Model-free component ultrasonic nondestructive testing trajectory planning method

Abstract

The invention discloses a model-free component ultrasonic non-destructive testing trajectory planning method, which comprises the following steps: acquiring point cloud information of all surfaces of a detected component through a scanning means, and preprocessing the point cloud information in space to enable the mass center of the detected component to be horizontally aligned; the method comprises the following steps: pre-planning a detection path of a detected component in a point cloud file, extracting point clouds through which a preset detection path passes, performing high-order curve fitting in software, eliminating outliers, and performing fitting to generate a surface scanning path line of the detected component; dispersing a surface scanning path line of the measured piece according to parameters such as scanning intervals set according to preset scanning parameters, extending along a normal line of a sampling point on a fitting curve to obtain a probe position corresponding to the sampling point, taking the probe position as a mechanical arm flange motion coordinate for clamping the probe, generating a mechanical arm flange motion and mechanical arm pose matrix, and determining the position of the measured piece according to the mechanical arm flange motion and mechanical arm pose matrix. And the scanning track of the mechanical arm is generated. According to the invention, the mechanical arm clamps the probe to automatically detect the model-free component.

Description

Technical Field

[0001] The invention relates to a trajectory planning method for non-destructive testing of a model-free component, and in particular to a trajectory planning method for an ultrasonic testing system including a multi-degree-of-freedom mechanical arm, and belongs to the field of non-destructive testing. Background Art

[0002] The rapid development of modern aviation industry has increasingly increased the requirements for the performance and appearance of complex curved surface workpieces. The detection and characterization of internal defects of complex morphology components has promoted the rapid development of ultrasonic non-destructive array testing technology. A large number of complex curved surface components made of high-strength and lightweight alloys are used in aerospace propulsion systems and load-bearing structures. In the current aerospace industry, there are many flight missions and long flight times, which puts higher requirements on the fatigue life of major components including engines. Due to the cumbersome and expensive processing process of complex curved surface workpieces, they are widely used in important load-bearing structures and core components of power systems, such as the upper wing skin, aircraft shell, engine blades and other structures mainly used in the aerospace field. The detection complexity of aircraft engine blades is relatively high, and it is difficult to effectively detect and quantify blade defects. Fatigue, cracks and corrosion are several common and important defects that aircraft engine blades may produce. At present, non-destructive testing methods are mainly used for defects in aircraft engine blades in service.

[0003] Ultrasonic non-destructive testing (UNDT) is an important detection method in non-destructive testing. It is widely used in various fields of detection because of its advantages such as low detection cost, wide detection objects, high sensitivity, and harmlessness to the human body. Ultrasonic imaging technology is based on the directivity, transmission and reflection characteristics of ultrasonic waves. It characterizes the acoustic characteristics of the tested object according to the time difference and strength of the received signal, and indirectly realizes internal imaging visualization through post-processing. The directivity of ultrasonic waves requires a strict definition of the incident angle of the detection transducer. Especially for complex surfaces, it is necessary to ensure that the position of the transducer is aligned with the normal vector direction of the measured surface to obtain the best detection effect. In order to ensure that the position of the ultrasonic transducer is perpendicular to the normal vector direction of the measured surface, high requirements are placed on the spatial motion ability of the clamping transducer. Traditional three-axis and five-axis motion mechanisms are usually used for the detection of plate-like components. When a multi-degree-of-freedom robot carries an ultrasonic transducer to complete automated detection tasks, it can ensure that the ultrasonic transducer is perpendicular to the surface of the workpiece and the spacing is stable, but the robot trajectory precision is required to be high. The six-degree-of-freedom industrial robot has high-precision repeated positioning capability and flexible posture transformation capability. The six-degree-of-freedom industrial robot is selected as the main body of the motion structure, and the ultrasonic non-destructive testing of the tested component is performed by clamping the ultrasonic probe. The multi-degree-of-freedom robot is applied to the non-destructive testing system, and the flexibility and detection range of the multi-degree-of-freedom are well utilized. However, for the non-destructive testing system containing the multi-degree-of-freedom robot, the path planning of the robot has always been a key content. Most of the existing detection systems at home and abroad require the detection component model diagram to perform path planning. There is no good detection method for components without model diagrams. In view of the current technical status, a trajectory planning algorithm for the six-degree-of-freedom robot is needed to control the robot arm to follow the contour of the tested surface during the detection, so as to realize high-precision ultrasonic non-destructive testing of model-free complex curved surface components. Summary of the invention

[0004] Aiming at the trajectory control of ultrasonic nondestructive testing of model-free components, the present invention innovatively proposes a method for planning the motion trajectory of a robot arm through a spatial point cloud to achieve high-precision scanning.

[0005] The present invention provides a method for realizing high-precision motion path planning in an ultrasonic detection system including a multi-degree-of-freedom mechanical arm. The surface point cloud information of the tested environment and components is obtained by using a data scanning method, and the point cloud file is aligned in space so that it is in the same world coordinate system as the mechanical arm. Then, according to the detection path requirements, the point cloud information of the components passing on the required path is extracted, and high-order curve fitting is performed in space to realize the generation of the surface route of the tested part. Then, according to the detection plan, the detection sampling points are discretized on the fitted curve to obtain the spatial coordinates of the discrete points, and the normals of the discrete points on the fitting curve are extended to the required distance for detection to obtain the spatial coordinates of the flange of the six-degree-of-freedom mechanical arm; finally, the spatial coordinates of all sampling points on the single-line scanning path are extended to obtain the path point information of the flange of the six-degree-of-freedom mechanical arm during the detection process, so as to obtain the high-precision path planning of the mechanical arm scanning path.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is to use laser reverse engineering technology to obtain the surface point cloud information of the component to be tested, then import the point cloud processing software to perform spatial correction on the component point cloud, pre-plan the path according to the actual detection requirements, import the point cloud file into MATLAB for data processing, perform high-order curve fitting on the pre-planned path point cloud to obtain a high-precision surface path line, and then obtain each fitting scanning path line and the sampling points on each line in turn according to the scanning interval and step distance of the automated detection plan, extend the normal of the sampling point to obtain the mechanical arm flange coordinates corresponding to the sampling point, connect the flange coordinates of all sampling points in space to obtain the mechanical arm scanning path, and finally use a six-degree-of-freedom mechanical arm to clamp the ultrasonic probe for ultrasonic detection according to the planned path.

[0007] A trajectory planning method for ultrasonic nondestructive testing of model-free components uses laser reverse engineering technology to obtain point cloud files, and performs multi-degree-of-freedom trajectory planning based on the point cloud files. The specific implementation steps of the method include:

[0008] S1. Obtain the surface point cloud file of the component to be tested, and perform spatial correction on the point cloud file to ensure that the center point of the tested component is in a horizontal position in space.

[0009] S2. Pre-plan the ultrasonic detection path, extract the point cloud passing through the pre-planned path, perform high-order curve fitting on it, and according to the pre-planned detection parameters, fit the component surface detection path corresponding to each scanning path in turn to obtain the surface detection path of the component to be tested.

[0010] S3. All sampling points are extended in the normal direction on the fitting curve to obtain the trajectory coordinates of the robot flange and the robot posture matrix during detection, and all flange space motion points are connected with the robot posture matrix to finally guide the multi-degree-of-freedom robot through the detection path.

[0011] In step S1, for components with complex morphology, manual detection methods are often used in ultrasonic testing. For components without models, commonly used automated testing equipment needs to plan the detection path through the model of the test piece. Therefore, the test piece is laser scanned before detection to obtain its point cloud file. Then import its point cloud file into the point cloud processing software. Obtain the center of mass of the component in space, adjust the point cloud in the point cloud processing software, align its center of mass with the origin of space, and ensure that the point cloud coordinates are consistent with the actual detection position when the component is placed horizontally / vertically.

[0012] In step S2, according to the actual detection requirements, the point cloud file is first pre-planned for detection, and the scanning path is planned according to the "bow" line commonly used in ultrasonic C scanning, and the scanning interval and step distance in ultrasonic detection are set. According to its step distance, the point cloud of its actual detection path is extracted, and a high-order curve fitting is performed for the point cloud involved in each path, and the points with excessive errors are deleted to fit the high-precision curve to obtain the actual surface detection path of the component under test.

[0013] In step S3, according to the pre-planned path and pre-detection parameters, all pre-set detection sampling points are separated, and their spatial coordinate points on the fitting curve are obtained, and they are extended along the normal of the fitting curve. The extension distance includes the water distance of the water spray ultrasonic detection and the length of the ultrasonic probe fixture, and the multi-degree-of-freedom manipulator flange coordinates in space are obtained. The manipulator motion matrix is ​​derived based on the flange coordinates corresponding to all sampling points to obtain the position and posture of the manipulator to each sampling point, and the manipulator position and posture corresponding to all sampling points are connected to obtain the manipulator motion trajectory, that is, the detection path.

[0014] Compared with the prior art, the present invention has the following gain effects.

[0015] 1. The present invention uses point cloud information files, selects corresponding point clouds by presetting paths in the point cloud files, and fits surface scanning lines through point cloud information, thereby realizing scanning path planning for complex morphology components in ultrasonic non-destructive testing. In current technology, traditional handheld devices are usually used to detect complex morphology components. The present invention provides a new detection path planning technology in terms of automated and intelligent non-destructive testing.

[0016] 2. Based on the scanning path of the point cloud file component, the present invention combines the multi-degree-of-freedom robot arm in actual application to perform motion trajectory planning, thereby realizing the automated detection of model-free components. In the current technology, the non-destructive testing system for automated detection requires a model of the test piece to perform trajectory planning. The present invention can realize the detection trajectory planning of model-free components in the multi-degree-of-freedom detection system, breaking through the current bottleneck of being unable to solve the detection of model-free components.

[0017] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. 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 should fall within the scope of protection of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a point cloud file image obtained by an embodiment of the present invention;

[0019] Figure 2 It is a schematic diagram of high-order path fitting of the present invention;

[0020] Figure 3 It is a schematic diagram of the trajectory matrix of the robot arm of the present invention; DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] At present, new practical applications of components with complex morphologies are increasing. Micro-damages often occur on the surface and inside of components during production and practical applications. However, due to the service scenarios of the components, their detection often requires the use of non-destructive testing techniques.

[0023] The embodiment of the present invention provides a trajectory planning method for non-destructive testing of model-free components. First, a point cloud scanning file of the component to be tested is obtained by using laser reverse engineering technology, which contains information on the outer surface of the component to be tested; secondly, the point cloud scanning file is imported into the point cloud processing software, and its spatial posture is adjusted so that its center of mass is aligned with the horizontal plane; then, the scanning path is pre-planned for the point cloud file, and the point cloud through which the planned path passes is selected, and high-order curve fitting is performed to generate a high-precision surface path line of the component to be tested; finally, according to the scanning parameters of the path pre-planning, the surface path line generated by discrete fitting is extended according to its normal extension line to obtain the robot arm flange coordinate matrix corresponding to each scanning point, and all flange coordinate matrices are connected to obtain the complete detection trajectory of the model-free component.

[0024] The equipment used in the embodiment of the present invention is a multi-degree-of-freedom ultrasonic non-destructive testing system, which includes a multi-degree-of-freedom mechanical arm with an ultrasonic probe fixture, an ultrasonic pulse excitation / receiving instrument, a 25MHz ultrasonic immersion probe, a digital acquisition card, and an industrial computer responsible for system control. In the actual detection of this system, the industrial computer is used to control the mechanical arm, and the ultrasonic probe fixture is used to clamp the immersion probe. The water spray structure is set in the fixture to adopt ultrasonic water spray coupling to perform ultrasonic non-destructive testing on the component under test, wherein the ultrasonic signal excitation and reception adopts an ultrasonic pulse excitation / receiving instrument, and the echo signal is collected by a digital acquisition card and fed back to the industrial computer. Finally, the collected data is analyzed and processed to realize ultrasonic non-destructive testing of the component under test. The specific implementation steps are as follows:

[0025] S1. Obtain the surface point cloud file of the component under test, and perform spatial correction on the point cloud file. The corrected point cloud file is shown as follows: Figure 1 As shown, ensure that the center point of the measured component is in a horizontal position in space. In this embodiment, a handheld laser scanner is used to obtain the point cloud file, which can scan the measured component with an accuracy of 0.05mm and generate a point cloud file in ply format. The retired blades on the aerospace engine are scanned. The blades are 4.5CM long, 2.2CM wide and 7CM high. A handheld laser scanner is used to scan the entire blade, and the information on each surface is converted into point cloud coordinates. The display of the point cloud file and subsequent calculation processing are implemented in MATLAB.

[0026] S2. Process the point cloud file in MATLAB, pre-plan the ultrasonic detection path, plan the scanning path according to the "bow" line commonly used in ultrasonic C scanning, set the measured range and the step interval and route during scanning. Then extract the scanned point cloud in the measured path, process the point cloud of each scanning path separately, and perform curve fitting on it. The fitting process is also processed in MATLAB. The large fluctuation of single point error may cause the fitting screenshot as shown below. Figure 2 As shown, in the fitting, high-order Gaussian fitting and Fourier fitting are usually used according to the actual situation. In this embodiment, 2nd-order Fourier fitting is used. Figure 2 The curve fitting equation shown in the figure is: f(x)=5.501-6.111*cos(x*0.07474)-0.3124*sin(x*0.07474)+0.5684*cos(2*x*0.07474)+0.2987*sin(2*x*0.07474). The goodness of fit parameters are: SSE: 2464; R-square: 0.7575; RMSE: 1.559

[0027] S3. Segment the path line generated after fitting according to the pre-designed scanning parameters to obtain the actual measured sampling points on the surface of the component under test, and extend the sampling points in the reverse direction according to the normal of the curve after fitting, that is, extend the normal to the water column in the actual test; obtain the position of the ultrasonic probe during the actual test, that is, the coordinate position of the robot flange. Use all the robot flange coordinates under the preset test path, and write the path file for the robot according to the robot posture transformation matrix to obtain the actual test path file. A partial screenshot of the path file generated in the embodiment is shown in the figure. Figure 3 As shown, trajectory planning for a multi-degree-of-freedom ultrasonic detection system is achieved.

[0028] According to the curve fitting method and the characteristics of the point cloud file, the present invention proposes an ultrasonic nondestructive testing path planning method for model-free components in the scanning preset stage before ultrasonic nondestructive testing, so as to ensure that the detection system can set a high-precision detection path when detecting model-free components, and ensure that the ultrasonic wave can be incident vertically on the surface of the tested component in real time during the detection, receive high-quality ultrasonic signals, and obtain the surface and internal acoustic information of the tested component. According to the robot arm posture description and coordinate transformation matrix, after obtaining the performance path information of the model-free tested component, the present invention discretizes the sampling points and extends the normal line to obtain the robot arm flange coordinates during actual detection. All flange coordinates are connected in sequence to obtain the posture transformation matrix in the robot arm detection, so as to realize the automated ultrasonic nondestructive testing of model-free components.

[0029] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A trajectory planning method for nondestructive testing of model-free components. It is characterized in that The method of using a robotic arm to clamp an ultrasonic probe to perform automated ultrasonic testing on a model-free component includes the following steps: S1. Obtain the surface point cloud file of the component to be tested, and perform spatial correction on the point cloud file to ensure that the centroid of the component to be tested is in a horizontal position in space; S2. Pre-plan the ultrasonic detection path, extract the point cloud passing through the pre-planned path, perform high-order curve fitting on it, and fit the component surface detection path corresponding to each scanning path in turn according to the pre-planned detection parameters to obtain the surface detection path of the component to be tested; S3. All sampling points are extended in the normal direction on the fitting curve to obtain the trajectory coordinates of the robot flange and the robot pose matrix during detection, and all flange space motion points are connected with the robot pose matrix to finally guide the multi-degree-of-freedom robot detection path planning.

2. The trajectory planning method for non-destructive testing of model-free components according to claim 1, Features: The scanning equipment is used to obtain the surface point cloud information of the measured component, and the point cloud file is spatially corrected to ensure that its center of mass is in a horizontal position in space; the point cloud file includes scanning parameters such as scanning range, scanning interval, step distance, and scanning direction, and the point cloud data passing through the preset path is re-extracted.

3. The trajectory planning method for non-destructive testing of model-free components according to claim 2, Features: The surface point cloud on each scanning path is extracted in turn, and high-order curve fitting is performed in space, wherein some points with excessive errors due to scanning accuracy or selection accuracy are removed, and the fitted high-order curve is the scanning path line on the surface of the measured component.

4. The trajectory planning method for non-destructive testing of model-free components according to claim 3, Features: The surface path line of the model-free component to be measured is fitted in claim 3. According to the preset scanning parameters, all sampling points on the surface path line are discretized, and the normals of the sampling points are extended on the fitting curve in turn to obtain the position of the ultrasonic probe in the actual detection.

5. The trajectory planning method for non-destructive testing of model-free components according to claim 4, Features: After obtaining the ultrasonic probe positions corresponding to all sampling points in the preset scanning path, they are used as the spatial coordinates of the flange of the multi-degree-of-freedom robotic arm during the detection process to obtain the corresponding flange motion trajectory and the robotic arm posture matrix, which are used to guide the movement of the robotic arm and realize automated ultrasonic non-destructive testing trajectory planning for model-free components.

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