On-machine calibration method of flexible ultrasonic probe

Abstract

The invention provides an on-machine calibration method of a flexible ultrasonic probe, which belongs to the technical field of ultrasonic detection, abandons the current traditional limitation, introduces flexible length and angle deviation parameters, adopts a hemispherical shell calibration piece and a main shaft turntable type machine tool, establishes a reasonable mathematical calibration model, and realizes accurate calibration of probe parameters. According to the method, a mathematical model for flexible ultrasonic probe parameter calibration is established, and accurate calibration of flexible ultrasonic probe parameters is realized by utilizing optimization of a data point fitting target and a strategy. Although some other correction methods based on different principles or technologies may still exist in the field of ultrasonic probe calibration, the correction methods may not reach the level of the method in the aspects of universality, precision and the like, or other limitations and defects may exist in the implementation process. Therefore, the flexible ultrasonic probe calibration method has unique advantages and innovativeness, and is an effective and advanced technical scheme for solving the problem at present.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic testing technology, and in particular to an in-machine calibration method for a flexible ultrasonic probe. Background Technology

[0002] Ultrasonic thickness measurement is an important method widely used in industrial non-destructive testing. It calculates the thickness of a material by measuring the propagation time of ultrasonic waves within it. Traditional ultrasonic thickness measurement typically uses rigid ultrasonic probes. However, rigid probes are not well-suited for measuring the thickness of parts with complex surfaces. Therefore, flexible ultrasonic probes have been introduced into the thickness measurement field due to their ability to conform to the measurement surface.

[0003] In ultrasonic thickness measurement, ensuring the probe is perpendicular to the measurement surface is crucial for guaranteeing measurement accuracy. Therefore, precise probe calibration is necessary before measurement to enable automated measurement through planned measurement trajectories. However, existing calibration methods are primarily designed for rigid probes, lacking specific calibration techniques for flexible probes, resulting in calibration accuracy that falls short of the demands of high-precision thickness measurement.

[0004] Therefore, there is an urgent need in this field for a technical solution that can accurately calibrate the probe.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a technical solution that enables precise calibration of the probe.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] An in-machine calibration method for a flexible ultrasonic probe includes the following steps:

[0009] S1. Prepare a hemispherical shell calibration part with known thickness s and radius R and a step test block with known thickness f. Install the hemispherical shell calibration part on the turntable of the AB axis machine tool, with the center of the hemispherical shell calibration part coinciding with the center of the turntable. Install the flexible ultrasonic probe on the spindle of the AB axis machine tool and clamp the tool holder. Fix the step test block on the turntable of the AB axis machine tool, ensuring that the step test block is in close contact with the surface of the turntable.

[0010] S2. After completing the calibration system construction according to S1, control the movement of the machine tool spindle so that the probe is in perpendicular contact with the step block. Then control the machine tool spindle to descend a fixed distance each time. Record the distance between the transmitting signal wafer and the workpiece surface, i.e., the water distance d, and the signal return time t. Fix the A and B axes of the machine tool and control the movement of the X, Y, and Z axes. Use the maximum amplitude of the ultrasonic signal when perpendicular to the surface to find the position of the probe perpendicular to the surface. Record the coordinates of the X, Y, Z, A, and B axes and the signal return time t. Then obtain the measurement point data at different positions on the hemispherical shell by changing the A and B axes.

[0011] S3. Based on the linear fitting data obtained in S2, with the signal return time t as the abscissa and the water distance d as the ordinate, the slope k of the linear relationship is obtained using least squares linear fitting. Based on the spherical fitting data obtained in S2, the coordinates of measurement points at different distribution positions on the same sphere are obtained using the coordinate transformation formula around a fixed axis. The sum of the squares of the distances between the theoretical measurement point coordinates and the actual measurement point coordinates is used as the optimization objective. The multi-starting point local search method is used to solve the problem and obtain the calibration parameter, the distance L from the main axis to the transmitting wafer.

[0012] Optionally, the linear relationship between the water distance d and the signal return time t in step S2 is based on the characteristics of sound propagation. The distance d between the probe signal transmitting crystal and the surface of the measured workpiece is proportional to the signal return time t, i.e., d = kt, where k is a proportionality parameter.

[0013] Optionally, the method of changing the A and B axes to obtain different measurement points in step S2 involves fixing the A and Y axes after finding the vertical position in step S2, rotating the B axis by a fixed angle, slightly adjusting the X and Z axes, finding the position with the maximum signal, which is the position of the next measurement point, and then only changing the A axis to finally obtain the measurement point at the corresponding position on the sphere.

[0014] Optionally, in step S2, finding the vertical position is based on the principle of sound reflection. When the received ultrasonic signal is at its maximum, the probe is perpendicular to the measuring surface. Therefore, during calibration, the X, Y, Z, and A axes can be adjusted slightly. If the signal amplitude is at its maximum, this position is the perpendicular position between the probe and the measuring surface.

[0015] Optionally, the rotational coordinates (x0, y0, z0) in the machine tool coordinate system in step S3 are calculated using the following formula:

[0016]

[0017] Among them, (x B ,y B ,z B Let (a, b, c) be the coordinates before rotation, B be the angle of rotation of the B-axis of the machine tool, and (a, b, c) be the coordinates of the center of the rotary table. Let the transformation matrix be R. y.

[0018] Optionally, the optimization objective of the spherical fitting method in step S3 is the coordinates (x, y) of the theoretical measurement point. t ,y t ,z t Using the coordinates of the rotated sphere's center The coordinates of the actual measurement point (x) are obtained by coordinate transformation calculation of the angle along the A-axis. p ,y p ,z p The calculation formulas are obtained using the X, Y, and Z axis coordinates of the machine tool, calibration parameters L and k, signal return time t, and the angular coordinate transformation of the A-axis.

[0019]

[0020] in, Let O be the coordinates of the center of the sphere after rotation, (o x ,o y ,o z Let α and β be the coordinates of the center of the sphere before rotation, and α and β be the deviations between the probe installation angle and the ideal angle. If the probe is exactly along the principal axis, then α = 90° and β = 90°, thus obtaining the optimized target. The calculation formula is as follows:

[0021]

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The in-machine calibration method for the flexible ultrasonic probe of this invention exhibits significant advantages over traditional calibration methods. Current ultrasonic probe calibration is primarily based on rigid probe designs, such as Renshaw's calibration procedure, which achieves calibration by performing multi-longitude and multi-latitude measurements on the surface of a sphere or other geometric body. However, this method has the following limitations: First, because the flexible probe head undergoes some compression under measurement conditions, the probe length changes, and a calibration method for the probe's flexible length has not yet been developed; second, the calibration parameters are limited to positional parameters and do not involve angular parameters, making it difficult to meet the high-precision measurement requirements for probe attitude accuracy.

[0024] This invention overcomes the limitations of current traditional methods by introducing flexible length and angular deviation parameters, employing a hemispherical shell calibration component and a spindle rotary table type machine tool, and establishing a reasonable mathematical calibration model to achieve accurate calibration of probe parameters. Specifically, this invention has the following significant advantages:

[0025] High-precision parameter calibration: By using linear fitting (the relationship between water distance d and signal return time t) and spherical fitting (coordinate optimization under multi-axis motion), the probe's flexible length L and angular deviation parameters were calibrated simultaneously, solving the problem that traditional methods only calibrate position parameters and significantly improving thickness measurement accuracy.

[0026] Greater adaptability: By combining hemispherical shell calibration parts and stepped test blocks with AB-axis machine tools, complex surface conditions are simulated through multi-axis coordinated motion, which effectively solves the problem of dynamic changes in rod length caused by compression of flexible probes, and is suitable for measuring curved or irregularly shaped workpieces.

[0027] Regarding the flexible ultrasound probe calibration method of this invention, no other alternative solution has been found that can completely replace the purpose of this invention. The method of this invention achieves accurate calibration of the flexible ultrasound probe parameters by establishing a mathematical model for flexible ultrasound probe parameter calibration and optimizing the data point fitting target and strategy. Although there may be other calibration methods based on different principles or technologies in the field of ultrasound probe calibration, they may not reach the level of this invention in terms of universality and accuracy, or they may have other limitations and shortcomings in their implementation. Therefore, the flexible ultrasound probe calibration method of this invention has unique advantages and innovation, and is currently an effective and advanced technical solution to this problem. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. 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 effort.

[0029] Figure 1 This is a schematic diagram of the calibration method provided in an embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The purpose of this invention is to provide a technical solution that enables precise calibration of the probe.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1:

[0034] This embodiment provides an in-machine calibration method for a flexible ultrasonic probe, such as... Figure 1 As shown, the implementation steps are as follows: constructing a calibration system, collecting calibration data, and performing linear fitting and spherical fitting on the data respectively. The calibration system includes an AB-axis machine tool, a hemispherical calibration component mounted at the center of the AB-axis machine tool's rotary table, a stepped test block fixed on the rotary table, and a flexible ultrasonic probe mounted on the A-axis spindle. Collecting calibration data includes collecting linear fitting data and spherical fitting data. For linear fitting data, the water distance d and signal return time t are obtained through uniform movement of the machine tool spindle. For spherical fitting data, the perpendicular position of the probe to the measurement surface is determined by controlling the movement of the X, Y, Z, A, and B axes of the machine tool, obtaining calibration data for different measurement points on the hemispherical calibration component. Linear fitting is performed on the data, and the linear relationship between the water distance d and the signal return time t is obtained by least squares linear fitting. The calibration parameter k is obtained by spherical fitting of the data and coordinate transformation is used to transform the coordinates of the rotated spherical points to the same spherical surface. The optimization objective is to minimize the sum of the squared distances between the ideal measurement point position and the actual measurement point position. The multi-starting point local search algorithm is used to solve the problem and obtain the calibration parameter L.

[0035] Includes the following steps:

[0036] S1. Prepare a hemispherical shell calibration piece with known thickness s and radius R, and a stepped test block with known thickness f. Install the hemispherical shell calibration piece on the rotary table of the AB-axis machine tool, ensuring the center of the hemispherical shell calibration piece coincides with the center of the rotary table. Install the flexible ultrasonic probe on the spindle of the AB-axis machine tool and clamp the tool holder. Fix the stepped test block on the rotary table of the AB-axis machine tool, ensuring it is in close contact with the rotary table surface.

[0037] S2. After completing the calibration system construction based on S1, control the machine tool spindle movement to make the probe make perpendicular contact with the step block. Then, control the machine tool spindle to descend a fixed distance each time, and record the distance between the transmitting signal wafer and the workpiece surface (i.e., the water distance d) and the signal return time t. Fix the A and B axes of the machine tool, and control the movement of the X, Y, and Z axes. Use the maximum ultrasonic signal amplitude when perpendicular to the surface to find the position of the probe perpendicular to the surface, and record the X, Y, Z, A, and B axis coordinates and the signal return time t. Then, obtain the measurement point data at different positions on the hemispherical shell by changing the A and B axes.

[0038] S3. Based on the linear fitting data obtained in S2, with the signal return time t as the abscissa and the water distance d as the ordinate, the slope k of the linear relationship is obtained using least squares linear fitting. Based on the spherical fitting data obtained in S2, the coordinates of measurement points at different distribution positions on the same sphere are obtained using the coordinate transformation formula around a fixed axis. The sum of the squared distances between the theoretical and actual measurement point coordinates is used as the optimization objective, and a multi-starting-point local search method is used to solve for the calibration parameter, the distance L from the main axis to the transmitting wafer.

[0039] In one embodiment, the machine tool configuration, ultrasonic probe installation position, stepped test block placement position, and hemispherical shell calibration component installation position in step S1 are determined by the need to achieve hemispherical shell rotation. Therefore, the machine tool is a single-swing head and single-turntable configuration. The ultrasonic probe is installed on the swing head, and the hemispherical shell calibration component is installed on the center of the turntable. According to the principle that the measurement surface is perpendicular to the probe, the stepped block is fixed to the turntable surface to ensure that it is in close contact with the turntable surface.

[0040] In one embodiment, the method of changing the A and B axes to obtain different measurement points in step S2 involves finding the vertical position in step S2, fixing the A and Y axes, rotating the B axis by a fixed angle, slightly adjusting the X and Z axes, finding the position of maximum signal, which is the position of the next measurement point, and then only changing the A axis to finally obtain the measurement point at the corresponding position on the sphere.

[0041] In one embodiment, the process of finding the vertical position in step S2 is based on the principle of sound reflection. When the received ultrasonic signal is at its maximum, the probe is perpendicular to the measuring surface. Therefore, the X, Y, Z, and A axes can be adjusted slightly during calibration. If the signal amplitude is at its maximum, this position is the vertical position between the probe and the measuring surface.

[0042] In one embodiment, the rotational coordinates (x0, y0, z0) in the machine tool coordinate system in step S3 are calculated using the following formula:

[0043]

[0044] Among them, (x B ,y B ,z B Let (a, b, c) be the coordinates before rotation, B be the angle of rotation of the B-axis of the machine tool, and (a, b, c) be the coordinates of the center of the rotary table. Let the transformation matrix be R. y .

[0045] In one embodiment, the optimization objective of the spherical fitting method in step S3 is the coordinates (x, y) of the theoretically measured point. t ,y t ,z t Using the coordinates of the rotated sphere's center The coordinates of the actual measurement point (x) are obtained by coordinate transformation calculation of the angle along the A-axis. p ,y p ,z p The calculation formulas are obtained using the X, Y, and Z axis coordinates of the machine tool, calibration parameters L and k, signal return time t, and the angular coordinate transformation of the A-axis.

[0046]

[0047] in, Let O be the coordinates of the center of the sphere after rotation, (o x ,o y ,o z Let α and β be the coordinates of the center of the sphere before rotation, and α and β be the deviations between the probe installation angle and the ideal angle. If the probe is exactly along the principal axis, then α = 90° and β = 90°, thus obtaining the optimized target. The calculation formula is as follows:

[0048]

[0049] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0050] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An in-machine calibration method for a flexible ultrasonic probe, characterized in that, Includes the following steps: S1. Prepare a hemispherical shell calibration part with known thickness s and radius R and a step test block with known thickness f. Install the hemispherical shell calibration part on the turntable of the AB axis machine tool, with the center of the hemispherical shell calibration part coinciding with the center of the turntable. Install the flexible ultrasonic probe on the spindle of the AB axis machine tool and clamp the tool holder. Fix the step test block on the turntable of the AB axis machine tool, ensuring that the step test block is in close contact with the surface of the turntable. S2. After completing the calibration system construction according to S1, control the movement of the machine tool spindle so that the probe is in perpendicular contact with the step block. Then control the machine tool spindle to descend a fixed distance each time. Record the distance between the transmitting signal wafer and the workpiece surface, i.e., the water distance d, and the signal return time t. Fix the A and B axes of the machine tool and control the movement of the X, Y, and Z axes. Use the maximum amplitude of the ultrasonic signal when perpendicular to the surface to find the position of the probe perpendicular to the surface. Record the coordinates of the X, Y, Z, A, and B axes and the signal return time t. Then obtain the measurement point data at different positions on the hemispherical shell by changing the A and B axes. S3. Based on the linear fitting data obtained in S2, with the signal return time t as the abscissa and the water distance d as the ordinate, the slope k of the linear relationship is obtained using least squares linear fitting. Based on the spherical fitting data obtained in S2, the coordinates of measurement points at different distribution positions on the same sphere are obtained using the coordinate transformation formula around a fixed axis. The sum of the squares of the distances between the theoretical measurement point coordinates and the actual measurement point coordinates is used as the optimization objective. The multi-starting point local search method is used to solve the problem and obtain the calibration parameter, the distance L from the main axis to the transmitting wafer.

2. The in-machine calibration method for a flexible ultrasonic probe according to claim 1, characterized in that, The linear relationship between the water distance d and the signal return time t in step S2 is based on the characteristics of sound propagation. The distance d between the probe signal transmitting crystal and the surface of the measured workpiece is proportional to the signal return time t, i.e., d = kt, where k is a proportionality parameter.

3. The in-machine calibration method for a flexible ultrasonic probe according to claim 1, characterized in that, The method of changing the A and B axes to obtain different measurement points in step S2 involves finding the vertical position in step S2, fixing the A and Y axes, rotating the B axis by a fixed angle, slightly adjusting the X and Z axes, finding the position with the maximum signal, which is the position of the next measurement point, and then only changing the A axis to finally obtain the measurement point at the corresponding position on the sphere.

4. The in-machine calibration method for a flexible ultrasonic probe according to claim 1, characterized in that, In step S2, finding the vertical position is based on the principle of sound reflection. When the received ultrasonic signal is at its maximum, the probe is perpendicular to the measuring surface. Therefore, during calibration, the X, Y, Z, and A axes can be adjusted slightly. If the signal amplitude is at its maximum, this position is the perpendicular position between the probe and the measuring surface.

5. The in-machine calibration method for a flexible ultrasonic probe according to claim 1, characterized in that, The coordinates (x0, y0, z0) after rotation in the machine tool coordinate system in step S3 are calculated using the following formula: Among them, (x B ,y B ,z B Let (a,c,b) be the coordinates before rotation, B be the angle of rotation of the B-axis of the machine tool, and (a,c,b) be the coordinates of the center of the rotary table. Let the transformation matrix be R. y .

6. The in-machine calibration method for a flexible ultrasonic probe according to claim 1, characterized in that, The optimization objective of the spherical fitting method in step S3 is the coordinates (x, y) of the theoretical measurement point. t ,y t ,z t Using the coordinates of the rotated sphere's center The coordinates of the actual measurement point (x) are obtained by coordinate transformation calculation of the angle along the A-axis. p ,y p ,z p The calculation formulas are obtained using the X, Y, and Z axis coordinates of the machine tool, calibration parameters L and k, signal return time t, and the angular coordinate transformation of the A-axis. in, Let O be the coordinates of the center of the sphere after rotation, (o x ,o y ,o z Let α and β be the coordinates of the center of the sphere before rotation, and α and β be the deviations between the probe installation angle and the ideal angle. If the probe is exactly along the principal axis, then α = 90° and β = 90°, thus obtaining the optimized target. The calculation formula is as follows:

Images