CN110500974B - Workpiece thickness detection method based on improved peak recognition - Google Patents

Workpiece thickness detection method based on improved peak recognition Download PDF

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CN110500974B
CN110500974B CN201910723328.9A CN201910723328A CN110500974B CN 110500974 B CN110500974 B CN 110500974B CN 201910723328 A CN201910723328 A CN 201910723328A CN 110500974 B CN110500974 B CN 110500974B
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workpiece
peak
value
thicknesses
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王国锋
钟才川
马凯乐
杨凯
盛延亮
赵云龙
曹增欢
户满堂
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Tianjin University
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    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
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Abstract

The invention discloses a workpiece thickness detection method based on improved peak recognition, which comprises the following steps of 1, calculating the propagation speed of an ultrasonic echo signal in a workpiece; step 2, setting a peak starting position aiming at the acquired ultrasonic echo signal waveform of the detected workpiece, and determining the position of a point corresponding to the maximum value after the position, namely a first peak point; setting a minimum distance between peaks, and determining a maximum value, namely the position of a second peak point, from the position obtained by adding the distance to the position of the first peak point; obtaining the time difference t' of two peak points from the positions of two adjacent peak points to calculate the thickness value of the workpiece to be measured; step 3, when the waveform has large change, namely the thickness is suddenly changed, the gate is made to stay at the previous position, only the last thickness value is measured, and when the waveform tends to be stable, the second peak value identification algorithm of the step 2 is called; and 4, correcting the thickness measurement result. The invention better solves the problem of inaccurate measurement of thickness mutation.

Description

Workpiece thickness detection method based on improved peak recognition
Technical Field
The invention relates to the technical field of ultrasonic continuous thickness measurement, in particular to a method for realizing ultrasonic continuous thickness measurement by utilizing an improved peak recognition algorithm.
Background
The thickness of a large thin-walled part is a quite important index in the process of manufacturing and measuring. For example: the thickness is too large, materials are wasted, the weight of the workpiece is too large, the performance of the related workpiece is affected, and the whole assembly body is further affected; too small a thickness also results in a workpiece that has too low a stiffness and strength to meet performance requirements. And more because the thickness of large thin-walled parts determines the material distribution throughout the workpiece. The material distribution of the workpiece, in turn, affects the operational performance of the entire workpiece including the moment of inertia, bending and torsion resistance characteristics of the workpiece. Therefore, the wall thickness measurement and control of large-sized thin-walled parts are very important, and the final workpiece can meet the requirements of size and precision only by a measurement method with enough precision and high speed, so that the final automobile and aerospace equipment can meet the design requirements, and the corresponding tasks are smoothly realized.
Because the ultrasonic probe can receive echoes in the whole contact area, not only the central point of the probe, the ultrasonic echoes with two thicknesses can appear at the position where the thickness of the workpiece changes suddenly, and the problem of inaccurate thickness measurement can appear when the conventional peak value identification algorithm is adopted for the ultrasonic echoes, the conventional peak value identification algorithm needs to be improved to realize continuous and accurate ultrasonic thickness measurement.
Disclosure of Invention
Aiming at the problem that the thickness measurement at the position of the sudden change of the thickness is inaccurate, the invention provides a workpiece thickness detection method based on improved peak value recognition, the ultrasonic echo signals at the position of the sudden change of the thickness are secondarily recognized based on an improved peak value recognition algorithm, and a gate retention method is introduced, so that the more accurate workpiece thickness detection is realized.
The invention discloses a workpiece thickness detection method based on improved peak recognition, which comprises the following specific steps of:
step 1, selecting a standard workpiece which is the same as the tested workpiece in material and known in thickness, respectively collecting two groups of ultrasonic echo signals of the tested workpiece and the standard workpiece, selecting time points of two front peak values of the ultrasonic echo signal waveform of the standard workpiece, and calculating time differencet，tThe time of the ultrasonic echo to and fro once on the upper interface and the lower interface of the standard workpiece is taken; calculating the propagation speed of the ultrasonic echo signal in the workpiece based on the following formula:
Figure 487969DEST_PATH_IMAGE001
wherein the content of the first and second substances,d standard workpieceThe thickness of a standard workpiece is shown,crepresenting the propagation speed of the ultrasonic wave in the workpiece;
step 2, setting a peak initial position for removing the influence of the transmitted wave aiming at the acquired ultrasonic echo signal waveform of the detected workpiece, and determining the maximum value corresponding point after the peak initial positionThe position is the first peak point; setting a minimum distance between peaks, and determining a maximum value, namely the position of a second peak point, from the position obtained by adding the distance to the position of the first peak point; obtaining the time difference of two peak points from the positions of two adjacent peak points
Figure 131440DEST_PATH_IMAGE002
，
Figure 997765DEST_PATH_IMAGE002
The time of the ultrasonic echo to and fro once on the upper interface and the lower interface of the workpiece to be detected is taken as the time of the ultrasonic echo; propagation velocity of simultaneous ultrasonic echocThat is, the propagation velocity obtained in step 1, can be combined with the following formula to obtain the thickness value of the measured workpiece:
Figure 260775DEST_PATH_IMAGE003
wherein the content of the first and second substances,d measured workpieceThe thickness of the workpiece to be measured is shown,crepresenting the propagation speed of the ultrasonic wave in the workpiece;
step 3, a method for retaining the gate is provided in the step, when the waveform is changed greatly, namely the thickness is changed suddenly, the gate is enabled to stay at the previous position, only the last thickness value is measured, and when the waveform tends to be stable, the second peak value identification algorithm in the step 2 is called; the waveform tends to be stable, which means that the amplitude of the first echo of the reflected wave with the former thickness is smaller than that of the reflected wave with the latter thickness;
step 4, obtaining a thickness-time sequence chart according to the measurement result in the step 3, and correcting the thickness measurement result, wherein the specific steps are as follows: starting from the Nth thickness, scanning the nearest N thicknesses in sequence every time one thickness is measured, subtracting the previous thickness from the current scanned thickness, marking the thickness if the difference value exceeds a preset threshold value T1, continuing to scan backwards after the N thicknesses are scanned, and if the serial number i of the corresponding point of the marked thickness and the serial number of the corresponding point of the previous marked thickness are respectively markedjIf the difference is less than the threshold T2, the two thicknesses and the distance between the two thicknesses are consideredAll the thicknesses are abnormal and are modified into a thickness value with the serial number of i-1; after the second scanning is finished, outputting a first thickness of the N thicknesses; when another new thickness is measured, the following operations are performed: sequentially scanning the latest N thicknesses, subtracting the previous thickness from the currently scanned thickness, marking the thickness if the difference value exceeds a preset threshold value T1, continuing to scan backwards after scanning the N thicknesses, considering that the two thicknesses and all the thicknesses between the two thicknesses are abnormal if the difference value between the serial number i of the marked thickness corresponding point and the serial number j of the previously marked thickness corresponding point is less than a threshold value T2, and modifying the thicknesses into the thickness value with the serial number of i-1; and the later thickness of the other new thickness is the second thickness, starting from the second thickness value, the thickness value measured each time is different from the thickness value measured last time, when the difference value is greater than the threshold value, the serial number corresponding to the thickness is marked, and when the difference value of two adjacent marked serial numbers is less than the threshold value, the two marked serial numbers and all the thickness values between the two marked serial numbers are modified into the thickness value of the serial number which is the former one of the two adjacent marked serial numbers.
Compared with the prior art, the invention better solves the problem of inaccurate measurement of thickness mutation.
Drawings
FIG. 1 is a schematic overall flow chart of a workpiece thickness detection method based on improved peak recognition according to the present invention;
FIG. 2 is a schematic diagram of a waveform of an ultrasonic echo signal;
fig. 3 is a schematic diagram of a thickness-time series diagram.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples.
As shown in fig. 1, a schematic overall flow chart of the workpiece thickness detection method based on improved peak recognition of the present invention specifically includes the following steps:
step 1, selecting a standard workpiece which is the same as the tested workpiece in material and known in thickness, acquiring an ultrasonic echo signal of the standard workpiece, selecting time points of two front peak values of an ultrasonic echo signal waveform of the standard workpiece, and calculating a time differencet，tAs the time of the ultrasonic echo to and fro once on the upper and lower interfaces of the workpiece; because the propagation speed of the ultrasonic wave in the workpiece with uniform material is basically constant, the thickness of the workpiece is calculated by adopting a pulse reflection method, and the propagation speed of the ultrasonic echo signal in the workpiece to be measured is calculated based on the following formula:
Figure 870748DEST_PATH_IMAGE004
wherein the content of the first and second substances,d measured workpieceThe thickness of the workpiece to be measured is shown,crepresenting the propagation speed of the ultrasonic wave in the workpiece;
step 2, setting a peak initial position (removing the influence of transmitted waves) aiming at the acquired ultrasonic echo signal waveform of the detected workpiece, and determining the position of a maximum value corresponding point behind the peak initial position, namely a first peak point; setting a minimum distance between peaks (in order to avoid the identification of a second peak point from being mistakenly set, the minimum distance between peaks is selected as large as possible on the premise that the minimum distance between peaks is smaller than the thickness of the workpiece to be measured), and determining a maximum value, namely the position of the second peak point, from the position obtained by adding the distance to the position of the first peak point; obtaining the time difference of two peak points from the positions of two adjacent peak points
Figure 899884DEST_PATH_IMAGE005
，
Figure 671531DEST_PATH_IMAGE005
The time of the ultrasonic echo to and fro once on the upper interface and the lower interface of the workpiece to be detected is taken as the time of the ultrasonic echo; propagation velocity of simultaneous ultrasonic echocFrom step 1, the thickness of the workpiece to be measured can be obtained by combining the following formula:
Figure 153328DEST_PATH_IMAGE006
wherein the content of the first and second substances,d measured workpieceThe thickness of the workpiece to be measured is shown,cindicating the presence of ultrasonic waves in the workpieceThe propagation speed of (c);
and 3, when the thickness of the T-shaped workpiece is continuously measured by moving the probe, the waveform is greatly changed at the position of the sudden change of the thickness, the reflected wave of the former thickness and the reflected wave of the latter thickness appear simultaneously, and the peak value identification usually makes mistakes at the moment. Aiming at the problem, a method of 'gate retention' is provided in the step, when the waveform has large change, namely, thickness mutation, the gate is enabled to stay at the previous position, only the last thickness value is measured, and when the waveform tends to be stable, the second peak value identification algorithm of the step 2 is called. Experiments show that the improvement better solves the problem of inaccurate measurement caused by the sudden change of the thickness. The waveform tends to be stable, which means that the amplitude of the first echo of the reflected wave with the former thickness is smaller than that of the reflected wave with the latter thickness; the gate reservation method introduced in the step (the gate is a picking interval of echo peak values, the maximum value in the interval where the gate is located is identified as the echo peak value by default by a system, and the product of the time difference of two echo peak values and the sound velocity is the thickness, so the key of thickness measurement lies in the selection of the position of the gate);
step 4, obtaining a thickness-time sequence chart according to the measurement result in the step 3, and correcting the thickness measurement result, wherein the specific steps are as follows: and (3) from the Nth thickness, each time one thickness is measured, scanning the nearest N thicknesses in sequence, subtracting the previous thickness from the current scanned thickness, marking the thickness if the difference value exceeds a preset threshold value T1, continuing to scan backwards after the N thicknesses are scanned, and if the difference value between the serial number i of the marked thickness corresponding point and the serial number j of the previously marked thickness corresponding point is less than a threshold value T2, considering that the two thicknesses and all the thicknesses between the two thicknesses are abnormal and modifying the thicknesses into the thickness value with the serial number of i-1. Outputting a first thickness of the N thicknesses after the second scanning; after another new thickness is measured, the above operation is performed again: and from the second thickness value, making a difference between the thickness value measured each time and the thickness value measured last time, marking the serial number corresponding to the thickness when the difference is greater than the threshold, and modifying the two serial numbers and all the thickness values between the two serial numbers into the previous thickness value of the first marked serial number when the difference between the two adjacent marked serial numbers is less than the threshold.

Claims (2)

1. A workpiece thickness detection method based on improved peak recognition is characterized by comprising the following specific steps:
step 1, selecting a standard workpiece which is the same as the tested workpiece in material and known in thickness, respectively collecting two groups of ultrasonic echo signals of the tested workpiece and the standard workpiece, selecting time points of two front peak values of the ultrasonic echo signal waveform of the standard workpiece, and calculating time differencet，tThe time of the ultrasonic echo to and fro once on the upper interface and the lower interface of the standard workpiece is taken; calculating the propagation speed of the ultrasonic echo signal in the workpiece based on the following formula:
Figure DEST_PATH_IMAGE001
wherein the content of the first and second substances,d standard workpieceThe thickness of a standard workpiece is shown,crepresenting the propagation speed of the ultrasonic wave in the workpiece;
step 2, setting a peak initial position for removing the influence of transmitted waves aiming at the acquired ultrasonic echo signal waveform of the detected workpiece, and determining the position of a maximum value corresponding point behind the peak initial position, namely a first peak point; setting a minimum distance between peaks, and determining a maximum value, namely the position of a second peak point, from the position obtained by adding the distance to the position of the first peak point; obtaining the time difference of two peak points from the positions of two adjacent peak points
Figure 684416DEST_PATH_IMAGE002
，
Figure DEST_PATH_IMAGE003
As ultrasonic echo, to and fro one on the upper and lower interfaces of the workpiece to be testedThe next time; propagation velocity of simultaneous ultrasonic echocThat is, the propagation velocity obtained in step 1, can be combined with the following formula to obtain the thickness value of the measured workpiece:
Figure 988359DEST_PATH_IMAGE004
wherein the content of the first and second substances,d measured workpieceThe thickness of the workpiece to be measured is shown,crepresenting the propagation speed of the ultrasonic wave in the workpiece;
step 3, a method for retaining the gate is provided in the step, when the waveform is changed greatly, namely the thickness is changed suddenly, the gate is enabled to stay at the previous position, only the last thickness value is measured, and when the waveform tends to be stable, the second peak value identification algorithm in the step 2 is called; the waveform tends to be stable, which means that the amplitude of the first echo of the reflected wave with the former thickness is smaller than that of the reflected wave with the latter thickness;
step 4, obtaining a thickness-time sequence chart according to the measurement result in the step 3, and correcting the thickness measurement result, wherein the specific steps are as follows: starting from the Nth thickness, scanning the nearest N thicknesses in sequence every time one thickness is measured, subtracting the previous thickness from the current scanned thickness, marking the thickness if the difference value exceeds a preset threshold value T1, continuing to scan backwards after the N thicknesses are scanned, and if the serial number i of the corresponding point of the marked thickness and the serial number of the corresponding point of the previous marked thickness are respectively markedjIf the difference is less than a threshold value T2, the two thicknesses and all the thicknesses between the two thicknesses are considered to be abnormal, and the two thicknesses and all the thicknesses are modified into a thickness value with the serial number of i-1; after the second scanning is finished, outputting a first thickness of the N thicknesses; when another new thickness is measured, the following operations are performed: sequentially scanning the latest N thicknesses, subtracting the previous thickness from the currently scanned thickness, marking the thickness if the difference exceeds a preset threshold value T1, continuing to scan backwards after scanning the N thicknesses, and considering that the two thicknesses and all the thicknesses between the two thicknesses are abnormal if the difference between the serial number i of the marked thickness corresponding point and the serial number j of the previously marked thickness corresponding point is less than a threshold value T2And modifying the thickness values into thickness values with the serial number of i-1; and the later thickness of the other new thickness is the second thickness, starting from the second thickness value, the thickness value measured each time is different from the thickness value measured last time, when the difference value is greater than the threshold value, the serial number corresponding to the thickness is marked, and when the difference value of two adjacent marked serial numbers is less than the threshold value, the two marked serial numbers and all the thickness values between the two marked serial numbers are modified into the thickness value of the serial number which is the former one of the two adjacent marked serial numbers.
2. The method for detecting the thickness of the workpiece based on the improved peak recognition as set forth in claim 1, wherein in the step 3, the gate is kept still when a plurality of thickness waveforms exist, and the gate is allowed to be reselected only when the amplitude and the amplitude change rate of the original thickness waveform meet certain conditions.
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