Thin-walled workpiece profile measuring system and measuring method

Abstract

The invention relates to a thin-wall part profile measuring system and method, and the system comprises a workpiece table which is used for placing a to-be-measured thin-wall part; the positive view angle data acquisition subsystem is used for acquiring positive view angle morphology data of the to-be-measured thin-walled workpiece; the anti-view-angle data acquisition subsystem is used for acquiring anti-view-angle morphology data of the to-be-measured thin-walled workpiece; the three-dimensional calibration plate is used for calibrating the relative positions of the positive view angle data acquisition subsystem and the negative view angle data acquisition subsystem; and the upper computer is used for controlling time-sharing triggering of the positive view angle data acquisition subsystem and the negative view angle data acquisition subsystem to obtain positive view angle morphology data and negative view angle morphology data, splicing the positive view angle morphology data and the negative view angle morphology data, and obtaining the three-dimensional reconstruction morphology of the to-be-measured thin-walled workpiece. Compared with the prior art, the method has the advantages of high measurement precision, low cost, high practicability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of automated measurement, and particularly to a thin-walled part surface measurement system and a measurement method that take into account both economy and speed. Background Art

[0002] Thin-walled parts have characteristics such as light weight and compact structure. There are many types of them, including T-shaped structures, L-shaped structures, and arc-shaped structures, etc., and they are widely used in industries such as aerospace and automotive. The surface topography and geometric dimensions of thin-walled parts after processing are important links for evaluating processing quality, and have a key impact on important indicators such as the service life and safety performance of products. At present, there are mainly three ways to measure the surface of thin-walled parts: one is a coordinate measuring machine. Although the coordinate measuring machine has high measurement accuracy, its measurement speed is slow. In addition, the equipment cost of high-precision coordinate measuring machines is relatively high, which further limits its application in mass production; the second is a laser scanner. The laser scanner requires the surface of the workpiece to be measured to have good reflectivity, and a specific label needs to be pasted on the surface of the workpiece. The measurement results are greatly affected by the environment; the third is the structured light surface measurement method, represented by fringe projection profilometry, which can quickly obtain three-dimensional topography data by extracting fringe phases. Compared with the coordinate measuring machine and the laser scanner, the structured light method has significant advantages such as fast measurement speed, high accuracy, and simple system structure, and is gradually favored in industrial applications.

[0003] Existing multi-view structured light workpiece measurement systems mainly have two working modes: one is to fix the camera and projector, and realize multi-view measurement by rotating the turntable; the other is to fix the position of the thin-walled part, and use the movement of the six-axis robotic arm equipped with a camera and a projector to complete multi-view measurement. However, both of these modes have inevitable mechanical errors, such as the rotation error of the turntable mode or the movement error of the robotic arm mode, resulting in an increase in multi-view fitting error. In addition, whether it is a high-precision turntable or a six-axis robot, their high equipment costs also increase the overall investment in thin-walled part detection, limiting their large-scale application. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a thin-walled part surface measurement system and a measurement method with high measurement accuracy, low cost, and strong practicability.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to the first aspect of the present invention, there is provided a thin-walled part surface measurement system, including:

[0007] A workpiece table is used to place the thin-walled workpiece to be measured; a front-view data acquisition subsystem is installed at the front-view of the thin-walled workpiece to be measured, and is used to acquire the front-view shape data of the thin-walled workpiece to be measured;

[0008] A reverse viewing angle data acquisition subsystem, installed at the reverse viewing angle of the thin-walled workpiece to be measured, for acquiring reverse viewing angle morphological data of the thin-walled workpiece to be measured;

[0009] A three-dimensional calibration plate, used to calibrate the relative positions of the positive viewing angle data acquisition subsystem and the reverse viewing angle data acquisition subsystem, and obtain calibration parameters;

[0010] The host computer is connected to the front-view data acquisition subsystem and the reverse-view data acquisition subsystem, respectively, and is used to control the time-sharing triggering of the front-view data acquisition subsystem and the reverse-view data acquisition subsystem to acquire the front-view morphology data and the reverse-view morphology data, splice the front-view morphology data and the reverse-view morphology data, and acquire the three-dimensional reconstructed morphology of the thin-walled part to be measured.

[0011] As a preferred technical solution, the positive viewing angle data acquisition subsystem includes: a first camera, a second camera and a first high-speed projector; the reverse viewing angle data acquisition subsystem includes: a third camera, a fourth camera and a second high-speed projector.

[0012] As a preferred technical solution, the host computer is also used for:

[0013] Controlling the first camera, the second camera and the first high-speed projector in the positive viewing angle data acquisition subsystem to be triggered synchronously;

[0014] And, controlling the third camera, the fourth camera and the second high-speed projector in the reverse viewing angle data acquisition subsystem to be triggered synchronously.

[0015] As an optimal technical solution, the stereo calibration plate is a double-sided structure, with calibration patterns printed on both sides; the size of the stereo calibration plate, the pattern spacing and the spatial transfer matrix of the patterns on both sides are used to provide a spatial reference to complete the global calibration of the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem, and obtain the triangular stereo model parameters corresponding to the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem, as well as the spatial transfer matrix for data conversion between the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem.

[0016] As a preferred technical solution, the host computer splices the front-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part to be measured, including: unwrapping the phase of the front-view morphology data and the reverse-view morphology data by using a deep learning neural network to obtain the true phase; converting the true phase into height data by using the triangular stereo model parameters; unifying the front-view height data and the reverse-view height data in the same world coordinate system by using the space transfer matrix of the front-view data acquisition subsystem and the reverse-view data acquisition subsystem; and aligning the front-view height data and the reverse-view height data by using a point cloud registration algorithm to generate a complete three-dimensional reconstructed morphology.

[0017] As a preferred technical solution, the system further includes: a first electric slide rail, a first background board, a second electric slide rail, and a second background board, and the first electric slide rail and the second electric slide rail are respectively connected to the host computer;

[0018] The first electric slide rail is installed on one side of the workpiece table away from the front-view data acquisition subsystem; the first background board is installed on the first electric slide rail and is used to provide a background when the front-view data acquisition subsystem acquires the front-view morphology data;

[0019] The second electric slide rail is installed on one side of the workpiece table away from the reverse-view data acquisition subsystem; the second background board is installed on the second electric slide rail and is used to provide a background when the reverse-view data acquisition subsystem acquires the reverse-view morphology data;

[0020] The host computer is further configured to: when the front-view data acquisition subsystem is triggered, control the first electric slide rail to drive the first background board to move to the working position, and control the second electric slide rail to drive the second background board to move to the non-working position; and when the reverse-view data acquisition subsystem is triggered, control the second electric slide rail to drive the second background board to move to the working position, and control the first electric slide rail to drive the first background board to move to the non-working position.

[0021] As a preferred technical solution, the front-view data acquisition subsystem is a data acquisition subsystem based on N (N≥1) structured light;

[0022] The reverse-view data acquisition subsystem is a data acquisition subsystem based on M (M≥1) structured light.

[0023] According to the second aspect of the present invention, there is provided a method for measuring the profile of a thin-walled part, which is applied to the thin-walled part profile measurement system provided in the first aspect or any one of the possible implementation manners of the first aspect. The method for measuring the profile of a thin-walled part includes:

[0024] Global calibration is performed on the front-view data acquisition subsystem and the reverse-view data acquisition subsystem using the parameters of the stereo calibration plate; wherein, the parameters of the stereo calibration plate include the size of the stereo calibration plate, the pattern pitch, and the spatial conversion relationship between the patterns on both sides.

[0025] Fix the thin-walled part to be measured on the workpiece table, control the electric slide rail to drive the first background plate to move to the working position, and control the electric slide rail to drive the second background plate to move to the non-working position.

[0026] Control the front-view data acquisition subsystem to be synchronously triggered to obtain the front-view morphology data of the thin-walled part to be measured.

[0027] Control the electric slide rail to drive the second background plate to move to the working position, and control the electric slide rail to drive the first background plate to move to the non-working position.

[0028] Control the reverse-view data acquisition subsystem to be synchronously triggered to obtain the reverse-view morphology data of the thin-walled part to be measured.

[0029] Stitch the front-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part to be measured.

[0030] The step of controlling the front-view data acquisition subsystem to be synchronously triggered to obtain the front-view morphology data of the thin-walled part to be measured includes: controlling the front-view data acquisition subsystem to be synchronously triggered to respectively obtain the first data and the second data collected by the first camera and the second camera; fusing the first data and the second data to obtain the front-view morphology data of the thin-walled part to be measured.

[0031] The step of controlling the reverse-view data acquisition subsystem to be synchronously triggered to obtain the reverse-view morphology data of the thin-walled part to be measured includes: controlling the reverse-view data acquisition subsystem to be synchronously triggered to respectively obtain the third data and the fourth data collected by the third camera and the fourth camera; fusing the third data and the fourth data to obtain the reverse-view morphology data of the thin-walled part to be measured.

[0032] As a preferred technical solution, the step of performing global calibration on the front-view data acquisition subsystem and the reverse-view data acquisition subsystem using the parameters of the stereo calibration plate includes:

[0033] Adopt a double-sided stereo calibration plate, let the side photographed by the first camera in the front-view data acquisition subsystem be the front of the calibration plate, and the side photographed by the third camera in the reverse-view data acquisition subsystem be the back of the calibration plate, and perform calibration on the front-view data acquisition subsystem and the reverse-view data acquisition subsystem respectively to obtain the calibration parameter matrix.

[0034] Calibrate the forward-view data acquisition subsystem and the reverse-view data acquisition subsystem, including: determining the relative positions of the first camera and the second camera in the forward-view data acquisition subsystem and the relative positions of the third camera and the fourth camera in the reverse-view data acquisition subsystem according to the binocular camera calibration principle, and using the rotation matrix R0 and the translation matrix T0 of the calibration patterns on the front and back sides of the stereo calibration board to determine the relative positions of the first and second camera coordinate systems and the third and fourth camera coordinate systems;

[0035] Let the origin of the world coordinate system be at the center of the front side of the stereo calibration board, the X-axis be horizontally to the right on the front side of the stereo calibration board, the Y-axis be vertically upward on the front side of the stereo calibration board, and the normal direction of the front side of the stereo calibration board be the Z-axis. Use the calibration parameter matrix to complete the unified mapping of all camera coordinate systems to the world coordinate system, and realize the global calibration of the forward-view data acquisition subsystem and the reverse-view data acquisition subsystem.

[0036] As a preferred technical solution, the stitching of the forward-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part to be measured includes:

[0037] Fix the thin-walled part to be measured at the center of the measurement field of view. Assume that the point cloud data coordinates of the thin-walled part to be measured measured in the first camera coordinate system are (X1, Y1, Z1), the point cloud data coordinates of the thin-walled part to be measured measured in the second camera coordinate system are (X2, Y2, Z2), the point cloud data coordinates of the thin-walled part to be measured measured in the third camera coordinate system are (X3, Y3, Z3), and the point cloud data coordinates of the thin-walled part to be measured measured in the fourth camera coordinate system are (X4, Y4, Z4). According to the calibration of the measurement system, there is the following conversion relationship:

[0038]

[0039] Unify the point cloud data in the first camera coordinate system to the world coordinate system, unify the point cloud data in the second camera coordinate system to the world coordinate system, and perform point cloud fusion in the first and second camera coordinate systems to obtain the front point cloud data (X5, Y5, Z5)

[0040] Unify the point cloud data in the third camera coordinate system to the world coordinate system, unify the point cloud data in the fourth camera coordinate system to the world coordinate system, and perform point cloud fusion in the third and fourth camera coordinate systems to obtain the back point cloud data (X6, Y6, Z6);

[0041] Stitch the front point cloud data (X5, Y5, Z5) and the back point cloud data (X6, Y6, Z6) in the world coordinate system to unify the data in all camera coordinate systems to the world coordinate system;

[0042] Precisely register the front point cloud data and the back point cloud data through a point cloud registration algorithm to reconstruct a complete three-dimensional topography.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] First, high measurement accuracy: The thin-walled part surface measurement system provided by the present invention adopts a multi-view and multi-device layout for both the front and back, avoiding the use of auxiliary devices such as high-precision turntables and robotic arms, and eliminating the multi-view fitting error caused by the mechanical errors of the turntable or robotic arm;

[0045] Second, low cost: The thin-walled part surface measurement system provided by the present invention adopts a multi-view and multi-device layout for both the front and back, without the need to use auxiliary devices such as high-precision turntables and robotic arms, greatly reducing the cost of thin-walled part surface measurement;

[0046] Third, strong practicability: The data acquisition subsystem in the thin-walled part surface measurement system provided by the present invention adopts a combination of short and long baselines. The short baseline camera can accurately capture the details of the thin-walled part, such as the edge contour and local micro-deformation, and the long baseline camera can improve the resolution ability of the overall shape and depth change of the thin-walled part; By fusing the data of the two baselines, it can not only cover the complex geometric shapes of the full size of the thin-walled part, but also ensure the true reliability of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic structural diagram of the thin-walled part surface measurement system provided by the embodiment of the present application;

[0048] Figure 2 It is a schematic working diagram of the thin-walled part surface measurement system provided by the embodiment of the present application;

[0049] Figure 3 It is a schematic diagram of the global calibration principle of the thin-walled part surface measurement system provided by the embodiment of the present application;

[0050] Figure 4 It is a schematic flowchart of the thin-walled part surface measurement method provided by the embodiment of the present application.

[0051] The reference numerals in the figures are shown as follows:

[0052] 1. Thin-walled part to be measured, 2. Host computer, A. Front-view data acquisition subsystem, C1. First camera, C2. Second camera, P1. First high-speed projector, B. Back-view data acquisition subsystem, C3. Third camera, C4. Fourth camera, P2. Second high-speed projector, D1. First background board, D2. Second background board. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0055] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0056] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0057] A thin-walled part refers to a part or component with a wall structure having a relatively small thickness, and its thickness is usually much smaller than its length and width dimensions. Such parts are very common in the fields of aerospace, automotive, electronics, mechanical manufacturing, etc. Because of their advantages such as light weight, compact structure, and high material utilization rate, they are widely used in various structural and functional components.

[0058] A profile refers to the external shape or contour surface of an object, especially those with complex geometric shapes. Profiles are usually used to describe the external shape characteristics of parts or components, including their two-dimensional contours and three-dimensional surfaces.

[0059] As Figure 1 and Figure 2 shown, the embodiments of this application provide a thin-walled part profile measurement system, and the system includes:

[0060] A workpiece table for placing the thin-walled part 1 to be measured;

[0061] A front-view data acquisition subsystem A is installed at the front-view of the thin-walled workpiece 1 to be measured, and is used to acquire the front-view topography data of the thin-walled workpiece 1 to be measured;

[0062] The reverse viewing angle data acquisition subsystem B is installed at the reverse viewing angle of the thin-walled workpiece 1 to be measured, and is used to collect the reverse viewing angle morphology data of the thin-walled workpiece 1 to be measured;

[0063] A stereo calibration plate is used to calibrate the relative positions of the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem to obtain calibration parameters;

[0064] The first background plate D1 is installed on the side of the workpiece table away from the front-view data acquisition subsystem A, and is used to provide a background when the front-view data acquisition subsystem A collects front-view topography data;

[0065] The second background plate D2 is installed on the side of the workpiece table away from the reverse-view data acquisition subsystem B, and is used to provide a background when the reverse-view data acquisition subsystem B collects reverse-view topography data;

[0066] The host computer 2 is connected to the positive-view data acquisition subsystem A and the reverse-view data acquisition subsystem B, respectively, and is used to control the time-sharing triggering of the positive-view data acquisition subsystem A and the reverse-view data acquisition subsystem B to obtain the positive-view morphology data and the reverse-view morphology data, splice the positive-view morphology data and the reverse-view morphology data, and obtain the three-dimensional reconstructed morphology of the thin-walled part 1 to be measured.

[0067] The first background plate D1 and the second background plate D2 can reduce the interference of ambient light and provide uniform background brightness during the profile measurement process.

[0068] Optionally, the orthographic data acquisition subsystem A includes: a first camera C1, a second camera C2, and a first high-speed projector P1, and a baseline distance between the first camera C1 and the first high-speed projector P1 is greater than a baseline distance between the second camera C2 and the first high-speed projector P1;

[0069] The reverse viewing angle data acquisition subsystem includes: a third camera C3, a fourth camera C4 and a second high-speed projector P2, and the baseline distance between the third camera C3 and the second high-speed projector P2 is smaller than the baseline distance between the fourth camera C4 and the second high-speed projector P2.

[0070] It can be understood that the camera with a relatively large baseline distance from the above-mentioned high-speed projector can be called a long-baseline camera, while the camera with a relatively small baseline distance from the high-speed projector can be called a short-baseline camera. The thin-walled parts machined by a milling cutter usually have complex three-dimensional shape features, including curved surfaces, sharp edges, and fine grooves left during milling. The short-baseline camera has a closer view to the projector, which can effectively reduce data loss caused by occlusion or surface reflection and accurately capture the details of the thin-walled parts, such as edge contours and local minute deformations. The long-baseline camera, on the other hand, improves the resolution of the overall shape and depth changes of the thin-walled parts through more significant parallax. Especially when measuring the airfoil surface or large-span areas of the thin-walled parts, it can provide higher depth accuracy. The fusion of the two baseline data can not only cover the complex geometric shapes of the full size of the thin-walled parts but also ensure the comprehensiveness and reliability of the measurement results.

[0071] Optionally, the host computer 2 is further configured to:

[0072] Fuse the first data and the second data to obtain the front-view morphology data of the thin-walled part 1 to be measured; wherein, the first data is the data collected by the first camera C1, and the second data is the data collected by the second camera C2;

[0073] Fuse the third data and the fourth data to obtain the reverse-view morphology data of the thin-walled part 1 to be measured; wherein, the third data is the data collected by the third camera C3, and the fourth data is the data collected by the fourth camera C4.

[0074] Optionally, the host computer 2 is further configured to:

[0075] Control the first camera C1, the second camera C2, and the first high-speed projector P1 in the front-view data acquisition system A to be synchronously triggered;

[0076] And control the third camera C3, the fourth camera C4, and the second high-speed projector P2 in the reverse-view data acquisition system B to be synchronously triggered.

[0077] It can be understood that in addition to using binocular structured light for data acquisition, the above-mentioned front-view data acquisition subsystem A and reverse-view data acquisition subsystem B can also be extended to other structures, such as:

[0078] The front-view data acquisition subsystem A can be a data acquisition subsystem based on N (N≥1)-eye structured light;

[0079] The reverse-view data acquisition subsystem B can be a data acquisition subsystem based on M (M≥1)-eye structured light.

[0080] Optionally, the host computer 2 splices the front-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part 1 to be measured, including:

[0081] The phase unwrapping is performed on the positive-view data and the negative-view data by using a deep learning neural network to obtain the true phase; the true phase is converted into height data by using the phase-height model parameters; the positive and negative-view height data are unified in the same world coordinate system by using the space transfer matrix of the positive and negative-view data acquisition subsystem; and the point cloud registration algorithm is used to accurately align the positive and negative-view height data to generate a complete three-dimensional reconstructed topography.

[0082] It can be understood that the phase data collected by the camera is usually wrapped phase. The wrapped phase refers to the phase value after folding due to phase overrun (usually 2π). In structured light measurement, the modulation of the structured light by each point on the object surface will cause the phase of the light to change. When obtaining the phase information by calculating the change in light intensity before and after phase shift, due to the periodicity of the arctangent function, its value range is usually limited to -π to π. These wrapped phases cannot directly provide the complete three-dimensional information of the object surface, and the true phase value needs to be restored through the unwrapping process.

[0083] Optionally, the above thin-walled part surface measurement system further includes: a first electric slide rail, a first background plate, a second electric slide rail, and a second background plate, and the first electric slide rail and the second electric slide rail are respectively connected to the host computer;

[0084] The first electric slide rail is installed on one side of the workpiece table away from the positive-view data acquisition subsystem A; the first background plate D1 is installed on the first electric slide rail and is used to provide a background when the positive-view data acquisition subsystem A acquires positive-view topography data;

[0085] The second electric slide rail is installed on one side of the workpiece table away from the negative-view data acquisition subsystem B; the second background plate D2 is installed on the second electric slide rail and is used to provide a background when the negative-view data acquisition subsystem B acquires negative-view topography data;

[0086] Both the first background plate and the second background plate are made of black acrylic PMMA material.

[0087] The host computer is further configured to: when the positive-view data acquisition subsystem A is triggered, control the first electric slide rail to drive the first background plate D1 to move to the working position, and control the second electric slide rail to drive the second background plate D2 to move to the non-working position. The background plate moving to the working position means rising to serve as the background of the thin-walled part to be measured, and moving to the non-working position means descending below the platform where the thin-walled part to be measured is located; and when the negative-view data acquisition subsystem B is triggered, control the electric slide rail to drive the second background plate D2 to move to the working position, and control the electric slide rail to drive the first background plate D1 to move to the non-working position.

[0088] The system calibration process of the above thin-walled part surface measurement system is introduced as follows: First, the principle of the global calibration process is introduced:

[0089] Binocular camera calibration is to further determine the specific positional relationship between the left and right cameras relative to the world coordinate system based on the results of monocular camera calibration, that is, by using the rotation matrices R l 、R r and translation matrices T l 、T r . Assuming there is a point P in the world coordinate system, the following relationship can be obtained, where P l and P r are the coordinates of point P in the left camera coordinate system and the right camera coordinate system respectively in the world coordinate system.

[0090] P l =R l P+T l

[0091] P r =R r P+T r

[0092] P r =RP l +T

[0093] From the above three equations, the rotation matrix R and translation matrix T for converting the left camera to the right camera can be obtained.

[0094]

[0095] T=T r -RT l

[0096] Projector calibration is completed by regarding the projector as a reverse camera. By projecting a calibration pattern onto the plane where the calibration board is located and collecting it with the camera, the three-dimensional coordinates of the projection feature points in the calibration board coordinate system can be solved using the camera calibration parameters, and then the calibration parameters of the projector can be calculated using the camera imaging model.

[0097] The relative position of the cameras in the forward and reverse views is determined based on the double-sided calibration pattern of the stereo calibration board. As Figure 3 shown, the following conversion relationship can be obtained, where [R E T E is the conversion matrix from the third camera coordinate system in the reverse view to the first camera coordinate system in the forward view:

[0098]

[0099] Secondly, the global calibration process of the above thin-walled part surface measurement system is introduced, including:

[0100] First, with the help of a three-dimensional calibration board with calibration patterns on both sides, the side photographed by camera C1 is set as the front of the calibration board, and the side photographed by camera C3 is set as the back of the calibration board. The projector-binocular camera system calibration for the front and back is carried out respectively to obtain their internal and external parameters. Then, according to the binocular camera calibration principle, the relative positions of the two cameras on the same side are determined. Next, according to the rotation matrix R0 and translation matrix T0 of the calibration patterns on the front and back sides of the three-dimensional calibration board, the relative positions of the first camera coordinate system and the third camera coordinate system are determined. Finally, the global calibration of the front and back multi-view projector-binocular camera system is realized.

[0101] Taking the T-shaped curved thin-walled part as an example, the working principle of the above-mentioned thin-walled part surface measurement system is introduced as follows:

[0102] 1. According to the required measurement accuracy and measurement field of view of the T-shaped curved thin-walled part, calculate the baseline distance, working distance, deflection angle, etc. of each group of cameras and projectors, and use the three-dimensional calibration board to perform the global calibration of the front and back multi-view projector-binocular camera system;

[0103] 2. Fix the position of the T-shaped curved thin-walled part, install the first background board D1 using the first electric slide rail, and lower the second background board D2. The host computer 2 controls the positive-view data acquisition subsystem A to trigger synchronously to collect the positive-view topography data of the thin-walled part;

[0104] 3. Keep the position of the T-shaped curved thin-walled part unchanged, install the second background board D2 using the second electric slide rail, and lower the first background board D1. The host computer 2 controls the negative-view data acquisition subsystem B to trigger synchronously to collect the negative-view topography data of the thin-walled part;

[0105] 4. The host computer 2 fuses the surface data collected by the two cameras in the positive view to obtain the point cloud of the positive-view topography data of the thin-walled part, and then fuses the surface data collected by the two cameras in the negative view to obtain the point cloud of the negative-view topography data of the thin-walled part;

[0106] 5. The host computer 2 performs the point cloud data stitching of the positive and negative views to generate a complete point cloud model of the T-shaped curved thin-walled part, and further realizes the high-precision measurement of the surface of the T-shaped curved thin-walled part. The method for stitching the point clouds of the positive and negative views is as follows:

[0107] The T-shaped curved thin-walled part is fixed at the center of the measurement field of view. Assume that the coordinates of the point cloud data of the thin-walled part measured in the camera C1 coordinate system are (X1, Y1, Z1), the coordinates of the point cloud data of the thin-walled part measured in the camera C2 coordinate system are (X2, Y2, Z2), the coordinates of the point cloud data of the thin-walled part measured in the camera C3 coordinate system are (X3, Y3, Z3), and the coordinates of the point cloud data of the thin-walled part measured in the camera C4 coordinate system are (X4, Y4, Z4). According to the calibration of the measurement system, there is the following conversion relationship:

[0108]

[0109] As Figure 4 shown, based on the same inventive concept, an embodiment of the present application further provides a method for measuring the profile of a thin-walled part for the above-mentioned thin-walled part profile measurement system. The method includes:

[0110] Step S101: Use the parameters of the stereo calibration board and perform global calibration on the front-view data acquisition subsystem A and the back-view data acquisition subsystem B;

[0111] The parameters of the above-mentioned stereo calibration board include: the size of the stereo calibration board, the pattern pitch, and the spatial transformation relationship between the patterns on both sides;

[0112] Using the parameters of the stereo calibration board to perform global calibration on the front-view data acquisition subsystem and the back-view data acquisition subsystem includes:

[0113] Adopt a double-sided stereo calibration board, let the side photographed by the first camera C1 in the front-view data acquisition subsystem A be the front of the calibration board, and the side photographed by the third camera C3 in the back-view data acquisition subsystem be the back of the calibration board. Calibrate the front-view data acquisition subsystem A and the back-view data acquisition subsystem B respectively to obtain the calibration parameter matrix;

[0114] Calibrating the front-view data acquisition subsystem A and the back-view data acquisition subsystem B includes: determining the relative positions of the first camera C1 and the second camera C2 in the front-view data acquisition subsystem A and the relative positions of the third camera C3 and the fourth camera C4 in the back-view data acquisition subsystem B according to the binocular camera calibration principle, and using the rotation matrix R0 and the translation matrix T0 of the calibration patterns on the front and back sides of the stereo calibration board to determine the relative positions of the first and second camera coordinate systems and the third and fourth camera coordinate systems;

[0115] Let the origin of the world coordinate system be the center of the front of the stereo calibration board, the horizontal right direction of the front of the stereo calibration board be the X axis, the vertical upward direction of the front of the stereo calibration board be the Y axis, and the normal direction of the front of the stereo calibration board be the Z axis. Use the calibration parameter matrix to complete the unified mapping of all camera coordinate systems to the world coordinate system, and realize the global calibration of the front-view data acquisition subsystem A and the back-view data acquisition subsystem B.

[0116] Step S102: Fix the thin-walled part 1 to be measured on the workbench, control the first electric slide rail to drive the first background board D1 to move to the working position, and control the second electric slide rail to drive the second background board D2 to move to the non-working position;

[0117] Step S103: Control the front-view data acquisition subsystem A to trigger synchronously to obtain the front-view morphology data of the thin-walled part 1 to be measured;

[0118] Step S104: Control the second electric slide rail to drive the second background board D2 to move to the working position, and control the first electric slide rail to drive the first background board D1 to move to the non-working position;

[0119] Step S105: Control the anti-view data acquisition subsystem B to trigger synchronously, and obtain the anti-view morphology data of the thin-walled part 1 to be measured;

[0120] Step S106: Stitch the front-view morphology data and the anti-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part 1 to be measured.

[0121] Optionally, control the front-view data acquisition subsystem A to trigger synchronously, and obtain the front-view morphology data of the thin-walled part 1 to be measured, including:

[0122] Control the front-view data acquisition subsystem A to trigger synchronously, and respectively obtain the first data and the second data collected by the first camera C1 and the second camera C2;

[0123] Fuse the first data and the second data to obtain the front-view morphology data of the thin-walled part 1 to be measured;

[0124] Control the anti-view data acquisition subsystem B to trigger synchronously, and obtain the anti-view morphology data of the thin-walled part 1 to be measured, including:

[0125] Control the anti-view data acquisition subsystem B to trigger synchronously, and respectively obtain the third data and the fourth data collected by the third camera C3 and the fourth camera C4;

[0126] Fuse the third data and the fourth data to obtain the anti-view morphology data of the thin-walled part 1 to be measured.

[0127] Optionally, stitch the front-view morphology data and the anti-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part 1 to be measured, including:

[0128] Fix the thin-walled part 1 to be measured at the center of the measurement field of view. Assume that the point cloud data coordinates of the thin-walled part 1 measured in the coordinate system of the first camera C1 are (X1, Y1, Z1), the point cloud data coordinates of the thin-walled part 1 measured in the coordinate system of the second camera C2 are (X2, Y2, Z2), the point cloud data coordinates of the thin-walled part 1 measured in the coordinate system of the third camera C3 are (X3, Y3, Z3), and the point cloud data coordinates of the thin-walled part 1 measured in the coordinate system of the fourth camera C4 are (X4, Y4, Z4). According to the calibration of the measurement system, there is the following conversion relationship:

[0129]

[0130] First, unify the point cloud data in the coordinate system of camera C1 to the world coordinate system, unify the point cloud data in the coordinate system of camera C2 to the world coordinate system, and perform point cloud fusion in the coordinate systems of the first camera C1 and the second camera C2 to obtain the front point cloud data (X5, Y5, Z5);

[0131] Unify the point cloud data in the coordinate system of camera C3 to the world coordinate system, unify the point cloud data in the coordinate system of camera C4 to the world coordinate system, and perform point cloud fusion in the coordinate systems of the third camera C3 and the fourth camera C4 to obtain the back point cloud data (X6, Y6, Z6);

[0132] Perform point cloud data stitching on the front point cloud data (X5, Y5, Z5) and the back point cloud data (X6, Y6, Z6) in the world coordinate system to unify all the data in the camera coordinate systems to the world coordinate system;

[0133] Perform precise registration on the front point cloud data and the back point cloud data through a point cloud registration algorithm to reconstruct the complete three-dimensional morphology.

[0134] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A thin-walled part profile measurement system, characterized in that: The system comprises: Workpiece table, used to place thin-walled parts to be measured; A front-view data acquisition subsystem, installed at the front-view of the thin-walled workpiece to be measured, for acquiring the front-view topography data of the thin-walled workpiece to be measured; A reverse viewing angle data acquisition subsystem, installed at the reverse viewing angle of the thin-walled workpiece to be measured, for acquiring reverse viewing angle morphological data of the thin-walled workpiece to be measured; A three-dimensional calibration plate, used to calibrate the relative positions of the positive viewing angle data acquisition subsystem and the reverse viewing angle data acquisition subsystem, and obtain calibration parameters; The host computer is connected to the front-view data acquisition subsystem and the reverse-view data acquisition subsystem, respectively, and is used to control the time-sharing triggering of the front-view data acquisition subsystem and the reverse-view data acquisition subsystem to acquire the front-view morphology data and the reverse-view morphology data, splice the front-view morphology data and the reverse-view morphology data, and acquire the three-dimensional reconstructed morphology of the thin-walled part to be measured.

2. The thin-walled part profile measurement system according to claim 1, characterized in that: The positive-view data acquisition subsystem includes: a first camera, a second camera and a first high-speed projector; the reverse-view data acquisition subsystem includes: a third camera, a fourth camera and a second high-speed projector.

3. The thin-walled part profile measurement system according to claim 2, characterized in that: The host computer is also used for: Controlling the first camera, the second camera and the first high-speed projector in the positive viewing angle data acquisition subsystem to be triggered synchronously; And, controlling the third camera, the fourth camera and the second high-speed projector in the reverse viewing angle data acquisition subsystem to be triggered synchronously.

4. The thin-walled part profile measurement system according to claim 1, characterized in that: The three-dimensional calibration plate is a double-sided structure, with calibration patterns printed on both the front and back sides; The size of the stereo calibration plate, the pattern spacing and the spatial transfer matrix of the patterns on both sides are used to provide a spatial reference to complete the global calibration of the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem, and obtain the triangular stereo model parameters corresponding to the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem, as well as the spatial transfer matrix for data conversion between the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem.

5. The thin-walled part profile measurement system according to claim 4, characterized in that: The host computer splices the front-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part to be measured, including: A deep learning neural network is used to perform phase unwrapping on the positive-view morphology data and the reverse-view morphology data to obtain a real phase; the real phase is converted into height data using the triangular stereo model parameters; the positive-view height data and the reverse-view height data are unified in the same world coordinate system using the spatial transfer matrix of the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem; the positive-view height data and the reverse-view height data are aligned using a point cloud registration algorithm to generate a complete three-dimensional reconstructed morphology.

6. The thin-walled part profile measurement system according to claim 1, characterized in that: The system further comprises: a first electric slide rail, a first background plate, a second electric slide rail and a second background plate, wherein the first electric slide rail and the second electric slide rail are respectively connected to the host computer; The first electric slide rail is installed on a side of the workpiece table away from the front-view data acquisition subsystem; the first background plate is installed on the first electric slide rail, and is used to provide a background when the front-view data acquisition subsystem acquires the front-view topography data; The second electric slide rail is installed on the workpiece table at a side away from the reverse viewing angle data acquisition subsystem; the second background plate is installed on the second electric slide rail, and is used to provide a background when the reverse viewing angle data acquisition subsystem acquires the reverse viewing angle topography data; The host computer is also used to: when the positive-view data acquisition subsystem is triggered, control the first electric slide rail to drive the first background plate to move to the working position, and control the second electric slide rail to drive the second background plate to move to the non-working position; and, when the reverse-view data acquisition subsystem is triggered, control the second electric slide rail to drive the second background plate to move to the working position, and control the first electric slide rail to drive the first background plate to move to the non-working position.

7. The thin-walled part profile measurement system according to claim 1, characterized in that: The positive viewing angle data acquisition subsystem is a data acquisition subsystem based on N (N≥1) structured light; The reverse viewing angle data acquisition subsystem is a data acquisition subsystem based on M (M≥1) eye structured light.

8. A method for measuring the profile of a thin-walled part, characterized in that: A thin-walled part profile measurement system according to any one of claims 1 to 6, the method comprising: The parameters of the stereo calibration plate are used to globally calibrate the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem; wherein the parameters of the stereo calibration plate include the size of the stereo calibration plate, the pattern spacing, and the spatial conversion relationship between the patterns on both sides; Fix the thin-walled workpiece to be measured on the workpiece table, control the electric slide rail to drive the first background plate to move to the working position, and control the electric slide rail to drive the second background plate to move to the non-working position; Controlling the front-view data acquisition subsystem to be triggered synchronously to obtain the front-view topography data of the thin-walled workpiece to be measured; Controlling the electric slide rail to drive the second background plate to move to the working position, and controlling the electric slide rail to drive the first background plate to move to the non-working position; Controlling the reverse viewing angle data acquisition subsystem to be triggered synchronously to obtain reverse viewing angle shape data of the thin-walled workpiece to be measured; splicing the front-view morphology data and the reverse-view morphology data to obtain a three-dimensional reconstructed morphology of the thin-walled part to be measured; The controlling the front-view data acquisition subsystem to be triggered synchronously to obtain the front-view shape data of the thin-walled workpiece to be measured comprises: controlling the front-view data acquisition subsystem to be triggered synchronously to obtain first data and second data collected by the first camera and the second camera respectively; fusing the first data and the second data to obtain the front-view shape data of the thin-walled workpiece to be measured; The controlling the synchronous triggering of the reverse-view data acquisition subsystem to obtain the reverse-view shape data of the thin-walled workpiece to be measured includes: controlling the synchronous triggering of the reverse-view data acquisition subsystem to respectively obtain the third data and the fourth data collected by the third camera and the fourth camera; fusing the third data and the fourth data to obtain the reverse-view shape data of the thin-walled workpiece to be measured.

9. The thin-walled part profile measurement method according to claim 8, characterized in that: The method of globally calibrating the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem using the parameters of the stereo calibration plate includes: A double-sided stereo calibration plate is used, and the side photographed by the first camera in the positive-view data acquisition subsystem is taken as the front side of the calibration plate, and the side photographed by the third camera in the reverse-view data acquisition subsystem is taken as the reverse side of the calibration plate. The positive-view data acquisition subsystem and the reverse-view data acquisition subsystem are calibrated respectively to obtain a calibration parameter matrix; Calibrate the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem, including: determining the relative positions of the first camera and the second camera in the positive-view data acquisition subsystem and the relative positions of the third camera and the fourth camera in the reverse-view data acquisition subsystem according to the binocular camera calibration principle, and determining the relative positions of the first and second camera coordinate systems and the third and fourth camera coordinate systems using the rotation matrix R0 and the translation matrix T0 of the calibration patterns on the front and back sides of the stereo calibration plate; Let the world coordinate system origin be the center of the front of the stereo calibration plate, the horizontal rightward direction of the front of the stereo calibration plate be the X-axis, the vertical upward direction of the front of the stereo calibration plate be the Y-axis, and the normal direction of the front of the stereo calibration plate be the Z-axis. Use the calibration parameter matrix to complete the unified mapping of all camera coordinate systems to the world coordinate system, and realize the global calibration of the positive-view data acquisition subsystem and the reverse-view data acquisition subsystem.

10. The thin-walled part profile measurement method according to claim 8, characterized in that: The step of splicing the front-view morphology data and the reverse-view morphology data to obtain the three-dimensional reconstructed morphology of the thin-walled part to be measured includes: Fix the thin-walled part to be measured at the center of the measurement field of view. Assume that the point cloud data coordinates of the thin-walled part to be measured measured in the first camera coordinate system are (X1, Y1, Z1), the point cloud data coordinates of the thin-walled part to be measured measured in the second camera coordinate system are (X2, Y2, Z2), the point cloud data coordinates of the thin-walled part to be measured measured in the third camera coordinate system are (X3, Y3, Z3), and the point cloud data coordinates of the thin-walled part to be measured measured in the fourth camera coordinate system are (X4, Y4, Z4). According to the calibration of the measurement system, the following conversion relationship exists: Unify the point cloud data in the first camera coordinate system into the world coordinate system, unify the point cloud data in the second camera coordinate system into the world coordinate system, perform point cloud fusion in the first camera coordinate system and the second camera coordinate system, and obtain front point cloud data (X5, Y5, Z5); Unify the point cloud data in the third camera coordinate system into the world coordinate system, unify the point cloud data in the fourth camera coordinate system into the world coordinate system, perform point cloud fusion in the third camera coordinate system and the fourth camera coordinate system, and obtain reverse point cloud data (X6, Y6, Z6); Performing point cloud data splicing on the front point cloud data (X5, Y5, Z5) and the back point cloud data (X6, Y6, Z6) in the world coordinate system, so as to unify the data in all camera coordinate systems into the world coordinate system; The front point cloud data and the back point cloud data are accurately registered by a point cloud registration algorithm to reconstruct a complete three-dimensional appearance.

Images