the two adjacent planes of the block are orthogonal, there is a pair of orthogonal planes in each of the two sets of point cloud data collected. The local coordinate systems of the line laser measuring instrument A and the line laser measuring instrument B are S1 and S2, respectively; Assume that the virtual coordinate system S0 of the system is located between the two line laser measuring instruments, and the origin of the virtual coordinate system S0 is a corner point of the standard block; Angle transformation steps: The scanning data of the line laser measuring instrument B is rotated 180° around the Y-axis so that its local coordinate system is in the same direction as the local coordinate system of the line laser measuring instrument A. That is, transformation matrix B1 is applied to the scanning data of the line laser measuring instrument B. The point cloud data collected from the two sets of adjacent surfaces are preprocessed; firstly, curvature downsampling is performed to simplify the data, and statistical filtering and radius filtering are used to remove a large amount of noise from the point cloud. The Ransac algorithm was used to fit and segment four planes in two sets of adjacent surface point cloud data. The larger plane in the point cloud data collected by line laser measuring instrument A was P1, and the smaller plane was P2; the larger plane in the point cloud data collected by line laser measuring instrument B was P3. Calculate the normal vectors of the larger planes P1 and P3 in the segmented point cloud data, and define the direction of the normal vectors. The normal vector of the larger plane of the line laser measuring instrument A is n. a1 =(x a1 y a1 , z a1 The larger plane normal vector of the line laser measuring instrument B is n. b1 =(x b1 y b1 , z b1 ); Calculate the included angle, rotation axis, and rotation angle of the two larger plane normal vectors to make the two normal vectors parallel, and construct the rotation matrix R1 using the formula R1·n. b1 The direction and n a1 The directions are the same; The formula for constructing the rotation matrix is ​​as follows: A ab =n a1 ×n b1 α1 = arccos(cos(α1)) In the formula, n a1 The normal vector of the larger plane in the point cloud data acquired by the line laser measuring instrument A; n b1 For the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument B, A ab Let α1 be the rotation axis, α2 be the rotation angle, and R1 be the rotation matrix. The rotation matrix R1 is applied to the data collected by the line laser measuring instrument B to make the two larger planes in the collected point cloud data parallel. The point cloud data with the applied rotation matrix R1 is segmented using Ransac fitting to obtain the smaller plane P4 in the point cloud data. Calculate the normal vectors of the smaller planes P2 and P4 in the segmented point cloud data, and define the direction of the normal vectors. The normal vector of the smaller plane of the line laser measuring instrument A is n. a2 =(x a2 y a2 , z a2 The larger plane normal vector of the line laser measuring instrument B is n. b2 =(x b2 y b2 , z b2 ); Using the formula (1), calculate the included angle, rotation axis, and rotation angle of the two smaller plane normal vectors to make the two normal vectors parallel, and construct the rotation matrix R2 using the formula, i.e., R2·n b2 The direction and n a2 The directions are the same, thus completing the angle transformation; The rotation matrix R1·R2 of the dual-line laser measuring instrument's local coordinate system is obtained, which transforms the local coordinate system to the same local coordinate system S1. The point cloud data collected by the dual-line laser measuring instrument is transformed to the same local coordinate system S1, and the larger and smaller planes are parallel to each other. The position transformation steps are as follows: The point cloud data of the two adjacent surfaces that have completed angle calibration are processed separately. The planes of the two sets of data are segmented by the Dbscan density clustering algorithm and the segmentation results are saved to obtain the point cloud data of the two larger relative planes of the standard block. Calculate the corner coordinates of the two larger opposing planes, and calculate the center coordinates of the point cloud plane. Assume the center coordinates of the larger plane in line laser measuring instrument A are C. a1 = (x1, y1, z1), the coordinates of the center point of the larger plane in line laser measuring instrument B are C. b1 = (x2, y2, z2); Using the thickness D of the standard block and the coordinates C of the center point of the plane. a1 C b1 and the plane normal vector n calculated in the angle calibration step a1 n b1 The coordinates C of the center point of the standard block in the two sets of scan data were calculated using a formula. a2 = (x3, y3, z3), C b2 = (x4, y4, z4); The formula for calculating the coordinates of the center point is as follows: C a2 =C a1 +v1 (2) Using the above formula, calculate C. b2 This will give you the coordinates of the center points of the two sets of standard block data; Calculate the difference in the coordinates of the center point of the standard block data in the x, y, and z directions to obtain the translation vector of the position transformation, T1 = (△x1, △y1, △z1); △x1=x3-x4 △y1=y3-y4 △z1=z3-z4 (3) In the formula, △x represents the translation in the x-direction; △y represents the translation in the y-direction; and △z represents the translation in the z-direction. The obtained translation vector is applied to the measurement data of the line laser measuring instrument B, that is, the position transformation from the dual-line laser local coordinate system to the same local coordinate system S1 is completed. The position transformation vector T1 of the dual-line laser measuring instrument is obtained by transforming the local coordinate system to the same local coordinate system S1, and the stitched data of the standard block point cloud under the local coordinate system S1 is obtained. By performing angle and position transformations, the transformation matrix M1 is obtained, which transforms the dual-line laser local coordinate system to the same local coordinate system S1:

3. The dual-line laser calibration method based on a standard block according to claim 2, characterized in that, Step 2 also includes: The process of converting the standard block data in the local coordinate system S1 to the virtual coordinate system S0 and calculating the transformation matrix is ​​the same as the process of converting the dual-line laser local coordinate system to the same local coordinate system S1. During measurement, the angle between the major axis of the standard block and the scanning direction is θ, and the normal vectors of the larger and smaller planes of the standard block in the virtual coordinate system are n and n respectively. a0 =(0,-sin(θ),cos(θ)),n b0 = (0, cos(θ), sin(θ)); Calculate the normal vector of the larger plane in the point cloud data collected by the line laser measuring instrument A and the normal vector of the corresponding plane in the virtual coordinate system, and use the formula (1) to calculate the rotation matrix R3; The rotation matrix R3 is applied to the point cloud data collected by the line laser measuring instrument A, and the rotation matrix R4 of the smaller plane normal vector is calculated according to the formula (1); The rotation matrix R4 is applied to the point cloud data of the line laser measuring instrument A to complete the angle transformation from the local coordinate system S1 to the virtual coordinate system S0; Calculate the coordinates of the center point of the larger plane in the point cloud data of the measuring instrument A after the angle transformation is completed, and use the formula (2) to calculate the coordinates of the center point of the point cloud data; Assuming the standard block has a length of L, a height of H, and a thickness of D, the coordinates of the center point of the standard block are: According to the formula (3), the position transformation vector from the local coordinate system to the virtual coordinate system can be calculated, T2=(△x2,△y2,△z2); By performing angle and position transformations, the transformation matrix M2 is obtained to transform the point cloud data in the local coordinate system S1 to the virtual coordinate system S0: The local coordinate system of the dual-line laser is transformed to the local coordinate system S1 of the line laser measuring instrument A, and then the local coordinate system is transformed to the virtual coordinate system S0 to complete the calibration of the dual-line laser. The calibration transformation matrix M2 of the line laser measuring instrument A and the calibration transformation matrix M1·M2 of the line laser measuring instrument B are obtained. The point cloud data collected by the line laser measuring instruments A and B in the local coordinate system are transformed to the virtual coordinate system, thus completing the point cloud data splicing and coordinate transformation of the standard block.

4. A calibration apparatus for implementing the method according to any one of claims 1-3, characterized in that, include: Line laser measuring instrument bracket (1), line laser measuring instrument one (2), connecting plate (3), standard block (4), wedge expansion clamp (5), line laser measuring instrument two (6), three-axis fine adjustment platform (7), precision linear module (8); Line laser measuring instrument 1 (2) and line laser measuring instrument 2 (6) are respectively mounted on the breadboard facing each other via bracket (1). The bracket (1) has multiple grooves for adjusting the position of line laser measuring instrument 1 (2) and line laser measuring instrument 2 (6). The precision linear module (8) is placed in the middle of line laser measuring instrument 1 (2) and line laser measuring instrument 2 (6). A three-axis fine adjustment platform (7) is fixed on the precision linear module (8). A connecting plate (3) is installed on the three-axis fine adjustment platform (7). Two wedge-type expansion clamps (5) are fixed on the connecting plate (3) for fixing the standard block (4). The triaxial fine-tuning platform (7) adjusts the angle and position of the standard block (4) between the dual-line laser measuring instrument to ensure that the two sets of adjacent surfaces of the standard block are within the measurement range.

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