JP3675780B2 - Metal fatigue / deterioration identification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal fatigue / deterioration identification device that identifies the progress of fatigue / deterioration of any metal, regardless of whether it is a magnetic material or a non-magnetic material.
[0002]
[Prior art]
Many attempts have been reported to quantitatively detect the progress of metal fatigue / degradation using eddy current magnetic sensors.
[0003]
An example of the general apparatus configuration will be described with reference to FIG. The metal fatigue / deterioration identification device includes an eddy current type magnetic sensor 1, an oscillating unit 2, a multiplier 3, a low pass filter 4, and a digital display 5. The test piece 6 is an eddy current type magnetic sensor. 1 is brought into contact with the magnetic core 13, an excitation voltage having a predetermined frequency is applied to the excitation primary winding 11, an eddy current is induced in the test piece 6, and this eddy current is detected by the detection secondary winding 12. Thus, fatigue and deterioration of the metal are detected.
[0004]
That is, the basic method for detecting fatigue or deterioration of a metal is to radiate magnetic flux from the eddy current magnetic sensor 1 to the test piece 6 at each stage where the metal test piece 6 gradually transitions from an unfatigue state to a fatigued state. Then, the information is detected and recorded by the change of the eddy current generated as a result. This change is considered to be caused by changes in the magnetic permeability and conductivity of the metal accompanying fatigue and deterioration of the metal. Thus, the change transition of the detection information is used to identify the progress degree of metal fatigue or deterioration.
[0005]
In order to know the degree of progress of fatigue and deterioration of the metal, if the measurement is performed on-site using an eddy current type magnetic sensor, various problems will appear as follows.
[0006]
1) The shape effect and terminal effect by the test piece are large. That is, when an eddy current is generated from the eddy current type magnetic sensor 1 in the non-fatigue test piece (reference test piece) 6 and the detected signal output is seen, the signal varies depending on the shape of the test piece and the distance to the end face of the magnetic core. The output is displayed and the so-called shape effect / terminal effect is large and cannot be ignored.
[0007]
2) Even if a change in permeability or conductivity due to the degree of progress of fatigue or deterioration of metal is detected as an electric signal, the level change of the detection signal is very small, and it may not be possible to get out of the measurement error range.
[0008]
As described above, when detecting the progress of metal fatigue and deterioration quantitatively, the change in detection level due to the shape effect and terminal effect is larger than the change in detection level due to factors of metal fatigue and deterioration. In some cases, the reproducibility of the detected data is lacking and the reliability is significantly impaired.
[0009]
Therefore, it is impossible to use the conventional eddy current type magnetic sensor mechanism utilizing the fact that the impedance changes suddenly at the crack occurrence point as it is for detecting the fatigue and deterioration of the metal.
[0010]
[Problems to be solved by the invention]
The present invention solves the above-described problems, and an object thereof is to provide an eddy current type magnetic sensor capable of detecting metal fatigue and deterioration without being affected by the shape effect or terminal effect of a test piece.
[0011]
Furthermore, an object of the present invention is to provide a metal fatigue / deterioration identification device capable of largely detecting changes in metal fatigue and deterioration without being affected by the shape effect and terminal effect of the test piece.
[0012]
[Means for Solving the Problems]
In order to solve these problems, the present invention investigated the basic operation of the magnetic sensor and reviewed the coil design method.
[0013]
That is, in order to solve the above-mentioned problem, the present invention has an excitation primary winding, a detection secondary winding, and a high-permeability magnetic core around which these windings are wound. In the eddy current type magnetic sensor for identifying metal fatigue / deterioration, the magnetic core has a multi-stage cylindrical shape having stepwise different diameters, and is configured such that the end surface of the minimum diameter portion is in contact with the test piece, and the primary for excitation. Winding the winding around the minimum diameter part of the magnetic core having a multi-stage cylindrical shape, and winding the secondary winding for detection separately into each part of the multi-stage cylindrical shape where the minimum diameter part and diameter part of the magnetic core become thicker It is characterized by that.
[0014]
Furthermore, the present invention comprises two sets of multi-stage cylindrical magnetic cores having different diameters as described above, a detection magnetic core and a reference magnetic core, and a primary coil for detection and reference excitation is provided for each magnetic core. Turn respectively around the minimum diameter portion, wound separately respectively detecting secondary winding for detection and reference to each part of the multi-stage cylindrical shape smallest diameter portion and the diameter portion is thicker in the respective core, respectively The magnetic core is placed in the outer cover in contact with the shielding metal that blocks the mutual interference of magnetic flux between the reference winding and the detection winding, and the end surface of the minimum diameter of the magnetic core is the test piece. Arranged in the outer cover so as to be in contact with the end face of the minimum diameter part of the upper reference magnetic core, the adjustment metal is provided so that the distance from the end face can be changed, and the secondary winding when there is no measurement metal The distance between the adjustment metal and the end face of the reference magnetic core is adjusted so that the output of . In the present invention, the magnetic core is made of permalloy.
[0015]
In order to solve the above problems, the present invention provides an eddy current type magnetic sensor for identifying metal fatigue / deterioration and an excitation voltage having a predetermined frequency applied to an excitation primary winding of the vortex type magnetic sensor for identifying metal fatigue / deterioration. A multiplier for multiplying the output of the secondary winding for detection of the eddy current magnetic sensor for identifying metal fatigue / deterioration and the excitation voltage of the oscillator, and a low pass for extracting a DC component of the output of the multiplier In a metal fatigue / deterioration identification device comprising a filter and a display for displaying the output of the low-pass filter, the measurement frequency f ₀ is taken on the horizontal axis, and the multiplier output and the detection secondary winding output are taken on the vertical axis. The peak value is measured in the region where the measured frequency fo indicates the peak value of the multiplication value measured with the reference test piece and the output voltage of the secondary winding for detection increases linearly before saturation. Measuring frequency f The secondary winding for detection is separately wound around each magnetic core portion of the detection magnetic core so that o substantially coincides, and this winding is connected in cascade to provide a transformer function electrically for detection 2 When the inductance value of the winding is selected and there is no measurement metal, the distance between the end surface of the minimum diameter of the coil core and the adjustment metal so that the differential output voltage of the secondary winding for detection is properly balanced with zero Is adjusted to detect the degree of progress of fatigue and deterioration of the metal to identify the fatigue and deterioration of the metal.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
A basic embodiment of a metal fatigue / deterioration identification apparatus using an eddy current type magnetic sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the structure of a metal fatigue / deterioration identification device, FIGS. 2 to 6 are diagrams for explaining electrical characteristics and equivalent circuits of a sensor, FIG. 7 is a diagram for explaining the shape of a magnetic core, and FIG. FIG. 9 is a diagram illustrating the relationship between the sensor input frequency versus the multiplication value characteristic, the output voltage characteristic, and the phase characteristic.
[0017]
As shown in FIG. 1, a metal fatigue / deterioration identification apparatus using an eddy current type magnetic sensor 1 according to the present invention includes an eddy current type magnetic sensor 1, an oscillator 2, a multiplier 3, a low-pass filter 4, and a digital display. The test piece 6 is brought into contact with the magnetic core 13 of the sensor to detect metal fatigue / deterioration. The basic configuration of a metal fatigue / deterioration discrimination apparatus using the eddy current type magnetic sensor according to the present invention is the same as the circuit system of a generally used metal fatigue / deterioration discrimination apparatus as shown in FIG.
[0018]
The signal output of the oscillator 2 is inputted to the primary winding 11 for excitation of the eddy current type magnetic sensor 1, and the magnetic core 13 is brought into close contact with the measurement metal (test piece) 6 to generate an eddy current in the measurement metal 6. The voltage (output signal) Vsig induced in the secondary winding for detection 12 wound around the magnetic core 13 by this eddy current is input to the multiplier 3.
[0019]
On the other hand, the multiplier 3 is supplied with a reference signal Vref having a constant voltage amplitude and phase from the oscillator 2. Since the signal frequency of the output signal Vsig and the reference signal Vref is the same, when the tuning frequency of the sensor circuit is close to the measurement frequency, the phase difference between the output signal Vsig and the reference signal Vref is small, and the output signal of the multiplier 3 is Maximum value. Only the DC component is taken out from the output signal by the low-pass filter 4 and is quantitatively displayed on the digital display 5 as a multiplication value.
[0020]
A method for detecting a minute change in the conductivity of a metal as the largest electric signal will be described below. In the eddy current type magnetic sensor, the general tendency of the sensor primary side excitation input frequency (hereinafter referred to as input frequency f) versus the sensor secondary side output voltage amplitude (hereinafter referred to as output voltage Vo) is shown in FIG. As shown in FIG.
[0021]
As shown in FIG. 2, the input frequency f vs. output voltage Vo characteristic shows that the output voltage Vo increases substantially linearly as the input frequency f increases from the low frequency zero region, and eventually enters the saturation region and becomes the output voltage Vo. Is a constant value. Comparing the measurement locations with large and small areas, as shown by curve I (large area of measurement location) and curve II (small area of measurement location), as input frequency f increases and output voltage Vo increases. The difference between the output voltages Vo of both I and II is also increased, and the shape effect is prominent.
[0022]
As the fatigue of the metal progresses and the conductivity decreases, the curves I 1 and II slope down to curves I ′ and II ′, respectively, and the output voltage Vo decreases. The sharper the rising slope of the curve, the greater the change can be detected.
[0023]
The tendency of the input frequency f vs. output voltage Vo characteristic using the magnetic permeability μ of the magnetic core 13 as a parameter will be described with reference to FIG. The magnetic core 13 around which the winding of the eddy current type magnetic sensor 1 is wound uses a high permeability member, but the value of the permeability μ is changed from, for example, μ = 1,000 to μ = 100,000. Then, the rising slope can be made steep.
[0024]
What can be said from FIGS. 2 and 3 is that in order to detect a small change in conductivity as an electric signal due to the progress of fatigue or deterioration of the metal, an output can be obtained by using a member having a high μ as the magnetic core 13. The design is such that the frequency band in the region where the voltage is increased and the influence of the shape effect is small becomes the measurement frequency.
[0025]
A method for detecting a minute change in the magnetic permeability of a metal as the largest electric signal will be described below.
[0026]
A general tendency of the phase characteristic of the input frequency f versus the output voltage Vo (hereinafter referred to as output phase φ) will be described with reference to FIG. The output phase φ changes linearly as the input frequency f increases as shown by the solid line III , but the linearity deteriorates when the frequency exceeds a certain frequency. In order to maintain this linearity up to a predetermined frequency as shown by the broken line III ', it is necessary to increase the inductance L2 of the secondary winding for detection 12 of the eddy current type magnetic sensor 1.
[0027]
An equivalent circuit of the secondary winding for detection 12 of the eddy current type magnetic sensor 1 is simply shown using FIG. L2 represents the inductance of the secondary winding for detection 12, C2 represents stray capacitance, and ΔL2 represents the change in inductance when the magnetic core 13 of the sensor is in close contact with the measurement metal. When there is no measurement metal, ΔL2 = 0.
[0028]
The frequency characteristic of the reactance component of the secondary winding for detection 12 in the sensor 1 will be shown using FIG. In the low frequency region, the reactance component is governed by the 1 / jωC2 component as shown by curve III in FIG. 4, and is governed by the jωL2 component shown by curve IV as the frequency increases.
[0029]
The following can be said from FIG. 4, FIG. 5, and FIG. The phase characteristic of FIG. 4 has a large change in the region where the input frequency f is low. This is because the 1 / jωC2 component of the stray capacitance C2 affects at a low frequency. The jωL2 component of the reactance L2 of the secondary winding for detection 12 changes in a region where the frequency is relatively high, as can be seen from the curve (4) in FIG.
[0030]
In order to increase the phase change in the measurement frequency band, the secondary side circuit of the eddy current type magnetic sensor 1 may be brought closer to the tuning characteristic with respect to the measurement frequency band. That increases the inductance L2 of the detecting secondary winding 12 shown in FIG. 5, 1 the characteristics of the secondary inductance L2 is shifted from the curve IV to the curve IV 'as shown in FIG. 6, is formed by the stray capacitance C2 By canceling out the / jωC2 component, the curve III in FIG. 4 becomes the characteristic of the curve III ′.
[0031]
In other words, as a method of maximally detecting the change component of the magnetic permeability, the phase change is greatly detected by increasing the inductance L2 of the secondary coil for detection 12 of the sensor 1 and forming a tuning characteristic with respect to the measurement frequency. Is possible. However, this is correct when the secondary circuit is considered to be only the lumped constant element, but here, the component that changes in the inductance of (L2 + ΔL2) in FIG. 5 is only ΔL2. Therefore, if L2 >> ΔL2, even if ΔL2 slightly changes due to progress of fatigue or deterioration, the phase change as a whole is poor.
[0032]
As a countermeasure, in the present invention, a step is provided by changing the diameter dimension (thickness) of the magnetic core 13 of the secondary winding for detection 12, and the secondary winding for detection 12 is divided into a plurality of portions in each magnetic core portion. In this way, we tried to increase the effective inductance without increasing the number of secondary windings for detection by cascading these windings and electrically having a transformer function. .
[0033]
With reference to FIG. 7, an example of the shape of a coil composed of the coil magnetic core 13, the exciting primary winding 11 and the detecting secondary winding 12 of the eddy current type magnetic sensor 1 used in the present invention will be described. The coil magnetic core 13 is formed in a shape that changes in a stepped manner into a portion 13-1 having a diameter D1, a portion 13-2 having a diameter D2, and a portion 13-3 having a diameter D3. The exciting primary winding 11 is wound around the surface of the portion 13-1 having a diameter D1. The secondary winding for detection 12 is wound around the surface of the first secondary winding 12-1 wound around the surface of the portion 13-1 having a diameter D1, and the surface of the portion 13-2 having a diameter of D2. The second secondary winding 12-2 and the third secondary winding 12-3 wound around the surface of the portion 13-3 having a diameter D3 are divided into two and are cascade-connected. In this state, the number of turns of each winding is determined so that the total inductance L2 on the secondary side becomes a required value.
[0034]
Although the example of FIG. 7 shows the case where the magnetic core 13 is configured in three stages, the number of stages of the magnetic core 13 may be two or four. If the number of steps is increased, the detected phase change is large, but there is a compromise because the shape effect is also surfaced.
[0035]
In addition, optimal design is performed so that the ratio of the core diameters D2 / D1, D3 / D2, and D4 / D3 can be adjusted to suit the type of metal being measured, such as magnetic or non-magnetic. It was.
[0036]
As described above, it was possible to find a good directionality by specifying the coil member, shape, and optimum measurement frequency according to the type of metal to be measured. However, when this region is reached, a slight imbalance in the differential transformer function of the secondary winding for detection 12 emerges as a problem.
[0037]
The internal structure of the eddy current type magnetic sensor 1 according to the present invention is configured by arranging two coils shown in FIG. 7 symmetrically as shown in FIG. The important thing is to select the correct measurement frequency according to the type of metal being measured.
[0038]
An example of the coil arrangement inside the sensor that deals with such imbalance will be described with reference to FIG.
[0039]
In this example, the coil is divided into two parts, and a metal shield 15 having a shielding effect is disposed in order to avoid mutual interference of magnetic flux between the two coils. It is characterized in that the adjustment metal 16 is arranged on the side opposite to the contact side with the test piece of the magnetic core so that the output voltage Vo becomes substantially zero with respect to the input frequency f when there is no test piece. .
[0040]
That is, the eddy current type magnetic sensor 1 includes an excitation primary winding 11 and a detection secondary winding 12. Generally, since the secondary side has a differential transformer function, the secondary winding for detection 12 is divided into two parts for use. However, due to manufacturing variations, the secondary side output voltage (output voltage Vo) is obtained when there is no measurement metal. Is difficult to achieve zero (fully balanced). Moreover, in the method of detecting the phase change with high sensitivity according to the present invention, this slight unbalanced output voltage cannot be ignored as the shape effect of the phase φ component.
[0041]
In the eddy current type magnetic sensor 1 of the present invention, by rotating the adjusting metal 16 shown in FIG. 8, the distance L between the magnetic core 13 and the adjusting metal 16 is changed to correct the unbalance. In order to minimize the shape effect, an externally adjustable mechanism was provided.
[0042]
The metal fatigue / deterioration identification device using the eddy current type magnetic sensor according to the present invention has a great feature in the operation characteristics and structure of the eddy current type magnetic sensor, and will be described in detail.
[0043]
FIG. 9 shows the relationship between the sensor input frequency f, the multiplication value characteristic, the output voltage Vo characteristic, and the phase characteristic. In this case, as shown in FIG. 9C, the input frequency f is fixed to 1.5 kHz where the multiplication value indicates the peak value. As shown in the characteristic diagram of input frequency f-output phase φ in FIG. 9A, when the area of the measurement portion is small and a shape effect occurs, the phase characteristic of curve a is shown. When the area of the measurement location is large, the phase characteristic of the curve c is shown. Therefore, when the sensor output phase characteristic φ is the curve a, the adjustment metal 16 is rotated to change the distance L, and the curve a is shifted to the curve b. The point where the shape effect is the smallest and the VWX point at which the multiplication value exhibits the peak value intersects with a straight line is referred to as a golden cross point by the inventors, and only that frequency is the measurement frequency.
[0044]
When fatigue / deterioration progresses from the non-fatigue state d of the specimen shown by the multiplication value characteristic in FIG. 9 (C), it shifts to the e curve, and the peak point of the multiplication value shifts in the lower frequency direction (phase change), The peak value of the multiplication value itself also decreases (change in output voltage). The peak value x of the multiplication value changes to the y point, and a decrease in the multiplication value is displayed.
[0045]
If the metal to be measured is first measured with a non-fatigue test piece (reference test piece) and the multiplication value is displayed as 200, for example, then the measurement is performed with a fatigue test piece and is displayed as 160, for example. It means that it has decreased by 20%. The degree of this decrease is accumulated as data and used to identify the progress of metal fatigue / deterioration.
[0046]
【The invention's effect】
The metal fatigue / deterioration identification device using the eddy current type magnetic sensor according to the present invention can easily detect the progress of fatigue and deterioration even in a non-magnetic metal, which has been considered very difficult in the past. Accumulation of measurement data up to the early detection of crack-prone areas and further measurement of damage increases the certainty of remaining life estimation, and there are significant economic benefits such as extending the useful life of the equipment.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a configuration of a metal fatigue / deterioration identification apparatus using an eddy current type magnetic sensor according to the present invention.
FIG. 2 is a sensor input frequency vs. sensor output voltage amplitude characteristic diagram.
FIG. 3 is a sensor input frequency vs. sensor output voltage amplitude characteristic diagram.
FIG. 4 is a phase characteristic diagram of sensor input frequency versus sensor output voltage.
FIG. 5 is an equivalent circuit of a secondary coil for detection.
FIG. 6 is a diagram for explaining a general tendency of reactance components of a secondary coil for detection.
FIG. 7 is a diagram schematically illustrating the shape of the magnetic core of the eddy current type magnetic sensor according to the present invention.
FIG. 8 is a diagram for explaining an example of a coil arrangement inside the eddy current type magnetic sensor according to the present invention.
FIG. 9 is a diagram for explaining a general tendency of input frequency versus multiplication value characteristics, output voltage characteristics, and phase characteristics.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Eddy current type magnetic sensor 11 Primary winding 12 for excitation Secondary winding 13 for detection 13 Magnetic core 14 Outer part 15 Shielding metal 16 Adjustment metal 2 Oscillator 3 Multiplier 4 Low-pass filter 5 Digital display 6 Test piece (metal piece )

Claims (4)

In an eddy current magnetic sensor for identifying fatigue / deterioration of metal having a primary winding for excitation, a secondary winding for detection, and a magnetic core having a high permeability around which these windings are wound,
The magnetic core has a multi-stage cylindrical shape having different diameters in stages, and is configured such that the end surface of the smallest diameter portion is in contact with the test piece,
The primary winding for excitation is wound around the minimum diameter portion of the magnetic core having a multistage cylindrical shape, and the secondary winding for detection is placed on each of the multistage cylindrical shape where the minimum diameter portion and the diameter portion of the magnetic core are thickened. An eddy current type magnetic sensor for metal fatigue / deterioration discrimination characterized by winding separately. There are two sets of multi-stage cylindrical magnetic cores having different diameters in the above-mentioned manner, including a detection magnetic core and a reference magnetic core, and primary windings for detection and reference excitation are provided at the minimum diameter portion of each magnetic core. Winding and winding the detection and reference secondary windings separately into multi-stage cylindrical parts where the minimum diameter part and diameter part of each magnetic core are thickened , and each magnetic core has the maximum diameter. Is placed in the outer cover part in contact with the shielding metal that blocks the mutual interference of magnetic flux between the reference winding and the detection winding, and the outer cover is so that the end surface of the smallest diameter part of the detection core is in contact with the test piece An adjustment metal is disposed in the portion so as to face the end surface of the smallest diameter portion of the reference magnetic core so that the distance from the end surface can be changed. When there is no measurement metal, the output of the secondary winding becomes zero. The distance between the adjustment metal and the end face of the reference magnetic core is adjusted as described above. Metal fatigue and deterioration identification vortex magnetic sensor mounting. The eddy current magnetic sensor for identifying metal fatigue / deterioration according to claim 1 or 2, wherein the magnetic core is made of permalloy. An eddy current type magnetic sensor for identifying metal fatigue / deterioration according to claim 2, an oscillator for applying an excitation voltage of a predetermined frequency to a primary winding for excitation of the vortex type magnetic sensor for identifying metal fatigue / deterioration, A multiplier that multiplies the output of the secondary winding for detection of the eddy current magnetic sensor for identifying metal fatigue / deterioration and the excitation voltage of the oscillator; a low-pass filter that extracts a DC component of the output of the multiplier; In the metal fatigue / deterioration identification device consisting of a display unit that displays the output,
Measurement frequency fo indicating the peak value of the multiplication value measured with the reference test piece when the measurement frequency f ₀ is taken on the horizontal axis and the multiplier output and the detection secondary winding output is taken on the vertical axis, and detection In the region where the output voltage of the secondary winding increases linearly before saturation, the measurement frequency fo indicating the peak value substantially coincides with each other to detect each 2 The next winding is wound separately, and the windings are cascaded to provide an electrical transformer function, and the inductance value of the two detection windings is selected.
When there is no measurement metal, the distance between the adjustment metal and the small-diameter end face of the coil core is adjusted so that the differential output voltage of the secondary winding for detection is properly balanced with zero. Metal fatigue / deterioration identification device that detects the progress of fatigue / deterioration.

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