CN109813211B - Method capable of simultaneously measuring displacement and thickness of metal workpiece - Google Patents

Abstract

The invention belongs to the technical field of information measurement, and discloses a method capable of simultaneously measuring the displacement and the thickness of a metal workpiece, which comprises the following steps: (21) arranging an eddy current sensor at one side of a metal workpiece, wherein the eddy current sensor generates a low-frequency sinusoidal excitation signal; (22) when the eddy current sensor is not adjacent to the metal workpiece, acquiring an output signal and a current signal of the eddy current sensor; when the eddy current sensor is close to the metal workpiece, data are collected again; (23) carrying out curve fitting on the obtained measured data pairs of a plurality of groups of metal workpieces with known thickness and displacement to obtain a mathematical expression of the eddy current sensor; (24) and (5) performing the steps (21) to (22) on any metal workpiece to be measured, and substituting the obtained data into a mathematical expression so as to measure the displacement and the thickness of the metal workpiece. The invention measures displacement and thickness simultaneously through specific excitation signals, is simple and easy to implement, has higher flexibility and wider application range.

Description

A method that can simultaneously measure the displacement and thickness of metal workpieces

This application is a divisional application of the application with the application number of 201710604578.1 and the application date of July 24, 2017. The invention-creation title is "an eddy current sensor and method that can simultaneously measure the displacement and thickness of a metal workpiece"

technical field

The invention belongs to the technical field of information measurement, and more particularly, relates to a method for simultaneously measuring the displacement and thickness of a metal workpiece.

Background technique

The measurement of the thickness of metal workpieces is a problem that needs to be often faced in the industrial production and manufacturing process, such as the thickness measurement or inspection of plates in strip processing in the metallurgical industry, the thickness monitoring of corroded pipes in chemical production equipment, and the processing of machined parts. Non-disassembly online thickness measurement, thickness measurement of metal casings such as automobiles and mobile phones, etc.

At present, the thickness measurement methods on the market can be divided into three categories. One is to use double-sided clamping equipment such as micrometers for measurement, which requires simultaneous contact with both sides of the metal; the other is to use displacement measurement equipment such as laser sensors. The thickness is measured by measuring the distance on both sides of the metal; the third is the single-sided contact thickness measurement by an ultrasonic thickness gauge. These methods either require the measuring element to be installed on both sides of the metal, or the measuring element needs to be in contact with the metal. However, in many occasions, the workpiece to be measured is in a state of motion, occlusion or high temperature, resulting in the inability of the measuring element to be in contact with the measured element. It cannot be performed normally, the flexibility is low, and the scope of use is limited.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the present invention provides a method for measuring the displacement and thickness of a metal workpiece at the same time. Sensors and methods are researched and designed. The main control component of the eddy current sensor can generate excitation signals containing both high-frequency signals and low-frequency signals, and excitation signals containing high-frequency signals or low-frequency signals, and a specific excitation signal can generate only displacement-sensitive and displacement-sensitive signals at the same time. The thickness is sensitive to the eddy current, and the decoupling measurement of displacement and thickness is carried out by measuring the magnetic field information generated by the eddy current, which is simple and easy to implement, and can achieve target measurement.

In order to achieve the above object, the present invention provides a method for simultaneously measuring the displacement and thickness of a metal workpiece, the method comprising the following steps:

(21) An eddy current sensor capable of simultaneously measuring the displacement and thickness of the metal workpiece is arranged on one side of the metal workpiece, and the eddy current sensor generates a low-frequency sinusoidal excitation signal;

(22) When the eddy current sensor is not adjacent to the metal workpiece, the output signal and the current signal of the eddy current sensor are collected to perform FFT analysis on the output signal and the current signal to obtain the measured amplitude and the corresponding excitation current of the magnetic field. Phase; when the eddy current sensor is adjacent to the metal workpiece, the corresponding amplitude and phase are obtained again in the same way, and the difference of the amplitude and phase obtained twice in the complex domain is obtained respectively, so as to obtain the space generated by the eddy current. Magnetic field amplitude and phase;

(23) Perform curve fitting on a plurality of sets of measurement data pairs of metal workpieces with known thickness and displacement obtained in step (22) to obtain the mathematical expression of the eddy current sensor, where the measurement data pairs are displacement and thickness The data pair between the spatial magnetic field amplitude and match;

(24) Steps (21)-(22) are performed on any metal workpiece to be measured, and the obtained spatial magnetic field amplitude and phase are brought into the mathematical expression to measure the displacement and thickness of the metal workpiece.

Further, the eddy current sensor includes a main control component, a closed-loop current amplifier, and a probe, the closed-loop current amplifier is electrically connected to the main control component and the probe, and the main control component is used to generate an excitation signal, and to The excitation signal is transmitted to the closed-loop current amplifier, and the excitation signal includes a high-frequency signal and a low-frequency signal, or any one of a low-frequency signal and a high-frequency signal; the closed-loop current amplifier is used to linearize the received excitation signal Converted into a driving current, and the driving current is transmitted to the probe; the probe includes a probe housing, a signal amplification module and an excitation coil sequentially superimposed in the probe housing, and a a magnetic sensor, the excitation coil is electrically connected to the closed-loop current amplifier, which is used to generate a changing magnetic field under the action of the driving current, and the changing magnetic field induces eddy currents on the surface and inside of the metal workpiece to be measured, The eddy current induces a magnetic field in space; the magnetic sensor is used to simultaneously sense the magnetic field generated by the excitation coil and the magnetic field generated by the eddy current, and transmit the sensed magnetic field signal to the signal amplification module , the signal amplification module amplifies the received magnetic field signal and transmits it to the main control component.

Further, the magnetic sensor is spaced a predetermined distance from the central axis of the probe housing.

Further, the number of the magnetic sensors is two, and the two magnetic sensors are arranged symmetrically with respect to the central axis of the probe housing.

Further, the magnetic sensor is a Z-direction sensitive magnetic sensor.

Further, the eddy current sensor is a superimposed structure.

In general, compared with the prior art through the above technical solutions conceived by the present invention, the method for simultaneously measuring the displacement and thickness of a metal workpiece provided by the present invention has the following beneficial effects:

1. The magnetic sensor is used to simultaneously sense the magnetic field generated by the excitation coil and the magnetic field generated by the eddy current, and transmit the sensed magnetic field signal to the signal amplification module, which will receive The obtained magnetic field signal is amplified and transmitted to the main control assembly, and then the displacement and thickness of the metal workpiece can be simultaneously measured according to the output signal and current signal of the magnetic sensor; the magnetic sensor does not need to be in contact with the metal workpiece during measurement. , which improves the application range and has high flexibility.

2. The excitation signal includes a high-frequency signal and a low-frequency signal, or any one of a low-frequency signal and a high-frequency signal. A specific excitation signal can generate eddy currents that are only sensitive to displacement and are both sensitive to displacement and thickness. Decoupling measurement of displacement and thickness by measuring the magnetic field information generated by eddy current is simple and easy to implement, and can realize multi-target measurement.

3. The eddy current sensor is a superimposed structure, which is compact in structure and reduces in volume.

4. The number of the magnetic sensors is two, and the two magnetic sensors are arranged symmetrically with respect to the central axis of the probe housing and are spaced apart from the central axis of the probe housing to increase the eddy current. magnetic field signal, thereby increasing the output sensitivity of the magnetic sensor signal.

Description of drawings

1 is a schematic structural diagram of a probe of an eddy current sensor that can simultaneously measure the displacement and thickness of a metal workpiece provided by a preferred embodiment of the present invention;

Fig. 2 is the flow chart of the method for measuring the displacement and the thickness of the metal workpiece using the eddy current sensor that can simultaneously measure the displacement and the thickness of the metal workpiece in Fig. 1;

FIG. 3 is a flowchart of another method for measuring the displacement and thickness of a metal workpiece by using the eddy current sensor in FIG. 1 that can simultaneously measure the displacement and thickness of the metal workpiece.

In all drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-magnetic sensor, 2-excitation coil, 3-signal amplifying module, 4-probe housing.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Please refer to FIG. 1 to FIG. 3 , the eddy current sensor provided by the preferred embodiment of the present invention can simultaneously measure the displacement and thickness of a metal workpiece. The eddy current sensor is excited by a specific signal to generate only the displacement information and is sensitive to the displacement information and thickness information at the same time. Sensitive eddy current distribution, decoupling measurement of displacement and thickness by measuring the magnetic field information generated by eddy current. The eddy current sensor is placed on one side of the metal workpiece, and can obtain the thickness of the measured metal workpiece and the displacement of the measured metal workpiece or the real-time relative distance between the measured metal workpiece and the eddy current sensor without contacting the workpiece.

The eddy current sensor includes a main control assembly, a closed-loop current amplifier and a probe, and the closed-loop current amplifier is electrically connected to the main control assembly and the probe. The main control assembly is used for generating an excitation signal, and includes a DA module and an AD module, the DA module is electrically connected to the closed-loop current amplifier, and the AD module is electrically connected to the probe. The closed-loop current amplifier is used to linearly convert the excitation signal in the form of voltage from the DA module into a driving current, and transmit the driving current to the probe. The AD module is used to measure the signal from the probe.

The probe includes a magnetic sensor 1, an excitation coil 2, a signal amplification module 3 and a probe housing 4. The signal amplification module 3 and the excitation coil 2 are sequentially arranged in the probe housing 4. The magnetic sensor 1 It is arranged below the excitation coil 2 and is located outside the probe housing 4 and is spaced apart from the central axis of the probe housing 4 by a certain distance. The excitation coil 2 is electrically connected to the closed-loop current amplifier, which generates a changing magnetic field under the action of the driving current. The changing magnetic field can induce eddy currents on the surface and inside of the metal workpiece, and the eddy currents will in turn generate eddy currents. Magnetic fields are induced in space. The magnetic sensor 1 is used to simultaneously sense the magnetic field generated by the excitation coil 2 and the magnetic field generated by the eddy current, and transmit the sensed magnetic field signal to the signal amplifying module 3, and the signal amplifying module 3 The received magnetic field signal is amplified and transmitted to the AD module. In this embodiment, the excitation signal includes a high-frequency signal and a low-frequency signal; of course, in other embodiments, by adjusting the main control component, the excitation signal can include either a high-frequency signal or a low-frequency signal. ; The current signal in the excitation coil 2 is used as the reference signal, which is also obtained by the main control component through the sampling resistor.

The magnetic sensor 1 is a Z-direction sensitive magnetic sensor, the number of which is two, and the two magnetic sensors 1 are symmetrically arranged relative to the central axis of the probe housing 4 and have a certain distance from the central axis to increase the The magnetic field signal generated by the eddy current increases the output sensitivity of the magnetic sensor signal. The two magnetic sensors 1 in this embodiment can be backups for each other to increase the operational reliability of the eddy current sensor, or the two magnetic sensors 1 can measure at the same time to reduce measurement fluctuations. In this embodiment, the eddy current sensor is a stacked structure, which effectively reduces the volume and makes the structure compact.

The present invention provides two methods for simultaneously measuring the displacement and thickness of metal workpieces, the details are as follows:

The first method is based on the high and low frequency method that can measure the displacement and thickness of the metal workpiece at the same time.

This method utilizes the frequency dependence of the penetration depth of the eddy current in the metal. The eddy current of the high frequency component is completely distributed on the metal surface and is only related to the displacement of the metal; the eddy current of the low frequency component can be distributed in all thicknesses of the metal, and at the same time Influenced by metal displacement and thickness information. By using the eddy current sensor as described above, the excitation signal can contain both high-frequency signals and low-frequency signals, so that the eddy current sensor can simultaneously obtain displacement and thickness information in one measurement.

The first method is divided into two steps of eddy current sensor calibration and measurement. Once the calibration is completed, continuous multiple measurements can be performed. The first method that can simultaneously measure the displacement and thickness of a metal workpiece mainly includes the following steps:

(11) The eddy current sensor generates an excitation signal that includes both a low-frequency signal and a high-frequency signal. The definition of low frequency signal and high frequency signal is:

where σ is the electrical conductivity, μ is the magnetic permeability, and h _max and h _min are the maximum and minimum measured thicknesses, respectively. Wherein, the type of the excitation signal can be any one of a high-low frequency sinusoidal superposition signal, a square wave signal, a pulse signal and a triangular wave signal. After the Fourier transform of the signal, the frequency components of the signals obviously contain high frequency components. and low-frequency components can be used as excitation signals.

(12) When the eddy current sensor is not close to the metal workpiece, the output signal B _e (t) and the current signal I (t) of the eddy current sensor with a predetermined length are collected, and the time domain current signal is used as a reference to take the zero-crossing point or rise of the current signal. , falling edge, etc. as the time zero point, intercept the sensor output signal within a predetermined time. The current signal is obtained by measuring the voltage across the sampling resistor. To ensure sampling accuracy, the sampling rate of the signal is not lower than 10 times the maximum frequency contained in the signal.

(13) The eddy current sensor is close to the metal workpiece and is not in contact with the metal workpiece for measurement, and the output signal B _s (t) and the current signal I (t) of the eddy current sensor are collected and obtained. Similarly, with The time domain current signal is used as a reference, and the output signal of the eddy current sensor of the same length as in step (12) is intercepted. Since the closed-loop current amplifier is used to process the excitation signal, the magnitude of the current can be precisely controlled, and the current signal is kept consistent with the current signal in step (12) through the closed-loop current amplifier.

(14) Calculate the difference B _c (t)=B _s (t)-B _e (t) between the two sets of output signals intercepted in step (13) and step (12), and then the space generated by the eddy current can be obtained Magnetic field signal B _c (t)=B _s (t)-B _e (t).

(15) Perform low-pass and high-pass filtering on the spatial magnetic field signal obtained in step (14), respectively, to obtain a filtered low-frequency signal B _cL (t) and a filtered high-frequency signal B _cH (t). Filtering can be done by software, such as MATLAB program, or by hardware filtering circuit. The filter cutoff frequencies are ω _l and ω _h given in step (11), respectively.

其中，C_cL为滤波后低频信号的积分，简称低频积分；C_cH为滤波后高频信号的积分，简称高频积分。(16) Perform a predetermined long time domain integration on the absolute values of the obtained filtered low-frequency signal and the filtered high-frequency signal to obtain

Among them, C _cL is the integral of the filtered low-frequency signal, referred to as the low-frequency integral; C _cH is the integral of the filtered high-frequency signal, referred to as the high-frequency integral.

(17) Using multiple sets of metal measurement data pairs (d, h)→(C _cL , C _cH ) with known thickness and displacement obtained from steps (12)-(16), perform cubic polynomial fitting to establish the The mathematical expression of the eddy current sensor:

In the formula, d represents the displacement of the metal workpiece (or the distance from the sensor), and h represents the thickness of the metal workpiece.

(18) For the metal workpiece with any unknown displacement and thickness to be detected, perform steps (11)-(16) to measure to obtain the low-frequency integral C _tL and the high-frequency integral C _tH , and substitute the obtained value in step (17) into The inverse solution is carried out in the mathematical expression to realize the simultaneous measurement of the displacement and thickness of the metal workpiece. First, the displacement information of the metal workpiece can be obtained from the high-frequency measurement data, and further, the thickness information of the metal workpiece can be obtained from the measured displacement information and the low-frequency measurement data.

In the formula, d _est and h _est represent the displacement and thickness of the metal workpiece to be measured measured by the eddy current sensor, respectively.

The second method is a phase-based method that can simultaneously measure the displacement and thickness of metal workpieces.

The second method uses low-frequency sinusoidal excitation to make the eddy current penetrate the entire metal workpiece. At this time, the amplitude and phase information of the eddy current magnetic field measured by the magnetic sensor can be extracted at the same time. The amplitude of the eddy current magnetic field is mainly affected by the metal displacement. The phase of the eddy current magnetic field is mainly related to the metal thickness. By establishing the mapping relationship between the amplitude phase and the displacement thickness, the displacement and thickness information can be simultaneously obtained through single-frequency eddy current excitation.

The second method is divided into two steps: sensor calibration and measurement. Once the calibration is completed, continuous multiple measurements can be performed. The second method that can simultaneously measure the displacement and thickness of metal workpieces mainly includes the following steps:

(21) The eddy current sensor generates a low-frequency sinusoidal excitation signal, and the signal frequency is selected as:

In the formula, σ is the electrical conductivity, μ is the magnetic permeability, and h _max is the maximum measured thickness. The amplitude of the signal should be such that the excited coil magnetic field does not exceed the range of the magnetic sensor.

(22) When the eddy current sensor is not close to the metal workpiece, the output signal Be(t) and the current signal I(t) of the eddy current sensor with limited length are collected. Among them, the current signal is obtained by collecting the voltage across the sampling resistor. To ensure sampling accuracy, the sampling rate of the signal is not lower than 10 times the maximum frequency contained in the signal. The output signal and the current signal are analyzed by FFT respectively, and the amplitude and phase information at the excitation frequency are obtained. Taking the current information as the reference signal, the measured amplitude Me after the current normalization and the phase P _e of the magnetic field relative to the excitation current are obtained _.

为FFT幅值相位提取函数。In the formula,

Extract function for FFT magnitude and phase.

(23) When the eddy current sensor is close to the surface of the metal workpiece, use the same method as step (22) to measure and use the same method to process the measured signal, the amplitude obtained at this time is M _s , the phase is P _s .

(24) Calculate the difference of the two sets of amplitudes and phases obtained in steps (23) and (22) in the complex domain, and obtain the spatial magnetic field amplitude M _c and phase P _c generated by the eddy current. The calculation formula is:

B _c =M _s ∠P _s -M _e ∠P _e ,M _c =abs(B _c ),P _c =angle(B _c )

(25) Perform surface fitting on multiple sets of metal measurement data pairs (d, h)→(M _c , P _c ) with known thickness and displacement obtained from steps (22)-(24) to obtain the eddy current Mathematical expression for the sensor:

In the formula, d represents the displacement of the metal workpiece (or the distance from the eddy current sensor), and h represents the thickness of the metal workpiece.

(26) For any metal workpiece with unknown displacement and thickness, perform steps (21)-(24), and substitute the obtained spatial magnetic field amplitude M _ct and phase P _ct into the mathematical expression obtained in step (25) to solve, It can realize the simultaneous measurement of the displacement and thickness of the metal workpiece.

According to the method for measuring the displacement and thickness of a metal workpiece at the same time, the main control component of the eddy current sensor can generate excitation signals including high-frequency signals and low-frequency signals at the same time, and excitation signals including high-frequency signals or low-frequency signals. The excitation signal can generate eddy current that is only sensitive to displacement and sensitive to both displacement and thickness. The decoupling measurement of displacement and thickness can be performed by measuring the magnetic field information generated by the eddy current, which is simple and easy to implement, and can achieve target measurement.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (5)

1. a method that can measure metal workpiece displacement and thickness simultaneously, is characterized in that, this method comprises the following steps: (21) An eddy current sensor capable of simultaneously measuring the displacement and thickness of the metal workpiece is arranged on one side of the metal workpiece, and the eddy current sensor generates a low-frequency sinusoidal excitation signal; (22) When the eddy current sensor is not adjacent to the metal workpiece, the output signal and the current signal of the eddy current sensor are collected to perform FFT analysis on the output signal and the current signal to obtain the measured amplitude and the corresponding excitation current of the magnetic field. Phase; when the eddy current sensor is adjacent to the metal workpiece, the corresponding amplitude and phase are obtained again in the same way, and the difference of the amplitude and phase obtained twice in the complex domain is obtained respectively, so as to obtain the space generated by the eddy current. Magnetic field amplitude and phase; (23) Perform curve fitting on a plurality of sets of measurement data pairs of metal workpieces with known thickness and displacement obtained in step (22) to obtain the mathematical expression of the eddy current sensor, where the measurement data pairs are displacement and thickness and the data pair between the spatial magnetic field amplitude and phase; (24) Steps (21)-(22) are performed on any metal workpiece to be measured, and the obtained spatial magnetic field amplitude and phase are brought into the mathematical expression to measure the displacement and thickness of the metal workpiece; Wherein, the eddy current sensor includes a main control component, a closed-loop current amplifier and a probe, the closed-loop current amplifier is electrically connected to the main control component and the probe; the main control component is used to generate an excitation signal, and the The excitation signal is transmitted to the closed-loop current amplifier, and the excitation signal includes a high-frequency signal and a low-frequency signal, or any one of a low-frequency signal and a high-frequency signal; the closed-loop current amplifier is used to linearly convert the received excitation signal In order to drive the current, and transmit the drive current to the probe; the probe includes a probe housing, a signal amplification module and an excitation coil that are sequentially superimposed in the probe housing, and a magnetic field disposed under the excitation coil. The sensor, the excitation coil is electrically connected to the closed-loop current amplifier, which is used to generate a changing magnetic field under the action of the driving current, and the changing magnetic field induces eddy currents on the surface and inside of the metal workpiece to be measured, so The eddy current induces a magnetic field in space; the magnetic sensor is used to simultaneously sense the magnetic field generated by the excitation coil and the magnetic field generated by the eddy current, and transmit the sensed magnetic field signal to the signal amplification module, The signal amplification module amplifies the received magnetic field signal and transmits it to the main control assembly; The eddy current sensor generates an eddy current distribution sensitive to both displacement information and thickness information through signal excitation, and performs decoupling measurement of displacement and thickness by measuring the magnetic field information generated by the eddy current. 2 . The method for simultaneously measuring the displacement and thickness of a metal workpiece according to claim 1 , wherein the magnetic sensor is spaced a predetermined distance from the central axis of the probe housing. 3 . 3 . The method for simultaneously measuring the displacement and thickness of a metal workpiece according to claim 2 , wherein the number of the magnetic sensors is two, and the two magnetic sensors are relative to the central axis of the probe housing. 4 . Symmetrical settings. 4 . The method for simultaneously measuring the displacement and thickness of a metal workpiece according to claim 1 , wherein the magnetic sensor is a Z-direction sensitive magnetic sensor. 5 . 5 . The method for simultaneously measuring the displacement and thickness of a metal workpiece according to claim 1 , wherein the eddy current sensor is a superimposed structure. 6 .

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