Automatic measurement device and identification and evaluation method for surface defects of cylindrical inner wall

Abstract

The invention discloses a cylindrical inner wall surface defect automatic measuring device and an identification and evaluation method. The device comprises a measuring unit, a supporting platform, a motion platform, a lengthening shaft and a control system. The measuring unit comprises one or more groups of laser profile sensors, is carried at the tail end of the lengthened shaft and is used for measuring the morphology data of the surface of the inner wall of a measured workpiece, the measuring unit is connected with the motion platform through the lengthened shaft, and the supporting platform is a V-shaped supporting platform and is used for placing the measured workpiece; the motion platform comprises an X-axis linear motion platform, a Z-axis linear motion platform and a rotary shaft motion platform; the measuring unit can realize horizontal scanning measurement, rotary scanning measurement and adjustment of a measuring range through the motion of the motion platform; and the control system is used for performing closed-loop feedback control on the X-axis linear motion platform, the Z-axis linear motion platform and the rotating shaft motion platform. According to the invention, the surface defects of the cylindrical inner wall can be automatically measured, identified and evaluated with high precision and high efficiency.

Description

Technical Field

[0001] The invention belongs to the field of geometric precision measurement, and in particular relates to an automatic measuring device for cylindrical inner wall surface defects and an identification and evaluation method. Background Art

[0002] Large cylindrical parts, such as rocket launchers, are widely used in defense industry, aerospace and other fields, and the inner wall is mostly made of black composite materials. Due to specific application requirements, large rocket launcher-shaped parts have the characteristics of narrow openings on both sides or one side, large inner wall diameter, and black inner wall. The three-dimensional measurement of its aperture and other dimensions and inner surface defects is difficult.

[0003] At present, the detection of deep hole size and inner wall surface morphology can be mainly divided into two directions: contact measurement and non-contact measurement. For contact measurement represented by internal diameter micrometers, coordinate measuring machines, etc., the measurement data is discrete points, the data volume is small, the measurement efficiency is low, and the measuring head cannot penetrate deep into the barrel. In terms of non-contact measurement, non-optical measurement methods such as eddy current method and ultrasonic method have certain requirements on the material and thickness of the measurement object, and cannot meet the measurement requirements of the inner wall surface morphology of the barrel; the camera measurement method is affected by the dim environment inside the barrel, and it is impossible to obtain a clear measurement image, and the depth information cannot be measured. Therefore, there is currently a lack of effective inner wall surface defect measurement devices for large shells with narrow openings, which are typically represented by barrel parts. Summary of the invention

[0004] The purpose of the present invention is to provide an automatic measuring device and identification and evaluation method for cylindrical inner wall surface defects, which can realize automatic measurement, identification and evaluation of cylindrical inner wall surface defects with high precision and efficiency.

[0005] In order to achieve the above-mentioned object, one aspect of the present invention provides an automatic measuring device for cylindrical inner wall surface defects, comprising a measuring unit, a supporting platform, a moving platform, an extended shaft and a control system;

[0006] The measuring unit includes one or more groups of laser profile sensors, which are mounted at the end of the extension shaft and are used to measure the topography data of the inner wall surface of the workpiece to be measured. The measuring unit is connected to the motion platform through the extension shaft. The support platform is a V-shaped support platform for placing the workpiece to be measured.

[0007] The motion platform includes an X-axis linear motion platform, a Z-axis linear motion platform and a rotary axis motion platform, and the measuring unit can realize horizontal scanning measurement through the horizontal movement of the X-axis linear motion platform, realize rotary scanning measurement through the rotation of the rotary axis motion platform, and adjust the measurement range through the vertical movement of the Z-axis linear motion platform;

[0008] The control system is used to perform closed-loop feedback control on the X-axis linear motion platform, the Z-axis linear motion platform and the rotary axis motion platform.

[0009] Preferably, the extended shaft is a hollow structure, and an extended shaft deflection monitoring system is arranged on the central axis of the extended shaft. The extended shaft deflection monitoring system is used to collect the deformation of the extended shaft and feed it back to the Z-axis linear motion platform, so as to compensate for the error caused by the deflection change of the extended shaft in real time.

[0010] Preferably, the motion platform also includes a linear grating, a grating code disk and a three-way photoelectric detection axial positioner, wherein there are two linear gratings, which are respectively arranged on the X-axis linear motion platform and the Z-axis linear motion platform for measuring linear displacement; the grating code disk is arranged on the rotary axis motion platform for measuring the rotational angular position; the three-way photoelectric detection axial positioner is used to realize the alignment and zeroing of the X-axis, Z-axis and rotary axis of the motion platform.

[0011] Preferably, the device further comprises an auxiliary support structure, and the auxiliary support structure is used for auxiliary supporting and protecting the extension shaft.

[0012] Another aspect of the present invention provides a method for identifying and evaluating surface defects of a cylindrical inner wall, which uses the above-mentioned device to measure surface defects of the cylindrical inner wall, and identifies and evaluates surface defects of the cylindrical inner wall based on the measured data, comprising:

[0013] A measuring step, using the measuring device to measure the surface defects of the cylindrical inner wall to obtain measurement data;

[0014] The measurement data preprocessing step uses collaborative filtering to remove spike-like point cloud noise in the measurement data;

[0015] In the data stitching step, the moving distance and direction of the moving platform are used to perform rough registration of the point cloud, and then the ICP registration algorithm is used to perform fine registration of the point cloud to obtain complete measurement data of the inner wall surface;

[0016] Defect recognition step: segment the point cloud data into supervoxels according to the normal vector angle and spatial distance of the measured data; determine the angle between the center line vector of adjacent supervoxels and the normal vector and the cross product of the normal vector of adjacent supervoxels as the basis for distinguishing concavity and convexity, and record the supervoxel adjacency graph; perform rough segmentation based on Gaussian curvature and mean curvature to obtain the point cloud of preliminary concave-convex defects, generate multiple initial seed points with the centroid of each defect point cloud, and use the region growing algorithm to cluster the regions with the same concavity and convexity to complete the identification, positioning and segmentation of defects;

[0017] In the defect evaluation step, the directed bounding box of the defect point cloud is calculated to obtain the length and width parameters of the defect, the defect point cloud is reconstructed, and the difference between the ideal surface point after defect reconstruction and the actual surface point is used as the depth value of the defect.

[0018] According to the automatic measuring device and identification and evaluation method of cylindrical inner wall surface defects of the above aspects of the present invention, automatic measurement, identification and evaluation of cylindrical inner wall surface defects can be achieved with high accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0020] Figure 1 It is a schematic structural diagram of an automatic measuring device for cylindrical inner wall surface defects according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] The embodiment of the present invention provides an automatic measuring device for cylindrical inner wall surface defects. Figure 1 FIG. 1 is a schematic diagram of the structure of an automatic measuring device for cylindrical inner wall surface defects according to an embodiment of the present invention. Figure 1 As shown, the automatic measuring device for cylindrical inner wall surface defects according to the embodiment of the present invention includes a measuring unit 2, a supporting platform 3, a moving platform, an extension shaft 7, an auxiliary supporting structure 8 and a control system 10.

[0023] The measuring unit 2 includes one or more groups of laser profile sensors, which are mounted at the end of the extension shaft 7 and are used to measure the morphological data of the inner wall surface of the workpiece 1 to be measured. The laser profile sensor is a point, line or surface laser profile sensor. The support platform 3 is a V-shaped support platform, which is used to place the workpiece 1 to be measured to ensure the accurate positioning of the measurement position of the large shell and the stability and reliability of the measurement work. The motion platform includes an X-axis linear motion platform 4, a Z-axis linear motion platform 6 and a rotary axis motion platform 5, wherein the X-axis linear motion platform 4 is a horizontal motion platform and the Z-axis linear motion platform 6 is a vertical motion platform. The auxiliary support structure 8 is used to provide auxiliary support and protection for the extension shaft. The control system 10 is used to perform closed-loop feedback control on the X-axis linear motion platform 4, the Z-axis linear motion platform 6 and the rotary axis motion platform 5. The control system 10 is, for example, a computer.

[0024] The measuring unit 2 is connected to the motion platform via the extension shaft 7. The measuring unit 2 can add multiple groups of different types of point, line or surface laser profile sensors through space optimization layout to meet the measurement requirements of different diameter ranges. The Z-axis linear motion platform 6 moves the extension shaft 7 to move along the axis normal direction of the measured workpiece 1, thereby increasing the measurement range of the device.

[0025] The extended shaft 7 is a hollow structure, and the extended shaft deflection monitoring system, data cables, power cables, etc. are arranged on the central axis of the extended shaft 7. By routing all cables from the hollow center of the extended shaft 7, the cable clutter and entanglement during rotation measurement can be prevented, and space can be saved at the same time. The extended shaft 7 deflection monitoring system can collect the deformation of the extended shaft 7 and feed it back to the Z-axis linear motion platform 6 to compensate for the error caused by the change of the extended shaft deflection in real time.

[0026] The measuring unit 2 can complete horizontal, vertical and rotational motions through the motion platform; the X-axis linear motion platform 4, the Z-axis linear motion platform 6 and the rotary axis motion platform 5 are closed-loop feedback motion platforms, and the motion platform also includes linear gratings, grating code disks, three-way photoelectric detection axial positioners 9 and other components, which can achieve precise motion positioning. Among them, the linear gratings are respectively arranged on the X-axis linear motion platform 4 and the Z-axis linear motion platform 6 for accurately measuring the linear displacement; the grating code disk is arranged on the rotary axis motion platform 5 for accurately measuring the rotation angle position; the three-way photoelectric detection axial positioner 9 is respectively installed near the three-axis gratings for axial zero return. Before each measurement, the X-axis, Z-axis and rotary axis of the motion platform are aligned and zeroed by the three-way photoelectric detection axial positioner 9, thereby completing the calibration of the initial position of the measuring unit 2 to complete the unification of the measurement coordinate system.

[0027] The embodiment of the present invention also provides a method for identifying and evaluating the surface defects of a cylindrical inner wall, which uses the above-mentioned measuring device to measure the surface defects of the cylindrical inner wall, and identifies and evaluates the surface defects of the cylindrical inner wall according to the measured data. The method includes a measuring step, a measurement data preprocessing step, a data splicing step, a defect identification step, and a defect evaluation step.

[0028] In the measuring step, the measuring device is used to measure the surface defects of the cylindrical inner wall to obtain measurement data, wherein the measuring method includes horizontal scanning measurement, rotational scanning measurement or mixed measurement. Specifically, the measuring unit can meet the appropriate measurement range by moving up and down (vertical movement) of the Z axis, and a single scanning measurement in the horizontal direction of the cylinder can be completed by horizontal movement (X axis) measurement. Since the area inside the cylinder is large and a single horizontal movement measurement cannot complete the measurement of the entire surface morphology of the cylinder wall, and the cylindrical object to be measured is heavy and cannot be rotated, a horizontal scanning measurement can be performed first and then a rotational scanning measurement, or a horizontal scanning measurement can be performed while performing a rotational scanning measurement, thereby forming a mixed measurement.

[0029] In the measurement data preprocessing step, the inner wall surface measurement data is read and stored in real time, and the spike-shaped point cloud noise in the measurement data is removed by collaborative filtering.

[0030] In the data stitching step, the measurement data obtained by multiple scans are stitched together. The point cloud is roughly aligned by recording the movement distance and direction of the motion platform, and then the point cloud is precisely aligned by a fast and robust ICP (Iterative Closest Point) alignment algorithm, thereby completing the alignment of multi-view point clouds and obtaining complete measurement data of the inner wall surface.

[0031] In the defect identification step, the point cloud data is first divided into supervoxels according to the normal vector angle and spatial distance of the measured data; the angle between the center line vector of adjacent supervoxels and the normal vector and the cross product of the normal vector of the adjacent supervoxels are determined as the basis for distinguishing the concavity and convexity, and the supervoxel adjacency graph is recorded; the point cloud is roughly segmented based on Gaussian curvature and mean curvature to obtain a point cloud of preliminary concave-convex defects, and multiple initial seed points are generated with the centroid of each defect point cloud. The region growing algorithm is used to cluster the regions with the same concavity and convexity, and the identification, positioning and segmentation of defects such as slits, cracks, grooves, steps, blind holes, etc. are completed. Different defect types are displayed with color differences to assist in determining the defect position and size, and the defect data is stored in sequence.

[0032] In the defect evaluation step, geometric parameters such as length, width and depth of the defect are quantified. The length and width of the defect are the defect point cloud obtained by segmentation. The directed bounding box of the point cloud is calculated to obtain the length and width parameters of the defect, which are then quantified by surface reconstruction. The depth value of the defect is the difference between the ideal surface point and the actual surface point after defect reconstruction.

[0033] To summarize, the automatic measuring device and identification and evaluation method for cylindrical inner wall surface defects of the embodiments of the present invention utilize a line laser profile sensor to measure in the horizontal, vertical and rotational directions, and obtain measurement data of the inner wall surface of a large shell through real-time closed-loop feedback compensation, and then perform data preprocessing, data splicing, defect identification segmentation and evaluation on the measurement data to complete the automatic identification and evaluation of the inner wall surface defects of the workpiece.

[0034] The cylindrical inner wall surface defect automatic measuring device and identification and evaluation method according to the embodiment of the present invention have the following beneficial effects:

[0035] 1. Aiming at the problem of narrow opening of tubular parts, the present invention utilizes a two-dimensional moving and rotating mechanism and relies on the accuracy and spatial volume advantages of the line laser profile sensor to achieve high-precision and high-efficiency scanning measurement, thus solving the problems of difficulty in in-depth measurement of the black surface of the inner wall of a tube with a narrow opening, difficulty in shape measurement due to black light absorption, and difficulty in locating and quantifying the position of surface defects.

[0036] 2. In order to solve the problems that the defect positions in the measured point cloud are difficult to identify and locate, and the performance of the region growing algorithm depends on the seed points, the present invention first performs an initial segmentation of the measured point cloud based on Gaussian curvature and mean curvature, and then uses the centroid of the obtained concave and convex area as the seed point for region growth, so that the defect segmentation algorithm can maintain good boundary properties and regional connectivity, reducing the difficulty of parameter adjustment.

[0037] 3. Compared with the prior art, the non-contact measurement method based on line laser measurement of the present invention has high accuracy, high efficiency, and is less affected by the environment, making it easier to process and evaluate data.

[0038] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An automatic measuring device for cylindrical inner wall surface defects, characterized in that: It includes measuring unit, supporting platform, motion platform, extension axis and control system; The measuring unit includes one or more groups of laser profile sensors, which are mounted at the end of the extension shaft and are used to measure the topography data of the inner wall surface of the workpiece to be measured. The measuring unit is connected to the motion platform through the extension shaft. The support platform is a V-shaped support platform for placing the workpiece to be measured. The motion platform includes an X-axis linear motion platform, a Z-axis linear motion platform and a rotary axis motion platform, and the measuring unit can realize horizontal scanning measurement through the horizontal movement of the X-axis linear motion platform, realize rotary scanning measurement through the rotation of the rotary axis motion platform, and adjust the measurement range through the vertical movement of the Z-axis linear motion platform; The control system is used to perform closed-loop feedback control on the X-axis linear motion platform, the Z-axis linear motion platform and the rotary axis motion platform.

2. The device according to claim 1, characterized in that The extended shaft is a hollow structure, and an extended shaft deflection monitoring system is arranged on the central axis of the extended shaft. The extended shaft deflection monitoring system is used to collect the deformation of the extended shaft and feed it back to the Z-axis linear motion platform, so as to compensate for the error caused by the change of the extended shaft deflection in real time.

3. The device according to claim 1 or 2, characterized in that: The motion platform also includes a linear grating, a grating code disk and a three-way photoelectric detection axial positioner, wherein there are two linear gratings, which are respectively arranged on the X-axis linear motion platform and the Z-axis linear motion platform for measuring linear displacement; the grating code disk is arranged on the rotary axis motion platform for measuring the rotation angle position; the three-way photoelectric detection axial positioner is used to realize the alignment and zeroing of the X-axis, Z-axis and rotary axis of the motion platform.

4. The device according to claim 1 or 2, characterized in that: It also includes an auxiliary support structure, which is used to provide auxiliary support and protection for the extended shaft.

5. A method for identifying and evaluating surface defects of a cylindrical inner wall, characterized in that: Using the device described in any one of claims 1 to 4 to measure the surface defects of the cylindrical inner wall, and identifying and evaluating the surface defects of the cylindrical inner wall according to the measurement data, comprising: A measuring step, using the measuring device to measure the surface defects of the cylindrical inner wall to obtain measurement data; The measurement data preprocessing step uses collaborative filtering to remove spike-like point cloud noise in the measurement data; In the data stitching step, the moving distance and direction of the moving platform are used to perform rough registration of the point cloud, and then the ICP registration algorithm is used to perform fine registration of the point cloud to obtain complete measurement data of the inner wall surface; Defect recognition step: segment the point cloud data into supervoxels according to the normal vector angle and spatial distance of the measured data; determine the angle between the center line vector of adjacent supervoxels and the normal vector and the cross product of the normal vector of adjacent supervoxels as the basis for distinguishing concavity and convexity, and record the supervoxel adjacency graph; perform rough segmentation based on Gaussian curvature and mean curvature to obtain the point cloud of preliminary concave-convex defects, generate multiple initial seed points with the centroid of each defect point cloud, and use the region growing algorithm to cluster the regions with the same concavity and convexity to complete the identification, positioning and segmentation of defects; In the defect evaluation step, the directed bounding box of the defect point cloud is calculated to obtain the length and width parameters of the defect, the defect point cloud is reconstructed, and the difference between the ideal surface point after defect reconstruction and the actual surface point is used as the depth value of the defect.

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