Method for measuring inner surface of composite tubular thin-walled part having high length-diameter ratio

Abstract

A method for measuring the inner surface of a composite tubular thin-walled part having a high length-diameter ratio, comprising: firstly, calibrating a tooling coordinate system (S1); then by means of a scanner, acquiring a point cloud map of the outer surface of a tubular part to be tested (S2), and at the same time, detecting a thickness value of a discrete point (S3); acquiring a normal vector of the discrete point on the basis of the point cloud map of the outer surface, and compensating for probe coordinates of the discrete point on the basis of the normal vector (S4); finally, on the basis of the normal vector, the thickness value, and outer surface coordinates, calculating inner surface coordinates corresponding to the discrete point (S5); and on the basis of an equal-thickness principle that the inner surface and the outer surface of the tubular part are of the same shape, in combination with a thickness parameter, the normal vector, and the point cloud map of the outer surface of the tubular part, acquiring structural points of the inner surface by means of offsetting, and constructing the inner surface of the tubular part on the basis of the structural points and the overall curve change of the outer surface (S6). The parameters are obtained through contact-type measurement and non-contact measurement, and the inner surface is obtained through fitting, so that comprehensive technical data is provided, and the obtained parameters are of high accuracy.

Description

A method for measuring the inner surface of a thin-walled composite tubular part with a large aspect ratio Technical Field

[0001] The present application relates to the field of profile detection technology, and in particular to a method for measuring the inner profile of a composite material tubular thin-walled part with a large aspect ratio. Background Art

[0002] Composite materials are increasingly used in aerospace, shipbuilding, and automobile manufacturing due to their specific strength, specific stiffness and other properties. In the above manufacturing fields, large aspect ratio composite tubular thin-walled parts are an important application of composite materials.

[0003] During the manufacturing and forming process of large aspect ratio composite tubular thin-walled parts, deformation occurs in the formed thin-walled parts due to errors between the surface of the mold used and the theoretical design surface, differences between the layer thickness during the wire laying process and the theoretical thickness, and factors related to the composite material's own characteristics. The deformation needs to be controlled and compensated during the production process. Accurately obtaining the external structural data of the inner and outer surfaces of the tubular parts using traceable digital measurement methods is an important part of this process.

[0004] However, for tubular parts with a relatively curved shape, due to the limited internal space, it is impossible to penetrate the interior of the tubular part in a straight line. Therefore, whether it is traditional contact measurement or non-contact measurement, the accessibility of the sensor limits its measurement range and cannot obtain the technical parameters of the inner surface.

[0005] Summary of the Invention

[0006] The main purpose of this application is to provide a method for measuring the inner surface of a thin-walled tubular composite material part with a large aspect ratio, aiming to solve the defect in the prior art that the technical parameters of the inner surface cannot be obtained.

[0007] This application achieves the above objectives through the following technical solutions:

[0008] A method for measuring the inner surface of a thin-walled tubular composite material part with a large aspect ratio comprises the following steps:

[0009] Installing a contact probe and calibrating a tooling coordinate system using the contact probe;

[0010] Obtaining a point cloud image of the outer surface of the tube-shaped part to be inspected, wherein the point cloud image of the outer surface refers to a point cloud image in the tooling coordinate system;

[0011] Determine discrete points on the outer surface of the tubular component to be inspected, obtain probe coordinates of the discrete points, and measure thickness values ​​at the discrete points;

[0012] Obtaining the normal vector of the discrete point according to the outer surface point cloud image, compensating the probe coordinates according to the normal vector, and obtaining the outer surface coordinates of the discrete point;

[0013] Calculate the inner surface coordinates corresponding to the discrete points according to the normal vectors of the discrete points, the thickness values ​​and the outer surface coordinates;

[0014] Select several discrete points, repeat the steps for each discrete point to determine the discrete point on the outer surface of the tubular part to be inspected, obtain the probe coordinates of the discrete points, measure the thickness values ​​at the discrete points, and construct the inner surface of the tubular part to be inspected through the coordinates of each inner surface.

[0015] Optionally, installing a contact probe and calibrating the tooling coordinate system using the contact probe includes the following steps:

[0016] Install the contact probe;

[0017] Install the tubular part to be inspected on the inspection fixture and obtain the fixture coordinate system;

[0018] Selecting at least one geometric feature on the inspection tool and obtaining a reference coordinate of the geometric feature in the tool coordinate system;

[0019] Acquiring the measurement coordinates of the geometric feature by the contact probe;

[0020] A first conversion relationship is acquired according to the reference coordinates and the measured coordinates, and the measured coordinates are converted according to the first conversion relationship.

[0021] Optionally, obtaining a point cloud image of the outer surface of the tube-shaped part to be inspected includes the following steps:

[0022] Establish the scanner coordinate system;

[0023] Acquire a second transformation relationship between the scanner coordinate system and the tooling coordinate system;

[0024] Scan the tubular part to be inspected by a scanner to obtain relevant data of the tubular part to be inspected;

[0025] According to the second conversion relationship, the data is converted into external surface point cloud data in a tooling coordinate system.

[0026] Optionally, determining discrete points on the outer surface of the tubular component to be inspected and obtaining probe coordinates of the discrete points includes the following steps:

[0027] Determine a number of discrete points;

[0028] Determine the detection coordinates of the discrete points by a contact probe;

[0029] The detection coordinates are converted into probe coordinates Pi of each discrete point according to the first conversion relationship, where i represents the number of the discrete point.

[0030] Optionally, measuring the thickness value of the discrete point includes the following steps:

[0031] Select several testing points at both ends of the tube to be tested;

[0032] Detecting the thickness of each detection point with a micrometer to obtain a standard thickness value d1;

[0033] Detect the thickness of each detection point using the thickness measuring device to be calibrated to obtain the detected thickness value d2;

[0034] Calibrate the thickness measuring device to be calibrated by combining the standard thickness value d1 and the detected thickness value d2;

[0035] The thickness of each discrete point is measured by a calibrated thickness measuring device to obtain the thickness value w of the discrete point.

[0036] Optionally, obtaining the normal vector of the discrete point according to the outer surface point cloud image, compensating the probe coordinates according to the normal vector, and obtaining the outer surface coordinates of the discrete point includes the following steps:

[0037] Obtaining a probe radius R of a contact probe, and setting a screening threshold according to the probe radius R;

[0038] Combined with the probe coordinates, the point Q closest to the discrete point is obtained in the surface point cloud map. t ;

[0039] According to the screening threshold, a fitting point set is obtained; wherein all points in the fitting point set and point Q t The distances between them are all less than the screening threshold;

[0040] Constructing a fitting space surface through the fitting point set;

[0041] Selecting the point in the fitted spatial surface that is closest to the discrete point as the end point, and the line connecting the end point and the discrete point is the normal vector of the discrete point;

[0042] The probe coordinates of the discrete points are compensated according to the normal vectors to obtain the external surface coordinates of the discrete points.

[0043] Optionally, the model expression for fitting the space surface is:

[0044] z=k1+k2x+k3y+k4x 2 +k5xy+k6y 2 +y7x 3+k8x 2 y+k9y 2 x+k 10 y 3 ; Among them, k1~k 10 are the coefficients of the cubic surface equation, and x, y, and z are the coordinates of each point on the surface.

[0045] Optionally, calculating the inner surface coordinates corresponding to the discrete points according to the normal vectors, the thickness values, and the outer surface coordinates of the discrete points comprises the following steps:

[0046] Establishing a K-neighborhood of the discrete point, and obtaining a set of measured thicknesses and measured thickness values ​​of m random samples within the K-neighborhood;

[0047] The standard deviation of the random sample point sampling experiment is calculated based on the measured thickness set and the measured thickness value, and the standard deviation satisfies Where m represents the number of random samples, S i represents the calculated thickness value of the i-th random sample, Indicates the measured thickness value;

[0048] Calculate the thickness value w and the measured thickness value If |e|<3σ, the measured thickness value is used as the actual thickness value of the discrete point; if it is not satisfied, the neighborhood K radius is reduced, and the steps are repeated to establish the K neighborhood of the discrete point, and the measured thickness set and measured thickness value of m random samples in the K neighborhood are obtained until |e|<3σ is satisfied;

[0049] The outer surface coordinates are corrected according to the normal vectors of the discrete points and the actual thickness values ​​to obtain the inner surface coordinates of the discrete points.

[0050] Optionally, obtaining a set of measured thicknesses and measured thickness values ​​of m random samples within a K neighborhood includes the following steps:

[0051] Randomly determine m random sampling points in the K neighborhood,

[0052] Selecting the i-th random sampling point from the m random samples as a detection point;

[0053] Measuring the thickness of the i-th random sampling point n times by a thickness measuring device to obtain n measured thickness values ​​of the i-th random sampling point;

[0054] Screening out distorted values ​​from the n measured thickness values, and calculating the calculated thickness value of the random sampling point using the screened measured thickness values;

[0055] Repeating the process of selecting the i-th random sampling point as the detection point among the m random samples until the calculated thickness values ​​of all random sampling points are obtained;

[0056] A measured thickness set and a measured thickness value are obtained according to the calculated thickness value of each of the random sampling points.

[0057] Optionally, the calculated thickness value satisfies the formula Among them D i，j represents the thickness value obtained by the jth measurement of the i-th sample position, l represents the number of distortion values; the measured thickness value is the mean of the measured thickness set.

[0058] Compared with the prior art, this application has the following beneficial effects:

[0059] The present application first calibrates the tooling coordinate system, then uses a scanner to obtain a point cloud image of the outer surface of the tubular part to be inspected, and simultaneously detects the thickness values ​​of discrete points; obtains the normal vectors of the discrete points from the outer surface point cloud image, and compensates the probe coordinates of the discrete points based on the normal vectors; finally, calculates the inner surface coordinates corresponding to the discrete points based on the normal vectors, the thickness values, and the outer surface coordinates;

[0060] Based on the principle of equal thickness, the inner surface of the tube is the same shape as its outer surface. Combining the thickness parameters and normal vector of the tube with the scanned outer surface point cloud, a large number of inner surface structural points can be quickly obtained through offset. Then, the inner surface of the tube can be quickly constructed based on the above structural points and the overall curve change of the outer surface.

[0061] The acquisition of the point cloud of the outer surface can be quickly obtained through scanning equipment or other non-contact equipment. It is not only fast in acquisition speed, but also conducive to improving construction efficiency. At the same time, compared with the occlusion of the inner surface, the acquisition of the outer surface is free of any occlusion, which minimizes the difficulty of implementing the measurement method and is conducive to improving work efficiency. At the same time, the reduction of occlusions also helps to improve detection accuracy.

[0062] At the same time, through the detection of contact measurement tools such as contact probes, a large number of detection parameters of the measurable area can be obtained to ensure the accuracy of the thickness parameters.

[0063] Therefore, compared with the prior art, the present application uses contact measurement to obtain parameters such as thickness that are difficult to accurately obtain through non-contact measurement. Parameters with lower requirements, such as changes in the outer curve of the tubular part, are obtained through non-contact measurement. At the same time, based on the principle of equal thickness, the difficult-to-measure inner surface is converted into an easy-to-measure outer surface, thereby achieving accurate construction of the inner surface.

[0064] It combines the advantages of contact measurement and non-contact measurement, while avoiding the weaknesses of both. Under the premise of ensuring detection accuracy, it improves the detection efficiency as much as possible and reduces the detection difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG1 is a flow chart of a method for measuring the inner surface of a thin-walled tubular composite material part with a large aspect ratio, provided in Embodiment 1 of the present application;

[0066] The purpose, features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0068] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0069] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0070] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "first conversion relationship and / or B" as an example, it includes the first conversion relationship scheme, or B scheme, or the scheme in which the first conversion relationship and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0071] Implementation Method 1

[0072] 1 , this embodiment, as an optional embodiment of the present application, discloses a method for measuring the inner surface of a thin-walled tubular composite material part with a large aspect ratio, comprising the following steps:

[0073] S1. Install a contact probe and calibrate the tooling coordinate system using the contact probe;

[0074] S11. Install the contact probe;

[0075] It should be pointed out that the contact probe can be an articulated arm, a T-Probe of a Lecia tracker, or a coordinate measuring machine;

[0076] S12, installing the tubular component to be inspected on the inspection tooling, and obtaining the tooling coordinate system;

[0077] Select an inspection tool that is compatible with the tubular component to be inspected, install the tubular component to be inspected on the tool, and obtain the tool's own coordinate system as the tool coordinate system;

[0078] S13, selecting at least one geometric feature on the inspection tool, and obtaining a reference coordinate of the geometric feature in the tool coordinate system;

[0079] Select at least one geometric feature on the inspection tool. The geometric feature point can be a plane, a straight line, a positioning hole, or other features that have obvious characteristics, are easy to detect, and have high positioning accuracy;

[0080] S14, obtaining the measurement coordinates of the geometric features by the contact probe;

[0081] After the geometric features are determined, the contact probe is controlled to measure the three-dimensional coordinates of the selected geometric feature points. However, it should be noted that the three-dimensional coordinates are the three-dimensional coordinates in the coordinate system of the contact probe itself.

[0082] S15. Acquire a first conversion relationship according to the reference coordinates and the measured coordinates, and convert the measured coordinates according to the first conversion relationship.

[0083] The unified feature point has corresponding three-dimensional coordinates in both the tooling coordinate system and the coordinate system of the contact probe itself. The first conversion relationship between the reference coordinate and the measured coordinate can be obtained through the two three-dimensional coordinates. The three-dimensional coordinates in the coordinate system of the contact probe itself can be converted into the tooling coordinate system through the first conversion relationship, thereby completing the calibration of the tooling coordinate system.

[0084] S2. Obtaining a point cloud image of the outer surface of the tubular component to be inspected, wherein the point cloud image of the outer surface refers to a point cloud image in the tooling coordinate system;

[0085] S21, establishing a scanner coordinate system;

[0086] S22, obtaining a second conversion relationship between the scanner coordinate system and the tooling coordinate system;

[0087] The acquisition of the second conversion relationship is the same as the acquisition of the first conversion relationship in step S1 , and both are obtained by coordinate conversion of one or more feature points in two coordinate systems.

[0088] S23, scanning the tubular component to be inspected by a scanner to obtain relevant data of the tubular component to be inspected;

[0089] Scan the appearance of the tube to be inspected using the installed scanner to obtain point cloud data in the scanner coordinate system;

[0090] S24, converting the data into surface point cloud data in a tooling coordinate system according to the second conversion relationship;

[0091] Since the contact probe, the inspection fixture, and the scanner are three independent devices, each having an independent coordinate system, steps 1 and 2 can unify the relevant three-dimensional coordinates obtained by the contact probe and the scanner into the same coordinate system, providing a unified platform for subsequent data calculations, which is conducive to improving calculation efficiency and accuracy.

[0092] S3, determining discrete points on the outer surface of the tubular component to be inspected, obtaining probe coordinates of the discrete points, and measuring thickness values ​​of the discrete points;

[0093] S31. Determine a number of discrete points;

[0094] The tubular part is divided into a plurality of cross sections perpendicular to the center line of the tubular part with a spacing of 100 mm to 150 mm, and a plurality of discrete points of the outer surface are selected at intervals of 50 mm to 150 mm on each interface;

[0095] Specifically, when the cross-sectional curvature variation is greater than its average value, an interval of 50 mm is selected, and when the cross-sectional curvature variation is less than its average value, an interval of 150 mm is selected;

[0096] S32, measuring the detection coordinates of the discrete points by a contact probe;

[0097] After the discrete points are selected, the detection coordinates of the discrete points are measured by the contact probe. It should be noted that the detection coordinates at this time are three-dimensional coordinates without rotation;

[0098] S33, converting the detection coordinates into the probe coordinates P of each discrete point according to the first conversion relationship i , where i represents the number of the discrete point;

[0099] The probe coordinates P of the discrete point in the tooling coordinates can be obtained by converting the above detection coordinates according to the first conversion relationship in step S15. i , where i represents the number of the discrete point;

[0100] S34, selecting a number of inspection points at both ends of the tubular member to be inspected;

[0101] Several inspection points are selected at both ends of the tubular component to be inspected. It should be noted that the inspection points are within the area where both ends of the tubular component to be inspected can be directly inspected by a micrometer, and the inspection points are randomly selected.

[0102] S35, measuring the thickness of each of the detection points with a micrometer to obtain a standard thickness value d1;

[0103] Directly measure the thickness of the detection point in step S34 using a micrometer, and use this value as the standard thickness value d1;

[0104] S36, using the thickness measuring device to be calibrated to detect the thickness of each detection point, and obtaining the detected thickness value d2;

[0105] S37, calibrating the thickness measuring device to be calibrated based on the standard thickness value d1 and the detected thickness value d2;

[0106] S38, measuring the thickness of each discrete point using the calibrated thickness measuring device to obtain the thickness value w of the discrete point;

[0107] The above procedure can be used to calibrate the thickness measuring device, ensure the accuracy of its detection, and thus improve the accuracy of the thickness value w of the discrete point.

[0108] Using a calibrated thickness measuring device to measure the thickness value at the discrete point N times, eliminating distorted data, and taking the average of the remaining results as the thickness value w of the discrete point;

[0109] Using a calibrated thickness measuring device to measure the thickness values ​​at the discrete points N times, where the specific parameter of N is determined according to actual conditions;

[0110] Set an allowable detection error range. If the data exceeds the detection error range, it is determined to be distorted data. The distorted data is removed, and then the average value of the remaining parameters is calculated, and the average value is used as the thickness value w of the discrete point.

[0111] S4. Obtaining the normal vector of the discrete point according to the outer surface point cloud image, compensating the probe coordinates according to the normal vector, and obtaining the outer surface coordinates of the discrete point;

[0112] S41, obtaining a probe radius R of a contact probe, and setting a screening threshold according to the probe radius R;

[0113] After the contact probe is selected, its probe radius R can be obtained by referring to the relevant technical parameters;

[0114] Set the screening threshold according to the probe radius R. The recommended screening threshold is 3R.

[0115] S42, combining the probe coordinates, obtaining the point Q closest to the discrete point in the outer surface point cloud map t ;

[0116] Retrieve the surface point cloud obtained in step S24 and the probe coordinates obtained in step S33, and automatically find the point Q closest to the discrete point through the computer. t ; It should be noted that the distance value here is Euclidean distance;

[0117] S43, obtaining a fitting point set according to the screening threshold; wherein all points in the fitting point set and point Q t The distances between them are all less than the screening threshold;

[0118] Q t A spherical space is established with a center point and a wing screening threshold as a radius, and all points in the outer surface point cloud image that are located in the spherical space are extracted and grouped into a set, which is the fitting point set;

[0119] S44, constructing a fitting space surface using the fitting point set;

[0120] Combined with the fitting point set obtained in step S43, and the fitting formula:

[0121] z=k1+k2x+k3y+k4x 2 +k5xy+k6y 2 +k7x 3 +k8x 2 y+k9y 2 x+k 10 y 3 Construct a fitting space surface; where k1~k 10 are the coefficients of the cubic surface equation, and x, y, and z are the coordinates of each point on the surface.

[0122] S45, selecting a point in the fitted spatial surface that is closest to the discrete point as an end point, and a line connecting the end point and the discrete point is a normal vector of the discrete point;

[0123] Calculate the point with the closest Euclidean distance to the discrete point in step S44 and use it as the end point. The direction of the line between the discrete point and the end point is the direction of the normal vector at the discrete point. The modulus of the normal vector is 1, thereby obtaining the normal vector.

[0124] S46, compensating the probe coordinates of the discrete points according to the normal vector to obtain the external surface coordinates of the discrete points;

[0125] The probe center coordinates are along the normal vector direction of the discrete point, minus the probe radius, and the discrete point Q t The coordinates of the compensated outer surface are Q i ': Then its expression satisfies: in is the normal vector of the discrete point;

[0126] The above calculation can eliminate the influence of the probe radius on the coordinate calculation of discrete points, thereby improving the accuracy of detection;

[0127] S5. Calculating the inner surface coordinates corresponding to the discrete point according to the normal vector of the discrete point, the thickness value, and the outer surface coordinates;

[0128] S51, establishing a K neighborhood of the discrete point, and obtaining a set of measured thicknesses and measured thickness values ​​of m random samples in the K neighborhood;

[0129] The K neighborhood refers to a set of points in the surface point cloud image whose Euclidean distance to the discrete point is not greater than the neighborhood radius, K represents the number of points, and the initial neighborhood radius can be set to 3 times the probe radius;

[0130] S511, randomly determine m random sampling points in the K neighborhood;

[0131] S512, selecting the i-th random sampling point from the m random samples in step S521 as a detection point; where i=1, 2, ..., m;

[0132] S513, measuring the thickness value at the i-th random sampling point n times by a thickness measuring device to obtain n measured thickness values ​​of the i-th random sampling point;

[0133] S514, filtering out distorted values ​​from the n measured thickness values, and calculating the calculated thickness value of the random sampling point using the filtered measured thickness values;

[0134] A distortion judgment parameter, such as c, is set, and all values ​​outside [ac, a+c] are distortion values. The specific value of the judgment parameter c is determined by those skilled in the art according to actual conditions;

[0135] All values ​​outside [ac, a+c] will be filtered out, and other values ​​will be retained;

[0136] Substitute all remaining parameters into the formula Among them D i，j represents the thickness value obtained from the jth measurement at the i-th sample position, and l represents the number of distortion values.

[0137] S515 , repeatedly selecting the i-th random sampling point from the m random samples as a detection point until the calculated thickness values ​​of all random sampling points are obtained.

[0138] S516 : Obtain a measured thickness set and a measured thickness value according to the calculated thickness value of each random sampling point.

[0139] Through the above steps, the measured thickness set {S1, S2, ..., S m};

[0140] By calculating the average value of each parameter in the measured thickness set, the above average value is used as the measured thickness value, that is,

[0141] S52, calculating the standard deviation of the random sample point sampling experiment based on the measured thickness set and the measured thickness value;

[0142] The standard deviation satisfies Where m represents the number of random samples, S i represents the calculated thickness value of the i-th random sample, Indicates the measured thickness value;

[0143] The measured thickness set {S1, S2, ..., S m} and measured thickness value Substituting this into the above formula, the standard deviation can be calculated;

[0144] S53, calculating the thickness value w and the measured thickness value If |e|<3σ, the measured thickness value is used as the actual thickness value of the discrete point; if it is not satisfied, the neighborhood K radius is reduced, and the steps are repeated to establish the K neighborhood of the discrete point, and the measured thickness set and measured thickness value of m random samples in the K neighborhood are obtained until |e|<3σ is satisfied;

[0145] According to the number of the discrete point, the thickness value w of the discrete point obtained in step S38 and the measured thickness value obtained in step S525 are retrieved. Calculate the difference e between the two;

[0146] At the same time, the standard deviation calculated in step S53 is retrieved. If e|<3σ, the measured thickness value is used as the actual thickness value of the discrete point.

[0147] If not, reduce the neighborhood radius of the K neighborhood, and repeat the steps to establish the K neighborhood of the discrete point, and calculate the thickness set in the K neighborhood until e<3S is satisfied. α (x); It should be noted that the neighborhood radius after reduction is half of the original neighborhood radius, and other ratios can also be set to determine the neighborhood radius after reduction.

[0148] S54, correcting the outer surface coordinates according to the normal vectors of the discrete points and the actual thickness values ​​to obtain the inner surface coordinates of the discrete points;

[0149] According to the discrete points Q of the outer surface calculated in step S46 i ', the direction vector of the discrete point The actual thickness value of the discrete point calculated in step S53 can be used to calculate the coordinates of the inner surface point according to the following expression: Among them, Pi is the coordinate of the inner surface point corresponding to the i-th outer surface discrete point.

[0150] S6. Select several discrete points, repeat the steps for each discrete point to determine the discrete point on the outer surface of the tubular component to be inspected, obtain the probe coordinates of the discrete points, measure the thickness values ​​at the discrete points, and construct the inner surface of the tubular component to be inspected using the inner surface coordinates.

[0151] Based on the principle of equal thickness, this application determines that the inner profile of a tubular component is the same shape as its outer profile. That is, if a quality defect occurs at a certain point on the outer profile, a corresponding inner profile defect will also occur on the inner profile. By combining the thickness parameters and normal vector of the tubular component with the scanned outer profile point cloud, a large number of inner profile structure points can be quickly obtained through offset. Then, the inner profile of the tubular component can be quickly constructed based on these structure points and the overall curve changes of the outer profile.

[0152] The acquisition of the point cloud of the outer surface can be quickly obtained through scanning equipment or other non-contact equipment. It is not only fast in acquisition speed, but also conducive to improving construction efficiency. At the same time, compared with the occlusion of the inner surface, the acquisition of the outer surface is free of any occlusion, which minimizes the difficulty of implementing the measurement method and is conducive to improving work efficiency. At the same time, the reduction of occlusions also helps to improve detection accuracy.

[0153] At the same time, through the detection of contact measurement tools such as contact probes, a large number of detection parameters of the measurable area can be obtained to ensure the accuracy of the thickness parameters.

[0154] Compared with the prior art, the present invention uses contact measurement to obtain parameters such as thickness that are difficult to accurately obtain using non-contact measurement. Parameters with lower requirements, such as changes in the outer curve of the tubular part, are obtained using non-contact measurement. Furthermore, based on the principle of equal thickness, the difficult-to-measure inner surface is converted into an easily measured outer surface, thereby achieving accurate construction of the inner surface.

[0155] At the same time, this application combines the advantages of contact measurement and non-contact measurement, and at the same time avoids the weaknesses of both. Under the premise of ensuring detection accuracy, it improves the detection efficiency as much as possible and reduces the detection difficulty.

[0156] The above are only preferred embodiments of the present application and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for measuring the inner surface of a large aspect ratio composite material tube-shaped thin-walled part, characterized in that: The following steps are involved: Installing a contact probe, and calibrating a tooling coordinate system by means of the contact probe; Acquire a point cloud image of the outer surface of the tube-shaped part to be inspected, wherein the point cloud image of the outer surface refers to a point cloud image in the tooling coordinate system; Determine discrete points on the outer surface of the tube-shaped part to be inspected, obtain the probe coordinates of the discrete points, and measure the thickness values ​​of the discrete points; Acquire the normal vector of the discrete point according to the outer surface point cloud image, compensate the probe coordinate according to the normal vector, and acquire the outer surface coordinate of the discrete point; Calculate the inner surface coordinates corresponding to the discrete points according to the normal vectors of the discrete points, the thickness values ​​and the outer surface coordinates; Select several discrete points, repeat the steps for each discrete point to determine the discrete points on the outer surface of the tubular part to be inspected, obtain the probe coordinates of the discrete points, measure the thickness values ​​at the discrete points, and construct the inner surface of the tubular part to be inspected through the inner surface coordinates.

2. The method for measuring the inner surface of a large aspect ratio composite material tubular thin-walled part according to claim 1, characterized in that: The method of calibrating the tooling coordinate system by using the contact probe comprises the following steps: Install the contact probe; Install the pipe to be inspected on the inspection tooling and obtain the tooling coordinate system; Selecting at least one geometric feature on the inspection tooling, and obtaining a reference coordinate of the geometric feature in the tooling coordinate system; Acquiring the measurement coordinates of the geometric feature by means of the contact probe; A first conversion relationship is acquired according to the reference coordinates and the measured coordinates, and the measured coordinates are converted according to the first conversion relationship.

3. The method for measuring the inner surface of a large aspect ratio composite material tubular thin-walled part according to claim 1, characterized in that: The step of obtaining a point cloud image of the outer surface of the tube-shaped part to be inspected comprises the following steps: Establish the scanner coordinate system; Acquire a second transformation relationship between the scanner coordinate system and the tooling coordinate system; Scanning the tube-shaped part to be inspected by a scanner to obtain relevant data of the tube-shaped part to be inspected; According to the second conversion relationship, the data is converted into external surface point cloud data in a tooling coordinate system.

4. The method for measuring the inner surface of a large aspect ratio composite tubular thin-walled part according to claim 2, characterized in that: The step of determining discrete points on the outer surface of the tube-shaped part to be inspected and obtaining the probe coordinates of the discrete points comprises the following steps: Determine a number of discrete points; Determine the detection coordinates of the discrete points by a contact probe; The detection coordinates are converted into probe coordinates Pi of each discrete point according to the first conversion relationship, where i represents the number of the discrete point.

5. The method for measuring the inner surface of a large aspect ratio composite material tubular thin-walled part according to claim 1, characterized in that: The step of measuring the thickness value of the discrete points comprises the following steps: Select several inspection points at both ends of the tube to be inspected; Detect the thickness of each detection point by using a micrometer to obtain a standard thickness value d1; The thickness of each detection point is detected by the thickness measuring device to be calibrated to obtain the detection thickness value d2; Calibrate the thickness measuring device to be calibrated by combining the standard thickness value d1 and the detected thickness value d2; The thickness of each discrete point is measured by a calibrated thickness measuring device to obtain the thickness value w of the discrete point.

6. The method for measuring the inner surface of a composite material tubular thin-walled part with a large aspect ratio according to claim 1, characterized in that: The step of obtaining the normal vector of the discrete point according to the outer surface point cloud image, compensating the probe coordinates according to the normal vector, and obtaining the outer surface coordinates of the discrete point comprises the following steps: Obtaining a probe radius R of a contact probe, and setting a screening threshold according to the probe radius R; Combined with the probe coordinates, the point Q closest to the discrete point is obtained in the outer surface point cloud map. i ; According to the screening threshold, a fitting point set is obtained; wherein all points in the fitting point set and point Q i The distances between them are all less than the screening threshold; Constructing a fitting space surface through the fitting point set; Selecting a point in the fitting space surface that is closest to the discrete point as an end point, and a line connecting the end point and the discrete point is a normal vector of the discrete point; The probe coordinates of the discrete points are compensated according to the normal vector to obtain the outer surface coordinates of the discrete points.

7. The method for measuring the inner surface of a large aspect ratio composite tubular thin-walled component according to claim 6, characterized in that: The model expression of the fitting space surface is: z=k1+k2x+k3y+k4x 2 +k5xy+k6y 2 +k7x 3 +k8x 2 y+k9y 2 x+k 10 y 3 ; Among them, k1~k 10 are the coefficients of the cubic surface equation, and x, y, and z are the coordinates of each point on the surface.

8. The method for measuring the inner surface of a large aspect ratio composite material tubular thin-walled part according to claim 1, characterized in that: The step of calculating the inner surface coordinates corresponding to the discrete points according to the normal vectors, the thickness values ​​and the outer surface coordinates of the discrete points comprises the following steps: Establishing a K neighborhood of the discrete point, and obtaining a measured thickness set and measured thickness values ​​of m random samples in the K neighborhood; The standard deviation of the random sample point sampling experiment is calculated based on the measured thickness set and the measured thickness value, and the standard deviation satisfies Where m represents the number of random samples, S i represents the calculated thickness value of the i-th random sample, Indicates the measured thickness value; Calculate the thickness value w and the measured thickness value If |e|<3σ, then the measured The measured thickness value is taken as the actual thickness value of the discrete point; if it is not satisfied, the radius of the neighborhood K is reduced, and the steps are repeated to establish the K neighborhood of the discrete point, and the measured thickness set and measured thickness value of m random samples in the K neighborhood are obtained until |e|<3σ is satisfied; The outer surface coordinates are corrected according to the normal vectors of the discrete points and the actual thickness values ​​to obtain the inner surface coordinates of the discrete points.

9. The method for measuring the inner surface of a large aspect ratio composite tubular thin-walled component according to claim 8, characterized in that: The method of obtaining a measured thickness set and measured thickness values ​​of m random samples in a K neighborhood includes the following steps: Randomly determine m random sampling points in the K neighborhood; Selecting the i-th random sampling point from the m random samples as a detection point; Measuring the thickness value at the i-th random sampling point n times by a thickness measuring device to obtain n measured thickness values ​​of the i-th random sampling point; Screening out distorted values ​​from the n measured thickness values, and calculating the calculated thickness value of the random sampling point by using the screened measured thickness values; Repeating the selection of the i-th random sampling point as the detection point among the m random samples until the calculated thickness values ​​of all random sampling points are obtained; A measured thickness set and a measured thickness value are obtained according to the calculated thickness value of each of the random sampling points.

10. The method for measuring the inner surface of a composite material tubular thin-walled part with a large aspect ratio according to claim 9, characterized in that: The calculated thickness value satisfies the formula Where D i，j represents the thickness value obtained by the jth measurement of the ith sample position, l represents the number of distortion values; the measured thickness value is the mean of the measured thickness set.

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